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Anaesthesia for obesity surgery
ENDOCRINOLOGY
Anaesthesia for obesity surgery
Learning objectives After reading this article you should be able to: C list four different types of obesity surgery C carry out a preoperative screening assessment for obstructive sleep apnoea (OSA) C identify and list six risk factors to determine which patients may require level II care postoperatively
Claire E Moore Mark Forrest Basil Ammori
induces much greater malabsorption coupled with a much larger gastric pouch and therefore lesser restriction. Contemporary bariatric surgery is reasonably safe with mortality in the region of 0.1e0.5%. The highest risk comes in older superobese males. The risks are less following an AGB than from an RYGB; however the latter offers superior long-term weight loss. The risk of complications from the procedure itself appears to be reduced when the surgery is performed by an experienced surgeon; as such guidelines suggest that surgery is carried out in dedicated bariatric centres.
Abstract The aim of this article is to give a brief but comprehensive overview of the current management of the patient undergoing bariatric (weight loss) surgery. This article will discuss the different types of obesity surgery commonly performed, and the practical aspects of how to manage these patients both perioperatively and postoperatively. The principles described can be utilized in the management of obese patients attending for other types of surgery.
Keywords Anaesthesia; bariatric; intraoperative management; obesity; postoperative care; preoperative assessment; surgery
Infrastructure Background
In 2007 the Association of Anaesthetists of Great Britain and Ireland (AAGBI) set out guidelines for the perioperative management of the morbidly obese patient. The AAGBI suggested that departments should initially provide a consultant lead for obesity anaesthesia to work closely with theatre staff in developing theatre set-up and provision of specialist equipment for obese patients. Bariatric patients benefit from a dedicated surgical pathway with a multidisciplinary team approach that incorporates appropriate obesity patient assessment, anaesthesia, surgical management and postoperative care.
In 2002 the National Institute for Clinical Excellence (NICE) issued recommendations to the NHS on the use of gastric surgery for the treatment of morbid obesity. It recommended that surgery to aid weight loss should be available as a treatment option for people with morbid obesity, which was defined as people with a body mass index (BMI) of 40 kg/m2 or more or a BMI of between 35 kg/m2 and 40 kg/m2 with significant co-morbidity.
Types of obesity surgery Weight loss surgery is now commonly performed laparoscopically and can be considered in two groups: Restrictive surgery limits the size of the stomach so the person feels full after eating a small amount of food. The most commonly performed are adjustable gastric banding (AGB) and sleeve gastrectomy. Restrictive plus malabsorptive surgery also involves shortening the digestive tract, thus creating malabsorption. The length of small bowel bypassed determines potential weight loss. The classical Roux-en-Y gastric bypass (RYGB) works mainly by restriction with a modest element of malabsorption and is considered the ‘gold standard’, whilst the duodenal switch and the biliopancreatic diversion involve an extensive bypass that
The conduct of bariatric anaesthesia Preoperative assessment The preoperative assessment is a vital part of the anaesthetic in obese patients. They can often be difficult to assess with reduced or poor mobility and commonly describe rapid onset exercise induced dyspnoea through the movement of their own body weight. The challenge is to correctly identify those patients at increased risk of perioperative morbidity and to carry out appropriate investigations to stratify this risk and allocate resources appropriately. The preoperative assessment should combine all the usual history, examination and investigations in light of the nature of proposed surgery, and to look at specific areas in more detail as described below.
Claire E Moore MBChB FRCA is a Specialist Registrar in the North Western Deanery, UK. Conflicts of interest: none declared.
Respiratory assessment Screening of all obese patients for obstructive sleep apnoea (OSA) with polysomnography is ideal, but may not be feasible. Instead questionnaires (Epworth/STOP-Bang/American Society of Anesthesiologists (ASA)/Berlin) with OSA scoring systems are used to identify patients with potentially significant OSA (Table 1). These patients then go on to have formal testing either with overnight oximetry or full polysomnography to determine
Mark Forrest MBChB FRCA is a Consultant in Anaesthesia at Central Manchester Foundation Trust, UK. Conflicts of interest: none declared. Basil Ammori MB ChB FRCS MD is a Consultant Lead Bariatric Surgeon at Salford Royal Hospital, UK and Honorary Senior Lecturer at the University of Manchester, UK. Conflict of interest: none declared.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 12:7
280
Ó 2011 Published by Elsevier Ltd.
ENDOCRINOLOGY
obese patients to help minimize their increased risk of DVT, pressure areas and respiratory morbidity.
STOP-Bang risk score for OSA
Monitoring
Snoring BMI >28 Tiredness during daytime Age >50 Observed apnoea Neck circumference >16 inches women >17 inches men Pressure (High BP) Gender e male
AAGBI monitoring standards should be adhered to in all cases. The conical nature of the upper forearm in obese patients makes measurement using automated devices unreliable, particularly in women. Use of the forearm for blood pressure (BP) measurement has gained widespread acceptance in bariatric anaesthesia practice and appears to be reliable. Arterial lines and central venous cannulation are rarely necessary. Venous access can be difficult, particularly in women, because their fat distribution is peripheral, and the anterior aspect of the forearm is often a useful site.
BMI, body mass index; BP, blood pressure; OSA, obstructive sleep apnoea.
Table 1
the need for continuous positive airway pressure (CPAP) or noninvasive positive pressure ventilation (NIPPV) postoperatively. These two scores indicate risk, such that if you answer yes for two or more STOP questions you are at risk of OSA. The more positive answers to the Bang questions the more likely it is that moderate to severe OSA is present, and formal referral for polysomnography preoperatively should be made.
Induction and maintenance of anaesthesia Consideration should be given to anesthetizing patients, especially the super-obese, in theatre, on the operating table that should be electrically powered. Weight limits should be confirmed before commencing the case. The patient positions themselves on the theatre table, and this helps minimize risk to both the patient and theatre staff during transfer. Care must be taken with intraoperative body positioning and relief of pressure areas as obese patients are particularly prone to pressure-related complications such as pressure sores, compartment syndrome and nerve palsy through the pressure of their own weight. Once asleep, the patient is placed in lithotomy with specialized boots and support under the buttocks (Figure 1). The pharmacodynamic and pharmacokinetic principles in the morbidly obese that should be considered have been outlined in the previous article. It is the authors’ practice to induce with propofol and maintain anaesthesia with desflurane. Muscle relaxation is achieved using rocuronium. Intra-operative opioids are used as deemed appropriate and supplemented with paracetamol and nonsteroidal anti-inflammatory drugs (NSAIDs). Acid reflux is common and prophylaxis should be given preoperatively.
Cardiovascular assessment Scoring patients using cardiac risk tools such as the Lees Cardiac risk index (LCRI) and obesity risk, through the Proposed Obesity Surgery Mortality Risk Score (OBSMRS) will highlight those requiring more specialist assessment and investigation. The OBSMRS comprises: BMI >50 kg/m2 male hypertension PE as co-morbidity age >45 years. Patients with history of ischaemic heart disease will undergo objective assessment of their coronary perfusion (stress perfusion scan or coronary angiography) and coronary intervention (stents or bypass) if there is significant reversible ischaemia, as well as an assessment of their cardiac function with echocardiogram. Transoesophageal echocardiography is often superior to transthoracic in this population. Functional assessment can be made using cardiopulmonary exercise testing. This provides a composite of cardiac and respiratory function, with peak VO2 <15.8 ml/kg predicting the majority of at-risk obese patients. It has been shown that exercise performance in the severely obese is inversely proportional to BMI. For those unable to exercise either through their weight or through orthopaedic issues, pharmacological stress testing may be necessary.
Airway Difficulties with obese airways in anaesthesia are well recognized, although the reported incidence of difficult intubation has
Thromboprophylaxis Obesity is an independent risk factor for perioperative deep vein thrombosis (DVT), with the incidence in bariatric surgery being reported as high as 2.5e4.5%. To help minimize risk, thromboprophylaxis measures need to be standardized and approached as part of the obese patient surgical pathway. DVT formation can begin intraoperatively and low-molecularweight heparin (LMWH) should be given perioperatively. This should be combined with good hydration with goal directed therapy where appropriate and the use of mechanical calf compression devices. Some advocate the continuation of mechanical compression devices postoperatively until the patient mobilizes. Early postoperative mobilization is paramount for
ANAESTHESIA AND INTENSIVE CARE MEDICINE 12:7
Figure 1 Patient positioned for laparoscopic bariatric surgery.
281
Ó 2011 Published by Elsevier Ltd.
ENDOCRINOLOGY
been lowered. The authors’ experience is that difficult intubation mirrors the general population, with around 10% generally found to be difficult to hand-ventilate. This is related to increased facial and neck soft tissue. Male sex, large neck circumference, presence of obesity hypoventilation syndrome or OSA, and a high airway Mallampati score are all considered risk factors for difficult airway management. Induction of anaesthesia should be performed, following thorough pre-oxygenation, with the patient in a 30 head-up position, with the addition of ramping (see Figure 2). Ramping either with pillows, blankets or a specifically-designed device elevates the head, shoulders and upper body. In doing so, it optimises visualization of the laryngeal inlet and has been shown to reduce the incidence of failed intubation in morbidly obese patients. Indications for fibreoptic intubation are similar to the general population (previous history of difficult intubation and a high Mallampati score), and it is not routinely necessary in obese patients. Extubation can either be performed on the theatre table or more commonly following transfer of the patient back to their bed. The patient should be sat up and extubated fully awake.
control ventilation appears to offer some advantage over volume control for obese patients, with better recruitment. Preoperative application of CPAP, maintenance of intraoperative PEEP (up to 10 cm H2O) and reverse trendelenberg positioning help reduce atelectasis. Post-operatively this can be combined with incentive spirometry to improve lung re-expansion and pulmonary function.
Cardiovascular care Despite significant cardiovascular pathology in the morbidly obese, cardiovascular complications are uncommon during obesity surgery. However, the combination of pneumoperitoneum and reverse Trendelenberg can cause significant hypotension, notably in the super-obese. This hypotension is readily treatable with fluids and small doses of vasopressors. Care should be taken to keep intra-abdominal insufflation pressures at recommended levels to minimize respiratory and cardiovascular complications along with potential pre-renal failure.
Postoperative care Laparoscopic bariatric surgery is not associated with severe post-operative pain. Most patients can be managed with patientcontrolled analgesia morphine supplemented with regular paracetamol and NSAIDs. Many patients actually use the PCA very little once any pain has been controlled in the recovery period. Significant abdominal pain after the first night should be investigated and surgical causes excluded. There is no recognized consensus for where obese patients should be managed postoperatively. Alongside the risk from cardiac and thromboembolic events, the primary concern is the perceived danger from OSA, combined with the effects of anaesthesia and the need for ongoing opiate analgesia. Significant post-operative complications are rare but hypoventilation, bleeding and oliguria can be seen early with pneumonia, wound infection and anastomotic breakdown occurring later in the postoperative course. Appropriate preoperative assessment will identify the highest risk patients with indicators including male gender, age >50 years, BMI >60 (55 for men) kg/m2, diagnosis of OSA, significant medical co-morbidities and revision surgery. These patients may benefit from level II care. Reassuringly, the majority of patients undergoing bariatric surgery do not require critical care postoperatively and are able to be managed safely in ward areas, with appropriate monitoring and a quick referral pathway (EWS) if the patient shows any signs of complications. A
Ventilation For all laparoscopic bariatric surgical procedures obese patients should be intubated and ventilated. The authors’ preference is to use pressure control ventilation with pressure limitation and moderate to high positive end-expiratory pressure (PEEP). Pressure
FURTHER READING Adams JP, Murphy PG. Obesity in anaesthesia and intensive care. Br J Anaesth 2000; 85: 91e108. Cadi P, Guenoun T, Journois D, Chevallier J-M, Diehl J, Safran D. Pressure controlled-ventilation improves oxygenation during laparoscopic obesity surgery compared with volume-controlled ventilation. Br J Anaesth 2008; 100: 709e16. Obesity: the prevention, identification, assessment and management of overweight and obesity in adults and children. NICE Guidelines, July 2002. Ogunnaike B, Jones S, Jones B, Provost D, Whitten C. Anaesthetic considerations for bariatric surgery. Anesth Analg 2002; 95: 1793e805.
Figure 2 Picture demonstrates the ear to sternal notch position (ramping). (Kindly reproduced with permission from Dr Richard Levitan, Airway Cam Technologies, Inc. www.airwaycam.com. Originally published in The Airway Cam Guide to Intubation and Practical Emergency Airway Management, Airway Cam Technologies, Inc. Wayne PA, 2004.).
ANAESTHESIA AND INTENSIVE CARE MEDICINE 12:7
282
Ó 2011 Published by Elsevier Ltd.
Anaesthesia for obesity surgery
Learning objectives After reading this article you should be able to: C list four different types of obesity surgery C carry out a preoperative screening assessment for obstructive sleep apnoea (OSA) C identify and list six risk factors to determine which patients may require level II care postoperatively
Claire E Moore Mark Forrest Basil Ammori
induces much greater malabsorption coupled with a much larger gastric pouch and therefore lesser restriction. Contemporary bariatric surgery is reasonably safe with mortality in the region of 0.1e0.5%. The highest risk comes in older superobese males. The risks are less following an AGB than from an RYGB; however the latter offers superior long-term weight loss. The risk of complications from the procedure itself appears to be reduced when the surgery is performed by an experienced surgeon; as such guidelines suggest that surgery is carried out in dedicated bariatric centres.
Abstract The aim of this article is to give a brief but comprehensive overview of the current management of the patient undergoing bariatric (weight loss) surgery. This article will discuss the different types of obesity surgery commonly performed, and the practical aspects of how to manage these patients both perioperatively and postoperatively. The principles described can be utilized in the management of obese patients attending for other types of surgery.
Keywords Anaesthesia; bariatric; intraoperative management; obesity; postoperative care; preoperative assessment; surgery
Infrastructure Background
In 2007 the Association of Anaesthetists of Great Britain and Ireland (AAGBI) set out guidelines for the perioperative management of the morbidly obese patient. The AAGBI suggested that departments should initially provide a consultant lead for obesity anaesthesia to work closely with theatre staff in developing theatre set-up and provision of specialist equipment for obese patients. Bariatric patients benefit from a dedicated surgical pathway with a multidisciplinary team approach that incorporates appropriate obesity patient assessment, anaesthesia, surgical management and postoperative care.
In 2002 the National Institute for Clinical Excellence (NICE) issued recommendations to the NHS on the use of gastric surgery for the treatment of morbid obesity. It recommended that surgery to aid weight loss should be available as a treatment option for people with morbid obesity, which was defined as people with a body mass index (BMI) of 40 kg/m2 or more or a BMI of between 35 kg/m2 and 40 kg/m2 with significant co-morbidity.
Types of obesity surgery Weight loss surgery is now commonly performed laparoscopically and can be considered in two groups: Restrictive surgery limits the size of the stomach so the person feels full after eating a small amount of food. The most commonly performed are adjustable gastric banding (AGB) and sleeve gastrectomy. Restrictive plus malabsorptive surgery also involves shortening the digestive tract, thus creating malabsorption. The length of small bowel bypassed determines potential weight loss. The classical Roux-en-Y gastric bypass (RYGB) works mainly by restriction with a modest element of malabsorption and is considered the ‘gold standard’, whilst the duodenal switch and the biliopancreatic diversion involve an extensive bypass that
The conduct of bariatric anaesthesia Preoperative assessment The preoperative assessment is a vital part of the anaesthetic in obese patients. They can often be difficult to assess with reduced or poor mobility and commonly describe rapid onset exercise induced dyspnoea through the movement of their own body weight. The challenge is to correctly identify those patients at increased risk of perioperative morbidity and to carry out appropriate investigations to stratify this risk and allocate resources appropriately. The preoperative assessment should combine all the usual history, examination and investigations in light of the nature of proposed surgery, and to look at specific areas in more detail as described below.
Claire E Moore MBChB FRCA is a Specialist Registrar in the North Western Deanery, UK. Conflicts of interest: none declared.
Respiratory assessment Screening of all obese patients for obstructive sleep apnoea (OSA) with polysomnography is ideal, but may not be feasible. Instead questionnaires (Epworth/STOP-Bang/American Society of Anesthesiologists (ASA)/Berlin) with OSA scoring systems are used to identify patients with potentially significant OSA (Table 1). These patients then go on to have formal testing either with overnight oximetry or full polysomnography to determine
Mark Forrest MBChB FRCA is a Consultant in Anaesthesia at Central Manchester Foundation Trust, UK. Conflicts of interest: none declared. Basil Ammori MB ChB FRCS MD is a Consultant Lead Bariatric Surgeon at Salford Royal Hospital, UK and Honorary Senior Lecturer at the University of Manchester, UK. Conflict of interest: none declared.
ANAESTHESIA AND INTENSIVE CARE MEDICINE 12:7
280
Ó 2011 Published by Elsevier Ltd.
ENDOCRINOLOGY
obese patients to help minimize their increased risk of DVT, pressure areas and respiratory morbidity.
STOP-Bang risk score for OSA
Monitoring
Snoring BMI >28 Tiredness during daytime Age >50 Observed apnoea Neck circumference >16 inches women >17 inches men Pressure (High BP) Gender e male
AAGBI monitoring standards should be adhered to in all cases. The conical nature of the upper forearm in obese patients makes measurement using automated devices unreliable, particularly in women. Use of the forearm for blood pressure (BP) measurement has gained widespread acceptance in bariatric anaesthesia practice and appears to be reliable. Arterial lines and central venous cannulation are rarely necessary. Venous access can be difficult, particularly in women, because their fat distribution is peripheral, and the anterior aspect of the forearm is often a useful site.
BMI, body mass index; BP, blood pressure; OSA, obstructive sleep apnoea.
Table 1
the need for continuous positive airway pressure (CPAP) or noninvasive positive pressure ventilation (NIPPV) postoperatively. These two scores indicate risk, such that if you answer yes for two or more STOP questions you are at risk of OSA. The more positive answers to the Bang questions the more likely it is that moderate to severe OSA is present, and formal referral for polysomnography preoperatively should be made.
Induction and maintenance of anaesthesia Consideration should be given to anesthetizing patients, especially the super-obese, in theatre, on the operating table that should be electrically powered. Weight limits should be confirmed before commencing the case. The patient positions themselves on the theatre table, and this helps minimize risk to both the patient and theatre staff during transfer. Care must be taken with intraoperative body positioning and relief of pressure areas as obese patients are particularly prone to pressure-related complications such as pressure sores, compartment syndrome and nerve palsy through the pressure of their own weight. Once asleep, the patient is placed in lithotomy with specialized boots and support under the buttocks (Figure 1). The pharmacodynamic and pharmacokinetic principles in the morbidly obese that should be considered have been outlined in the previous article. It is the authors’ practice to induce with propofol and maintain anaesthesia with desflurane. Muscle relaxation is achieved using rocuronium. Intra-operative opioids are used as deemed appropriate and supplemented with paracetamol and nonsteroidal anti-inflammatory drugs (NSAIDs). Acid reflux is common and prophylaxis should be given preoperatively.
Cardiovascular assessment Scoring patients using cardiac risk tools such as the Lees Cardiac risk index (LCRI) and obesity risk, through the Proposed Obesity Surgery Mortality Risk Score (OBSMRS) will highlight those requiring more specialist assessment and investigation. The OBSMRS comprises: BMI >50 kg/m2 male hypertension PE as co-morbidity age >45 years. Patients with history of ischaemic heart disease will undergo objective assessment of their coronary perfusion (stress perfusion scan or coronary angiography) and coronary intervention (stents or bypass) if there is significant reversible ischaemia, as well as an assessment of their cardiac function with echocardiogram. Transoesophageal echocardiography is often superior to transthoracic in this population. Functional assessment can be made using cardiopulmonary exercise testing. This provides a composite of cardiac and respiratory function, with peak VO2 <15.8 ml/kg predicting the majority of at-risk obese patients. It has been shown that exercise performance in the severely obese is inversely proportional to BMI. For those unable to exercise either through their weight or through orthopaedic issues, pharmacological stress testing may be necessary.
Airway Difficulties with obese airways in anaesthesia are well recognized, although the reported incidence of difficult intubation has
Thromboprophylaxis Obesity is an independent risk factor for perioperative deep vein thrombosis (DVT), with the incidence in bariatric surgery being reported as high as 2.5e4.5%. To help minimize risk, thromboprophylaxis measures need to be standardized and approached as part of the obese patient surgical pathway. DVT formation can begin intraoperatively and low-molecularweight heparin (LMWH) should be given perioperatively. This should be combined with good hydration with goal directed therapy where appropriate and the use of mechanical calf compression devices. Some advocate the continuation of mechanical compression devices postoperatively until the patient mobilizes. Early postoperative mobilization is paramount for
ANAESTHESIA AND INTENSIVE CARE MEDICINE 12:7
Figure 1 Patient positioned for laparoscopic bariatric surgery.
281
Ó 2011 Published by Elsevier Ltd.
ENDOCRINOLOGY
been lowered. The authors’ experience is that difficult intubation mirrors the general population, with around 10% generally found to be difficult to hand-ventilate. This is related to increased facial and neck soft tissue. Male sex, large neck circumference, presence of obesity hypoventilation syndrome or OSA, and a high airway Mallampati score are all considered risk factors for difficult airway management. Induction of anaesthesia should be performed, following thorough pre-oxygenation, with the patient in a 30 head-up position, with the addition of ramping (see Figure 2). Ramping either with pillows, blankets or a specifically-designed device elevates the head, shoulders and upper body. In doing so, it optimises visualization of the laryngeal inlet and has been shown to reduce the incidence of failed intubation in morbidly obese patients. Indications for fibreoptic intubation are similar to the general population (previous history of difficult intubation and a high Mallampati score), and it is not routinely necessary in obese patients. Extubation can either be performed on the theatre table or more commonly following transfer of the patient back to their bed. The patient should be sat up and extubated fully awake.
control ventilation appears to offer some advantage over volume control for obese patients, with better recruitment. Preoperative application of CPAP, maintenance of intraoperative PEEP (up to 10 cm H2O) and reverse trendelenberg positioning help reduce atelectasis. Post-operatively this can be combined with incentive spirometry to improve lung re-expansion and pulmonary function.
Cardiovascular care Despite significant cardiovascular pathology in the morbidly obese, cardiovascular complications are uncommon during obesity surgery. However, the combination of pneumoperitoneum and reverse Trendelenberg can cause significant hypotension, notably in the super-obese. This hypotension is readily treatable with fluids and small doses of vasopressors. Care should be taken to keep intra-abdominal insufflation pressures at recommended levels to minimize respiratory and cardiovascular complications along with potential pre-renal failure.
Postoperative care Laparoscopic bariatric surgery is not associated with severe post-operative pain. Most patients can be managed with patientcontrolled analgesia morphine supplemented with regular paracetamol and NSAIDs. Many patients actually use the PCA very little once any pain has been controlled in the recovery period. Significant abdominal pain after the first night should be investigated and surgical causes excluded. There is no recognized consensus for where obese patients should be managed postoperatively. Alongside the risk from cardiac and thromboembolic events, the primary concern is the perceived danger from OSA, combined with the effects of anaesthesia and the need for ongoing opiate analgesia. Significant post-operative complications are rare but hypoventilation, bleeding and oliguria can be seen early with pneumonia, wound infection and anastomotic breakdown occurring later in the postoperative course. Appropriate preoperative assessment will identify the highest risk patients with indicators including male gender, age >50 years, BMI >60 (55 for men) kg/m2, diagnosis of OSA, significant medical co-morbidities and revision surgery. These patients may benefit from level II care. Reassuringly, the majority of patients undergoing bariatric surgery do not require critical care postoperatively and are able to be managed safely in ward areas, with appropriate monitoring and a quick referral pathway (EWS) if the patient shows any signs of complications. A
Ventilation For all laparoscopic bariatric surgical procedures obese patients should be intubated and ventilated. The authors’ preference is to use pressure control ventilation with pressure limitation and moderate to high positive end-expiratory pressure (PEEP). Pressure
FURTHER READING Adams JP, Murphy PG. Obesity in anaesthesia and intensive care. Br J Anaesth 2000; 85: 91e108. Cadi P, Guenoun T, Journois D, Chevallier J-M, Diehl J, Safran D. Pressure controlled-ventilation improves oxygenation during laparoscopic obesity surgery compared with volume-controlled ventilation. Br J Anaesth 2008; 100: 709e16. Obesity: the prevention, identification, assessment and management of overweight and obesity in adults and children. NICE Guidelines, July 2002. Ogunnaike B, Jones S, Jones B, Provost D, Whitten C. Anaesthetic considerations for bariatric surgery. Anesth Analg 2002; 95: 1793e805.
Figure 2 Picture demonstrates the ear to sternal notch position (ramping). (Kindly reproduced with permission from Dr Richard Levitan, Airway Cam Technologies, Inc. www.airwaycam.com. Originally published in The Airway Cam Guide to Intubation and Practical Emergency Airway Management, Airway Cam Technologies, Inc. Wayne PA, 2004.).
ANAESTHESIA AND INTENSIVE CARE MEDICINE 12:7
282
Ó 2011 Published by Elsevier Ltd.