| | Airway management in obese patientsSummary Airway management is often the principal concern of the majority of anaesthetists when presented with an obese patient for general anaesthesia. Many anaesthetists will be increasingly encountering obese patients requiring all types of surgery. With the expansion of bariatric surgery both worldwide and in the UK, there is now a greater evidence base to inform and guide airway management in the obese patient. This article aims to improve understanding of the term ‘difficult airway’ in the obese population and focuses primarily on evidence related to pre-operative airway assessment and intra-operative airway management in the obese patient. 1. Introduction  Anaesthesia in morbidly obese patients can present many challenges. The overriding concern of most anaesthetists however, is airway management, as traditionally, obese patients have been thought to be at greater risk of difficult airway and/or difficult intubation, when compared with the general population. There is plenty in the literature regarding this subject area, but the mundane is rarely reported, and so this article aims to clarify the incidence and objectively review, the evidence for difficult airway in the obese population. The term ‘difficult airway’ has been defined by the American Society of Anesthesiologists (ASA) taskforce as the clinical situation in which a conventionally trained anaesthetist experiences problems with mask ventilation or tracheal intubation or both.1 Difficult endotracheal intubation has also been defined by the ASA as more than 2 attempts at intubation or attempts lasting more than 10 min. The literature concerning difficult intubation uses numerous different definitions of ‘difficult intubation’ and this lack of consensus translates to difficulty in comparing airway studies. Some authors use the Cormack and Lehane grading of 3 or 4 (C & L, grades 3–4) as an end-point to define difficult laryngoscopy and hence difficult intubation, in an attempt to simplify the issue. However ‘difficult laryngoscopy’ does not always equate with ‘difficult tracheal intubation’ and ‘easy laryngoscopy’ does not always equate with ‘easy intubation’. Other definitions of the difficult airway include complete failure to intubate and more than three attempts to pass the endotracheal tube. Although the view at laryngoscopy is a frequently used definition, the relationship between the number of laryngoscopies, the number of tracheal intubation attempts and the degree of post-operative morbidity has not been clearly defined.2 The Intubation Difficulty Scale score3 has been used in several studies to assess difficult intubation and takes into account difficult laryngoscopic view, number of attempts required to intubate the trachea and other factors associated with difficulty. It is a validated objective scale producing a score that can be used to evaluate intubating conditions and techniques. It correlates with time to intubation and a Visual Analogue Scale (VAS) assessment of difficulty. A point is scored for each variable encountered. The variables used in the score are as follows: N1 – number of additional attempts; N2 – number of additional operators; N3 – number of alternative intubation techniques used; N4 – glottic exposure as defined by Cormack and Lehane; N5 – lifting force applied during laryngoscopy; N6 – need to apply external laryngeal pressure to improve view; N7 – position of vocal cords at intubation. A summary of how the IDS score is calculated and the interpretation of this score is given in Table 1.  | Interpretation of IDS Score | Degree of difficulty | |
|---|
| 0 | Easy | | | 0 < IDS ≤ 5 | Slight difficulty | | | 5 < IDS | Moderate to major difficulty | | | IDS = ∞ | Impossible intubation | | | | |
2. The obese airway For the purpose of comparison with obese subjects (BMI > 30 kg/m2), the incidence of ‘difficult intubation’ in unselected, non-obstetric patients has been quoted as 1.8–7.5%.2, 4, 5 Comparisons are difficult because the literature is confusing with some airway studies suggest obesity to be a risk factor for difficult intubation, yet others conclude difficult intubation is no more common than in non-obese subjects. The studies vary depending upon whether they examine the association of obesity with difficult laryngoscopy alone or include other measures of difficult intubation. The findings of recent, relatively large and well-designed comparative studies looking at these associations will be briefly reported. In a prospective study of 764 mixed surgical patients presenting for surgery, it was found that increased BMI correlated with increased Mallampati (MP) class, but not with increased grade of laryngoscopy.6 In a controlled study of 200 morbidly obese patients undergoing elective surgery, the magnitude of BMI had no influence on difficulty of laryngoscopy (C & L, grade 3–4)7 when examining the various risk factors for difficult laryngoscopy. Again, using C & L, grade 3–4 as the descriptor of difficult laryngoscopy, a recent study (Difficult Airway Society annual conference, 2008) of 397 patients with a BMI >50 kg/m2, found an incidence of 6% to be similar to the quoted incidence for the general population.8 Similarly, Juvin et al.9 have previously found the incidence of difficult laryngoscopy (C & L, grade 3–4) to be the same in 134 lean (BMI < 30 kg/m2) patients when compared with 129 obese (BMI ≥ 35 kg/m2) patients (10.4 vs 10.1% respectively). However, the IDS score was ≥5, indicating moderate to major difficulty in intubation, in 3 lean (2.2%) and 20 (15.5%) obese patients (P = 0.0001). In another recent study using the IDS scoring system to prospectively compare 70 obese (BMI ≥ 30 kg/m2) and 61 lean patients (BMI < 30 kg/m2), the IDS score was >5 more frequently in obese compared to lean patients (14% vs 3% respectively, P = 0.03). This study also analysed which pre-operative measurements were associated with difficult intubation (see Section on Predictors of difficult airway below).10 In a large prospective, Canadian study of 18,205 non-obstetric, general surgical patients, undergoing direct laryngoscopy, there was a significantly increased proportion of overweight patients (defined as male >120 kg, female >100 kg, n = 451) in whom tracheal intubation was recorded as ‘difficult’ and who required >2 laryngoscopies before successful intubation (5.5% described as ‘difficult’ vs 2.4% described as ‘easy’, P < 0.01).2 However, Gaszynski et al. analysed the incidence of difficult intubation in 87 morbidly obese patients using the ASA definition of difficult intubation (attempts lasting more than 10 min or greater than two attempts) and found that the incidence was similar to that in lean patients (4.6%).11 In summary, most studies suggest that difficult intubation, if defined by difficult laryngoscopy alone, does not appear to be more common in the obese. However some well-designed studies suggest that there may be an increased incidence when including other measures to define difficult intubation, but this is dependent on which measure or definition of difficult intubation is used. It appears that the IDS score is a more objective and reliable measure of difficult intubation and has been increasingly used in studies of obese patients. Despite the difficulty in reaching a consensus from the literature, it is apparent that there are a high proportion of obese patients that do not present an ‘airway problem’. However, identifying the individual factors that appear to be more closely associated with difficult intubation is paramount and these are further discussed below. 3. Predictors of difficult airway As anaesthetists, rather than making assumptions based on BMI alone, we must aim to identify particular features in obese patients likely to predict problems with airway management. The associated features are outlined below. 3.1. BMI It would seem intuitive that the higher the BMI, the greater the expected difficulty of intubation. However, several studies have now refuted this and BMI itself has not been shown to be an independent risk factor for difficult tracheal intubation in obese patients.9, 11, 12 This suggests that the super obese (BMI >50 kg/m2) are no more difficult to intubate than the obese or morbidly obese. 3.2. Mallampati classification The Mallampati (MP) classification, first described by a group from Boston in 1985, uses the structures visible at the back of the mouth to predict difficult tracheal intubation. As has been previously described, the Mallampati score has a poor sensitivity and specificity and this calls into question its usefulness in clinical practice. However, it has nonetheless become an integral part of the routine pre-operative airway assessment and the evidence for its use in obesity is considered here. In the study by Juvin et al. a Mallampati score of 3 or 4 was the only independent risk factor for difficult intubation in obese patients with a specificity and positive predictive value of 62% and 29% respectively.9 This reflected the findings of another study of 100 morbidly obese patients (BMI > 40 kg/m2), where the product of the graded laryngoscopy view and number of intubation attempts was used to define difficult intubation.12 Mallampati score of 3 or 4 was also significantly associated with difficult tracheal intubation in the study by Gonzalez et al.10 3.3. Neck circumference Neck circumference is generally measured at the level of the superior border of the cricoid cartilage. Large-neck circumference has been shown in several studies to be a predictor of difficult intubation in morbidly obese patients.10, 11, 12 In the study by Brodsky et al., a neck circumference of 40 cm was associated with a 5% probability of problematic intubation (described as grade of laryngoscopy view multiplied by intubation attempts ≥3), whereas at 60 cm, the probability was 35% (P = 0.02). Furthermore, a large-neck circumference was significantly associated with male gender (P < 0.001), a higher MP score (P = 0.0029), grade 3 laryngoscopy (P = 0.0375) and Obstructive Sleep Apnoea (OSA) (P = 0.0372).12 Ezri et al. carried out an ultrasound examination of the anterior neck in 50 morbidly obese patients. Laryngoscopy was found to be more difficult in patients with a greater amount of pre-tracheal soft tissue and greater overall neck circumference.13 3.4. Thyromental distance Thyromental (TM) distance (also known as Patil's test) is the distance from the tip of the thyroid cartilage to the tip of the mandible with the neck fully extended. A problematic intubation is associated with a TM distance less than 6.5 cm and this estimates the potential space into which the tongue can be displaced on laryngoscopy. A distance of less than 6 cm is associated with difficult laryngoscopy and predicts 75% of difficult laryngoscopies in the general surgical population. Difficult tracheal intubation was associated with reduced thyromental distance in the study by Gonzalez et al.,10 but this association has not been reported by other investigators.12 3.5. Other airway descriptors Reduced mouth opening (inter-incisor gap) has not been found to be a significant independent predictor of difficult intubation in the obese.9, 12 Mandibular recession and ‘buck teeth’ were also not found to be significant risk factors in the study by Juvin et al.9 There was no evidence that the authors could find for the use of sterno-mental distance in obese subjects. 3.6. Obstructive sleep apnoea Obstructive Sleep Apnoea (OSA) is defined as intermittent and repeated upper airway collapse, leading to partial or total airway occlusion for short periods of time during sleep. This results in an irregular breathing pattern, episodic sleep-associated oxygen desaturation and hypercarbia, along with cardiovascular dysfunction and excessive daytime sleepiness. It is widely under-diagnosed in the obese and has a prevalence of up to 70%. OSA has not been shown to be an independent risk factor for difficult intubation in the aforementioned studies.9, 12 However, some studies have shown that difficult intubation is more common in obese patients with OSA and large-neck circumference compared to non-obese subjects.14 It has been demonstrated that patients with OSA have larger necks than equally obese patients without OSA.15, 16 The evidence suggests increased neck soft tissue volume, along with a more collapsible airway, results in both intubation and ventilation difficulties in obese patients with OSA. Literature reviews concerning obesity, OSA and the airway have identified many disastrous respiratory outcomes. These mainly relate to failure of intubation, airway obstruction following extubation and respiratory arrest after opioid and sedative medication in the post-operative period. Pre-operative CPAP treatment in obese patients with OSA has been shown to improve early anatomical and later functional aspects of the upper airway. In addition, many authors report generally improved cardio-respiratory function with this therapy and would advocate a period of pre-operative optimisation. More detailed information on OSA and the other sleep disorders can be found in the article by Dakin and Margarson17 elsewhere in this supplement. In summary, the literature suggests that standard clinical tests for predicting difficult intubation are less useful in the morbidly obese.11 It appears there exists good evidence for measuring neck circumference as part of the pre-operative airway evaluation in obese patients, in addition to MP scoring and TM distance. However, the actual neck size that is predictive of problems with airway management or that justifies interventions such as awake fibreoptic intubation (AFOI) is not known and further work is required to elucidate this. 4. Pre-operative airway assessment Particular features that should be noted in the patient history are; the presence of suspected or diagnosed OSA, problems with previous anaesthetics/airway management and the presence of treated or untreated gastro-oesophageal reflux disease (GORD). Additionally, a thorough review of previous anaesthetic records is essential wherever possible. Obese patients at risk of airway obstruction under general anaesthesia have previously been characterized as having; a short mental-hyoid distance, flattened, compressed anterior–posterior craniofacial architecture, retrognathism, relative macroglossia, and a narrower, bulky oropharynx. For optimal airway examination in obese patients, the following should be noted: neck circumference, MP score, thyromental distance, assessment of mouth opening and jaw protrusion, range of neck movement and general assessment of craniofacial architecture. The presence of a cervical fat pad or ‘hump’ should also be noted as this can lead to difficulty in positioning the patient optimally for intubation (see Section on Airway management below). 5. Airway management An individualised strategy for airway management that is based on published standards should be formulated for each obese patient presenting for surgery. In the UK, the Association of Anaesthetists of Great Britain and Ireland have recently published guidelines on the ‘Perioperative Management of the Morbidly Obese Patient’ which include advice on airway management, staffing and equipment requirements.18 A range of difficult airway equipment should be prepared and checked in advance, and a trained assistant, in addition to more experienced anaesthetic input should be available if required. If a history of GORD has been found at the pre-operative visit, appropriate antacid prophylaxis with either a Histamine-2 receptor antagonist or proton pump inhibitor, should be considered prior to arrival in the anaesthetic room. In general, any sedating pre-medication should be avoided because of the risk of increased sensitivity to the central respiratory-depressant effects. 5.1. Positioning A ‘ramped’ or semi-sitting position has been shown to produce a better view at laryngoscopy compared with the standard ‘sniffing the morning air’ position (a conventional “sniff” position was obtained by placing a firm 7-cm cushion underneath the patient's head).19 More specifically, several authors recommend that the patient's head, upper body and shoulders be significantly elevated above the chest with the head extended to optimise the view at laryngoscopy. A towel or folded blankets under the shoulders and head can compensate for an exaggerated flexed position from a posterior cervical fat pad. Head elevation beyond the ‘sniffing’ position by raising the back and shoulders has been described as the ‘Head-Elevated Laryngoscopy Position’ (HELP) and facilitates alignment of the pharyngeal, laryngeal and oral axes of the airway during intubation, especially in the obese patient.20 It has been suggested that the optimal intubating position can be achieved by ensuring an imaginary horizontal line connecting the patient's sternal notch and external auditory meatus.21 The exact method used to achieve this position does not appear important. Blankets, pillows (including a pre-manufactured elevation pillow) and towels have all been used, in addition to the reverse Trendelenburg (RTP), or ‘ramped’ table position with adjustment of head position. 5.2. Induction Morbid obesity is associated with a reduction in the time to desaturation after apnoea following standard pre-oxygenation and induction of general anaesthesia. There are several strategies available that can be employed to minimise this occurrence. Pre-oxygenation should be carried out in the head-up or sitting, rather than the supine, position as this increases functional residual capacity (FRC) and allows a higher oxygen tension to develop. This results in a clinically significant increase in the desaturation safety period and allows greater time for airway control and intubation. In a randomised controlled trial (RCT) of morbidly obese patients undergoing laparoscopic gastric banding (BMI > 40 kg/m2), oxygen saturation and the desaturation safety period following 3 min of pre-oxygenation was measured in either the supine or 25° head-up position. The group in the 25° head-up position achieved a 23% higher pre-induction oxygen tension compared with the supine group (442 ± 104 vs 360 ± 99 mmHg respectively, P = 0.012) and took longer to reach an oxygen saturation level of 92% (201 ± 55 vs 155 ± 69 s, P = 0.023).22 In another study comparing the pre-oxygenation of obese patients in the sitting and supine position, the tolerance to apnoea post-intubation was significantly increased in the sitting group. The mean time to desaturate to 90% was 214 (28) in the sitting group vs 162 (38) seconds (P < 0.05) in the supine group.23 The RTP may be even better for prolonging the time to desaturation following induction of anaesthesia. Thirty degrees of RTP has been shown to prolong the safe apnoea period in obese neurosurgical patients following induction when compared to the supine position.24 Thirty degrees of RTP was also found to provide the longest time before desaturation to 92% following induction of anaesthesia and 5 min of ventilation, compared to both the supine and 30° sitting positions.25 CPAP may enhance pre-oxygenation further, although the optimal level and duration of applied positive pressure has not been fully elucidated. In one study, 7.5 cmH2O CPAP during 3 min of pre-oxygenation did not have any effect on the time to desaturate to 90% during apnoea following induction and intubation in a group of 20 morbidly obese women. However, another did find significant benefit from CPAP and PEEP prior to intubation.26 Patients were pre-oxygenated with 10 cmH2O CPAP for 5 min prior to induction and then ventilated with 10 cmH2O PEEP for 5 min post-induction until tracheal intubation. The time taken to desaturate to 90% during apnoea was then measured and arterial gas tensions recorded just before apnoea commenced and at 92% oxygen saturation. In the control group, pre-oxygenation and ventilation were similarly carried out but without the application of CPAP or PEEP. The duration of non-hypoxic apnoea was 50% longer in the CPAP/PEEP group compared with the control group (188 ± 46 vs 127 ± 43 s respectively, P = 0.002). In addition, PaO2 was significantly higher before apnoea in the CPAP group. Nasopharyngeal oxygen insufflation in morbidly obese patients following induction of anaesthesia has also been shown to decrease the severity of desaturation after 4 min of apnoea. Nasopharyngeal insufflation may therefore be useful during intubation attempts to ‘buy more time’. Some authors and many centres still advocate rapid sequence induction (RSI) with cricoid pressure in all morbidly obese patients, although this practice is now controversial. The risks and benefits of any induction method must be carefully considered in each individual patient. In the elective, fasted obese patient not anticipated to be at increased risk of airway problems and without risk factors for pulmonary aspiration, there now appears to be anecdotal consensus that RSI is not necessary in every obese patient. Although residual gastric volume and acidity are increased in fasting morbidly obese compared with lean surgical patients, recent studies have failed to demonstrate a relationship between obesity and the incidence of pulmonary aspiration. However, when indicated by symptomatic GORD or hiatus hernia, suxamethonium remains the neuromuscular blocking agent of choice. In the group of patients who have previously undergone bariatric surgery, anatomical and physiological changes in the stomach appear to increase the risk of aspiration when compared with non-bariatric patients.27 It is therefore also recommended that RSI is used in such patients, even where there has been substantial weight loss following bariatric intervention. Further detail on induction techniques and choice of anaesthetic agents in the obese population can be found in the article by O'Neill & Allam elsewhere in this issue.28 5.3. Facemask ventilation and supraglottic devices In the authors' experience, if correctly positioned, most obese patients are relatively easy to ventilate with a facemask, with or without a Guedel airway. An audit of a sequential group (n = 48) of obese patients (BMI of 45.9 ± 6.6 kg/m2) undergoing bariatric surgery and presented at the Difficult Airway Society (DAS) 2008 annual conference, found all patients to be either ‘easy’ or ‘manageable’ when ventilated with a facemask ± Guedel airway.29 Other studies have shown that the incidence of difficult mask ventilation (DMV) is increased in overweight and obese patients. For example, in a prospective study of 1502 general surgical patients, Langeron et al. showed that DMV was associated with BMI >26 kg/m2.30 The possibility of this must be borne in mind when developing a strategy for intubation. Supraglottic airways may provide a satisfactory airway for minor procedures in obese patients who are not at an enhanced risk of gastroesophageal reflux, but this may not be an ideal technique. Supraglottic devices are perhaps most useful when ventilating obese patients prior to planned endotracheal intubation or for facilitating intubation by a secondary technique (see section on Secondary intubation techniques). Both the standard Laryngeal Mask Airway (LMA) and ProSeal Laryngeal Mask Airway (PLMA) can be used to ventilate obese patients. A study comparing 60 obese patients (BMI > 30 kg/m2) randomised for ventilation with either the LMA or PLMA, found that both are effective in ventilating obese patients.31 The LMA however, did require a greater cuff pressure than the PLMA, but this was not associated with an increased incidence of sore throat. It was also found that in 10% of cases where the PLMA was used, the drainage tube was not patent, and the authors recommend this be checked with a gastric tube prior to use. 6. Primary intubation techniques 6.1. Direct laryngoscopy The problems associated with direct laryngoscopy and techniques for optimising success are discussed above. However, there are several alternative methods to direct laryngoscopy as a primary intubation strategy. These include indirect laryngoscopy, the use of semi-rigid scopes and fibreoptic intubation. 6.2. Indirect laryngoscopy Several studies and audits have reported on the use of indirect laryngoscopy to facilitate tracheal intubation in obese patients. The Airtraq® laryngoscope (Prodol Meditec, Vizcaya, Spain) is designed to enable visualisation of the glottis and passage of the endotracheal tube (ETT) through the vocal cords without necessary alignment of the oral, pharyngeal and laryngeal axes. A study of 106 morbidly obese patients (BMI > 35 kg/m2) undergoing surgery were randomised for intubation with either the standard Macintosh or Airtraq® laryngoscope.32 If tracheal intubation was not achieved within 120 s with the selected device, laryngoscopes were switched. In the Airtraq® group, all patients were successfully intubated within 120 s, whereas in the Macintosh group, six patients required intubation with the Airtraq® laryngoscope. The mean time (SD) taken for tracheal intubation was 24 (16) and 56 (23) seconds for the Airtraq® and Macintosh laryngoscopes respectively (p < 0.001). In addition, oxygen saturation was better maintained in the Airtraq® group. Using the Intubation Difficulty Scale score, a score >5 (indicating difficult intubation) was recorded in 11 patients in the Macintosh group, but in none of the Airtraq® group. In the latter group, all patients were documented to have C & L grade 1 laryngoscopic view. It is relevant to note that patients were not optimally positioned in a standardised fashion for direct laryngoscopy and this may have favoured better outcomes with the Airtraq® device. The same study also recorded 10 intubations when using the Airtraq® as traumatic, due to difficulty in passing the device into the pharynx. It is important to note that the Airtraq® may be difficult to use in patients with restricted mouth opening as the laryngoscope has a thickness of 1.8 cm and width of 2.8 cm. Interestingly, there is a case report of the use of the Airtraq® for awake intubation in a morbidly obese patient (BMI 38 kg/m2) with a history of GORD, where both ventilation and intubation were anticipated to be difficult. Laryngoscopy and tracheal intubation in this case were successfully achieved using sedation and topical airway anaesthesia. Several different types of videolaryngoscope are now available. Videolaryngoscopy has been shown to significantly improve the C & L grade of view compared to direct laryngoscopy in almost a third of morbidly obese patients.33 There is good emerging evidence for the use of the Glidescope® videolaryngoscope (GVL, Verathon Medical, Aylesbury, Bucks, UK) in morbidly obese patients. In one series of 32 patients (BMI 54.1 ± 8.1 kg/m2), all were successfully intubated with the GVL, 93.1% on the first attempt.34 In another series of 48 patients at our institution, (BMI 45.9 ± 6.6 kg/m2), 95.8% were successfully intubated using the GVL with 72.9% of these achieved on the first attempt. At the time of the audit, the GVL was new to our department and all grades of junior anaesthetist were permitted to intubate under supervision.29 In both of these reports, the Glidescope® was used with a styletted endotracheal tube as recommended by the manufacturer. Other indirect laryngoscopes reported on for use in morbidly obese patients include the Bullard laryngoscope, and a case report exists on its successful emergency use in a morbidly obese parturient with documented previous difficult intubation. 6.3. Awake fibreoptic intubation Routine awake intubation of the morbidly obese patient has not been validated, does not appear necessary in most cases35 and it can prove difficult and unpleasant for the patient. However, it is still the preferred method of some clinicians and may be essential if there is significant restriction of mouth opening. Awake fibreoptic intubation (AFOI) certainly does have a place in the morbidly obese where there is history of DMV and/or difficult intubation, or where these are suspected from the airway examination. However, the emergence of indirect laryngoscopes and secondary intubation techniques utilising ventilation through an LMA or supraglottic device, have made awake fibreoptic intubation less common in the obese. A technique using nasal CPAP applied to the contralateral nostril during nasotracheal fibreoptic intubation has been described. Simultaneous application of 20 cmH2O CPAP using a nasal pillow helped maintain oxygenation during intubation, with a ‘splinting’ effect on the pharynx reported to facilitate visualisation of anatomical landmarks and translaryngeal passage of the fibrescope. 7. Secondary intubation techniques These techniques involve use of an LMA or supraglottic device to allow ventilation prior to tracheal intubation by a secondary technique. The secondary intubation techniques include ‘blind’ tracheal intubation, e.g. through an intubating LMA, (ILMA, Intavent Orthofix, Maidenhead, Berks, UK), fibreoptic intubation through an LMA or other supraglottic device, and video-guided tracheal intubation, e.g. using an LMA CTrach™ (Intavent Orthofix, Maidenhead, Berks, UK). Some clinicians consider the additional time required between loss of consciousness and securing the airway in these secondary intubation strategies as more risky in terms of aspiration in the morbidly obese patient. However, there are several studies that have used LMA devices to facilitate tracheal intubation in obese patients who have low regurgitation risk and normal gastric emptying and more detail on these are given below. They may have the advantage of providing better oxygenation during the intubation process and produce less airway stimulation compared to direct laryngoscopy.36 Fibreoptic intubation through a standard LMA is nearly 100% successful in most series and is a technique that may be considered in the obese patient. There is presently however, little evidence for its use in obese subjects. The PLMA has been described as an efficacious temporary ventilatory device in obese patients prior to direct laryngoscope-guided tracheal intubation. In a study of 60 obese patients (BMI 35–60 kg/m2), an effective airway was obtained using a PLMA on the first or second insertion attempt and positive pressure ventilation (8 ml/kg) was possible in 95% of patients after muscle relaxation. A fibreoptic view of the vocal cords from the airway tube was achieved in 75% of patients.37 The ILMA or Fastrach™ (Intavent Orthofix, Maidenhead, Berks, UK) is a specific device that allows effective ventilation and blind tracheal intubation in patients with normal and abnormal airways. It has several original features that provide better conditions than the standard LMA for achieving effective ventilation and tracheal intubation. These include an anatomical curve, rigid airway tube with guiding handle, epiglottic elevating bar and guiding ramp to guide insertion of the tracheal tube. One prospective study using the ILMA as an elective ventilatory device and intubation guide in 118 obese (BMI 45 ± 5 kg/m2) patients, revealed successful tracheal intubation in 96.7%, with the majority of these on first attempt and within 120 s.38 Failures were due to unsuccessful attempts to pass the tracheal tube into the trachea, and these patients were successfully intubated with a Macintosh laryngoscope, although a fibrescope through the ILMA could also have been used. There were no cases of DMV, and ventilation through the ILMA was easily achieved without arterial hypoxaemia. The ILMA may be a valuable device in airway management of obese patients and its use complements conventional laryngoscopy. The LMA CTrach™ (CT) is a modified version of the ILMA with two integrated fibreoptic bundles emerging at the distal end of the airway tube. It is attached to a full colour viewer that provides both the light source and image treatment to allow continuous video-endoscopy of illuminated anatomical structures. The CT facilitates positioning of the mask in the pharynx to optimise laryngeal view and observe tracheal intubation. A study comparing 104 morbidly obese patients (BMI 43.5 ± 9 kg/m2) randomised for intubation with either direct laryngoscopy or the CT, found all patients could be successfully intubated with either method.36 It is important to note that the clinicians using the CT had extensive training in its use and methods of view optimisation. Of the patients from the CT group, 49% required laryngeal mask manipulation (for ventilation and view optimisation) resulting in prolonged time to intubation by approximately 1 min when compared to the direct laryngoscopy group. Blind tracheal intubation was required in 17% of patients in the direct laryngoscopy group, while tracheal intubation was witnessed in all patients in the CT group. The CT group were also found to have improved oxygenation during the intubation period with significantly fewer patients reaching saturation levels below 92% A recent case report however, describes pulmonary aspiration in a male, morbidly obese patient during tracheal intubation when using the CT. The patient did have a history of symptomatic GORD and the CT was only employed following failed intubation with direct laryngoscopy and difficult facemask ventilation. Reassuringly, the CT did enable good quality ventilation, early recognition of regurgitation and tracheal intubation was eventually achieved. 8. The unanticipated difficult airway Algorithms to manage the unanticipated difficult airway in general surgical patients have been published by the Difficult Airway Society in the UK. However, in the obese patient, the exact strategy used will depend on local guidelines, experience of the anaesthetist and equipment available. The range of techniques that may be employed are as listed in section on Secondary intubation techniques. Case reports regarding emergency intubation and/or unanticipated difficult airway in morbidly obese patients do exist. The ILMA has been used for rescue oxygenation and tracheal intubation in a morbidly obese patient in an out-of-hospital location.39 The Combitube (Armstrong Medical, Lincolnshire, Illinois, USA) has been used for successful emergency airway management following failed intubation prior to formal tracheostomy.40 8.1. Surgical airway Surgical access to the airway is technically more difficult in obese patients and is associated with an increased risk of peri-operative complications. Ultrasound guidance for percutaneous dilatational tracheostomy has been described in a morbidly obese patient in the critical care unit setting and may help delineate the anatomy in obese patients with large-neck circumference. 9. Post-operative airway complications Post-operative airway and respiratory complications in obese subjects are discussed in greater detail by O'Neill & Allam.28 The incidence of atelectasis has been reported as 45% in obese patients after upper abdominal surgery. Laparoscopic, compared with open techniques, have less detrimental effects on respiratory dynamics. Treatment with prophylactic post-operative CPAP or BiPAP has been advocated in obese subjects to reduce post-operative airway obstruction and pulmonary dysfunction, and there is also evidence to suggest it may decrease rates of respiratory infection. Adult obese patients with suspected or confirmed OSA, present a formidable challenge throughout the peri-operative period. Tracheal intubation and extubation strategies must be made with particular care in these patients. They have increased sensitivity to opioid-induced respiratory depression and depression of the arousal to obstructed breathing, and in the post-operative period, continuous visual and electronic monitoring is recommended, ideally in a high dependency or intensive care unit setting.41, 42 Other measures aimed at improving post-operative pulmonary function include incentive spirometry, deep breathing exercises and intermittent positive pressure breathing, although good evidence for benefit from these is lacking. Adequate analgesia is necessary to aid and improve pulmonary function, although care should be taken with opioid analgesics in those with OSA. Epidural analgesia may be beneficial in some patients undergoing open surgery, but respiratory arrest has been reported in patients with OSA on the third or fourth post-operative day, after accumulation of neuraxial opioids. Many abdominal procedures require free naso-gastric drainage post-operatively. This may help to reduce the risk of reflux and aspiration following surgery. 10. Conclusion With an increasing incidence of obesity in the general surgical population, appropriate management of the airway in this group of patients is an important topic for all anaesthetists. The intra-operative management of ventilation, extubation strategy and general post-operative monitoring of these patients is an equally important topic discussed elsewhere in this issue by O'Neill and Allam.28 This article has focussed on the evidence for pre-operative airway assessment and airway management of obese patients requiring general anaesthesia. There is a rapidly expanding body of evidence in this area, with an array of new intubation devices available on how this may be best achieved. As always, the patient must have an individualised management plan and the chosen techniques must be familiar to all involved, with a clear back-up plan for when unexpected difficulties in airway management arise. Conflict of interest None. References 1. 1Practice guidelines for management of the difficult airway. A report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology. 1993;78:597–602. MEDLINE |
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Magill Department of Anaesthesia, Chelsea & Westminster Hospital, 369 Fulham Road, London, SW10 9NH, UK  Corresponding author. Tel.: +44 (0)7811 354 907; fax: +44 (0)7092 052 604.
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