- Email: [email protected]
Airway Management in the Obese Patient
Airway Management i n t h e Ob e s e P a t i e n t William A. Loder,
MD
a,b,
*
KEYWORDS Intubation Airway Laryngoscope Obese
Any patient can have a difficult airway, but obese patients have anatomic and physiologic features that can make airway management particularly challenging. Changes in respiratory mechanics, such as a decreased functional residual volume, may result in rapid onset of hypoxemia in the obese patient. Excess soft tissue around the neck and in the oropharynx can make mask ventilation difficult or impossible. Increased intra-abdominal pressure from abdominal adiposity increases the risk of regurgitation and aspiration. To effectively manage airways in obese patients, health care providers working in the intensive care unit (ICU) setting must be proficient in airway evaluation and management in all types of patients. They need to be skilled in mask ventilation and direct laryngoscopy. The providers need to know how to safely manage a difficult airway situation, both anticipated and unanticipated1–4 and should be familiar with the American Society of Anesthesiology’s Difficult Airway Algorithm (Fig. 1). It is unclear whether obese patients are at an increased risk of difficulty associated with endotracheal intubation. Studies focusing on obesity as a risk factor for airway problems have reported a wide range of risks. One study found that obese individuals (body mass index [BMI]>35, calculated as the weight in kilograms divided by the height in meters squared) were 7 times more likely to have a difficult intubation,5 but in a study of more than 90,000 intubations, obesity was shown to be a statistically significant but weak predictor of difficult intubation, with an odds ratio of only 1.34.6 In a study using the intubation difficulty scale (IDS),7 105 obese patients were compared with 99 nonobese patients. The obese patients had higher average IDS scores, but all the patients were intubated successfully using direct laryngoscopy. The average time to intubation was 46 seconds in the obese group. The lowest oxygen saturation reported for any patient was 97%.8 Another study found no relationship between BMI, neck circumference, or obstructive sleep apnea and difficult intubations.9
The author has no financial or other conflicts of interest to disclose. a Department of Anesthesiology, Geisinger Medical Center, Danville, PA 17822-2025, USA b Department of Critical Care Medicine, Geisinger Medical Center, Danville, PA 17822-2025, USA * Department of Anesthesiology, Geisinger Medical Center, Danville, PA 17822-2025. E-mail address: [email protected] Crit Care Clin 26 (2010) 641–646 doi:10.1016/j.ccc.2010.08.002 criticalcare.theclinics.com 0749-0704/10/$ – see front matter Ó 2010 Elsevier Inc. All rights reserved.
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Loder
Fig. 1. Difficult Airway Algorithm. LMA, laryngeal mask airway. (From American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Practice guidelines for management of the difficult airway: an updated report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology 2003;98:1273; with permission.)
There have been several studies on multiple risk factors including the Mallampati score, thyromental distance, cervical spine extension, interincisor distance, upper lip bite test,10,11 neck circumference, and BMI. Three articles11–13 have calculated the positive and negative predictive values (PPV and NPV, respectively) of several
Airway Management in the Obese Patient
of these individual risk factors. None of the factors have a PPV greater than 50% but all have an NPV greater than 95%. Several studies have examined a combination of factors, trying to improve on the prediction of a difficult airway. One study12 on the combination of neck circumference (>43 cm) and Mallampati score (>3) found that the combination was better than either factor alone with a PPV of 44%. Another article14 on the combination of the Mallampati score (>3) and thyromental distance (<6 cm) demonstrated improved prediction of difficult intubation. Rao and colleagues15 reported that positioning obese patients so that the ear is aligned with the sternal notch (the ramp position) seemed to facilitate tracheal intubation. Another article on the combination of a class III upper lip bite test (unable to bite upper lip with lower incisors) with the interincisor, thyromental, or sternomental distances reported that all 3 combinations had low PPVs.16 All this confirms the clinical impression that the prediction of difficult intubation is, at best, imprecise.14,17,18 If a patient tests positive for any risk factor, there may be a difficulty in intubation and obesity is one additional factor to be taken into consideration. The more risks that individuals have the more likely they are to have a difficult airway and intubation. If individuals test negative for all risk factors, they are unlikely to have a difficult airway and intubation. In addition to the aforementioned risk factors that suggest a difficult airway, there are additional factors that must be considered when managing a patient’s airway. Clinical conditions such as a cervical spine injury, full stomach, and intravascular volume status influence the management of the airway. In addition, patients in the ICU who require endotracheal intubation are frequently hypoxic, hypercapnic, and/ or hypotensive, which add to the complexity and the urgency of the situation. Before any attempt to instrument an airway, it is vital that the patient be, at least briefly, evaluated. Essential equipment should be gathered. The exact list of equipment needed may vary slightly depending on the intubating individual’s preference, but endotracheal tubes with stylets, functioning suction, a bag-valve device connected to an oxygen source, laryngoscope and blades, oral/nasal airways, and a device to detect end-tidal carbon dioxide are essential. Nonemergent potentially difficult airways should be managed conservatively. Additional help and equipment should be sought, and a plan to safely intubate the patient should be formulated. There are many ways of handling the anticipated difficult airway and they depend on the individual’s training, the techniques that the individual is comfortable with, and the patient’s condition. The possibilities include, but are not limited to, maintaining bag ventilation until help arrives, placing a supraglottic airway device, performing an awake intubation with a flexible fiberoptic bronchoscope, or proceeding with direct laryngoscopy. The best method depends on the skills and experience of the individuals involved. In the ICU setting, evaluation of the airway can be difficult, and if initial intubation attempts fail, the situation can quickly deteriorate and become life threatening. Between 8% and 12% of intubations in the ICU are difficult, usually defined as 2 or more attempts by someone skilled in direct laryngoscopy.19–21 In the unanticipated difficult intubation, the skills and knowledge of the individual managing the airway are of paramount importance if a disaster is to be avoided. Obese patients are especially difficult to manage. When compared with nonobese patients, obese patients desaturate more rapidly and recover from hypoxia more slowly. In obese patients, effective bag-mask ventilation may be very difficult or impossible and they are at an increased risk for aspiration.13,22 An increased neck size can make retrograde wire intubation and emergent surgical airway procedures difficult. To add to the complexity, many of the techniques used to manage difficult airways are a bit toilsome
643
644
Loder
in the obese patient. The effective use of adjunctive devices, such as flexible bronchoscopes, supraglottic devices, and lightwands,23,24 requires the acquisition and practice of a specific set of skills that a given intensivist may or may not have. As described earlier, health care providers who deal with airways must have the abilities to safely manage them and must know when to ask for help. In case of a failed intubation, consideration should be given to calling for help early before the situation becomes irretrievable with a catastrophic patient outcome. There is controversy regarding whether hypnotics or neuromuscular blocking agents should be given to facilitate intubation. Some individuals prefer to support and assist a patient’s respiratory efforts and intubate a patient with spontaneous respiration. Others think that having a patient asleep and paralyzed improves mask ventilation and laryngoscopy and makes intubation easier. Both methods have advantages and disadvantages. Giving a muscle relaxant may make laryngoscopy easier and decrease the chances of difficult intubation,25 but if the patient is paralyzed and cannot be intubated, the airway has to be maintained until the intubation can be successfully accomplished or the patient returns to spontaneous respiration. In obese patients, maintaining an adequate airway, particularly after multiple intubation attempts, can be challenging. Like so many other areas of medicine, clinical judgment and a low threshold to ask for additional expertise are required. In review, there is little difference in how the airway is approached in obese and nonobese patients. Obesity does not seem to be an independent risk factor for difficult intubation but is one of the several factors that need to be considered as part of an airway evaluation. However, if an obese patient cannot be intubated, maintaining an adequate airway is more likely to be challenging and may lead to a “cannot intubate, cannot ventilate” situation. Patients in the ICU are frequently unstable and need to be intubated in a relatively emergent manner. This sense of urgency can lead to mistakes, with the occasional disastrous outcome. Health care providers who manage airways and intubate patients need to have the skills, experience, and confidence to do so safely. In summary, the risk of a difficult airway/intubation situation in an obese patient is similar to that in the nonobese patient. In addition, individuals who manage airways and endotracheally intubate patients as part of their practice need to be skilled at bag-mask ventilation and direct laryngoscopy. Some individuals prefer using a short or stubby laryngoscope handle when dealing with obese patients. These individuals should also be proficient with at least 1 alternative method of airway management, such as flexible fiberoptic bronchoscope, supraglottic devices (LMA, COBRA PLA, EngineeredMedical Systems, IN, USA), lightwand, or video laryngoscopy. There are several types of rigid stylets as well as more invasive techniques, such as transtracheal jet ventilation, retrograde wire techniques, and emergent cricothyrotomy. Finally, knowing how to quickly evaluate an airway and when to call for help, either before or after the difficulty is encountered, are critical skills and judgments that must be acquired by anyone dealing with the airway. REFERENCES
1. Langeron O, Amour J, Vivien B, et al. Clinical review: management of difficult airways. Crit Care 2006;10:243–7. 2. Rose DK, Cohen MM. The airway: problems and predictions in 18,500 patients. Can J Anaesth 1994;41:372–83. 3. Walz JM, Zayaruzny M, Heard SO. Airway management in critical illness. Chest 2007;131:608–20.
Airway Management in the Obese Patient
4. Drolet P. Management of anticipated difficult airway—a systematic approach: continuing professional development. Can J Anaesth 2009;56:683–701. 5. Juvin P, Lavaut E, Dupont H, et al. Difficult tracheal intubation is more common in obese than in lean patients. Anesth Analg 2003;97:595–600. 6. Lundstrom LF, Moller AM, Rosenstock C, et al. High body mass index is a weak predictor for difficult and failed tracheal intubation. Anesthesiology 2009;110: 266–74. 7. Adnet F, Borron SW, Racine SX, et al. The intubation difficulty scale (IDS): proposal and evaluation of a new score characterizing the complexity of endotracheal intubation. Anesthesiology 1997;87:1290–7. 8. Lavi R, Segal D, Ziser A. Predicting difficult airways using the intubation difficulty scale: a study comparing obese and non-obese patients. J Clin Anesth 2009;21: 264–7. 9. Neligan PJ, Porter S, Max B, et al. Obstructive sleep apnea is not a risk factor for difficult intubation in morbidly obese patients. Anesth Analg 2009;109:1182–6. 10. Salimi A, Farzanegan B, Rastegarpour A, et al. Comparison of the upper bite test with measurement of thyromental distance for prediction of difficult intubations. Acta Anaesthesiol Taiwan 2008;46(2):61–5. 11. Eberhart L, Arndt C, Cierpka T, et al. The reliability and validity of the upper lip bite test compared with the Mallampati classification to predict difficult laryngoscopy an external prospective evaluation. Anesth Analg 2005;101(1):284–9. 12. Gonzalez H, Minville V, Delanoue K, et al. The importance of increased neck circumference to intubation difficulties in obese patients. Anesth Analg 2008;106:1132–6. 13. Kheterpal S, Han R, Tremper KK, et al. Incidence and predictors of difficult and impossible mask ventilation. Anesthesiology 2006;105:885–91. 14. Shiga T, Wajima Z, Inoue T, et al. Predicting difficult intubation in apparently normal patients. Anesthesiology 2005;103:429–37. 15. Rao SL, Kunselman AR, Schuler HG, et al. Laryngoscopy and tracheal intubation in the head elevated position in obese patients: a randomized, controlled equivalence trial. Anesth Analg 2008;107:1912–8. 16. Khan ZH, Mohammadi M, Rasouli MR, et al. The diagnostic value of the upper lip bite test combined with sternomental distance, thyromental distance and interincisor distance of prediction of easy laryngoscopy and intubation: a prospective study. Anesth Analg 2009;109:822–4. 17. Karkouti K, Rose DK, Wigglesworth D, et al. Predicting difficult intubation: a multivariable analysis. Can J Anaesth 2000;47:730–9. 18. Lee A, Fan LT, Gin T, et al. A systematic review (meta-analysis) of accuracy of the Mallampati test to predict the difficult airway. Anesth Analg 2006;102:1867–78. 19. Schwartz DE, Matthay MA, Cohen NH. Death and other complications of emergency airway management in critically ill adults. A prospective investigation of 297 tracheal intubations. Anesthesiology 1995;82:367–76. 20. Jaber S, Amraoui J, Lefrant JY, et al. Clinical practice and risk factors for immediate complications of endotracheal intubation in the intensive care unit: a prospective, multiple-center study. Crit Care Med 2006;34:2355–61. 21. Griesdale DE, Bosma TL, Kurth T, et al. Complications of endotracheal intubation in the critically ill. Intensive Care Med 2008;34:1835–42. 22. Yildiz TS, Solak M, Toker K. The incidence and risk factors of difficult mask ventilation. J Anesth 2005;19:7–11. 23. Wong SY, Coskunfirat ND, Hee HI, et al. Factors influencing time of intubation with a lightwand device in patients without known airway abnormality. J Clin Anesth 2003;16:326–31.
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Loder
24. Dhonneur G, Abdi W, Ndoko SK, et al. Video-assisted versus conventional tracheal intubation in morbidly obese patients. Obes Surg 2009;19:1096–101. 25. Lundstrom LH, Moller AM, Rosenstock C, et al. Avoidance of neuromuscular blocking agents may increase the risk of difficult tracheal intubation: a cohort study of 103812 consecutive adult patients recorded in the Danish Anaesthesia Database. Br J Anaesth 2009;103:283–90.
MD
a,b,
*
KEYWORDS Intubation Airway Laryngoscope Obese
Any patient can have a difficult airway, but obese patients have anatomic and physiologic features that can make airway management particularly challenging. Changes in respiratory mechanics, such as a decreased functional residual volume, may result in rapid onset of hypoxemia in the obese patient. Excess soft tissue around the neck and in the oropharynx can make mask ventilation difficult or impossible. Increased intra-abdominal pressure from abdominal adiposity increases the risk of regurgitation and aspiration. To effectively manage airways in obese patients, health care providers working in the intensive care unit (ICU) setting must be proficient in airway evaluation and management in all types of patients. They need to be skilled in mask ventilation and direct laryngoscopy. The providers need to know how to safely manage a difficult airway situation, both anticipated and unanticipated1–4 and should be familiar with the American Society of Anesthesiology’s Difficult Airway Algorithm (Fig. 1). It is unclear whether obese patients are at an increased risk of difficulty associated with endotracheal intubation. Studies focusing on obesity as a risk factor for airway problems have reported a wide range of risks. One study found that obese individuals (body mass index [BMI]>35, calculated as the weight in kilograms divided by the height in meters squared) were 7 times more likely to have a difficult intubation,5 but in a study of more than 90,000 intubations, obesity was shown to be a statistically significant but weak predictor of difficult intubation, with an odds ratio of only 1.34.6 In a study using the intubation difficulty scale (IDS),7 105 obese patients were compared with 99 nonobese patients. The obese patients had higher average IDS scores, but all the patients were intubated successfully using direct laryngoscopy. The average time to intubation was 46 seconds in the obese group. The lowest oxygen saturation reported for any patient was 97%.8 Another study found no relationship between BMI, neck circumference, or obstructive sleep apnea and difficult intubations.9
The author has no financial or other conflicts of interest to disclose. a Department of Anesthesiology, Geisinger Medical Center, Danville, PA 17822-2025, USA b Department of Critical Care Medicine, Geisinger Medical Center, Danville, PA 17822-2025, USA * Department of Anesthesiology, Geisinger Medical Center, Danville, PA 17822-2025. E-mail address: [email protected] Crit Care Clin 26 (2010) 641–646 doi:10.1016/j.ccc.2010.08.002 criticalcare.theclinics.com 0749-0704/10/$ – see front matter Ó 2010 Elsevier Inc. All rights reserved.
642
Loder
Fig. 1. Difficult Airway Algorithm. LMA, laryngeal mask airway. (From American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Practice guidelines for management of the difficult airway: an updated report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology 2003;98:1273; with permission.)
There have been several studies on multiple risk factors including the Mallampati score, thyromental distance, cervical spine extension, interincisor distance, upper lip bite test,10,11 neck circumference, and BMI. Three articles11–13 have calculated the positive and negative predictive values (PPV and NPV, respectively) of several
Airway Management in the Obese Patient
of these individual risk factors. None of the factors have a PPV greater than 50% but all have an NPV greater than 95%. Several studies have examined a combination of factors, trying to improve on the prediction of a difficult airway. One study12 on the combination of neck circumference (>43 cm) and Mallampati score (>3) found that the combination was better than either factor alone with a PPV of 44%. Another article14 on the combination of the Mallampati score (>3) and thyromental distance (<6 cm) demonstrated improved prediction of difficult intubation. Rao and colleagues15 reported that positioning obese patients so that the ear is aligned with the sternal notch (the ramp position) seemed to facilitate tracheal intubation. Another article on the combination of a class III upper lip bite test (unable to bite upper lip with lower incisors) with the interincisor, thyromental, or sternomental distances reported that all 3 combinations had low PPVs.16 All this confirms the clinical impression that the prediction of difficult intubation is, at best, imprecise.14,17,18 If a patient tests positive for any risk factor, there may be a difficulty in intubation and obesity is one additional factor to be taken into consideration. The more risks that individuals have the more likely they are to have a difficult airway and intubation. If individuals test negative for all risk factors, they are unlikely to have a difficult airway and intubation. In addition to the aforementioned risk factors that suggest a difficult airway, there are additional factors that must be considered when managing a patient’s airway. Clinical conditions such as a cervical spine injury, full stomach, and intravascular volume status influence the management of the airway. In addition, patients in the ICU who require endotracheal intubation are frequently hypoxic, hypercapnic, and/ or hypotensive, which add to the complexity and the urgency of the situation. Before any attempt to instrument an airway, it is vital that the patient be, at least briefly, evaluated. Essential equipment should be gathered. The exact list of equipment needed may vary slightly depending on the intubating individual’s preference, but endotracheal tubes with stylets, functioning suction, a bag-valve device connected to an oxygen source, laryngoscope and blades, oral/nasal airways, and a device to detect end-tidal carbon dioxide are essential. Nonemergent potentially difficult airways should be managed conservatively. Additional help and equipment should be sought, and a plan to safely intubate the patient should be formulated. There are many ways of handling the anticipated difficult airway and they depend on the individual’s training, the techniques that the individual is comfortable with, and the patient’s condition. The possibilities include, but are not limited to, maintaining bag ventilation until help arrives, placing a supraglottic airway device, performing an awake intubation with a flexible fiberoptic bronchoscope, or proceeding with direct laryngoscopy. The best method depends on the skills and experience of the individuals involved. In the ICU setting, evaluation of the airway can be difficult, and if initial intubation attempts fail, the situation can quickly deteriorate and become life threatening. Between 8% and 12% of intubations in the ICU are difficult, usually defined as 2 or more attempts by someone skilled in direct laryngoscopy.19–21 In the unanticipated difficult intubation, the skills and knowledge of the individual managing the airway are of paramount importance if a disaster is to be avoided. Obese patients are especially difficult to manage. When compared with nonobese patients, obese patients desaturate more rapidly and recover from hypoxia more slowly. In obese patients, effective bag-mask ventilation may be very difficult or impossible and they are at an increased risk for aspiration.13,22 An increased neck size can make retrograde wire intubation and emergent surgical airway procedures difficult. To add to the complexity, many of the techniques used to manage difficult airways are a bit toilsome
643
644
Loder
in the obese patient. The effective use of adjunctive devices, such as flexible bronchoscopes, supraglottic devices, and lightwands,23,24 requires the acquisition and practice of a specific set of skills that a given intensivist may or may not have. As described earlier, health care providers who deal with airways must have the abilities to safely manage them and must know when to ask for help. In case of a failed intubation, consideration should be given to calling for help early before the situation becomes irretrievable with a catastrophic patient outcome. There is controversy regarding whether hypnotics or neuromuscular blocking agents should be given to facilitate intubation. Some individuals prefer to support and assist a patient’s respiratory efforts and intubate a patient with spontaneous respiration. Others think that having a patient asleep and paralyzed improves mask ventilation and laryngoscopy and makes intubation easier. Both methods have advantages and disadvantages. Giving a muscle relaxant may make laryngoscopy easier and decrease the chances of difficult intubation,25 but if the patient is paralyzed and cannot be intubated, the airway has to be maintained until the intubation can be successfully accomplished or the patient returns to spontaneous respiration. In obese patients, maintaining an adequate airway, particularly after multiple intubation attempts, can be challenging. Like so many other areas of medicine, clinical judgment and a low threshold to ask for additional expertise are required. In review, there is little difference in how the airway is approached in obese and nonobese patients. Obesity does not seem to be an independent risk factor for difficult intubation but is one of the several factors that need to be considered as part of an airway evaluation. However, if an obese patient cannot be intubated, maintaining an adequate airway is more likely to be challenging and may lead to a “cannot intubate, cannot ventilate” situation. Patients in the ICU are frequently unstable and need to be intubated in a relatively emergent manner. This sense of urgency can lead to mistakes, with the occasional disastrous outcome. Health care providers who manage airways and intubate patients need to have the skills, experience, and confidence to do so safely. In summary, the risk of a difficult airway/intubation situation in an obese patient is similar to that in the nonobese patient. In addition, individuals who manage airways and endotracheally intubate patients as part of their practice need to be skilled at bag-mask ventilation and direct laryngoscopy. Some individuals prefer using a short or stubby laryngoscope handle when dealing with obese patients. These individuals should also be proficient with at least 1 alternative method of airway management, such as flexible fiberoptic bronchoscope, supraglottic devices (LMA, COBRA PLA, EngineeredMedical Systems, IN, USA), lightwand, or video laryngoscopy. There are several types of rigid stylets as well as more invasive techniques, such as transtracheal jet ventilation, retrograde wire techniques, and emergent cricothyrotomy. Finally, knowing how to quickly evaluate an airway and when to call for help, either before or after the difficulty is encountered, are critical skills and judgments that must be acquired by anyone dealing with the airway. REFERENCES
1. Langeron O, Amour J, Vivien B, et al. Clinical review: management of difficult airways. Crit Care 2006;10:243–7. 2. Rose DK, Cohen MM. The airway: problems and predictions in 18,500 patients. Can J Anaesth 1994;41:372–83. 3. Walz JM, Zayaruzny M, Heard SO. Airway management in critical illness. Chest 2007;131:608–20.
Airway Management in the Obese Patient
4. Drolet P. Management of anticipated difficult airway—a systematic approach: continuing professional development. Can J Anaesth 2009;56:683–701. 5. Juvin P, Lavaut E, Dupont H, et al. Difficult tracheal intubation is more common in obese than in lean patients. Anesth Analg 2003;97:595–600. 6. Lundstrom LF, Moller AM, Rosenstock C, et al. High body mass index is a weak predictor for difficult and failed tracheal intubation. Anesthesiology 2009;110: 266–74. 7. Adnet F, Borron SW, Racine SX, et al. The intubation difficulty scale (IDS): proposal and evaluation of a new score characterizing the complexity of endotracheal intubation. Anesthesiology 1997;87:1290–7. 8. Lavi R, Segal D, Ziser A. Predicting difficult airways using the intubation difficulty scale: a study comparing obese and non-obese patients. J Clin Anesth 2009;21: 264–7. 9. Neligan PJ, Porter S, Max B, et al. Obstructive sleep apnea is not a risk factor for difficult intubation in morbidly obese patients. Anesth Analg 2009;109:1182–6. 10. Salimi A, Farzanegan B, Rastegarpour A, et al. Comparison of the upper bite test with measurement of thyromental distance for prediction of difficult intubations. Acta Anaesthesiol Taiwan 2008;46(2):61–5. 11. Eberhart L, Arndt C, Cierpka T, et al. The reliability and validity of the upper lip bite test compared with the Mallampati classification to predict difficult laryngoscopy an external prospective evaluation. Anesth Analg 2005;101(1):284–9. 12. Gonzalez H, Minville V, Delanoue K, et al. The importance of increased neck circumference to intubation difficulties in obese patients. Anesth Analg 2008;106:1132–6. 13. Kheterpal S, Han R, Tremper KK, et al. Incidence and predictors of difficult and impossible mask ventilation. Anesthesiology 2006;105:885–91. 14. Shiga T, Wajima Z, Inoue T, et al. Predicting difficult intubation in apparently normal patients. Anesthesiology 2005;103:429–37. 15. Rao SL, Kunselman AR, Schuler HG, et al. Laryngoscopy and tracheal intubation in the head elevated position in obese patients: a randomized, controlled equivalence trial. Anesth Analg 2008;107:1912–8. 16. Khan ZH, Mohammadi M, Rasouli MR, et al. The diagnostic value of the upper lip bite test combined with sternomental distance, thyromental distance and interincisor distance of prediction of easy laryngoscopy and intubation: a prospective study. Anesth Analg 2009;109:822–4. 17. Karkouti K, Rose DK, Wigglesworth D, et al. Predicting difficult intubation: a multivariable analysis. Can J Anaesth 2000;47:730–9. 18. Lee A, Fan LT, Gin T, et al. A systematic review (meta-analysis) of accuracy of the Mallampati test to predict the difficult airway. Anesth Analg 2006;102:1867–78. 19. Schwartz DE, Matthay MA, Cohen NH. Death and other complications of emergency airway management in critically ill adults. A prospective investigation of 297 tracheal intubations. Anesthesiology 1995;82:367–76. 20. Jaber S, Amraoui J, Lefrant JY, et al. Clinical practice and risk factors for immediate complications of endotracheal intubation in the intensive care unit: a prospective, multiple-center study. Crit Care Med 2006;34:2355–61. 21. Griesdale DE, Bosma TL, Kurth T, et al. Complications of endotracheal intubation in the critically ill. Intensive Care Med 2008;34:1835–42. 22. Yildiz TS, Solak M, Toker K. The incidence and risk factors of difficult mask ventilation. J Anesth 2005;19:7–11. 23. Wong SY, Coskunfirat ND, Hee HI, et al. Factors influencing time of intubation with a lightwand device in patients without known airway abnormality. J Clin Anesth 2003;16:326–31.
645
646
Loder
24. Dhonneur G, Abdi W, Ndoko SK, et al. Video-assisted versus conventional tracheal intubation in morbidly obese patients. Obes Surg 2009;19:1096–101. 25. Lundstrom LH, Moller AM, Rosenstock C, et al. Avoidance of neuromuscular blocking agents may increase the risk of difficult tracheal intubation: a cohort study of 103812 consecutive adult patients recorded in the Danish Anaesthesia Database. Br J Anaesth 2009;103:283–90.