Obstructive Sleep Apnoea

Obstructive sleep apnoea (OSA) is the repetitive collapse of the upper airway during sleep despite ongoing respiratory effort, producing intermittent hypoxaemia, sleep fragmentation and a host of cardiometabolic consequences. For NEET PG it sits at the crossroads of ENT, Respiratory Medicine, Cardiology and Paediatrics — the favourite anchors being the apnoea-hypopnoea index (AHI), polysomnography as the gold standard, the STOP-BANG screen, and CPAP as the cornerstone of therapy.

Definitions & basic terminology

Sleep-disordered breathing is a spectrum running from simple snoring → upper airway resistance syndrome → obstructive sleep apnoea-hypopnoea syndrome. The events are defined on polysomnography:

Term	Definition
Apnoea	Cessation of airflow ≥ 90% drop for ≥ 10 seconds
Obstructive apnoea	Absent airflow with continued/exaggerated thoraco-abdominal effort (paradoxical movement)
Central apnoea	Absent airflow with absent respiratory effort (no drive)
Mixed apnoea	Begins as central, ends as obstructive
Hypopnoea	≥ 30% drop in airflow ≥ 10 s plus ≥ 3–4% desaturation or an arousal
RERA	Respiratory effort-related arousal — airflow limitation causing arousal but not meeting apnoea/hypopnoea criteria
AHI	(Apnoeas + hypopnoeas) per hour of sleep
RDI	Respiratory disturbance index = AHI + RERAs per hour
ODI	Oxygen desaturation index — number of ≥ 3–4% desaturations per hour

High-yield: The defining feature of OBSTRUCTIVE apnoea is persistent respiratory effort against a closed airway — paradoxical chest and abdominal movement. In CENTRAL apnoea, effort is absent. This single distinction is the most commonly tested OSA fact.

Diagnostic criteria (AASM)

OSA is diagnosed when either:

• AHI ≥ 15/hour (irrespective of symptoms), OR
• AHI ≥ 5/hour WITH symptoms (excessive daytime sleepiness, choking/gasping arousals, witnessed apnoeas, snoring) or an associated comorbidity (hypertension, mood disorder, coronary disease, stroke, diabetes).

Severity classification by AHI

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

High-yield: Memorise the cut-offs 5 – 15 – 30. Mild 5–15, Moderate 15–30, Severe > 30. NEET PG loves giving an AHI value and asking the grade.

Etiology & risk factors

OSA results from anatomical narrowing plus reduced pharyngeal dilator muscle tone during sleep. The pharynx (oropharynx/hypopharynx) is the only collapsible segment of the airway lacking rigid support.

Major risk factors:

• Obesity — the single strongest modifiable risk (fat deposition in the parapharyngeal walls; increased neck circumference).
• Male sex (androgens favour fat distribution and pharyngeal anatomy).
• Increasing age.
• Neck circumference > 43 cm (17 in) in men, > 41 cm (16 in) in women.
• Craniofacial anomalies — retrognathia, micrognathia, midface hypoplasia.
• Macroglossia (hypothyroidism, acromegaly, Down syndrome, amyloidosis).
• Tonsillar/adenoid hypertrophy (the dominant cause in children).
• Nasal obstruction (DNS, polyps).
• Alcohol and sedatives (reduce genioglossus tone), smoking (mucosal oedema).
• Hypothyroidism, acromegaly, PCOS.

High-yield: Adenotonsillar hypertrophy is the commonest cause of paediatric OSA, whereas obesity dominates in adults.

Pathophysiology

The cycle is best understood as a self-perpetuating loop:

Sleep onset → loss of pharyngeal dilator (genioglossus) tone → airway collapse → apnoea/hypopnoea → progressive hypoxaemia & hypercapnia → increased respiratory effort & sympathetic surge → cortical arousal → airway reopens (loud gasp/snore) → return to sleep → repeat.

The recurring arousals fragment sleep (loss of slow-wave and REM sleep → daytime somnolence). The intermittent hypoxia–reoxygenation generates oxidative stress, systemic inflammation and endothelial dysfunction, while repeated sympathetic surges raise nocturnal and daytime blood pressure. Negative intrathoracic pressure swings against a closed glottis (Müller manoeuvre physiology) increase cardiac transmural pressure and venous return, predisposing to atrial stretch and arrhythmia.

High-yield: The intermittent hypoxia → sympathetic overactivity and endothelial dysfunction link OSA to resistant systemic hypertension, the classic exam association. OSA is the commonest identifiable secondary cause of hypertension.

Clinical features

Nocturnal: loud habitual snoring (the most sensitive symptom — its absence makes OSA unlikely), witnessed apnoeas, choking/gasping arousals, restless sleep, nocturia, nocturnal sweating.

Daytime: excessive daytime sleepiness (hallmark), non-restorative sleep, morning headaches (CO₂ retention), poor concentration and memory, irritability/depression, reduced libido/erectile dysfunction, and increased motor-vehicle accident risk.

Examination: obesity (high BMI), large neck circumference, crowded oropharynx (high modified Mallampati / Friedman tongue position), enlarged tonsils, retrognathia, nasal obstruction, and signs of cor pulmonale in advanced disease.

Screening tools

Tool	What it measures
Epworth Sleepiness Scale (ESS)	Subjective daytime sleepiness; score > 10 (max 24) = excessive sleepiness
STOP-BANG	Pre-test probability of OSA (validated, widely used pre-operatively)
Berlin questionnaire	Risk stratification (snoring, sleepiness, BP/BMI)
Friedman staging	Tonsil size + Mallampati + BMI → predicts UPPP success

STOP-BANG mnemonic — each item scores 1:

• S — Snoring (loud)
• T — Tiredness (daytime)
• O — Observed apnoea
• P — Pressure (hypertension)
• B — BMI > 35 kg/m²
• A — Age > 50 years
• N — Neck circumference > 40 cm
• G — Gender male

High-yield: STOP-BANG ≥ 3 → intermediate/high risk; ≥ 5 → high probability of moderate–severe OSA. It is the favourite pre-operative screening tool because untreated OSA raises peri-operative airway and cardiac risk.

Diagnosis & investigation of choice

Polysomnography (PSG) — attended, level I, in-laboratory — is the GOLD STANDARD. It simultaneously records:

• EEG, EOG, chin EMG → sleep staging and arousals
• Nasal/oral airflow (thermistor + nasal pressure)
• Thoraco-abdominal effort belts (to separate obstructive vs central)
• Pulse oximetry (SpO₂)
• ECG, leg EMG, body position, snore sensor

PSG yields the AHI, ODI, sleep architecture and event type, enabling both diagnosis and severity grading.

Home sleep apnoea testing (HSAT / level III portable study) is acceptable for uncomplicated patients with high pre-test probability of moderate–severe OSA and no significant comorbidity (no heart failure, COPD, neuromuscular disease or suspected central apnoea). A negative or technically inadequate HSAT must be followed by full PSG.

Approach to a suspected case:

1. Clinical suspicion (snoring + daytime sleepiness + risk factors) →
2. Screen with STOP-BANG / Epworth →
3. Confirm with PSG (or HSAT if uncomplicated, high-probability) →
4. Grade severity by AHI →
5. Initiate therapy (behavioural + CPAP ± surgery) →
6. Treat comorbidities & re-titrate.

Adjuncts: fibre-optic nasendoscopy with Müller manoeuvre and drug-induced sleep endoscopy (DISE) localise the site of collapse before surgery; lateral cephalometry assesses craniofacial skeleton; TSH to exclude hypothyroidism.

Management

Treatment is tailored to severity, anatomy and patient preference. The pillars are behavioural measures, positive airway pressure, oral appliances and surgery.

1. Behavioural / general measures (all patients)

• Weight reduction — even 10% loss markedly lowers AHI; bariatric surgery for morbid obesity.
• Avoid alcohol and sedatives, especially before sleep.
• Positional therapy for positional OSA (events mainly supine) — encourage lateral sleeping.
• Treat nasal obstruction; smoking cessation; optimise hypothyroidism/acromegaly.

2. CPAP — the cornerstone (drug/device of choice)

High-yield: Continuous Positive Airway Pressure (CPAP) is the first-line and most effective treatment for moderate-to-severe OSA, and for symptomatic mild OSA. It is a pneumatic splint keeping the pharynx open.

• CPAP abolishes apnoeas, restores sleep architecture, reduces daytime sleepiness, lowers blood pressure and accident risk.
• APAP (auto-titrating) adjusts pressure breath-to-breath; BiPAP (separate higher inspiratory/lower expiratory pressure) is used when high pressures are poorly tolerated, in hypoventilation/overlap syndromes, or CPAP failure.
• The main limitation is adherence (nasal dryness, mask discomfort, claustrophobia).

3. Oral appliances

Mandibular advancement devices (MAD) pull the mandible/tongue forward, enlarging the retroglossal airway. Indicated in mild–moderate OSA, simple snoring, or CPAP-intolerant patients.

4. Surgery

Reserved for CPAP failure/intolerance with a surgically correctable anatomical obstruction:

• Adenotonsillectomy — the definitive treatment of paediatric OSA and the first-line surgery in children.
• Uvulopalatopharyngoplasty (UPPP) — resects redundant soft palate, uvula and tonsillar tissue; best in retropalatal collapse (Friedman stage I). Success ~ 40–50% in unselected adults.
• Nasal surgery (septoplasty, turbinate reduction) — improves CPAP tolerance.
• Genioglossus advancement / hyoid suspension, maxillomandibular advancement (MMA) — MMA has the highest surgical cure rate for skeletal/retrolingual obstruction.
• Hypoglossal nerve stimulation — implantable device for selected moderate–severe OSA intolerant of CPAP.
• Tracheostomy — bypasses the obstruction entirely; the historical "100% curative" option, now reserved for severe life-threatening disease unresponsive to all else.

High-yield: In a child with OSA from adenotonsillar hypertrophy, adenotonsillectomy is curative and first-line — a recurrent NEET PG single-best-answer.

Complications & systemic associations

Untreated OSA is a multisystem disease:

• Cardiovascular: systemic (especially resistant) hypertension, pulmonary hypertension and cor pulmonale, coronary artery disease, congestive heart failure, nocturnal arrhythmias (bradyarrhythmias during apnoea, atrial fibrillation), and increased risk of sudden cardiac death (often in the early-morning hours).
• Cerebrovascular: increased stroke and TIA risk.
• Metabolic: insulin resistance, type 2 diabetes, dyslipidaemia — OSA is a recognised component of the metabolic syndrome.
• Neurocognitive/psychiatric: daytime sleepiness, impaired cognition, depression, road and occupational accidents.
• Obesity-hypoventilation (Pickwickian) syndrome: obesity + daytime hypercapnia (PaCO₂ > 45 mmHg) ± OSA.
• Paediatric: failure to thrive, behavioural problems and ADHD-like features, poor school performance, enuresis, and chest-wall deformity.

High-yield: OSA → secondary erythrocytosis/polycythaemia (chronic hypoxia drives erythropoietin) and is the commonest treatable cause of resistant hypertension. New-onset or refractory atrial fibrillation should prompt a search for OSA.

Key differentials

Condition	Distinguishing feature
Central sleep apnoea	Apnoeas with absent respiratory effort; seen in heart failure (Cheyne-Stokes), stroke, opioids, high altitude
Obesity-hypoventilation syndrome	Awake hypercapnia (daytime PaCO₂ > 45) in the obese; OSA often coexists
Narcolepsy	Sleepiness + cataplexy, sleep paralysis, hypnagogic hallucinations; short sleep latency + ≥ 2 SOREMPs on MSLT; low CSF orexin
Periodic limb movement disorder / RLS	Repetitive limb movements fragmenting sleep, no airflow cessation
Hypothyroidism	Macroglossia, fatigue, weight gain — can cause OSA; check TSH
Simple snoring (primary)	Snoring without apnoeas/desaturation; AHI < 5

Recently asked / exam angle

• Gold standard investigation for OSA → Polysomnography (most repeated single fact).
• AHI severity cut-offs → 5/15/30 grading; "AHI of 22 = moderate".
• Obstructive vs central apnoea on PSG → presence vs absence of respiratory effort (effort belts/paradoxical movement).
• Treatment of choice for moderate–severe OSA → CPAP.
• Commonest cause of OSA in children → adenotonsillar hypertrophy; treatment adenotonsillectomy.
• STOP-BANG — what each letter stands for and its role in pre-operative screening (anaesthesia integration).
• OSA association — resistant hypertension, atrial fibrillation, metabolic syndrome, secondary polycythaemia, pulmonary hypertension.
• Müller manoeuvre / DISE — used to localise the site of upper airway collapse before surgery.
• Most curative surgical procedure historically → tracheostomy; highest cure-rate skeletal surgery → maxillomandibular advancement.
• Pickwickian syndrome — obesity-hypoventilation with daytime hypercapnia.
• Epworth Sleepiness Scale quantifies daytime sleepiness; Friedman staging predicts UPPP outcome.

Rapid revision

1. OSA = airway collapse with persistent respiratory effort; central apnoea = no effort.
2. Polysomnography is the gold standard; HSAT only for uncomplicated high-probability cases.
3. AHI severity: < 5 normal, 5–15 mild, 15–30 moderate, > 30 severe.
4. Diagnose if AHI ≥ 15, or AHI ≥ 5 with symptoms/comorbidity.
5. Obesity is the chief adult risk factor; adenotonsillar hypertrophy the chief paediatric cause.
6. Neck circumference cut-off: > 43 cm men, > 41 cm women.
7. STOP-BANG ≥ 3 intermediate, ≥ 5 high risk — best pre-operative screen.
8. CPAP is first-line for moderate–severe OSA (a pneumatic splint); BiPAP/APAP as alternatives.
9. Adenotonsillectomy cures most paediatric OSA.
10. OSA is the commonest treatable cause of resistant hypertension and a trigger for atrial fibrillation.
11. Chronic hypoxia → secondary polycythaemia, pulmonary hypertension, cor pulmonale.
12. Tracheostomy is the historical 100% cure; maxillomandibular advancement has the highest surgical success rate.