A 58-year-old man presents with excessive daytime sleepiness, loud snoring, and worsening morning headaches over the past year. His wife reports frequent episodes of gasping and pauses in breathing during sleep. He feels fatigued throughout the day and occasionally falls asleep while watching television. The patient has gained 11 kg (25 lb) in the past 3 years. His medical history is significant for resistant hypertension (despite 4 medications) and type 2 diabetes mellitus. He does not smoke or drink alcohol. On examination, his blood pressure is 165/96 mm Hg, heart rate is 81/min, and oxygen saturation is 94% on room air. His BMI is 39 kg/m². Physical exam shows a neck circumference of 18.5 inches, a Mallampati class IV airway, and 1+ bilateral pitting edema to the mid-calf. Heart sounds are distant, and the lungs are clear to auscultation.

Laboratory results reveal:

• Hemoglobin    172 g/L (normal: 130–170 g/L)
• HCO₃⁻              28 mmol/L (normal: 22–28 mmol/L)