Summary

Obstructive Sleep Apnoea (OSA) is a disorder characterized by repetitive collapse of the upper airway during sleep, leading to transient cessation of breathing (apnoea) or reduction in airflow (hypopnoea), oxygen desaturation, and sleep fragmentation. It is the most common respiratory sleep disorder and a major cause of cardiovascular morbidity and road traffic accidents.

Key Definitions (OSAHS)

• Apnoea: Cessation of airflow ≥10 seconds.
• Hypopnoea: Reduction in airflow ≥30% for ≥10s + ≥3% desaturation or arousal.
• AHI (Apnoea-Hypopnoea Index): The key metric. Total events / Hours of sleep.
  • Mild: 5-15 events/hr.
  • Moderate: 15-30 events/hr.
  • Severe: >30 events/hr.
• OSAHS: Obstructive Sleep Apnoea Hypopnoea Syndrome. This diagnosis requires BOTH:
  1. AHI > 5.
  2. Evidence of symptoms (Excessive Daytime Sleepiness).

Epidemiology

• Prevalence: 2-4% of adult men, 1-2% of women. Up to 10-20% in obese populations.
• Gender: Male > Female (2:1). Post-menopausal women catch up to men.
• The "Obesity Tsunami": Prevalence is skyrocketing globally alongside obesity rates.
• Mortality: Untreated severe OSA doubles the risk of stroke/MI.

Image: Airway Collapse

The Starling Resistor Model

Think of the pharynx as a collapsible tube (like a wet paper straw).

1. Suction Pressure: When you inhale, negative pressure inside the chest pulls the airway walls INWARDS.
2. Muscle Tone: The pharyngeal muscles (Genioglossus) pull the walls OUTWARDS to keep it open.
3. The Failure: During REM sleep, muscle tone vanishes (atonia). If the tube is structurally narrow (fat neck) or floppy, the suction pressure wins. The walls collapse.

Risk Factors (The "Crowded Airway")

• Obesity: Fat pads technically narrow the pharyngeal lumen (parapharyngeal fat).
• Neck Circumference: The strongest predictor.
  • >17 inches (43cm) in Men.
  • >16 inches (40cm) in Women.
• Craniofacial: Retrognathia (set back jaw), Micrognathia (small jaw), Macroglossia (Down's, Acromegaly).
• Tonsils: Huge tonsils (Kissing tonsils) are the #1 cause in children.

The Cycle of Doom

1. Sleep Onset: Muscles relax. Airway collapses.
2. Apnoea: Airflow stops. SpO2 drops. CO2 rises.
3. Fight or Flight: The brain senses suffocation. A massive sympathetic burst occurs (BP spikes).
4. Arousal: The patient wakes up just enough to restore muscle tone (Micro-arousal). They gasp/snort. Airway opens.
5. Repeat: They fall back to sleep. Cycle repeats 30-500 times a night. Result: No deep sleep (Stage 3/REM). Chronic exhaustion. Nocturnal hypertension.

Image: Polysomnography Trace

History Taking (The "Bed Partner" Protocol)

The patient often denies symptoms ("I sleep fine"). The bed partner tells the truth.

• The Snore: Is it "Social" (quiet, steady) or "Apnoeic" (loud, choking, silence... GASP)?
• Witnessed Apnoeas: "Does he stop breathing?" (If yes, likelihood ratio is high).
• Nocturina: Why? Respiratory effort against a closed glottis creates negative intrathoracic pressure -> False signal of volume overload -> Heart releases ANP -> Diuresis.

Daytime Symptoms

• EDS (Excessive Daytime Sleepiness): Falling asleep at traffic lights, in meetings, watching TV.
• Morning Headache: Frontal/bitemporal. Caused by hypercapnia (CO2 vasodilation) during sleep. Clears within 30 mins of waking.
• Libido: Erectile dysfunction is common (low testosterone/exhaustion).

Physical Examination

• The Neck: Measure it. >17 inches (Men).
• The Chin: Retrognathia? (Chin recedes behind the lip line).
• The Throat (Mallampati Score):
  • Class I: Full view of uvula.
  • Class IV: Hard palate only. (High OSA risk).

Image: Mallampati Score

1. Screening: Epworth Sleepiness Scale (ESS)

A self-reported score out of 24.

• Questions: "Chance of dozing off while..." (Reading, TV, Public place, Car passenger, etc).
• Scoring:
  • 0-10: Normal.
  • 11-15: Mild-Mod.
  • >16: Severe sleepiness.
• Interpretation: High ESS correlates with accident risk, but NOT necessarily with AHI severity.

2. Home Sleep Study (Respiratory Polygraphy)

The standard NHS test. Patient wears a kit at home for one night.

• Channels Used: SpO2 (finger), Airflow (nasal cannula), Effort (chest belt), Position.
• Result: Measures AHI and Desaturation Index (ODI).
• Limitation: Cannot measure "Sleep/Wake" (no EEG). Might underestimate severity if patient was awake half the night.

3. Polysomnography (PSG) - Gold Standard

• Adds EEG (Brain waves).
• Why?: To prove the patient is actually sleeping. Required for complex cases (Narcolepsy, Parasomnias).

Severity Grading (AHI)

• Mild (5-15): Treat only if symptomatic or high risk job (Pilot).
• Moderate (15-30): Treat.
• Severe (>30): Treat urgently.

1. The Foundation (Lifestyle)

Before any machine, address the mechanics.

• Weight Loss: The single most effective disease-modifying intervention. 10% weight loss can reduce AHI by 26%.
• Alcohol: It relaxes pharyngeal muscles. Avoid it 4 hours before bed.
• Positional Therapy: "Tennis ball technique" (sewn into back of pyjamas) stops patient sleeping on back (where gravity collapses airway).

2. CPAP (Continuous Positive Airway Pressure) - The Gold Standard

• Mechanism: It is a "Pneumatic Splint". By blowing air at positive pressure (e.g., 10cm H2O), it pushes the soft palate and tongue away from the posterior pharyngeal wall.
• Indication: AHI >15 (Moderate/Severe) OR Symptomatic Mild OSA.
• Compliance: The biggest challenge. Defined as usage >4 hours/night for >70% of nights.
• Benefits: Abolishes snoring immediately. Restores alertness. Reduces BP by ~2-3 mmHg.

Image: CPAP Mechanism

3. Mandibular Advancement Devices (MAD)

• What is it?: A gumshield worn at night that protrudes the lower jaw (Mandible) forward.
• Mechanism: Pulls the tongue forward (Genioglossus muscle attaches to mandible), opening the retroglossal airway.
• Indication: Mild/Moderate OSA, or CPAP intolerant.

4. Surgery (The Last Resort)

• Tonsillectomy: Curative in children.
• UPPP (Uvalopalatopharyngoplasty): Removal of uvula/soft palate. Painful, unpredictable success rate. Rarely done now.
• Hypoglossal Nerve Stimulation: Implantable "pacemaker" for the tongue. Emerging therapy.

CRITICAL NOTICE: You must know this for exam scenarios.

UK DVLA Rules

1. Group 1 (Car):
   • Diagnosis: Is the patient prone to Excessive Sleepiness? If YES -> Must stop driving and notify DVLA.
   • Diagnosis without symptoms: If AHI is 30 but Epworth is 0 (asymptomatic), they generally do NOT need to notify.
   • Restarting: Can restart when symptoms are controlled on CPAP (usually confirms compliance data).
2. Group 2 (HGV/Bus):
   • Much stricter. Any diagnosis of OSA must be notified.

1. History Checklist

• The "Killer" Question: "Do you ever fall asleep at the wheel?" (Safety first).
• The "Witness": "Does your partner say you stop breathing?"

2. Viva Questions

• Q: Why does neck size matter?
  • A: It correlates with parapharyngeal fat pads which directly compress the airway lumen.
• Q: How does CPAP reduce blood pressure?
  • A: It eliminates the nocturnal hypoxic surges that trigger sympathetic vasoconstriction.
• Q: Why is Oxygen therapy ALONE dangerous?
  • A: Like COPD, chronic OSA patients may rely on hypoxic drive. Also, O2 prolongs apnoeas by delaying the hypoxia trigger that wakes the brain (arousal threshold).

"Why do I need this mask?"

"Think of your throat like a floppy tent. At night, the tent poles (muscles) collapse, and the tent falls on you, stopping you breathing. The machine acts like a leaf blower inside the tent—it blows air to keep the walls puffed out so you can breathe freely. It protects your heart from the stress of suffocating."

"Can I just have surgery?"

"In adults, surgery involves cutting away the soft palate. It is extremely painful and often the throat just collapses lower down instead. The mask is 100% effective if worn; surgery is a gamble."

Key Guidelines

Landmark Trials

• SAVE Trial (2016): CPAP improved symptoms/mood but missed significance on secondary CV prevention (likely due to poor adherence in study).
• MERGE Trial (2020): CPAP effective for QoL even in Mild OSA.

Evidence-Based Recommendations