Current practice guidelines recommend obstructive sleep apnea (OSA) patients to stay in the post anesthetic care unit (PACU) until the risk of respiratory depression has subsided. Inevitably, a greater demand on hospital resource utilization in these patients will increase health care cost. Polysomnography (PSG) and screening questionnaires can identify OSA but they are limited by accessibility and false positive results, respectively. Inaccurate OSA identification misguides postoperative surveillance plan. In contrast with MRI and CT scans, ultrasound is more accessible and more likely a practical tool for OSA screening. However, before clinical application, airway ultrasound (US) exam must undergo vigorous testing to check its utility, accuracy, inter-observer reliability and its ability to identify OSA and its severity.

The investigators plan to recruit surgical patients at risk of OSA, exposed to sedatives,and/or general anesthesia. Surface ultrasound measurements will be conducted in a separate setting, and be correlated with the sleep study results, and a set of ultrasound parameters will be validated in this setting. Relevant clinical outcomes will be captured as well.

Inclusion criteria

• age≥18
• ASA physical status I - IV;
• Suspected to have OSA for clinical reasons such as high risk on screening questionnaire i.e., a STOP-Bang score >3, and referred to have a sleep study for OSA diagnosis by the clinical team at any point of care during the perioperative period (such as the clinic using the screening tool, during or after surgery in the ward experiencing recurrent upper airway obstructive events, need for CPAP in the postoperative period and / or suspected to have obstructive airway events). Or;
• Patients who were recently diagnosed to have OSA and underwent a laboratory sleep study within the last year.
• Patients who were recently diagnosed to have OSA but are non-compliant with treatment. Compliance defined as: median nightly CPAP or APAP use > 70% of the nights, and for longer than 4 hours of nightly use during the last 3 months),43 or using oral appliance use (use > 70% of nights, and for longer than 4 hours of nightly use in the last 3 months.

Exclusion criteria

• failure to understand and provide consent
• past history of oral, head and neck surgery (e.g., OSA corrective surgery)
• active head & neck disease (e.g., cancer, infection and radiotherapy);
• inability to perform breathing tests per instruction
• Patients currently on treatment for OSA (as this may interfere with the upper airway dimensions and the US assessment may not be accurate)

Suspected / Recently diagnosed untreated Obstructive Sleep Apnea (amendment authorized 20/12/2017) / Non-compliant to OSA treatment