A large number of patients have ambulatory surgery [8]. The perioperative period is particularly high risk for patients with or at high risk for OSA due to the effect of anesthesia, narcotics and sedatives. Several studies found patients with OSA undergoing non-cardiac surgery have higher incidence of post-operative hypoxia, respiratory failure, cardiac events and ICU transfers compared to those without OSA [4,9]. An ability to predict patients at greater risk for postoperative complications would help hospitals target effective resource utilization while complying with various guidelines for managing OSA patients postoperatively. The 2006 American Society of Anesthesiologists (ASA) guideline for perioperative management of patients with OSA, which the SJHC protocol was based upon, recommends postoperative monitoring in the PACU for at least 4 hours, and for 7 hours after an episode of airway obstruction or hypoxemia.¹ Subsequent publications have recommended different approaches to postoperative monitoring. Despite these recommendations, many institutions do not have a policy for perioperative management of patients with OSA [10], due to a lack of evidence clarifying duration of monitoring and or prevention of clinically significant adverse events. The implementation of the postoperative monitoring of OSA patients can have significant resource implications for hospitals. Our institution adopted a 4 hours PACU monitoring policy on the basis of the 2006 ASA guidelines. The protocol was chosen as it identifies only higher risk patients, which allowed us to restrict the number of patients monitored. This retrospective chart review found the mean time for patients who had desaturations in the PACU occurred at 1.46 hours of admission; 69/75 (92.00%) with desaturation between 0-2 hours and 6/75 (8.00%) with desaturation between 2-3 hours. Females with BMI≥35 with or at risk for OSA were more likely to have desaturation. These findings are similar to that of a study of perioperative risk assessment in patients with a propensity for OSA [11].

In general sleep physiology changes with age and gender [12-14]. Female have better objective sleep quality with shorter sleep onset latency and better sleep efficiency than male [12,15]. Factors that can impact female more than male sleep efficiency including anxiety and depression and hormonal changes specifically luteal phase of the menstrual cycle [16-18]. However, OSA is more common in men than women in the general population with a male to female ratio ranges 3:1 to 5:1 [19-21]. Obesity a well-known risk for OSA, and higher body mass index (BMI) is associated with greater severity of OSA for both sexes.²² But for the same AHI women tends to be more obese than men [23,24], this is likely due to differences in fat distribution between the sexes [25]. In our study, women with moderate AHI had similar proportion of desaturation as compared to male with sever AHI which can be explained by the fat distribution differences between genders which has physiological and mechanical effect in patients with OSA [26]. Female who are obese and with OSA have shown to have significantly increased hypercapnic and hypoxic response, which is not the case in male [27]. Furthermore, women with OSA are less likely to be evaluated and diagnosed for OSA [28]. In our study, the limitation for gender difference specifically female is the small numbers (N=62) with BMI >35 (N=24) and AHI moderate-severe (N=12/16)) are more likely to have post-operative desaturation.

Procedural related risk factors such as surgical site, surgical (anesthesia) duration, anesthetic techniques and emergency surgery have been shown to predict peri-operative complications [29]. In particular pulmonary complications for non-cardiac-thoracic surgeries requiring greater than 2-hours anesthesia and mechanical ventilation would need for prolonged oxygen therapy and atelectasis which required ICU admission may complicated by increasing post-operative-mortality and increasing ICU/hospital length of stay [30]. Russell KM et al. [31] reported patients after ophthalmologic surgery found that the expected duration of PACU recovery depends on the operations that requires general anesthesia. Patients having orbitotomy and strabismus procedures had a median anesthesia recovery time 2 to 3 times longer than for other procedures and more likely to have prolonged recovery with other procedures. In addition, their post-hoc analysis found a higher proportion of patients with respiratory depression during anesthesia recovery also had OSA [31. Our study indicated that in our ambulatory surgery cohort 56/75 (78.67%) of the patients with desaturation had longer anesthesia duration between 181-200 minutes than those with shorter anesthesia duration.

A major determinant for discharge after ambulatory surgery is the quality of post-operative pain control. Opioid consumption in the PACU can be used as an earlier surrogate for poor global quality of recovery after surgery. An inverse relationship noted between opioid consumption in the PACU and global quality of recovery at 24-hours after the surgical procedure [32]. It is also known obese patients with or without OSA experiences frequent oxygen desaturation episodes post-operatively after total anesthesia followed by patient-controlled intravenous analgesia with morphine [33]. However, in our study the adjusted opioid dose is much less as compared to other published studies [32,34], which had a much higher opioid dose for the higher pain patients than the lower pain patients. This may well be because our anesthesiologists focus on opiate sparing techniques for OSA patients. Multimodal analgesia and regional analgesia techniques are used routinely.

Certain co-morbidities predispose adult patients for high risk of post-operative OSA includes obesity, hypertension, diabetes, male sex, alcohol use and large neck size [35], coupled with chronic opioid use [36]. In our study there is a high proportion of patients with desaturation had hypertension and diabetes. Therefore a robust screening questionnaire would be very useful to select that patient at risk such as the STOP-BANG questionnaire [37]. Studies have shown that the STOP-BANG questionnaire can identify 93% of those patients as being at risk for OSA [35,38]. However, that sensitivity would lead to the inclusion of substantially larger numbers of patients, which would have taxed hospital resources significantly.

In an aging population the frequency of OSA increases and plateau after 65 years [39]. In our study group, patients > 50 years old had a higher number of desaturations as compared those patient ≤ 50 years old. There are multiple risk factors associated with the older population desaturation post ambulatory surgery such as preferential deposition of fat around the pharynx which reduces airway patency [40]; overnight fluid shift to the neck affect the surface tension of the upper airway [41,42] and restriction of chest wall movement due to decrease lung volume [43]. The greatest exacerbation of OSA and sleep-disordered breathing has been shown to occur on postoperative day three [3], at which point all of our patients had been discharged home. We did not identify evidence of OSA related complications following discharge from hospital. It is not clear whether increased AHI and increase in desaturations after general anesthesia are associated with clinically significant events.

There are several limitations with our study. Due to a small study population and exclusion of higher risk patients from this ambulatory surgical hospital we did not find any clinically significant adverse postoperative events in our study patients. Patients admitted to the inpatient ward for postoperative oximetry can be awakened by the oximeter alarm, and commence breathing prior to developing any further complication. Another limitation of this study was the lack of dedicated apnea monitoring, both in PACU and on the ward. Apneas presumable occurred but the events were only recognized when there was a resulting desaturation and oximeter alarm. Our protocol did not include assessment for sedation analgesia mismatch, but patients in the cohort did not exhibit this finding: there was a low rate of opiate requirement, and minimal sedation.

The absence of clinically significant adverse effects is notable. We cannot know whether the overnight oximetry monitoring, and application of oxygen to those with desaturations, prevented any complications. However, the data show that the majority of patients in our cohort of select lower acuity patients could safely be discharged home on the day of surgery. These findings echo that of a recent study of patients undergoing surgery to relieve obstructive sleep apnea symptoms [44].

In conclusion, this retrospective chart review found that all desaturation events in PACU occurred within the first 3 hours of arrival to PACU. Patients with a PSG diagnosis of OSA appear to be at higher risk than those identified by preoperative screening. Females and those with a BMI >35 were more likely to have desaturations. We did not capture any clinically significant adverse events in our study patients. A larger study may be required to determine the utility and optimal duration of postoperative monitoring.