Thyromental Distance Ratio in Predicting Difficult Intubation

THE EFFECTIVENESS OF EXTENDED MALLAMPATI TEST, HYOMENTAL DISTANCE RATIO AND NECK CIRCUMFERENCE – THYROMENTAL DISTANCE RATIO IN PREDICTING DIFFICULT INTUBATION

EZIKE AMECHI CHUKWUDUM DEPARTMENT OF ANAESTHESIA UNIVERSITY OF CALABAR TEACHING HOSPITAL CALABAR, NIGERIA

A DISSERTATION SUBMITTED TO NATIONAL POSTGRADUATE MEDICAL COLLEGE OF NIGERIA IN PARTIAL FULFILLMENT OF THE FINAL FELLOWSHIP OF THE MEDICAL COLLEGE IN ANAESTHESIA (FMCA) EXAMINATION REQUIREMENT

MAY 2017

SUPERVISORS ATTESTATION

We hereby affirm that we supervised this study carried out by Dr. Amechi

Chukwudum Ezike titled EFFECTIVENESS OF EXTENDED MALLAMPATI

SCORE, HYOMENTAL DISTANCE RATIO AND NECK CIRCUMFERENCE-

THYROMENTAL DISTANCE RATIO IN PREDICTING DIFFICULT INTUBATION

, in partial fulfillment for the requirement of the award of the Fellowship of the National Postgraduate Medical College of Nigeria.

First Supervisor……………………………………………… Date……………………………..

Prof. Atim I. Eshiet (MBBCh, DA, FMCA, FICS, FWACS)

Consultant Anaesthetist,

University of Calabar Teaching Hospital,

Calabar, Nigeria.

Second Supervisor …………………………………… Date………………………………

DR. Iniabasi Udoh Ilori (MBBCh; DA; FWACS).

Consultant Anaesthetist,

University of Calabar Teaching Hospital,

Calabar, Nigeria.

CERTIFICATION

I affirm that this dissertation titled ‘Effectiveness Of Extended Mallampati

Score, Hyomental Distance Ratio And Neck Circumference-Thyromental

Distance Ratio In Predicting Difficult Intubation’ was carried out by Dr. Ezike

Amechi Chukwudum and supervised by consultants in the Department of

Anaesthesiology, University of Calabar Teaching Hospital. This is in partial fulfillment of the requirement for the award of the Fellowship of the National

Postgraduate Medical College of Nigeria.

…………………………………………… Date……………………….

DR. OBOKO OKU (MBBCh; DA; FWACS).

The Head,

Department of Anaesthesiology,

University of Calabar Teaching Hospital (UCTH),

Calabar, Nigeria.

DECLARATION

I hereby declare that this work is original unless otherwise stated. It has neither been presented to any other College for Fellowship nor submitted for publication anywhere else.

------Date------

NAME: Dr. EZIKE AMECHI CHUKWUDUM

DEDICATION

I dedicate this dissertation to God Almighty for His guidance and inspirations throughout the duration of this study.

ACKNOWLEDGEMENT

I would like to express my gratitude to God for giving me the grace to see the conclusion of this work.

I am also sincerely grateful to my supervisors and teachers; Prof. Atim I.

Eshiet and Dr. Iniabasi Ilori, for their patience, wise counsel and excellent teaching skills. They made the conception and actualization of this project possible.

I wish to sincerely thank my assessors for their insightful and invaluable guidance towards producing an acceptable research work. They have helped to make me a better researcher.

I appreciate the help I received from Mrs. Fond Success, Dr. Affiong Oku and Dr. Augustine Bello, for their contributions in the study design and analysis.

I am also very grateful to the Head of Department and Consultants in the

Department of Anaesthesia for providing a suitable environment and to fellow residents for their invaluable help during the data collection.

TABLE OF CONTENTS PAGES

Title Page i

Supervisors Attestation ii

Certification iii

Declaration iv

Dedication v

Acknowledgement vi

Table of Contents vii

List of Tables ix

List of Figures xi

List of Appendices xii

List of Abbreviations xiii

Summary 1

CHAPTER ONE

Introduction 3

Objectives 6

Hypothesis and Alternative Hypothesis 7

CHAPTER TWO

Literature Review 8

CHAPTER THREE

Methodology 23

CHAPTER FOUR

Results 30

CHAPTER FIVE

Discussion 45

Recommendations 51

Limitations of the study 52

References 53

Appendices 67

LIST OF TABLES

PAGES

Table I: Socio-demographic Characteristics of participants 30

Table II: Descriptive statistics of participants’ demography 31

Table III: BMI and Incidence of difficult laryngoscopy using IDS 31

Table IV: Age and gender showing ease of intubation using IDS 32

Table V: Predictors and findings at laryngoscopy 32

Table VI: Prediction of difficult intubation by the three predictors 33

Table VII: Agreement between IDS and the three predictors 33

Table VIII: Predictive profiles for EMT, HMDR and NC/TMDR 35

Table IX: Area under the Curve for the predictors 36

Table Xa: Risk Estimate for EMT/HMDR 37

Table Xb: Risk Estimate for EMT/NCTMDR 37

Table Xc: Risk Estimate for HMDR/NCTMDR 38

Table XI: Association between BMI and IDS 39

Table XIIa: Correlations 40

Table XIIb: Model Summary 41

Table XIIc: Anova 41 9

Table XIId: Coefficients 42

Table XIII: Multivariate Logistic regression forward Wald analysis 42

LIST OF FIGURES

Figure 1: AUC for NCTMDR 43

Figure 2: AUC for HMDR 43

Figure 3: AUC for EMT 44

LIST OF APPENDICES

PAGES Appendix I: Ethical Approval 67

Appendix II: Patient’s informed consent form 68

Appendix III: Questionnaire 71

Appendix IV: Grading for Comarck and Lehane / Intubation

Difficulty Score 72

ABBREVIATIONS

ASA: American Society of Anesthesiologists

BP: Blood Pressure

BMI: Body Mass Index cm: Centimeter

CI: Confidence Interval

CL Cormack and Lehane

X2: Chi-square

DI Difficult Intubation eg: Example

EI Easy Intubation

ECG: Electrocardiography

EHN EMT+ HMDR+NCTMDR

EMS/EMT: Extended Mallampati Score/ Test

FN: False Negative

FP: False Positive

G: Gauge

Ht: Height

HMDR: Hyomental Distance ratio

HMDe: Hyomental distance in neck extension position

HMDn: Hyomental distance in neutral position

IL: Illinois

IDS: Intubation Difficulty Score

IV: Intravenous

<: Less than mm: Millimeter

MMT: Modified Mallampati Test

>: More than

≥: More than or equal to

NC/TMDR OR NCTMDR: Neck Circumference-Thyromental Distance Ratio

OR: Odd Ratio

SpO2: Peripheral oxygen saturation

+ : Plus

PPV: Positive Predictive Value

PACU: Post Anaesthesia Care Unit

ROC curve: Receiver Operative Characteristic Curve

RR: Relative Risk

SPSS: Statistical Package for Social Sciences ie: That is

TN: True negative

TP: True positive

TMD: Thyromental distance

Wt: Weight

SUMMARY

Laryngoscopy and intubation could become unexpectedly difficult and this is a significant source of morbidity and mortality in anaesthetic practice. Pre-operative airway assessment identifies those at risk of difficult laryngoscopy / intubation so as to adopt safer alternative strategies at induction of anaesthesia. This study evaluated the usefulness of Extended Mallampati Test (EMT), Hyomental distance ratio (HMDR) and

Neck-circumference-thyromental distance ratio (NCTMDR) in isolation and in combinations in apparently normal patients and correlated these predictors with difficult intubation using Intubation Difficulty Score.

Three hundred and fourteen ASA I & II adults scheduled for elective general anaesthesia with tracheal intubation were randomly selected. During pre-operative review, each patient’s weight (Wt), height (Ht), and neck circumference (NC) were measured and noted. The EMT, HMDR and NC/TMDR were also assessed for each patient and noted. EMT class ≥3, HMDR< 1.2 and NC/TMDR ≥ 5 were considered predictive of difficult intubation. Intraoperatively, laryngoscopy was performed and the

Cormack and Lehane (CL) grading recorded for each patient. Grades 3 and 4 were considered difficult intubation in the CL grading. The Intubation difficulty score (IDS) was then calculated and noted. The sensitivity, specificity, positive predictive value

(PPV), negative predictive value (NPV) and false positive (FP) values for each airway predictor in isolation and then in combinations were determined using a 2x2 contingency table.

Difficult intubation occurred in 5 out of 314 patients (1.6 %). The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), false positive and positive likelihood Ratio (PLR) for the three predictors were: EMT (50%,

99.7%, 80%, 98.7%, 1, 153.0), HMDR (4.05%, 99.1%, 60%, 77%, 2, 4.86), and

NC/TMDR (33.3%, 99.7%, 80%, 97.4%, 1, 100.7) respectively. Although their low false positive values (1 for EMT, 2 for HMDR and 1 for NC/TMDR) and their areas under the curves (AUC) of receiver operator characteristic curve (ROC) showed they were all useful predictors, the EMT was the most accurate single predictor of difficult intubation with an AUC of ROC of 0.878 (p- value 0.000). Furthermore, the Univariate analyses also showed that though EMT, HMDR, and NC/TMDR were related to difficult intubation, the relationship was significant only for EMT and NC/TMDR.

EMT however had the highest precision of this relationship with a kappa coefficient of

0.608 ( p-value < 0.001). The multivariate analysis odds ratios also estimated that EMT predicted difficult intubation about 12 times better than HMDR and also about 1.5 times better than NC/TMDR. Again, the combination of the anatomical distances (HMDR plus NC/TMDR) was less accurate than EMT alone ( AUC of 0.797 as against 0.878 for EMT). Combining the EMT to the anatomical distances increased their accuracy significantly at a p-value < 0.05. Both univariate analyses and Logistic regression showed that at a p-value of < 0.05, there was no relationship between age, gender, body mass index (BMI), neck circumference and difficult intubation.

In conclusion, EMT had the greatest predictive profile of all the three predictors assessed singly. EMT improved the predictive values of the anatomical distances

(HMDR and NC/TMDR) in all the combinations. There was no relationship between age, gender, BMI, neck circumference and difficult intubation.

CHAPTER ONE

INTRODUCTION

Difficult intubation remains a relatively constant and significant source of morbidity and mortality in anaesthetic practice.1,2 Thus airway management is an important patient safety issue and still remains a matter of great concern for the anaesthetists.3,4 Different authors have different definitions for difficult intubation and many national societies of Anaesthetists have developed algorithms and guidelines for management of difficult airways.5 However, in February 2013, the American Society of

Anesthesiologists (ASA) Task Force Committee on management of difficult airway published an amended version of the "Practice guidelines for management of the difficult airway’’. They saw difficult airway as a complex interaction between patient factors, the clinical setting, and the skills of the practitioner.6 Thus in their publication, the committee defined difficult airway as a clinical situation in which a conventionally trained anaesthesiologist experiences difficulty with facemask ventilation of the upper airway, difficulty with tracheal intubation or both. They also defined difficult intubation as when an experienced laryngoscopist, using direct laryngoscopy, requires more than two attempts with the same blade or; a change in the blade or an adjunct to a direct laryngoscope (i.e. bougie) or use of an alternative device or technique following a failed intubation. The same committee described difficult laryngoscopy as not being able to

visualize any portion of the vocal cords with the conventional laryngoscope (Cormack-

Lehane classification grade 3 and 4).6

Some authors believe the incidence of difficult tracheal intubation is between 1 to 5.8%, others think it is between 1 to 18%.7,8 In 2001, it was reported that 30% to

40% of all anaesthetic deaths in the United States of America are due to failure of difficult airway management.9 These figures are certainly higher in the developing world.10 A systematic review showed that the overall incidence of difficult intubation was 5.8% ( 95% confidence interval, 4.5–7.5%).11

Glottis visualization is a major determinant of a successful direct laryngoscopy and intubation.12 However the laryngoscopy / intubation could become unexpectedly difficult sometimes ( unanticipated ).13 Therefore anaesthetists should be prepared to manage every patient as if they possessed a potentially difficult airway.14

Anaesthetists thus have to estimate the risk of difficult intubation by way of thorough preoperative airway assessment to finally adopt a different / alternative airway management strategy before and during induction of the anaesthesia.15 Such thorough evaluations underscore the need for establishment of Preoperative Assessment Clinics in every Hospital. Insufficient or lack of airway assessment is a major cause of unanticipated difficult intubation.16 This is probably because airway evaluation has not always been regarded as a standard procedure.17

Anaesthesia in a patient with a difficult airway could eventually lead to morbidity from interruption of gas exchange (hypoxia and hypercapnia) leading to brain damage, cardiopulmonary arrest, and death.6,18

A worldwide used scoring system that many anaesthetists rely on as a predictor of difficult intubation was Mallampati test. It is a clinical sign ( the concealment of faucial pillars {palatoglossal and palatopharyngeal arches} and the uvula by the base of the tongue, when the tongue is maximally protruded in a seated patient) evaluated in 1985 by Mallampati ( an Indian-born American Anaesthetist ) and his colleagues.19 Several other preoperative difficult airway predictors had also been in use. However the predictors are all characterized by low sensitivity, low positive predictive value and high false positives and none of them has 100% accuracy.20 Thus the American Society of Anesthesiologists (ASA ) advised that more than one predictor of difficult airway should be used during airway assessement.21 The emphasis therefore is on finding simple and reliable bedside airway assessment combinations that have high sensitivity, high positive predictive value and high accuracy with few false positives.

Although Modified Mallampati with head extension {described by George et al22 as Extended Mallampati Test (EMT)}, hyomental distance ratio (HMDR) and neck circumference-thyromental distance ratio (NCTMDR) are not popularly used during pre-anaesthetic reviews, their usefulness as predictors of difficult intubation has not been properly evaluated in adults patients in our society especially in this combination.

The combination of Extended Mallampati Test (EMT), hyomental distance ratio

(HMDR) and neck circumference-thyromental distance ratio (NC/TMDR) could help predict difficult or impossible intubations with higher accuracy. This study evaluated

Extended Mallampati Score (EMS), hyomental distance ratio (HMDR) and neck circumference-thyromental distance ratio (NCTMDR) in predicting difficult intubation in patients requiring general anaesthesia.

OBJECTIVES

GENERAL OBJECTIVE

To ascertain the efficacy of Extended MallamPati, hyomental distance ratio and neck-circumference-thyromental distance ratio in predicting difficult intubation.

SPECIFIC OBJECTIVES

1. Estimate the incidence of difficult intubation in University of Calabar Teaching

Hospital (U.C.T.H).

2. To determine the sensitivity, specificity, accuracy, positive predictive value

(PPV), and false positive (FP) values of Extended Mallampati Score (EMS),

hyomental distance ratio (HMDR) and neck circumference-thyromental distance

ratio (NC/TMDR) singly and in combination.

3. To determine if a combination of anatomical distances (HMDR and NC/TMDR)

is a better predictor of difficult laryngoscopy/intubation compared to subjective

test (Extended Mallampati Score).

4. To determine the relationship between age, gender, neck circumference, body

mass index (BMI), and difficult intubation.

HYPOTHESIS

NULL HYPOTHESIS: There is no difference in efficacy of Extended Mallampati

Score (EMS), Hyomental Distance Ratio (HMDR) and Neck circumference-

Thyromental Distance Ratio (NCTMDR) in the prediction of difficult intubation.

ALTERNATIVE HYPOTHESIS: In the prediction of difficult intubation, the efficacy of Extended Mallampati Score (EMS), Hyomental Distance Ratio (HMDR) and Neck circumference-Thyromental Distance Ratio (NCTMDR) differ.

LITERATURE REVIEW

Sperati et al23 reported that tracheostomy was once considered the most reliable method of tracheal intubation until in 1858 when Eugene Bouchut, a paediatrician from

Paris, developed a new technique (laryngeal intubation) to bypass laryngeal obstruction from diphtheria. Hirsch et al24 also noted that this laryngeal intubation with small metallic tubes (redesigned by an American, Joseph O’Dwyer) was without the aid of a laryngoscope until 23rd April 1895 when a German, Alfred Kirstein (1863–1922) described direct visualization of the vocal cords using an autoscope /oesophagoscope.

Zeitels25 maintained that although Alfred Kirstein could have been the first to suggest the laryngoscopy position (the classic "sniffing the morning air" position), the credit went to Chevalier Jackson for observing that alignment of oral, pharyngeal, and laryngeal axes is necessary for successful visualisation of the larynx and subsequent tracheal intubation. Sniffing position should be the starting head position during direct laryngoscopy as it position the oral, pharyngeal, and laryngeal axes more nearly into a straight line thus provides the best chance of adequate exposure of the glottis.12,26

Orfanos et al27 reported that retrognathic mandible, the experience of the laryngoscopist and the device used could be predisposing factors to difficult intubation while the presence of beard, edentulism, history of snoring and age greater than 55 years could predispose to difficult mask ventilation. Other compromising conditions associated with possible difficult airway include: acquired (obesity, goiter, lipoma, retropharyngeal abscess, epiglottitis, arthritis of cervical spine and temporomandibular joint, neck and oral cavity tumours, facial trauma, history of radiotherapy to the head, burns contractures of the face or neck, massive angioedema of the tongue, wire fixation of the jaw) or congenital anomalies ( Down syndrome, Treacher Collins syndrome, cleft

lip and palate, cystic hygroma).28,29 Eberhart et al30 while working on simplified risk score for predicting difficult intubation, evaluated 3763 patients and demonstrated that the presence of upper front teeth (protrusive maxillary incisors), a history of difficult intubation, mouth opening less than 4 cm and any Mallampati status different from '1' and equal to '4' are independent risk factors for difficult endotracheal intubation.

In 1985, Mallampati et al19 recruited 210 consecutive ASA I and II patients who required general anaesthesia with endotracheal intubation. The patients were divided based on visibility of pharyngeal structures into three ( Class I: Visualization of the faucial pillars, soft palate, and uvula; Class II : Visualization of faucial pillars and soft palate, but uvula was masked by the base of the tongue.; Class III : Visualization of soft palate only). In order to assess the degree of difficult intubation, they developed their own system of four grades of laryngeal view as follows: Grade 1- glottis {including anterior and posterior commissures} could be fully exposed; Grade 2- glottis could be partly exposed {anterior commissure not visualized}; Grade 3- glottis could not be exposed {corniculate cartilages only could be visualized}; Grade 4- glottis including corniculate cartilages could not be exposed. They noted that out of 155, 40 and 15 patients belonging to classes I, II and III respectively, the number of difficult laryngeal visualization ( i.e grade 3 or 4 on laryngoscopy) seen were none, 14 and 14 for the three classes respectively. However a lot of bias could have been introduced in the study as they included 6 patients with arthritis (5 rheumatoid arthritis and 1 osteoarthritis), 8 patients that were edentulous, 12 patients with prominent incisors and nurse anaesthetists were included as part of their laryngoscopists. Again the same individuals that assessed the patients did the intubation (failure to blind observers) and they used

different definition for difficult tracheal intubation. Futhermore, they did not use the

Cormack and Lehane grading of laryngeal view, which had been published only the year before but had not been in widespread use at that time.31 They however concluded that there is a significant correlation between the degree of difficulty in visualizing the three oropharyngeal structures and direct laryngoscopy (p < 0.001).

In 1987, Samsoon and Young32 modified the Mallampati test by introducing a fourth class ( hard palate seen or soft palate not seen ). This modification became one of the most widely accepted clinical scoring systems for prediction of difficult intubation.33 The Cormack-Lehane system initially described by R.S Cormack and J.

Lehane34 in 1984 primarily as a means of simulating difficult tracheal intubation situations in order to teach anaesthesia residents to be prepared for obstetric general anaesthesia. This simulated difficult tracheal intubation drill was designed to achieve a laryngoscopic view of grade 3 by lowering the lifting force during the laryngoscopy so that intubation has to be performed blind. The system classifies views obtained by direct laryngoscopy based on the structures seen (grade I: full view of the glottis,vocal cords visible; grade II: glottis partly exposed, only posterior commissure or arytenoids seen; grade III: only epiglottis seen; grade IV = epiglottis not seen).

In a prospective study on recognition of difficult airway in normal adult

Nigerians, Ita et al2 studied 57 ASA I and II adult patients (for general anaesthesia with endotracheal intubation. They compared the modified Mallampati test (MMT) of each patient obtained pre-operatively with the Cormack and Lehane (CL) grade obtained during laryngoscopy. The result showed out of the 4 patients classified as MMT III, 2 had CL III at laryngoscopy and intubation failed in these two patients. Thirty nine (39) 25

patients (68.42%) were classified as Mallampati I while 36 (63.16%) were graded as

CL I at laryngoscopy. No patients had Mallampati IV class or CL IV grade. Thus the modified Mallampati classification correlated well with the findings at laryngoscopy

(Cormack and Lehane classification) and they concluded that MMT can predict / recognize difficult airway.

Similarly, Merah et al35 evaluated modified Mallampati test (MMT) and compared it with some anatomical distances (thyromental distance {TMD},

Sternomental distance {SMD}, and interincissor gap {IIG}) in 80 consecutive obstetrics

Nigerian patients scheduled for elective Caesarean sections. They observed that MMT had a sensitivity, specificity and positive predictive value (PPV) of 87.1%, 99.6%, and

70% respectively. The values obtained for TMD was 62.5%,93.1% and 50% respectively and the other tests were not able to predict difficult intubation significantly.

When all the tests were combined, the sensitivity, specificity and PPV were 100%,

36.1%, and 14.8% respectively. Combination of MMT and TMD had values of 100%,

93.1% and 61.5% for the three statistical tests respectively. A drawback for this study was that parturients were used. Total body water increases during pregnancy causing oedema of the oropharynx and laryngeal structures. This often increases MMT class for each patient. They however came to the conclusion that MMT can be used as the sole predictor of difficult intubation in Nigerian obstetric patients.

This also agreed with the work done by Mehmet and co-workers36 in Turkey on the value of thyromental distance, ratio of height to thyromental distance (RHTMD), modified Mallampati (MMT), and upper lip bite test (ULBT), in two hundred and fifty

(250) paediatrics patients aged 5-11 years. They noted that the sensitivity and specificity 26

for the four tests were 76.92% and 95.54%; 69.23% and 97.32%; 57.69% and 86.61%;

61.54% and 99.11% respectively. The MMT was the most sensitive of the tests while the RHTMD was the least sensitive test. This could be because children do not completely understand the instructions. They concluded that MMT and ULBT tests are useful and their Area under the curve (AUC) values were higher than those of other tests; thus they can be used for predicting difficult laryngoscopy in paediatric patients. Babu et al37 observed a similar result when they compared modified

Mallampati test and upper lip bite test in prediction of difficult endotracheal intubation.

By observing their sensitivity, specificity, positive predictive value, negative predictive value and accuracy, they arrived at the conclusion that modified Mallampati test is a better test at predicting difficult endotracheal intubation than upper lip bite test.

However many of the patients involuntarily phonated during the test which could have significantly altered the Mallampati classifications.

In yet another study, Merah et al13 demonstrated that of the five predictors tested

(modified Mallampati, thyromental distance, interincisor gap, sternomental distance, horizontal length of the mandible), modified Mallampati test is the most useful single predictor of difficult laryngoscopy or intubation in West Africans ( sensitivity, specificity and positive predictive value of 61.5%, 98.4% and 57.1 % respectively).

But the accuracy of modified Mallampati test continued to be questioned.

Adamus et al20 while working on the accuracy of the modified Mallampati test in one thousand five hundred and eighteen (1,518) patients showed that modified Mallampati test (MMT) when compared to Mallampati test had a lower sensitivity, specificity, positive predictive value and accuracy than the original Mallampati test. But this study 27

was non-blinded and this could be a potential source of bias. However, they concluded that MMT is of limited value when used alone and cannot be relied on.

Similarly, Lundstrom et al38 in 2011 conducted a meta-analysis of 55 published studies (involving 177088 patients after comprehensive electronic and manual searches

) to evaluate the Mallampati score as a prognostic test. The receiver operating curve demonstrated an area under the curve of 0.75, the pooled odds ratio for a difficult intubation with a modified Mallampati score of III or IV was 5.89 [95% confidence interval (CI), 4.74–7.32] while the pooled estimates of the speciﬁcity and sensitivity were 0.91 (CI, 0.91–0.91) and 0.35 (CI, 0.34–0.36), respectively. The pooled positive and negative likelihood ratios were 4.13 (CI, 3.60–4.66) and 0.70 (CI, 0.65–0.75), respectively.

However, the pooled estimates from this meta-analysis could have been influenced by a high degree of clinical diversity. Thus, who and how the test was performed, and the type of patient population evaluated, varied considerably between the individual studies. This could be a source of bias. The researchers concluded that the prognostic value of the modified Mallampati score was worse than that estimated by previous meta-analyses, thus it is inadequate as a stand-alone test of a difficult laryngoscopy or tracheal intubation.

In a previous extensive review of 42 studies, Lee et al39 also found poor to good accuracy of modified Mallampati test (MMT). The drawbacks of this meta-analysis were that dissimilar scales/criteria were used, Mallampati supplied the raw data without the calculations and the interobserver reliability was also poor.

Lewis et al40 had reported that the best way to perform the Modified Mallampati test for predicting difficult laryngoscopy, is putting the patient in sitting position, with the head in full extension, tongue out and with phonation. This was also in tandem with the study by Oates et al41 titled “phonation affects Modified Mallampati classification.

There was a theoretical argument that craniocervical extension is related to mouth opening. Ashish et al33 tried to compare Modified Mallampati Test (MMT) and

Extended Mallampati Score (EMS) in 39 acromegaly patients undergoing surgery for the excision of pituitary tumour. They showed that in both the control group and the acromegaly group, EMS and MMT had the same sensitivity. However EMS had lower specificity, positive and negative predictive values than MMT. Limitations of this research were the paucity of the sample size, non-usage of external laryngeal manipulation from the beginning and forgetting to mention that maximal head extension depends on the level of participation by the patient (intersubject variability). They however concluded that no additional benefit of neck extension was found. But the work done by George and co-workers22 revealed that craniocervical extension leads to lowering of scores for Modified Mallampati II, III, and IV patients. It also showed that

Extended Mallampati Score (EMS) had a higher specificity (80% vs 70%) and predictive values (98% vs 97%) than modified Mallampati test (MMT). When a patient is kept in neutral position and full head extension prevented, mouth opening becomes limited by about 12mm. Craniocervical extension limited by soft cervical collar limits mouth opening. Therefore their submission was that airway evaluation using MMT depends on craniocervical extension.

In order to increase the predictive values of difficult airway predictors, researchers now combine the predictors.42 Shikha and his colleagues43 reported an evaluation of modified Mallampati test, thyromental distance, upper lip bite test, head extension, and Wilson’s Score (considers 5 variables: weight, upper cervical spine mobility, mandibular mobility, retrognathia and buck teeth each scored from 0-2; a total score ≥2 predicts 75% of difficult intubation). They compared the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of all individual tests singly and then in combinations in one hundred and fifty ASA I and II patients. They concluded that no method whether individual or in combination with others identified all the cases of difficult intubation.

However combination of modified Mallampati test and Wilson’s Score could identify most of the cases of difficult intubation correctly but when one more test (Upper lip bite test) was added, there was no increase in the accuracy. Thus combination of three tests is not required when two tests combined together can give better results.

Sushil et al44 in India verified the combination of modified Mallampati Test (

MMT ), thyromental distance, anatomical abnormality, and cervical mobility into a single scoring system with the acronym M-TAC, and evaluated it against Mallampati scoring. They observed that M-TAC score more than or equal to four (4 ) had a significantly higher sensitivity (96% versus 72%) and specificity (86% versus 78%) with a high positive predictive value (44% versus 28%) and a very low false negative value (2% versus 15%) in comparison with Mallampati scoring (p<0.05). They thus concluded that M-TAC combination scoring system is a better predictor of difficult laryngoscopy than Mallampati classification. 30

Again other researchers systematically determine the diagnostic accuracy of

Mallampati oropharyngeal classification, thyromental distance, sternomental distance, mouth opening, and Wilson risk score in fifty thousand seven hundred and sixty patients selected using electronic database.45 They noted that each test yielded poor to moderate sensitivity (20–62%) and moderate to fair speciﬁcity (82–97%). The most useful bedside test for prediction was found to be a combination of the Mallampati classification and thyromental distance (positive likelihood ratio, 9.9; 95% confidence interval, 3.1–

31.9). The poor sensitivity could be because most of the studies defined difficult intubation based on Cormack–Lehane grading (3 or greater), while other studies used other classification systems like Intubation Difficulty Score.

Secondly, laryngoscopy with application of external laryngeal pressure in some of the studies and then without external laryngeal pressure in others could have affected the Cormack–Lehane grade in individual studies. The authors however submitted that combinations of tests added some incremental diagnostic value in comparison to the value of each test alone.

Badhe V.K et al46 studied Modified Mallampati Test (MMT), thyromental distance (TMD), sternomental distance (SMD), Inter Incisor Gap (IIG) and combination of the modified Mallampati test and thyromental distance for predicting difficult intubation in three hundred and one (301) non-obese, ASA class I or II patients scheduled for elective surgery requiring general anesthesia. All the tests except TMD

(71.43%) showed very poor sensitivity and very high specificity. Posttest probability showed that all of the bedside tests have limited clinical value. They then concluded that all the four predictor tests for difficult intubation have only poor to moderate 31

discriminative power when used alone. However, combination of Modified Mallampati and Thyromental distance test adds some incremental diagnostic value in comparison to the value of each test alone.

Iohom et al8 investigated if a combination of the Mallampati classification of the oropharyngeal view with either the thyromental or sternomental distance measurement improved the predictive value using a total of 212 non-obstetric surgical adult patients undergoing elective surgical procedures requiring tracheal intubation. They also concluded that rather than using the Mallampati classification alone, using other airway evaluation tests together is more useful in predicting difficult intubation.

This also agreed with the study done by Ajinkya et al47 in India who evaluated the efficacy of HMDR in predicting difficult visualization of larynx (DVL) along with

MMT and body mass index (BMI). They observed from their analysis that extended position hyomental distance (EPHMD), HMDR, MMT and Height showed significant relation with DVL whereas age, sex, weight, BMI and neutral position hyomental distance (NPHMD) were statistically insignificant in predicting correlation with DVL.

Their limitations were that extending the head maximally depended on the voluntary participation of each subject. This could have introduced some bias into the study.

Secondly, accurate measurement of the distances and appropriate reporting of laryngoscopy finding were dependent on the persons doing them. HMDR with cutoff of 1.2, MMT class 3 and 4 are clinically reliable predictors of DVL but none of them provided 100% prediction of difficult laryngoscopy. Thus, they recommended an optimal combination of the tests (HMDR, MMT and EPHMD) for prediction of intubation than using them separately. 32

Takenaka and co-workers48 were the first to define Hyomental distance ratio

(HMDR) as the ratio of HMD at the extremes of neck extension to the HMD in neutral position. They demonstrated that the extension angles of occipitoatlantal and atlantoaxial joints correlated well with surface measurements of the hyomental distance ratio (HMDR) in 40 patients with rheumatoid arthritis (P < 0.0001, r = 0.88). They concluded that HMDR was a good predictor of a reduced occipitoatlantoaxial extension capacity in patients with rheumatoid arthritis.

Huh Jin and his colleagues49 supported this finding while evaluating the usefulness of HMDR for predicting difficult visualization of the larynx in normal patients. They compared HMDR with Hyomental distance (in neutral and extended positions), modified Mallampati and thyromental distance. HMDR test alone was found to have the greatest diagnostic accuracy than any combination of tests in the study. But they still believe that no one difficult airway test is sufficiently reliable.

Kim and co-workers50 in a bid to know whether intubation is more difficult in the obese, assessed the ability of the ratio of the neck circumference to thyromental distance (NC/TMDR) to predict difficult intubation in these group of patients. Among these three indices assessed (Mallampati score, the Wilson’s score and NC/TMDR),

NC/TMDR showed the highest sensitivity and a negative predictive value (88.2 and

97.8 respectively) and largest area under the curve on an Receiver Operator

Characteristic (ROC) curve. This could be because the jaw mobility is often limited by a mass effect (especially in the obese) which now reduces the sensitivity of Mallampati and Wilson’s scores without affecting NC/TMDR. Their conclusion was that the

NC/TMDR was a better method for predicting difficult intubation than other established indices.

This was also in agreement with the study by Anahita and colleagues51 who evaluated neck circumference to thyromental distance ratio (NCTMDR) in comparison with hyomental distance ratio (HMDR), ratio of height to thyromental distance

(RHTMD), modified mallampati test and upper lip bite test to predicted difficult laryngoscopy in seven hundred and sixteen (716) pregnant women undergoing elective caesarean section. Their study showed that the ratio of Height to thyromental distance

(RHTMD) is the least sensitive of the tests, with the sensitivity of 41.6%, followed by

HMDR (45.4%), with AUC=0.55 (P=0.071). The MMT and NC/TMD had the highest sensitivities, among the predictors (73.4% and 58.3%, respectively). The AUC for

MMT was 0.582,(95%CI, 0.545-0.619); AUC for NC/TMD was 0.600, (95%CI, 0.563-

0.637); HMD in extended position (AUC=0.672, 95%CI, 0.636- 0.706) and HMD in neutral position (AUC=0.651, 95%CI, 0.614-0.686). They concluded that, in addition to MMT, NC/TMD, HMD in neutral and extended positions, in parturients are good and reliable predictors of difficult laryngoscopy and intubation, using a standard laryngoscope.

Sangeeta et al52 equally reported the diagnostic accuracy of bedside tests ( body mass index, modified Mallampati grading, inter-incisor distance, neck circumference- thyromental distance { NC/TMD} ratio ) in predicting difficult intubation in 200 ASA

I and II Indians. They observed that NC/TMD ratio was the most statistical significant as an independent risk factor for difficult intubation with an AUC of the ROC curves of

0.710. They concluded that the diagnostic accuracy of NC/TMD ratio was better compared to other bedside tests to predict difficult intubation among Indian population.

The ASA closed claims analysis involving incidents of airway injury found that

80% of laryngeal injuries occurred when laryngoscopy and intubation was thought to have been easy because inability to see the larynx generally leads to multiple or prolonged laryngoscopic attempts with increasing force which is associated with oesophageal, pharyngeal and dental injury.53,54 There could be arterial desaturation, unplanned intensive care unit admissions and haemodynamic instability.55 This instability is from reflex sympathetic stimulation and are associated with raised levels of plasma catecholamines leading to hypertension, tachycardia, myocardial ischemia, depression of myocardial contractility, ventricular arrhythmias and intracranial hypertension.56

Tanaka et al57 measured laryngeal resistance before and after anaesthesia administered via endotracheal tube and a standard laryngeal mask airway. They also performed endoscopic comparisons of the vocal cords in the two groups. They found higher laryngeal oedema, vocal cord swelling and increase in airway resistance in patients who had been managed by endotracheal intubation compared with those managed by laryngeal mask airway. Attempted intubation of the trachea under light anaesthesia could cause laryngospasm and the presence of an endotracheal tube in the trachea can produce reflex bronchoconstriction58, drying of secretions, depressed ciliary motility, and impaired mucous clearance59. Poor laryngeal exposure may still be associated with successful intubation but this should be regarded as near-miss/risky as it relies upon luck and encourages multiple or forceful laryngoscopies.60 35

There are numerous ways of intubating the trachea that do not require direct laryngoscopy. Some of these methods could be blind like blind digital technique, the blind nasotracheal intubation, lighted stylet-assisted technique ( trachlight / lightwand; imaging fiberoptic lighted stylet and Vital light) and blind trachear intubation through intubating laryngeal mask airway.61 Some other methods could be visual like flexible fibreoptic bronchoscope ( though less stimulating to the airway, it is expensive, sophisticated and secretions may reduce mucosal contact and obscure the view ) and the third group facilitate endotracheal intubation by indirect visualization of glottis structures through optical system. They are the video laryngoscopes (indirect laryngoscopy is performed without aligning the oral, pharyngeal and laryngeal axes, making the device ideal for patients with cervical spine abnormality.62 Examples V-

Mac and C-Mac, Glide scope, McGrath, Airway Scope, Airtraq, Bonfils and Bullard laryngoscope).

Difficult intubation could be very subjective and it is difficult to measure the degree of difficulty.63 Thus Adnet et al64 proposed a semiquantitative score considering difﬁculties at tracheal intubation. It is called Intubation Difficulty Scale (IDS) score, which is a function of seven parameters, resulting in a progressive, quantitative determination of intubation complexity. It considers the number of supplementary attempts, the number of additional persons directly attempting intubation, the number of alternative techniques used, the glottic exposure as defined by the Cormack grade, lifting force applied during laryngoscopy, the necessity of applied external laryngeal pressure to optimize the glottic exposure, and the position of vocal cords.

Some of the statistical terms for describing the efficacy of each airway assessment test were defined as follows:35,65

True positive (TP) = difficult intubation that had been predicted to be difficult.

False positive (FP) = easy intubation that had been predicted to be difficult.

True negative (TN) = easy intubation that had been predicted to be easy. False negative

(FN) = difficult intubation that had been predicted to be easy.

Sensitivity = percentage of correctly predicted difficult intubations as a proportion of all intubations that were truly difficult [= TP/ (TP + FN)]. Specificity = percentage of correctly predicted easy intubations as a proportion of all intubations that were truly easy [=TN/(TN+FP)].

Positive predictive value (PPV) = percentage of correctly predicted difficult intubations as a proportion of all predicted difficult intubations [=TP/(TP+FP].

Negative predictive value (NPV) = percentage of correctly predicted easy intubations as a proportion of all predicted easy intubations [=TN/ (TN+FN)].

Relative risk (RR) = ratio of the probability of difficult intubation occurring in patients with anticipated difficult airway to those with unanticipated difficult airway. Expressed mathematically as (TP/TP+FP)/(FN/FN+TN). Odd Ratio (OR) = compares the probability of difficult intubation in anticipated and unanticipated difficult intubation.

(Pa/1-Pa)/(Pb/1-Pb). Accuracy = percentage of correct results (both true positives and true negatives) as a proportion of all intubations [=(TP+TN)/ (TP+TN+FP+FN)].

CHAPTER THREE

METHODOLOGY

STUDY AREA: The study was carried out at the University of Calabar Teaching

Hospital (UCTH) Calabar after approval from the Health Research and Ethical

Committee of the hospital. The University of Calabar Teaching Hospital established in

1979 is a tertiary healthcare facility with four hundred and ten (410) beds. It serves as a training institution for Medical students, Postgraduate doctors and Allied Medical personnel.

STUDY DESIGN: This study was a descriptive cross-sectional study.

STUDY POPULATION: Three hundred and eighteen (318) adults requiring general anaesthesia with endotracheal intubation were evaluated after consenting for the study.

. INCLUSION

CRITERIA:

1. American Society of Anesthesiologists (ASA) grade I and II patients

2. Patients aged 18 years and above

EXCLUSION CRITERIA: includes

1. Edentulous patients,

2. Patients with midline neck swelling,

3. Patients with increased risk for aspiration of gastric contents (pregnant

patients/patients for emergencies),

4. Patients unable to sit or stand erect,

5. Patients allergic to drugs to be used in the study,

6. Patients undergoing general anaesthesia without tracheal intubation

7. Those with upper airway pathology (e.g maxillofacial fractures, tumours)

8. Patients that would rather benefit from fiberoptic tracheal intubation (e.g.

unstable cervical spine, previous impossible intubation)

SAMPLE SIZE: was obtained using the Cochrane formula for single proportion

n= Z2 p.q/ d2

Where: n = desired sample size when population >10,000. z = standard normal deviate which is 2.17 corresponding to the desired level of confidence (97% confidence interval).

p = proportion that have difficult intubation from previous study (5.8 %) q=1.0– p d = margin of error which is 0.03 ( desired level of precision ) n= (2.17)2(0.058) (0.942)/ (0.03)2≈286.

Attrition is 10% of the sample size (n).

So 90% of n =286 × 90n/100=317.77 n≈318.

Thus allowing for a margin of error of 3% or a degree of accuracy of 97% and 10% attrition, the needed sample size is 318.

SAMPLING TECHNIQUE: Patients who met the inclusion criteria were recruited using simple random sampling method.

EQUIPMENT:

1. Suction machine

2. Appliances: Macintosh Laryngoscope and blades, endotracheal tubes, stilletes.

3. Weighing scale (TCS, Shenyang Longteng Electronic ltd, Liaoning, China)

4. Measuring tape

5. Rigid meter rule (Prestige model, Hardik Medi-Tech,Sonipat,India )

6. Multiparameter patient monitors ( Mindray Mec1000, Shanghai Bio-Medical

Electronics Co.ltd, China )

7. Difficult airway cart with rescue medications: laryngeal mask airway, gum

elastic bougie, defibrillator, atropine, epinephrine, normal saline.

DATA COLLECTION: Pre-anaesthetic reviews (including airway assessment) were performed by the researcher. Each patient’s biodata including age, gender, ethnicity, body weight (Wt) and height (Ht) were obtained and body mass index (BMI) calculated

(Wt/Ht2). The height of each patient was measured in centimeters (using the standard rigid meter rule) from vertex to heel with the patient standing. This was rounded to the nearest 1cm.

The predictive tests performed on all the patients included:

Modified Mallampatti Test (MMT): assessed by asking the patient to sit such that the examiner’s eye is at the same level with the patient’s mouth. With the head in neutral position, the mouth is opened maximally and the tongue maximally protruded, without phonation. This test is graded as follows:

Class I: soft palate, fauces, entire uvula, and tonsillar pillars are visible; Class II: soft palate, fauces, tonsillar pillars and base of the uvula visible; Class III: Only soft palate visible

Class IV: Soft palate not visible

Grades III and IV were predictive of difficult intubation.

Then the MMT was repeated but with head in full extension {(Extended Mallampati

Score (EMS)}: Patient sitting, neck maximally extended, mouth maximally opened,

tongue maximally protruded and eye at same level with the examiner. This is graded same way as MMT. Neck circumference (NC) was taken in centimeters (cm) using measuring tape at the level of the thyroid cartilage and noted. Subsequently patient lay supine on a firm surface with the head fully extended and the mouth closed, thyromental distance (TMD) was measured using rigid ruler from the superior thyroid notch to the anterior-most part of the mandibular mentum. The distance was rounded to nearest 0.5 cm and graded as follows:

Class I: TMD>6.5cm

Class II: TMD=6.0-6.5cm

Class III: TMD<6.0cm

TMD less than 6.0 cm was considered predictive of difficult laryngoscopy and or intubation.15 Then NC/TMD ratio was calculated and values ≥ 5 was considered predictive of difficult intubation.51 While still on supine position with the head fully extended and the mouth closed, hyomental distance (HMD) was measured using rigid ruler from the tip of the skin surface just above the hyoid bone ( identified as the horseshoe shaped bone in the midline of the neck between the chin and the thyroid cartilage at the level of the base of the mandible anteriorly and the third cervical vertebra behind) to the anterior-most part of the mandibular mentum. This measurement was repeated with the head in neutral position and the mouth closed. Hyomental distance ratio (HMDR) is the ratio of HMD at extreme of head extension to HMD in neutral position. The distances were rounded to nearest 0.5cm.

HMD less than 3.5cm and HMDR <1.2, was considered predictive of difficult laryngoscopy and or intubation. These cut off points for different tests were chosen considering their previous use in earlier studies. Measurement of any distance was repeated and the average taken to reduce bias.

PROCEDURE

Standardized anaesthetic protocol for tracheal intubation followed in our hospital was used. Devices / tools (like laryngeal mask airway, gum elastic bougie, defibrillator ) and drugs like atropine and epinephrine for the management of the difficult airway were readily available in all the cases. After positioning the patient supine on a tiltable operation table, baseline vital signs (non-invasive blood pressure, electrocardiograph, heart rate, peripheral oxy-haemoglobin saturation, axillary temperature) were obtained using a Mindray Mec1000 multiparameter patient monitor

( Shanghai Bio-Medical Electronics Co.ltd, Hi-tech industrial park, China). An intravenous access was established with an l8 G cannula. Premedication with intravenous (i.v) midazolam 0.05 mg/kg and i.v pethidine 0.5 mg /kg was administered

10 minutes prior to induction of anaesthesia. After preoxygenation for about five minutes with 100% oxygen via a tight fitting face mask, anaesthesia was induced with i.v propofol 2mg/kg. After checking for loss of consciousness, i.v suxamethonium chloride (1.5 mg/kg) was administered to facilitate tracheal intubation. The patient's head was placed in a sniffing position after disappearance of fasciculations.

Laryngoscopy was then performed by the senior registrar working under the supervision of a consultant or the attending consultant anaesthetist (who were blinded to the preoperative assessments), using an appropriately sized Macintosh laryngoscope blade. 43

The direct laryngoscopic grading, as defined by Cormack and Lehane were noted. An appropriately sized stilleted endotracheal tube ( 7-8mm internal diameter ) was passed and the stillete removed. The cuff was inflated, capnograph attached, the tube connected to a breathing circuit (closed circuit) and the lungs ventilated manually. Correct tube placement was then verified (curve analysis of carbondioxide in the exhaled gas and by bilateral auscultation of lungs) and the tube secured with tape. Intubation time was noted by an independent observer (from the face mask removal to the appearance of the first capnography waveform). Anaesthesia was maintained with halothane in oxygen, i.v pancuronium 0.1mg/kg, and the analgesic (i.v pethidine). Each patient was routinely monitored during the whole procedure. The parameters monitored were non-invasive blood pressure, electrocardiography, peripheral oxygen saturation (SpO2), heart rate, end-tidal carbondioxide and axillary temperature.

At the end of surgery, the patient was adequately reversed with i.v neostigmine

0.05 mg/kg and i.v glycopyrrolate 0.008mg/kg. After thorough oral suctioning, patients were extubated awake, oxygenated and transfered to Post-Anaesthesia Care Unit

(PACU). The ease of intubation was correlated with the recently validated objective scale called the Intubation Difficulty Score (IDS) which encompases Comarck and

Lehane laryngoscopic grading64. A score of zero (0) is indicative of intubation under ideal conditions. Those with an IDS score of ≥5 and <5 is defined as the difficult and easy intubation groups, respectively.50

DATA ANALYSIS

The pre-operative airway assessment data and the findings during intubation were used to determine the sensitivity, specificity, accuracy, positive predictive value

(PPV), and false positive (FP) values of each predictor singly and then in combinations.

This was on a 2x2 contingency table. A receiver operating characteristic curve

{obtained by calculating the sensitivity (true positive fraction) and specificity (true negative fraction) of every observed data value (cut-off value), and plotting sensitivity against 1-specificity (false positive fraction)}. A corresponding p-value of < 0.05 indicated that the Area Under the Curve(AUC) was greater than was observed by chance alone.61 Statistical analysis was performed with Statistical Package for Social Sciences

(SPSS) Inc version 20.0, Chicago, IL, USA. The level of agreement between the predictors and intubation difficult score was presented in tables and significant differences determined using Chi-square(X2) test. This test also determined whether there was significant differences between gender and intubation difficulty score.

Student’s t-tests was performed to determine whether there would be significant differences in age, BMI, neck circumference and intubation difficulty score.

CHAPTER FOUR

RESULTS

A total of 318 patients were studied but 4 sets of data could not be retrieved

(missing) and 314 were thus reported. Of these, 125 (39.81%) were male and 189

(60.19%) were female. There was no failed intubation. Ninety three (29.62%) of the patients were 50 years old and above while 221 (70.38%) were below 50 years of age

(Table I). The mean age of the patients was 39.59 ± 15.39 years (Table II). Twenty nine

(9.23%) had a BMI lower than 18.5, while those in the 18.5-25.0 category were 169

(53.82%) and 116 (35.94) had a BMI higher than 25.0 (Table I). The mean weight of the patients was 64.20 ± 10.34 kg, and their mean height was 1.64 ± 0.055m. Their mean BMI was 23.84 ± 4.41 while the average neck circumference (NC) for men and women were 35.55±3.23cm, and 35.08±3.07 respectively as seen in Table II.

Table I: Socio-Demographic Characteristics Of The Participants

Variables Test Variables Frequency Percentage (%)

Sex Male 125 39.81

Female 189 60.19

Age < 50 221 70.38

 50 93 29.62

BMI <18.5 29 9.23

18.5-25.0 169 53.82

>25.0 116 36.94

BMI= Body Mass Index (kg/m2)

Table II: Descriptive Statistics of participants’ demography

PARAMETER MEAN (S.D) RANGE

AGE (Yrs) 39.59±15.39 18---85

Wt (Kg) 64.21±10.35 35----112

Ht (m) 1.65±0.06 1.54----1.85

BMI (Kg/m2) 23.85±4.42 11.69----42.97

NC (cm) 35.55±3.23(male) 30----40.5

35.08±3.07(female) 30-----38

S.D= Standard deviation, NC= Neck Circumference, Ht=Height

A total of 314 patients were successfully intubated. Out of this, 5 (1.59%) had difficult intubation based on the Intubation Difficulty Score (scores ≥5); two were males (0.64%) and 3 were females (0.96%). Three hundred and nine (98.41% ) had easy intubation on the same scale ( scores<5); one hundred and twenty three were males

(39.17%) while 186 were females (59.24%) as shown in Tables III and IV . Thus the incidence of difficult intubation in University of Calabar Teaching Hospital according to this study was estimated to be 1.59% (Table III).

Table III: BMI and Incidence of difficult laryngoscopy using IDS

BMI IDS Total % (Kg/m2) E.I D.I

Frequency % Frequency % 18.5-25 167 53.18 2 0.64 169 53.82 >25 115 36.62 1 0.32 116 36.94 <18.5 27 8.61 2 0.64 29 9.24 Total 309 98.41 5 1.59 314 100.0 *IDS = Intubation Difficulty Score

Table IV: Age and Gender showing ease of intubation using IDS

IDS GENDER AGE (yrs)

M(freq) % F(freq) % Total ≥50 % <50 % Total

2 0.64 3 0.96 5 3 0.96 2 0.64 5

EI 123 39.16 186 59.24 309 214 68.15 95 30.26 309

Total 125 39.80 189 60.20 314 217 69.11 97 30.90 314

E.I = Easy intubation; D.I = Difficult Intubation

The EMT predicted that 8 out of the 314 participants (2.55%) were to have difficult intubation (DI) and 306 (97.45%) easy intubation (EI) as shown in Table VI.

The HMDR predicted 74 DI (23.57%) and 240 EI (76.43%) while NCTMDR predicted

12 DI (3.82%) and 302 EI (96.18%). These predictions however did not correspond to the findings intraoperatively (during laryngoscopy) as all the patients were either

Cormack and Lehane grade I (184 patients) or II (130 patients). There was no grade III or IV patient (Table V)

TABLE V : Predictors and Findings at Laryngoscopy

PREDICTORS EASE OF INTUBATION BASED ON CORMACK AND

LEHANE GRADES

Grade I & II % Grade III & IV %

EMT (I/II) 306 97.45 0 0

III/IV 8 2.55 0 0

HMDR>1.2 240 76.43 0 0

<1.2 74 23.57 0 0

NC/TMDR<5 302 96.18 0 0

≥5 12 3.82 0 0

The three predictors had low false positive values ( 1 for EMT, 2 for HMDR and 1 for

NC/TMDR) as depicted on the 2 by 2 contingency table ( Table VII ). EMT had the least false negative (4), followed by NC/TMDR (8) and HMDR the largest (71).

Table VI: Prediction of difficult Intubation by the three predictors

PREDICTOR OUTCOMES

EI % DI % Total

EMT 306 97.45 8 2.55 314

HMDR 240 76.43 74 23.57 314

NCTMDR 302 96.18 12 3.82 314

E.I = Easy intubation; D.I = Difficult Intubation; Total= EI + DI

The relationship / agreement between intubation difficulty score and the three predictors (Table VII ) showed that although each of them was an independent predictor of difficult intubation, the agreement was far more significant only for EMT and NC/TMDR. The EMT had the highest precision of the agreement/relationship with a

kappa coefficient of 0.608 (p-value <0.001). Thus the degree of accuracy of EMT was better than that of the anatomical distances.

Table VII: Agreement between IDS and the three predictors

PREDICTORS EASE OF INTUBATION BASED ON IDS

EI (<5) DI(≥5) Kappa coe. P-value

EMT (I/II) 305(97.13) 1(0.32) 0.608 <0.001 III/IV 4(1.27) 4(1.27)

HMDR>1.2 238(75.80) 2(0.64) 0.048 0.053 <1.2 71(22.61) 3(0.96)

NC/TMDR<5 301(95.86) 1(0.32) 0.458 <0.001 ≥5 8(2.55) 4(1.27)

Figures in parentheses are in percentage. Percentage was calculated by dividing every cell number by 314.

Table VIII presents sensitivity, specificity, positive predictive value (PPV), and negative predictive values (NPV) of each predictor (EMT, HMDR and NC/TMDR) singly and in combinations based on the IDS classification. It showed that the EMT was the most sensitive of the single tests in the prediction of difficult intubation with a sensitivity of 50.0% (95% CI: 15.7-84.3), specificity of 99.7% (95% CI:98.19- 99.99),

PPV of 80%, NPV of 98.7% with a positive likelihood ratio of 153. The significance were at P-values < 0.05 (5%). The HMDR was the least sensitive of the single tests having a sensitivity value of 4.05%, specificity of 99.1% (Table VIII). All the test had

very high specificity values with the EMT and the NC/HMDR having a tie at 99.7%

(95% CI: 98.17- 99.99). The P-values were all significant ranging between 0.000 to

0.092.

Generally, the area under the curve (AUC) for a receiver operator characteristic curves (ROC) of a perfect test is 1.0 and that of a less sensitive test is < 0.5. Values of area under the curve (AUC) between 0.5 to 0.7 are associated with marginally useful test, an area of 0.7 to 0.9 with a good test and an area greater than 0.9 with an excellent test. The area under the curve (AUC) was good for each of the predictors (> 0.5 but less than 0.9 ) and also significant ( p-values<0.05) as shown in Tables VIII and IX. The

EMT was the most accurate single predictor of difficult intubation with area under the curve (AUC) of receiver operator characteristic curve (ROC) of 0.878 (p-value<0.001;

Figure III). HMDR was the least with AUC of 0.568 (Table IX; Figure II)

Table VIII: Predictive profiles for EMT, HMDR and NC/TDR

Tests Sen 95% Spec 95% CI +LR -LR PPV NPV AUC p- SE 95% CI (%) CI (%) (%) value (%) of ROC Curve

15.7- 98.19- 0.779- EMT 50.0 99.7 153.0 0.50 80.0 98.7 0.878 0.000 0.050 84.30 99.99 .0977

0.84- 97.02- 0.493- HMDR 4.05 99.1 4.86 0.97 60.0 77.0 0.568 0.076 0.038 11.39 99.90 0.644

9.92- 98.17- 0.564- NCTMDR 33.3 99.7 100.7 0.67 80.0 97.4 0.736 0.006 0.088 65.11 99.99 0.908

6.76- 97.20- 0.000- EMT + HMDR 50.0 99.0 51.67 0.5 40.0 99.4 0.745 0.092 0.161 93.24 99.80 1.000

19.41- 97.69- 0.000- EMT + NCTMDR 75.0 99.4 116.25 0.25 60.0 99.7 0.872 0.011 1.30 99.37 99.92 1.000

14.66- 97.68- 0.000- HMDR + NCTMDR 60.0 99.4 92.70 0.40 60.0 99.4 0.797 0.023 0.137 94.73 99.92 1.000

EMT+HMDR + 15.81- 97.22- 0.000- 100.0 99.0 104 0.00 40.0 100.0 0.995 0.016 0.004 NCTMDR 100.0 99.80 1.000

+LR: Positive Likelihood ratio, -LR: Negative Likelihood ratio, +PPV: Positive predictive value; -PPV: Negative predictive value; SE: Standard error. 95% confidence interval, EMT: extended allampati test; NCTMDR: Neck circumference over Thyromental distance ratio; HMDR: Hyromental distance ratio;

Table IX: Area under the Curve (AUC) for the Predictors

Test IDS Confidence

Interval

AUC Std. Error P-Value Lower Upper

Bound Bound

EMT 0.878 0.050 0.000 0.779 0.977

HMDR 0.568 0.038 0.076 0.493 0.644

NC/TMDR 0.736 0.88 0.06 0.564 0.908

The multivariate analysis odds ratios (95% CI) of the different combinations of the predictors ( EMT+ HMDR, EMT+ NC/TMDR and the HMDR+NC/TMDR ) were

11.79 ( 5.578 - 24.937), 1.52 ( 0.613 - 3.771) and 0.129 ( 0.068 - 0.243) respectively (

Table Xa, Xb and Xc). Thus it was estimated that EMT could predict difficult intubation about 12 times better than HMDR and also about 1.5 times better than NC/TMDR. Thus there was a significant difference in the efficacy / predictive profile of Extended

Mallampati test (EMT), hyomental distance ratio (HMDR) and neck circumference- thyromental distance ratio (NC/TMDR) in the prediction of difficult intubation.

Table Xa: Risk Estimate

95% Confidence Interval

Value Lower Upper

Odds Ratio for TEST 11.794 5.578 24.937

(EMT / HMDR)

For cohort DI = No 1.275 1.196 1.359

For cohort DI = Yes .108 .053 .220

No of Valid Cases 628

Table Xb: Risk Estimate

95% Confidence Interval

Value Lower Upper

Odds Ratio for TEST 1.520 .613 3.771 (EMT / NCTMDR)

For cohort DI = No 1.013 .985 1.042

For cohort DI = Yes .667 .276 1.609

No of valid cases 628

Table Xc: Risk Estimate

95% Confidence

Interval

Value Lower Upper

Odds Ratio for TEST .129 .068 .243

(HMDR / NCTMDR)

For cohort DI = No .795 .744 .848

For cohort DI = Yes 6.167 3.420 11.120

No of Valid Cases 628

When compared with the EMT, the combination of the three predictors increased the sensitivity to 100% at the expense of decreasing the specificity to 99%, the positive predictive value (PPV) to 40% and the positive likelihood ratio (PLR) to 104. The combination with the best results was the EMT and NC/TMDR with sensitivity, specificity, positive Likelihood Ratio (PLR), positive predictive value (PPV), the area under the curve (AUC) of ROC curve of 75.0%, 99.4%, 116.25, 60.0% and 0.872

respectively (Tables VIII and IX). When the hyomental distance ratio (HMDR) was combined with neck circumference-thyromental distance ratio (NC/TMDR), it showed a higher sensitivity (60%) compared to the sensitivity of EMT (50.0%) alone (Table

VIII). However, their specificity in this combination (HMDR and NC/TMDR) was lower ( 99.4% ) than that of EMT (99.7%). The EMT also had a higher area under the curve at 0.878 (95% CI: 0.779-0.977) than the combination of HMDR and NC/TMDR which was at 0.872 (95% CI: 0.000-1.000). It was finally noted that the EMT improved the predictive values of the anatomical distances (HMDR and NC/TMDR) in all the combinations (Table VIII).

Univariate analysis showed no significant relationship between body mass index

(BMI) and difficult intubation based on intubation difficulty score ( p- value 0.055) as shown in Table XI.

Table XI: Association between BMI and Difficult Intubation Score (IDS)

Chi-Square Test

Asymp. Sig.

Value Df (2-sided)

Pearson Chi- 5.795 2 .055

Square

Likelihood Ratio 3.563 2 .168

N of Valid Cases 314

The correlation matrix of a simple linear regression showed that the two variables, neck circumference and body mass index (BMI), are related with Pearson’s correction coefficient of 0.019 but this relationship was not strong as the level of

significance was 0.743 (Table XIIa). The model summary also showed that the coefficient of determination ( R-square) was 0.000 suggesting that approximately 0 % of the dependent variable ( neck circumference) could be predicted by the BMI (Table

XIIb). Again the analysis of variance (ANOVA) revealed a significance level of 0.743 suggesting that for the model regression, BMI was not a better predictor of the outcome

/ dependent variable ( neck circumference) as depicted in Table XIIc.

TABLE XIIa : CORRELATIONS

BMI NC

BMI Pearson Correlation 1 .019

Sig. (2-tailed) .743

N 314 314

NC Pearson Correlation .019 1

Sig. (2-tailed) .743

N 314 314

TABLE XIIb : Model Summary

Adjusted R Std. Error of the

Model R R Square Square Estimate

1 .019a .000 -.003 2.015

TABLE XIIc : ANOVAb

Sum of Mean

Model Squares df Square F Sig.

1 Regressio .436 1 .436 .107 .743a

Residual 1266.659 312 4.060

Total 1267.096 313

a. Predictors: (Constant), BMI; b. Dependant variable: NC

The slope/grading of the regression line showed that at every point increase

in BMI, the neck circumference increases by 0.008 times. However, this

increase was not significant as the p- value was 0.743 (Table XIId).

TABLE XIId: Coefficientsa

Unstandardized Standardized

Coefficients Coefficients

Model B Std. Error Beta t Sig.

1 (Constant) 35.232 .625 56.347 .000

BMI .008 .026 .019 .328 .743

a. Dependent Variable: NC

The multivariate logistic regression with a level of significance considered at p-values

< 0.05, showed no significant relationship between the patients’ characteristics (age, gender, BMI and neck circumference) and difficult intubation (Table XIII). However, at p-value < 0.06, BMI was more related to difficult intubation than other patients’ characteristics / variables.

Table XIII: Multivariate logistic regression (forward-Wald) analysis

Variables in the Equation

B S.E. Wald Df Sig. Exp(B)

AGE .047 .033 2.099 1 .147 1.049

BMI -.270 .145 3.461 1 .063 .763

GENDER .086 .945 .008 1 .927 1.090

NC .013 .220 .004 1 .953 1.013

Constant -.524 7.675 .005 1 .946 .592

Variable(s) entered : AGE, BMI, GENDER, NC

BMI= Body Mass Index, NC= Neck Circumference, Sig= p- value

FIGURE 1: AUC FOR NCTMDR

AUC=0.736

FIGURE 2: AUC FOR HMDR

AUC=0.568

FIGURE 3: AUC FOR EMT

AUC=0.878

CHAPTER FIVE

DISCUSSION

The incidence of airway and haemodynamic complications increases beyond two laryngoscopic attempts especially during emergency airway management.66 Thus this study becomes clinically significant as repeated tracheal intubation attempts during difficult intubation may contribute to patient morbidity (including permanent brain damage) and mortality.67,68 Prediction of a difficult airway to prevent unanticipated difficult tracheal intubation and consequent events and development of plan to convert a difficult intubation into an easy one is an important concern for anaesthesiologists.69

This study also advocates on the need for establishment of Preoperative Assessment

Clinics in every hospital. Sunanda et al28 in their work titled Airway assessment:

Predictors of difficult airway stated that Difficult Airway Clinics/Preoperative

Assessment Clinics allow time for optimal preparation, proper selection of equipment and technique and participation by personnel experienced in difficult airway management.

In this study, the incidence of difficult intubation was found to be 1.6% which was within the 0.5-18% stated by Zahid et al10 and what Merah et al21 reported

(incidence of 1-4%). It was also comparable to other studies that stated the incidence to be between 1% and 15%.70,71 One of the major reasons for these variations could be traced to the type and size of laryngoscope blade used72, the degree of muscle relaxation, different definitions for difficult intubations and the different reference standards used for the different studies. Some of the reference standards were based on Cormack and

Lehane intubation grades,69,73 others on number of laryngoscopic attempts74 and use of

Backward Upward Rightward Pressure (BURP) manoeuvre.75 In this study Intubation difficulty score (IDS) was used and it encompasses the number of supplementary attempts, the number of additional persons directly attempting intubation, the number of alternative techniques used, the glottic exposure as defined by the Cormack and

Lehane grading , the lifting force applied during laryngoscopy, the necessity of applied external laryngeal pressure to optimize the glottic exposure, and the position of vocal cords.64

Allahyary et al76 stated that any preoperative assessment test of difficult tracheal intubation should have a high sensitivity and specificity to result in minimal false positive or false negative. This was in concordance with the findings from this study as it showed that Extended Mallampati test (EMT) was the most sensitive among the three predictors with a sensitivity of 50.0% (95% CI: 15.7-84.3), specificity of 99.7%

(95% CI:98.19- 99.99), positive predictive value (PPV) of 80%, negative predictive value (NPV) of 98.7%, positive likelihood ratio (PLR) of 153, false positive value of 1 and false negative value of 4. The low false positive and false negative has a clinical implication of reducing the chances of missing a difficult intubation.77 Mohammedreza et al78 equally reported a higher sensitivity for EMT (66.67%) though the specificity,

PPV, NPP and PLR they got were lower (68.62%, 13.7%, 96.5% and 2.12 respectively).

Similarly, Mashour et al79 also demonstrated that craniocervical extension increases both the sensitivity and specificity of Modified Mallampati test ( 83% and 80% respectively). However Ashish et al33 argued that the addition of neck extension did not improve the predictive value of modified Mallampati test and showed that the sensitivity and specificity of EMT were 13% and 65% respectively. But their study was carried out not in normal patients but in acromegalics who were only 39 in number.

This could have introduced bias into the study.

Mohammedreza et al78 observed that EMT had an area under the curve (AUC) of

Receiver Operator Characteristic curve of 0.703. This study however did not only show that AUC value of EMT was 0.878 which was suggestive of higher accuracy but also showed that though EMT, HMDR, and NC/TMD are related to difficult intubation, the relationship is statistically significant only for EMT and NC/TMDR. EMT however had the highest precision of this relationship with a kappa coefficient of 0.608 (p-value <

0.001).

Vikas et al80 showed in their study that the sensitivity and specificity of HMDR were 27.78% and 98.89% respectively. Similarly, Huh et al49 reported higher sensitivity for HMDR ( 88% ) at the expense of low specificity (60%). Their worked further stated that by having an area under the curve (AUC) of receiver operator characteristic curve of 0.782, HMDR had the greatest diagnostic accuracy than other single predictors in that study (modified Mallampati Test, HMD in neutral position, HMD in extended neck position, and TMD in extreme of neck extension). This study on the contrary showed that the sensitivity and specificity of HMDR were 4.05% and 99.1% respectively. It 69

also demonstrated that HMDR was the least accurate of the single predictors with AUC of 0.568 and the least significantly related to the intubation difficulty score (IDS) with a p-value of 0.053 and the least kappa coefficient of 0.048. These differences in the predictive profile could be from interobserver variability and also from possible differences in anthropometrical characteristic of the different populations used.

When in combination with the EMT, the sensitivity of HMDR was however found to be increased to 50%. These results were comparable with the work done by

Khan et al75 which concluded that combination of predictors increases sensitivity. In this study, EMT improved the predictive profile of the anatomical distances (HMDR and NC/TMDR) in all combinations. Merah et al13 reported that combination provided the best predictive profile in their study involving three predictors which were MMT,

Thyromental distance and interincisor gap ( sensitivity of 84.6%, specificity of 94.6%, and positive predictive value of 35.5%). The best predictive profile in this study was also the combination of the three predictors EMT, HMDR and NCTMDR (sensitivity of 100%, specificity of 99%, positive predictive value of 40% and Area under the curve of 0.995).

Rose et al54 reported that risk factors for difficult endotracheal intubation included being aged 40-59, male, and obese. In this study, out of the five participants that had difficult intubation, 3 were females and 2 were males; three (3) were between

50 – 54 years old and the remaining 2 were between 18 and 33 years old. This is similar to what Ezri et al81 reported that laryngoscopy grades and airway classes increase with age most likely owing to changes in bone joints and poor dental condition. Hyoung-Yong et al82 further also demonstrated that factors related to difficult endotracheal intubation 70

statistically increased with age as the old age group (≥60 years) had low head and neck movement, a short thyromental distance, poorer dentition, limited head and neck movement, small interincisor gap, a high Mallampati score, rigid cervical joints and higher frequency of Cormack and Lehane grades 3 or 4 than the middle age group (40-

59) and the young group (<40 years). However this study showed that statistically age has no significant relationship with difficult intubation as depicted by the Chi-square and the Logistic regression.

Ben-Noun et al83 reported that neck circumference (NC) ≥37 cm for men and

≥34 cm for women were the best cutoff levels for determining subjects with BMI ≥

25.0 kg/m2. Thus Mendane et al84 in their work reported an average neck circumference

(NC) of 40.27±3.4 cm for the men and 33.43±3.17 cm women in 411 participants.

Eighty five percent ( 85% ) of the men and 38.8% of women had NC ≥37cm and ≥34 cm respectively. In this study, the mean neck circumference (NC) for men and women were 35.55±3.23cm, 35.08±3.07 cm respectively. Approximately 30% of men and

70.1% of women had NC ≥37cm and ≥34 cm respectively. However, 82.2% of males had neck circumference >35cm. Mendane et al84 however worked on Turkish adults and adult Nigerians only participated in this study. This could account for differences in neck circumferences in these different studies. Helene et al85 further demonstrated that in obese patients with intubation difficulty score (IDS) ≥5, large neck circumference is a predictor of potential intubation problems besides thyromental distance, body mass index (BMI) and Mallampati score. Raid et al86 opined from their study on 104 morbidly obese patients that only neck circumference more than 42cm (p=0.44) was an independent predictor of difficult intubation. This study however showed no statistical 71

correlation between neck circumference and difficult intubation (at p-value <0.05). This could be from the paucity of obese participants in this study ( only 7% {22 in number } of the participants in this study were obese).

Even though BMI showed a relation with difficult intubation in this study (as shown by the Chi square analysis and logistic regression), it was not statistically significant. This was in agreement with the study by Brodsky et al74 which reported that morbid obesity is not an independent predictor of difficult intubation. Furthermore,

Wilson87 developed a five factor evaluation mechanism after reviewing the features of patients who had proven to be difficult to intubate. Patient weight, head and neck movement, jaw movement, mandibular size and prominence of the upper incisors were each graded (0-2) and a rank sum score was determined. Of the five factors identified by multivariate analysis as contributing to difficult intubation, obesity was the weakest predictor. However, Merah et al13 observed that apart from MMT, TMD and interincissor gap (IIG), patient’s weight was also an independent predictor of difficult visualization of the larynx.

In conclusion, in the prediction of difficult intubation, the predictive profile / efficacy of Extended Mallampati Score, hyomental distance ratio (HMDR) and neck circumference-thyromental distance ratio differ. The null hypothesis was rejected and the alternative accepted. Though EMT, HMDR and NC/TMD are related to difficult intubation, the relationship is significant only for EMT and NC/TMDR. EMT however had the highest precision of this relationship and improved the predictive profile of the anatomical distances in all combinations. Thus EMT represents a useful means of achieving a faster, simpler and yet more accurate prediction of difficult airway than 72

the anatomical distances (HMDR and NC/TMDR). Though BMI showed a relationship with difficult intubation, this relationship was not significant. There was no statistically significant relationship between age, gender, neck circumference, BMI and difficult intubation.

RECOMMENDATIONS

Several preoperative difficult airway predictors had been in use in the past but they were characterized by low sensitivity, low positive predictive value and high false positives and none of them has 100% accuracy.68 Thus airway assessment during pre- anaesthetic reviews need to be comprehensive as advised by ASA as it is now known that the more the predictors used, the higher the accuracy of prediction.68 This study showed that only EMT and NC/TMD are significantly related to intubation difficulty score. Therefore for an optimum combination of predictors of difficult intubation, EMT and NC/TMD together with any other predictor(s) is strongly recommended. If one predictor alone could be used for prediction of difficult intubation , the EMT should be opted for. 73

LIMITATIONS OF THE STUDY

Intraoperatively, positioning of the patients may have affected the incidence of difficult intubation as obese patients were better placed in ramped position instead of the ‘sniff’ position. Furthermore, the interobserver variability seen during direct

laryngoscopy performed by different experienced anaesthetists could have introduced bias into the study as the Cormark and Lehane classification is still subjective. Again because the experience of the laryngoscopist could actually increase the incidence of difficult intubation during laryngoscopy, experienced laryngoscopists (consultants and senior registrar) were used in the study.

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APPENDIX I

ETHICAL APPROVAL

APPENDIX II

PATIENT’S INFORMED CONSENT FORM

I am carrying out a study titled ‘Effectiveness of Extended Mallampati Score,

Hyomental Distance Ratio and Neck Circumference-Thyromental Distance Ratio in

Predicting Difficult Intubation’. You have been selected to participate in the study.

When a person comes in for general anaesthesia in an operating room, there is need for his/her airway to be maintained and protected once unconscious. The anaesthetist uses a tube called endotracheal tube for this purpose. But sometimes it may become difficult or impossible for the anaesthetist to pass this tube down the patient’s airway/throat. The person stands a risk of reduced oxygen supply to the brain which may lead to serious brain damage or even death. The aim of this study is to predict before surgery intubations that would be difficult or impossible with high accuracy using conventional direct laryngoscopy.

Name and affiliations of researcher: This study is being conducted by Dr. Amechi

Chukwudum Ezike in the department of Anaesthesia and Intensive Care of University of Calabar Teaching Hospital (U.C.T.H) Calabar.

Purpose of research: The purpose of this research is to predict before surgery intubations that would be difficult or impossible with high accuracy.

Procedure and requirement for each patient: This study will involve opening your mouth for some seconds for assessment of some structures in your mouth and using

weighing scale, metre rule, measuring tape and caliper (as the case may be) to check your weight, height, neck circumference and some distances below your jaw.

Expected duration of participant’s involvement: we expect you to be involved in the research for about twenty (20) minutes.

Risk(s): There is no risk you are exposed to in participating in this study.

Costs of participation: All the measurements in this study are free (that is there will be no additional charges to you for taking part in this study).

Benefit: The study will lead to improvement in management of patients with difficult airways coming for surgery. By participating, you are contributing to advancement of medical knowledge and improvement in healthcare.

Confidentiality: All information obtained from you will be treated with strict confidentiality and no part of such information shall be divulged to anybody except the investigators. They will be used for research purposes only.

Voluntariness: Your participation in the study is entirely voluntary.

Alternative to participation: If you choose not to participate, this will not affect your treatment in any way.

Consequences of withdrawal: You can also choose to withdraw your participation at any time during the study without prejudice. This will neither affect the care you will receive in any way nor add to the cost of your surgery.

What happens to participants when research is over: You will be informed of the outcome of the research especially if the research detected you have difficult airway.

This would be boldly written at the front page of your folder to alert any anaesthetist in case you come for operation another time.

Statement of the Researcher: I have fully explained this research to

……………………………………………………..and have given sufficient information including the risks and benefits to make an informed decision.

DATE: ……………………………

SIGNATURE OF THE RESEARCHER: ………………………

NAME OF RESEARCHER:

…………………………………………………………………

Statement of the participant: I have read the description of the research or have had it translated into a language I understand. I have also talked it over with the doctor to my satisfaction and understood that my participation is voluntary. I now know enough about the purpose, methods, risks and benefits of the research study to judge that I want to take part in it. I understand i may freely stop being part of this study at any time. I have received a copy of this consent form and additional information sheet to keep for myself.

DATE: ……………………………

SIGNATURE/THUMBPRINT OF THE PARTICIPANT:

……………………………………

NAME OF THE PARTICIPANT: …………………………………………………..

NAME OF THE WITNESS: …………………………………………

SIGNATURE OF THE WITNESS: ………………………………………

APPENDIX III

QUESTIONNAIRE

BIODATA Serial

Number in the study:…..……… Patient’s Initials: ……………

Hospital No:….……… Age (yr):….……… Tribe :………… Weight

(kg):………..… Height (cm):………….. Neck Circumference(cm) : ………

ASA class: ……………... BMI………………… GENDER……………….

AIRWAY ASSESSMENT TEST

Modified Mallampati class:……………. Extended Mallampati class: …......

HMD (neutral position):……..… HMD (in extreme head extension): ……… TMD

(in extreme head extension): ……… NC/TMD:……………………..

INTRA-OPERATIVELY Cormack

& Lehane class: ………Number of attempts at laryngoscopy: ……….

Failed Intubation: Yes/No Number of helpers needed at laryngoscopy:…… Need for other Intubation aids: Yes / No

If Yes, specify ……………………………………………

Lifting force: Considerable or inconsiderable.

Use of external laryngeal manoeuvre: Yes or No

Vocal cords: Abducted or adducted

The Intubation Difficulty Score (IDS) =......

APPENDIX IV

GRADES FOR COMARCK/ LEHANE AND INTUBATION

DIFFICULTY SCORE

Cormack and Lehane laryngeal view is graded as follows:

Grade I = full view of the glottis, vocal cords visible

Grade II = glottis partly exposed, only posterior commissure or arytenoids seen,

Grade III = only epiglottis seen, Grade IV = epiglottis not seen.18

The Intubation Difficulty Score (IDS) is graded as follows:

N1, number of additional intubation attempt;

N2, number of additional Anaesthetist for the laryngoscopy/intubation. N3, number of alternative intubation techniques used i.e the use of different intubation skills( N3=1 if patient would be repositioned or a change in intubation technique, such as a blade or a tube change) N4, laryngoscopic view as defined by

Cormack and Lehane (grade 1, N4=0; grade 2, N4=1; grade 3, N4=2; grade 4, N4=3);

N5, lifting force applied during laryngoscopy (N5=0 if inconsiderable and N5=1 if considerable);

N6, needed to apply external laryngeal pressure for optimized glottic exposure (N6=0 if no external pressure or only the Sellick manoeuvre was applied and N6=1 if external laryngeal pressure was used);

N7, position of the vocal cords at intubation (N7=0 if abducted or not visible and N7=1 if adducted). The IDS score is the sum of N1 through N7.