Update in Anaesthesia 37 12.Pierce Jr EC, Lembertesen CJ, Deutsch S, Chase PE,Linde 18. Rosa G, Sanafilippo M, Vilandi V, Orfei P & Gusparetto HW, Dripps RD & Price HL Cerebral circulation and A Effects of vecuronium bromide on intracranial pressure metabolism during thiopental anaesthesia and hypoventilation and cerebral perfusion pressure: A preliminary report British in man. Journal of Clinical Investigation 1962;41:1664-1671 Journal of Anaesthesia 1986;58:437-440 13. Hunter AR Thiopentone supplemented anaesthesia for 19. Werner C, Kochs E, Bause H, Hoffman WE & Sculte am neurosurgery. British Journal of Anaesthesia 1972;44:506 Esch J The effects of sufentanil on cerebral hemodynamics 510 and intracranial pressure in patients with brain injury. 14. Leslie K, Sessler DI, Smith WD, Larson MD, Ozaki M, Anesthesiology 1995;83:721-726 Blanchard D, & Crankshaw DP Prediction of movement 20. Warner DS, Hindman BJ, Todd MM, Sawin PD, Kirchner during propofol/nitrous oxide anesthesia. Performance of J, Roland CL & Jamerson BD Intracranial pressure and concentration, electroencephalographic, pupillary and hemodynamic effects of remifentanil versus alfentanil in hemodynamic indicators. Anesthesiology 1996;84:52-63 patients undergoing supratentorial craniotomy. Anesthesia 15. Roberts FL, Dixon J, Lewis GTR, Tackley RM & Prys and Analgesia 1996;83:348-353 Roberts C Induction and maintenance of propofol anaesthesia 21. Guy J, Hindman BJ, Naker KZ, Borel CO, Maktabi M, Anaesthesia 1988;43(Suppl):14-17 Ostapkovich N, Kirchner J, Todd MM, Fogarty-Mack P, 16. Thiagarajah S Anaesthetic management of neurosurgical Yancy V, Sokoll MD, McAllister A, Roland C, Young WL, procedures. Current Opinion in Anaesthesiology 1988;1:277 & Warner DS Comparison of remifentanil and fentanyl in 281 patients undergoing craniotomy for supratentorial space occupying lesions. Anesthesiology 1997;86:514-524 17. Kovarik WD, Mayberg TS, Lam AM, Mathisen TL, Winn HR Succinylcholine does not change intracranial pressure, 22. Thompson JP & Rowbotham DJ Remifentanil - an opioid cerebral blood flow velocity, or the electroencephalogram in for the 21st century. British Journal of Anaesthesia patients with neurologic injury. Anesthesia & Analgesia 1996;76:341 343 1994;78:69-73 PREDICTION AND MANAGEMENT OF DIFFICULT TRACHEAL INTUBATION Dr I H Wilson, Department of Anaesthesia, Royal Devon and Exeter Hospital, Exeter, EX2 5DW Dr Andreas Kopf, Department of Anaesthesia, Benjamin Franklin Medical Centre, Free I II University of Berlin, Hindenburgdamm 30 12200 Berlin-Lichterfelde, Germany INTRODUCTION During routine anaesthesia the incidence of difficult III IV tracheal intubation has been estimated at 3-18%. Difficulties in intubation have been associated with serious complications, particularly when failed Fig. 1 The classification of the views at laryngoscopy. intubation has occurred. Occasionally in a patient In class I the vocal cords are visible, in class II the with a difficult airway, the anaesthetist is faced vocals cords are only partly visible, in class III only the epiglottis is seen and in class IV the epiglottis cannot be with the situation where mask ventilation proves seen. difficult or impossible. This is one of the most critical emergencies that may be faced in the practice There have been various attempts at defining what of anaesthesia. If the anaesthetist can predict which is meant by a difficult intubation. Repeated attempts patients are likely to prove difficult to intubate, he at intubation, the use of a bougie or other intubation may reduce the risks of anaesthesia considerably. aid have been used in some papers, but perhaps the This paper reviews clinical techniques used for most widely used classification is by Cormack and predicting difficulties in intubation and suggests Lehane [1] which describes the best view of the different approaches to manage these patients. larynx seen at laryngoscopy (figure 1). This should be recorded in the patient’s notes whenever an 38 Update in Anaesthesia anaesthetic is administered so there is a record for 1 2 future use. PREDICTING DIFFICULT INTUBATION Tracheal intubation is best achieved in the classic “sniffing the morning air” position in which the neck is flexed and there is extension at the cranio- cervical (atlanto-axial) junction. This aligns the structures of the upper airway in the optimum position for laryngoscopy and permits the best 3 4 view of the larynx when using a curved blade laryngoscope. Abnormalities of the bony structures and the soft tissues of the upper airway will result in difficult intubation. History and examination Fig. 2 View obtained during Mallampati test. 1. Faucial Pregnant patients, those suffering from facial/ pillars, soft palate and uvula visualised, 2, faucial maxillary trauma, those with small mandibles or pillars and soft palate visualised, but uvula masked by intra-oral pathology such as infections or tumours the base of the tongue, 3, only soft palate visualised, 4, are all more likely to present difficulties during soft palate not seen. intubation. Thyromental distance This is a measurement Patients who suffer with rheumatoid disease of the taken from the thyroid notch to the tip of the jaw neck or degenerative spinal diseases often have with the head extended. The normal distance is reduced neck mobility making intubation harder. 6.5cm or greater and is dependant on a number of In addition spinal cord injury may result from anatomical factors including the position of the excessive neck movements during intubation larynx. If the distance is greater than 6.5cm, attempts. Poor teeth and the inability to open the conventional intubation is usually possible. If it is mouth are obvious other factors as are obesity, and less than 6cm intubation may be impossible [3]. inexperience on the part of the anaesthetist. By combining the modified Mallampati and Specific Screening Tests to Predict Difficult thyromental distance, Frerk showed that patients Intubation. who fulfilled the criteria of Grade 3 or 4 Mallampati A history of successful or unsuccessful intubation who also had a thyromental distance of less than during previous anaesthesia is obviously significant. 7cm were likely to present difficulty with intubation There a number of specific clinical assessments [4]. Frerk suggests that using this combined that have been developed to try to identify patients approach should predict the majority of difficult who will prove difficult to intubate. intubations. A 7cm marker can be used (eg a cut off pencil or an appropriate number of examiners Mallampati suggested a simple screening test which fingers) to determine whether the thyromental is widely used today in the modified form produced distance is greater that 7cm. by Samsoon and Young [2]. The patient sits in front of the anaesthetist and opens the mouth wide. The Sternomental distance is measured from the patient is assigned a grade according to the best sternum to the tip of the mandible with the head view obtained (figure 2). Clinically, Grade 1 usually extended and is influenced by a number of factors predicts an easy intubation and Grade 3 or 4 suggests including neck extension. It has also been noted to a significant chance that the patient will prove be a useful screening test for pre-operative prediction difficult to intubate. The results from this test are of difficult intubation. A sternomental distance of influenced by the ability to open the mouth, the size 12.5cm or less predicted difficult intubation [5]. and mobility of the tongue and other intra-oral Extension at the atlanto-axial joint should be structures and movement at the craniocervical assessed by asking the patient to flex their neck by junction. putting their head forward and down. The neck is then held in this position and the patient attempts to Update in Anaesthesia 39 raise their face up testing for extension of the l introducers for endotracheal tubes (stylets or atlanto-axial joint. Laryngoscopy is optimally better, flexible bougies) performed with the neck flexed and extension at the l oral and nasal airways atlanto-axial joint. Reduction of movement at this l a cricothyroid puncture kit (a 14 gauge joint is associated with difficulty. cannula and jet insufflation with high pressure Protrusion of the mandible is an indication of the oxygen is the simplest and cheapest kit (see mobility of the mandible. If the patient is able to Update No 1996;6:4-5). protrude the lower teeth beyond the upper incisors l reliable suction equipment intubation is usually straightforward [6]. If the l a trained assistant patient cannot get the upper and lower incisors into alignment intubation is likely to be difficult. l laryngeal mask airways, sizes 3 & 4 Wilson et al [7] studied a combination of these The safety of laryngoscopy can be increased by factors in a surgical population assigning scores preoxygenating the patient prior to induction and based on the degree of limitation of mouth opening, attempts at intubation. The anaesthetist should reduced neck extension, protuberant teeth and ensure that the patient is in the optimal position for inability to protrude the lower jaw. Although their intubation and must be able to oxygenate the patient method can predict many difficult intubations, it at all times. also produces a high incidence of false positives After intubation correct placement of the tube should (someone who is assessed as a likely difficult be confirmed by: intubation, but who proves easy to intubate when l a stethoscope listening over both lung anaesthetised) which limits its usefulness. fields in the axillae X ray studies Various studies have been used to try l observing the tube pass through the cords to predict difficult intubation by assessing the l successful inflation of the chest on manual anatomy of the mandible on X ray. These have ventilation shown that the depth of the mandible may be important, but they are not commonly used as a Additional tests include the use of the oesophageal screening test. detector device (see Update No 1997;7:27-30) and a capnograph (if available).