AIRWAY MANAGEMENT IN OBSTETRICS

Transcription

1 328 Indian J. PG Anaesth. ISSUE 2005; : AIRWAY 49 (4) : MANAGEMENT INDIAN JOURNAL OF ANAESTHESIA, AUGUST AIRWAY MANAGEMENT IN OBSTETRICS Dr. Rudra A. Introduction Although the use of general anaesthesia has been declining in obstetric patients, it may still be required in some cases. Maintenance of the airway during obstetric anaesthesia is difficult to estimate, still remains the single most important cause of anaesthesia related maternal morbidity and mortality. 1-4 It has been recognized that the physiologic and anatomic changes during pregnancy, and emergency intervention in an inadequately prepared patient make the problem more challenging. Deaths from anaesthesia related cause are particularly lamentable because many of these anaesthetics are elective, they are provided to young pregnant women in the prime of life, and some might be prevented if more experienced personnel were provided. The two outstanding differences in the care of the obstetric patient include (a) consideration of the needs of the foetus and (b) dramatically reduced maternal oxygen reserves in the presence of greater metabolic requirements. The difficult airway is a clinical situation which include either one or altogether the concepts of failed intubation, difficult intubation, difficult laryngoscopy, and difficult mask ventilation. Failed intubation is the inability to place the endotracheal tube. It occurs in approximately 0.13% to 0.35% or 1:750 to 1:280, of obstetric patients. 5 Difficult intubation can be defined as, when the proper insertion of the endotracheal tube with conventional laryngoscopy requires more than three attempts and/or more than 10 minutes. 5 Difficult laryngoscopy can be defined when it is not possible to visualize any portion of the vocal cords with conventional laryngoscope. 5 Difficult mask ventilation can be defined as not possible for the unassisted anaesthesiologist to maintain oxygen saturation more than 90% using 100% oxygen and positive pressure mask ventilation in a patient whose oxygen saturation was more than 90% before anaesthetic intervention, and/or it is not possible for the unassisted anaesthesiologist to prevent or reverse signs of inadequate ventilation during positive pressure mask ventilation. 5 M.D., FAMS Prof. of Anaesthesiology Calcutta National Medical College, Kolkata Although, the American Society of Anaesthesiologists (ASA) difficult airway algorithm and several modifications have been published, specific problems of the obstetric patient, to date, have not been addressed. 5-9 Therefore, the spectrum of challenges presented by a parturient requiring anaesthesia, make the role of anaesthesiologist both challenging and rewarding. 10 This review highlights some recent developments in predicting airway difficulties, advances in airway management and also strategies and techniques for management of predicted and unpredicted difficult airway in obstetric patients. Differences in obstetric airways Recognition and evaluation The incidence of failed intubation in the parturients has been estimated between 1.3 to 3 per thousand and difficult endotracheal intubation of 64 per thousand. 11,12 Therefore, one of the most critical, if not the most crucial, part of the physical examination is the assessment of airway to avoid disaster associated with airway problems, particularly for those at risk for operative delivery. There are numerous methods for assessing the airway, which may help in predicting a difficult airway. However, a simple three step method of airway evaluation may be performed that includes a assessment of (1) the mouth opening and the visibility of the posterior pharyngeal structures (supine versus sitting), (2) the mandibular length, and (3) the neck mobility. Mallampati hypothesized that the degree to which oropharyngeal structures could be visualized upon examination should correlate with the structures that could be seen on larygoscopy and develop a scoring system. However, Mallampati classification used alone is imprecise. If combined with other predictors of difficult airway criteria (thyromental distances, neck extension, interincisor space, submandibular compliance), the specificity and sensitivity of the preoperative assessment are improved. 13 Thyromental distance, when the distance between the boney point of the mentum and the upper border of the thyroid bone is less than 6.5 cm, would correlate with difficult laryngoscopy. 14,15 Neck extension (atlanto-occipital extension) importance lies with alignment of the oral and pharyngeal axes during laryngoscopy. Normal value is 35 degree. A decrease of more than one-third correlates with difficult endotracheal intubation. 16 Neck extension may be affected by ankylosis,

2 RUDRA : AIRWAY MANAGEMENT IN OBSTETRICS 329 short/stocky neck and dwarfism. Interincisor space - is the degree to which a patient can open her mouth. When the interincisor gap is less than 5 centimetres, intubation may be difficult. 17 Submandibular Compliance-airway difficulty may be encountered if the compliance of the tissue in the submandibular space is compromised where, the soft tissue is displaced during laryngoscopy. Tumor infiltration, scarring from radiation, burns, surgery may affect visualization of the larynx. 18 No single test can be used to predict difficult airway with certainty. Combining two or more tests improves the positive predictive value (the percentage of difficult laryngoscopies correctly predicted as difficult) and increase the specificity (the ability to correctly identify normal patients as normal), but decreases the sensitivity (to detect true difficult intubations). If all the above tests are positive the anaesthesiologist should have a high index of suspicion that airway maintenance would be difficult in anaesthetised parturient. In the obstetric patient, it is also prudent to attempt to estimate the severity of local oedema and friability of mucosal tissues. Also, evaluation of the airway may need to be repeated, since changes may occur throughout the pregnancy as well as during the course of labour. 19 The key to any approach is to realize that any and all external assessments are at least estimates or educated guesses as to what will actually be visualized on direct laryngoscopy of the sedated and paralysed patient. Difficult or impossible intubations will occur, and the only safe way to manage them is to be well prepared. Vigilance is the key, along with backup plans and the availability of any necessary equipment in case of difficulty. Pregnancy induced anatomical and physiological changes The anatomical and physiological factors place the pregnant woman at greater risk of airway management complications and difficult intubation than the nonpregnant woman. 6,20 Anatomical changes Anatomical factors that place the pregnant woman at increased risk for airway management complications and difficult intubation include pregnancy-induced generalised weight gain and particularly, increase in breast size, respiratory mucosal oedema, and an increased risk of pulmonary aspiration. 21 In the supine position, the enlarged breasts tends to fall back against the neck, which can interfere with insertion of the laryngoscope and intubation. Preexisting conditions that appear in the non-obstetric population include full dentition, small mandible, protruding incisors, limited mouth opening or neck extension, short neck, high-arched palate, large breasts 21 would act additionally to cause airway more difficult. Several systemic diseases such as rheumatoid arthritis, diabetes mellitus, dwarfism, systemic sclerosis, sarcoidisms, ankylosing spondylitis, and tumours of the neck may hinder mouth opening or neck extension in the obstetric patient. 21 Finally, increased abdominal contents raise the diaphragm and alter the normal anatomical alignment of the upper airway. Moreover, a badly placed hip wedge causing a thoracic lift effect, as well as misapplied cricoid, inadequate anaesthesia plus muscle relaxation because of propensity to minimize doses and anxiety on the part of the inexperienced anaesthesiologist during induction of anaesthesia may also complicate airway management in the obstetric population. Many of these changes can be overcome with preparation and attention to details such as positioning. Physiologic changes Anatomic changes enhance the likelihood of difficulty in airway management, it is the physiologic changes that make the consequences much more severe. The obstetric patient has a 20% to 30% higher oxygen consumption at term due to increased work of breathing and foetal metabolic requirements. In addition, total compliance of the chest is reduced because of the upward displacement of the abdominal contents by the uterus and the weight of the enlarged breasts. This is particularly true in patients in the supine position. The most important pregnancy-induced change the reduction in the functional residual capacity (oxygen reserve or supply). Closing capacity (CC) however remains unchanged. The resulting decrease in the FRC/CC ratio causes faster small airway closure when lung volume is reduced; thus parturient can desaturate at a higher rate than non-pregnant woman can. 10 Moreover, airway closure at tidal volume in the supine position increases the shunt fraction and furthers the potential for hypoxaemia. Patient with preexisting neuromuscular disease, or had received narcotics for pain relief during labour, or magnesium sulphate for preterm labour or pregnancy-induced hypertension are prone to inadequate minute ventilation. The clinical effects of these physiologic changes is rapid desaturation during apnoea on induction of anaesthesia. During this time, apnoeic oxygenation can be accomplished by ensuring a patent airway and delivering 100% oxygen. This will increase the time available before oxygen saturation falls. Furthermore, induction of anaesthesia in the head up position may have an advantage because of increased functional residual capacity. Approximately in 12 to 15% of parturients at term, the gravid uterus may compress the venacava and

3 330 PG ISSUE : AIRWAY MANAGEMENT INDIAN JOURNAL OF ANAESTHESIA, AUGUST 2005 aorta in the supine position, causing decreased venous return, decreased cardiac output, blood pressure, and uterine blood flow. Therefore, pregnant women should not be allowed to assume the supine position. Pregnant women are more prone to aspiration of gastric contents after induction of general anaesthesia than nonpregnant patients. Heartburn caused by reflux of gastric contents occurs in upto 80% of parturients at term. These effects are due to an elevated gastric acid content, with decreased ph, and reduced function of the gastroesophageal sphincter secondary to the mechanical and hormonal effects that occur early in pregnancy. Elevated levels of progesterone cause gastric emptying to be delayed and lower oesophageal sphincter pressure to be decreased, and placental gastrin causes gastric acid production to increase. The changes are clinically significant by 10 to 12 weeks of gestation. By 20 weeks of gestation, the gravid uterus exerts physical pressure on the stomach causing its upward displacement and rotation, which alters the angle of the gastroesophageal junction and increases pressure. Furthermore, intragastric pressure is increased in patients with polyhydramnios, multiple gestations, and by the lithotomy position. In addition, fundal pressure at delivery either vaginally or by caesarean section increases the intragastric pressure. Hence, all obstetric patients are at increased risk of pulmonary aspiration and should receive aspiration pharmacoprophylaxis and mechanoprophylaxis before any manipulation of the airway. Pharmacoprophylaxis would include preoperative administration of nonparticulate antacid such as 0.3 M sodium citrate, 30 millilitres. This has a duration of action of 40 to 60 minutes. Thus, problems of aspiration may occur however during emergence from anaesthesia, when the effect of sodium citrate is much less predictable. Intravenous administration of histamine receptor (H 2 ) blocking agent 40 minutes before airway managements, are useful adjuncts. Ranitidine is preferred than cimetidine because the latter may cause haemodynamic instability when given parenterally and has been associated with changes in liver function. In an event of an extreme emergency, it is still useful to administer intravenous ranitidine at induction because it would be effective by the time the mother emerges from anaesthesia, when sodium citrate is unreliable. Omeprazole, an proton pump inhibitor and antisecretory agent require 40 minutes to reduce gastric acidity Administration of metoclopramide decreases gastric volume as a prokinetic agent within minutes. It crosses the placenta but has not been shown to have any lasting adverse neurobehavioural effects on the newborn. 23 It should be noted that none of these combinations are fully effective, particularly after large meal had recently been eaten. The use of a nasogastric or orogastric tube prior to induction of anaesthesia, to enable physical emptying of the stomach has been suggested, particularly a parturient has had opiates in labour and is therefore most likely to have a full stomach. Physical removal of gastric contents would reduce the volume by a greater degree than pharmacological methods, but the remaining volume may still make the pregnant woman vulnerable to aspiration. In a parturient at high risk of aspiration, it may be more practical to insert a nasogastric or orogastric tube after induction of anaesthesia, once the airway is secured. As the risk of aspiration continues into the recovery period, this may be a logical approach and one that is more acceptable to the mother. During the induction of anaesthesia, cricoid pressure is applied which supplies the necessary barrier to regurgitation of gastric contents during the induction of anaesthesia and prevents inflation of the stomach during positive pressure ventilation. 25 The cricoid cartilage is the only tracheal cartilage with a ring structure. The thumb and middle finger are placed on either side of the cricoid to prevent lateral movement of the cartilagenous ring which could make intubation difficult. The backward pressure compress the oesophagus on the vertebral column and causes it to be occluded, while the airway remains patent because the cricoid is a complete ring of cartilage. If active vomiting occurs, cricoid pressure should be abandoned to prevent rupture of oesophagus. The present recommendation is to use a constant backward force of 30 Newtons to the cricoid (equivalent to a force of 3 kg on a weighing scale). However, recent debate has centred around 20 Newtons would be an adequate force to occlude the oesopagus with less distortion of airway than a greater force. 26 It has been well established that total body water significantly increases in pregnancy, that also has important effect in respect of airway. Increase in the body water is due to the effect of increased progesterone levels. 21 An increase in the total body water leads to mucosal oedema of the larynx, nasopharynx, and vocal cords. This engorgement may be further worsened by pregnancy-induced hypertension or strenuous labour, and concurrent respiratory tract infection. 11,19,27 Moreover, the patients who are receiving oxytocin may be more prone to fluid overload due to its antidiuretic side effect. This results in decreased space (partial obstruction) and increased risk of bleeding with standard airway management techniques. 28 Therefore, it is recommended for them to have smaller sized endotracheal tube and vasoconstrictor agents with minimal effect on uteroplacental blood flow. Enlargement of tongue may make it difficult to retract onto the mandibular space during direct laryngoscopy.

4 RUDRA : AIRWAY MANAGEMENT IN OBSTETRICS 331 The weight gain that accompanies pregnancy is frequently 20 kg or more. Obesity has been reported to further increase the risk of anaesthetic complications in parturients. 5,6 A high body mass index (BMI) has been associated with an increased risk of airway management problems including difficult intubation. 21,29 [BMI is the bodyweight in kilograms over height in metres squared. The normal BMI is 20-25; a BMI of is overweight, a BMI of is obese, and a BMI more than 40 is morbidly obese. In other words, an overweight patient weighs less than 20% more than the predicted IBW, obese patient weighs more than of IBW, and morbidly obese patient weighs more than twice of IBW (IBW = Ideal Body Weight)]. 29 The breast enlargement that accompanies pregnancy is more pronounced in the presence of excessive weight gain. Intubation of this patient with enlarged breasts is facilitated by the use of a short handled lanyrgoscope and breast retraction during laryngoscopy. Proper positioning of the patient facilitates intubation attempts and increases the likelihood of success. Regional anaesthesia may also be more difficult to perform, and extra long needles (spinal or epidural) should be available. Associated changes in respiratory parameters in addition to the changes due to pregnancy include, reduction or decrease in functional residual capacity (FRC), vital capacity (VC), total lung capacity (TLC), and chest wall compliance. Moreover, there would be increase in the work of breathing as the abdominal contents press against the diaphragm and make respiratory excursion of the diaphragm difficult. 28 Furthermore, morbidly obese patients have a higher incidence of other complicating medical conditions such as diabetes mellitus, chronic hypertension, and pregnancy induced hypertension. Morbid obesity has been implicated as a contributing factor in up to 80% of anaesthesia related maternal deaths. Therefore, evaluation of the airway is most important. Measurement of oxygen saturation in the sitting and supine positions provides an early way to assess the degree of airway closure and the potential for deterioration with further decrease in functional residual capacity. If general anaesthesia is inevitable and a difficult airway is anticipated, proper positioning of the patient with elevated shoulders by folded towels below the occiput and place the head in sniffing position so that, the enlarged breasts could be fallen from the neck and chin. These manoeuvres would open up the area that is often lost in rolls of fat, allowing easy insertion of the laryngoscope blade. 28 In these patients, some of the airway gadgets and alternative methods of securing the airway become important. 29,30 Management options and plans Although the use of general anaesthesia has been declining in obstetric patients, it may still be required in selected cases. Difficult endotracheal intubation can be expected due to the anatomic and physiologic changes associated with pregnancy. As 50% of difficult intubations in obstetric practice occur unexpectedly, protocols dealing with the management of difficult airway should be at anaesthesia locations. 31 Moreover, it is essential for the anaesthesiologists to perform a proper pre-anaesthetic evaluation and identify the factors predictive of difficult intubation. The recognized difficult airway Early recognition and Planning The key to proper management of any airway is anticipation of difficulty, adequate preparation (patient and equipment), and a detailed plan of action should problems arise. Management of the obstetric patient must also take into account the condition of the foetus and the urgency of the operative procedure. A difficult airway may be either recognized or unrecognized before intubation, and airway management varies accordingly. There is strong agreement among experts in airway management that specific strategies lead to improved outcome. All patients in the obstetric unit should have assessments of their airway. Because preparation is important to avoid disaster associated with airway problems, a careful assessment of the parturient airway is necessary, particularly for those at risk for operative delivery. Their evaluation should include a record of prior surgeries and anaesthesia. The interview allows the initial establishment of rapport between the anaesthesia providers and the patient during the time of invasive procedures, such as awake intubation. Certain anatomical features indicate that endotracheal intubation via conventional means is very likely to be difficult, if not impossible. Very large breasts and heavy chest wall, large tongue, no teeth and shrunken cheeks, fixed head or neck flexion, massive jaw may also render mask ventilation difficult or impossible. Any doubt regarding the ability to maintain airway patency would lead to the consideration of alternative methods of anaesthesia. Options include the use of regional anaesthesia, awake intubation followed by general anaesthesia, or local infiltration anaesthesia. Regional anaesthesia Aspiration pharmacoprophylaxis minimizes the potential for aspiration. Regional anaesthesia is a controversial solution in the presence of a recognized potentially difficult airway. Still, spinal or epidural anaesthesia is acceptable if there is no contraindication.

5 332 PG ISSUE : AIRWAY MANAGEMENT INDIAN JOURNAL OF ANAESTHESIA, AUGUST 2005 However, the anaesthesiologist should anticipate the possibility of failed anaesthesia, development of seizures, high block or total spinal anaesthesia resulting in respiratory arrest. Therefore, the anaesthesiologist should be fully prepared (both mentally and technically) to administer general anaesthesia. 6,21 Epidural anaesthesia provide the advantage of slow titration of the level of anaesthesia (graded epidural), which could avoid major haemodynamic shifts or respiratory compromise. However, disadvantage of epidural anaesthesia include inadvertent intravascular injection, injection of local anaesthetic into an unintended space (subarachnoid space), compared with spinal anaesthesia. Awake intubation followed by general anaesthesia A very safe option to secure the airway with an endotracheal tube while the patient remains awake. 2,3,6,20 The reasons for awake intubation in a patient with recognized difficult airway are : (a) the natural airway is better maintained, (b) the presence of normal muscle tone helps to maintain the natural separation of the upper airway structures, which facilitate identification of anatomical landmarks and (c) induction of general anaesthesia and muscle paralysis result in anterior movement of larynx, which impede visualization of the larynx during laryngoscopy. 32 Because of foetal concerns, the use of routine sedation is not recommended in the parturient. An anticholinergic, such as glycopyrrolate that does not cross the placenta easily due to quaternary in nature is a useful adjunct to decrease secretion and allows better application of local anaesthetic spray to airway mucosa, improves visualization, and inhibits vagal reflexes. 21 Supplemental oxygen via nasal prongs should be provided during the procedure. Minimal monitoring should include the use of an automated blood pressure cuff, pulse oxymeter, and an ECG. If the nasal route is chosen, the nasal mucosa should be sprayed with a vasoconstrictor. An awake look may be undertaken with topical spray applied to the oropharynx or a glossopharyngeal nerve block, or both, in order to facilitate tolerance of the laryngoscope in the oropharynx. The glossopharyngeal nerve provides innervation to the posterior third of the tongue, vallecula, anterior surface of the epiglottis, posterior and lateral walls of the pharynx, and tonsiller pillars. Blocking this nerve, especially if this is combined with topicalization of the oral cavity, may allow the patient to tolerate attempts at awake visualization of the oropharynx Before intubation, topicalization of vocal cords should be performed. Laryngeal reflexes should be maintained by avoiding injections of lignocaine into the trachea, as obstetric patients are prone for aspiration of stomach contents. The choice of technique regarding tracheal intubation depends on several factors, including skill, experience of the laryngoscopist and the urgency of caesarean section. Awake intubation is usually accomplished by the use of a flexible fibreoptic bronchoscope. Otherwise, it may also be performed with the aid of intubating laryngeal mask airway, a light wand, or a rigid fibreoptic laryngoscope (Bullard, Upsher, Wu). Local infiltration for caesarean delivery If a patient with a difficult airway requires urgent caesarean delivery, local infiltration and field block could be provided. Moreover, it should be considered as last resort when spinal/epidural/general techniques of anaesthesia are not viable or have failed. 37,38 However, this technique may not be the most pleasant option for either the obstetrician or the patient. Local anaesthetic infiltration is a technique rarely used today for caesarean delivery. General anaesthesia When general anaesthesia is to be used in obstetric, the method of airway management would depend on the urgency of the procedure and the anticipated ease of difficulty of intubation and ventilation. Before the administration of general anaesthetic, all patients should be thoroughly evaluated, receive aspiration pharmacoprophylaxis and cricoid pressure, and be positioned in the optimal position for intubation. All equipments for routine and emergency airway management should be immediately available. If tracheal intubation is unsuccessful with initial attempt, the anaesthesiologist must make a judgement whether to attempt a second laryngoscopy directly, or attempt mask ventilation. An immediate second laryngoscopy is acceptable if oxygen desaturation has not occurred. The second laryngoscopy may be successful by molar approach. 39 The laryngoscope is inserted directly down the left side of the mouth to access the larynx. Improved view of the larynx could be achieved because the tongue does not need to be compressed. The technique should be practised on an intubation dummy and on elective cases before being used in the obstetric situation. At whatever time intubation is successful, the caesarean section may proceed. If intubation is not successful after second laryngoscopy, oxygenation is most likely to be successful by two handed jaw thrust and bag ventilation by a third party. This manoeuvre may open the airway and allow adequate oxygenation bypassing three primary areas of airway obstruction (tongue, epiglottis, and soft palate). It is important to ensure that the jaw thrust is applied to the posterior border of the ramus of the mandible

6 RUDRA : AIRWAY MANAGEMENT IN OBSTETRICS 333 with the thrust being applied towards the ceiling. With adequate jaw thrust and a proper mask seal, oxygenation should be possible in most of the cases, but cricoid pressure may need to be removed or adjusted to improve the airway. The unrecognized difficult intubation Emergency airway management in the unprepared and unfamiliar patient is often challenging. Occasionally, in spite of careful assessment of the airway, general anaesthesia may be induced and then endotracheal intubation of the parturient may prove to be impossible. Although, many predictions of a difficult laryngoscopic intubation have been developed, they all have low positive predictive values, and thus the unanticipated difficult laryngoscopic intubation would continue to occur in our day to day practice for the foreseeable future. However, it cannot be overemphasized that a plan of action should be detailed before hand and followed once the situation occurs and supplies should be immediately available to implement that plan to mitigate the associated morbidity and mortality. 6,21 Once it has been determined that it is not possible to visualize the larynx, maternal oxygenation must be accomplished with gentle mask ventilation while maintaining cricoid pressure. If ventilation is unsuccessful, correct positioning of the head, remove misapplied cricoid pressure, and request for more experienced or different anaesthesia practitioner. 2,3,6,20 The key is to not keep trying the same thing over and over and to not panic. Multiple laryngoscopies lead to a catecholamine response that may reduce uterine blood flow in the foetus who may already be subjected to maternal hypoxaemia. Moreover, continued laryngoscopy may also increase the likelihood of aspiration. Numerous, repeated attempts at laryngoscopies should not be done to avoid pharyngeal trauma which would make ventilation progressively more difficult if not impossible. 40 Mask ventilation Failure to intubate the obstetric patient is often followed by difficulty with mask ventilation and possible by pulmonary aspiration. Either of these conditions rapidly leads to hypoxaemia for both the mother and the foetus. The adequacy of mask ventilation and the presence or absence of foetal distress are extremely important factors that must be taken into account in these situations. The patient who cannot be intubated but can be adequately ventilated by mask with no foetal distress When the anaesthesiologist is unable to intubate the trachea of an anaesthetized patient, it is essential to try to maintain gas exchange by mask ventilation. During positive pressure mask ventilation, maintenance of cricoid pressure is mandatory until the patient is fully able to protect her airway. After awakening the patient, option include awake intubation, regional anaesthesia, and local infiltration anaesthesia. Continuation of general anaesthesia without significant foetal distress by face mask would be dangerous in obstetric patient as they are very much prone to aspirate gastric contents. The patient who cannot be intubated but who can be adequately ventilated by mask with foetal distress This is a situation where welfare of both the mother and child depend. Therefore, a delicate balance should be achieved to manage the situation. The initial step is to evaluate the adequacy of mask ventilation. Ventilation and oxygenation should be easy to maintain, rather than marginal, or tenuous upon which the following options depend. The first option, awake the patient. 2,21 This difficult decision would probably preserve the life of the mother, but it may result in the demise of the foetus. The second option is to continue anaesthesia via mask ventilation, while an assistant maintains cricoid pressure. When the lungs can be ventilated easily with a face mask after a failed intubation, it is better to use either a laryngeal mask airway (LMA) or an oesophageal tracheal combitube (ETC) in order to rescue airway. 41,42 However, the laryngeal mask airway (LMA) offers little advantage. The LMA may promote gastric regurgitation and may prevent escape of regurgitated stomach contents from the pharynx which provokes pulmonary aspiration. Application of cricoid pressure should be maintained unless it interferes with the maintenance of a clear airway. The proseal LMA (PLMA) may provide better protection against aspiration than LMA. Surgery can start when the patient is well anaesthetized using a volatile agent in 100% oxygen. Traditionally, halothane has been the agent of choice in this situation, however sevoflurane could be used due to its advantages over halothane. Sevoflurane is probably a more logical agent to use because of the ease of induction without breath holding and coughing, if available. It has similar properties of halothane in the spontaneously breathing patient, depth of anaesthesia is easier to control because of its low blood gas solubility and it is less cardio depressant. Fundal pressure and uterine exteriorization should be avoided to prevent regurgitation of stomach contents. Failed intubation drill Following induction of anaesthesia, if the anaesthesiologist fails to intubate the trachea, then a failed intubation drill should be initiated. There exist a multiplicity of failed intubation drills, some more complicated than others, but the essential requirement of all of them is to maintain oxygenation. If necessary, cricoid pressure

7 334 PG ISSUE : AIRWAY MANAGEMENT INDIAN JOURNAL OF ANAESTHESIA, AUGUST 2005 should be altered or released, since oxygenation takes precedence over protection from aspiration. Oxygenation is most likely to be successful by a two handed jaw thrust and bag ventilation by a third party. Sometimes, cricoid pressure may need to be removed or adjusted to improve the airway. A simple failed intubation drill is illustrated below. In the original failed intubation drill proposed by Tunstall, 43 the recommendation included, turning the patient to their side, passing an orogastric tube to empty the stomach, and providing inhalational anaesthesia by mask. Inadequate mask ventilation Fig. : Algorithm for failed intubation in obstetric patient 17 The last resort is to perform a tracheostomy or cricothyrotomy before the ability to ventilate with the mask is lost. Transtracheal jet ventilation via a catheter placed through the cricothyroid membrane is probably the fastest route to oxygenation in a patient who is desaturating. When performing jet ventilation, it is extremely important to ensure adequate exhalation in order to prevent excessive barotrauma. Extubation If the patient was difficult to intubate, extreme care should be taken at extubation. Extubation to be done in sitting upright position which allow free excursion of diaphragm and decrease the risk of reflux. 26 After full recovery, patient should be informed and counselled regarding problems encountered and its relevance to further anaesthetics. Clear description regarding the problem and subsequent management should be kept in the hospital notes. Summary Failed tracheal intubation in obstetric anaesthesia is every anaesthesiologist s nightmare. Because of the physiologic and anatomic changes associated with pregnancy, the difficult airway must be anticipated. The true incidence of difficult intubation and ventilation is difficult to estimate. 44 There is no universal method to predict the problem, nor the technology to overcome it. Airway catastrophies are leading contributory factor to anaesthesia related maternal morbidity and mortality. 45 Patients die from hypoxia and acid aspiration, if the failed intubation is unrecognized or the corrective measures are inadequate. Careful and timely evaluation of all parturient should identify the majority of parturients with difficult airway. However, management of the patient with a difficult airway is a crisis situation that anaesthesiologists must be most able to handle successfully. 46 Thus, the problem could only be managed successfully by increasing knowledge and awareness. Each anaesthesiologist must develop a plan, consistent with his or her expertise, to deal with the unexpected difficult airway. Anaesthesiologists should familiarize themselves with various airway devices/ gadgets in the event of a difficult airway. Caesarean section should wait until the patient is stabilized.

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Current Opinion in Anesthesiology 2004; 17: CORRIGENDUM Ref : Indian J. Anaesth 2005; 49(3): In the contents page name of Dr. Pratyush Gupta co-author of article titled Carotico Cavernous Fistula is missing. Error is regretted.