The STOP-Bang questionnaire is a scoring model consisting of eight easily administered questions starting with the acronym STOP-Bang (Appendix) and is scored based on Yes/No answers (score: 1/0). Thus, the scores range from a value of 0 to 8. A score of ≥3 has shown a high sensitivity for detecting OSA: 93% and 100% for moderate and severe OSA, respectively.¹¹

Owing to its high sensitivity at a score of ≥3, the STOP-Bang questionnaire is considered very helpful to rule out patients having moderate and severe OSA.¹¹ However, the specificity at the same cut-off is low: 47% and 37% for moderate and severe OSA, respectively, resulting in fairly high false-positive rates. The objective of this study is to evaluate the predictive probabilities for OSA at different scores on the STOP-Bang questionnaire. We hypothesize that a high STOP-Bang score indicates a high probability of moderate/severe OSA.

All the patients were asked to complete the STOP questionnaire.¹¹ Information concerning BMI, age, neck circumference, and gender (Bang) were collected by a research assistant. In the initial 2 yr period of the study, the patients were invited to undergo a laboratory PSG. During the subsequent 2 yr of the study, the patients underwent a portable PSG study at home. The results of the PSG were used to evaluate the various scores of the STOP-Bang questionnaire.

The portable PSG was performed with a level 2 portable sleep device (Embletta X100) which is shown to be a reliable alternative for standard PSG in surgical patients.¹⁴ The PSG recordings were performed at the patients’ home. The recording montage consisted of two EEG channels (C3 and C4), electrooculogram (left or right), and chin muscle EMGs. Thoracic and abdominal respiratory effort bands, body position sensors, and pulse oximeter were also used.

The device was attached to patients by a well-trained PSG technician at their home and the overnight recordings were unattended. The patients were advised on how to remove the device which was picked up the next morning from the patients’ home by the same sleep technician. A certified PSG technologist who was blinded to the study information analysed the PSG. The manual scoring was performed using Somnologia Studio 5.0 as the scoring platform. Manual scoring was performed according to the Manual of the American Academy of Sleep Medicine.¹⁵

The laboratory PSG was performed overnight and patients went to bed at their usual bedtime. A standard EEG montage consisting of EEG, electrooculogram, submental EMG, and ECG obtained with surface electrodes were used to collect the sleep architectural data. A pulse oximeter measured the oxygen saturation. Additional recordings included the respiratory effort by thoraco-abdominal excursion, respiratory inductive plethysmography, and oronasal airflow.

A certified polysomnographic technologist scored the polysomnographic recordings under the supervision of a sleep physician who assessed and approved the reports. The technologist was blinded to the results of the STOP-Bang questionnaire and other clinical information about the patients. The sleep stages and apnoea–hypopnea index (AHI) were scored according to the American Academy of Sleep Medicine Task Force recommendations.¹⁶

The diagnosis of OSA was based on an AHI >5 with fragmented sleep and daytime sleepiness. The severity of OSA with both laboratory and portable PSG was classified based on the AHI values: >5–15 as mild OSA, >15–30 as moderate OSA, and >30 as severe OSA.^15,16

The summary of age, gender, BMI, and neck circumference of the different patient groups is shown in Table 1. The patient characteristics were similar between the 930 patients who underwent a PSG and the 5439 patients who did not undergo a PSG due to the reasons of no consent or no show. The 184 patients, who underwent a PSG but did not complete all the elements of the STOP-Bang questionnaire, were excluded from the analysis set. Patient characteristics other than the neck circumference were similar between the 184 patients excluded from the analysis set and the 746 patients used for the analysis.

Of the 746 patients used for analysis, there were 510 (68.4%), 287 (38.5%), and 134 (18.0%) patients who had OSA (AHI>5), moderate/severe OSA (AHI>15), and severe OSA (AHI>30), respectively. The distribution of each of the STOP-Bang scores is detailed in Figure 2. Most patients had a STOP-Bang score of 3 (22.9%) and 4 (22.3%).

The area under the receiver operating curves was 0.65 (95% CI: 0.61–0.70), 0.67 (95% CI: 0.63–0.70), and 0.71 (95% CI: 0.66–0.75) for all OSA, moderate/severe OSA, and severe OSA, respectively. Although the areas under the receiver operating curves do not show perfect discrimination, the confidence intervals do not include 0.5, confirming the diagnostic ability of the STOP-Bang questionnaire. The STOP-Bang questionnaire had the best discrimination with severe OSA.

For a STOP-Bang score of 5, the OR for moderate/severe was 4.8 (95% CI: 2.8–8.0) and for severe OSA was 10.4 (95% CI: 4.5–24.3). For a STOP-Bang score of 6, the OR for moderate/severe was 6.3 (95% CI: 3.4–11.7) and for severe OSA was 11.6 (95% CI: 4.6–28.7). For a STOP-Bang score of 7 and 8, the OR for moderate/severe was 6.9 (95% CI: 3.3–14.3) and for severe OSA was 14.9 (95% CI: 5.6–39.6) (Table 2).

The sensitivity, specificity, PPVs, and NPVs for all OSA, moderate/severe OSA, and severe OSA are summarized in Table 3. As the STOP-Bang score increased from 3 to 8, the sensitivity decreased from 68.4% to 0.4% for moderate/severe OSA patients, and 94.8% to 0% for severe OSA patients. When the STOP-Bang score was 5, the specificity for moderate/severe OSA was 56.1% and for severe OSA was 74.2%.

It is estimated that nearly 80% of men and 93% of women with moderate-to-severe sleep apnoea are undiagnosed,¹⁷ which poses a variety of problems for anaesthesiologists. OSA patients are known to have a higher incidence of difficult intubation,¹⁸ postoperative complications,^19,20 increased intensive care unit admissions,⁷ and greater duration of hospital stay.²¹ Memtsoudis and colleagues⁹ found that OSA was associated with a significantly higher incidence of pulmonary complications. However, no association between postoperative complication and OSA severity was found in obese patients undergoing bariatric surgery.²² This may be due to the fact that most patients with OSA (93%) received perioperative positive airway pressure therapy, and all patients were closely monitored after operation with pulse oximetry on either regular nursing floors or in intensive or intermediate care units.²² Recently, a Canadian publication²³ and the American Society of Anesthesiologists guidelines²⁴ both stressed the importance of preoperative diagnosis and perioperative management of OSA patients to avoid postoperative complications.

To identify patients at high risk of OSA is the first step for the perioperative care of OSA patients and prevention of adverse events. Although no test or parameter has been widely accepted as a tool to identify the OSA patients who are particularly at risk for severe postoperative pulmonary adverse events, a recent study does show that patients classified as STOP-Bang high risk had an increased incidence of postoperative complications.²⁵

The STOP-Bang questionnaire is concise and easy to use. It consisted of eight questions with a yes or no answer and has been used as a preoperative screening tool for OSA.^12,26–28

Recently, the STOP-Bang questionnaire has been validated in two studies of patients referred to the sleep clinic.^29–30 Farney's study showed that the STOP-Bang questionnaire can be used to estimate the probabilities of no, mild, moderate, and severe OSA. The greater the cumulative score of risk factors as reflected by the STOP-Bang model, the greater the probability of severe OSA.²⁹ With any score >4, the probability of having severe OSA increases continuously. With a score of 8, the probability of severe OSA was 81.9%.²⁹ Although our results also showed a similar association between the probabilities of having severe OSA and the score on STOP-Bang, we did not see such a high probability of severe OSA with a higher STOP-Bang score. This may be due to the difference in the study population. Our patients were preoperative patients. The patients in Farney's study were the patients referred to sleep clinic population which have a high prevalence of severe OSA.

Since a STOP-Bang score of ≥3 demonstrated a very high sensitivity and NPV for moderate/severe OSA, this cut-off may be good for a surgical population with high OSA prevalence such as bariatric surgical patients. We would be confident in excluding the possibility of moderate/severe or severe OSA in patients with a STOP-Bang score of 0–2. On the other hand, the patients with a STOP-Bang score of 5–8 have a high specificity to detect moderate and severe OSA. These scores may be useful in the general patient population which has a low OSA prevalence to reduce false-positive rate. It enables identification of those patients most in need of urgent evaluation and to exclude patients from possible harm due to unrecognized sleep apnoea.²⁹ However, further research is needed so that the STOP-Bang can be validated in the different clinical populations.

It is a challenge to establish a practical perioperative care pathway for OSA patients. It is not known whether patients with a STOP-Bang score of 5–8 with co-morbidities having major surgery would benefit from sleep medicine referral, expedited polysomnography (PSG), and continuous positive airway pressure (CPAP) treatment. There have been no studies in the literature to prove that preoperative PSG is of benefit to the surgical patients with suspected OSA. Overnight-attended PSG is an old standard in the diagnosis of OSA, but it is expensive and cumbersome. Often, there is a timeline for patients undergoing surgery. Portable home-based monitoring devices or single channel recording such as nocturnal oximetry might be used as an alternative for the diagnosis of OSA in patients with high probability of moderate-to-severe OSA.³¹ Thus, a combination of STOP-BANG questionnaire to identify patients at risk of OSA and nocturnal oximetry may allow for a more rapid diagnosis of OSA. Alternatively, in the patients classified as high risk of OSA by the STOP-Bang questionnaire, especially those with a STOP-Bang score of ≥5, practicing perioperative precautions (preparation for possible difficult intubation, using short-acting anaesthesia agents, adequate neuromuscular blocking agent reversal, and use of CPAP after operation) and postoperative monitoring is helpful to prevent adverse outcomes.^23,24,32 If patients get earlier treatment for their OSA because of screening in preoperative clinics, there may be long-term health benefits for the patients, besides reducing risk for OSA-related perioperative adverse event. More collaboration between anaesthesiologists, surgeons, and sleep physicians is needed.

There are a few limitations with our study. The study could be criticized because PSG was performed with both the standard PSG in the laboratory and the portable PSG at home. Embletta X-100 is a level 2 diagnostic device for SDB. When installed by a well-trained technician and scored by a certified PSG technologist, parameters measuring sleep-disordered breathing and sleep architecture from Embletta X-100 were comparable with in-laboratory standard PSG.¹⁵ Although home monitoring is validated^15,33 and all PSG recordings were scored by certified PSG technologists, some inconsistency in the two approaches may exist. Secondly, the study population is surgical patients referred to preoperative clinics. These results may not be applicable to other patient populations. Further validation in the different population, especially the general population, needs to be done. Also, there may be a selection bias involved in the patient recruiting process, the subjects having some OSA-related symptoms might be more motivated to give consent to this study. Finally, like all other screening studies for sleep apnoea, central apnoeas were also not evaluated separately in the report.