Patient Safety Tip of the Week

March 26, 2013

Failure to Recognize Sleep Apnea Before Surgery



In two of our recent Patient Safety Tips of the Week (February 12, 2013 “CDPH: Lessons Learned from PCA Incident” and February 19, 2013 “Practical Postoperative Pain Management”) we discussed problems related to postoperative opioid therapy in patients with sleep apnea. Obstructive sleep apnea (OSA) is one of the conditions we recommend be considered a relative contraindication to initiation of PCA (patient-controlled analgesia) or other opioid therapy. Also, because sleep apnea is associated with many other complications in patients undergoing surgery we have long recommended that screening for sleep apnea be part of the pre-operative evaluation of patients (see our August 17, 2010 Patient Safety Tip of the Week “Preoperative Consultation – Time to Change” August 18, 2009 “Obstructive Sleep Apnea in the Perioperative Period” and our July 2010 Whats New in the Patient Safety World column “Obstructive Sleep Apnea in the General Inpatient Population”).


A very timely study (Singh 2013) was just published by Frances Chung and her colleagues at the University of Toronto, who have been pioneers in addressing sleep apnea in surgical patients. They looked at patients in preoperative clinics and screened them for possible OSA using the STOP-BANG questionnaire and performed polysomnography (PSG) on almost 1000 patients scheduled to have surgery. They found 111 patients with a pre-existing diagnosis of OSA. Of the remaining patients PSG showed mild OSA in 31%, moderate OSA in 21%, and severe OSA in 17%.


They then reviewed the medical charts of those patients who underwent surgery to see whether surgeons and anesthetists (who were blinded to PSG results) had recognized the patient had OSA. Of patients with a pre-existing known diagnosis of OSA 58% were not diagnosed by surgeons and 15% were not diagnosed by anesthetists before surgery. Of the 267 patients with moderate or severe OSA by PSG, 92% were not recognized by surgeons and 60% were not recognized by anesthetists. And this is coming from facilities at which we suspect the general level of recognition of OSA is probably higher than in most!


It’s long been known that the percentage of patients with OSA undergoing surgery is higher than that of the general population (Finkel 2009). That shouldn’t be surprising since obesity and other comorbidities that are risk factors for OSA are also risk factors for conditions requiring surgery, such as a variety of orthopedic procedures.


A previous study (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. On the other hand, a new study (Lockhart 2013) showed no difference in 30-day or 1-year mortality for surgical patients with a prior history of OSA or positive screen for OSA compared to controls.


When we’ve talked to primary care physicians about screening for OSA with tools like the STOP-BANG questionnaire during their preop medical evaluations they usually ask “What will be done differently if we suspect or know they have OSA?”. (They are usually a bit annoyed that we’d add an additional burden onto their already hectic days.) But the STOP-BANG takes less than a minute to administer and there are, in fact, numerous things that should be done differently if OSA is suspected in a patient undergoing surgery.


In the ideal world if you suspected a patient had OSA you’d have time to schedule a polysomnogram and the preoperative evaluation by anesthesiology would 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. But in the real world practicalities often preclude studies such as polysomnography and often you must assume the patient might have OSA based on screening tools.


The American Society of Anesthesiologists published Practice Guidelines for the Perioperative Management of Patients with Obstructive Sleep Apnea in 2006 (ASA 2006). However, considerable research has been done since that time and more up-to-date best practices have since been developed. Those have recently been summarized in a consensus statement by the Society for Ambulatory Anesthesia (Joshi 2012). But, as we have said in the past, while there are many practical, rational and consensus-based recommendations for perioperative management of OSA, few are actually evidence-based. Even this new consensus statement is based upon a limited number of studies in the literature that met fairly strict criteria for inclusion.


The new consensus statement focuses on determining whether patients at high risk for OSA might still be candidates for outpatient surgery or whether they should be admitted as inpatients for surgery. The first big difference from the 2006 ASA guidelines regards the screening tool used. The ASA guideline recommended a 12-point checklist that has not been validated. A number of screening tools for OSA are available including the STOP-Bang tool noted above and its predecessor the STOP questionnaire, but also the Berlin questionnaire, the Flemons questionnaire, the ASA checklist, and others. The new consensus statement recommends use of the STOP-Bang questionnaire because of its ease of administration and high sensitivity. It also notes that its relatively low specificity can be improved by using a greater number of positive indicators (eg. >6) and there is some evidence that the higher the score the greater the probability of severe OSA.


The consensus statement suggests that if a high likelihood of OSA is predicted by the STOP-Bang questionnaire the patient should be approached as if they have OSA.


The decision about outpatient vs. inpatient surgery in patients with suspected or known OSA depends upon the nature of the surgical procedure, the status of comorbidities, and the likelihood of the need for opioid analagesics after surgery. Opioids, of course, are prime contributors to postop complications in patients with OSA. As we noted in our February 19, 2013 Patient Safety Tip of the Week “Practical Postoperative Pain Management” the use of multimodal approaches to postop pain management can significantly reduce the need for opioids. If it is determined that a patient’s postop pain can likely be managed without opioids, they may be a candidate for outpatient surgery. On the other hand, if it is highly likely the patient will need postop opioid analgesia the patient should probably have surgery as an inpatient.


For patients known to have OSA and receiving CPAP at home continued compliance with CPAP after discharge home is important. Such patients should generally bring their CPAP device with them to the ambulatory surgery facility and be advised about the importance of complying with their CPAP after discharge because the increased risk postoperatively lasts for several days. That use of CPAP should extend to any time they are sleeping, including daytime naps. The patients should also be advised against sleeping in the supine position, which increases the likelihood of airway obstruction.


Patients with OSA only suspected by the screening tool should be told to contact their primary care physician after discharge for possible sleep studies.


They do note that data is still lacking to determine whether a preoperative sleep study and initiation of CPAP or BiPAP preoperatively improves perioperative outcomes in patients with suspected OSA. (Our November 22, 2011 Patient Safety Tip of the Week “Perioperative Management of Sleep Apnea Disappointing” highlighted a study (O’Gorman 2013) that showed that autotitrating positive airway pressure (APAP) failed to prevent obstructive apnea in surgical patients deemed high risk for the disorder.) They call for larger, adequately powered, and well-controlled studies to evaluate whether preop or postop CPAP/BiPAP reduce complications or not.


The consensus statement also differs from the 2006 ASA guideline in the types of surgical procedures that might be considered for ambulatory surgery, stating that laparoscopic upper abdominal procedures may be safely performed on an ambulatory basis if all perioperative precautions are followed.


Several good reviews of the perioperative management of patients with OSA have been done in 2008 (Chung 2008) and 2010 (Adesanya 2010) and 2011 (Minokadeh 2011, Chung 2011).


Airway management may be more difficult in the patient with OSA. Such patients may be more difficult to intubate. They may also be at greater risk of gastroesophageal reflux and, hence, at greater risk for aspiration pneumonitis. Because airway obstruction in OSA is more common in the supine position, many advocate use of the sitting position for preoxygenation and anesthetic induction.


Minokadeh et al have a good discussion about sedatives, induction agents, and volatile anesthetics in the OSA patient (Minokadeh 2011), favoring short-acting agents but noting that redistribution of agents in tissues can lead to prolonged action of many drugs. They note that if intraoperative opioids are necessary, remifentanil may be preferred because of its rapid metabolism. All stress the importance of complete reversal of any neuromuscular blockade at the end of the procedure.


The stay in the PACU is especially critical in the OSA patient. Extubation is a time of very high risk. In addition to verifying complete reversal of neuromuscular blockade, one needs to ensure return of airway reflexes, adequate tidal volume and respiratory rate, adequate oxygenation without CO2 retention, and full consciousness prior to considering extubation. Putting the patient in a semi-upright recovery position is advisable, avoiding the supine position. Obviously, the patient must be closely monitored after extubation. The ASA guidelines recommend PACU observation for 3 hours for patients without respiratory events and 7 hours for patients with observed respiratory events in the PACU.


Aside from the time of extubation, the most critical vulnerability is when the patient requires opioids for pain management. As before, it is always preferable to utilize multimodal analgesia, with non-opioid analgesics and local/regional blocks where possible.


If the patient does require opioids, they need close monitoring. That includes frequent monitoring of vital signs and continuous monitoring of oxygenation status. Capnography has also now become the standard of care for monitoring patients with OSA who are on opioids. As in our February 12, 2013 Patient Safety Tip of the Week “CDPH: Lessons Learned from PCA Incident” sidestream capnography used in unintubated patients may not be particularly good at detecting hypercarbia but is useful in monitoring respiratory rate and detecting apnea. And don’t forget that sedative/hypnotic drugs may also be dangerous in patients with OSA, particularly when used in conjunction with opioids.


Night time is obviously a high risk time for patients with OSA. However, several reviews have noted that, while the first 12-hours post-operatively is a vulnerable period, REM rebound may be seen and REM-associated hypoxemic events may increase 3-fold on the second and third postoperative nights, with associated risk of complications. Patient positioning may be important, as patients with OSA are more likely to develop hypoxemic episodes when they are supine so patients should be encouraged to sleep on their side.


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 and there remain problems with the threshold-based alarm systems most often used today. Lynn and Curry (Lynn 2011) described 3 patterns of unexpected in-hospital deaths (see our February 22, 2011 Patient Safety Tip of the Week “Rethinking Alarms”). The third pattern they describe is one that is typically seen in sleep apnea. In this 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.


As mentioned above, continuous capnography has become the standard of care for monitoring patients on opioids, particularly those with suspected or known OSA. The ability for capnography to detect apneic events may be even more important than the ability to detect hypercarbia.



So back to the questions “Why should I screen for OSA preoperatively? What will they do differently?” The response should be “There’s plenty that will be done and your patients will be much safer”.




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           Obstructive Sleep Apnea in the Perioperative Period

August 17, 2010           Preoperative Consultation – Time to Change

July 13, 2010               Postoperative Opioid-Induced Respiratory Depression

February 22, 2011       Rethinking Alarms

November 22, 2011     Perioperative Management of Sleep Apnea Disappointing

May 22, 2012              Update on Preoperative Screening for Sleep Apnea

February 12, 2013       CDPH: Lessons Learned from PCA Incident

February 19, 2013       Practical Postoperative Pain Management


What’s New in the Patient Safety World columns:

July 2010                     Obstructive Sleep Apnea in the General Inpatient Population

November 2010           More on Preoperative Screening for Obstructive Sleep Apnea

March 2012                 Postoperative Complications with Obstructive Sleep Apnea








Singh M, Liao P, Kobah S, Wijeysundera DN, Shapiro C, Chung F. Proportion of surgical patients with undiagnosed obstructive sleep apnoea. Br J Anaesth 2013; 110(4): 629-636



Finkel KJ, Searleman AC, Tymkew H. Prevalence of undiagnosed obstructive sleep apnea among adult surgical patients in an academic medical center. Sleep Med 2009; 10(7): 753–758



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



Lockhart EM, Willingham MD, Abdallah AB, et al. Obstructive sleep apnea screening and postoperative mortality in a large surgical cohort. Sleep Medicne 2013; Published online March 15, 2013



American Society of Anesthesiologists (ASA). 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



Joshi GP, Ankichetty SP, Gan TJ, Chung F. Society for Ambulatory Anesthesia Consensus Statement on Preoperative Selection of Adult Patients with Obstructive Sleep Apnea Scheduled for Ambulatory Surgery. Anesthesia & Analgesia 2012; 115(5): 1060-1068



O’Gorman SM, Gay PC, Morgenthaler TI. Does Auto-Titrating Positive Airway Pressure Therapy Improve Postoperative Outcome in Patients at Risk for Obstructive Sleep Apnea Syndrome? A Randomized Controlled Clinical Trial. Chest 2013; online first January 3, 2013



Minokadeh A, Biship ML, Benumof JL. Obstructive Sleep Apnea, Anesthesia, and Ambulatory Surgery. Anesthesiology News 2011;



Chung F, Davidson T, Hillman D, et al. Perioperative Management of OSA Patients. Practical Solutions and Care Strategies. 2011 (an assimilation of material presented at the Challenges in the Perioperative Management of OSA Patients symposium, held in October 2010)



Lynn LA, Curry JP. Patterns of unexpected in-hospital deaths: a root cause analysis. Patient Safety in Surgery 2011, 5:3 (11 February 2011)







Print PDF version












Tip of the Week Archive


What’s New in the Patient Safety World Archive