The prevalence of obesity is rapidly increasing worldwide. Pathophysiological changes associated with obesity influence multiple organs and increase the risk of comorbidities.1-4 Therefore, this patient population may be at a higher risk of perioperative morbidity. Nevertheless, it is generally recommended that body weight or body mass index (BMI) alone should not be used as the sole indicator of suitability for surgery or its location.5 Most anesthesiologists use a body weight or BMI “cut off” in their ambulatory anesthesia practice, which has gradually increased over the years. So what is the current evidence assessing the appropriate selection of obese patients scheduled for ambulatory surgery?
Selection of Adult Obese Patients for Ambulatory Surgery
In recent years, several large observational trials have evaluated the incidence of perioperative complications in the obese population. The factors contributing to increased adverse outcome include patient characteristics (e.g., male gender, coexisting medical conditions such as presence of obstructive sleep apnea [OSA], history of DVT or PE, history of bleeding disorder and impaired functional status) as well as surgical characteristics (i.e., degree of invasiveness) and surgeon’s experience.
We conducted a systematic review of the literature addressing the selection of adult obese patients scheduled for ambulatory surgery, which included 23 studies (13 prospective and 10 retrospective studies) and one systematic review.6 A total of 106,119 patients (n=62,476 in the prospective trials and n=43,643 in retrospective trials) were included in the analysis. Of these, 39,548 patients underwent laparoscopic gastric banding (not including the systematic review of laparoscopic bariatric surgery, which included 2,549 patients). This systematic review revealed that BMI alone might not influence perioperative complications or unplanned admission after ambulatory surgery.
The patients undergoing non-bariatric surgical procedures had an average BMI of 30 kg/m2, which typically has a low burden of comorbidities. This might suggest a conservative approach to selection in the obese population. The patients undergoing bariatric surgery had an average BMI of >40 kg/m2. However, bariatric surgical population (i.e., laparoscopic gastric banding) underwent screening for comorbidities, which were optimized, preoperatively. Thus, one could suggest morbidly obese patients (BMI>40 kg/m2) with optimized comorbid conditions could undergo ambulatory surgery.
This systematic review also revealed that super obesity (i.e., BMI >50 kg/m2) might be associated with a higher risk of postoperative complications, particularly if these patients have significant comorbidities such as OSA, obesity-related hypoventilation syndrome, pulmonary hypertension, resistant systemic hypertension, significant coronary artery disease, resistant cardiac failure, bleeding disorder and chronic renal failure on dialysis.7
Selection of Adult Patients With OSA for Ambulatory Surgery
One of the major co-morbidities associated with obesity includes OSA.8,9 It is estimated that 60-70 percent of the morbidly obese have OSA. Because 60-70 percent of patients with OSA are undiagnosed, preoperative evaluation should include screening for OSA using tools such as the STOP-BANG questionnaire. However, it is recommended that five or six positive responses out of a possible eight questions on the STOP-BANG tool be used to determine a possibility of moderate to severe OSA.10,11 If OSA is suspected during preoperative evaluation, one could proceed with a presumptive diagnosis of OSA.9,12
A recent systematic review of published literature assessed the perioperative complications in patients with OSA undergoing ambulatory surgery.12 Patients with OSA had a greater number of comorbidities, including hyper-tension, diabetes, and obesity and higher ASA Physical Status score. Although more frequent oxygen desaturation requiring oxygen supplementation was documented in patients with OSA, there were no differences between the OSA and non-OSA patients with respect to anesthesia-related complications, unanticipated hospital admission and mortality. However, it must be emphasized that most studies used protocol-based perioperative care, which may have contributed to a safe perioperative course. There is emphasis on limiting opioid dose and exercise of caution in patients who develop prolonged and frequent severe respiratory events (e.g., sedation analgesic mismatch with opioids, desaturation and apneic episodes) in the postoperative period.
Overall, patients with inadequately treated co-morbid conditions are not suitable for ambulatory surgery. Patients with a known diagnosis of OSA (who are typically prescribed CPAP preoperatively) may be considered for ambulatory surgery if their comorbid medical conditions are optimized and they are able to use a CPAP device in the postoperative period. It appears that postoperative CPAP use may be protective against opioid-induced respiratory depression. Patients who are unable or unwilling to use CPAP after discharge may not be appropriate for ambulatory surgery.
Patients with a presumed diagnosis of OSA, based on screening tools such as the STOP-BANG questionnaire, can be considered for ambulatory surgery if their comorbid conditions are optimized and if postoperative pain relief can be provided predominantly with non-opioid analgesic techniques. Of note, no guidance could be provided for OSA patients undergoing upper-airway surgery due to limited evidence.
Postoperative Care After Discharge Home
One of the major con-cerns after ambulatory surgery is nocturnal apnea with catastrophic consequences. Postopera-tive surgical stress response, anxiety, pain, and opioid use can cause sleepdeprivation and fragmenta-tion, which may reduce REM sleep. Upon resolution of the stress response rebound REM sleep may ensue, which may exacerbate sleep disorders and increase the potential airway obstruction and life-threatening apnea. Of note, fewer sleep disturbances occur after mild to moderately invasive surgery, commonly performed on an outpatient basis, than inpatient surgical procedures. Because the risk of respiratory complications may last for several days after surgery, it is important that post-discharge instructions emphasize the potential for aggravation of OSA and the need to use opioids judiciously for several days after recovery from the surgical procedure.
It is necessary that we be involved with post-discharge care, which includes education of patients and their caregivers regarding the need for increased vigilance after discharge home. Because opioids are the biggest culprits in post-discharge complications, patients should be advised to limit opioid use and, importantly, surgeons should be advised not to primarily use opioid-based analgesia. Patients on preoperative CPAP should be advised to use their CPAP device whenever sleeping, even during the daytime, and for several days postoperatively. Also, patients should be advised against sleeping in the supine position. Patients who are assumed to have OSA based on the screening questionnaire should be advised to follow up with their primary physician for possible sleep study.
Obese patients, particularly those with OSA, are at a high risk of perioperative complications that might last for several days after surgery. There is uncertainty regarding scheduling obese and/or OSA patients for outpatient surgery. Clearly, selecting a patient for an ambulatory procedure is a dynamic process, which depends on the complex interplay between patient characteristics (i.e., coexisting medical conditions), invasiveness of the procedure and anesthetic technique as well as postoperative opioid requirements. Therefore, attempts to address individual factors without consideration of others is fraught with flaws. Finally, developing and implementing protocols (clinical pathways) is the best way to avoid adverse events and improve postoperative outcome.
Girish P. Joshi, M.D., M.B.B.S., FFARCSI is Professor of Anesthesiology and Pain Management, and Director, Perioperative Medicine and Ambulatory Anesthesia, University of Texas Southwestern Medical Center, Dallas.