When an OSA patient becomes deprived of oxygen following an apnea event, the brain arouses the person out of sleep to reopen the airway. During surgery, anesthesia can further impair the function of airway muscles, causing apnea events to occur more frequently.1 Additionally, residual effects of anesthesia can make it more difficult for the patient to wake up and take a breath.

Knowledge of the increased health risks associated with OSA and anesthesia is widespread among sleep professionals. However, due to a lack of awareness among anesthesiologists, undiagnosed OSA patients can go under the knife without the team of surgeons knowing about the issue.

In order to make OSA screening easier for anesthesiologists, Frances Chung, MD, FRCPC, Department of Anesthesia, Toronto Western Hospital, created the STOP questionnaire. The STOP test consists of four questions: S: Do you snore loudly? T: Do you often feel tired, fatigued, or sleepy during daytime? O: Has anyone observed you stop breathing during sleep? P: Do you have or are you being treated for high blood pressure? If a patient answers “yes” to two or more of these questions, then they are ranked as being at high risk for OSA.

Sleep Review spoke with Chung about OSA awareness among anesthesiologists and the new OSA screening tool, the STOP questionnaire.

Frances Chung, MD, FRCPC

SR: In general, do anesthesiologists know the serious risks associated with obstructive sleep apnea and surgery?

Chung: At the present, there is a lack of knowledge among all anesthesiologists. Anesthesiologists are interested in obstructive sleep apnea only when an unexpected mortality occurs that can be attributed to OSA and the effects of the general anesthetic or OPI [opiates] medications.

SR: Why is it important for anesthesiologists to screen patients for OSA?

Chung: Obstructive sleep apnea patients have difficult airways, making them more difficult to manage with intubation or after extubation of the airways, which increases mortality. Anesthesiologists are experts in airways, and we see a large number of patients who come in for surgery. We know the airway, and we know when the patient has problems in the airway.

SR: How did the development of the STOP test take place?

Chung: In 2006, the American Society of Anesthesiologists (ASA) published obstructive sleep apnea guidelines for anesthesiologists. In these guidelines, the ASA recommends that the anesthesiologist should screen for obstructive sleep apnea, and recommends the ASA checklist of 14 questions (12 for adults and 14 for children) to do so. This is not very practical in a busy preoperative practice, because there are too many questions. I designed the STOP questionnaire, which is only four questions, to more practically screen patients for OSA. Essentially, if answers to two questions on the STOP test are positive, the patient may be at high risk of OSA. The Berlin Questionnaire, another choice for screening patients, is valid only in the primary care setting.

SR: How does the STOP test size up with the Berlin Questionnaire and the ASA’s 14-point checklist as an effective method of screening?

Chung: We actually validated the STOP questionnaire against the ASA checklist and the Berlin Questionnaire, and we found that our test is very similar [study from Anesthesiology, May 2008]. Our STOP test is very small in comparison to the other screening methods, but similar to the larger questionnaires in effectiveness.

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SR: Why is there a push for more awareness all of a sudden?

Chung: The increased awareness is due in part to the ASA taking a leadership role and publishing the guidelines in 2006. Additionally, there are patients who have died suddenly after surgery and they are suspected to have OSA. We have used the STOP questionnaire to prove that patients who score positively on the questionnaire have higher postoperative complications. However, there is still a lot of work to be done because there are very few studies on the topic, and most of the studies available right now are retrospective.

SR: If someone is screened using one of these tools, and they look like they have OSA, then what? Should they be recommended for a sleep study or is it just taken into consideration as the surgery goes on?

Chung: If the patient is coming for surgery and has a high risk of OSA, the ASA guidelines say the next step depends on the result of the screening, on the type of surgery, and on whether the pain will require morphine after surgery.

A) If the patient screens positive, the surgery is major, they have a lot of pain, and therefore they require morphine afterward, then the patient may need to be referred as time allows. If they are not, they have to be monitored and referred later.

B) If the patient is not having major surgery and requires only local or regional anesthetic, then they don’t need to be referred before surgery, because these types of anesthetic will not cause a problem. Also, if a patient doesn’t need morphine and can receive an oral painkiller that does not have a respiratory effect, the referral can wait and the patient can be monitored.

SR: Since the STOP questionnaire is only four questions, should anesthesiologists screen every patient they see? Or is it only necessary for those who are suspected to have OSA by looking at them?

Chung: It depends on the preference of the center. We screen every patient who comes through because it is difficult to tell if someone has sleep apnea just by looking at them. If you think someone might have sleep apnea, you might not be correct. You cannot always pick out OSA patients by looking at them. The ASA guidelines do recommend that a screening should be done on every patient.

SR: What is the key message that sleep professionals should get out to the anesthesiologist community?

Chung: Sleep professionals need to help increase awareness of risks associated with OSA among anesthesiologists. Undiagnosed OSA patients have a much higher risk of diabetes, stroke, heart attack, and other diseases. Sleep professionals should be informing anesthesiologists of the seriousness of sleep-disordered breathing so that the anesthesiologists will understand that these conditions could have serious effects.


  1. Obstructive sleep apnea and anesthesia: what are the risks? www.mayoclinic.com/health/obstructive-sleep-apnea/AN01625. Accessed September 5, 2008.