Obstructive Sleep Apnoea - OSA

Original article by Tom Leach | Last updated on 15/6/2015
Printer-friendly version

Obstructive Sleep Apnoea (OSA) is a condition whereby there are periods of apnoea lasting >10 seconds on multiple occasions during sleep. It is a common chronic disorder of increasing prevalence, which often requires life-long care, and can have serious complications.
The condition causes periods of apnoea, typically of 20 to 40 seconds whilst patients are sleeping. This leads to restless sleep, which in turn causes day-time somnolence (sleepiness), fatigue and memory / cognitive problems.
The apnoeic periods also cause hypoxia and hypercapnia, which leads to hypertension, and can cause pulmonary hypertension and cor pulmonale.

It is part of a spectrum of sleep disorders (SDB - sleep disordered breathing), which also includes sleep hypopnoea, where there are periods of reduced ventilation, without true apnoea. Hypopnoea is defined as a period of sleep lasting >10 seconds in which ventilation is reduced by >50%

Epidemiology

  • The diagnosed prevalence of OSA is abour 2-4%
  • The actual prevalence is thought to be closer to 20-30%
  • Higher incidence in males

Aetiology

  • Obesity
  • Age - increases with age from young adulthood to 6th decade
  • Typical patient is obese middle aged male
  • Can occur in patients of normal weight
  • Upper airway anatomical abnormalities - such as large tonsils
  • Smoking
  • Alcohol
  • Sedative medications
  • Predisposing medical conditions:

Pathophysiology

OSA is caused by a collapse of the soft-tissue of the upper airway (oropharynx and velopharynx, or "throat") during sleep. This is most likely to occur during stage 3 NREM, and REM sleep, as this is the period of the least muscle tone. 
The muscles of breathing continue to act, but are unable to perform ventilation.
As a result, blood oxygen levels fall (hypoxia) and CO2 levels may rise (hypercapnia).
This causes a period of 'neurological arousal' - whereby the REM sleep is disturbed, and the brain is aroused to a higher state, and the airway is restored. This does not usually result in full awakening, but severely disrupts deep sleep periods.

The hypoxia associated with apnoeic episodes causes vasoconstriction, which leads to hypertension and pulmonary hypertension, and can ultimately cause cor pulmonale
The hypertension seen in OSA often does not follow normal diurnal variation, and does not fall  with sleep. In some patients it may actually paradoxically increase with sleep. 

Diagnosis

Diagnosis is not always straight forward. Most patients snore when sleeping and have day time sleepiness, but neither of these symptoms are very specific.
Differentials include:

Polysomnography

This is traditionally the gold standard of diagnostic test. The exact method of testing can vary, but usually including an EEG to measure brain wave activity, EOG (electro-oculogram) to measure eye movements, and an electromyogram to measure muscle activity.

Most tests will also now use pulse oximetry.

Polysomnography is expensive, and requires the patient stay overnight at the testing facility. 

Questionnaires and risk stratification

Several question based systems exist for the diagnosis and classification of OSA. 

The Epworth Sleepiness Score is sometimes used as a self-selective tool for identifying sleepiness of any cause. It asks patients to rate their chance of dozing off whilst doing a variety of activities. 

The STOP BANG questionnaire is used by clinicians to assess a patient's risk of OSA. More than three positive risk factors indicates high risk. Less than 3; low risk. 
S - Snoring
T - Tired
O - Observed to stop breathing during sleep
P -  (Blood) Pressure - Hypertension

B - BMI > 35
A - Age >50
N - Neck circumference >40cm
G - Gender - male

Classification

The apnoa-hypopnoea index is used to classify levels of OSA.
The index is calculated as the number of apnoeas + hypopnoeas per hour:

  • Mild - 0-15 per hour
  • Moderate - 15-30 per hour
  • Severe >30 per hour

Complications

Cognitive

  • Memory problems
  • Day time somnolence
  • Poor concentration
  • Increased risk of accidents - e.g. when driving
  • Irritability
  • Personality change

Cardiovascular

Other

  • Increased risk of stroke
  • Increased risk of all cause mortality, independant of other risk factors described above
  • Increased risk of insulin resistance and type 2 diabetes
  • Increased risk of peri-operative complications

Management

  • Weight loss
  • Home CPAP

These are the two main interventions in OSA and both have been proven in RCTs (randomized control trials). CPAP need to be regularly (every night), but those who are complaint have greatly reduced risk of complications.

Other lifestyle  interventions include:

  • Cessation of smoking
  • Avoidance of alcohol in the evening
  • Avoidance of sedating medications

Other Interventions have inconclusive evidence, but may be of benefit in some patients, usually those with mild symptoms. These include:

  • Surgery
  • Mechanical devices, including oropharyngeal devices
  • Medications, e.g. modafinil