16th February 2025

Obstructive sleep apnoea syndrome (OSA)

OSA is the third most common respiratory problem in the UK after asthma and COPD, with 2.5% of women and 5% of men in Western populations having severe enough disease to warrant treatment.

Pathophysiology and risk factors

Loss of pharyngeal dilator tone during REM (rapid eye movement) sleep results in occlusion of the upper airway, leading to apnoea lasting at least 10 seconds, with transient hypoxia and hypercapnia. The patient partially wakes, leading to an increase in airway tone to allow ventilation. The cycle repeats hundreds of times per night, leading to fragmented sleep.

Sympathetic stimulation during apnoeas with resultant hypertension is thought to explain the increased risk of poor cardiovascular outcomes, which is independent of obesity.

Risk factors include obesity, large neck circumference, large tonsils, hypothyroidism, acromegaly, increasing age, smoking, and use of sedatives or alcohol. Although obesity is a risk factor, OSA is also common in those without a raised BMI.

Presentation and diagnosis

Presentation may include loud snoring, daytime sleepiness, morning headaches, mood change, and poor memory and concentration. Their partner may have observed apnoeic episodes.

The STOP-BANG score and Epworth Sleepiness Score are frequently used screening tools.

Polysomnography (sleep study) is the diagnostic investigation of choice; it is comprised of six continuous elements: oximetry, EEG, EMG, ECG, airflow monitoring and electrooculogram.

The apnoea hypopnoea index (AHI) is the number of apnoeas or hypopnoeas per hour. An AHI > 14 in the presence of symptoms indicates moderate disease.

Polysomnography will differentiate OSA from other causes of daytime sleepiness, such as: central sleep apnoea (for example due to heart failure or stroke), nocturnal seizures, gastro-oesophageal reflux disease (GORD), restless legs syndrome, and periodic limb movement disorder.

Management of OSA

Management options include:

• Conservative – weight loss, smoking cessation, avoidance of alcohol/sedatives, mandibular advancement devices
• CPAP (continuous positive airway pressure) – typically nasal CPAP is used with pressures of 5-15 cmH2O. It works by splinting open the upper airway and has been shown to be highly effective in improving quality of life
• Surgical – pharyngeal surgery, bariatric surgery