Brian P McGlinch
Department of Anesthesiology
Mayo Clinic College of Medicine
Humans are genetically predisposed to store fat. Although this survival mechanism served our ancestors well, in our current era the improved access to high-calorie food and the more sedentary lifestyles we have compared with our ancestors has led to an obesity pandemic. The causes of obesity in any culture are multiple, interacting and complex. Weight loss through diet, exercise and/or medication is often short-lived or inadequate. Increasingly, weight loss surgery (WLS) is being performed to reduce excess body weight and improve obesity-related co-morbidities in both adults and adolescents after other attempts at weight loss have failed.
The World Health Organization defines “overweight” as a body mass index of 25–30 kg/sqm and obesity as a BMI 30 kg/sqm or greater (BMI is calculated as weight in kilograms divided by the square of height in metres). “Extreme” or “medically complicated” obesity is considered present when BMI is >40 kg/sqm, representing 35 kg and 45 kg of excess weight for women and men, respectively. In many patients with BMI >35 kg/sqm, obesity-related co-morbidities contribute to the doubling of mortality risk when compared with the non-obese.(1) As a result, patients with BMI >35 kg/sqm with obesity-related comorbidities and those with BMI >40 kg/sqm are considered candidates for WLS.
Weight loss surgery
Surgical procedures leading to weight loss impose a restrictive physiology with or without a maldigestive component. Restrictive procedures (eg, gastric banding, gastric balloons) reduce gastric volume, leading to early satiety and reduced caloric intake. Maldigestive procedures (eg, Roux-en-Y gastric bypass [RYGB], duodenal switch and the very, very long-limb RYGB) are usually combined with a restrictive physiology and further alter calorie absorption through bypassing the duodenum. The restrictive component in conjunction with the bypassed duodenum induces neurohormonal changes resulting in perceptions of early satiety and reduced appetite. Procedures combining both restrictive and maldigestive physiologies demonstrate more significant and sustained weight loss as well as resolution/improvement of most weight-related co-morbidities.(2,3) In patients with BMI >50 kg/sqm, a maldigestive procedure is modified to a malabsorptive procedure by increasing the length of the Roux limb, resulting in greater and sustained weight loss. Malabsorptive procedures increase weight loss but may result in protein malnutrition, bone mineral disease, oxalate nephropathy and diarrhoea.(4) However, the benefit of massive weight loss often outweighs the risk for malnutrition in this bariatric subset.
WLS should only be performed in high-volume centres with surgeons experienced in bariatric procedures using laparoscopic approaches whenever possible. Surgeons who have performed more than 100 laparoscopic bariatric procedures have the lowest major complication rates.(5–7) Hospitals with high-volume WLS experience (>75 WLS procedures per year) have overall mortality rates of <0.5%.(5,8) Patients over 55 years of age undergoing bariatric surgery (the highest-risk patient population) in high-volume WLS centres had significantly less mortality than lower-volume facilities (0.9% vs 3.1%).(9)
Preoperative evaluations for bariatric surgery
Candidates for bariatric surgery normally have established relationships with primary care physicians who have evaluated underlying medical conditions and optimised medical therapies prior to surgery. Although prevalent, weight-related co-morbidities do not seem to increase major surgical risk.(10,11) The only consistent finding associated with perioperative morbidity and mortality for WLS was age – the only factor primary-care physicians cannot modify.(12–14)
Perioperative management of the WLS patient
The anaesthetic management of patients undergoing WLS is not complicated in most cases. Preoperative epidurals are useful with open procedures but unnecessary in laparoscopic approaches. Intravenous fluid administration should be conservative, given the absence of preoperative bowel preps and minimal blood loss associated with these procedures. Prolonged intubation and mechanical ventilation is rarely required when the laparoscopic approach is used. Antiemetic therapy is useful.
Bariatric surgery is an important component in treating extreme obesity but requires ongoing lifestyle changes toward healthy living and exercise. Along with routine postoperative evaluations assuring adequate weight loss, compliance with dietary restrictions and vitamin/mineral supplements, prescription medication should be reassessed.
Emerging technology may induce a restrictive weight loss physiology by simply stimulating the stomach with a pacemaker-type device. Gastroenterologists may soon be performing restrictive procedures on the stomach, requiring only sedation care. Surgeons and gastroenterologists might advance natural orifice-based procedures and make these WLS procedures even less invasive.
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