You’ve heard us talk on numerous occasions about identifying potential obstructive sleep apnea (OSA) as a risk factor for procedural sedation, surgery, postoperative care, and pain management (see the summary of our previous columns at the end of today’s column). Obesity and sleep apnea, conditions that predispose further to opioid-induced respiratory depression, are also becoming more and more prevalent. See our July 2010 What’s New in the Patient Safety World column “Obstructive Sleep Apnea in the General Inpatient Population” for a study that found a potential 60% prevalence of obstructive sleep apnea in patients admitted to general medicine units in an urban academic hospital, most of whom had never been diagnosed with OSA.
Surgical patients probably have an even higher prevalence. We previously mentioned two clinical studies by the Toronto group headed by Frances Chung that emphasized the need to identify OSA patients using screening procedures prior to surgery. One study using either standard nocturnal polysomnograms or portable home sleep studies on over 800 patients prior to anticipated surgery found that 536 of the 819 patients enrolled had obstructive sleep apnea. Of those with severe sleep apnea, 85.5% were not diagnosed by surgeons and 47% were not diagnosed by anesthesiologists. Notably 84% of the patients overall had at least one symptom or sign of OSA such as snoring, excess daytime drowsiness, or observed sleep apnea.
In the second study the STOP-Bang questionnaire and a wristwatch pulse oximeter were used during the preoperative evaluation in 367 patients. Of these 61% were ranked at high risk for OSA using the STOP-Bang questionnaire. The accuracy of the data extracted from the pulse oximeter to detect moderate and severe sleep apnea was strong. The sensitivity to detect moderate and severe obstructive sleep apnea was 92.8 percent and 100 percent. The specificity to predict moderate and severe obstructive sleep apnea was 74.8 percent and 64.6 percent. There was a strong correlation between those scoring high risk on the STOP-Bang and those with an oxygen desaturation index greater than 10 on the wristwatch oximeter and having confirmed obstructive sleep apnea. The authors therefore suggest a screening process of administering the STOP-Bang, followed by the wristwatch pulse oximetry in those scoring as high risk.
Another group (Vasu 2010) found that 41.5% of 135 patients who scored high risk on the STOP-Bang questionnaire had higher rates of postoperative complications than those who scored low risk (19.6% vs. 1.3%). They did not confirm OSA with polysomnograms so the association here is with the STOP-Bang score rather than confirmed OSA. Nevertheless, the association was strong and applied across a wide range of types of surgery.
So it logically makes sense to consider identifying patients with potential OSA early so that appropriate preoperative assessment, intraoperative management, and postoperative management and monitoring can be undertaken. Of course, we’d like to know that recommendations for the perioperative management of OSA or potential OSA actually improve patient outcomes. Surprisingly, while there are many practical, rational and consensus-based recommendations for perioperative management of OSA, few are actually evidence-based.
In 2006, the American Society of Anesthesiologists (ASA) published practice guidelines for the perioperative management of patients with OSA (ASA 2006). And good reviews of the perioperative management of patients with OSA have been done in 2008 (Chung 2008) and 2010 (Adesanya 2010). All 3 papers readily admit there is a paucity of evidence-based recommendations for care of surgical patients with suspected or known OSA.
And just last month one of the few randomized controlled studies of surgical patients deemed at high risk of OSA had disappointing results (O’Gorman 2011). That study, presented by Mayo Clinic researchers at the CHEST 2011: American College of Chest Physicians Annual Meeting, showed that autotitrating positive airway pressure (APAP) failed to prevent obstructive apnea in surgical patients deemed high risk for the disorder. They did find that patients deemed to be at high risk for OSA via the Flemons questionnaire (Flemons 1994) did have longer lengths of stay and more complications than those deemed to be at low risk. They randomized 85 patients deemed at high risk for OSA to either standard postoperative care or standard care plus APAP but found no significant difference in LOS or complications between the two groups. Admittedly, the number of patients studied was small and further research is needed. But it leaves one more gap of evidence-based recommendations.
So what are the recommendations for patients with suspected OSA who are to undergo surgery?
One is that the preoperative evaluation by anesthesiology should take place far enough in advance of the planned surgery so that there is adequate time for any further evaluation and time for the surgeon and anesthesiologist to jointly develop a management plan. The importance of involving family members in the evaluation is emphasized since much of the history suggestive of OSA may come from, for example, a spouse who notes the patient snores and has apneic spells. Assessments of common comorbidities in patients with OSA (hypertension, diabetes, CHF, etc.) should be done. The physical examination should take into account BMI, neck circumference, craniofacial abnormalities, tonsil size, tongue size, etc. Patients with OSA also may have airways that are difficult to manage so a good assessment of potential difficulties managing the airway is indicated.
Both the Chung and Adesanya reviews discuss the clinical screening tools, which include not only the STOP-Bang tool noted above, but also the Berlin questionnaire, the ASA checklist, and others.
The severity of the OSA risk and the nature of the surgical procedure should be discussed. The surgeon and anesthesiologist need to consider the urgency of the procedure and decide whether there is time to delay the surgery while further evaluations, such as polysomnography, are undertaken. Also, a discussion about ambulatory vs. inpatient surgery is beyond today’s column but, while ambulatory surgery in OSA patients is generally felt to be relatively safe, there are special recommendations about monitoring, equipment, transfer agreements, etc. that should be followed.
Intraoperatively, it would make sense to use local or regional anesthesia in preference to general anesthesia, where possible. Agents used are preferred to be shorter-acting and one needs to consider drugs (anesthetics, analgesics, and sedatives) that are less likely to produce respiratory depression or neuromuscular weakness.
Post-operatively, the major discussion centers around monitoring and the use of opiates. Certainly, where opiates can be avoided, it makes sense to use drugs like acetaminophen or nonsteroidal anti-inflammatory agents or even non-pharmacological modalities for analgesia. In those who do use patient-controlled analgesia (PCA) avoiding a basal infusion may be wise. Patients with OSA are often found to require lower doses of opiates for analgesia. As we’ve noted in many prior columns, the risks of opiates probably apply equally to any means of use of opiates, not just PCA.
Patient positioning may be important, as patients with OSA are more likely to develop hypoxemic episodes when they are supine.
The issue of oxygenation is much debated. If a patient has known OSA and has been on CPAP at home, they should get CPAP post-operatively (preferably with their own CPAP equipment brought in from home). As above, the use of CPAP, NIPPV, BiPAP, or APAP are not currently evidence-based in those not previously on CPAP at home.
Monitoring is probably the most important aspect of care of the patient with suspected OSA. Most recommend continuous pulse oximetry (rather than periodic assessment of O2 saturation) but our previous columns have highlighted the problems associated with just using pulse oximetry and the false sense of security that one may develop. Very important in that light is the work of Lynn and Curry (Lynn 2011) who describe 3 patterns of unexpected in-hospital deaths and demonstrate the problems with threshold-based alarms (almost all currently used alarm systems use threshold-based principles) in detecting early deterioration. Indeed, they posit that threshold-based alarms themselves often cause us to miss signs of early deterioration. The second pattern of deterioration they note is the classic CO2 narcosis but they note many of these cases are complicated by the third pattern typical of sleep apnea. The important point is that there may be a huge difference when the patient is awake and when he/she is asleep and that has important implications for monitoring. In the third pattern one sees repetitive reductions in airflow and oxygen saturation during sleep followed by arousals. The arousals rescue the patient but eventually the capacity or reserve of the patient to recover with arousals becomes impaired (often in response to narcotics or sedatives) and the patient may experience sudden death during sleep. The authors discuss the inability of currently used oximeters to recognize this pattern. They even imply that this pattern may give rise to oximeters alarming and being interpreted as “false” alarms attributed to motion artifact, etc. because when staff respond to the alarm the patient is now awake, breathing normally and has a normal oxygen saturation. So even systems using continuous pulse oximetry and end-tidal CO2 monitoring may fail to adequately identify these patients.
In both the second and third patterns, use of supplemental oxygen may mask the deterioration, provide a false sense of security, and delay critical responses to a deteriorating clinical situation. Hence, it’s important not to use oxygen unless there is a legitimate indication for its use (see our January 4, 2011 Patient Safety Tip of the Week “Safer Use of PCA”). The authors go on to discuss the flaws in current threshold-based alarm systems and the need for true “smart” alarms that integrate multiple physiological parameters and respond to patterns of changes in these.
The timing of deterioration is discussed in several of the above reviews. While the first 12-hours post-operatively is a vulnerable period, they also note that REM rebound may be seen and that REM-associated hypoxemic events may increase 3-fold on the second and third postoperative nights, with associated risk of complications.
We were indeed surprised that so many of the recommendations for managing patients with suspected OSA in the perioperative period lack a solid evidence base. But lots of research is ongoing and hopefully we’ll have more evidence-based interventions in the future. In the meantime, many of the practical recommendations made in the above reviews make sense.
Does your organization or facility have a formal approach to identifying patients at risk for OSA before surgery and putting in place common sense management guidelines?
See some of our prior columns on obstructive sleep apnea in the perioperative period:
Patient Safety Tips of the Week:
June 10, 2008 “Monitoring the Postoperative COPD Patient”
August 18, 2009 “ ”
August 17, 2010 “ ”
July 13, 2010 “Postoperative Opioid-Induced Respiratory Depression”
February 22, 2011 “Rethinking Alarms”
What’s New in the Patient Safety World columns:
November 2010 “More on Preoperative Screening for Obstructive Sleep Apnea”
American Society of Anesthesiologists. Studies Reveal a Need to Identify and Implement a Screening Procedure for Obstructive Sleep Apnea Prior to Surgery. Newswise 10/17/2010
Vasu TS, Doghramji K, Cavallazzi R, et al. Obstructive Sleep Apnea Syndrome and Postoperative Complications: Clinical Use of the STOP-BANG Questionnaire. Arch Otolaryngol Head Neck Surg. 2010; 136(10): 1020-1024
American Society of Anesthesiologists. Practice Guidelines for the Perioperative Management of Patients with Obstructive Sleep Apnea. A Report by the American Society of Anesthesiologists Task Force on Perioperative Management of Patients with Obstructive Sleep Apnea. Anesthesiology 2006; 104: 1081–93
Chung SA, Yuan H, Chung F. A Systemic Review of Obstructive Sleep Apnea and Its Implications for Anesthesiologists. Anesthesia & Analgesia 2008; 107(5): 1543-1563
Adesanya AO, Lee W, Greilich NB, Joshi GP. Perioperative Management of Obstructive Sleep Apnea. Chest December 2010; 138(6): 1489-1498
O'Gorman S, Horlocker T, Huddleston J, et al. Does Self-Titrating CPAP Therapy Improve Postoperative Outcome in Patients at Risk for Obstructive Sleep Apnea Syndrome? A Randomized Controlled Clinical Trial. Chest 2011; 140: 4 Meeting Abstracts 1071A; doi:10.1378/chest.1119434
also reported in: Harrison L. Postop APAP Fails in High-Risk Sleep Apnea Patients. Medscape Medical News. November 3, 2011
Flemons WW, Whitelaw WA, Brant R, Remmers JE. Am. J. Respir. Crit. Care Med. 1994; 150(5): 1279-1285.
Likelihood ratios for a sleep apnea clinical prediction rule
Lynn LA, Curry JP. Patterns of unexpected in-hospital deaths: a root cause analysis. Patient Safety in Surgery 2011, 5:3 (11 February 2011)