Difficult Airway in Obstetric Anesthesia

Volume 56, Number 10 OBSTETRICAL AND GYNECOLOGICAL SURVEY Copyright © 2001 by Lippincott Williams & Wilkins, Inc. CME REVIEWARTICLE 28 CHIEF EDITOR’S NOTE: This article is the 28th of 36 that will be published in 2001 for which a total of up to 36 Category 1 CME credits can be earned. Instructions for how credits can be earned appear on the last page of the Table of Contents. Difficult Airway in Obstetric Anesthesia: A Review Tiberiu Ezri, MD,* Peter Szmuk, MD,† Shmuel Evron, MD,‡ Daniel Geva, MD,§ Zion Hagay, MD,¶ and Jeffrey Katz, MDʈ From the *Director, Department of Anesthesia and ‡Head, Obstetric Anesthesia Unit, Wolfson Medical Center, Holon, Israel; §Director, Department of Anesthesiology and ¶Professor and Chairman, Department of Obstetrics and Gynecology, Kaplan Hospital, Rehovot, Israel; and †Assistant Professor and Head, P.A.C.U. and ʈProfessor and Chairman, Department of Anesthesiology, University of Texas-Houston Medical School, Houston, Texas Failed intubation and ventilation are important causes of anesthetic-related maternal mortality. The purpose of this article is to review the complex issues in managing the difficult airway in obstetric patients. The importance of prompt and competent decision making in managing difficult airways, as well as a need for appropriate equipment is emphasized. Four case reports reinforce the importance of a systematic approach to management. The overall preference for regional rather than general anesthesia is strongly encouraged. The review also emphasizes the need for professional and experienced team cooperation between the obstetrician and the anesthesiologist for the successful management of these challenging cases. Target Audience: Obstetricians & Gynecologists, Family Physicians Learning Objectives: After completion of this article, the reader will be able to break down the complex issues in managing the difficult airway in the obstetric patient, outline the reasons for difficult intubations in pregnancy, and describe the evaluation used to predict a difficult intubation. The inability to maintain a patent airway after tical points of this review are exemplified by presen- failed or difficult intubation and ventilation remains a tation of reports of problematic airway cases. major concern of anesthesia-related maternal mor- bidity or mortality and a significant source of mal- practice claims in obstetrics (1, 2). The purpose of DEFINITION OF DIFFICULT AIRWAY this review is to define the difficult airway, highlight The difficult airway is defined according to the the main reasons for difficult or failed intubation, and stage of airway management in which it is encoun- propose a practical approach to management. It is tered; i.e., laryngoscopy, intubation, or ventilation intended that this review will enrich the practitioner’s (3). Difficult laryngoscopy is defined as the inability knowledge of the complex issues of airway manage- to visualize any portion of the vocal cords. Endotra- ment and enhance his involvement in anesthetic de- cheal intubation is considered difficult if it requires cision making. As noted throughout the review, an more than three attempts or takes longer than 10 important component is the necessity for teamwork minutes. This definition has been recently challenged between anesthesiologist and obstetrician. The prac- by Benumof (4), who considers that a reasonably experienced anesthesiologist would be able to recog- Reprint requests to: Tiberiu Ezri, MD, Director, Department of nize a difficult intubation (laryngoscopy) from the Anesthesia, Wolfson Medical Center, Holon, Israel. Email: [email protected] first attempt. Difficult mask ventilation means an The authors have disclosed no significant financial or other inability to maintain oxygen saturation (SaO2) over relationship with any commercial entity. 90% with an inspired oxygen concentration of 100% 631 632 Obstetrical and Gynecological Survey (O2) and positive-pressure ventilation. These defini- Preexisting airway deformities. Airway abnormal- tions are intended to establish clear-cut criteria and ities may interfere with intubation mainly by one or an exact quantification of the time and number of more of the following mechanisms: decreased mo- attempts at intubation and may help the anesthesiol- bility of the neck, limited mouth opening, and re- ogist in deciding whether to call for assistance or to duced submandibular space. Table 1 depicts some choose another approach for securing the airway. changes in airway anatomy (not specific for pregnant However, it should be understood that it is the failure patients) that interfere with the normal visualization in oxygenation and ventilation that causes a fatal of the cords. Of these, the most frequently encoun- outcome and not the inability to intubate per se. tered are “bull neck,” “buck teeth” and micrognathia. Thus, the ability to ventilate the patient effectively is In any of these cases, the anesthesiologist should of paramount importance. expect difficult intubation. Pilkington et al. (10) dem- onstrated in 242 pregnant women that the incidence of Class III airway (Mallampati classification) in- INCIDENCE OF DIFFICULT INTUBATION creased by 34% as pregnancy progressed. Mallam- AND VENTILATION pati classification is based on the view of the back of In obstetric anesthesia, difficult intubation is fre- the mouth with the tongue protruded. The higher the quently unexpected. Although the incidences of air- grade (grade IV), the less visible is the junction way difficulties encountered were low (7.9%) (5), between the soft and hard palate. The lower the grade they were still greater than those in the nonobstetric (grade I), the more visible is the whole soft palate population (2.5%) (6). The reasons for the higher (uvula). incidence of difficult airway in obstetric patients are Airway edema. Airway edema results from hor- not always evident. Interestingly, the incidence of monally induced fluid retention during pregnancy. very difficult intubation is very similar in both ob- This process is augmented by pregnancy-induced stetric and nonobstetric populations, 2% versus hypertension, if present, and by other conditions, 1.8%, respectively (6, 7). However according to such as excess weight gain, fluid overload, head- Hawthorne et al. (8), the incidence of failed intuba- down position, oxytocin infusion (fluid retention due tion in the obstetric population is 0.4%—approxi- to the antidiuretic effect), and prolonged Valsalva mately 10 times more frequent than in the general efforts (11). Repeated intubation attempts may result surgical patient population. The number of failed in mucosal congestion that may lead to airway edema intubations has not decreased over the last 10 years. and bleeding. Edema of the face and neck should Mask ventilation was found to be laborious or im- alert the anesthesiologist to the possibility of difficult possible in 0.02% of patients (9), an incidence com- intubation, whereas edema of the tongue may herald mon to obstetric and other surgical patients. It is imminent airway compromise. evident that not only pregnancy itself, but also other Diseases involving the airway. Table 2 presents factors (i.e., distorted anatomy of the airway) are some of the more frequently encountered diseases causes for intubation difficulties in pregnancy, al- involving the airway. As a typical example, rheuma- though airway edema in pregnancy may certainly toid arthritis may render standard intubation impos- worsen the problem. sible, necessitating the use of alternative airway management techniques (see “Airway Management for Cesarean Delivery”). REASONS FOR DIFFICULT INTUBATION Obesity. Obesity is frequently encountered during IN PREGNANCY pregnancy. Difficult intubation in the obese patient The reasons for difficult intubation in pregnancy may be divided into two groups: problems related to changes in airway anatomy and problems with the TABLE 1 Abnormal airway anatomy (individual variations) intubation technique. 1 Bull neck 2 Large breasts 3 Large floppy epiglottis Airway Anatomy 4 Large tongue 5 Limited cervical movement The anatomy of the airway may be impacted by 6 Limited mouth opening and narrow mouth four mechanisms: preexisting anatomical deformi- 7 Limited movement of the jaw ties, airway edema, coexisting diseases involving the 8 Prominent upper teeth airway, and obesity. 9 Receding jaw Difficult Airway in Obstetric Anesthesia Y CME Review Article 633 TABLE 2 Diseases involving the airway No. Disease Problem 1 Ankylosing spondylitis Immobility and fractures of the cervical spine 2 Congenital syndromes Down Macroglossia Klippel-Feil Fusion of cervical vertebrae with limited cervical movement 3 Goiter Deviation of the airway 4 Infections Epiglottitis Supralaryngeal and laryngeal edema; poor visualization of the larynx Ludwig’s angina Trismus, distortion of the airway 5 Preeclampsia Laryngeal edema 6 Rheumatoid arthritis Restricted cervical spine and jaw (TMJ*) mobility; cricoarytenoid joint arthritis; intubation with conventional laryngoscopy may be impossible. 7 Tumors of the upper airway Distortion of the airway 8 Airway trauma Cervical spine and laryngeal damage due to edema, hematoma and fractures leading to difficult intubation and ventilation * TMJ ϭ temporomandibular joint. may be due to a short neck or large tongue and axes for a better laryngoscopic view. The application of breasts, which make laryngoscopy and intubation cricoid pressure (used to prevent regurgitation of gastric laborious (12). In the morbidly obese

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