The results of the study showed that with an increase in the STOP-Bang score, there was a corresponding increase in the predicted probability, OR, and specificity for having OSA, moderate/severe, and severe OSA. This was accompanied by a progressive decrease in sensitivity. For a STOP-Bang score of 5, the OR for moderate/severe and severe OSA was 4.8 and 10.4, respectively. For STOP-Bang 7 and 8, the OR for moderate/severe and severe OSA was 6.9 and 14.9, respectively. The STOP-Bang questionnaire was initially introduced as a scoring model for the preoperative patients.11
The results from this study further validated the value of STOP-Bang questionnaire as a screening tool in surgical patients. The association between the STOP-Bang score and the probability of OSA would provide the perioperative care team a useful tool to stratify patients for unrecognized OSA and triage patients for diagnosis and treatment.
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
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 validated15,33
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.
In conclusion, the predicted probabilities were greater as the STOP-Bang score increased, showing that patients had a greater probability of having OSA when they scored higher on the STOP-Bang questionnaire. A STOP-Bang score of <3 will allow the healthcare team to rule out patients who do not have OSA. A STOP-Bang score of 5–8 will allow the team to identify patients with increased probability of moderate/severe OSA. The STOP-Bang score can help the healthcare team to stratify patients for unrecognized OSA, practice perioperative precautions, or triage patients for diagnosis and treatment.