Ambulatory surgery is becoming increasingly popular, with the majority of surgeries now being performed on an outpatient basis. In 2018, there were over 19 million outpatient surgeries performed, and the volume of ambulatory surgery continues to grow each year ( The cost effectiveness, convenience, and efficiency of same-day surgeries has contributed to its popularity for both physicians and patients. As the prevalence of obesity continues to increase worldwide, so does the frequency of obese patients presenting for ambulatory surgery. According to the most recent National Health and Nutrition Examination Survey, 74.6% of the U.S. population is overweight or obese and an additional 9% is severely obese ( Even though obesity has been associated with a higher burden of medical comorbidities such as cardiovascular disease, diabetes, and obstructive sleep apnea (OSA), it has not been found to be an independent risk factor for perioperative complications (Mayo Clin Proc 2008;83:908-16). Many ambulatory surgery centers (ASCs) use a maximum BMI of 50 kg/m2 as the cutoff, often based upon the capacity of their equipment (Table 1) (Curr Opin Anaesthesiol 2020;33:724-31). However, to date, there have been conflicting recommendations regarding obese patients undergoing outpatient surgery.


Patient appropriateness for outpatient surgery must be established to minimize unanticipated admission, morbidity, and mortality. A thorough history with attention to comorbidities and physical examination is necessary. Functional capacity can be difficult to assess in obese patients due to limited mobility. There should be a low threshold for obtaining an EKG and investigating an abnormal result for undiagnosed cardiovascular disease and pulmonary hypertension. Altered airway anatomy and respiratory physiology puts obese patients at risk for hypoventilation and hypoxemia. As with every patient, a careful airway assessment is essential prior to the administration of anesthesia. With diminished neck mobility, increased neck circumference, and redundant tissues, obese patients have a higher incidence of difficult mask ventilation. However, Moon et al. concluded that obese patients do not have a higher incidence of difficult intubation compared to non-obese patients (Curr Opin Anaesthesiol 2016;29:141-5).

OSA is becoming more prominent among ASC patients. The prevalence of OSA in the general population ranges from 9%-25% and increases to 70% among bariatric surgical patients (Anesth Analg 2017;125:1301-8). Up to 90% of patients with OSA are untreated or undiagnosed. In addition, the diagnosis becomes more frequent with increasing BMI (Curr Opin Anaesthesiol 2016;29:141-5; Sleep 1997;20:705-6). The STOP-Bang questionnaire has high sensitivity in detecting moderate to severe OSA across different geographic regions and can be used as a reliable screening tool for the adult population (Table 2) (JAMA Netw Open 2021;4:e211009). Surgical patients with a STOP-Bang score of 3 are considered to be in the high-risk OSA (HR-OSA) category and have increased rates of perioperative complications (Anesth Analg 2016;123:452-73).


Undiagnosed and noncompliant HR-OSA patients have been shown to have a greater number of comorbidities and a four-fold increased likelihood of postoperative pulmonary complications, reintubation, and cardiac dysrhythmias (Anesth Analg 2017;125:1301-8). HR-OSA patients’ length of hospital stay after surgery is on average two days longer (Anesthesiology 2014;120:268-86). These high-risk patients are more likely to experience MI after surgery at a rate two- to five-fold higher than the non-OSA or low-risk (LR)-OSA populations (Curr Opin Anaesthesiol 2016;29:141-5; Anesth Analg 2017;125:1301-8). Patients with known OSA should be encouraged to increase CPAP compliance, including for daytime sleep, and be reminded to bring their CPAP machines on the day of surgery (Curr Opin Anaesthesiol 2020;33:724-31).

Even though robust studies are needed on the perioperative use of CPAP, the current ASA guidelines recommend preoperative use for at least three days and continued use postoperatively for previously noncompliant or undiagnosed patients. This has been demonstrated to improve ventilatory function in morbidly obese patients with severe OSA (Anesthesiology 2014;120:268-86; Indian J Anaesth 2016;60:420-3).

Given the overwhelming evidence available, consideration of LR-OSA versus HR-OSA status as well as whether the disease is treated or untreated may help determine if a patient is appropriate for the ASC. The Society of Anesthesia and Sleep Medicine does not recommend delaying or canceling surgery for further workup on the basis of presence of OSA alone. However, if evidence of ventilatory or diffusion defects are present, consideration for further evaluation is recommended (Anesth Analg 2016;123:452-73). Alternative anesthetic management strategies should be implemented for OSA patients at risk for opioid-induced postoperative airway obstruction and respiratory depression, including the use of opioid-sparing techniques (Curr Opin Anaesthesiol 2016;29:141-5). Patients with coexisting obesity-hypoventilation syndrome (OHS) will be especially sensitive to opioids and sedatives, and the American Thoracic Society clinical practice guidelines recommend CPAP over noninvasive ventilation (nasal cannula or a face mask) in ambulatory patients with coexistent OHS and OSA (Am J Respir Crit Care Med 2019;200:e6-24).

The planned surgery, patient condition, and potential anesthetic options should be considered when determining the venue for surgery. The Society for Ambulatory Anesthesia consensus suggests that obtaining disease optimization will allow for safe performance of the appropriate surgery in the outpatient setting, and that poor control merits in-hospital surgery (Curr Opin Anaesthesiol 2016;29:141-5).

Large, retrospective database studies highlight both the low complication rates (less than 1%) and the low mortality rates (ranging from 1 in 50,000-100,000) for outpatient surgery. Most readmissions are related to surgical causes (Curr Opin Anaesthesiol 2020;33:724-31). However, unanticipated hospital transfers and readmissions do occur. Whippey et al. found that surgery duration greater than one hour, high ASA Physical Status, advanced age, and increased BMI were common predictors of readmission (Can J Anaesth 2013;60:675-83). In addition, Mathis et al. highlighted seven independent risk factors contributing to 72-hour morbidity or mortality: overweight BMI, obese BMI, COPD, TIA/stroke, hypertension, previous cardiac surgery, and prolonged operative time (Curr Opin Anaesthesiol 2020;33:724-31; Anesthesiology 2013;119:1310-21). Ranum et al. published the leading causes of anesthesia-related liability claims in ASCs and determined that peripheral nerve injury and harm related to intubation were the most common reasons for litigation. The most common comorbidity for both types of claims was obesity. Anatomical changes related to obesity predisposes this patient population to these specific injuries (J Patient Saf 2021;17:513-21).

For years, ASCs have provided high patient satisfaction with lower costs as compared to traditional hospitals. In addition, improved surgical techniques allow for more types of procedures being performed at ASCs. BMI alone should not be the deciding factor in determining suitability for surgery at an ASC. The availability of resources, experience of the staff, and type of surgical procedure should also be taken into consideration for this important decision. Thoughtful preoperative assessment of patients’ comorbidities can help to guide the selection of analgesia and anesthetic management for the obese ASC patient.