Obstructive Sleep Apnoea (Adult)

1. Overview

Obstructive Sleep Apnoea (OSA) is a prevalent sleep-related breathing disorder characterized by recurrent episodes of complete (apnoea) or partial (hypopnoea) upper airway obstruction during sleep, resulting in intermittent hypoxia, hypercapnia, sleep fragmentation, and excessive daytime sleepiness. [1] These repetitive airway collapses occur despite ongoing respiratory effort, distinguishing OSA from central sleep apnoea where respiratory drive is absent.

OSA represents a major public health challenge with profound cardiovascular, metabolic, and neurocognitive consequences. The condition is strongly associated with obesity, hypertension, atrial fibrillation, stroke, metabolic syndrome, and road traffic accidents. [2,3] Despite its high prevalence and serious complications, OSA remains significantly underdiagnosed, with an estimated 80-90% of cases unrecognized in clinical practice.

The clinical importance of OSA extends beyond respiratory medicine. Untreated moderate-to-severe OSA increases cardiovascular mortality risk by approximately 3-fold and is independently associated with development of hypertension, heart failure, and cerebrovascular events. [3,4] Early recognition and treatment with continuous positive airway pressure (CPAP) therapy can substantially reduce these risks and improve quality of life.

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2. Epidemiology

Prevalence and Incidence

The global prevalence of OSA has increased dramatically over the past three decades, primarily driven by the obesity epidemic. [5] Current estimates suggest:

The true prevalence varies significantly depending on the diagnostic criteria used (AHI threshold) and whether symptomatic disease (OSA syndrome with excessive daytime sleepiness) or asymptomatic disease is included.

Demographic Factors

Age: Prevalence increases progressively with age, peaking in the 6th-7th decade, with some evidence of plateau or decline in the very elderly (> 80 years). [8]

Sex: Male predominance (2-3:1 ratio) in middle age. Post-menopausal women approach male prevalence rates, suggesting protective effects of female sex hormones. [6]

Ethnicity: Higher prevalence observed in African American, Hispanic, and Asian populations compared to Caucasians, partly attributable to craniofacial morphology differences. [6]

Obesity: The strongest modifiable risk factor. Each 10% increase in body weight increases OSA risk by approximately 32%. [7] Conversely, 10% weight reduction can decrease AHI by up to 26%. [9]

Temporal Trends

Epidemiological studies demonstrate alarming increases in OSA prevalence:

• 14-55% increase in prevalence between 1990 and 2010 in Western populations [5]
• Projected to affect > 1 billion adults globally by 2030 [5]
• Increasing recognition in children and adolescents (estimated 1-5% prevalence)

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3. Aetiology & Pathophysiology

Upper Airway Anatomy and Collapsibility

The pharynx lacks rigid structural support (unlike the trachea with cartilaginous rings) and depends entirely on neuromuscular tone to maintain patency during sleep. [10] OSA results from an imbalance between:

1. Collapsing Forces (negative intraluminal pressure during inspiration)
2. Dilating Forces (pharyngeal dilator muscle activity - primarily genioglossus)

Starling Resistor Model: The pharyngeal airway behaves as a collapsible tube. When transmural pressure (intraluminal minus extraluminal pressure) becomes negative during inspiration, the airway collapses if muscle tone is insufficient to counteract this pressure.

Anatomical Risk Factors

Pathophysiological Mechanisms

Exam Detail: 1. Neural Control Abnormalities

During wakefulness, central respiratory drive compensates for anatomical narrowing by increasing pharyngeal dilator muscle activity. During sleep, particularly REM sleep, this compensatory mechanism fails:

• Sleep-related hypotonia: Reduced pharyngeal dilator muscle tone during REM sleep (physiological atonia) precipitates airway collapse
• Impaired arousal threshold: Delayed arousal response to hypoxia/hypercapnia prolongs apnoeic episodes
• Ventilatory control instability: Oscillations in respiratory drive contribute to periodic breathing patterns [10]

2. The Apnoeic Cycle

1. Sleep onset → Reduction in genioglossus activity → Upper airway narrowing
2. Airway obstruction → Complete (apnoea) or partial (hypopnoea) cessation of airflow
3. Progressive hypoxia and hypercapnia → Rising CO₂ and falling O₂ despite continued respiratory efforts
4. Arousal (micro-arousal 3-15 seconds) → Restoration of muscle tone → Airway reopening
5. Resumption of airflow → Often with loud snort/gasp → Return to sleep → Cycle repeats

This cycle may occur 5-100+ times per hour in severe cases, completely fragmenting sleep architecture.

3. Intermittent Hypoxia - The Key Pathogenic Driver

Repetitive cycles of hypoxia-reoxygenation trigger multiple pathophysiological cascades:

• Oxidative stress: Generation of reactive oxygen species (ROS) during reoxygenation phases
• Sympathetic activation: Persistent elevation in sympathetic nervous system activity (persists during wakefulness)
• Systemic inflammation: Elevated inflammatory markers (CRP, IL-6, TNF-α)
• Endothelial dysfunction: Impaired nitric oxide bioavailability, increased arterial stiffness
• Metabolic dysregulation: Insulin resistance, dyslipidaemia, hepatic steatosis [3,4,11]

Risk Factors Summary

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4. Clinical Presentation

OSA diagnosis relies heavily on collateral history from bed partners or family members, as patients are often unaware of nocturnal events.

Nocturnal Symptoms

Witnessed Apnoeas (Diagnostic Gold Mine)

The observation by a bed partner of breathing cessation followed by gasping or choking has high diagnostic value (likelihood ratio > 10). [1] Characteristically:

• Episodes last 10-60 seconds
• Associated with apparent struggle to breathe (paradoxical chest/abdominal movements)
• Terminated by loud snort, gasp, or body movement
• May occur hundreds of times per night

Snoring (Universal but Non-specific)

Present in > 95% of OSA patients but also in 40% of adult population. [6] OSA-related snoring characteristics:

• Loud: Audible outside bedroom
• Interrupted: Crescendo pattern followed by silence (apnoea), then explosive resumption
• Positional: Worse supine, improved lateral position
• Long-standing: Usually present for years before symptom recognition

Other Nocturnal Features

Daytime Symptoms

Excessive Daytime Sleepiness (EDS)

The cardinal daytime symptom, resulting from chronic sleep fragmentation and non-restorative sleep:

• Inappropriate sleep propensity: Falling asleep during meetings, conversations, watching TV
• Safety-critical scenarios: Dozing at traffic lights, while driving (7-fold increased accident risk) [13]
• Quantified by Epworth Sleepiness Scale (ESS): Score > 10/24 suggests pathological sleepiness

Important: Severity of sleepiness correlates poorly with AHI. Some patients with severe OSA (AHI > 50) report minimal sleepiness, while others with mild OSA are profoundly symptomatic.

Non-restorative Sleep

Patients wake feeling unrefreshed despite seemingly adequate sleep duration (7-9 hours). Partners may observe patient appears to sleep continuously, contrasting with patient's subjective experience.

Neurocognitive Dysfunction

• Concentration difficulties: Reduced attention span, difficulty multitasking
• Memory impairment: Particularly short-term and working memory
• Mood disturbance: Irritability, depression (present in 30-50% of OSA patients) [14]
• Reduced executive function: Impaired decision-making and problem-solving

Morning Headaches

Present in 20-25% of OSA patients. Characteristics:

• Frontal or bi-temporal distribution
• Present on waking, improving within 30-60 minutes
• Mechanism: Nocturnal hypercapnia → Cerebral vasodilation [1]
• Non-specific: Also occurs in tension headache, medication overuse

Other Daytime Features

• Erectile dysfunction: Present in 40-70% of male OSA patients (multifactorial: testosterone reduction, endothelial dysfunction, fatigue) [15]
• Reduced libido: Both sexes
• Personality changes: Irritability, mood swings
• Gastro-oesophageal reflux: Exacerbated by negative intrathoracic pressure

Physical Examination

General Inspection

Anthropometric Measurements

Neck circumference - Single best clinical predictor:

• Men: > 43 cm (17 inches) - Sensitivity 60%, Specificity 90% for moderate-severe OSA [6]
• Women: > 40 cm (16 inches)
• Measure at level of cricothyroid membrane

Body Mass Index (BMI):

• Risk increases exponentially above 25 kg/m²

• 30 kg/m²: 4-fold increased risk

• 35 kg/m²: 10-fold increased risk [7]

Upper Airway Examination

Oropharyngeal Assessment - Mallampati Score:

Tonsillar Size (Brodsky grading):

• Grade 0: Within tonsillar fossa
• Grade 4: "Kissing tonsils" (meeting in midline) - Common paediatric cause

Tongue: Assess for macroglossia (seen in acromegaly, hypothyroidism, Down syndrome)

Palate: High-arched or elongated soft palate/uvula

Craniofacial Assessment

• Retrognathia: Receding chin (mandible posterior to vertical line from forehead)
• Micrognathia: Small mandible (seen in Pierre Robin sequence, Treacher Collins)
• Maxillary hypoplasia: Midface deficiency (seen in cleft palate, craniofacial syndromes)

Nasal Examination

• Septal deviation, turbinate hypertrophy, nasal polyps
• Assess nasal airflow patency
• Consider anterior rhinoscopy/nasoendoscopy if structural abnormality suspected

Cardiovascular System

• Blood pressure: Hypertension present in 50-60% of OSA patients [4]
• Cardiac examination: Signs of heart failure, arrhythmia (particularly AF)
• Assess for peripheral oedema (cor pulmonale in severe cases)

Respiratory System

• Usually normal unless coexisting lung disease (COPD-OSA overlap syndrome)
• Signs of cor pulmonale in severe, untreated OSA: Elevated JVP, peripheral oedema, hepatomegaly

Endocrine Features

Screen for conditions associated with OSA:

• Hypothyroidism: Periorbital oedema, bradycardia, delayed relaxation reflexes
• Acromegaly: Enlarged hands/feet, coarse facial features, macroglossia, prognathism

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5. Differential Diagnosis

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6. Investigations

Screening Tools

Epworth Sleepiness Scale (ESS)

Self-administered questionnaire assessing likelihood of dozing in 8 common situations. [1]

Interpretation:

• 0-10: Normal
• 11-15: Mild excessive sleepiness
• 16-24: Severe excessive sleepiness

Limitations:

• Subjective measure
• Poor correlation with OSA severity (AHI)
• Cannot diagnose OSA (only indicates sleepiness)
• Some patients with severe OSA deny sleepiness

STOP-BANG Questionnaire

Clinical prediction tool with high sensitivity (90%) for moderate-severe OSA:

Scoring:

• 0-2: Low risk
• 3-4: Intermediate risk
• 5-8: High risk for moderate-severe OSA

Diagnostic Sleep Studies

Polysomnography (PSG) - Gold Standard

Level 1 Sleep Study - Supervised, laboratory-based, full polysomnography. [1]

Channels monitored:

1. EEG (Electroencephalography): Sleep staging, arousal detection
2. EOG (Electrooculography): Eye movements (REM detection)
3. EMG (Electromyography): Chin muscle tone, leg movements
4. Respiratory monitoring:
   • Nasal/oral airflow (thermistor, nasal pressure transducer)
   • Respiratory effort (chest/abdominal belts - detect paradoxical movement)
   • Oxygen saturation (pulse oximetry)
   • Transcutaneous or end-tidal CO₂ (optional)
5. Cardiac: ECG (arrhythmia detection)
6. Body position: Supine vs lateral
7. Audio-video recording: Behaviour, movements, snoring

Indications for in-laboratory PSG:

• Suspected sleep-related movement disorders (periodic limb movements, REM behaviour disorder)
• Suspected central sleep apnoea or hypoventilation syndromes
• Complex patients: Heart failure, neuromuscular disease, COPD-OSA overlap
• CPAP titration if home titration unsuccessful
• Pre-operative assessment for bariatric or upper airway surgery

Home Sleep Apnoea Testing (HSAT)

Level 2-4 Studies - Portable devices used at home (also called respiratory polygraphy). [1]

Advantages:

• Convenient (home environment)
• Cost-effective (£50-100 vs £500-1000 for PSG)
• Faster access (reduced waiting times)
• Reflective of usual sleep patterns

Limitations:

• No EEG → Cannot stage sleep → May underestimate AHI (uses recording time, not true sleep time)
• No detection of arousals → Cannot diagnose Upper Airway Resistance Syndrome
• Poor quality data if patient sleeps poorly
• Not suitable for non-OSA sleep disorders

Standard NHS pathway: Home sleep study first-line unless specific indication for PSG.

Sleep Study Metrics

Apnoea-Hypopnoea Index (AHI)

Primary diagnostic metric: Number of apnoeas + hypopnoeas per hour of sleep. [1]

Definitions:

• Apnoea: ≥90% reduction in airflow for ≥10 seconds
• Hypopnoea: ≥30% reduction in airflow for ≥10 seconds with either:
  • ≥3% oxygen desaturation, OR
  • Arousal from sleep (requires EEG)

Severity Classification:

Oxygen Desaturation Index (ODI)

Number of ≥3% or ≥4% oxygen desaturations per hour. Correlates closely with AHI but can be derived from oximetry alone (no airflow measurement needed).

ODI ≥5 events/hour: Sensitivity ~90% for OSA diagnosis

Other Metrics

• Nadir SpO₂: Lowest oxygen saturation reached (e.g., 78% indicates severe intermittent hypoxia)
• T90 (Time less than 90% SpO₂): Percentage of night spent with SpO₂ less than 90% (marker of sustained hypoxia)
• Arousal Index: Number of EEG arousals per hour (requires PSG)
• Sleep efficiency: Total sleep time / time in bed × 100 (normal > 85%)
• REM AHI: AHI specifically during REM sleep (often higher than overall AHI)

Exam Detail: Polysomnography Trace Interpretation:

A typical OSA event demonstrates:

1. Continued respiratory effort (chest/abdominal movements persist or increase - paradoxical movement)
2. Absent or markedly reduced airflow (flat thermistor/pressure transducer trace)
3. Progressive oxygen desaturation (SpO₂ drops from 95% → 85% → 78%)
4. EEG arousal (shift from deep sleep to lighter sleep stage)
5. Restoration of airflow (large breath, often with artefact from body movement)
6. Rapid resaturation (SpO₂ returns to baseline within 10-30 seconds)

This contrasts with central apnoea where both airflow AND respiratory effort cease simultaneously.

Additional Investigations

Baseline Blood Tests

Arterial Blood Gas (if suspecting OHS)

Indications:

• Severe obesity (BMI > 40)
• Daytime symptoms of hypoventilation (morning headaches, peripheral oedema)
• Very severe OSA with marked hypoxia on sleep study

Findings in Obesity Hypoventilation Syndrome:

• pH 7.35-7.42 (compensated respiratory acidosis)
• PaCO₂ > 6 kPa (45 mmHg) while awake
• HCO₃⁻ elevated (metabolic compensation)

Cardiology Investigations

Indications: Suspected cardiovascular complications or pre-treatment assessment.

• ECG: Arrhythmias (AF, ventricular ectopy), LVH, P-pulmonale
• 24-hour ECG/ambulatory monitoring: Nocturnal arrhythmias, bradycardia-tachycardia patterns
• Echocardiography: Left ventricular hypertrophy, diastolic dysfunction, pulmonary hypertension, right heart strain [4]

Imaging

• Lateral cephalometry: Craniofacial assessment (primarily surgical planning)
• Nasendoscopy: If structural nasal obstruction suspected (ENT referral)
• Drug-induced sleep endoscopy (DISE): Localises site of airway collapse under sedation (surgical planning tool)

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7. Classification & Severity

OSA vs OSAHS

OSA (Obstructive Sleep Apnoea): AHI ≥5 with or without symptoms

OSAHS (Obstructive Sleep Apnoea-Hypopnoea Syndrome): AHI ≥5 + excessive daytime sleepiness or other symptoms attributable to sleep disruption [1]

Clinical relevance: Treatment decisions historically based on OSAHS (i.e., required both elevated AHI AND symptoms). Current guidelines increasingly recommend treating based on AHI alone given cardiovascular risks. [4]

Severity Stratification

Positional OSA

Definition: AHI in supine position ≥2× higher than non-supine AHI

Prevalence: 50-60% of OSA patients demonstrate positional pattern [1]

Mechanism: Gravity causes posterior displacement of tongue and soft palate when supine

Management implications: Positional therapy (devices preventing supine sleep) may be sufficient for mild-moderate positional OSA

REM-related OSA

Definition: AHI during REM sleep significantly higher than non-REM

Mechanism: REM sleep associated with profound skeletal muscle atonia (except diaphragm, extraocular muscles)

Clinical relevance: May be missed if sleep study contains insufficient REM sleep; may respond well to REM-suppressing medications (e.g., antidepressants) in select cases

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8. Management

Management of OSA requires multi-modal approach addressing lifestyle modification, treatment of underlying causes, symptomatic therapy, and management of comorbidities.

Conservative & Lifestyle Measures

Weight Loss - Disease-Modifying Intervention

Evidence: 10% weight reduction → 26% reduction in AHI [9]

Mechanisms:

• Reduced parapharyngeal fat deposition
• Decreased abdominal mass → Improved lung volumes → Increased pharyngeal dilator muscle effectiveness
• Reduced systemic inflammation

Thresholds:

• Target BMI less than 30 kg/m² (ideally less than 25)
• Even modest weight loss (5-10 kg) provides benefit
• Bariatric surgery: May cure OSA in 40-80% depending on procedure [17]

CPAP still required in most patients despite weight loss (may allow pressure reduction or upgrade from severe to moderate classification).

Positional Therapy

Indications: Positional OSA (supine AHI ≥2× non-supine AHI)

Methods:

• "Tennis ball technique": Ball/foam device sewn into back of nightwear preventing supine sleep
• Commercial devices: Vibratory alarms, inflatable devices, positional belts
• Side-sleeping pillow: Encourages lateral position

Efficacy: May reduce AHI by 50-60% in carefully selected positional OSA patients [1]

Limitations: Long-term compliance often poor (40-50% at 1 year)

Alcohol and Sedative Avoidance

Mechanism: Alcohol, benzodiazepines, opioids → Pharyngeal muscle relaxation, prolonged apnoea duration, reduced arousal threshold

Recommendation: Avoid alcohol ≥4 hours before bedtime

Smoking Cessation

Current smokers: 2-3 fold increased OSA risk (mechanisms: upper airway inflammation, fluid retention, altered sleep architecture) [6]

Sleep Hygiene Optimization

• Regular sleep schedule (consistent bedtime/wake time)
• Avoid sleep deprivation (worsens OSA severity)
• Elevate head of bed 30-45° if concurrent GORD

Nasal Decongestants

If nasal obstruction present: Saline irrigation, nasal corticosteroid sprays, short-term decongestants may improve CPAP tolerance and reduce AHI

Medical Management

Continuous Positive Airway Pressure (CPAP) - Gold Standard

Mechanism: Delivers pressurised air via nasal/oronasal mask creating a "pneumatic splint" that maintains positive transmural pressure, preventing pharyngeal collapse. [1,18]

Typical Pressure Range: 4-20 cm H₂O (most patients 8-12 cm H₂O)

Efficacy:

• Eliminates apnoeas/hypopnoeas in > 95% when used correctly
• Reduces AHI from 40-50 to less than 5 events/hour typically
• Improves symptoms within days-weeks
• Reduces blood pressure by 2-3 mmHg (greater in resistant hypertension) [4]
• May reduce cardiovascular events by 30-40% in adherent patients [4]

Indications (UK NICE Guidelines NG202):

• Moderate-severe OSA (AHI ≥15): Offer CPAP
• Mild OSA (AHI 5-14): Offer CPAP if symptomatic or high cardiovascular risk

Types of PAP Therapy:

Initiation Process:

1. Patient education: Explain rationale, demonstrate equipment, set expectations
2. Mask fitting: Trial multiple interfaces (nasal mask, nasal pillows, oronasal mask)
3. Pressure titration:
   • In-laboratory titration (PSG-guided)
   • Auto-CPAP home titration (download data after 1-2 weeks to set fixed pressure)
4. Follow-up: Review at 1 month, then 3-6 monthly

Adherence - The Major Limitation:

"Good adherence" defined as > 4 hours/night for > 70% of nights [18]

Adherence rates: 40-60% at 1 year (highly variable between studies)

Factors predicting good adherence:

• Severe symptoms (particularly sleepiness)
• Partner encouragement
• Early education and support
• Effective mask fit
• Side effects promptly addressed

Strategies to improve adherence:

• Intensive early support: Phone calls, clinic visits weeks 1, 2, 4
• Heated humidification: Reduces nasal dryness, congestion
• Mask optimization: Try alternative styles if discomfort/leak
• Pressure adjustment: Reduce if discomfort (use auto-CPAP mode or BiPAP)
• Cognitive behavioural therapy: Addresses claustrophobia, mask anxiety
• Download compliance data: Discuss usage patterns objectively

Side Effects & Troubleshooting:

Contraindications (Relative):

• Pneumothorax (untreated)
• Bullous lung disease (risk of rupture - use low pressure)
• CSF leak, skull base fracture (theoretical risk of pneumocephalus)
• Severe epistaxis

Clinical Pearl: CPAP Pressure Too High? Patients often report feeling "unable to breathe out" against the pressure. Solutions:

1. Enable EPR (Expiratory Pressure Relief) - reduces pressure by 1-3 cm H₂O during expiration
2. Trial BiPAP - different inspiratory and expiratory pressures
3. Gradual ramp feature - starts at low pressure, increases over 20-30 minutes

CPAP Pressure Too Low? Persistent snoring, residual apnoeas, or arousals visible on device download data. Increase pressure by 1-2 cm H₂O increments.

Mandibular Advancement Devices (MAD)

Mechanism: Custom-fitted oral appliance worn during sleep that protrudes the mandible forward by 5-10 mm, pulling the tongue forward and opening the retropharyngeal airway space. [1]

Efficacy:

• Reduces AHI by 40-50% on average
• Less effective than CPAP but better adherence
• Response rate: 50-70% achieve AHI less than 10, 30-40% achieve AHI less than 5

Indications:

• Mild-moderate OSA (AHI 5-30) first-line alternative to CPAP
• CPAP intolerant patients (any severity)
• Patient preference

Requirements:

• Adequate dentition (minimum 8 teeth per arch)
• No severe temporomandibular joint disease
• Fitted by dentist trained in sleep medicine

Side Effects:

• Temporomandibular joint pain (15-30%) - usually transient
• Excessive salivation (20-30%)
• Dental discomfort, tooth movement (5-10% long-term)
• Occlusal changes (rare with properly fitted device)

Follow-up:

• Repeat sleep study with device in situ to confirm efficacy
• Dental review 6-monthly

Pharmacotherapy (Limited Role)

No pharmacological agent is first-line treatment for OSA. Investigational approaches include:

• Atomoxetine + oxybutynin combination: Noradrenergic and antimuscarinic agents. Pilot studies show 50% AHI reduction but not yet licensed. [19]
• Acetazolamide: Carbonic anhydrase inhibitor, may benefit central sleep apnoea component
• Modafinil/Armodafinil: Wake-promoting agents for residual sleepiness despite CPAP (not treating OSA itself)
• Oxygen therapy: May reduce intermittent hypoxia but prolongs apnoea duration (generally avoid as sole therapy)

Treatment of underlying causes:

• Hypothyroidism: Levothyroxine replacement may reduce OSA severity
• Acromegaly: Somatostatin analogues, surgery
• Nasal obstruction: Intranasal corticosteroids, allergen avoidance

Surgical Management

Surgery generally third-line after CPAP/MAD failure or intolerance, OR first-line for specific anatomical lesions.

Upper Airway Surgery

Uvulopalatopharyngoplasty (UPPP):

• Procedure: Excision of uvula, posterior soft palate, tonsillar tissue
• Success rate: 40-60% achieve AHI reduction > 50% (highly variable)
• Complications: Pain, bleeding, velopharyngeal insufficiency (nasal regurgitation), voice changes
• Candidate selection: Isolated oropharyngeal collapse on endoscopy, failed medical therapy
• Not curative in most adults

Tonsillectomy ± Adenoidectomy:

• Curative in children with tonsillar hypertrophy causing OSA (first-line)
• Limited role in adults unless gross tonsillar enlargement

Nasal Surgery:

• Procedures: Septoplasty, turbinate reduction, polypectomy
• Aim: Improve nasal airflow, facilitate CPAP adherence
• Rarely curative for OSA alone

Maxillomandibular Advancement (MMA):

• Procedure: Orthognathic surgery advancing maxilla and mandible forward
• Efficacy: > 90% success rate (AHI reduction > 50%), 40-60% cure rate
• Indications: Severe OSA refractory to medical therapy, significant craniofacial abnormality
• Complications: Major surgery - bleeding, infection, nerve injury, malocclusion

Hypoglossal Nerve Stimulation (HNS)

Mechanism: Implanted neurostimulator delivers electrical stimulation to hypoglossal nerve synchronised with inspiration, causing genioglossus contraction and tongue protrusion. [20]

Device: Similar to cardiac pacemaker (pulse generator in chest, electrode to hypoglossal nerve)

Efficacy:

• 65-70% achieve ≥50% AHI reduction
• Mean AHI reduction from 32 to 9 events/hour
• Improvements in sleepiness, quality of life sustained to 5 years [20]

Indications (UK/European criteria):

• Moderate-severe OSA (AHI 15-65)
• CPAP failure (intolerant or inadequate response)
• BMI less than 35 kg/m²
• No complete concentric collapse at velum on drug-induced sleep endoscopy

Complications: Tongue weakness, pain, device malfunction (5-10%)

Availability: Approved in USA (FDA), Europe (CE mark). NHS England commissioning limited (specialist centres only).

Bariatric Surgery

Indication: Morbid obesity (BMI > 40 or > 35 with comorbidities) with OSA

Procedures: Gastric bypass, sleeve gastrectomy, adjustable gastric banding

Effect on OSA:

• 75-85% experience significant AHI improvement
• 40-80% achieve OSA resolution (depending on definition, surgery type) [17]
• May allow CPAP discontinuation in responders

Recommendation: Continue CPAP peri-operatively (reduces post-operative complications)

Special Populations

Pregnancy

OSA prevalence increases during pregnancy (particularly 3rd trimester):

• Maternal risks: Pre-eclampsia, gestational diabetes, hypertension
• Fetal risks: Intrauterine growth restriction, lower Apgar scores

Management:

• CPAP is safe during pregnancy
• Weight loss inappropriate during pregnancy
• Positional therapy (avoid supine sleeping - also benefits placental perfusion)

Elderly (> 65 years)

• Higher OSA prevalence but often asymptomatic
• Benefits of CPAP in asymptomatic elderly less clear
• Lower adherence rates
• Individualise treatment decisions (quality of life, comorbidities, patient preference)

Pre-operative Assessment

OSA increases peri-operative risks:

• Difficult intubation
• Peri-operative hypoxia
• Post-operative respiratory complications

Recommendations:

• Continue CPAP peri-operatively
• Avoid excessive opioids
• Extended monitoring post-procedure

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9. Complications

Untreated OSA drives multiple pathophysiological cascades leading to serious systemic complications.

Cardiovascular Complications

Mechanisms: Sympathetic activation, oxidative stress, endothelial dysfunction, inflammation [4]

Refractory Hypertension and OSA:

• Up to 90% of patients with resistant hypertension (BP uncontrolled on ≥3 agents) have OSA
• Always screen resistant hypertension patients for OSA
• CPAP therapy reduces BP more effectively in this subgroup (5-10 mmHg reduction) [4]

Metabolic Complications

Mechanisms: Intermittent hypoxia → Insulin resistance, lipolysis, hepatic steatosis [3,11]

Bidirectional relationship: OSA worsens glycaemic control; diabetes worsens OSA through neuropathy affecting airway reflexes.

Neurocognitive Complications

Dementia risk: Emerging evidence suggests OSA associated with increased Alzheimer's disease risk (mechanism: impaired cerebral amyloid clearance during fragmented sleep).

Occupational & Safety Risks

• Motor vehicle accidents: 2-7 fold increased risk [13]
• Occupational injuries: 2-fold increased risk
• Workplace errors: Reduced productivity, increased absenteeism

Driving regulations (UK DVLA):

• Group 1 (car/motorcycle): Must notify DVLA if excessive sleepiness affecting driving ability. Licence suspended until adequate treatment established.
• Group 2 (HGV/PCV): Any diagnosis of moderate-severe OSA must be notified. Licence suspended until CPAP treatment demonstrating adherence > 4 hours/night for > 70% nights and symptom control.

Surgical & Anaesthetic Risks

• Difficult intubation (3-5 fold increased risk)
• Post-operative respiratory complications (2-3 fold increased)
• Prolonged hospital stay
• Increased ICU admission rates

Recommendations:

• Disclose OSA diagnosis to anaesthetist
• Continue CPAP peri-operatively
• Avoid excessive sedation/opioids

Pregnancy-Related Risks

• Pre-eclampsia (2-3 fold increased)
• Gestational diabetes (1.5-2 fold increased)
• Intrauterine growth restriction
• Preterm delivery

Other Complications

• Gastro-oesophageal reflux: Negative intrathoracic pressure promotes reflux
• Nocturia: Atrial natriuretic peptide release → Diuresis [12]
• Sexual dysfunction: Erectile dysfunction (40-70% males), reduced libido both sexes [15]
• Glaucoma: 2-fold increased risk (mechanism unclear - possibly vascular)
• Polycythaemia: Chronic hypoxia → Elevated haemoglobin (rare in OSA alone, more common in OHS)

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10. Prognosis

Natural History (Untreated)

• Progression: AHI typically increases by 1-2 events/hour/year without intervention
• Spontaneous remission: Rare (less than 5%) unless significant weight loss achieved
• Cardiovascular mortality: 2-3 fold increased in severe untreated OSA [4]
• All-cause mortality: 1.5-2 fold increased

Outcomes with Treatment

CPAP Therapy

Symptomatic Benefits:

• Excessive daytime sleepiness: Improved in 80-90% within 2-4 weeks [18]
• Quality of life: Significant improvement in SF-36, FOSQ scores
• Cognitive function: Partial improvement in attention, vigilance
• Snoring: Eliminated in > 95% with adequate adherence

Cardiovascular Outcomes:

• Blood pressure reduction: 2-3 mmHg (meta-analysis > 4000 patients) [4]
• Greater effect in resistant hypertension: 5-10 mmHg reduction
• Atrial fibrillation recurrence: 40-50% reduction after ablation in CPAP-treated patients [4]
• Cardiovascular events: ~30% reduction in adherent patients (> 4 hours/night) [4]
• Heart failure: Improved ejection fraction, reduced hospitalisations

Metabolic Outcomes:

• Insulin sensitivity: Improved (effect size moderate)
• Glycaemic control: HbA1c reduction 0.2-0.4% in diabetic patients [3]
• Weight: No significant change (CPAP does not cause weight loss)

Limitations of CPAP:

• SAVE Trial (2016): CPAP did not reduce cardiovascular events in secondary prevention RCT (likely explained by poor adherence - mean 3.3 hours/night) [4]
• Adherence-dependent benefits: Effects proportional to nightly usage

Mandibular Advancement Devices

• Symptom improvement similar to CPAP in mild-moderate OSA
• Better adherence than CPAP (60-80% vs 40-60%)
• Long-term dental changes possible (10-year data available)

Surgical Outcomes

• UPPP: Variable success (40-60%); long-term data limited
• Hypoglossal nerve stimulation: 5-year efficacy data show sustained benefit in ~70% [20]
• Bariatric surgery: 40-80% OSA resolution; weight regain → OSA recurrence

Prognostic Factors

Predicting Treatment Response:

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11. Prevention & Screening

Primary Prevention

• Weight management: Maintain BMI less than 25 kg/m² (greatest modifiable risk factor)
• Alcohol moderation: Avoid excessive alcohol, particularly evening consumption
• Smoking cessation: Reduces upper airway inflammation
• Sleep hygiene: Adequate sleep duration (7-9 hours), regular schedule

Screening Recommendations

No population-based screening currently recommended due to:

• High prevalence in general population
• Resource implications of testing/treatment
• Unclear benefit of treating asymptomatic OSA

Targeted screening indicated in high-risk groups:

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12. Guidelines & Evidence

Key Guidelines

Landmark Trials & Evidence

Evidence-Based Treatment Recommendations

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13. Examination Focus (MRCP, FRACP, Respiratory SCE)

PACES/Clinical Examination Scenarios

Station 5 - Communication Skills

"This 52-year-old man has been referred by his GP with excessive daytime sleepiness and snoring. His wife is concerned. Please take a history and explain the likely diagnosis and investigations."

Key Tasks:

1. Take focused sleep history (witness account critical)
2. Assess cardiovascular risk factors
3. Explain OSA in lay terms
4. Explain sleep study process
5. Discuss treatment options (particularly CPAP)

Mark-winning points:

• Asking about witnessed apnoeas (high diagnostic value)
• Enquiring about driving (safety critical)
• DVLA notification requirements
• Explaining CPAP mechanism clearly ("air splint")

Viva Voce Scenarios

Opening Statement:

"Obstructive Sleep Apnoea is a highly prevalent condition affecting 4-10% of the adult population, characterised by recurrent upper airway collapse during sleep, leading to intermittent hypoxia, sleep fragmentation, and excessive daytime sleepiness. It is an independent risk factor for hypertension, atrial fibrillation, stroke, and metabolic syndrome, with major implications for cardiovascular morbidity and mortality." [1,4]

Common Questions & Model Answers:

Q1: How does neck circumference relate to OSA risk?

A: "Neck circumference > 43cm in men and > 40cm in women is the single best clinical predictor of OSA, with approximately 90% specificity for moderate-severe disease. This reflects parapharyngeal fat deposition which mechanically narrows the pharyngeal lumen, increasing collapsibility during sleep. It's a more reliable predictor than BMI alone because it captures central adiposity distribution." [6]

Q2: Explain the mechanism of CPAP therapy.

A: "CPAP acts as a 'pneumatic splint'. By delivering continuous positive pressure (typically 8-12 cm H₂O), it maintains positive transmural pressure across the pharyngeal walls throughout the respiratory cycle. This prevents the negative intraluminal pressure generated during inspiration from causing airway collapse, thereby eliminating apnoeas and hypopnoeas. The pressure required is determined by individual anatomy and severity." [1,18]

Q3: Why is oxygen therapy alone potentially dangerous in OSA?

A: "Firstly, like in COPD, some chronic OSA patients may rely on hypoxic ventilatory drive, and supplemental oxygen could blunt this, worsening hypoventilation. Secondly, and more importantly, oxygen prolongs apnoea duration by removing the hypoxic stimulus that triggers arousal and airway reopening. This results in longer apnoeic episodes with worse hypercapnia, without addressing the underlying mechanical obstruction. CPAP is preferable as it maintains airway patency." [1]

Q4: What is the relationship between OSA and hypertension?

A: "Approximately 50-60% of OSA patients have hypertension, and conversely, 30-40% of hypertensive patients have OSA. The mechanism involves intermittent hypoxia-induced sympathetic activation, oxidative stress, endothelial dysfunction, and activation of the renin-angiotensin-aldosterone system. OSA is particularly prevalent in resistant hypertension (80-90%), and CPAP therapy reduces blood pressure by 2-3 mmHg on average, with greater reductions in resistant cases." [4]

Q5: What is Obesity Hypoventilation Syndrome and how does it differ from OSA?

A: "OHS is defined by the triad of obesity (BMI > 30), daytime hypercapnia (PaCO₂ > 6 kPa while awake), and sleep-disordered breathing, in the absence of other causes of hypoventilation. It often coexists with OSA (90% of OHS patients have OSA), but the key distinguishing feature is daytime hypercapnia, which is absent in isolated OSA. OHS requires BiPAP rather than standard CPAP, targeting both upper airway patency and ventilatory support." [16]

Q6: Describe the DVLA regulations for OSA.

A: "For Group 1 licences (car/motorcycle), patients must notify the DVLA if they have excessive sleepiness affecting safe driving. The licence is suspended until adequate treatment is established with demonstrated symptom control. For Group 2 licences (HGV/PCV), any diagnosis of moderate-severe OSA must be notified, and the licence is suspended until CPAP treatment shows adherence > 4 hours/night on > 70% of nights with symptom control, confirmed by device download data."

Common Exam Mistakes

❌ Failing to recognise "witnessed apnoeas" as the single most diagnostic symptom (likelihood ratio > 10)

❌ Confusing AHI cut-offs: Remembering less than 5 normal, 5-15 mild, 15-30 moderate, ≥30 severe

❌ Stating "all OSA patients need CPAP": Mild OSA may only require lifestyle measures if asymptomatic

❌ Forgetting to screen for hypothyroidism: Common mimic and exacerbating factor

❌ Not addressing DVLA notification: Critical safety and medicolegal issue

❌ Quoting outdated evidence: SAVE trial often misinterpreted - understand adherence limitations

❌ Confusing OSA with Central Sleep Apnoea: OSA has persistent respiratory effort; CSA has absent effort

Data Interpretation Stations

Scenario: "This polysomnography trace is from a 58-year-old obese male. Interpret the findings."

Look for:

• Airflow cessation (flat trace on nasal/oral thermistor)
• Continued or increased respiratory effort (paradoxical chest/abdominal movements)
• Oxygen desaturation (SpO₂ drops from baseline to nadir)
• EEG arousal (shift from deep to light sleep stage)
• Restoration of airflow (large inspiratory effort, often with artefact)

Report: "This trace demonstrates obstructive apnoeas characterised by absent airflow despite persistent and increasing respiratory effort, associated with progressive oxygen desaturation to a nadir of [X]%, terminating with an arousal and restoration of airflow. This is consistent with obstructive sleep apnoea."

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14. Patient Information & Counselling

Explaining OSA to Patients

"Obstructive Sleep Apnoea means your throat keeps blocking while you sleep. The muscles in your throat relax when you sleep, and if you're overweight or have a narrow throat, this can cause it to collapse completely, stopping you breathing for 10-30 seconds at a time. Your brain has to wake you up briefly to start breathing again - this can happen hundreds of times a night without you realising. That's why you feel exhausted during the day, even though you think you've slept all night."

Explaining CPAP

"The CPAP machine is like a small air pump that gently blows air through a mask you wear over your nose (or nose and mouth). The air pressure acts like an invisible splint, holding your throat open all night so it can't collapse. Most people notice they feel more alert within a few days to weeks. It takes time to get used to - think of it like wearing glasses: strange at first, but soon you won't want to sleep without it."

Common Patient Questions

Q: "Will I need this machine forever?"

A: "If you lose a lot of weight, your sleep apnoea might improve enough to stop the machine. But for most people, it's a long-term treatment, like glasses for your eyes or tablets for high blood pressure. The good news is it works - it completely fixes the problem while you're using it."

Q: "Can I just lose weight instead?"

A: "Weight loss definitely helps - losing 10% of your body weight can reduce sleep apnoea by about a quarter. But it's usually not enough to cure it completely, and it takes time. We recommend using the machine while you work on losing weight, then we can reassess. Some people who lose a lot of weight (30-40 kg) can stop the machine eventually."

Q: "What happens if I don't use it?"

A: "Untreated sleep apnoea increases your risk of high blood pressure, stroke, heart attacks, and diabetes. It also makes you very sleepy, which increases your risk of accidents, particularly car crashes. If you're excessively sleepy, you're legally required to notify the DVLA, and you may not be allowed to drive until treated."

Q: "How will I sleep with a mask on?"

A: "Most people find it strange for the first few nights, but you'll get used to it quickly. We can try different mask styles - some just go in your nostrils (nasal pillows), others cover your nose, or your nose and mouth. We'll help you find one that's comfortable. Using the machine every night, even for naps, helps you adapt faster."

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15. Red Flags & When to Refer Urgently

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16. Summary - High-Yield Points for Revision

Definitions (Must Know)

• OSA: Recurrent upper airway collapse during sleep (AHI ≥5)
• Apnoea: ≥90% airflow reduction ≥10 seconds
• Hypopnoea: ≥30% airflow reduction ≥10 seconds + ≥3% desaturation or arousal
• AHI severity: Mild 5-15, Moderate 15-30, Severe ≥30

Epidemiology (Exam Favourites)

• Prevalence: 4-10% adults (higher in obesity, elderly, males)
• Gender: M:F = 2-3:1 (equalises post-menopause)
• Strongest predictor: Neck circumference > 43cm (M), > 40cm (F)

Pathophysiology (Viva Gold)

• Starling resistor model: Collapsible pharyngeal tube
• Intermittent hypoxia → Oxidative stress, sympathetic activation, inflammation, endothelial dysfunction
• Cycle: Sleep → Hypotonia → Collapse → Hypoxia → Arousal → Repeat (30-100+/hour)

Clinical Features (Diagnostic Pearls)

• Witnessed apnoeas: LR > 10 (most diagnostic symptom)
• Loud, intermittent snoring: Universal but non-specific
• Excessive daytime sleepiness: ESS > 10 pathological
• Morning headaches: Frontal, improve within 30-60 mins
• Nocturia: ANP release from negative intrathoracic pressure

Investigations (Must Dos)

• Screening: ESS, STOP-BANG (score ≥5 high risk)
• Gold standard: Polysomnography (PSG)
• First-line: Home sleep apnoea test (HSAT) - cost-effective, convenient
• Key metric: AHI (apnoeas + hypopnoeas per hour of sleep)
• Severity: Mild 5-15, Moderate 15-30, Severe ≥30

Management (Treatment Algorithm)

1. Lifestyle: Weight loss (↓10% weight = ↓26% AHI), alcohol avoidance, positional therapy
2. CPAP: Gold standard for moderate-severe (AHI ≥15) or symptomatic mild
3. MAD: Alternative for mild-moderate or CPAP intolerant
4. Surgery: Third-line (UPPP, hypoglossal nerve stimulation, MMA)

Complications (Exam Essentials)

• CV: HTN (50-60%), AF (40-50%), stroke, MI
• Metabolic: Diabetes (2× risk), metabolic syndrome (60-70%), NAFLD (50-70%)
• Neurocognitive: Cognitive impairment, depression (30-50%)
• Safety: 2-7× MVA risk, occupational injuries

DVLA Rules (Medicolegal Must-Know)

• Group 1: Stop driving if excessive sleepiness; notify DVLA
• Group 2: Notify any moderate-severe OSA; suspended until CPAP adherence > 4hrs/night > 70% nights

Evidence (Trials to Quote)

• SAVE 2016: CPAP didn't reduce CV events (poor adherence 3.3 hrs/night)
• Meta-analyses: CPAP ↓ BP by 2-3 mmHg (5-10 mmHg in resistant HTN)
• Weight loss: 10% reduction → 26% AHI reduction

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