Preoperative Risk Reduction

by Adrienne Youdim, MD

Dr. Youdim is Medical Director, Comprehensive Weight Loss Center, Cedars Sinai Medical Center, Los Angeles, California, and Assistant Clinical Professor of Medicine, David Geffen School of Medicine, University of California Los Angeles, California.

Bariatric Times. 2011;8(1):8–9

Acknowledgment
This article is part of a series of articles being published in Bariatric Times that are based on sessions presented at the “Comprehensive Approach to the Treatment of Obesity,” by Cedars Sinai Medical Center on October 22, 2010.

Abstract
Bariatric surgery remains safe and effective for the treatment of obesity. While overall complication rates are low, patient-inherent factors have been identified that portend higher morbidity and mortality with bariatric surgery. Routine preoperative weight loss may not be indicated in all weight loss surgery patients given low overall complication rates, but may be of benefit in the higher risk patient population.

Introduction

Obesity remains a growing and ongoing problem in the United States. While recent reports have shown obesity rates have stabilized, severe classes of obesity are on the rise,[1] having important implications in regard to treatment. Weight loss surgery remains a durable treatment for obesity, effectively resulting in remission of many obesity-related conditions.[2] In addition, recent reports have demonstrated a mortality benefit in patients who have had bariatric surgery.[3] As a result, weight loss surgeries are on the rise. Studies have shown a five-fold increase in the number of bariatric surgeries between 1998 and 2003.[4] The number of weight loss surgeries performed in the United States has increased in all groups despite age, income, or insurance status or type. However, this elective surgery is not without complications. Surgeon experience appears to be a significant predictor of postoperative morbidity and mortality,[5] however, patient-inherent risks have also been identified. While studies have been conflicting, age, smoking history, superobesity, and certain comorbidities are factors implicated in increasing morbidity and mortality with bariatric surgery.[6–8] One validated risk score identified five perioperative variables that predicted 30-day mortality. These variables include superobesity, male gender, hypertension, age greater than 45, and risk factors for pulmonary embolism, including obstructive sleep apnea. Patients who had 4 to 5 of the above risk factors had a 12-fold greater (2.4%) 30-day mortality than patients who had none to one risk factor (0.2%).[8] Certain high-risk patient groups may benefit from optimizing their medical status prior to weight loss surgery through medical nutritional therapy and preoperative weight loss.

Diabetes
The relationship between type 2 diabetes and obesity is well documented as the incidence of diabetes increases incrementally with rising body mass index (BMI).[9,10] Recent guidelines recommend long-term glycemic control with HbA1c of 7.2 percent or less prior to bariatric surgery.[11] While pharmacotherapy is appropriate, medical nutritional therapy remains the mainstay of treatment. Studies have shown weight loss of as little as 5 to 10 percent results in effective reduction of fasting blood glucose and HbA1c. In one study,[12] weight loss of up to 14 percent resulted in a two-point reduction in HbA1c, comparable to targets achieved by pharmacotherapy.[12] Given the favorable effect of modest weight loss on glycemic control, preoperative weight loss should be used to achieve glycemic targets in bariatric surgery patients.

Hypertension
Obesity is associated with other cardiometabolic conditions, including hypertension. Mechanisms of this association are multifactorial and include secretion by adipocytes of many proteins of the renin-angiotensin system, the pathway that mediates hypertension through sodium and water reabsorption and increased vascular tone.[13] The presence of hypertension is a significant risk factor for perioperative complications.[14] Validated risk scores have demonstrated hypertension to be associated with higher 30-day mortality following bariatric surgery,[8] and guidelines recommend optimal hypertensive control prior to bariatric surgery.[11] Modest weight loss has been shown to reduce both systolic and diastolic blood pressure. Prior studies have shown reductions in blood pressure of 1mmHg per kilogram weight loss.[15] A more recent systemic review[16] suggests that for 10kg weight loss there is a 4.6mmHg and 6.0mmHg reduction in diastolic and systolic blood pressure, respectively.[16] Moreover, change in macronutrient intake to reduce sodium and increase fruits, vegetables, and limit saturated fats can itself result in reductions in blood pressure independent of weight loss.[17] While pharmacotherapy is often necessary to control hypertension, medical nutritional therapy and preoperative weight loss is a useful adjunct to optimize hypertensive control in patients with morbid obesity.

Obstructive Sleep Apnea
Concomitant obstructive sleep apnea (OSA) is frequently present in the patient population with morbid obesity. Obesity is a leading cause of OSA, and a 10-percent increase in BMI results in a 32-percent increase in apnea-hypopnea index (AHI). A diagnosis of OSA is an independent risk factor for 30-day morbidity and mortality following bariatric surgery.[18,19] Surgical patients with OSA are vulnerable to the effects of sedation, anesthesia, and analgesia. Patients with OSA have been shown to have a higher number of postoperative complications, including but not limited to respiratory complications, and patients with more severe OSA (higher AHI or more significant oxygen desaturations) can be at greater risk for these complications.20 Modest weight loss can result in significant improvements in OSA. In one study,21 an average weight loss of 13.5 percent at 6 and 12 months resulted in reduction of the oxygen desaturation index (desaturation events per hour of sleep exceeding 4% from baseline) by 28 and 26 points, respectively. Modest weight reduction will improve OSA and may optimize patient-inherent risk related to OSA prior to bariatric surgery.

Superobesity
Superobesity, as defined by a BMI of 50kg/m2 or greater, has consistently been implicated in increasing surgical risk with bariatric surgery.[6–8,18,22] In one study,[22] BMI ≥50kg/m2 was independently associated with higher 30-day mortality with an odds ratio of 3.6. Additionally, preoperative weight loss of 5 to 10 percent has been associated with more rapid postoperative weight loss and greater one-year excess weight loss (EWL).[23–24] This may be particularly relevant to a patient with super obesity who requires a greater overall weight loss to achieve normal BMI.

Preoperative Weight Loss
Studies have specifically evaluated the effect of preoperative weight loss prior to bariatric surgery. Studies[25,26] have shown preoperative weight loss resulted in reduced liver size and visceral fat. In one study,[25] 4.1-percent weight loss resulted in 5.1-percent mean reduction in liver size and fat. In another study,26 patients who participated in a 12-week very low energy diet (VLED) lost an average of 11 percent (80% of which occurred in the first two weeks of the dietary intervention) and achieved 28.7- and 24.1-percent reduction in liver size and visceral adipose tissue, respectively. Smaller liver size and reduced visceral adiposity may improve technical feasibility of the surgery. In a study by Liu et al,[27] preoperative weight loss resulted in a reduced likelihood to encounter an enlarged liver and reduced likelihood of deviating from standard operative procedure. Specifically, average weight loss of 3.3kg resulted in a 17-percent reduction in the number of cases that deviated from standard operation, including use of additional trocars and conversion to an open procedure during laparoscopic Roux-en-Y gastric bypass (RYGB) surgery.[27]

Preoperative weight loss has also been associated with reduced probability of surgical complications after gastric bypass surgery, particularly in open gastric bypass. In one study,[28] EWL of up to 10 percent resulted in reduced major and minor complications. Statistically significant trends revealed reduced likelihood of any complication with increasing preoperative weight loss for the entire cohort of 881 patients (p=0.004) and for those who underwent open gastric bypass (p=0.02). This relationship was preserved after adjusting for age, BMI, number of comorbidities, and type of surgery. In addition, the degree of weight loss was significant in the reduction of complications. When compared to those who lost 10 percent or more excess body weight (EBW), those who gained five percent or more EBW had a two-fold increased likelihood of a complication.[28] Patients who underwent preoperative weight loss have also shown reduced intraoperative blood loss, shorter operative times,[27,29] and reduced length of hospital stay,[23] which may have important implications in resource utilization and reducing cost of surgery.

Conclusions
Bariatric surgery remains safe and effective for the treatment of obesity with recent studies placing 30-day mortality at 0.03 percent.[18] Determining patient-inherent risk factors allows clinicians to appropriately advise patients of individual surgical risk and to optimize that risk when possible prior to surgery. Several studies have identified patient-inherent variables that portend higher morbidity and mortality with bariatric surgery. Superobesity and certain comorbidities, including diabetes, OSA, and hypertension, are factors implicated in increasing surgical risk. Routine preoperative weight loss may not be indicated in all weight loss surgery patients given low overall complication rates, but may be of benefit in the higher-risk patient population.

References
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Tags: bariatric, complications, preoperative weight loss

Category: Past Articles, Review