For 24,157 surgical patients given general anesthesia, but not specifically diagnosed with OSA, the risk of a critical respiratory event in the postanesthesia care unit (PACU) was 1.3% (hypoxemia 0.9%, hypoventilation 0.2%, airway obstruction 0.2%).103 Significant risk factors for adverse respiratory events postoperatively were older age, male gender, diabetes, and obesity. The choice of anesthetic drug was also an important contributing factor. Use of opioids, fentanyl, atracurium or thiopental, either alone or in combination, were associated with greater anesthetic risk with odds ratios ranging from 1.6 to 2.5.103 However, the risk factor of an OSA diagnosis was not studied in this population.103
Not all studies have endorsed a greater perioperative risk in OSA patients. A retrospective study of 234 OSA patients versus control group117 concluded that a preoperative diagnosis of OSA was not a risk factor for unanticipated admissions (23.9% vs 18.8%, odds ratio 1.4 95% CI 0.8–2.5). However, this study had a number of serious limitations that bring their findings into question. The study patients were scheduled for outpatient surgery implying that these OSA patients may have had less preexisting morbidity. Other limitations included a lack of information on the screening process and whether the anesthesia and surgical team altered their perioperative management based on the OSA diagnosis. A further confound was that the majority of OSA patients were using continuous positive airway pressure (CPAP) treatment. In addition, the incidence of unanticipated admission was an exceptionally high 19%–24% in both OSA and control groups, whereas the rate of unanticipated admission in ambulatory surgical surgery is normally around 1%–2%.118
In contrast to the above findings, a retrospective matched case-controlled study of OSA patients undergoing hip or knee replacement surgery95 reported longer hospital stays (OSA vs control 6.8 days vs 5.1 days, P < 0.007) and 2.5 times the number of serious postoperative complications (OSA vs control 24% vs 9%, P < 0.04). These serious complications included the need for urgent respiratory support and more ICU transfer. Despite the different findings, this study95 suffers from many of the same limitations as the above study117 given the retrospective nature and the inability to exclude a diagnosis of OSA in their control groups.
There are also a number of reports of OSA patients undergoing upper airway surgery, including UPPP, for surgical management of their sleep apnea.98,100–102,119–122 Postoperatively, there are reports of increased obstructions and desaturations98,119,121 and changes in systolic and diastolic blood pressure.119 It was further documented that postoperative complications were more frequent in OSA patients that had an increased AHI and higher levels of desaturation preoperatively (Table 3).98,102,121
Most studies are case reports, retrospective reviews or noncontrolled observational studies. This may contribute to the varied findings, i.e., why some studies, but not others, report more perioperative adverse events. Thus, although multiple case reports support increased perioperative risk of patients with OSA, there remains insufficient level 1 or 2 evidence to clarify if treated or untreated OSA patients are at increased risk during the perioperative period for either respiratory or cardiovascular adverse events. As level 1 studies may be difficult to perform, we may have to accept that these case reports or retrospective studies are sufficient evidence that OSA patients are at greater risk for perioperative adverse outcomes and greater emphasis should be placed on diagnosing patients with OSA and determining best practices during the perioperative period to reduce the risk for adverse outcomes.
Apneas and hypopneas have been shown to produce acute changes in systolic and diastolic blood pressure123 in patients not undergoing surgery. In a population of middle-aged adults with subclinical sleep-disordered breathing, large fluctuations in systolic blood pressure (23 ± 10 mm Hg) and diastolic pressure (13 ± 6 mm Hg) were observed during and after apneic events. Transient changes in heart rate mirror the acute arterial blood pressure responses to apneas; bradycardia develops during the obstructive event and is followed by abrupt tachycardia and decreases in left ventricular stroke volume immediately after apnea termination.124,125
As a consequence of the OSA-related increases in systolic blood pressure, high levels of myocardial blood flow are required to maintain the oxygen balance in heart muscles.126 In an animal model of limited coronary flow reserve, oxygen desaturation can result in myocardial ischemia, thus subsequently impairing left ventricular function.127 Preoperative hypoxemia, especially in OSA patients has been found to be a predictor of severe postoperative hypoxemia98,119,121 while decreases in arterial oxygen saturation (Spo2) have been found to be significantly higher on postoperative nights than preoperatively128,129 (Table 3). Thus patients with moderate to severe OSA may be at increased risk for myocardial infarction or congestive cardiac failure in the postoperative period.
There are numerous reports that support the link between OSA and cardiac arrhythmias and conduction disturbances.130–135 In a retrospective analysis of 400 nonsurgical OSA patients, sinus bradycardia was seen in 7%, second degree atrioventricular conduction block in 8%, and sinus arrest in 11% of these patients.104,133 Another study130 confirms 7% frequency of heart block (sinus arrest, II and III atrioventricular block) in nonsurgical OSA patients. Earlier studies suggested that heart block occurred exclusively with arterial oxygen desaturation below 72%,104 however, heart block with oxygen desaturation exceeding 4% has been noted.133 In 121 coronary artery bypass surgery patients, atrial fibrillation was more common in OSA patients and preoperative OSA with nocturnal hypoxemia was an independent predictor of postoperative atrial fibrillation.107
Pulmonary hemodynamics are also acutely altered during apneas resulting in oscillations in pulmonary artery pressure with each apnea.136 Prolonged severe hypoxemia results in greater changes in intrathoracic pressure and larger swings in pulmonary artery pressure. Greater inspiratory effort during the apnea in OSA patients promotes an increase in pulmonary capillary wedge pressure resulting in decreased right ventricular stroke volume. This reduction in ventricular stroke volume, in turn, leads to a diminished cardiac output at apnea resolution which occurs regardless of the postapneic tachycardia. In the animal model, pulmonary edema and deterioration of gas exchange has been shown to occur after 8 h of recurrent obstructive apneas.137 Incidences of fatal pulmonary edema have been reported in the postoperative setting138,139 and particularly in patients with OSA.140 With the increased risk of prolonged hypoxia in OSA patients, there is the distinct possibility of pulmonary edema occurring in the perioperative period.
Difficult tracheal intubation is a significant concern for anesthesiologists. Difficult tracheal intubation and OSA seem to share similar etiological pathways of predisposing upper airway abnormalities. A retrospective case-controlled study of 253 patients was conducted to determine the occurrence of difficult intubation in OSA patients.96 The OSA patients were matched with controls of the same age, gender, and type of surgery. Difficult intubation was assessed by laryngoscopy using the Cormack and Lehane classification.141 Difficult intubation was found to occur 8 times as often in OSA patients versus controls (21.9% vs 2.6%, P < 0.05).96 In OSA patients undergoing ear, nose, and throat surgery, a 44% prevalence of difficult intubation had similarly been reported.142 Furthermore, patients with severe OSA (AHI ≥40) were found to have a much higher prevalence of difficult intubation.143 A study of more than 1500 nonobese and obese patients concluded that increased age, male gender, pharyngo-oral pathology, and the presence of OSA are all associated with a more frequent occurrence of difficult intubation.144 The corollary of the relationship is also true, that is, patients with difficult tracheal intubation have also been shown to be at greater risk of having OSA.145 In a small retrospective study of 15 patients with difficult intubation, 53% (8 of 15) of patients were diagnosed with OSA.145 In a prospective study, 66% of patients with difficult intubation were subsequently found to have AHI >5.146 These reports suggest that anesthesiologists should refer patients with difficult intubation for PSG sleep investigation of OSA.
Apart from the above-mentioned studies, there is no research investigating the causal and anatomical relationship between OSA and difficult tracheal intubation and the implications for perioperative management. It can be assumed, but has yet to be proven, that a combination of the two conditions would increase the perioperative risk of patients. Despite the higher prevalence of OSA in patients with difficult intubation, it needs to be determined whether it is cost effective for all patients with difficult intubation to undergo a diagnostic sleep study and if preoperative CPAP treatment could ameliorate the difficulty with tracheal intubation.
Nasal application of CPAP is the most widely used treatment for OSA because of its efficacy and low level of invasiveness.147 CPAP acts as a pneumatic splint to prevent occlusion of the airway during sleep, thereby significantly reducing apneas and hypopneas and the associated hypoxic and hypercapnic events. CPAP has been shown unequivocally to alleviate the symptoms of OSA including: amelioration of excessive daytime sleepiness,148 restoration of quality of life,149 improvement in vigilance,150 concentration and memory,151 lessening of fatigue,152 reduction in health care usage,1 and a decrease in traffic accidents.148
The efficacy of CPAP has not been established in the perioperative setting. There is insufficient evidence from the literature to evaluate whether the perioperative use of CPAP may reduce adverse events in OSA patients undergoing surgery. It is not known whether CPAP can reduce the risk of perioperative cardiorespiratory events in OSA patients when the upper airway is further compromised by sedation, anesthesia or analgesia. There are no randomized controlled studies that specifically address this issue. The following is a summary of the possible potential beneficial effects of CPAP in OSA patients undergoing surgery.
In general, acute elevation in arterial blood pressure is a common adverse event in the perioperative setting that accounts for more than 10% of the complications in the PACU.153 There are a number of reports of serious postoperative hypertensive events in OSA patients.100,112,119 The efficacy of long-term CPAP treatment in reducing arterial blood pressure in OSA patients not undergoing surgery has been demonstrated.154–157 Acute CPAP use for 1–3 days in nonsurgical OSA patients with hypertension can lead to a reduction of arterial blood pressure (systolic blood pressure from 125 ± 15 mm Hg to 120 ± 10 mm Hg, diastolic pressure from 86 ± 16 mm Hg to 83 ± 12 mm Hg).158,159 However, the literature is not without controversy as others160 have reported that acute CPAP does not alter blood pressure. Apart from one case report112 documenting the beneficial effects of CPAP in treating hypertension in the postoperative period, there is no available evidence from randomized controlled studies. Evidence that acute CPAP treatment can reduce blood pressure perioperatively is required before the use of CPAP in the perioperative setting can be considered.
With regards to cardiac rhythm abnormalities, CPAP treatment reduces the number of apnea-associated cardiac arrhythmias133,161,162 and the beneficial effects of CPAP on sinus arrest and episodes of heart block during sleep have been reported.163 In a study of 17 patients, CPAP treatment reduced the number of arrhythmias from 1575 to 165 episodes per night (P < 0.01).163 These studies provide preliminary support for the use of CPAP for perioperative cardiac rhythm abnormalities among OSA surgical patients.
Cardiovascular adverse events with OSA patients in the perioperative setting are a growing concern. CPAP has been shown to improve cardiac function with long-term use164–166 but evidence of a beneficial cardiovascular effect with short-term CPAP use is required. A single night of CPAP was documented to reduce the variability in systolic and diastolic blood pressure and pulse interval during sleep.167 Also, a 10-min application of CPAP in patients with congestive heart failure was found to improve oxygen saturation, significantly decrease left ventricular stroke volume, reduce myocardial oxygen consumption, and reduce cardiac output.168 A favorable hemodynamic effect within a few minutes of application suggests a potential role for postoperative CPAP.
The level of evidence is poor regarding the benefits of postoperative CPAP. There are only three studies on the benefits of postoperative CPAP in OSA patients: a small prospective study,169 one case report109 and one retrospective study.95 The findings of these studies suggest that CPAP can alleviate postoperative airway obstruction, decrease major postoperative complications, and reduce the length of hospital stay in OSA patients undergoing surgery. However, all three studies have low evidence levels and suffer from methodological problems, including small sample sizes and the lack of an appropriate prospective, randomized, controlled design, thus, limiting the ability to generalize the results of these studies.
A randomized, controlled and nonblinded study was conducted in abdominal surgery patients without a diagnosis of OSA. Either routine oxygen or a trial of CPAP plus oxygen was administered to these non-OSA patients who developed severe postoperative hypoxemia.170 Patients using CPAP were found to have decreased need of reintubation to treat respiratory failure and less postoperative complications. Conversely, two studies, one in nonsurgical non-OSA patients admitted to intensive care171 and another in abdominal surgery patients without a history of OSA,172 found no benefit of postoperative CPAP use.
Well-designed research studies on the postoperative effect of CPAP in OSA surgical patients are lacking. Such studies would need to be geared towards evidence-based medicine and would have to address the following questions: how long should CPAP be applied, preoperatively and/or postoperatively, for optimum efficacy, what type of surgery would benefit most from CPAP treatment, should OSA severity influence the decision to use CPAP postoperatively, would use of preoperative prophylactic CPAP confer a reduced postoperative risk, and would CPAP allow for safer administration of analgesics?
The evidence of the potential deleterious effect of sedatives, anesthesia and analgesics in OSA patients and the increased risk of perioperative adverse events implies that clinical management strategies need to be specifically tailored. It is important for anesthesiologists to meet the challenge of maintaining upper airway patency and preventing perioperative complications in these patients. The recently developed ASA guidelines3 emphasize the importance of evaluation, detection and preparation in the preoperative workup and the necessity of using forethought and vigilance when developing perioperative management for OSA patients undergoing surgery. The following questions arise: is it feasible for anesthesiologists to identify patients with undiagnosed OSA in the preoperative clinic, can we identify factors that may increase the perioperative risk in OSA patients, is it possible to modify anesthetic techniques to reduce perioperative risk in OSA patients, are there safer alternatives to opioid analgesics for postoperative pain control, and finally, what are the optimal postoperative management strategies for OSA patients?
The current “gold standard” in the clinical diagnosis of OSA is an overnight sleep laboratory study with PSG.173 PSG is a highly reliable diagnostic tool but screening of every surgical patient is not feasible due to the time-commitment, expense and burden on the health care system. Moreover, PSG is not practical for rapid screening in a fast-paced preoperative clinic. A number of questionnaire-based screenings are available in the literature.174–177 In general, the problem is that these questionnaires ask a variety of questions about sleep that are not specifically geared towards identifying which patients have OSA. To complicate matters, 2 of the questionnaires contain 100 or more items, thereby reducing their practicality.
The BQ is a self-report instrument specifically designed to identify undiagnosed OSA. It has been shown to perform well in a large population of 744 primary care patients with a sensitivity of 0.89 and specificity of 0.71.10,178 The BQ has also been validated in atrial fibrillation patients and shown to perform with a similar sensitivity (0.86) and specificity (0.89). The 10-item BQ is comprised of 5 questions on snoring, 3 on excessive daytime sleepiness, 1 on sleepiness while driving, and 1 inquiring about a history of hypertension. Details of age, gender, weight, height, and neck circumference are also recorded. The BQ stratifies patients into high or low risk of having OSA based on their endorsement of symptom severity.
The BQ has been shown to be a valuable tool for OSA screening in primary care and atrial fibrillation patients, but its usefulness in determining which surgical patients are at greater risk of having OSA has yet to be established. Recently, we screened 318 patients using BQ at our hospital and 24% (n = 76, 95% CI 19%–29%) were found to be at high risk of having OSA.31
The number of questions and the complicated scoring procedure of BQ may be too cumbersome for anesthesiologists and their patients. To facilitate the widespread usage of an OSA screening tool, we developed a shorter 4-item OSA screening questionnaire (STOP). The STOP questionnaire contains four questions: S: “Do you snore loudly, loud enough to be heard through closed door,” T: “Do you feel tired or fatigued during the daytime almost every day,” O: “Has anyone observed that you stop breathing during sleep,” and P: “Do you have a history of high blood pressure with or without treatment”? Patients answering “yes” to two or more questions were assigned as being at high risk of having OSA. The sensitivity of the STOP questionnaire at AHI >5, >15, and >30 cutoff levels was 65.6%, 74.3%, and 79.3%, respectively.179 When incorporating BMI more than 35 kg/m−2 (B), age over 50 yr (A), neck circumference larger than 40 cm (N) and male gender (G) into the STOP questionnaire, STOP-BANG, the sensitivity was increased to 83.6%, 92.9%, and 100% for the same AHI cutoffs above.179
With the development of the BQ, STOP, and ASA checklist, a necessary step before their use as an OSA screening tool in the preoperative clinic is the determination of their validity. We have conducted a study to compare the validity of the BQ, STOP, and ASA checklist in 177 surgical patients who were concurrently studied with PSG.180 The sensitivity of the BQ, the ASA checklist, and the STOP questionnaire was 68.9%, 72.1%, and 65.6% at AHI > 5; 78.6%, 78.6%, and 74.3% at AHI >15; 87.2%, 87.2%, and 79.5% at AHI >30, respectively. There is no significant difference in the predictive parameters of the three screening tools.180 The STOP questionnaire is a concise and easy to use screening tool for OSA. It has been validated in surgical patients at the preoperative clinic and is equivalent to the BQ and ASA checklist. Incorporating BMI, age, neck size, and gender with the STOP questionnaire, STOP-BANG, will give a higher sensitivity and negative predictive value for patients with moderate to severe OSA.180 A recent study found that the percentage of patients with oxygen desaturation index (the number of times per hour the oxygen saturation decreases by ≥4% from baseline) >10 was significantly higher in patients identified as being at high risk of having OSA and having recurrent PACU respiratory events.181 The anesthesiologist may be the first health professional to inquire about sleep, and therefore, will have an important role in identifying these patients and preventing both short and long-term complications. Use of a practical screening tool in the preoperative clinic is highly recommended.
Certainly, not all OSA patients undergoing surgery have serious adverse perioperative events and of those who do, the time course of the serious adverse events varies greatly (Table 3). A review of the findings points to possible multiple factors in surgical patients with OSA that could lead to perioperative adverse events. Further research in this area is needed, not only to identify these factors, but to elucidate their level of involvement by determining the varying odds ratios. The impact of anesthetics and analgesics in OSA patients is a definite consideration in determining risk. These will be discussed below.
Other factors related directly to the etiology of OSA or the associated morbidity also merit consideration. Studies of patients undergoing surgical treatment for their OSA98–100,119,121 or major surgery, excluding upper airway procedures, have documented that patients with a preoperative history of more severe OSA tend to have more perioperative complications (Table 3). These findings would imply that preoperative screening and identification of those patients with more severe OSA would allow for better preparation for perioperative complications. However, these studies are either retrospective or observational and are of too low evidence level (Level IV) to enable firm conclusions Moreover, two other studies102,117 at the same evidence level found that higher AHI and lower SaO2 levels preoperatively were not correlated with postoperative complications (Table 3). Therefore, more research is needed to correlate AHI and preoperative oxygen level with perioperative complications.
Further information on this matter can be gleaned from studies of obese surgical patients with a high prevalence of OSA. While obesity is associated with a greater risk of perioperative complications,182,183 multivariate analyses do not implicate a history of OSA as a risk factor for increased surgical complications in patients undergoing gastric bypass surgery.184 Rather, it seems that preexisting pulmonary disorders are more predictive of the need for postoperative ICU monitoring and longer hospital stay.185 This suggests that it is not the obesity per se, but the associated morbidity that increases perioperative risk. That OSA may not feature prominently as a cause of postoperative complications may also be explained by the fact that bariatric surgery candidates undergo extensive preoperative medical examination before being allowed to undergo surgery.186 Overnight PSG screening for OSA is also commonly included in the preoperative work-up so that OSA can be identified and treated before surgery. It remains to be determined whether preoperative treatment of OSA could significantly reduce the perioperative risk in these patients.
An alternative hypothesis is that long-standing untreated OSA is associated with greater morbidity and preoperative morbidity may be a more sensitive indicator of perioperative complications. A retrospective study of 311 patients undergoing bariatric surgery for weight reduction reported that OSA was associated with a longer length of hospital admissions (OR 5.5) but that stronger predictors of longer hospitalization included coronary artery disease (OR 8.7) and the presence of the metabolic syndrome (OR 6.7–10.2).187
The change in sleep architecture with surgery could possibly contribute to a greater postoperative risk in OSA patients. Among patients undergoing abdominal surgery, anesthesia initially suppresses rapid eye movement (REM) sleep but there is intense REM rebound towards the middle of the first postoperative week.188 This alteration in sleep architecture can have a substantial impact on the respiratory variables in OSA patients. In REM sleep, upper airway muscle activity in the late apneic phase is reduced189 and, consequently, apneas are of larger duration and are associated with a greater degree of hypoxemia during REM sleep than non-REM sleep.190 Hemodynamic changes are also evident in REM sleep as REM-related incidences of desaturation were found to be linked to significantly higher postapnea increases in arterial blood pressure.191 Coincidentally, numerous ventilatory disturbances, including apneas and hypopneas, have been observed on the second and third postoperative nights.192 There are no studies directly linking changes in sleep stage with ventilatory disturbances during the postoperative period.
There are also reports of numerous obstructive hypopnic and/or apneic events within the first 12 h postoperatively.77 Moreover, the respiratory disturbances in the early postoperative period have been reported to occur mainly in Stages 1 and 2 sleep since most patients did not have slow wave sleep or REM sleep in the early postoperative period.52 More recent studies have documented that the more serious complications occurred within the first 24 h after surgery in OSA patients.95 In a study of non-OSA surgical patients,193 more than 75% of postoperative patients had respiratory events within 13 to 24 h after surgery and significant risk factors included older age, having more than one comorbidity and whether hydromorphone was administered for analgesia. Similar studies in OSA patients undergoing surgery are needed to determine if the timing of respiratory events is similar and which risk factors are significant for this population. The time course of adverse postoperative events suggests the involvement of other factors than sleep architecture, but it may help to elucidate the period of greatest postoperative risk. That is, the REM-related impact on respiratory events would take place a number of days postoperatively and may represent a second period of greater risk of postoperative respiratory complications. However, the above studies suggest that postoperative complications are quite common within the first 24 h postoperatively.
There are numerous reviews on the subject of anesthetic management of OSA patients111,113,194–197 that emphasize that the type of anesthesia may have differential impact on the respiration of patients. Despite these reviews, there are no randomized controlled trials of the safety of various anesthetics in the perioperative period. As mentioned previously, different analgesics have different margins of safety and result in varying levels of respiratory depression. A relatively recent study36 has documented the impact of propofol on upper airway collapsibility by investigating the relationship between varying concentrations and the critical airway closing pressure. The use of healthy individuals, and not patients with OSA, as subjects coupled with the lack of a randomized controlled design, are significant limitations of this study. Nevertheless, the findings highlight that a carefully chosen concentration of anesthetic may play an important role in the airway management of OSA patients.
An important consideration in the choice of inhaled anesthesia is the presence of any carryover anesthetic effects into the postoperative period that could impair respiration and/or enhance the deleterious respiratory effects of analgesics. In OSA patients undergoing UPPP, there was delayed recovery in those patients receiving isoflurane versus propofol. Propofol anesthesia was found to result in better oxygen saturation in the first postoperative hour and more rapid recovery of spontaneous breathing versus isoflurane.97 However, these studies were not done on OSA patients. Short-acting anesthetics, such as remifentanil, have also been shown to result in a rapid postoperative recovery, better oxygen saturation profile and shorter postoperative length of stay.198,199 Also, morbidly obese patients who underwent major abdominal surgery awoke significantly faster after desflurane than after sevoflurane anesthesia. The patients anesthetized with desflurane had higher oxygen saturation on entry to the PACU.200
Premedication sedatives, especially benzodiazepines, such as flunitrazepam or midazolam, have been shown to cause postoperative airway obstruction.41 In this study, 12 patients did not have a premorbid history of OSA but were observed to snore loudly postoperatively. Conversely, some premedication drugs have been shown to be beneficial in OSA patients. In a case report of a morbidly obese woman with tracheal stenosis, dexmedetomidine, an α-2 adrenergic agonist, was used as a premedication due its anxiolytic and sedative properties. The benefit of dexmedetomidine is the lack of significant respiratory depression within the clinical dose range. Similarly, in a randomized controlled trial, orally administered clonidine was found to reduce the propofol dose required for induction of anesthesia.201 Unfortunately, there are no trials of the efficacy of varying premedication drugs in OSA patients undergoing surgery, but the above studies illustrate their importance.
Postoperative analgesia is another factor that can influence respiration in surgical patients with OSA. In a retrospective study of 1600 patients, not specifically OSA patients, who had received postoperative patient-controlled analgesia with IV opioids, 8 cases of serious respiratory depression were reported.202 Contributing factors were the concurrent use of a background infusion of opioids, advanced age, concomitant administration of sedative or hypnotic medications and a preexisting history of sleep apnea. Two retrospective reviews of more than one-thousand surgical patients indicated that postoperative respiratory depression after morphine-based patient-controlled analgesia was observed to occur in about 1%–2% of patients.203,204 This respiratory depression occurred between 2 to 31 h after initiation of the IV patient-controlled analgesia203 indicating the need for long-term diligent patient monitoring.
A review conducted to identify the risk factors for respiratory depression subsequent to patient-controlled analgesia concluded that there is no single indicator for respiratory depression but that OSA, whether suspected or verified by patient history, is one of the risk factors for respiratory depression. Other factors include older age, hepatic, pulmonary or cardiac disease, concurrent use of central depressants, obesity, and higher bolus doses of patient-controlled analgesia.205 There are no prospective randomized studies examining the respiratory effect of patient-controlled analgesia in OSA patients.
In general, the consensus is that opioids are to be avoided in OSA patients, if possible, especially when they undergo upper airway surgical treatment for OSA.206 The ASA guidelines recommend regional anesthesia to reduce the possibility of negative adverse events associated with systemic opioids.3 A multimodal approach with combinations of analgesics from different classes and different sites of analgesic administration is a prudent strategy for perioperative pain management.207–209 The use of nonsteroidal antiinflammatory analgesics210 is strongly recommended.3 Drugs such as acetaminophen, tramadol, and other nonopioid analgesics and their combination can be used to provide effective pain relief and reduce opioid consumption, thus alleviating the opioid-related adverse effect of respiratory depression. Other novel approaches, such as ketamine, clonidine, or gabapentin can be used.201,207–209 In a case report, the nonopioid sedative dexmedetomidine45 has been shown to reduce the need for postoperative opioids. Other techniques that avoid medication, such as transcranial magnetic stimulation,211 are also being investigated. The opiate-sparing strategies geared towards OSA patients are summarized (Table 4). A major drawback of these studies is that they are predominantly case reports. Unfortunately, there are no studies comparing the safety and efficacy of different anesthesia technique, general anesthesia, regional anesthesia or monitored anesthesia care in OSA patients undergoing surgery or studies on different analgesic or adjuvants.
Clearly, anesthesiologists need to develop effective management strategies to minimize perioperative risk for patients with OSA undergoing surgery. To that end, the ASA recently published guidelines,3 a Level IV evidence document based on expert consensus report, that propose strategies for overall perioperative care of OSA patients. The clinical practice review committee of the American Academy of Sleep Medicine also indicated that the scientific literature regarding the perioperative risk and best management techniques for OSA patients was scanty and of limited quantity. They used the available data to make a statement on the perioperative management of OSA patients instead of standards of practice recommendations.212
Due to the high risk of complications and morbidity associated with upper airway surgery for OSA treatment, suggestions for perioperative monitoring in OSA patients undergoing upper airway surgery were initially introduced 15 yr ago,76 however, no consensus-based guidelines for the perioperative management of OSA patients undergoing airway surgery were formulated. Moreover, the upper airway surgical literature is specifically oriented towards upper airway procedures thus lessening the applicability of these management strategies to other types of surgery. For example, steps to minimize upper airway edema with topical corticosteroids213 are crucial with upper airway surgery but have much less applicability to other types of surgery. Nonetheless, a closer examination of management strategies for upper airway surgery may help to provide information that is applicable to OSA patients undergoing surgery.
Pertinent information can also be gleaned from reports of patients undergoing bariatric surgery for obesity. A major confound with the bariatric surgery population is the presence of obesity and the added risk of the associated morbidity184 that render it difficult to extrapolate these findings to the general surgical population. Of positive note, it was shown that anesthesia need not be associated with postoperative complications in obese patients with OSA undergoing bariatric surgery.214 With careful postoperative monitoring in the PACU and the ward, surgery was reported to be safe in this high-risk group of patients.
Surgery in OSA patients is associated with significant perioperative risk. As mentioned earlier, cardiovascular morbidity is common in patients with long-standing untreated OSA thus further increasing the likelihood of adverse perioperative events. The incidence of perioperative complications associated with upper airway surgery for OSA is about 3.5% (range, 0.6–8.9),215 and a 0.4% to 1.6% incidence of mortality has been reported.216,217 Airway-related postoperative complications occur in about 6% of patients, oxygen desaturations in 9% and electrocardiogram changes in 1%.98 Others have documented that about one-third of the complications involve the airway.102 Cardiac complications, such as hypertension, have also been commonly reported.122 Alerting surgeons, anesthesiologists, and nurses to the potential perioperative complications associated with surgery in OSA patients is a first step to reducing the rate of morbidity and mortality.
As maintenance of upper airway patency in OSA patients is a major consideration, caution is needed to ensure that extubation should only be done after the patient is fully conscious and airway patency is ensured. However, the ASA guidelines state that this need be the case only for patients at increased perioperative risk from OSA.3 The use of postoperative supplemental oxygen has been suggested76 for OSA patients undergoing upper airway surgery to maintain appropriate oxygen saturation. The ASA guidelines caution that oxygen supplementation should be used only until patients are able to maintain baseline oxygen saturation with room air.3 A side effect of the use of prolonged supplemental oxygen in patients with chronic obstructive pulmonary disease is the increased duration of obstructive apneas or hypopneas.218 The ASA guidelines further recommend that continuous oximetry may be used in the step down unit in patients with increased perioperative risk from OSA, but it does not support the need of continuous oxygen monitoring in all patients. There is no evidence-based determination if the cost of routine monitoring is warranted as there are no studies examining whether such monitoring reduces the postoperative risk in OSA patients.
Other postoperative strategies for reducing postoperative risk, such as the influence of sleep position on OSA, also warrant investigation. Lateral position is reported to improve the maintenance of the passive pharyngeal airway in patients with OSA.219 The lateral position improves upper airway stability during sleep which may allow reduction of the therapeutic levels of CPAP.220 The study by Penzel et al. also supported the idea that lower CPAP pressure was needed during lateral positions versus supine positions.221 However, the ASA guidelines recommend a semi-upright position for extubation and recovery in OSA patients3 and the use of a nonsupine position postoperatively. However, this position may not be feasible for certain orthopedic procedures.
There is a frequent prevalence of undiagnosed OSA. Also, the severity of OSA varies among patient groups and perioperative complications are probably related to the interaction of the severity of the diseases and the degree of respiratory depression induced by opioids. Sleep apnea is associated with other preexisting medical conditions such as obesity, hypertension, coronary artery disease, and diabetes that negatively impact perioperative outcomes. It may be difficult to separate the impact of OSA per se from the other associated conditions.
Surgical patients with OSA may be vulnerable to sedation, anesthesia and analgesia. Episodic sleep-related desaturation and incidence of unexplained cardiorespiratory arrest may be attributable to undiagnosed OSA in surgical patients, but this connection needs to be tested within randomized, controlled trials. It also remains to be determined whether the perioperative risk of OSA patients could be reduced by appropriate screening to detect undiagnosed OSA and implementation of a perioperative management plan for OSA. Evidence-based research on perioperative management of OSA patients is sorely lacking.
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