Obstructive Sleep Apnoea (OSA)

Definition

Obstructive sleep apnoea/hypopnoea (OSAH; formerly termed 'obstructive sleep apnoea' by NICE):

• Sleep-related breathing disorder marked by repeated episodes of complete or partial upper airway obstruction, causing apnoea OR hypopnea respectively.

Obstructive sleep apnoea/hypopnoea syndrome (OSAHS)

• OSAHS refers to OSAH that is symptomatic, particularly with daytime sleepiness. 

Epidemiology

Prevalence (population surveys): ^{[Ref 1], [Ref 2]}

• 8.7% men, 5.6% women
• BMI 30-39.9 → Up to 44.6% men, 13.5% women  
• Prevalence increases sharply with obesity & age

Sex: ♂:♀ (2:1) 

Aetiology

Cause → upper airway obstruction, typically due to a combination of anatomical narrowing and reduced neuromuscular tone of pharyngeal dilator muscles. 

Risk factors 

• Adults 
  • Demographic & General 
    • Increasing age 
    • Male sex 
    • Family Hx 
  • Anthropometric 
    • Obesity (strongest risk factor)
    • Wide neck circumference (>40.6cm) 
  • Lifestyle 
    • Smoking 
    • Alcohol (esp. before sleep) 
    • Sleeping supine 
  • Endocrine & Metabolic 
    • Hypothyroidism 
    • Acromegaly 
    • PCOS
    • Type 2 diabetes
  • Craniofacial & Upper Airway Anatomy 
    • Adenotonsillar hypertrophy 
    • Macroglossia (large tongue)
    • Craniofacial abnormalities (e.g., retrognathia, narrow oropharyngeal opening)

 

• Children 
  • Anatomical 
    • Adenotonsillar hypertrophy (most common) 
    • Craniofacial abnormalities (e.g., retrognathia, microgrnathia, cleft palate)
  • Obesity 
  • Neuromuscular conditions
    • Cerebral palsy (↓ airway tone)
  • Syndromic/Genetic 
    • Down's syndrome (craniofacial abnormalities + ↓ muscle tone)
    • Achondroplasia 
    • Prader-Willi syndrome

 

Clinical Features

NICE recommends suspecting OSAHS if there are ≥2 of the following:

• Snoring
• Witnessed apnoeas
• Unrefreshing sleep
• Waking headaches
• Unexplained excessive sleepiness, tiredness or fatigue
• Nocturia 
• Choking during sleep
• Sleep fragmentation or insomnia
• Cognitive dysfunction or memory impairment

Associated Conditions and Complications

Age group	System	Associated Condition / Complication	Notes
Adults	Cardiovascular	Hypertension (inc. non-dipping nocturnal BP)
		Stroke / Cerebrovascular disease	↑ Risk of first-ever stroke (OR ≈ 2.24) ↑ Risk of recurrent stroke and possibly stroke-related mortality
		Ischaemic heart disease (e.g., angina)
		Arrythmias	Atrial fibrillation commonly reported
		Heart failure	Especially with longstanding OSAH(S)
		Pulmonary hypertension	Secondary to chronic nocturnal hypoxaemia
	Metabolic / Endocrine	Type 2 diabetes mellitus	OSAH(S) contributes to insulin resistance
	Neuropsychiatric	Depression	Higher prevalence in OSAH(S)
	Safety-related	Workplace accidents	~2× higher risk, especially in occupational drivers
		Road traffic collisions (RTCs)	Mean crash risk ≈ 2.5× higher; due to daytime sleepiness and reduced vigilance
Children	Neurobehavioural / Growth	Behavioral problems (irritability, hyperactivity, mood changes)
		Reduced concentration / School performance
		Faltering growth (especially in severe, untraeted cases)

 

Prognosis

General 

• Untreated OSAHS is associated with increased morbidity and mortality, particularly from cardiovascular and cerebrovascular causes 
• Treatment improves symptoms and reduces risk of complications, especially when adherence is high 

Adults 

CPAP may cause improvements in / lower risk of:

• Blood pressure (daytime/nocturnal) 
• Arrythmias / Stroke 
• LVEF in heart failure 

Children 

• Adenotonsillectomy → in the majority of uncomplicated cases, resolves symptoms 

Investigation and Diagnosis

Initial Assessment

Use the Epworth Sleepiness Scale to assess sleepiness.

Note that not all patients with OSAHS have excessive sleepiness

Diagnostic Tests

Perform a sleep study with:

• 1st line: home respiratory polygraphy

 

• 2nd line: home oximetry (may be inaccurate)

 

• 3rd line: hospital respiratory polygraphy

Gold standard: polysomnography (only considered if respiratory polygraphy results are normal but symptoms continue)

The AHI index is a key metric used to diagnose and determine the severity of OSAHS:  

• <5: normal
• 5-15: mild
• 15-30: moderate
• >30: severe

Management

Mild OSAHS

No Symptoms or Symptoms Do Not Affect Usual Daytime Activities

No treatment is needed 

Advise on lifestyle changes:

• Weight loss
• Regular physical activity
• Advice on sleep hygiene
• Smoking cessation
• Limit alcohol consumption

Symptoms Affect Quality of Life and Usual Daytime Activities

1st line: offer CPAP

• Consider heated humidification for those with upper airway side effects (e.g. nasal and mouth dryness, CPAP-induced rhinitis)

2nd line: mandibular advancement splint

• Only if >18 y/o and has optimal dental and periodontal health

3rd line: consider positional modifier (device that encourages the person to not sleep on their back)

Consider tonsillectomy in those if:

• Large obstructive tonsils, and
• BMI <35 kg/m

Moderate and Severe OSAHS

1st line (all patients):

• CPAP, and
• Advice on lifestyle changes
  • Weight loss
  • Regular physical activity
  • Advice on sleep hygiene
  • Smoking cessation
  • Limit alcohol consumption

2nd line: Mandibular advancement splint 

• o​​​​​nly if >18 y/o and has optimal dental and periodontal health

3rd line: Consider positional modifier (device that encourages the person not to sleep on their back)

• Note that it is unlikely to be effective in severe OSAHS

Consider tonsillectomy in those with:

• Large obstructive tonsils, and
• BMI <35 kg/m²

 

Obesity Hypoventilation Syndrome (OHS)

Definition

Obesity hypoventilation syndrome: ^[Ref]

• Defined by a triad of 1) obesity (BMI ≥30 kg/m²), 2) daytime hypercapnia, 3) sleep-disordered breathing (e.g., OSAHS) that cannot be explained by other causes of hypoventilation (e.g., neuromuscular, mechanical, metabolic)
• ~ 90% with OHS have OSAH 

Epidemiology

Prevalence ^{[Ref 1], [Ref 2]}

• ~0.4% in general adult population.
• 8-20% of obese patients referred for sleep studies.

Overlap 
~90% have coexistent OSAH

Aetiology

OHS is multifactorial but largely driven by severe obesity (main determinant), sleep-disordered breathing (e.g., OSAH), and impaired ventilatory control. ^[Ref]

Risk factors

• Severe obesity (main risk factor) 
• Older age
• Female sex (esp. post-menopausal)
• Nocturnal hypoxaemia
• Poor glycaemic control (insulin resistance, diabetes) 

Clinical Features

Two commons presentations of OHS are 

• 1) Acute on chronic hypercapnic respiratory failure (needing ICU admission)
• 2) Incidental finding 

Clinical features may include:

• Classic OSAHS features, but typically more severe 
• Dyspnoea (not typical in pure OSAHS)
• Signs of cor pulmonale in stable disease (e.g., peripheral oedema, prominent P2) 
• Respiratory failure  

Investigation and Diagnosis

1st line (screening) test: serum venous bicarbonate

• ≥27 mmol/L (high): possible OHS but requires further testing
  • Chronic hypercapnia (elevated PCO₂) leads to renal compensation with increased bicarbonate. 
• <27 mmol/L (normal): OHS is unlikely

Confirmatory test: ABG while awake:

• Chronic hypercapnia (↑ PaCO₂) is diagnostic (indicating daytime hypercapnia)

Offer respiratory polygraphy (hospital / home) to determine the presence of OSAHS in those with suspected OHS.
 

Diagnostic Criteria

Although this is not in NICE guideline, but a general requirement for OHS to be diagnosed (as per OHS definition):

• Daytime hypercapnia, and
• Obesity, and
• Exclude other hypoventilation causes (e.g. COPD, neuromuscular causes)

Management

Advice on lifestyle changes

• Weight loss
• Regular physical activity
• Advice on sleep hygiene
• Smoking cessation
• Limit alcohol consumption

OHS with no acute ventilatory failure:

• 1st line: CPAP
• 2nd line: non-invasive ventilation (BiPAP)
• 3rd line: consider adding supplemental oxygen therapy to CPAP or non-invasive ventilation

OHS with acute ventilatory failure → non-invasive ventilation (BiPAP)

 

References

Original Guideline