Obesity refers to an abnormally high percentage of body fat. The degree of obesity is generally estimated by the Body Mass index (BMI). More than 1/3 of US adults are considered obese, with a BMI ≥ 30 [1].

Approximately 4% of US adults are categorized as morbidly obese with a BMI ≥ 40 [2].

BMI = weight (kg)/Height (m²)

The calculated BMI does not take into account the nature of the patient’s frame or degree of muscularity. Therefore, the calculation generally overestimates obesity in patients with more lean body mass and underestimates it in those with less lean body mass.

While BMI-defined obesity showed high specificity (95% for men and 99% for women), it demonstrated poor sensitivity (36% for men and 49% for women) [3].

The utility of BMI is its convenience as a screening tool, not for diagnosis. It is strictly a height and weight-based calculation, and as such does not require calipers, submersion tubs, radiation-based scans, or impedance measurements.

Obesity can be described as peripheral or central. Central or android obesity is generally associated with increased oxygen consumption and higher rates of heart disease. Higher levels of proinflammatory cytokines, also seen in central obesity, are thought to contribute to increased levels of insulin resistance [4]. Gynecoid or peripheral obesity relates to patients with adipose tissue primarily deposited in the hips, buttocks, and thighs. It has been shown to be less metabolically active and not as strongly associated with cardiovascular disease.

Metabolic syndrome is a constellation of conditions associated with higher rates of heart disease and diabetes. It applies to individuals in whom at least three out of the following five diagnoses have been made: central obesity, hypertension, hypertriglyceridemia, low HDL, and elevated fasting glucose [5].

The incidence of metabolic syndrome in the US is approximately 40% by age 60 [6]. Patients at risk for metabolic syndrome should be screened appropriately for the comorbid conditions associated with the diagnosis, as this may impact anesthetic management and risk stratification.

Bariatric surgery is generally reserved for patients with a BMI of at least 40 kg/m². However, an individual with a BMI above 30 kg/m² may also be a candidate if any associated conditions are expected to improve with significant weight loss. Prior to surgery, patients are routinely involved in a multidisciplinary evaluation to select individuals in whom the likelihood of success justifies the risks of the procedure.

Obesity may be related to hypothyroidism, Cushing syndrome, insulinoma, hypogonadism, and hypothalamic disorders, to name a few. Related syndromes may also include Prader–Willi, leptin-deficiency, and Bardet–Biedl. Prior to surgery, a workup should exclude many of the various medical causes that may render a patient prone to excessive weight gain.

Obesity increases the risk of CAD, CVA, HTN, and NIDDM. It is also associated with liver disease, gallbladder disease, OSA, polycythemia, osteoarthritis, and infertility. It may also raise the risks of developing endometrial, breast and colon cancers as well as being an independent risk factor for DVT [7].

This procedure involves the creation of an anastomosis of the proximal gastric pouch to a segment of the proximal jejunum, bypassing most of the stomach and the duodenum. Patients lose an average of 50–60% of excess body weight within 1–2 years.

Procedures can be classified as either restrictive, malabsorptive, or both. The simplest restrictive procedure entails the laparoscopic placement of an inflatable gastric band around the upper portion of stomach. This serves to create a small pouch, which fills quickly upon eating to promote a feeling of fullness. This lower risk surgery offers the benefits of being reversible and having less chance of malabsorption.

A sleeve gastrectomy is also performed laparoscopically and promotes weight loss through the removal of approximately 80% of the stomach. This reduces the amount of food that can be consumed (restrictive) and may also decrease both absorptive and endocrinologic functions of the stomach.

Obstructive sleep apnea (OSA) is defined as the cessation of airflow during sleep, for at least 10 s, despite continuing ventilatory effort. To diagnose OSA, these events must occur five or more times per hour and result in a decreased SpO₂ of at least 4%.

In addition to the physiologic consequences of chronic hypoxemia and hypercarbia, patients with OSA are at higher risk for postoperative respiratory complications. This may potentially alter the anesthetic plan and postoperative disposition [8].

OSA is generally associated with central obesity, increased neck circumference, and/or micrognathia. It should also be considered in the differential diagnosis for patients presenting with RVH, LVH, polycythemia, or pulmonary hypertension. Although obesity is the biggest risk factor for OSA, it is possible to have one without the other. Only about 70% of patients with OSA are obese, so screening should not be limited solely to overweight patients.

It has been estimated that 4% of men and 2% of women have symptoms consistent with OSA. Furthermore, 82% of these men and 92% of these women, with moderate or severe sleep apnea, have not been diagnosed [9].

The STOP-BANG questions are answered “yes” or “no.”

For females, is your shirt collar 16 in./41 cm or larger?

The sensitivities of the STOP-BANG screening tool for an AHI (apnea hypopnea index) of >5, >15, and >30 were 86.1, 92.8, and 95.6%, respectively, with negative predictive values of 84.5 and 93.4% for moderate and severe OSA [10].

OSA is diagnosed with a polysomnogram or “sleep study.” This test detects and records the EEG, EKG, electrooculogram, pulse oximetry, capnography, airflow, esophageal pressure, blood pressure, pharyngeal and extremity electromyography, and room noise.