Sleep apnoea occurs during sleep when a cessation of airflow occurs for at least 10 seconds (usually 20-30 s but rarely >2 min). The apnoeas (absences of breath) are accompanied by snoring, sleep arousals, and hypoxia.
The term "Sleep Apnoea" describes 2 major sleep-related clinical problems:
- Obstructive Sleep Apnoea (OSA), and
- Central Sleep Apnoea.
OSA is caused by upper airway (UA) obstruction at the level of the pharynx and is the most common form of sleep apnoea. Central apnoea is the result of impairment in respiratory control of breathing.
Sleep Apnoea syndrome encompasses a spectrum of sleep-related breathing disorders - ranging from simple snoring to severe sleep apnoea with associated Neuro cognitive deficits, residual daytime sleepiness, pauses in breathing, and cardiovascular consequences such as hypertension and stroke.
Sleep Apnoea is defined in adults as a temporary absence or cessation of breathing during sleep for 10 or more seconds. It’s symptoms are as follows:
- Repetitive episodes of UA obstruction during sleep
- Arterial oxygen desaturation in association with apnoeas
- Daytime hypersomnolence
- Snoring
Types of Sleep Apnoea
In obstructive apnoea, ventilatory effort is present but airflow ceases due to closure of the UA. In central apnoea, ventilatory effort is absent and, therefore, airflow ceases. In mixed apnoea, ventilatory effort is not observed initially (central apnoea component) but ventilatory effort follows (obstructive apnoea component). Partial reductions in inspiratory airflow (hypopneas) also have been identified in patients with SDB. A hypopnea is a decrease in inspiratory flow to 50% of baseline and is associated with desaturation.
Apnoea index
The apnoea index (AI), which is the total number of apnoeas during sleep divided by the total number of hours of sleep, is a relative measure of apnoea severity. Traditionally, an AI of 5 or more has been used to define the presence of OSA. Many laboratories are reporting the apnoea-hypopnea index, also known as the respiratory disturbance index (RDI).
OSA Assessment Guide for General Practitioners
Check for indications of snoring and sleep apnoea:
- Daytime sleepiness (not tiredness) e.g. reduced alertness, poor memory and difficulty concentrating and making decisions; nodding off during less stimulating activities: reading, watching TV, meetings, etc. Best assessed with the Epworth Sleepiness Scale.
- Spouse has noticed episodes of stopping breathing (although any snorer will occasionally have such events, especially when supine).
- Patient experiences waking with choking/obstructed episodes (although they will only recognise a small proportion of the number of such episodes actually occurring).
- Regularly waking unrefreshed in the morning.
- Neck circumference over 45cm diameter (which will usually, but not always, indicate overweight).
- Small pharynx on visual inspection.
