Obstructive Sleep Apnoea

Obstructive sleep apnoea (OSA) is the commonest sleep-related breathing disorder, defined by repetitive collapse of the upper airway during sleep causing intermittent hypoxia, sleep fragmentation and daytime somnolence. It sits at the crossroads of respiratory, cardiovascular and metabolic medicine, and is a recurring favourite in NEET PG because of its crisp diagnostic cut-offs (AHI), its gold-standard test (polysomnography) and its drug-free first-line therapy (CPAP).

Definition and classification

Sleep-disordered breathing (SDB) is an umbrella term for abnormal respiration during sleep. The key entities are:

• Obstructive sleep apnoea (OSA): airflow ceases or reduces despite continued respiratory effort because the pharyngeal airway collapses. Thoraco-abdominal movement continues (often paradoxically).
• Central sleep apnoea (CSA): airflow ceases because of loss of respiratory drive — both airflow and effort stop together. Seen in heart failure (Cheyne-Stokes respiration), high altitude and opioid use.
• Obesity hypoventilation syndrome (OHS / Pickwickian syndrome): awake daytime hypercapnia (PaCO₂ > 45 mmHg) in an obese patient (BMI > 30) not explained by another cause.

The respiratory events are graded by airflow change:

Event	Definition
Apnoea	≥90% drop in airflow for ≥10 seconds
Hypopnoea	≥30% drop in airflow for ≥10 s with ≥3–4% desaturation or an arousal
RERA (respiratory effort–related arousal)	Increasing effort/flow limitation leading to an arousal, not meeting apnoea/hypopnoea criteria

High-yield: In obstructive apnoea, respiratory effort persists (the diaphragm keeps working against a closed airway); in central apnoea, effort is absent. This single distinction is the most-tested concept.

The Apnoea–Hypopnoea Index (AHI) = (number of apnoeas + hypopnoeas) per hour of sleep. The Respiratory Disturbance Index (RDI) additionally includes RERAs, so RDI ≥ AHI.

Severity grading by AHI

Severity	AHI (events/hour)
Normal	< 5
Mild	5 – 15
Moderate	15 – 30
Severe	> 30

High-yield: Memorise 5 / 15 / 30 as the AHI thresholds. Diagnosis of OSA requires AHI ≥ 5 with symptoms, or AHI ≥ 15 regardless of symptoms.

Etiology and risk factors

OSA results from an anatomically narrow or collapsible upper airway combined with reduced neuromuscular tone of the pharyngeal dilators (chiefly genioglossus) during sleep. During wakefulness, tonic dilator activity keeps the airway patent; sleep abolishes this, and in susceptible individuals the airway collapses at the level of the soft palate and tongue base.

Major risk factors:

• Obesity — the single strongest modifiable risk factor; fat deposition in the parapharyngeal tissues narrows the lumen.
• Increased neck circumference — > 43 cm (17 inches) in men, > 41 cm (16 inches) in women is a strong predictor.
• Male sex and post-menopausal status in women.
• Craniofacial abnormalities: retrognathia, micrognathia, a high-arched palate.
• Tonsillar / adenoidal hypertrophy — the commonest cause of OSA in children.
• Hypothyroidism (macroglossia, myxoedematous tissue) and acromegaly (macroglossia).
• Alcohol, sedatives and benzodiazepines at night — reduce dilator tone and blunt arousal.
• Nasal obstruction, smoking, supine sleep posture, advancing age.

High-yield: Adenotonsillar hypertrophy is the leading cause of paediatric OSA, and adenotonsillectomy is the first-line treatment in children — not CPAP.

Pathophysiology

The recurring cycle is:

Sleep onset → loss of pharyngeal dilator tone → airway collapse → apnoea/hypopnoea → falling SpO₂ and rising PaCO₂ → arousal restoring airway → return to sleep → cycle repeats

Two downstream mechanisms drive the systemic damage:

1. Intermittent hypoxia–reoxygenation generates reactive oxygen species, systemic inflammation and endothelial dysfunction → atherosclerosis and insulin resistance.
2. Repetitive arousals + surges in sympathetic tone raise nocturnal and daytime blood pressure and provoke arrhythmia. The large negative intrathoracic pressure generated against a closed airway increases cardiac afterload and atrial stretch (a substrate for atrial fibrillation).

Sleep fragmentation from hundreds of micro-arousals destroys restorative slow-wave and REM sleep, producing the daytime hypersomnolence that defines the clinical syndrome.

Clinical features

Nocturnal:

• Loud, habitual snoring (most sensitive symptom but poorly specific).
• Witnessed apnoeas — the bed partner reports the patient stops breathing then gasps/chokes (most specific symptom).
• Nocturia, restless sleep, diaphoresis, gastro-oesophageal reflux.

Daytime:

• Excessive daytime sleepiness (EDS) — the cardinal symptom; dozing while driving, at work, watching TV.
• Morning headaches (from nocturnal CO₂ retention), poor concentration, irritability, depressed mood, reduced libido/erectile dysfunction.

Examination: obesity, crowded oropharynx (high Mallampati / modified Friedman score), enlarged tonsils, retrognathia, hypertension; in long-standing severe disease — signs of pulmonary hypertension and cor pulmonale.

High-yield: Witnessed apnoeas by the partner are the most specific historical clue; snoring is the most sensitive. OSA is a leading medical cause of resistant hypertension and motor vehicle accidents.

Epworth Sleepiness Scale (ESS)

A self-administered questionnaire asking how likely the patient is to doze in 8 everyday situations (sitting reading, watching TV, sitting in a public place, as a car passenger, lying down to rest, sitting talking, after lunch, in a car stopped in traffic). Each scored 0–3.

Total ESS (max 24)	Interpretation
0 – 10	Normal daytime sleepiness
11 – 24	Excessive daytime sleepiness

High-yield: ESS measures subjective sleepiness and is a screening / monitoring tool — it does not diagnose OSA and does not correlate tightly with AHI.

STOP-BANG screening

A bedside questionnaire (1 point each) — Snoring, Tiredness, Observed apnoea, Pressure (hypertension), BMI > 35, Age > 50, Neck > 40 cm, Gender male. Score ≥ 3 = intermediate-to-high risk; ≥ 5 = high risk of moderate-severe OSA.

Mnemonic — STOP-BANG: Snore, Tired, Observed apnoea, Pressure / BMI, Age, Neck, Gender.

Diagnosis and investigation of choice

Diagnostic approach:

Clinical suspicion (snoring + EDS + risk factors) → screening questionnaire (STOP-BANG, ESS) → confirmatory sleep study → grade severity by AHI → assess comorbidity

• In-laboratory, attended, level-1 polysomnography (PSG) is the gold-standard / investigation of choice. It records EEG, EOG, chin and leg EMG, ECG, airflow (thermistor + nasal pressure), thoraco-abdominal effort bands, pulse oximetry and body position — allowing sleep staging and accurate AHI calculation.
• Home sleep apnoea testing (HSAT / level-3 study) is an acceptable alternative in patients with a high pre-test probability of moderate–severe OSA and no significant cardiopulmonary comorbidity. It underestimates AHI (denominator is recording time, not true sleep time) so a negative HSAT in a symptomatic patient should be followed by in-lab PSG.

Confirmatory PSG findings in OSA: AHI ≥ 5 with obstructive events (effort present during apnoea), cyclical desaturations, and arousals terminating events.

Adjuncts: arterial blood gas (daytime hypercapnia suggests OHS), TSH (exclude hypothyroidism), ECG/echocardiography (right heart strain, pulmonary hypertension), and haemoglobin/haematocrit (secondary polycythaemia from chronic hypoxia).

High-yield: Attended in-lab polysomnography is the gold standard for diagnosing OSA and for titrating CPAP pressure. Overnight pulse oximetry alone is not sufficient to diagnose or exclude OSA.

Management and treatment of choice

Management combines behavioural measures, the airway device, and treatment of comorbidity.

General / behavioural measures (for everyone):

• Weight reduction — the most important long-term modifier; even 10% weight loss meaningfully lowers AHI.
• Avoid alcohol and sedatives, especially before bed.
• Positional therapy (avoid supine sleep) for position-dependent OSA.
• Treat nasal obstruction; optimise thyroid status; smoking cessation.

Continuous Positive Airway Pressure (CPAP) — first-line, definitive therapy:

• CPAP delivers continuous positive pressure that acts as a pneumatic splint, holding the pharynx open throughout the respiratory cycle.
• Indicated as first-line for moderate–severe OSA (AHI ≥ 15) and for symptomatic mild OSA.
• Benefits: abolishes apnoeas, improves daytime sleepiness and quality of life, lowers blood pressure, and reduces cardiovascular risk.
• The main limitation is adherence (mask discomfort, dryness, claustrophobia). Auto-titrating CPAP (APAP) and BiPAP (for those needing high pressures, OHS or coexisting hypoventilation) are alternatives.

Mandibular advancement devices (oral appliances):

• Custom dental devices that protrude the mandible forward, enlarging the retroglossal airway.
• Indicated for mild–moderate OSA, snoring, or patients intolerant of / unwilling to use CPAP.
• Less effective than CPAP in severe disease but better tolerated.

Surgery:

• Uvulopalatopharyngoplasty (UPPP) — for selected patients with retropalatal obstruction; results are variable.
• Adenotonsillectomy — treatment of choice in children.
• Maxillomandibular advancement — highly effective in selected adults with craniofacial abnormalities.
• Hypoglossal nerve stimulation — an implantable device for moderate-severe OSA intolerant of CPAP with favourable airway anatomy.
• Bariatric surgery in morbid obesity.
• Tracheostomy — definitive but reserved for severe life-threatening disease unresponsive to other measures.

High-yield: CPAP is the first-line treatment of choice for adult OSA, especially moderate-severe disease. Mandibular advancement devices are reserved for mild-moderate OSA or CPAP-intolerant patients. There is no effective drug for OSA — modafinil only treats residual sleepiness in CPAP-treated patients.

CPAP vs mandibular advancement device

Feature	CPAP	Mandibular advancement device
Mechanism	Pneumatic splint of airway	Protrudes mandible, opens retroglossal space
Best for	Moderate–severe OSA	Mild–moderate OSA / CPAP intolerance
Efficacy	Highest (gold standard therapy)	Lower, but good adherence
Limitation	Adherence (~50%)	Dental/TMJ side-effects, less effective if severe

Complications

OSA is an independent risk factor for multisystem morbidity:

• Cardiovascular: systemic hypertension (especially resistant and non-dipping nocturnal hypertension), atrial fibrillation and other arrhythmias (nocturnal bradyarrhythmia during apnoea), coronary artery disease, heart failure, stroke.
• Pulmonary: pulmonary hypertension and cor pulmonale (more so when combined with OHS/COPD — "overlap syndrome").
• Metabolic: insulin resistance, type 2 diabetes and metabolic syndrome; OSA aggravates obesity.
• Neurocognitive: daytime somnolence, impaired memory and concentration, depression, and a markedly increased risk of road traffic and occupational accidents.
• Perioperative: difficult airway, sensitivity to sedatives/opioids, increased post-operative respiratory failure.
• Secondary polycythaemia from chronic intermittent hypoxia.

High-yield: OSA is among the commonest correctable causes of resistant hypertension and a major risk factor for atrial fibrillation — treating OSA improves blood pressure control and reduces AF recurrence after cardioversion/ablation.

Key differentials

Distinguish OSA from other causes of excessive daytime sleepiness and from other sleep-disordered breathing:

Condition	Distinguishing features
Central sleep apnoea	Apnoea with absent respiratory effort; Cheyne-Stokes pattern in heart failure; seen with opioids, high altitude
Obesity hypoventilation syndrome	Obese, awake daytime hypercapnia (PaCO₂ > 45); often overlaps with OSA
Narcolepsy	EDS + cataplexy, sleep paralysis, hypnagogic hallucinations; low CSF orexin/hypocretin; short REM latency on MSLT
Hypothyroidism	Weight gain, cold intolerance, can cause OSA; check TSH
Depression / poor sleep hygiene / insufficient sleep	Fatigue without true apnoeas; normal sleep study
Periodic limb movement disorder	Repetitive limb movements fragmenting sleep, leg EMG on PSG

Recently asked / exam angle

• Single-best AHI cut-offs: mild 5–15, moderate 15–30, severe > 30 — and the rule that diagnosis needs AHI ≥ 5 with symptoms or ≥ 15 without.
• Gold-standard investigation = polysomnography (recur as one-liner stems).
• First-line treatment = CPAP; mechanism = pneumatic splint of the upper airway.
• Difference between obstructive vs central apnoea on the respiratory effort channel of PSG.
• Pickwickian syndrome = obesity hypoventilation; do not confuse with OSA (though they often coexist).
• Epworth Sleepiness Scale as a subjective sleepiness tool (cut-off > 10/11); STOP-BANG as a screening tool.
• Neck circumference cut-offs (> 43 cm men, > 41 cm women).
• Commonest cause and treatment in children: adenotonsillar hypertrophy → adenotonsillectomy.
• OSA as a cause of resistant hypertension, atrial fibrillation and metabolic syndrome.
• Image/clinical-vignette stems: obese man, loud snoring, witnessed apnoeas, morning headache, falling asleep while driving → diagnosis OSA, next step PSG, treatment CPAP.

Rapid revision

1. OSA = airway collapse with preserved respiratory effort; central apnoea = effort absent.
2. AHI cut-offs: 5–15 mild, 15–30 moderate, > 30 severe; normal < 5.
3. Diagnose OSA at AHI ≥ 5 with symptoms, or ≥ 15 regardless of symptoms.
4. Polysomnography is the gold-standard / investigation of choice.
5. Snoring = most sensitive symptom; witnessed apnoea = most specific.
6. Excessive daytime sleepiness is the cardinal daytime feature; quantify with the Epworth Sleepiness Scale (> 10/11 = abnormal).
7. Biggest modifiable risk factor = obesity; warning neck size > 43 cm (men) / 41 cm (women).
8. CPAP is first-line treatment, acting as a pneumatic splint of the upper airway.
9. Mandibular advancement device for mild-moderate OSA or CPAP intolerance.
10. In children, adenotonsillar hypertrophy is the commonest cause → adenotonsillectomy is first-line.
11. OSA causes resistant hypertension, atrial fibrillation, pulmonary hypertension, metabolic syndrome and road accidents.
12. Pickwickian syndrome = obesity hypoventilation with awake hypercapnia (PaCO₂ > 45 mmHg); no effective drug cures OSA.