May 6, 2008
Preoperative Screening for Obstructive Sleep Apnea
Ever tried to convince a friend or family member they need to get a polysomnogram because they have symptoms or signs of possible obstructive sleep apnea (OSA)? Then you know how hard it is! You have to keep nagging at them and many months typically pass before they finally agree to get the study, if they ever agree at all. (Note that it is usually easier to convince a patient who comes to see you because of symptoms that bothered them and could be due to OSA).
But suppose you are an anesthesiologist or surgeon and are preparing a patient for upcoming surgery. Knowing they have OSA would be very helpful in planning their management in the preoperative, operative, and postoperative settings. Most cases of OSA are undiagnosed, yet OSA patients have higher rates of postoperative complications and death. So having a screening tool to identify patients likely to have OSA would be extremely useful. Screening tools currently available are either not validated for a surgical population or are too cumbersome to be used from a practical standpoint in the presurgical evaluation.
Enter the STOP Questionnaire, a screening tool for OSA developed by Frances Chung and colleagues at the University of Toronto and several affiliated Toronto area hospitals. They noted that two of the more widely used screening tools for OSA, the Berlin Questionnaire and the American Society of Anesthesiologists checklist, had not been validated in the surgical population. They looked at the Berlin questions and did factor analysis on patient responses to those questions to derive the four questions below:
S “Do you snore loudly?”
T “Do you often feel tired, fatigued or sleep during daytime?”
O “Has anyone ever observed you stop breathing during your sleep?”
P “Do you have or are you being treated for high blood pressure?”
They did a pilot study, administering the STOP questionnaire to 596 surgical patients and then inviting them to undergo polysomnography (in-lab). That pilot study showed a sensitivity of 72% and positive predictive value (PPV) of 75% and high level of correlation when the test was administered a second time. They then moved on to a validation study in which the STOP questionnaire was given to almost 3000 patients scheduled for a variety of surgical procedures. 17% of those patients agreed to have polysomnography, though only about half of those actually showed up for the polysomnogram. Using a cutoff apnea/hypopnea index of greater than 5, the sensitivity of the STOP questionnaire was 66%, specificity 60%, PPV 78%, and NPV 44%. Using higher AHI cutoffs (corresponding to more severe degrees of OSA) the sensitivities and PPV’s were even higher, reaching a sensitivity of 79% and PPV of 89% at an AHI of greater than 30. When they looked at it in patients with certain other known risk factors for OSA (BMI >35, age>50, neck circumference >40, male gender) they found that the “STOP-bang” questionnaire had even better sensitivities and PPV’s and NPV’s, especially for moderate and severe OSA.
The American Society of Anesthesiologists has published Practice guidelines for the perioperative management of patients with obstructive sleep apnea. They stress working with the surgeons to allow enough time to develop a perioperative management plan. Based on the degree of clinical suspicion for OSA and suspected severity, a decision needs to be made as to whether to get formal polysomnography to confirm a diagnosis or to simply proceed and assume OSA based on clinical grounds. Similarly, a decision needs to be made as to whether CPAP should be started prior to the surgery. And it must be decided whether the surgery needs to be done in an inpatient setting or outpatient setting, keeping in mind the postoperative requirements. Since many patients with OSA have difficult airways, the airway should be managed per the ASA Practice Guideline for Management of the Difficult Airway.
OSA patients are especially susceptible to the respiratory depressant and airway effects of sedatives, opiods, and inhaled anesthetics so selection of intraoperative agents is important. Local or regional anesthesia should be considered where appropriate. But when sedation is needed, continuous monitoring is required and CPAP or an oral appliance should be considered. They stress that general anesthesia with a secure airway is probably preferable to deep sedation without a secure airway. They also stress that the patients should be extubated while awake and after verification of full reversal of neuromuscular blockade. Use of a nonsupine position (eg. lateral or semiupright) during extubation and recovery is advised.
In the postoperative period, techniques to reduce or avoid systemic opiods are stressed and it is pointed out that sedative agents like barbiturates and benzodiazepines further increase the risk of respiratory depression or airway obstruction. They discuss monitoring issues and possible need for CPAP or NIPPV and supplemental oxygen. They discuss the various venues where a patient may be recovered, stressing the adequacy of the technological and personnel monitoring capabilities.
And they end with a good discussion of the factors to be considered in the inpatient vs. outpatient decision and a discussion about the criteria for discharge to unmonitored settings.
So the bottom line is that because there are so many potential risks and management considerations for OSA patients before, during and after surgery, it is extremely important to consider the possibility of OSA in each patient contemplating surgery. Use of a screening tool such as STOP or STOP-bang Questionnaires may be a major step toward the goal of rendering surgery safe in such patients.
Update: See our August 18, 2009 Patient Safety Tip of the Week “ ”.
Chung F, Yegneswaran B, Balaji M, Liao P, Chung S, Vairavanathan S, Islam S, Khajehdehi A, Shapiro CM. STOP Questionnaire: A Tool to Screen Patients for Obstructive Sleep Apnea. Clinical Investigations. Anesthesiology. 108(5):812-821, May 2008. http://www.anesthesiology.org/pt/re/anes/abstract.00000542-200805000-00008.htm;jsessionid=LP3F46NfyKvvTMzsnkPKh2hJlfKJZCLCMx8N7QqTwPv7WmJQjhdR!-859253161!181195629!8091!-1?index=1&database=ppvovft&results=1&count=10&searchid=1&nav=search
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 May;104(5):1081-93. http://www.asahq.org/publicationsAndServices/sleepapnea103105.pdf