Patient Safety Tip of the Week


May 22, 2012

Update on Preoperative Screening for Sleep Apnea



We have been advocates for screening for obstructive sleep apnea (OSA) preoperatively (see links to prior columns listed below). This month there are 2 new papers on this topic from Frances Chung and her group in Toronto. One is further validation of the utility of the STOP-Bang questionnaire in predicting OSA. The other is one that looked at simple nocturnal oximetry and found that an oxygen desaturation index (ODI) >10 would predict most cases of moderate and severe OSA (though not good at picking up central apnea). Since delaying surgery to get formal polysomnographic studies might not be feasible in many cases, having alternative means of identifying high-risk patients is very desirable.


The first paper (Chung 2012a) extended their previous work on using the STOP-Bang questionnaire to predict OSA. 746 patients scheduled for inpatient surgery underwent both the STOP-Bang questionnaire and polysomnography (lab-based or home-based). Overall, OSA was present in 68.4% of patients (note that it is highly likely that patients having symptoms of OSA may have been more likely to consent to this study). They then looked at the sensitivities and specificities and positive and negative predictive values of various STOP-Bang scores to predict moderate or severe OSA and concluded that a STOP-Bang score of 5-8 identified a population with a high probability of moderate/severe OSA.


In the second study (Chung 2012b) 475 patients scheduled for inpatient surgery underwent home-base polysomnography and nocturnal oximetry with a wristwatch-based oximeter. Compared to those patients having an oxygen desaturation index (ODI) less than 5, those with an ODI greater than 5 had a significant increase in frequency of sleep disordered breathing. Using a cutoff ODI >10 had a sensitivity of 93% to detect moderate or severe OSA. The nocturnal ODI was not as sensitive in identifying central apnea.


Taking the two studies together leads to a potential strategy for identifying patients with OSA preoperatively without having to do a formal polysomnogram, that is using the STOP-Bang questionnaire followed by nocturnal oximetry in appropriate cases.


Though we don’t know whether CPAP is effective perioperatively in this population (the only study showed no benefit), knowing that someone has OSA has perioperative implications in airway management, opiate and other drug selection, post-op monitoring, pulmonary complications, overall complications and LOS. A previous study (Kaw 2012) found that patients with OSA undergoing cardiac surgery were almost 7 times more likely to have overall complications, 8 times more likely to have postoperative hypoxemia, and over 4 times more likely to require transfer to an ICU. They also had longer lengths of stay. Another study (Memtsoudis 2011) had also shown about a 5-fold increase in respiratory failure in patients with OSA undergoing noncardiac surgery. The latter study showed patients with OSA developed pulmonary complications more frequently than their matched controls after both orthopedic and general surgical procedures.


However, what we need to do now is demonstrate that outcomes can be improved by doing such preoperative screening and then implementing care management programs for this high-risk population.


A recent review of sleep disorders in hospitalized patients (Venkateshiah 2012) describes the physiology of sleep disturbances in this population and the factors contributing to disturbed sleep in the hospital. It also summarizes the ASA recommendations for perioperative management of OSA. Pain is the most common cause of disturbed sleep. One of the key occurrences in the immediate post-surgical period is a suppression of REM (rapid eye movement) sleep. This may be related to factors such as catecholamine levels and treatment with opioids. Then, on the second and third post-op days there is a REM rebound. During this period there is a significant increase in episodic oxygen desaturations due to disordered breathing.


Venkateshiah and Collop go on to summarize the American Society of Anesthesiologists (ASA) practice guidelines for the perioperative management of patients with OSA (ASA 2006). Like other reviews of the perioperative management of patients with OSA (Chung 2008, Adesanya 2010) they readily admit there is a paucity of evidence-based recommendations for care of surgical patients with suspected or known OSA.


There are obviously many reasons to identify patients preoperatively who are at high risk for OSA. Such patients are at greater risk for difficult intubation and are at risk for multiple post-operative complications. Anesthesiologists would like to use local anesthesia or peripheral nerve blocks where appropriate or otherwise use short-acting anesthetic agents in such patients and completely reverse the effects of neuromuscular blocking agents. Avoidance of the supine position as much as possible is recommended since some OSA is position-dependent.


Monitoring of the patient with OSA is obviously a key consideration. But Venkateshiah and Collop are quick to point out that there is a lack of an evidence base that monitoring with either pulse oximetry or capnography improves outcomes in this population.


Our February 22, 2011 Patient Safety Tip of the Week “Rethinking Alarms” highlighted an excellent study by 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. Even systems using continuous pulse oximetry and end-tidal CO2 monitoring may fail to adequately identify these patients. Nevertheless, we recommend monitoring with oximetry, capnography, and a rate/apnea monitor post-operatively. And while the first 12-hours post-operatively is a vulnerable period, the REM rebound and REM-associated hypoxemic events may increase 3-fold on the second and third postoperative nights, with associated risk of complications. Thus, monitoring should not be stopped before this period


Similarly, most of the recommendations for management of OSA in the post-op patient are consensus recommendations, as there has been a paucity of evidence. So most recommendations remain based on consensus opinion.


In patients with known OSA who are on CPAP at home, it is usually recommended that you have the patient bring in their CPAP machine from home. But in patients with suspected OSA or just recently diagnosed OSA who have not yet been on CPAP the effectiveness of CPAP in the hospital has not been demonstrated. In our November 22, 2011 Patient Safety Tip of the Week “Perioperative Management of Sleep Apnea Disappointing” we noted one of the few randomized controlled studies of surgical patients deemed at high risk of OSA had disappointing results (O’Gorman 2011). That study 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 had 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 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.


Many of the recommendations are to minimize the use of opioids. These would include using regional analgesic techniques or use of NSAID’s where possible. Most also recommend avoiding continuous background opioid infusions in patients on PCA pumps.


The guidelines recommend continuous oxygen supplementation until the patient has been shown to maintain adequate baseline oxygen saturation on room air. When to stop oxygem supplementation is less clear. We’ve cautioned on numerous occasions the possibility that oxygen supplementation in patients receiving systemic opioids may actually mask impending respiratory failure.



So, once again, we recommend you consider setting up a screening program for likely OSA prior to scheduled surgery. The STOP-Bang questionnaire is easy to administer in a few minutes and could be done at the time of surgical booking or other time the surgical team contacts the patient. Having a clinical guideline for dealing with those who score high on the STOP-Bang would be wise, keeping in mind that most of those recommendations will be consensus-based rather than evidence-based.





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



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








Chung F, Subramanyam R,  Liao P, Sasaki E, Shapiro C, Sun Y. High STOP-Bang score indicates a high probability of obstructive sleep apnoea. British Journal of Anaesthesia 2012; 108 (5): 768–75 (2012)



Chung F, Liao P, Elsaid H, et al. Oxygen Desaturation Index from Nocturnal Oximetry: A Sensitive and Specific Tool to Detect Sleep-Disordered Breathing in Surgical Patients. Anesthesia & Analgesia 2012; 114(5): 993-1000 Published online before print February 24, 2012



Venkateshiah SB, Collop NA. Sleep and Sleep Disorders in the Hospital. CHEST 2012; 141(5): 1337-1345



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



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



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















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