Anestesia En Cx Obeso

Endocrinology

Anaesthesia for obesity surgery

Adjustable gastric banding

Claire Dowse

Gastric pouch above band

Mark Pyke

Port placed under the skin

Abstract Surgery to aid weight loss is termed bariatric surgery and is becoming increasingly common as the prevalence of obesity rises. Bariatric surgery has been shown to have a sustained long-term therapeutic effect on obesity and is recommended by the National Institute for Health and Clinical Excellence as part of a complete weight loss programme. It is usually performed by a minimally invasive laparoscopic technique. Anaesthesia for bariatric surgery provides challenges for the anaesthetist in perioperative management owing to the surgical techniques and the comorbidities associated with obesity. Caution also needs to be taken with patients who have had bariatric surgery when they present for subsequent surgery.

Keywords

bariatric surgery; obstructive sleep apnoea

Small intestine

Saline is injected or removed through the port to vary the size of the adjustable band

Figure 1 gastric

banding;

morbid

obesity;

leading to a sensation of fullness and an inability to eat more. The band can be inflated or deflated by injecting saline into a subcutaneous port in the abdominal wall. • Malabsorptive: limits the size of the stomach and also short­ ens the length of the gut so reducing the amount of food ab­ sorbed. The gastric bypass (Roux-en-Y) is the commonest form of this. It involves stapling across the stomach to create a small neo-stomach and creating a bypass by joining it to a distal part of the intestine. Other procedures include the duodenal switch and the bilopancreatic diversion. These operations are increasingly being carried out laparoscopically.

The National Institute for Health and Clinical Excellence has ­recommended that surgery to aid weight loss should be available as a treatment option for people with morbid obesity. A person is defined as being morbidly obese if he or she has a body mass index (BMI) either equal to or greater than 40 kg/m2, or between 35 kg/m2 and 40 kg/m2 in the presence of significant comorbid conditions that may be improved by weight loss (such as dia­ betes mellitus, hypertension and osteoarthritis). Bariatric surgery should be offered only as part of a complete weight loss programme. Patients must have proven unsuccessful attempts at medically supervised weight loss before undergoing surgery. There are two main types of bariatric surgical procedure. • Restrictive: limits the size of the stomach by stapling (verti­ cally banded gastroplasty) or fitting a band around it (gastric ­banding). Laparoscopic adjustable gastric banding (Figure 1) is now the most popular restrictive operation because of its potential ­reversibility and low morbidity. The band is placed around the top part of the stomach, creating a small pouch with a ­capacity of about 25 ml. This pouch fills after a small amount of food,

Preoperative assessment of patients for bariatric surgery Multidisciplinary involvement Patients should ideally be assessed in a multidisciplinary clinic. This usually includes a consultant physician with an interest in obesity (often an endocrinologist), a dietitian, a psychologist and advice from a consultant anaesthetist with an interest in bariat­ ric anaesthesia. All patients should have their height and weight recorded and their BMI calculated.1 Airway/breathing assessment Ezri et al.2 concluded that being morbidly obese carries the risk of difficult laryngoscopy, not because of an increase in BMI per se but because of other factors associated with obesity that might have an impact on laryngoscopic difficulty such as a his­ tory of obstructive sleep apnoea and abnormal upper teeth. Bag/ mask ventilation may be more difficult between attempts at intu­ bation and time to desaturation is quicker, which all adds to the airway difficulty. Obstructive sleep apnoea is present in approximately 25% of morbidly obese males and 9% of morbidly obese females.3 All

Claire Dowse, MRCP, Bsc (Hons), FRCA, is Specialist Registrar at Bristol School of Anaesthesia. She trained in Cardiff and Southampton. Mark Pyke, MBBS, BSc, FRCA, is Consultant Anaesthetist Southmead Hospital, Bristol and Lead Anaesthetist for Bariatric Surgery at Southmead Hospital and the Avon Obesity service. He trained in Bristol, Australia and New Zealand, and his interests include preoperative assessment and regional anaesthesia.

ANAESTHESIA AND INTENSIVE CARE MEDICINE 9:7

303

© 2008 Elsevier Ltd. All rights reserved.

Endocrinology

patients are assessed preoperatively with the Epworth sleepi­ ness scale. This is a self-administered questionnaire that gives a numerical value to the subjective sleepiness of patients. If they score highly they undergo full overnight polysomnography, from which the type and severity of any apnoea may be deter­ mined. Continuous positive airway pressure (CPAP) or bi-level positive airway pressure (BiPAP) should be considered for those affected.

the quickest and shortest-acting neuromuscular blocker and can be a good choice if the airway looks difficult. Maintenance with oxygen/air and desflurane is a popular choice owing to its low fat solubility. There are proponents of total intravenous anaesthesia with propofol because of its proposed lower rate of postopera­ tive nausea and vomiting; however, dosing may be difficult and wake-up times longer. An orogastric tube needs to be passed to deflate the stomach and this may need to be pulled back during surgery. Intraoperative ventilation is not usually a problem as operations take place in a steep head-up position. It may be difficult to measure blood pressure accurately with a cuff. A standard-sized cuff placed around the forearm may work or an arterial line may be needed. Both the pneumoperitoneum needed for laparoscopy and the steep head-up table tilt decrease venous return, so blood pressure often drops significantly, requir­ ing vasopressors. Most patients are put in the most extreme head-up position that the table will allow (Figure 2). This requires careful position­ ing; if the patient slips intraoperatively, the momentum may be unstoppable. There is also an increased risk of peripheral nerve damage owing to the weight of the patient and the peripheries overhanging the operating table. To minimize the risk to patient and staff, walk patients into the operating theatre and instruct them to position themselves on the table. A hover mattress can be used to ‘float’ the patient off the table and avoid injury to staff. The patient should be extubated awake and sitting up on their electric bed.

Circulation Cardiovascular disease is more common in obese patients. Car­ diac investigations should be arranged, as indicated by symp­ toms; however, trans-thoracic echocardiography may be difficult because of excess body fat and exercise tolerance may be dif­ ficult to gauge. Patients should be medically optimized in the multi­disciplinary clinic, and medications should be continued throughout the perioperative period. Gastrointestinal system Obese patients have a high incidence of diabetes mellitus, so good glycaemic control should be maintained perioperatively to decrease the risk of infection, dehydration and other complica­ tions. An insulin sliding scale can be used preoperatively and until the patient is tolerating a liquid diet. There is a greater risk of acid reflux in the obese population. This may have been investigated with an endoscopy and the find­ ings may help the anaesthetist to decide on the risk of as­piration at induction. Antacid prophylaxis such as ranitidine and sodium citrate should be prescribed if necessary. For the week preceding their operation, some patients take a very low-fat diet such as the yoghurt diet. This decreases the size of the liver and so facilitates surgery as retraction of the liver is needed to gain surgical access to the stomach. Obese patients are at greater risk of venous and pulmonary thromboembolism and will require mechanical and pharmacolo­ gical thromboprophylaxis such as Flotron boots and ­enoxaparin.

Postoperatively If the patient uses CPAP or BiPAP it may be needed in the recov­ ery room; however, some machines and masks do not allow oxy­ gen enrichment. Good postoperative analgesia is important to speed recovery. Epidural analgesia will be difficult and fentanyl or morphine may be required. Postoperative vomiting can cause gastric damage, so prophylactic anti-emetics are used. Intravenous fluids may be needed in addition to the sliding-scale insulin and fluid require­ ments will be higher in morbidly obese patients.

Intraoperative care Tracheal intubation and positive pressure ventilation are nearly always required for bariatric surgery. Previous anaesthetic charts should be checked for evidence of airway problems. Obese patients may be more difficult to venti­ late by mask and to intubate because of increased fat in the soft tissues of the oropharynx, a large tongue and a posterior fat pad that may prevent neck extension. Sleep apnoea is common and predicts loss of airway control after induction of general anaes­ thesia and in the early postoperative phase. Until the airway is secure and mechanical ventilation insti­ tuted, the patient should be placed in the reverse Trendelenberg position. Preoxygenation is performed in a head-up position as this prolongs time to desaturation during apnoea.4,5 Intubation in the ‘ramped’ position can help.6 Intravenous access can be chal­ lenging and use of portable ultrasound can be helpful. Awake fibre-optic intubation is the safest way to secure the airway, but in practice most patients in the UK are given an intra­ venous induction with fentanyl, propofol and a neuromuscular blocker then intubated by direct laryngoscopy. Suxamethonium (succinyl choline) at 1 mg/kg (up to a maximum of 140 mg) is

ANAESTHESIA AND INTENSIVE CARE MEDICINE 9:7

Figure 2 Most patients are put in the most extreme head-up position that the table will allow.

304

© 2008 Elsevier Ltd. All rights reserved.

Endocrinology

Patients are initially not allowed any solid tablets or oral nonsteroidal anti-inflammatory drugs because of the risk of tablets getting stuck and eroding the oesophagus or stomach remnant. Postoperative analgesia should therefore be soluble (e.g. cocodamol) or given intravenously. The high risk of deep vein thrombosis and pulmonary throm­ boembolism should be reduced by early mobilization, heparin regimes and lower limb pneumatic compression devices.

London: Association of Anaesthetists of Great Britain & Ireland, 2007. 2 Ezri T, Medalion T, Weisenberg M, et al. Increased body mass per se is not an indicator of difficulty laryngoscopy. Can J Anaesth 2003; 50: 179–83. 3 Adams IP, Murphy PG. Obesity in anaesthesia and intensive care. Br J Anaesth 2000; 85: 91–108. 4 Altermatt FR, Munoz HR, Delfino AE, Cortinez LI. Pre-oxygenation in the obese patient: effects of position on tolerance to apnoea. Br J Anaesth 2005; 95: 706–9. 5 Dixon BJ, Dixon JB, Carden R, et al. Pre-oxygenation is more effective in the 25 degrees head-up position. Anaesthesiology 2005; 102: 1110–15. 6 Collins JS, Lemmens HJ, Brodsky JB, et al. Laryngoscopy and morbid obesity: a comparison of the ‘sniff’ and ‘ramped’ positions. Obes Surg 2004; 14: 1171–5. 7 Sjöström L, Lindroos AK, Peltonen M, et al. The Swedish Obese Subjects Study Group. Lifestyle, diabetes, and cardiovascular risk factors 10 years after bariatric surgery. N Engl J Med 2004; 351: 2683–93. 8 Brolin RE, Kenler HA, Gorman JH, Cody RP. Long-limb gastric bypass in the super-obese, a prospective randomized study. Ann Surg 1992; 215: 387–95. 9 Sjöström L, Narbro K, Sjöström CD, et al. The Swedish Obese Subjects Study Group. Effects of bariatric surgery on mortality in Swedish obese subjects. N Engl J Med 2007; 357: 741–52. 10 Kral JG. ABC of obesity. Management. Part III. Surgery. BMJ 2006; 333: 900–3.

Outcome Bariatric surgery for obesity has been shown to result in signifi­ cant weight loss after 2 years. This is sustained at 10 years,7 along with an improvement in obesity-related comorbidities8 and decreased overall mortality.9 Complications Operative complications occur in 10% of patients and include bleeding, thromboembolism, infection and peritonitis. Gastric banding procedures have fewer surgical complications than bypass operations. The risk of death is 1% or less.10 Longer-term complications depend on the type of surgery. Restrictive proce­ dures can cause dysphagia and oesophageal dilatation with an increased risk of vomiting. Malabsorptive procedures can lead to ongoing weight loss and vitamin deficiencies.

Patients who have undergone previous bariatric surgery Patients may be at higher risk of reflux from previous restrictive surgery. If they have a gastric band in situ and they are at risk of vomiting, the band should be deflated before anaesthesia to decrease the risk of stomach rupture and band slippage. ◆

Further reading Bouillion T, Shafer SL. Does size matter? Anaesthesiology 1998; 89: 557–60. Klasen J, Junger A, Hartmann B, et al. Increased body mass index and peri-operative risk in patients undergoing non-cardiac surgery. Obes Surg 2004; 14: 275–81.

References 1 Association of Anaesthetists of Great Britain & Ireland. Guidelines for the peri-operative management of the morbidly obese patient.

ANAESTHESIA AND INTENSIVE CARE MEDICINE 9:7

305

© 2008 Elsevier Ltd. All rights reserved.