Obstructive Sleep Apnea (OSA)

Obstructive sleep apnoea (OSA) is a sleep-related breathing disorder characterised by repetitive episodes of partial (hypopnoea) or complete (apnoea) upper airway collapse during sleep, resulting in intermittent hypoxaemia, hypercapnia, intrathoracic pressure swings, sleep fragmentation, and sympathetic nervous system activation. It is the most common sleep-disordered breathing condition and is a significant contributor to cardiovascular morbidity, metabolic dysfunction, neurocognitive impairment, occupational accidents, and reduced quality of life.

In Australia, the 2016 Sleep Health Foundation National Survey estimated that approximately 8% of adults have been diagnosed with sleep apnoea, with many more undiagnosed. Population-based studies using objective sleep monitoring suggest that the true prevalence of moderate-to-severe OSA (AHI ≥ 15) is around 10–14% in men and 5–8% in women aged 30–70 years. Prevalence increases sharply with age, male sex, obesity (BMI ≥ 30 kg/m²), neck circumference >43 cm (men) or >38 cm (women), craniofacial factors, and menopausal status in women.

The economic burden is substantial: the Sleep Health Foundation estimated that sleep disorders cost the Australian economy over $26 billion annually in healthcare expenditure, lost productivity, and accident-related costs. OSA contributes to increased road traffic accidents (two- to seven-fold risk), workplace injuries, reduced work productivity, and increased utilisation of primary care and emergency department services.

Key Australian Risk Factors

OSA results from the interplay of three principal mechanisms operating during sleep when pharyngeal dilator muscle tone naturally declines:

Mechanisms of Upper Airway Collapse

1. Anatomical narrowing (critical closing pressure, Pcrit): Bony and soft-tissue craniofacial structure, tongue volume, lateral pharyngeal wall fat, and tonsillar/adenoid hypertrophy determine the baseline calibre of the upper airway. Obesity increases Pcrit by depositing fat in the parapharyngeal space and reducing lung volumes (which normally provide caudal traction on the trachea, splinting the pharynx open).
2. Compensatory neuromuscular drive failure: Pharyngeal dilator muscles (particularly genioglossus) respond to negative intraluminal pressure and hypercapnia during wakefulness to maintain airway patency. During sleep, this reflexive activation diminishes, and in susceptible individuals is insufficient to counterbalance the collapsing forces.
3. Loop instability (low arousal threshold, high loop gain): Some patients have unstable ventilatory control — small perturbations in ventilation cause large corrective responses (high controller gain), leading to over-breathing followed by central apnoea, which destabilises the airway. Patients with a low arousal threshold wake before oxygen normalises, perpetuating repetitive cycling.

Pathophysiological Consequences

• Intermittent hypoxaemia → sympathetic activation: Cyclical desaturation and reoxygenation generates reactive oxygen species (ROS), activates the sympathetic nervous system, and increases catecholamine release, driving systemic hypertension.
• Intrathoracic pressure swings (Müller manoeuvre): Vigorous inspiratory efforts against a closed airway generate intrathoracic pressures as low as −60 cmH₂O, increasing transmural cardiac wall stress, favouring atrial fibrillation and impairing cardiac output.
• Sleep fragmentation: Repeated cortical arousals suppress slow-wave and REM sleep, impairing memory consolidation, executive function, and daytime alertness.
• Inflammatory cascade: Intermittent hypoxia activates NF-κB, increases CRP, IL-6, TNF-α, and endothelin-1, promoting endothelial dysfunction, atherosclerosis, and insulin resistance.
• Metabolic dysregulation: Intermittent hypoxaemia impairs glucose tolerance independently of obesity, increases hepatic gluconeogenesis, and promotes visceral adiposity through HPA axis activation.

Clinical Screening Tools

Polysomnography (PSG)

Full, attended, in-laboratory polysomnography remains the gold standard for diagnosis of sleep-disordered breathing. PSG records electroencephalography (EEG), electrooculography (EOG), electromyography (EMG), nasal/oral airflow, thoracoabdominal effort, oximetry (SpO₂), ECG, body position, and leg movements. It is performed in accredited sleep laboratories under the supervision of qualified sleep scientists.

Home Sleep Apnoea Testing (HSAT)

Home sleep apnoea testing (HSAT), also known as portable monitoring or home sleep studies, uses simplified devices (typically Level 3 or Level 4) to record airflow, respiratory effort, oximetry, and heart rate in the patient's own home over 1–3 nights.

AHI Interpretation & Clinical Significance

Additional Sleep Parameters

• Respiratory Disturbance Index (RDI): Includes apnoeas, hypopnoeas, and respiratory effort-related arousals (RERAs). RDI ≥ 5 with symptoms defines Upper Airway Resistance Syndrome (UARS).
• ODI (Oxygen Desaturation Index): Number of ≥3% or ≥4% desaturation events per hour. ODI ≥ 5 correlates with clinically significant OSA. ODI ≥ 15 associated with increased cardiovascular risk.
• Mean and nadir SpO₂: Nadir SpO₂ <85% correlates with severe disease and increased cardiovascular risk. Mean SpO₂ <93% during sleep warrants evaluation for hypoventilation.
• T90 (time spent with SpO₂ <90%): T90 >30% of total sleep time indicates significant nocturnal hypoxaemia and may warrant supplemental oxygen in addition to CPAP.
• Central Apnoea Index (CAI): CAI ≥ 5/hour suggests central sleep apnoea component; CPAP alone may be insufficient and ASV or BiPAP may be required.

Investigations

Continuous positive airway pressure (CPAP) is the gold-standard treatment for moderate-to-severe OSA and for mild OSA with significant symptoms. CPAP acts as a pneumatic splint, maintaining upper airway patency throughout the respiratory cycle, eliminating apnoeas, hypopnoeas, and snoring.

CPAP Modes

CPAP Titration Protocols

The goal of titration is to identify the minimum effective pressure that eliminates obstructive apnoeas, hypopnoeas, flow limitation, snoring, and respiratory effort-related arousals in all sleep stages and body positions.

Mask Selection

Adherence Strategies

• Early follow-up (within 1–2 weeks): The first fortnight is critical. Troubleshoot mask fit, pressure comfort, and nasal symptoms early. Telehealth review is effective and increasingly used in Australian sleep services.
• Ramp and expiratory pressure relief (EPR/C-Flex): Ramp feature starts at a low pressure and gradually increases over 5–45 minutes to ease sleep onset. EPR reduces expiratory pressure by 1–3 cmH₂O, improving comfort.
• Heated humidification: Reduces nasal dryness, congestion, and epistaxis. Consider in all patients, especially those on high pressures, mouth breathers, or in dry climates (common in inland Australia).
• Mask refitting: Multiple mask trials may be necessary. Ensure adequate supply of replacement cushions (every 1–3 months) and headgear (every 6 months) — most Australian CPAP suppliers provide these on subscription.
• Patient education and support groups: Referral to sleep psychologist for CBT-based CPAP desensitisation for anxious patients. Support groups (e.g., Sleep Health Foundation resources, CPAP Australia online forums).
• Telemonitoring: ResMed AirView, Philips Care Orchestrator, and Löwenstein platforms allow real-time monitoring. Nursing staff can intervene when usage drops below thresholds. Widely adopted in Australian public and private sleep services.
• Ongoing follow-up: Review at 1 month, 3 months, and 6 months after initiation; annually thereafter. Download device data at each visit. Adjust pressure if residual AHI >5 or if significant leak persists.

Troubleshooting CPAP Problems

CPAP Access & Funding in Australia

• Public hospital sleep services: Many state health services provide CPAP devices on loan (especially for concession card holders). Wait times vary (4–12 weeks).
• Private purchase: CPAP devices cost $800–2,500 AUD. Mask and supply kits $50–300. Most Australian suppliers offer rental-to-own and payment plans.
• Private health insurance: Many extras policies cover CPAP devices and supplies (partially or fully). Check individual fund limits.
• Department of Veterans' Affairs (DVA): CPAP devices and supplies are covered for eligible veterans with a Gold or White Card.
• NDIS: CPAP may be funded under NDIS for participants with disability-related sleep-disordered breathing.

Alternative treatments are indicated when CPAP is refused, not tolerated despite adequate troubleshooting, or when the patient has mild-to-moderate OSA and prefers a non-CPAP approach. Treatment selection should be guided by disease severity, anatomical site of obstruction, patient preference, and availability of specialist services.

Oral Appliances (Mandibular Advancement Splints — MAS)

Mandibular advancement splints (MAS), also termed mandibular advancement devices (MAD), are custom-fitted oral appliances worn during sleep that protrude the mandible forward, increasing the anteroposterior dimension of the pharyngeal airway and reducing collapsibility.

Positional Therapy

Positional OSA (supine-predominant) is defined as an AHI at least twice as high in the supine position compared to the lateral position. Approximately 20–30% of OSA patients have a significant positional component.

• Positional devices: Vibrotactile devices (e.g., NightShift™, Philips NightBalance™) worn on the neck or chest deliver gentle vibrations when the patient adopts the supine position, prompting positional change without awakening. Available in Australia through sleep device suppliers.
• Modified sleep positioning: Elevated head of bed 30°; body positioning pillows; tennis ball technique (less tolerated long-term); side-sleeping pillows. Low cost but adherence is often poor.
• Evidence: Positional therapy alone may reduce AHI by 50% in positional OSA. Often used as adjunct to CPAP or MAS rather than standalone therapy for moderate-to-severe disease.

Upper Airway Surgery

Surgical options are considered when CPAP and oral appliances have failed or are refused, and when a surgically correctable anatomical abnormality is identified. Drug-induced sleep endoscopy (DISE) is increasingly used to guide surgical planning.

Hypoglossal Nerve Stimulation (HGNS)

Hypoglossal nerve stimulation (e.g., Inspire® Upper Airway Stimulation) is an implantable device that delivers electrical stimulation to the hypoglossal nerve (specifically the genioglossus branch) during inspiration, synchronised with respiratory effort, to protrude the tongue and maintain airway patency.

• Candidacy criteria: Age ≥ 18; moderate-to-severe OSA (AHI 15–65); CPAP-intolerant (failed ≥ 3 months with optimised therapy); BMI <32 kg/m² (some protocols <35); absence of complete concentric collapse at the palatal level on DISE.
• Efficacy: STAR trial showed AHI reduction from 29 to 9 events/hour at 12 months; 66% of patients achieved AHI <15; ESS improved by ~6 points.
• Australian availability: The Inspire system received TGA approval. Implantation is available at select tertiary centres in Australia (e.g., Royal Melbourne Hospital, Westmead Hospital). Limited access and high cost (device + surgery ~$40,000–60,000 AUD) remain significant barriers. Not PBS-listed; private health fund coverage varies.
• Complications: Tongue abrasion, infection, device malfunction, nerve injury (rare); requires long-term follow-up and device programming.

Pharmacological Adjuncts

OSA is independently associated with a range of cardiovascular, metabolic, and neurological comorbidities. Bidirectional relationships exist: OSA worsens comorbidity outcomes, and comorbidities may exacerbate OSA severity. Integrated management by the GP, sleep physician, and relevant specialists is essential.

Cardiovascular Disease

• OSA is an independent risk factor for coronary artery disease (adjusted OR 2.6), heart failure (OR 2.4), and stroke (OR 2–4). The Wisconsin Sleep Cohort study demonstrated a dose-response relationship between AHI severity and incident cardiovascular events.
• CPAP treatment reduces sympathetic activity, lowers nocturnal and daytime blood pressure (by 2–10 mmHg systolic), and improves endothelial function. The SAVE trial (2016) showed that CPAP did not significantly reduce major cardiovascular events in patients with moderate-to-severe OSA and established cardiovascular disease, but post-hoc analyses suggested benefit with adequate adherence (≥4 hours/night).
• Screen for OSA in all patients with heart failure (especially HFrEF), recent stroke, or recurrent atrial fibrillation — prevalence of OSA in these populations is 40–60%.

Resistant Hypertension

Atrial Fibrillation

• OSA increases the risk of atrial fibrillation (AF) 2–4 fold. Prevalence of OSA in AF populations is ~50–65%.
• Untreated OSA reduces the effectiveness of cardioversion, catheter ablation, and anti-arrhythmic therapy for AF. Recurrence rates after ablation are significantly higher in untreated OSA.
• Screen all AF patients for OSA (AHA/ASA recommendation Level B). Treat OSA concurrently with rhythm management. CPAP use in OSA patients with AF reduces AF recurrence post-ablation.

Metabolic Syndrome & Type 2 Diabetes

• OSA is independently associated with insulin resistance, impaired glucose tolerance, and type 2 diabetes mellitus, even after adjustment for BMI and waist circumference. Intermittent hypoxaemia directly impairs pancreatic β-cell function.
• Prevalence of OSA in type 2 diabetes is 50–70%. Conversely, the prevalence of impaired glucose tolerance in OSA is approximately 30–40%.
• CPAP treatment modestly improves insulin sensitivity and HbA1c (by 0.2–0.4% in some studies), though the effect is variable and less pronounced than with weight loss. CPAP and weight loss are complementary strategies.
• Screen for OSA in patients with metabolic syndrome (waist circumference ≥102 cm men / ≥88 cm women, triglycerides ≥1.7 mmol/L, HDL <1.0 men / <1.3 women, BP ≥130/85, fasting glucose ≥5.6 mmol/L).

Perioperative Risk

Obesity is the single most important modifiable risk factor for OSA. Weight gain exacerbates OSA through increased pharyngeal fat deposition, reduced lung volumes, and decreased upper airway calibre. Weight loss, conversely, reduces AHI, improves CPAP adherence, and may in some cases resolve OSA entirely.

Weight Loss Targets

Weight Loss Interventions

• Lifestyle intervention: Structured diet and exercise programmes targeting 500–750 kcal/day deficit; Mediterranean or low-glycaemic-index diet preferred. Referral to accredited practising dietitian (APD) recommended. The Look AHEAD trial demonstrated that intensive lifestyle intervention improved AHI in overweight adults with type 2 diabetes.
• Pharmacotherapy for obesity: GLP-1 receptor agonists (liraglutide [Saxenda®], semaglutide [Wegovy®]) are TGA-approved for chronic weight management. The STEP trials showed mean weight loss of 10–17% with semaglutide 2.4 mg SC weekly. Subcutaneous tirzepatide (Mounjaro®) shows even greater weight loss (~20%). These agents may significantly improve OSA severity in parallel with weight loss. Access and cost remain barriers in Australia.
• Behavioural support: Multidisciplinary teams including dietitians, exercise physiologists, psychologists. Telehealth-delivered weight management programmes are increasingly used in rural and remote Australia.

Bariatric Surgery

Bariatric surgery is the most effective intervention for sustained weight loss in severe obesity and has the highest OSA remission rate of any treatment modality.

• Australian criteria: BMI ≥ 40 kg/m², or BMI ≥ 35 with obesity-related comorbidities (including OSA), who have failed ≥6 months of supervised conservative management. MBS items exist for bariatric surgery.
• Pre-operative requirement: Sleep study for all bariatric surgery candidates. CPAP initiation before surgery if OSA diagnosed — reduces perioperative anaesthetic risk.
• Post-operative requirement: Repeat sleep study 12–18 months post-surgery regardless of symptom improvement. Many patients with resolved symptoms still have residual moderate OSA. CPAP may need to be continued or re-titrated to lower pressure.

Obesity Hypoventilation Syndrome (OHS)

Key clinical tip: A serum bicarbonate ≥ 27 mmol/L on a venous blood gas in an obese patient should raise suspicion for OHS and prompt arterial blood gas assessment. Daytime hypercapnia (PaCO₂ ≥ 6.0 kPa) confirms the diagnosis. These patients require sleep physician and respiratory medicine referral for initiation of non-invasive ventilation (NIV/BiPAP).

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