Preanesthesia medical evaluation of the patient with obesity

INTRODUCTION — As the prevalence of obesity increases worldwide, an increasing number of surgical patients with obesity will require anesthesia. Planning for anesthesia and recovery must take into account the physiologic changes caused by obesity, the presence of comorbid conditions associated with obesity, the nature of the anticipated procedure, and the anticipated recovery from surgery and anesthesia. Consequently, the preanesthetic evaluation should determine and evaluate the relevant issues for the individual patient.

The preanesthetic evaluation and management of patients with obesity who are undergoing noncardiac surgery are reviewed here. Preanesthetic evaluation of the healthy patient, perioperative considerations specific to obstructive sleep apnea (OSA), and anesthetic management of patients with obesity are discussed separately. (See "Preoperative medical evaluation of the healthy adult patient" and "Surgical risk and the preoperative evaluation and management of adults with obstructive sleep apnea" and "Anesthesia for the patient with obesity".)

CLASSIFICATION OF OBESITY — Obesity is typically defined by body mass index (BMI), the ratio of weight (in kilograms) to the square of height (in meters) (calculator 1). In adults, the World Health Organization [1] and the National Institutes of Health [2] have adopted a classification of obesity defined by BMI:

●Overweight – BMI of ≥25 to 29.9 kg/m².

●Obesity – BMI of ≥30 kg/m².

●Obesity class 1 – BMI of 30 to 34.9 kg/m².

●Obesity class 2 – BMI of 35 to 39.9 kg/m².

●Obesity class 3 – BMI of ≥40 kg/m². This type of obesity is also referred to as severe, extreme, or massive obesity. (See "Obesity in adults: Prevalence, screening, and evaluation".)

Some organizations and authors have added Class 4 for BMI ≥50 kg/m² (super obesity) and Class 5 for BMI ≥60 kg/m² (super super obesity) (table 1) [3,4].

PERIOPERATIVE RISKS IN PATIENTS WITH OBESITY

Class 1 obesity — Otherwise healthy patients who are overweight and those with class 1 obesity do not have an increased risk of most major adverse outcomes following noncardiac surgery compared with patients with normal body mass index (BMI) [5], with the exception of venous thromboembolism. (See "Preoperative medical evaluation of the healthy adult patient", section on 'Obesity' and "Overview of the causes of venous thrombosis", section on 'Cardiovascular diseases'.)

It has been suggested that overweight and mostly class 1 obesity are associated with decreased morbidity and mortality in a number of surgical, critical care, and medical studies [6-8]; this has been called the "obesity paradox." In several studies of surgical and critical care patients, otherwise healthy patients who are overweight and patients with class 1 obesity had comparable or decreased morbidity and mortality compared with patients with normal BMI, although outcomes were worse for underweight patients and for those with more severe obesity [9-11]. However, patients with class 1 obesity with metabolic syndrome or other comorbidities do have higher risks of postoperative morbidity and mortality than patients with normal BMI [12,13].

Class 2 and 3 obesity — Increased BMI has been identified as a modest independent risk factor associated with several specific perioperative outcomes:

●In two database studies, increasing BMI was independently associated with perioperative pulmonary complications following ambulatory and bariatric surgery, respectively [14,15].

●Increasing BMI has also been independently associated with a variety of adverse outcomes after cardiovascular [8], spine [16], and kidney [17] surgery, including greater hospital length-of-stay, estimated blood loss, longer operative times, surgical site infections, renal failure, and prolonged assisted ventilation.

●In a large Danish registry study of patients who underwent hip or knee replacement surgery, the incidence of major adverse cardiovascular events and mortality followed a U-shaped curve, with highest risk in patients who were underweight or severely obese [18]. However, high burden of comorbidities may have explained increased risk in patients with severe obesity.

●A validated scoring system (the Obesity Surgery Mortality Risk Score [OS-MRS]) for mortality after gastric bypass for severe obesity includes five variables, one of which is a BMI of >50 kg/m² [19]. Most, but not all, studies have reported that the OS-MRS is useful for predicting mortality after obesity surgery [20].

Comorbid conditions may be more important than BMI for perioperative risk assessment of patients with obesity. BMI does not account for sex, adipose tissue distribution, visceral fat accumulation, and age-related changes in muscle mass. These factors are critical determinants of metabolically healthy versus metabolically compromised severe obesity. Although BMI is easy to obtain and therefore used universally to categorize severity of obesity, including in outcome studies, indices other than BMI (eg, waist to hip ratio, waist circumference, and percent body fat) may more accurately predict metabolic health and comorbid conditions, and may also better stratify perioperative risk [21,22].

PREOPERATIVE EVALUATION — In addition to the usual preanesthesia evaluation, for patients with obesity we focus the evaluation on conditions that are more prevalent in the patients with obesity, require optimization, may affect the decision to operate, and/or could affect anesthesia care (figure 1). These issues are evaluated with a medical history, review of systems, anesthesia directed physical examination, and in some cases, preanesthesia testing. (See "Preoperative evaluation for anesthesia for noncardiac surgery" and "Preoperative medical evaluation of the healthy adult patient".)

For major surgery in the patients with severe obesity, many experts, including this author, recommend that the preoperative evaluation should include consultation with an anesthesiologist [23]. However, there is no high-quality evidence to identify which patients would benefit from an anesthesiology consultation prior to the day of surgery.

Patients with obesity and others with significant medical issues may benefit from the expanding multidisciplinary concept of perioperative medicine. This integrative approach includes patient-centered shared decision-making among the patient and various medical caregivers, starting with the decision to perform surgery, through preoperative preparation, procedure, discharge, and recovery. This framework may also incorporate evidence-based and often procedure-specific enhanced recovery after surgery (ERAS) standardized evaluation and care protocols; definitive data regarding outcomes of ERAS pathways specific to patients with obesity undergoing general surgery are not yet available. However, ERAS protocols for bariatric surgery have been developed [24,25] and implemented with results suggesting outcomes improvement for pain, opioid consumption, nausea, length-of-stay, and cost, without increased morbidity, provided protocol adherence is high [26-28]. (See "Enhanced recovery after gynecologic surgery: Components and implementation" and "Enhanced recovery after colorectal surgery" and "Anesthetic management for enhanced recovery after major noncardiac surgery (ERAS)".)

Comorbidities — Medical conditions associated with obesity are discussed separately; those that may affect perioperative care are discussed here. (See "Overweight and obesity in adults: Health consequences".)

Obstructive sleep apnea — Obstructive sleep apnea (OSA) is the most prevalent sleep-related breathing disorder in patients with severe obesity. All patients, including those with obesity, should be specifically screened for OSA and sleep-related breathing disorders preoperatively, as these disorders often go undiagnosed. Screening should include the use of a screening tool (eg, STOP-Bang (table 2) or Berlin (table 3) questionnaires) and assessment for clinical features of OSA (table 4). For patients who screen positive, serum bicarbonate should be measured. An elevated serum bicarbonate increases the specificity of OSA screening tools, and may indicate carbon dioxide (CO₂) retention, which can be associated with sleep-related breathing disorders [29]. Screening for OSA is discussed separately. (See "Surgical risk and the preoperative evaluation and management of adults with obstructive sleep apnea", section on 'Screening with a questionnaire'.)

For patients with known OSA, the severity of the disease and adequacy of treatment should be assessed preoperatively. They should also be assessed for associated medical conditions, including obesity hypoventilation syndrome (OHS), hypertension, coronary artery disease, cardiac arrhythmias, pulmonary hypertension, insulin resistance, and type 2 diabetes mellitus. (See "Surgical risk and the preoperative evaluation and management of adults with obstructive sleep apnea", section on 'Patients with known OSA'.)

OSA is associated with increased sensitivity to the respiratory-depressant effects of sedatives and opioids, a tendency to obstruct the airway when sedated or during mask ventilation, and more difficult laryngoscopy. (See "Intraoperative management of adults with obstructive sleep apnea".)

Preoperative risk assessment, recommended evaluation, and preoperative management of patients with known OSA are discussed separately. (See "Surgical risk and the preoperative evaluation and management of adults with obstructive sleep apnea".)

Obesity hypoventilation syndrome — OHS is defined as the presence of awake alveolar hypoventilation in an individual with obesity, which cannot be attributed to other conditions associated with alveolar hypoventilation. Patients with obesity and a strong clinical suspicion of OHS who are to undergo moderate or high-risk surgery should be screened for CO₂ retention and hypoxemia with serum electrolytes and arterial blood gases. An echocardiogram to assess global cardiac function, pulmonary hypertension, and specifically right heart function is suggested by some experts, including the author, for patients with clinical signs of OHS and CO₂ retention. (See "Clinical manifestations and diagnosis of obesity hypoventilation syndrome", section on 'Assess complications'.)

The vast majority of patients with OHS have OSA, and up to two-thirds have pulmonary hypertension. Hypertension, congestive heart failure, and insulin resistance are more common in patients with OHS than in patients with eucapnic obesity. (See "Clinical manifestations and diagnosis of obesity hypoventilation syndrome", section on 'Assess complications'.)

Patients with OHS are sensitive to the respiratory-depressant effects of sedatives and opioids, and supplemental oxygen may increase hypercapnia unless administered with noninvasive positive airway pressure therapy. (See "Treatment and prognosis of the obesity hypoventilation syndrome", section on 'Avoidance of alcohol and sedatives'.)

Because of these issues, patients with OHS are more likely to have difficulty weaning from mechanical ventilation than other patients, including during emergence from anesthesia. (See "Clinical manifestations and diagnosis of obesity hypoventilation syndrome", section on 'Clinical manifestations'.)

Hypertension — Hypertension is strongly associated with excess body weight (both overweight and obesity) [30]. Poorly controlled hypertension is associated with labile blood pressure (BP) during general anesthesia and increases in cardiac, neurologic, and renal complications. Baseline BP measurements should be recorded prior to the day of surgery to assess the level of control, and nonurgent surgery postponed to improve management of poorly controlled hypertension (systolic >170 mmHg; diastolic >110 mmHg). (See "Anesthesia for patients with hypertension", section on 'Perioperative risk assessment'.)

Cardiovascular disease — Obesity is associated with increased risks for cardiovascular disease (CVD), including coronary heart disease (CHD), cerebrovascular disease, heart failure, and atrial fibrillation. There is a linear relationship between body mass index (BMI) and the incidence of CVD. (See "Overview of established risk factors for cardiovascular disease", section on 'Obesity' and "Obesity: Association with cardiovascular disease", section on 'Association of obesity with various conditions'.)

The usual assessment for CVD by history and physical examination can be misleading due to obesity-related symptoms such as poor exercise tolerance, dyspnea, and lower extremity edema, which may not be of cardiac origin. We agree with the a 2009 statement from the American Heart Association on cardiovascular evaluation and management of surgical patients with severe obesity [4]. That advisory recommends that patients with severe obesity and at least one risk factor for CHD (diabetes, smoking, hypertension, or hyperlipidemia) or poor exercise tolerance should have a 12-lead electrocardiogram (ECG) and chest radiograph prior to surgery. Further cardiac work-up may be indicated based on the results of these tests. Other elements of preoperative cardiac evaluation and management are similar to those for patients with normal BMI and are discussed separately. (See "Evaluation of cardiac risk prior to noncardiac surgery" and "Management of cardiac risk for noncardiac surgery".)

Recommendations for preoperative evaluation and management of patients with obesity and with a history of cardiac disease are discussed elsewhere. (See "Management of cardiac risk for noncardiac surgery" and "Evaluation of cardiac risk prior to noncardiac surgery", section on 'Patient risk factors'.)

Diabetes mellitus — Type 2 diabetes mellitus is strongly associated with obesity. A detailed history of diabetes management and an assessment of the level of glycemic control are helpful in guiding diabetic therapy in the perioperative period. For elective major surgery preoperative glycosylated hemoglobin (HbA1C) assessment is indicated in patients with obesity, as preoperative optimization may be needed. Elevated preoperative HbA1C levels are associated with an increased risk of perioperative morbidity, although not specific to patients with obesity alone. (See "Anesthesia for patients with diabetes mellitus and/ or hyperglycemia", section on 'Level of blood glucose control'.)

Recommendations for HbA1C targets prior to bariatric surgery include a value of 6.5 to 7 percent or less for all patients, or 7 to 8 percent or less in difficult to control diabetic patients [31]. A study of the Scandinavian Obesity Surgery Registry showed an increased risk for severe complications following gastric bypass surgery at HbA1C levels above 5.7 percent even in the absence of diabetes [32].

Perioperative management of diabetic patients is discussed separately. (See "Anesthesia for patients with diabetes mellitus and/ or hyperglycemia" and "Perioperative management of blood glucose in adults with diabetes mellitus", section on 'Preoperative evaluation and planning'.)

Metabolic syndrome — Metabolic syndrome is defined as the co-occurrence of metabolic risk factors for both type 2 diabetes and CVD (abdominal obesity, insulin resistance, dyslipidemia, and hypertension). The definition and medical implications of this syndrome are described in detail elsewhere. (See "Metabolic syndrome (insulin resistance syndrome or syndrome X)".)

The diagnosis of metabolic syndrome is associated with a higher risk of morbidity after surgery. Each pathophysiologic element contributing to metabolic syndrome should be assessed to identify which components can be optimized prior to surgery and to guide the perioperative care. In a retrospective single-institution study of patients who underwent total joint arthroplasty, patients with well controlled metabolic syndrome had similar rates of complications and length of hospital stay as healthy patients, whereas patients with at least one uncontrolled component of metabolic syndrome had higher rates of complications and length-of-stay [33]. Examples of other studies that have reported increased perioperative risk in patients with metabolic syndrome include the following:

●A registry study of data from the Bariatric Outcomes Longitudinal Database found that metabolic syndrome was an independent risk factor for postoperative pulmonary complications and mortality after bariatric surgery [15].

●Registry studies using data from the American College of Surgeons National Surgical Quality Improvement Program (NSQIP) database have found that patients with modified metabolic syndrome (ie, obesity, hypertension, and diabetes) were at higher risk of complications and prolonged length-of-stay after laparoscopic adrenalectomy [34] and pancreatectomy [35], and in addition, mortality after various noncardiac procedures [12] and liver surgery [36].

Kidney disease — The risk of chronic kidney disease (CKD) is increased (relative risk [RR] 2.3, 95% CI 1.1-4.9) in patients with severe obesity (BMI of ≥35 kg/m²) compared with persons with normal BMI [37], but it is unclear whether obesity is an independent risk factor for CKD. We screen patients with obesity preoperatively for kidney disease as we would for normal weight patients, based on other risk factors (eg, hypertension, diabetes, age >65 years, surgical risk). (See "Preoperative medical evaluation of the healthy adult patient", section on 'Kidney function' and "Preoperative evaluation for anesthesia for noncardiac surgery", section on 'Kidney disease' and "Early detection of chronic kidney disease", section on 'Risk factors' and "Overweight and obesity in adults: Health consequences", section on 'Chronic kidney disease'.)

Older age — For patients over 50 years of age with severe obesity, we have a low threshold to ask for preoperative pulmonary and cardiology consultation, and to order preoperative sleep studies and echocardiography. Older patients with severe obesity should receive enhanced preoperative efforts towards improving mobility, exercise tolerance, diet, sleep, and pain management before surgery. (See "Overview of prehabilitation for surgical patients".)  

The combination of increasing age and severe obesity may increase perioperative morbidity and mortality more significantly than either alone; the combination of the two is associated with delayed discharge, increased complications, readmission, and early postoperative mortality [38-40]. Multiple studies have reported increased perioperative mortality in older patients with obesity, primarily studied in patients undergoing bariatric surgery [19,41-43].

Older age and severe obesity each decrease cardiovascular reserve and musculoskeletal fitness, which may increase perioperative risk. In a retrospective database review of over 44,000 patients who underwent bariatric surgery, poor preoperative functional status was the strongest predictor of early postoperative mortality [38]. Thus, older patients with obesity may require more intensive and extended monitoring in the immediate postoperative period than younger patients.

Older age is associated with multiple comorbidities that increase perioperative risk. These issues are discussed separately. (See "Anesthesia for the older adult", section on 'Impact of age-related physiologic changes on anesthetic care'.)

Airway assessment — The preanesthetic evaluation of all patients, regardless of the planned type of anesthesia, must include an airway assessment, including risk factors for difficulty with airway management, the history of prior attempts at airway management, and risk factors for aspiration. The plans for airway management during anesthesia follow from this assessment, and may require advanced airway management techniques. Patients with obesity desaturate more quickly during apnea (eg, during attempts at securing the airway). Therefore, equipment and personnel for a variety of airway management strategies should be arranged in advance for these patients. Awake intubation may be necessary in some cases (algorithm 1 and algorithm 2). (See "Airway management for induction of general anesthesia", section on 'Airway assessment' and "Management of the difficult airway for general anesthesia in adults", section on 'Recognition of the difficult airway' and "Management of the difficult airway for general anesthesia in adults", section on 'Planning the anesthetic approach'.)

Obesity and/or an increase in neck circumference are risk factors for difficulty with mask ventilation, supraglottic airway ventilation, and video laryngoscopy (table 5 and table 6 and table 7 and table 8). It is less clear whether obesity increases difficulty with direct laryngoscopy or endotracheal intubation if patients are optimally positioned and prepared [39-43]. (See "Airway management for induction of general anesthesia", section on 'Obesity as a risk factor'.)

Preoperative testing — The need for preoperative testing should be determined by the patient's comorbidities and the surgical risk, including the expected recovery and need for opioid analgesia. Most preoperative testing for patients with obesity is performed as it would be for normal weight patients. (See "Preoperative evaluation for anesthesia for noncardiac surgery", section on 'Preoperative testing'.)

Our general approach to preoperative testing for patients with obesity is as follows:

●All patients with obesity – Blood pressure (BP), HBA1C, screening test for OSA, such as STOP-Bang questionnaire (table 2), and clinical assessment for sleep-related breathing disorders. (See 'Obstructive sleep apnea' above and 'Obesity hypoventilation syndrome' above.)

●Obesity with known sleep-related breathing disorders or who screen positive for such disorders – Further testing individualized, taking into account the extent and nature of the planned procedure; may include serum electrolytes with bicarbonate determination, arterial blood gases, ECG, and echocardiogram. (See "Surgical risk and the preoperative evaluation and management of adults with obstructive sleep apnea" and "Preoperative medical evaluation of the healthy adult patient", section on 'Obstructive sleep apnea' and 'Obesity hypoventilation syndrome' above.)

●Obesity (BMI of >40 kg/m²) with a risk factor for CHD (diabetes, smoking, hypertension, or hyperlipidemia) or poor exercise tolerance – Twelve-lead ECG and chest radiograph (posteroanterior and lateral). (See 'Cardiovascular disease' above.)

We have a low threshold to order preoperative sleep studies and echocardiography for patients with severe obesity who are >50 years of age, as discussed above. (See 'Older age' above.)  

PREOPERATIVE PREPARATION — Most preoperative instructions for patients with obesity, such as fasting duration, do not differ from normal weight patients. Preoperative evaluation and perioperative medication management are discussed separately:

●(See "Preoperative evaluation for anesthesia for noncardiac surgery".)

●(See "Preoperative medical evaluation of the healthy adult patient".)

●(See "Perioperative medication management".)

●(See "Preoperative fasting in adults".)

Positive airway pressure therapy — Patients with obesity with a diagnosis of obstructive sleep apnea (OSA) or obesity hypoventilation syndrome (OHS) who have been using continuous positive airway pressure (CPAP) or bilevel positive airway pressure (BPAP) therapy should be instructed to adhere to their treatment regimen up to the day of elective surgery to maintain the benefits of treatment. The most important of these include reduced tongue volume and increased volume of the pharyngeal space (an effect that occurs following four to six weeks of therapy) [44], improved cardiac parameters [45-47], and improved ventilatory drive in patients with OHS [46]. CPAP or BPAP should be continued perioperatively whenever possible. (See "Obstructive sleep apnea: Overview of management in adults", section on 'Positive airway pressure (PAP) therapy' and "Noninvasive positive airway pressure therapy for the obesity hypoventilation syndrome".)

The decision to initiate therapy in patients newly diagnosed with OSA or OHS or to delay surgery for treatment is discussed separately. (See "Treatment and prognosis of the obesity hypoventilation syndrome" and "Surgical risk and the preoperative evaluation and management of adults with obstructive sleep apnea", section on 'Proceeding with further evaluation or surgery' and "Surgical risk and the preoperative evaluation and management of adults with obstructive sleep apnea".)

Other aspects of the evaluation and preoperative management of patients with OSA are discussed in detail separately. (See "Surgical risk and the preoperative evaluation and management of adults with obstructive sleep apnea".)

Patients with previous weight-loss surgery — Following weight-loss surgery, particularly gastric banding or sleeve gastrectomy, patients should be assessed for any signs or symptoms of dysphagia that may indicate an increased aspiration risk. (See "Anesthesia for the patient with obesity", section on 'Choice of airway device'.)

Ambulatory versus inpatient surgery — The decision to perform surgery on an inpatient or outpatient basis must be individualized. Many clinicians, including the author, agree that comorbidities should be considered when making the decision to perform ambulatory surgery in patients with severe obesity, including those with OSA. Other important considerations include the type of anesthesia administered (ie, monitored anesthesia care, regional anesthesia, or general anesthesia), the risk level of the surgical procedure, and requirements for postoperative care. We consider patients with super obesity (body mass index [BMI] >50 kg/m²) poor candidates for ambulatory surgery if the procedure requires general anesthesia and postoperative opioid administration. We admit such patients to the hospital for at least overnight observation in a monitored setting. (See "Office-based anesthesia", section on 'Patient selection' and "Surgical risk and the preoperative evaluation and management of adults with obstructive sleep apnea", section on 'Ambulatory versus inpatient surgery'.)

Anesthesia for patients with obesity is performed in the ambulatory surgery setting for many procedures, including bariatric surgery. The literature on perioperative outcomes after ambulatory surgery for such patients is limited [48-50]. A systematic review conducted by the Society for Ambulatory Anesthesia Committee on Clinical Practice Guidelines found that there was insufficient evidence to create guidelines for selection of patients with obesity for ambulatory surgery [3]. However, the review found that patients with super obesity (BMI of >50 kg/m²) may be at increased risk of perioperative complications, some of which occur in the immediate postoperative period [51,52]. Patients with lower BMIs were not at increased risk of complications as long as comorbidities were minimal or optimized [48,49].

For patients with severe obesity, logistical factors are important when determining the feasibility of outpatient surgery performed at a freestanding facility (eg, availability of appropriately sized equipment, sufficient personnel, and transfer agreements with external facilities).

In general, the decision to discharge patients with obesity following surgery should be based on the usual surgical factors, patient comorbidities, and the patient's home support structure.

In addition, an established clinical pathway with tailored discharge criteria for patients with severe obesity is ideal [53-55]. Many new enhanced recovery after surgery (ERAS) protocols aim to achieve such optimized pathways for specific populations and procedures. (See "Anesthesia for the patient with obesity", section on 'Discharge criteria' and "Office-based anesthesia", section on 'Recovery and discharge'.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Preoperative medical evaluation and risk assessment".)

SUMMARY AND RECOMMENDATIONS

●Perioperative risk – Healthy patients who are overweight and those with class 1 obesity do not appear to be at increased risk of adverse outcomes following noncardiac surgery (with the exception of venous thromboembolism) compared with patients who are not obese. Severe obesity or obesity with comorbidities increases the risk of postoperative morbidity and mortality (table 1). (See 'Perioperative risks in patients with obesity' above.)

●Preoperative evaluation

•Comorbidities prevalent in patients with obesity include obstructive sleep apnea (OSA), obesity hypoventilation syndrome (OHS), hypertension, heart disease, diabetes, metabolic syndrome, and kidney disease. For patients with known comorbidities, the preoperative medical evaluation should assess the status of the disease and initiate measures to minimize the risk of complications from surgery and anesthesia. (See 'Comorbidities' above.)

•For patients without known comorbidities, the possibility of undiagnosed disorders associated with obesity should be evaluated by review of systems and, in selected cases, by screening tests. Our approach to preoperative testing is as follows (see 'Preoperative testing' above):

-All patients with obesity – Blood pressure (BP), glycated hemoglobin (HBA1C), screening test for OSA, such as STOP-Bang questionnaire, and clinical assessment for sleep-related breathing disorders (table 2). (See 'Obstructive sleep apnea' above and 'Obesity hypoventilation syndrome' above.)

-Obesity with known sleep-related breathing disorders or who screen positive for such disorders – Further testing individualized, taking into account the extent and nature of the planned procedure; may include serum electrolytes with bicarbonate determination, arterial blood gases, electrocardiogram (ECG), and echocardiogram. (See 'Obstructive sleep apnea' above and 'Obesity hypoventilation syndrome' above.)

-Severe obesity (body mass index [BMI] >40) with a risk factor for coronary heart disease (CHD; diabetes, smoking, hypertension, or hyperlipidemia) or poor exercise tolerance – Twelve-lead ECG and chest radiograph (posteroanterior and lateral). (See 'Cardiovascular disease' above.)

-Severe obesity in patients >50 years of age – We have a low threshold to ask for preoperative pulmonary and cardiology consultation, and to order preoperative sleep studies and echocardiography.

●Airway assessment – Patients with obesity should be evaluated for predictors of both difficult mask ventilation and difficult intubation, as additional equipment and skilled personnel should be readily available when difficulty is anticipated. These patients desaturate more quickly during periods of apnea than patients without obesity. (See 'Airway assessment' above.)

●Preoperative preparation

•Most preoperative instructions for patients with obesity, such as fasting duration, do not differ from normal weight patients. (See 'Preoperative preparation' above.)

•Patients who have been using continuous positive airway pressure (CPAP) or bilevel positive airway pressure (BPAP) therapy should continue this treatment regimen up to the day of surgery and perioperatively whenever feasible. (See 'Positive airway pressure therapy' above and "Surgical risk and the preoperative evaluation and management of adults with obstructive sleep apnea", section on 'Elective surgery'.)

•The decision to schedule surgery as an outpatient should be based on the usual surgical factors, patient comorbidities, and postdischarge home support structure. Patients with superobesity (ie, BMI of ≥50 kg/m²) may be at increased risk of complications in the immediate postoperative period; we admit these patients to the hospital for at least overnight observation in a monitored setting if surgery requires general anesthesia and postoperative opioid administration. (See 'Ambulatory versus inpatient surgery' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Roman Schumann, MD, who contributed to earlier versions of this topic review.