Bariatric Surgery: Selection & Pre-Operative Work Up 2020-08-26T16:26:59-04:00

Bariatric Surgery: Selection & Pre-Operative Work Up

  • Criteria for selection of appropriate candidates for bar­iatric surgery have been established to minimize surgical complications and to maximize the benefit of these important and limited procedures.
  • The preoperative workup should evaluate a patient’s medical, nutritional, mental and functional health status.
  • Special attention should be given to the care of patients living with type 2 diabetes (T2DM) who are considering bariatric surgery to minimize complications from uncon­trolled diabetes in the perioperative period.
  • Because of the risks of postoperative complications associated with tobacco use, cessation prior to bariatric surgery is mandatory and should be maintained lifelong.
  • In patients living with severe obesity, bariatric surgery, in combination with behavioral interventions, is a more effective option for long-term weight loss and control of chronic conditions, such as T2DM, hypertension, sleep apnea and dyslipidemia, as well as other conditions associated with increased adiposity.
  • We suggest a comprehensive medical and nutritional evaluation be completed and nutrient deficiencies corrected in candidates for bariatric surgery (Level 4, Grade D).1,2
  • Preoperative smoking cessation can minimize postoperative complications (Level 2a, Grade B).3
  • We suggest screening for and treatment of obstructive sleep apnea in people seeking bariatric surgery (Level 4, Grade D).4,5
  • Bariatric surgery is the beginning of a life-long journey. You should educate yourself about the necessary changes required to optimize your long-term outcomes for a healthier life.
  • Before surgery you will be asked to perform several investi­gations such as blood work, cardiac or pulmonary testing, to ensure that you are ready and safe for surgery.
  • If you are at high risk for obstructive sleep apnea, you may be asked to undergo a sleep study to determine if you have significant sleep apnea.
  • A current or recent history of smoking or nicotine con­sumption puts you at risk of complications after bariatric surgery. Smoking is cessation is required before surgery, and must be maintained for life.
  • You may be given a low-calorie diet two to three weeks before surgery in order to shrink your liver size and make your surgery easier.
  • If you are living with diabetes, you will have to follow your blood sugars very closely and obtain instructions on how to adjust your diabetes medications while on the low-calorie diet prior to bariatric surgery.
  • Because changes in the absorption of some medications may occur with certain bariatric surgical procedures, you may be asked to change either the type or preparation of the medication you are currently taking.

Selection of appropriate patients for bariatric surgery

Extensive preparation of patients prior to bariatric surgery is re­quired. Potential candidates for bariatric surgery undergo multi­disciplinary evaluation and optimization of their medical, mental, nutritional and functional health to assess their eligibility and safety to proceed with surgery. Further medical evaluations may include cardiac, respiratory, metabolic, gastrointestinal and sleep apnea testing. Once adequate evaluation and preparation have been undertaken, the patient may proceed for bariatric surgery if stable. It is recommended that patients engage in behavioral interventions prior to bariatric surgery and maintain those behav­ioral changes after bariatric surgery, as well.

Bariatric surgery is indicated in patients greater than 18 years of age with a body mass index (BMI) of 35 kg/m², who have at least one major obesity-related complication including type 2 diabetes (T2DM), hypertension, hyperlipidemia, pseudotumor cerebri, obesi­ty hypoventilation syndrome or Pickwickian syndrome, debilitating arthritis, nonalcoholic fatty liver disease or nonalcoholic steatohep­atitis, coronary artery disease, severe reflux or obstructive sleep ap­nea.1 Bariatric surgery is also indicated for patients with a BMI of 40 kg/m² independent of the presence of obesity related compli­cations.6 Bariatric surgery may also provide therapeutic benefit in patients with a BMI between 30 and 34.9 kg/m² who have been refractory to nonsurgical attempts at weight loss with obesity-re­lated complications, especially T2DMs. The indications for surgery in these patients may be predicated heavily on the obesity-related complications that are present and weighing the durable response to bariatric surgery compared with existing medical interventions.7,8

Adolescent candidates who have a BMI greater than or equal to 35 kg/m² may be considered for a bariatric procedure if they possess additional significant complications, including T2DM, sig­nificant obstructive sleep apnea with an apnea-hypopnea index measured at 15 or higher, pseudotumor cerebri or severe nonal­coholic steatohepatitis. In addition, consideration may be given to those adolescent candidates with a BMI of greater than or equal to 40 kg/m2 with other complications, such as hypertension, insu­lin resistance or glucose intolerance, significant impairment with their quality of life or activities of daily living, hyperlipidemia, or obstructive sleep apnea.114

General considerations for bariatric surgery candidates

Potential surgical candidates should have a history of identifiable at­tempts at the medical management of obesity. All patients must be committed to engage in the educational process involved in preparing for bariatric surgery as well as adhering to the necessary long-term follow-up, both from a nutritional and medical perspective. Appropriate surveillance and treatment of potential long-term nutritional deficiencies as well as assessment and intervention for their obesity-related complications and mental health is crucial for long-term success.

Patients with unstable psychiatric illness, malignancy or other dis­eases associated with decreased life expectancy, substance abuse or an inability to adhere to long-term follow-up may be consid­ered inappropriate candidates for surgery due to a high risk of short- and long-term complications.

Advanced patient age is not an absolute contraindication to bar­iatric surgery. The outcomes and complication rates for patients greater than 60 years of age appear to be comparable to those of a younger population, regardless of the surgical procedure performed.9

Nonalcoholic steatohepatitis (NASH) is common in patients living with obesity and can lead to liver cirrhosis. The risk of bariatric surgery in patients carefully selected with Child-Pugh Class A liver cirrhosis is not prohibitive, but caution and additional surveillance should be undertaken as their overall risk for perioperative com­plications and mortality is increased.10,11 In addition, nonalcoholic steatohepatitis is the third most common indication for transplanta­tion of the liver, and, with growing incidence, NASH is becoming an increasingly frequent cause for liver transplantation.12–14

The morbidity and mortality rate of bariatric surgery before or after liver transplantation is increased but remains acceptable in tertiary care centers.15

Predictors of successful post-operative weight loss

Behavioural changes

Exercise in conjunction with obesity management programs has been demonstrated to improve weight loss and body composition. Thirty minutes per day (150 minutes per week) of moderate-in­tensity exercise after bariatric surgery is associated with a 3.6 kg additional weight loss compared with individuals who do not ex­ercise after bariatric surgery.16

In preparation for bariatric surgery, candidates may benefit from im­plementing health behavior change interventions. Interventions in­clude extensive education on nutrition and the need for exercise, and behavioral strategies for successful weight loss and weight mainte­nance, exploring topics such as self-monitoring, mindless eating and goal setting. However, bariatric surgical patients subjected to a be­havioral intervention program for six months prior to bariatric surgery experienced no significant difference in the degree of their weight loss at 24 months after surgery compared with control subjects.17

Patients’ concurrent eating patterns may play a significant role in the effect of postoperative weight loss. In addition, past traumas may also impact upon weight-loss outcomes post-bariatric sur­gery. The presence of a history of binge eating disorder or a pre­vious history of sexual abuse did not seem to predict difference in weight loss outcomes at two years post-bariatric surgery, but this area remains controversial and requires further study.18

Pre-operative weight loss

Weight reduction is associated with improvement of cardiac risk factors and the associated complications of obesity. As little as 5%–10% weight loss can improve cardiovascular risk factors and reduce complications, such as hypertension, hyperlipidemia, T2DM, visceral fat and hepatic steatosis, as well as liver volume. High-protein diets produce rapid weight loss, provide adequate satiety, experience less lean body mass loss and have a decreased reduction in the resting energy expenditure.19 There does not ap­pear to be any compromise in immune function or any effect on wound healing with the use of high-protein diets.

Failure to achieve adequate postoperative weight loss outcomes is often attributed to preoperative psychosocial characteristics and eating behaviors, as well as poor adherence to the recommended postoperative nutrition plan after bariatric surgery.20 Past weight management attempts preoperatively may reflect a patient’s abil­ity to follow a strict medical nutrition plan and exercise program postoperatively.20

Preoperative weight stability is desired for patients prior to bar­iatric surgery. Preoperative weight loss may decrease the difficulty of performing bariatric surgery, minimize blood loss, improve short-term weight loss and short-term complications, as well as decrease operative time.21–23

Patients who achieved ≥ 5% excess body weight loss preopera­tively experienced more substantial weight loss at one year com­pared with those with less preoperative weight loss.24 However, longer-term studies reviewing preoperative weight loss outcomes did not confer any advantage at four years with respect to weight loss outcomes.25

Overall, there is no compelling evidence mandating weight loss prior to bariatric surgery for the long-term efficacy of weight management, but rather only for the technical simplicity of the surgery.20

Pre-surgical medical nutrition therapy

Many preoperative protocols include the use of a liquid-based, low-calorie diet for two to three weeks prior to surgery.26 Low-cal­orie diets in Canada provide around 900 calories per day, consist­ing of low carbohydrates, high protein and low-fat intake.

Bariatric surgical patients are requested to consume very low-calorie meal supplements in the form of commercially available protein shakes totaling 650–900 kcal/day for two to three weeks prior to surgery. A low-calorie diet which is low in carbohydrates may cause reduced liver volume by up to 19% and a 17% reduction in visceral adipose tissue.26,27

A systematic review found that very low-calorie diets (VLCDs) are effective at reducing body weight and hepatic volume prior to surgery. These diets do not reduce intraoperative or post-surgical risks.26 They do result in a surgeon’s perception that the difficulty of performing the operation is decreased.21

The effect of preoperative weight management also provides ad­ditional motivation to the patient in preparation for bariatric sur­gery. However, adherence and compliance with preoperative meal supplements may be poor and occasionally not well tolerated. In addition, meal supplements may be expensive. Preoperative weight loss with a two-week VLCD may approach approximately 6 kg.28

Preoperative patients taking a VLCD using Optifast® 800 kcal per day for two weeks prior to surgery were compared with patients ingesting the same caloric intake from a normal diet. There was a non-significant difference in the operating time, but there was a higher surgeon–perceived scale of difficulty in control patients compared with patients who received a VLCD prior to surgery. The 30-day complication rate was higher in control patients, including wound GI and deep hemorrhage, infection, dehiscence and anas­tomotic leak.21 In another study, preoperative weight loss of ≥8% excess weight in patients following a VLCD for four weeks prior to surgery was associated with decreased hospital length of stay and greater three-month and one-year postoperative weight loss compared with those who did not follow a VLCD.22,29 Neither the major complication rate nor conversion rates were affected by the degree of preoperative weight loss.22

Risk assessment prior to bariatric surgery

Nutritional evaluation

Limited high-quality evidence has reviewed preoperative malnutri­tion status in patients seeking bariatric surgery. Nonetheless, ob­servational studies have indicated that patients living with obesity have a higher risk for inadequate nutritional status2,30–32 and mal­nutrition.30,33,34 Preoperative evaluation and collaborative support from a registered dietitian is recommended for all patients consid­ering bariatric surgery.1,2

A large, multicenter retrospective observational study (n=106,577) found that ~6% of patients undergoing bariatric surgery were malnourished and had increased risk of death or serious morbidity and 30-day readmission rates.33 This study also found that >10% weight loss prior to surgery was associated with nine-times higher rates of DSM (Diagnostic and Statistical Manual of Mental Disorders) in patients with mild malnutrition, and 10-times higher DSM in those with severe malnutrition.33 Similarly, a retrospective cohort study concluded that 32% of the patient cohort (n=533) had malnutrition prior to surgery.34 Higher BMI was associated with increased risk for malnutrition, and post-operative nausea and vomiting were associated with preoperative malnutrition.34

Prevalence of preoperative micronutrient deficiencies is also high­er in patients with obesity.35 Preoperative lab work should include complete blood count, creatinine, iron panel, vitamin D, calcium, albumin and vitamin B12. Fasting plasma glucose, hemoglobin A1C, lipid panel and liver enzymes can also be measure at the same time, as part of the evaluation of obesity-related metabolic complications. Vitamin A, parathormone, phosphate, zinc, seleni­um and copper levels can be assessed more selectively, due to cost considerations. Preoperative optimization of micronutrient levels prior to surgery, specifically levels of vitamin D, vitamin B12 and iron, is recommended.2 Preoperative multivitamin complex with vitamin B1 is usually started at least one month prior to surgery. Of note, patients taking proton pump inhibitors and/or metformin have a higher prevalence of vitamin B12 deficiency.2

Smoking and nicotine use

Smoking and nicotine cessation should be recommended for all patients undergoing bariatric surgery. Surgical centers recom­mend that smoking cessation should be achieved for at least six weeks up to six months prior to bariatric surgery to ensure ade­quate extinction of consumption.36

Nicotine contributes to ulcer development by potentiating acid and pepsin secretion, increases bile salt reflux, increases H. pylori infection risk and diminishes prostaglandin synthesis, mucosal blood flow and gastric mucus.113

Cigarette smoking may be associated with increased risk of mar­ginal ulceration and may increase the risk of stricture formation. Complications related to smoking exposure on average may occur post operatively around 14 months.37

Smoking post-bariatric surgery may also be associated with pneu­monia and postoperative complications with subsequent surgeries involving body contour surgery and mastopexy.3,3842

Preoperative investigations

The preoperative evaluation of a bariatric surgical candidate is similar to those patients considered for similar-risk surgery, with some caveats. Bariatric surgical candidates may have additional factors which may make their clinical evaluation more challeng­ing. Many patients referred for bariatric surgery may have a low or exceptionally low functional capacity.

Cardiac evaluation: Exercise tolerance is a predictor for surgical outcomes; symptom-limited stairclimbing, for example, is predic­tive of postoperative cardiopulmonary complications in patients undergoing high-risk surgery.43 In addition, obesity is an indepen­dent risk factor for cardiovascular disease. Many patients with obesity may also convey symptoms of shortness of breath or chest pain, and the etiology of these symptoms may be varied. Fur­thermore, the physical examination in patients living with obesity may be challenging in that physical findings such as distant heart sounds or the evaluation of the jugular venous pressure may be difficult to obtain.

Patients undergoing bariatric surgery may have abnormalities in their electrocardiogram (ECG). An abnormal ECG in patients un­dergoing bariatric surgery may be independently associated with a higher likelihood of a complicated postoperative course, includ­ing the need for postoperative intensive care (ICU) admissions.44 Obesity may also be associated with changes in cardiac morphology, including left ventricular hypertrophy, diastolic dysfunction or left ventricular dysfunction. Bariatric surgery is associated with a decrease in left ventricular mass index, left ventricular end-diastolic volume, improvement in diastolic dysfunction and systolic function, and left atrial diameter.45

Cardiac echo is not typically performed during preoperative eval­uations, but may be required to detect suspected left or right ventricular dysfunction, valvular heart disease or pulmonary hy­pertension. The visualization of the echocardiographic images is often suboptimal, and echocardiographic contrast agents improve the ability to identify endocardial borders and to assess ven­tricular wall motion abnormalities. A radionuclide angiography (RNA) multigated acquisition (MUGA) scan may also be helpful in the assessment of ejection fraction. Cardiac nuclear stress test­ing may be required to investigate chest pain. In patients with BMI > 30 kg/m2, an abnormal nuclear stress test was associated with a higher annual cardiac event rate, cardiac death or death from any cause.46 Computed tomographic coronary angiography may be difficult with increased body habitus due to depth-de­pendent spatial resolution. In addition, computerized tomography scanner tables may be limited by weight restriction. The gold stan­dard for cardiac evaluation remains coronary angiography, which was not associated with an increase in minor or major complica­tion rates in patients living with obesity.47

Pulmonary evaluation: The respiratory system is also significant­ly affected in patients with an elevated BMI. Impairment in pulmo­nary function due to restriction in lung volumes and abnormalities in respiratory mechanics resulting in increased work of breathing may detrimentally affect the respiratory status of bariatric surgical candidates.48,49

Sleep apnea: It is not uncommon for people living with obesity to experience sleep-related disorders, which may result in signifi­cant respiratory, cardiovascular and neuropsychiatric conditions.72 Obstructive sleep apnea, one type of a sleep-related disorder, is either the complete cessation of airflow (apnea) or the significant reduction of airflow (hypopnea) measured during sleep. The pres­ence of obstructive sleep apnea has been associated with prema­ture death,73 motor vehicle accidents,74 hypertension,75 coronary artery disease and cerebrovascular accidents,76 nocturnal cardiac arrhythmias,77 and T2DM.78 In addition, obstructive sleep apnea has been associated with a significant increase in the incidence of sudden death from all cardiac causes.79 Obstructive sleep ap­nea has been demonstrated to affect the white matter within the limbic system, pons, frontal, temporal and parietal cortices, and projections connecting the cerebellum, which are key areas for brain function and memory.80

The incidence of obstructive sleep apnea in middle-aged adults in the Wisconsin Sleep Cohort Study was approximately 24% in males and 9% in females.81 In patients undergoing bariatric surgery, the prevalence of obstructive sleep apnea can be ≥ 90%, with clinically significant sleep apnea underdiagnosed in as many as 50% of these patients.4,5 The prevalence of obstructive sleep apnea is much high­er in males compared with female bariatric surgical candidates.82 The recognition of the diagnosis of obstructive sleep apnea is even more challenging as there may be no correlation between the se­verity of obstructive sleep apnea and BMI.83

Bariatric surgery results in improvement or resolution of a patient’s obstructive sleep apnea.84 Obstructive sleep apnea in the bariatric population is believed to be caused by excess fat deposition in or around the neck, causing the patient’s upper airway passag­es to collapse.85 Patients undergoing bariatric surgery who have obstructive sleep apnea may have a higher complication rate, which may include a prolonged hospital stay, the occurrence of thromboembolic phenomena, the need for reintervention, and an increased 30-day mortality rate.71 In addition, the presence of obstructive sleep apnea may be associated with more challenging intubations and increased ICU admissions.86,87

The gold standard in the diagnosis of obstructive sleep apnea is a level 1 polysomnogram (PSG).88 Resources for overnight in-labora­tory PSG testing can be limited and expensive.89 As a result, alter­native methods for identifying patients at risk for obstructive sleep apnea have been established. Utilizing screening questionnaires, including the STOP-Bang Questionnaire, Berlin Questionnaire and Epworth Sleepiness Scale, has become routine for patients under­going surgery. To identify bariatric surgical patients with clinically significant obstructive sleep apnea, relying on subjective screening questionnaires may fail to identify at risk patients.5,90 While some advocate that all bariatric surgical patients should be subjected to formal PSG, such resources are limited and costly.83

The STOP-Bang or the Berlin Questionnaire may not be effective tools for detecting moderate- or high-risk patients for obstructive sleep apnea in patients undergoing bariatric surgery, and so more effective tools should be considered or developed.5 There may also be no significant correlation between the Epworth sleepiness score and severity of obstructive sleep apnea.91 There should be a high clinical suspicion for the presence of obstructive sleep apnea in bariatric patients undergoing surgery, with a low threshold for subjecting the patient to a formal PSG. In addition, the use of continuous positive airway pressure immediately postoperatively after gastric bypass is safe and, should be administered if deemed clinically indicated.92

Bariatric surgery is beneficial in improving obstructive sleep ap­nea.93 However, despite significant weight loss postoperatively, bariatric surgical patients may have persistence of moderate to severe obstructive sleep apnea at one year postoperatively.94

The long-term relationship between weight loss and sleep apnea is complex. There should be hypervigilance for recurrence of the presence of obstructive sleep apnea in patients previously diag­nosed with obstructive sleep apnea, as reappearance can occur in the absence of weight regain.95,96

Endoscopy: There exists controversy in the utility of preopera­tive endoscopy in patients undergoing bariatric surgery. Most patients who undego endoscopy have normal or non-clinically significant findings. The consideration for performing endosco­py should be individualized based on symptoms, risk factors and type of procedure being considered for each patient.50 Patients considering sleeve gastrectomy who have dyspepsia, reflux, dys­phagia or symptoms suggestive of foregut pathology, as well as those on chronic anti-acid therapy, should undergo preoperative endoscopy to rule out the presence of hiatal hernia, esophagitis or Barrett’s esophagus, or other diseases such as peptic ulcer dis­ease and tumors.5155 Screening for H. pylori can be performed at the time of endoscopy. The incidence of H. pylori in patients with obesity planning to undergo bariatric surgery is variable, rang­ing between 15 and 85%.55,61 H. pylori may be implicated in the development of gastritis, peptic ulcer and gastric carcinoma.62,63 Screening for H. pylori is recommended for this reason, in patients undergoing gastric bypass procedure. The benefits for patients undergoing other types of surgeries is controversial.64 Screening investigations for malignancy should also be considered prior to bariatric surgery due to the association between certain malig­nancies and obesity. This may include screening colonoscopy for malignancy in patients 50 years of age and over, mammography and Pap smears in appropriate candidates.56–58

Risk of thromboembolism: The 90-day incidence of venous thromboembolism after bariatric surgery is 0.42%. Although uncommon, the clinical consequences can be devastating. Up to 40% of perioperative deaths may be attributed to pulmonary em­bolism. This remains one of the most common cause of periop­erative death along with myocardial infarction and sepsis from anastomotic leak.59 Prophylaxis with low molecular weight hepa­rin to prevent thromboembolism postoperatively after gastric by­pass is common practice. The prophylactic use of an inferior vena cava filter is no longer recommended, even in patients at high risk of pulmonary embolism, as it is associated with increased risk of postoperative deep vein thrombosis and overall mortality without decreasing the risk of pulmonary embolism.60

Other consideration: Patients with obesity are at increased risk for several gastrointestinal, hepatobiliary and intra-abdominal processes. Evaluation of the bariatric surgical patient with an ab­dominal ultrasound is not routinely recommended, except in those patients requiring an investigation for symptomatic biliary disease and elevated liver enzymes or nonalcoholic fatty liver disease.65

Following bariatric surgery, decreases in bone density may be observed due to bone loss. Mixed restrictive and malabsorptive procedures such as Roux-en-Y gastric bypass and biliopancreat­ic diversion are at increased risk for bone fractures. Sleeve gas­trectomy may result in bone loss to a lesser degree. Bone loss post-bariatric surgery may be attributed to many factors including nutritional factors, skeletal unfolding, calciotropic hormone ab­normalities, body and bone marrow fat changes, and changes in gut hormones. Baseline bone density evaluation may be consid­ered prior to bariatric surgery and two years post bariatric surgery depending on risk factors, which include postmenopausal wom­en, older men, patients with prior fragility fractures or a family history of osteoporosis. Vitamin D and parathyroid hormone levels may be obtained preoperatively in the screening for patients at risk for metabolic bone disease.66

Preoperative management of patients living with diabetes

In preparation for bariatric surgery, blood glucose readings of patients living with T2DM should be optimized. Reevaluation of the comprehensive care plan should be undertaken, as well as reevaluation of their dietary intake, activity level and the status of other pharmacotherapy. Existing guidelines recommend targets for diabetic glycemic control with the hope of improving bariatric surgical outcomes. Suggested targets include A1c less than 7%, fasting blood sugar level less than 6.1 mmol/L, and a two-hour postprandial blood sugar of 7.7 mmol/l. However, there is limit­ed data guiding the management of glycemic control in bariatric surgery, both preoperatively and postoperatively. With other sur­geries, such as orthopedic and colorectal surgery, an elevated A1C preoperatively may be associated with prolonged length-of-stay postoperatively and worsened postoperative outcomes.97101

Elevated blood sugars prior to surgery may be associated with increased postoperative complications, decreased weight loss and less resolution of the patient’s T2DM.102

Randomized controlled trials suggest that neither intensive manage­ment of patients’ glycemic control three months prior to Roux-en-Y gastric bypass, nor intensive control of glycemia in the first two weeks postoperatively, resulted in better hemoglobin A1c levels one year after surgery.103

Less aggressive blood glucose targets may be required prior to bar­iatric surgery, as often bariatric surgical patients with T2DM have high insulin resistance, resulting in suboptimal control.104 While the patient with T2DM is on a controlled VLCD in preparation for bariatric surgery, reevaluation of their diabetic medications should be undertaken, as a patient’s requirements for medication to con­trol blood sugars may be significantly altered. For diet-controlled patients with T2DM, no significant interventions are required.

Avoiding sulfonylureas and meglitinides while on VLCD should be considered to avoid hypoglycemia. In addition, sodium glucose co-transporter 2 inhibitors should be stopped while on a VLCD due to the risk of diabetic ketoacidosis.105 Alpha-glucosidase, alpha-amylase enzyme inhibitors and thiazolidinediones may be stopped during this period of time. In addition, dipeptidyl pep­tidase-4 inhibitors and glucagon-like peptide 1 (GLP-1) agonists may also be held, especially with adequate blood sugar control.

Insulin requirements while on meal replacement therapy in prepara­tion for surgery drop dramatically. Intermediate and long-acting insu­lin require a decreased dose, often by 50%, and short-acting insulins require significant readjustment, as well.106,107 Frequent blood sugar monitoring is required while on VLCDs in preparation for bariatric surgery. Symptomatic hypoglycemia is treated in the usual fashion.108

While on meal replacement therapy, there may be an increased risk of intravascular volume depletion. Close observation of a pa­tient’s volume status, electrolytes and kidney function is a prudent and cautious approach.109 Diuretics should be dose adjusted or held. In addition, close evaluation of blood pressure readings is required, and adjustment to antihypertensive medication may be necessary.110 Patients with hypertension on blood pressure medi­cation and concurrent meal replacement therapy should be edu­cated about the possibility of developing orthostatic hypotension.

Individuals on meal replacement therapy and warfarin may also require closer observation of their INR level.111,112


Bariatric surgery is a life-altering and effective obesity management intervention. Several considerations must be undertaken to prepare a potential candidate for surgery. The patient’s medical, mental, nu­tritional and functional health should be evaluated prior to surgery. Once adequate evaluation, preparation and optimization have been undertaken, establishing an acceptable perioperative risk profile, the patient may proceed with bariatric surgery.

Stephen Glazer MDi, Laurent Biertho MDii

i) Department of Internal Medicine, University of Toronto

ii) Department of Surgery, Laval University

A complete list of author’s competing interests can be found on the CMAJ website, HERE

Cite this Chapter

Glazer S, Biertho L. Canadian Adult Obesity Clinical Practice Guidelines: Bariatric Surgery: Selection & Pre-Operative Workup. Available from: Accessed [date].

Update History

Version 1, August 4, 2020. The Canadian Adult Obesity Clinical Practice Guidelines are a living document, with only the latest chapters posted at

  1. Mechanick JI, Youdim A, Jones DB, et al. Clinical practice guidelines for the perioperative nutritional, metabolic, and nonsurgical support of the bariatric sur­gery patient-2013 update: Cosponsored by American association of clinical endo­crinologists, the obesity society, and American society of. Obesity. 2013;21(SUP­PL. 1):S1-S27. doi:10.1002/oby.20461
  2. Parrott J, N RD, Frank L, et al. American Society for Metabolic and Bariatric Sur­gery Integrated Health Nutritional Guidelines for the Surgical Weight Loss Pa­tient 2016 Update : Micronutrients. Surg Obes Relat Dis. 2017;13(5):727-741. doi:10.1016/j.soard.2016.12.018
  3. Myers K, Hajek P, Hinds C, McRobbie H. Stopping smoking shortly before surgery and postoperative complications: A systematic review and meta-analysis. Arch Intern Med. 2011;171(11):983-989. doi:10.1001/archinternmed.2011.97
  4. Gasa M, Salord N, Fortuna AM, et al. Obstructive sleep apnoea and met­abolic impairment in severe obesity. Eur Respir J. 2011;38(5):1089-1097. doi:10.1183/09031936.00198810
  5. Glazer SA, Erickson AL, Crosby RD, Kieda J, Zawisza A, Deitel M. The Evaluation of Screening Questionnaires for Obstructive Sleep Apnea to Identify High-Risk Obese Patients Undergoing Bariatric Surgery. Obes Surg. 2018;28(11):3544- 3552. doi:10.1007/s11695-018-3547-7
  6. National Institutes of Health. National Heart, Lung and BI. clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults. 1998;158(17):1855-1867. doi:10.1001/archinte.158.17.1855
  7. Busetto L, Dixon J, De Luca M, Shikora S, Pories W, Angrisani L. Bariatric surgery in class I obesity. Obes Surg. 2014;24(4):487-519. doi:10.1007/s11695-014-1214-1
  8. ASMBS Clinical Issues Committee. Bariatric surgery in class I obesity (body mass index 30–35 kg/m2). Surg Obes Relat Dis. 2013;9(1):e1-e10. doi:10.1016/j. soard.2012.09.002
  9. Giordano S, Vvictorzon M. Bariatric surgery in elderly patients: A systematic re­view. Clin Interv Aging. 2015;10:1627-1635. doi:10.2147/CIA.S70313
  10. Shimizu H, Phuong V, Maia M, et al. Bariatric surgery in patients with liver cirrho­sis. Surg Obes Relat Dis. 2013;9(1):1-6. doi:10.1016/j.soard.2012.07.021
  11. Jan A, Narwaria M, Mahawar KK. A Systematic Review of Bariatric Surgery in Patients with Liver Cirrhosis. Obes Surg. 2015;25(8):1518-1526. doi:10.1007/ s11695-015-1727-2
  12. Agopian VG, Kaldas FM, Hong JC, et al. Liver transplantation for nonalcoholic ste­atohepatitis: The new epidemic. Ann Surg. 2012;256(4):624-633. doi:10.1097/ SLA.0b013e31826b4b7e
  13. Mandell MS, Zimmerman M, Campsen J, Kam I. Bariatric surgery in liver trans­plant patients: Weighing the evidence. Obes Surg. 2008;18(12):1515-1516. doi:10.1007/s11695-008-9712-7
  14. Angulo P. Nonalcoholic fatty liver disease and liver transplantation. Liver Trans­plant. 2007;12(4):523-534. doi:10.1002/lt
  15. Lazzati A, Iannelli A, Schneck AS, et al. Bariatric Surgery and Liver Transplan­tation: a Systematic Review a New Frontier for Bariatric Surgery. Obes Surg. 2015;25(1):134-142. doi:10.1007/s11695-014-1430-8
  16. Egberts K, Brown WA, Brennan L, O’Brien PE. Does exercise improve weight loss after bariatric surgery? A systematic review. Obes Surg. 2012;22(2):335-341. doi:10.1007/s11695-011-0544-5
  17. Kalarchian MA, Marcus MD, Courcoulas AP, Cheng Y, Levine MD. Preoperative lifestyle intervention in bariatric surgery: a randomized clinical trial. Surg Obes Relat Dis. 2016;12(1):180-187. doi:10.1016/j.physbeh.2017.03.040
  18. Fujioka K, Yan E, Wang HJ, Li Z. Evaluating preoperative weight loss, binge eating disorder, and sexual abuse history on Roux-en-Y gastric bypass outcome. Surg Obes Relat Dis. 2008;4(2):137-143. doi:10.1016/j.soard.2008.01.005
  19. Goldstein DJ. Beneficial health effects of modest weight loss. Int J Obes Relat Metab Disord J Int Assoc Study Obes. 1992;16(6):397-415.
  20. Ríos B. Integrated Health in Bariatric Surgery.; 2015.
  21. Van Nieuwenhove Y, Dambrauskas Z, Campillo-Soto A, et al. Preoperative very low-calorie diet and operative outcome after laparoscopic gastric bypass: A ran­domized multicenter study. Arch Surg. 2011;146(11):1300-1305. doi:10.1001/ archsurg.2011.273
  22. Alami RS, Morton JM, Schuster R, et al. Is there a benefit to preoperative weight loss in gastric bypass patients? A prospective randomized trial. Surg Obes Relat Dis. 2007;3(2):141-145. doi:10.1016/j.soard.2006.11.006
  23. Cassie S, Menezes C, Birch DW, Shi X, Karmali S. Effect of preoperative weight loss in bariatric surgical patients: a systematic review. Surg Obes Relat Dis. 2011;7(6):767-768. doi:10.1016/j.soard.2011.09.003
  24. Solomon H, Liu GY, Alami R, Morton J, Curet MJ. Benefits to Patients Choosing Pre­operative Weight Loss in Gastric Bypass Surgery: New Results of a Randomized Trial. J Am Coll Surg. 2009;208(2):241-245. doi:10.1016/j.jamcollsurg.2008.09.028
  25. Becouarn G, Topart P, Ritz P. Weight loss prior to bariatric surgery is not a pre-requisite of excess weight loss outcomes in obese patients. Obes Surg. 2010;20(5):574-577. doi:10.1007/s11695-010-0083-5
  26. Holderbaum M, Casagrande DS, Sussenbach S, Buss C. Effects of very low calorie diets on liver size and weight loss in the preoperative period of bariatric surgery: a systematic review. Surg Obes Relat Dis. 2018;14(2):237-244. doi:10.1016/j. soard.2017.09.531
  27. Benjaminov O, Beglaibter N, Gindy L, et al. The effect of a low-carbohydrate diet on the nonalcoholic fatty liver in morbidly obese patients before bariatric surgery. Surg Endosc Other Interv Tech. 2007;21(8):1423-1427. doi:10.1007/s00464-006-9182-8
  28. Schouten R, van der Kaaden I, van ’t Hof G, Feskens PGBM. Comparison of Pre­operative Diets Before Bariatric Surgery: a Randomized, Single-Blinded, Non-infe­riority Trial. Obes Surg. 2016;26(8):1743-1749. doi:10.1007/s11695-015-1989-8
  29. Hutcheon DA, Hale AL, Ewing JA, et al. Short-Term Preoperative Weight Loss and Postoperative Outcomes in Bariatric Surgery. J Am Coll Surg. 2018;226(4):514- 524. doi:10.1016/j.jamcollsurg.2017.12.032
  30. Peterson LA, Cheskin LJ, Furtado M, et al. Malnutrition in Bariatric Surgery Candidates: Multiple Micronutrient Deficiencies Prior to Surgery. Obes Surg. 2016;26(4):833-838. doi:10.1007/s11695-015-1844-y
  31. Sánchez A, Rojas P, Basfi-fer K, et al. Micronutrient Deficiencies in Morbidly Obese Women Prior to Bariatric Surgery. Obes Surg. 2016;26(2):361-368. doi:10.1007/ s11695-015-1773-9
  32. Dagan SS, Zelber-Sagi S, Webb M, et al. Nutritional Status Prior to Laparoscopic Sleeve Gastrectomy Surgery. Obes Surg. 2016;26(9):2119-2126. doi:10.1007/ s11695-016-2064-9
  33. Fieber JH, Sharoky CE, Wirtalla C, Williams NN, Dempsey DT, Kelz RR. The mal­nourished patient with obesity: a unique paradox in bariatric surgery. J Surg Res. 2018;232:456-463. doi:10.1016/j.jss.2018.06.056
  34. Major P, Małczak P, Wysocki M, et al. Bariatric patients’ nutritional status as a risk factor for postoperative complications, prolonged length of hospital stay and hospital readmission: A retrospective cohort study. Int J Surg. 2018;56:210-214. doi:10.1016/j.ijsu.2018.06.022
  35. Gehrer S, Kern B, Peters T, Christofiel-Courtin C, Peterli R. Fewer nutrient De­ficiencies after laparoscopic sleeve gastrectomy (LSG) than after Laparoscopic Roux-Y-gastric bypass (LRYGB)-a prospective study. Obes Surg. 2010;20(4):447- 453. doi:10.1007/s11695-009-0068-4<


  36. Devlin CA, Smeltzer SC. Temporary perioperative tobacco cessation: A literature review. AORN J. 2017;106(5):415-423. doi:10.1016/j.aorn.2017.09.001
  37. Fakulujo A, Fong B, Abdemur A, Szomstein S, Rosenthal RJ. PL-114: Preva­lence and implications of cirgarette smoking in morbidly obese patients un­dergoing bariatric surgery. Surg Obes Relat Dis. 2010;6(3):S6. doi:10.1016/j. soard.2010.03.019
  38. Felix EL, Kettelle J, Mobley E, Swartz D. Perforated marginal ulcers after lapa­roscopic gastric bypass. Surg Endosc. 2008;22(10):2128-2132. doi:10.1007/ s00464-008-9996-7
  39. Gupta PK, Gupta H, Kaushik M, et al. Predictors of pulmonary complications after bariatric surgery. Surg Obes Relat Dis. 2012;8(5):574-581. doi:10.1016/j. soard.2011.04.227
  40. Gravante G, Araco A, Sorge R, Araco F, Delogu D, Cervelli V. Wound infections in body contouring mastopexy with breast reduction after laparoscopic adjust­able gastric bandings: The role of smoking. Obes Surg. 2008;18(6):721-727. doi:10.1007/s11695-007-9252-6
  41. Coupaye M, Sabaté JM, Castel B, et al. Predictive factors of weight loss 1 year af­ter laparoscopic gastric bypass in obese patients. Obes Surg. 2010;20(12):1671- 1677. doi:10.1007/s11695-010-0159-2
  42. Garb J, Welch G, Zagarins S, Kuhn J, Romanelli J. Bariatric surgery for the treat­ment of morbid obesity: a meta-analysis of weight loss outcomes for laparo­scopic adjustable gastric banding and laparoscopic gastric bypass. Obes Surg. 2009;19(10):1447-1455. doi:10.1007/s11695-009-9927-2
  43. Girish M, Trayner E, Dammann O, Pinto-Plata V, Celli B. Symptom-limited stair climbing as a predictor of postoperative cardiopulmonary complications after high-risk surgery. Chest. 2001;120(4):1147-1151. doi:10.1378/chest.120.4.1147
  44. Gonzalez R, Bowers SP, Venkatesh KR, Lin E, Smith CD. Preoperative factors pre­dictive of complicated postoperative management after Roux-en-Y gastric by­pass for morbid obesity. Surg Endosc Other Interv Tech. 2003;17(12):1900-1904. doi:10.1007/s00464-003-8810-9
  45. Aggarwal R, Harling L, Efthimiou E, Darzi A, Athanasiou T, Ashrafian H. The Ef­fects of Bariatric Surgery on Cardiac Structure and Function: a Systematic Review of Cardiac Imaging Outcomes. Obes Surg. 2016;26(5):1030-1040. doi:10.1109/ ciced.2018.8592188
  46. Elhendy A, Schinkel AFL, Van Domburg RT, et al. Prognostic stratification of obese patients by stress 99mTc- tetrofosmin myocardial perfusion imaging. J Nucl Med. 2006;47(8):1302-1306.
  47. McNulty PH, Ettinger SM, Field JM, et al. Cardiac catheterization in morbidly obese patients. Catheter Cardiovasc Interv. 2002;56(2):174-177. doi:10.1002/ccd.10186
  48. Aguiar IC, Freitas WR, Santos IR, et al. Obstructive sleep apnea and pulmonary function in patients with severe obesity before and after bariatric surgery: A ran­domized clinical trial. Multidiscip Respir Med. 2014;9(1):43. doi:10.1186/2049- 6958-9-43
  49. Wei YF, Wu HD. Candidates for bariatric surgery: Morbidly obese patients with pulmonary dysfunction. J Obes. 2012. doi:10.1155/2012/878371
  50. Parikh M, Liu J, Vieira D, et al. Preoperative Endoscopy Prior to Bariatric Sur­gery: a Systematic Review and Meta-Analysis of the Literature. Obes Surg. 2016;26(12):2961-2966. doi:10.1007/s11695-016-2232-y
  51. Praveenraj P, Gomes RM, Kumar S, et al. Diagnostic yield and clinical implications of preoperative upper gastrointestinal endoscopy in morbidly obese patients un­dergoing bariatric surgery. J Laparoendosc Adv Surg Tech. 2015;25(6):465-469. doi:10.1089/lap.2015.0041
  52. Peromaa-Haavisto P, Victorzon M. Is routine preoperative upper GI endoscopy needed prior to gastric bypass? Obes Surg. 2013;23(6):736-739. doi:10.1007/ s11695-013-0956-5
  53. Che F, Nguyen B, Cohen A, Nguyen NT. Prevalence of hiatal hernia in the morbidly obese. Surg Obes Relat Dis. 2013;9(6):920-924. doi:10.1016/j.soard.2013.04.005
  54. Steinbrook R. Surgery for Severe Obesity. N Engl J Med. 2004;350(11):1075- 1079. doi:10.1177/1559827612467420
  55. Küper MA, Kratt T, Kramer KM, et al. Effort, safety, and findings of routine pre­operative endoscopic evaluation of morbidly obese patients undergoing bariatric surgery. Surg Endosc. 2010;24(8):1996-2001. doi:10.1007/s00464-010-0893-5
  56. U.S. Preventive Services Task Force. Recommendations for primary care practice. Recommendations. recommendations. Published 2018.
  57. Himbert C, Delphan M, Scherer D, Bowers LW, Hursting S, Ulrich CM. Signals from the adipose microenvironment and the obesity-cancer link-a systematic review. Cancer Prev Res. 2017;10(9):494-506. doi:10.1158/1940-6207.CAPR-16-0322
  58. Lashinger LM, Ford NA, Hursting SD. Interacting Inflammatory and Growth Factor Signals Underlie the Obesity-Cancer Link. J Nutr. 2014;144(2):109-113. doi:10.3945/jn.113.178533
  59. Omalu BI, Ives DG, Buhari AM, et al. Death rates and causes of death after bariatric surgery for Pennsylvania residents, 1995 to 2004. Arch Surg. 2007;142(10):923- 928. doi:10.1001/archsurg.142.10.929
  60. Kaw R, Pasupuleti V, Wayne Overby D, et al. Inferior vena cava filters and postop­erative outcomes in patients undergoing bariatric surgery: A meta-analysis. Surg Obes Relat Dis. 2014;10(4):725-733. doi:10.1016/j.soard.2014.04.008
  61. Al-Akwaa A. Prevalence of Helicobacter pylori infection in a group of morbidly obese Saudi patients undergoing bariatric surgery: A preliminary report. Saudi J Gastroenterol. 2010;16(4):264. doi:10.4103/1319-3767.70610
  62. Carabotti M, D’Ercole C, Iossa A, Corazziari E, Silecchia G, Severi C. Helicobacter pylori infection in obesity and its clinical outcome after bariatric surgery. World J Gastroenterol. 2014;20(3):647-653. doi:10.3748/wjg.v20.i3.647
  63. Sauerland S, Angrisani L, Belachew M, et al. Obesity surgery: Evidence-based guidelines of the European Association for Endoscopic Surgery (E.A.E.S.). Surg Endosc Other Interv Tech. 2005;19(2):200-221. doi:10.1007/s00464-004-9194-1
  64. Goday A, Castañer O, Benaiges D, et al. Can Helicobacter pylori Eradication Treatment Modify the Metabolic Response to Bariatric Surgery? Obes Surg. 2018;28(8):2386-2395. doi:10.1007/s11695-018-3170-7
  65. Abou Hussein BM, Khammas A, Makki M, et al. Role of Routine Abdominal Ultra­sound Before Bariatric Surgery: Review of 937 Patients. Obes Surg. 2018;28(9). doi:10.1007/s11695-018-3210-3
  66. Mechanick JI, Kushner RF, Sugerman HJ, et al. American Association of Clini­cal Endocrinologists, The Obesity Society, and American Society for Metabolic & Bariatric Surgery Medical guidelines for clinical practice for the periopera­tive nutritional, metabolic, and nonsurgical support of the bariatric. Obesity. 2009;14(S1):1-83. doi:10.1038/oby.2009.28
  67. Martin KA, Lee CR, Farrell TM, Moll S. Oral Anticoagulant Use After Bariatric Surgery: A Literature Review and Clinical Guidance. Am J Med. 2017;130(5):517- 524. doi:10.1016/j.amjmed.2016.12.033
  68. Geraldo M de SP, Fonseca FLA, Veiga Gouveia MR de F, Feder D. The use of drugs in patients who have undergone bariatric surgery. Int J Gen Med. 2014;7:219- 224. doi:10.2147/IJGM.S55332
  69. Padwal R, Brocks D, Sharma AM. A systematic review of drug absorption follow­ing bariatric surgery and its theoretical implications. Obes Rev. 2010;11(1):41-50. doi:10.1111/j.1467-789X.2009.00614.x
  70. Miller AD, Smith KM. Medication and nutrient administration considerations af­ter bariatric surgery. Am J Heal Pharm. 2006;63(19):1852-1857. doi:10.2146/ ajhp060033
  71. Longitudinal Assessment of Bariatric Surgery (LABS) Consortium. Perioper­ative safety in the longitudinal assessment of bariatric surgery. N Engl J Med. 2009;361(5):445-454. doi:10.1056/NEJMoa0901836
  72. Shahi B, Praglowski B, Deitel M. Sleep-related Disorders in the Obese. Obes Surg. 1992;2(2):157-168. doi:10.1381/096089292765560358
  73. Hallowell PT, Stellato TA, Schuster M, et al. Potentially life-threatening sleep ap­nea is unrecognized without aggressive evaluation. Am J Surg. 2007;193(3):364- 367. doi:10.1016/j.amjsurg.2006.09.022
  74. Marshall NS, Wong KK, Liu PY, Cullen SR, Knuiman MW, Grunstein RR. Sleep apnea as an independent risk factor for all-cause mortality: the Busselton Health Study. Sleep. 2008;31(8):1079-1085.
  75. Terán-Santos J, Jiménez-Gómez A, Cordero-Guevara J. The association between sleep apnea and the risk of traffic accidents. N Engl J Med. 1999;340(11):847- 851. doi:10.1056/NEJM199903183401104
  76. Somers VK, Dyken ME, Clary MP, Abboud FM. Sympathetic neural mechanisms in obstructive sleep apnea. J Clin Invest. 1995;96(4):1897-1904. doi:10.1172/ JCI118235
  77. Parra O, Arboix A, Bechich S, et al. Time course of sleep-related breathing disor­ders in first-ever stroke or transient ischemic attack. Am J Respir Crit Care Med. 2000;161(2 I):375-380. doi:10.1164/ajrccm.161.2.9903139
  78. Mehra R, Benjamin EJ, Shahar E, et al. Association of nocturnal arrhythmias with sleep-disordered breathing: The sleep heart health study. Am J Respir Crit Care Med. 2006;173(8):910-916. doi:10.1164/rccm.200509-1442OC
  79. Tasali E, Mokhlesi B, Van Cauter E. Obstructive sleep apnea and type 2 diabetes: Interacting epidemics. Chest. 2008;133(2):496-506. doi:10.1378/chest.07-0828
  80. Macey PM, Kumar R, Woo MA, Valladares EM, Yan-Go FL, Harper RM. Brain structural changes in obstructive sleep apnea. Sleep. 2008;31(7):967-977. doi:10.1017/CBO9781139088268
  81. Young T, Palta M, Dempsey J, Skatrud J, Weber S, Badr S. The Occurrence of Sleep-Disordered Breathing among Middle-Aged Adults. N Engl J Med. 1993;328(17):1230-1235. doi:10.1056/NEJM199304293281704
  82. Peromaa-Haavisto P, Tuomilehto H, Kössi J, et al. Prevalence of Obstructive Sleep Apnoea Among Patients Admitted for Bariatric Surgery. A Prospective Multicentre Trial. Obes Surg. 2016;26(7):1384-1390. doi:10.1007/s11695-015-1953-7
  83. O’Keeffe T, Patterson EJ. Evidence Supporting Routine Polysomnography before Bar­iatric Surgery. Obes Surg. 2004;14(1):23-26. doi:10.1381/096089204772787248
  84. Quintas-Neves M, Preto J, Drummond M. Assessment of bariatric surgery efficacy on obstructive sleep apnea (OSA). Rev Port Pneumol (English Ed. 2016;22(6):331- 336. doi:10.1016/j.rppnen.2016.05.006
  85. Fritscher LG, Canani S, Mottin CC, et al. Bariatric Surgery in the Treatment of Ob­structive Sleep Apnea in Morbidly Obese Patients. Respiration. 2007;74(6):647- 652. doi:10.1159/000107736
  86. Gupta RM, Parvizi J, Hanssen AD, Gay PC. Postoperative complications in patients with obstructive sleep apnea syndrome undergoing hip or knee replacement: a case-control study. Mayo Clin Proc. 2001;76(9):897-905.
  87. Chesson J, Ferber RA, Fry JM, et al. Practice parameters for the indications for polysomnography and related procedures. Sleep. 1997;20(6):406-422. doi:10.1093/sleep/20.6.406
  88. Gentil B, De Larminat JM, Boucherez C, Lienhart A, Chou HC, Wu TL. Difficult in­tubation and obstructive sleep apnoea syndrome. Br J Anaesth. 1994;72(3):368.
  89. Nagappa M, Liao P, Wong J, et al. Validation of the stop-bang questionnaire as a screening tool for obstructive sleep apnea among different populations: A systematic review and meta-Analysis. PLoS One. 2015;10(12):e0143697. doi:10.1371/journal.pone.0143697
  90. Sharkey KM, Orff HJ, Tosi C, Harrington D, Roye GD, Millman RP. Subjective sleep­iness and daytime functioning in bariatric patients with obstructive sleep apnea. Sleep Breath. 2013;17(1):267-274. doi:10.1007/s11325-012-0685-3
  91. Serafini FM, Anderson WM, Rosemurgy AS, Strait T, Murr MM. Clinical pre­dictors of sleep apnea in patients undergoing bariatric surgery. Obes Surg. 2001;11(1):28-31. doi:10.1381/096089201321454079
  92. Ramirez A, Lalor PF, Szomstein S, Rosenthal RJ. Continuous positive airway pressure in immediate postoperative period after laparoscopic Roux-en-Y gas­tric bypass: is it safe? Surg Obes Relat Dis. 2009;5(5):544-546. doi:10.1016/j. soard.2009.05.007
  93. Sarkhosh K, Switzer NJ, El-Hadi M, Birch DW, Shi X, Karmali S. The impact of bariatric surgery on obstructive sleep apnea: a systematic review. Obes Surg. 2013;23(3):414-423. doi:10.1016/B978-0-12-420168-2.00040-5
  94. Peromaa-Haavisto P, Tuomilehto H, Kössi J, et al. Obstructive sleep apnea: the effect of bariatric surgery after 12 months. A prospective multicenter trial. Sleep Med. 2017;35(July):85-90. doi:10.1016/j.sleep.2016.12.017
  95. Sampol G, Muñoz X, Sagalés MT, et al. Long-term efficacy of dietary weight loss in sleep apnoea/hypopnoea syndrome. Eur Respir J. 1998;12(5):1156-1159. doi: 10.1183/09031936.98.12051156
  96. Pillar G, Peled R, Lavie P. Recurrence of sleep apnea without concomitant weight increase 7.5 years after weight reduction surgery. Chest. 1994;106(6):1702- 1704. doi:10.1378/chest.106.6.1702
  97. Estrada CA, Young JA, Nifong LW, Chitwood WR. Outcomes and perioperative hyperglycemia in patients with or without diabetes mellitus undergoing coronary artery bypass grafting. Ann Thorac Surg. 2003;75(5):1392-1399. doi:10.1016/ S0003-4975(02)04997-4
  98. Marchant MH, Viens NA, Cook C, Vail TP, Bolognesi MP. The impact of glycemic control and diabetes mellitus on perioperative outcomes after total joint arthro­plasty. J Bone Jt Surg – Ser A. 2009;91(7):1621-1629. doi:10.2106/JBJS.H.00116
  99. Walid MS, Newman BF, Yelverton JC, Nutter JP, Ajjan M, Robinson JS. Prevalence of previously unknown elevation of glycosylated hemoglobin in spine surgery pa­tients and impact on length of stay and total cost. J Hosp Med. 2010;5(1):10-14. doi:10.1002/jhm.541
  100. O’Sullivan CJ, Hynes N, Mahendran B, et al. Haemoglobin A1c (HbA1C) in Non-di­abetic and Diabetic Vascular Patients. Is HbA1C an Independent Risk Factor and Predictor of Adverse Outcome? Eur J Vasc Endovasc Surg. 2006;32(2):188-197. doi:10.1016/j.ejvs.2006.01.011
  101. Gustafsson UO, Thorell A, Soop M, Ljungqvist O, Nygren J. Haemoglobin A1c as a predictor of postoperative hyperglycaemia and complications after major colorectal surgery. Br J Surg. 2009;96(11):1358-1364. doi:10.1002/bjs.6724
  102. Perna M, Romagnuolo J, Morgan K, Byrne TK, Baker M. Preoperative hemoglobin A1c and postoperative glucose control in outcomes after gastric bypass for obe­sity. Surg Obes Relat Dis. 2012;8(6):685-690. doi:10.1016/j.soard.2011.08.002
  103. Chuah LL, Miras AD, Papamargaritis D, Jackson SN, Olbers T, Le Roux CW. Im­pact of perioperative management of glycemia in severely obese diabetic patients undergoing gastric bypass surgery. Surg Obes Relat Dis. 2015;11(3):578-584. doi:10.1016/j.soard.2014.11.004
  104. Kahn BB, Flier JS. Obesity and insulin resistance. J Clin Invest. 2000;106(4):473- 481. doi:10.1172/JCI10842
  105. Mazer CD, Arnaout A, Connelly KA, et al. Sodium-glucose cotransporter 2 inhibitors and type 2 diabetes: clinical pearls for in-hospital initiation, in-hos­pital management, and postdischarge. Curr Opin Cardiol. 2019. doi:10.1097/ HCO.0000000000000704
  106. Sievenpiper JL, Chan CB, Dworatzek PD, Med CF, Williams Med SL. 2018 Clinical Practice Guidelines Nutrition Therapy Diabetes Canada Clinical Practice Guidelines Ex­pert Committee. Can J Diabetes. 2018;42:S64–S79. doi:10.1016/j.jcjd.2017.10.009
  107. Shiau JY, So DYF, Dent RR. Effects on Diabetes Medications, Weight and Gly­cated Hemoglobin Among Adult Patients With Obesity and Type 2 Diabetes: 6-Month Observations From a Full Meal Replacement, Low-Calorie Diet Weight Management Program. Can J Diabetes. 2018;42(1):56-60. doi:10.1016/j. jcjd.2017.03.006
  108. Nestle Health Science. Is Optifast VLCD suitable for diabetes? https://www.opti­
  109. Saiki A, Nagayama D, Ohhira M, et al. Effect of weight loss using formula diet on renal function in obese patients with diabetic nephropathy. Int J Obes. 2005;29(9):1115-1120. doi:10.1038/sj.ijo.0803009
  110. Valenta LJ, Elias AN. Modified fasting in treatment of obesity: effects on se­rum lipids, electrolytes, liver enzymes, and blood pressure. Postgrad Med. 1986;79(4):263-267. doi:10.1080/00325481.1986.11699329
  111. Couris R, Tataronis G, McCloskey W, et al. Dietary vitamin K variability affects International Normalized Ratio (INR) coagulation indices. Int J Vitam Nutr Res. 2006;76(2):65-74. doi:10.1024/0300-9831.76.2.65
  112. Pedersen FM, Hamberg O, Hess K, Ovesen L. The effect of dietary vitamin K on warfarin‐induced anticoagulation. J Intern Med. 1991;229(6):517-520. doi:10.1111/j.1365-2796.1991.tb00388.x
  113. Endoh K, Leung F. Effects of Smoking and Nicotine on the Gastric Mucosa: A Re­view of Clinical and Experimental Evidence. Gastroenterology 1994;107:884-878
  114. Pratt JSA, Browne A, Browne NT, Bruzoni M, Cohen M, Desai A, Inge T, Linden BC, Mattar SG, Michalsky M, Podkameni D, Reichard KW, Stanford FC, Zeller MH, Zitsman J. ASMBS pediatric metabolic and bariatric surgery guidelines, 2018. Surg Obes Relat Dis. 2018;14(7):882-901.
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). For reprint and all other inquiries please contact / +1-(780)-492-8361.

The summary of the Canadian Adult Obesity Clinical Practice Guidelines is published in the Canadian Medical Association Journal, and contains information on the full methodology, management of authors’ competing interests, a brief overview of all recommendations and other details. More detailed guideline chapters are published on the Obesity Canada website at

Join our online communities!

Free, secure and moderated forums for
healthcare pros and people living with
Click here to join
Support Obesity Canada! Donations $20 + receive a tax receipt.
Appuyez Obésité Canada!  Les dons de plus de 20$ recevront un reçu fiscal.