Patient population
In this cross-sectional study, we included adult patients (> 18 years of age) with American Society of Anesthesiologists (ASA) class I–III who were scheduled to undergo non-cardiothoracic surgery from December 2018 to February 2019. All patients provided written informed consent before participating in the study, and the study was performed in accordance with the Declaration of Helsinki. Patients were excluded if they had an artificial airway (e.g., endotracheal tube, tracheostomy), a history of poorly controlled pulmonary disease, and undergoing bariatric surgery.
The study was approved by the ethics committee of Ramathibodi Hospital, Mahidol University, Bangkok, Thailand (ID 04–61-51) and was registered on the Thai Clinical Trials Registry, identifier TCTR20181129001, registered 23 November 2018 (Prospectively registered) http://www.clinicaltrials.in.th/index.php?tp=regtrials&menu=trialsearch&smenu=fulltext&task=search&task2=view1&id=4205. The reporting of this study was performed by adhering to the Standards for Reporting of Diagnostic Accuracy Studies (STARD) statement for the reporting of diagnostic accuracy studies.
Our primary objective was to investigate the association between the incidence of perioperative adverse events and OSA risk (high vs. low) based on the original and modified STOP-Bang questionnaires. Our secondary objective was to identify the incidence of difficult facemask ventilation, difficult intubation, Cormack–Lehane classification of laryngoscopic view ≥3, need for oxygen supplement during the recovery period, intensive care unit admission, risk factors of perioperative adverse events, and 30-day mortality.
Instruments and definitions
The modified STOP-Bang questionnaire was used by anesthesiologists during the preoperative period. The investigators determined the occurrence of postoperative complications (cardiovascular, pulmonary), difficult ventilation, difficult intubation, Cormack–Lehane classification of laryngoscopic view ≥3 and unexpected ICU admission rates.
The modified STOP-Bang includes eight items: snoring, tiredness, observe apnea, high blood pressure, BMI > 30 kg/m2, age > 50 years, neck circumference > 40 cm, and male gender. Patients who had STOP-BANG scores ≥3 identified as high risk for OSA.
Difficult ventilation was defined as facemask ventilation that is not adequately ventilated after inserting the oral airway or required using a two-person technique.
Difficult intubation was defined as ≥3 attempts of intubation by an experienced anesthesiologist or an intubation period of > 10 min.
The perioperative adverse events included a history of hypoxemia, reintubation, arrhythmia, myocardial infarction, congestive heart failure, respiratory adverse events and hypertensive events, which were reported by the attending anesthetist. The definitions are detailed in Additional file 1.
Data analysis and statistics
Sample size estimation
The sample size calculation was based on the prevalence of postoperative complications among patients with high-risk OSA based on the original STOP-Bang questionnaire [15], which was 19.6%. The confidence level (1 − α) was used for statistical reporting, where α = 0.05 and precision (e) was 0.04. The required sample size was 385 participants.
Data analysis
Statistical analyses were performed using SPSS v 22.0 (SPSS, Chicago, IL, USA). Data on patient characteristics are presented as mean ± standard deviation or frequency (percentage). The relationship between risk of OSA, based on a modified STOP-Bang questionnaire, and perioperative complications was evaluated using the chi-square test. For pairwise relationships, a two-sample t test was used to compare continuous variables and the chi-square test for binary variables.
Performance predictors, including sensitivity, specificity, positive likelihood ratio (+LR), and negative likelihood ratio (−LR), were calculated and compared. The receiver operating characteristic curve (ROC) was used to compare the ability of the original and modified STOP-Bang questionnaires to predict perioperative adverse events.
Logistic regression was used to determine the association between OSA risk and perioperative adverse events. Covariates included ASA physical status, preoperative oxygen saturation, type of anesthesia, and opioid dosage, were categorized to account for the potential association of adverse outcomes with each predictor. P < 0.05 was set as significant.