According to the World Health Organization, the prevalence of obesity has significantly increased over the past few decades [1]. The Center for Disease Control and Prevention cites that approximately a third of all adults in the United States are now obese [1]. Obesity is associated with multiple comorbidities, such as hypertension, type II diabetes mellitus, and coronary artery disease, many of which place patients at higher risk during surgery [1]. Consequently, the incidence of anesthesia-related problems is also higher in obese patients as compared to patients that are not obese [1]. Since obesity increases the risk for perioperative complications, it is imperative for anesthesia providers to understand special considerations for patients with high BMI and be equipped to manage these patients effectively [1]. 

Obesity is defined by body mass index (BMI), which is calculated by dividing body weight (kg) by height (m²) [1]. A BMI of 30 kg/m² or greater is used to define obesity [1]. Because fat distribution in the body can vary, obesity is often described as either peripheral or central [1]. Peripheral obesity involves increased fat deposition in the lower regions of the body, whereas central obesity involves higher abdominal or visceral fat deposition [1]. A waist circumference greater than 88 cm in women and 102 cm in men defines central obesity [1]. The classification of central obesity is an important distinction as it is more commonly associated with pathologic conditions [1]. Adipose tissue distributed in the central region of the body is more likely to produce inflammatory mediators that can increase the risk of metabolic disease and result in anesthesia complications [1]. 

Preoperatively, most anesthesia-related issues in patients with high BMI are associated with the respiratory system, and many of the special considerations for these patients are related to airway and breathing [1]. Obese patients are more likely to experience decreased lung volume, lung collapse, and abnormalities in lung and chest wall compliance [1]. Therefore, a thorough preoperative respiratory and airway assessment should be completed for all obese patients [1]. Anesthesiologists should especially enquire about a history of sleep-disordered breathing, gastroesophageal reflux, and difficulty with anesthesia in the past [1]. If needed, patients can be asked about sleep-disordered breathing using the STOP-BANG questionnaire [1]. A score of 5 or more indicates sleep-disordered breathing and would warrant referral to a specialist prior to surgery [1]. The measurement of neck circumference can be helpful to determine intubation difficulty, as a circumference over 60 cm increases the odds of unsuccessful intubation [1]. Arterial oxygen saturation also should be determined, as an arterial PCO₂ greater than 6 kPa has been associated with an increased risk of respiratory failure [1]. 

Another anesthesia consideration is that patients with high BMI should receive a detailed preoperative cardiovascular assessment [2]. The use of EKGs is critical as they allow for diagnosis of cardiac abnormalities that increase risk for developing potentially fatal arrythmias [1]. Elevated blood pressure should be noted since a systolic blood pressure ≥ 140 mmHg or a diastolic blood pressure of ≥ 90 mmHg is an independent risk factor for the development intraoperative cardiovascular injury [3]. 

Intraoperatively, steps should be taken to prevent or reduce the chance for a fall in oxygen saturation during anesthesia induction, as obese patients are more prone to hypoxia [1]. During preoxygenation, patients should maintain an upright head position of about 25 degrees [1]. Administration of metoclopramide prior to induction is appropriate to reduce the risk of aspiration [2]. Propofol is the induction anesthetic agent of choice, given its fast onset and short duration [2]. Its dose for continuous infusion is typically calculated based on total body weight [2]. However, some studies have concluded that for anesthesia induction, lean body mass is a more appropriate weight-based scale for propofol [2]. In general, dosages of almost all anesthetic drugs are reduced in obese patients, especially for those with sleep apnea who may be sensitive to general anesthetics [2]. Regional anesthesia can also be considered in obese patients as it does not require airway manipulation or general anesthetic agents [2]. 

By optimizing perioperative risk factors, anesthesiologists can increase the likelihood of a good surgical outcome for obese patients [3]. A thorough medical history considering respiratory and cardiovascular status, as well as routine screening for common medical conditions like obstructive sleep apnea, can decrease complications for obese patients undergoing surgery [3]. 

References 

1. Seyni-Boureima, R., Zhang, Z., Antoine, M., & Antoine-Frank, C. (2022). A review on the anesthetic management of obese patients undergoing surgery. BMC anesthesiology, 22(1), 1-13. 

2. Domi, R., & Laho, H. (2012). Anesthetic challenges in the obese patient. Journal of anesthesia, 26(5), 758-765. 

3. Ortiz, V. E., & Kwo, J. (2015). Obesity: physiologic changes and implications for preoperative management. BMC anesthesiology, 15(1), 1-12.