Obstructive sleep apnea (OSA) is the most common sleep-related breathing disorder and is typically associated with obesity. It is characterized by obstruction of the upper airways due to the collapse of the pharyngeal muscles during sleep, which causes multiple episodes of interrupted breathing (apnea and hypopnea events), leading to alveolar hypoventilation. Severe daytime sleepiness due to sleep disruption is a common symptom. Partners of affected individuals commonly describe observing restless sleep and irregular snoring, gasping, or choking episodes. The diagnosis is based on polysomnography or home sleep apnea testing. Many patients develop hypertension secondary to OSA, the cardiovascular consequences of which can reduce life expectancy. First-line treatment consists of nightly continuous positive airway pressure (CPAP); alternatives include oral appliances and surgical interventions. Lifestyle changes such as weight loss, avoidance of precipitating factors (e.g., alcohol), and improvement of sleep hygiene are recommended.
- Obstructive sleep apnea: (OSA): a upper airway obstruction in which airflow significantly decreases or ceases due to (typically in the oropharynx) 
Abnormal breathing events
- Apnea: complete or nearly complete (≥ 90%) cessation of inspiratory airflow for ≥ 10 seconds 
- Hypopnea: airflow reduction by ≥ 30% of the pre-event baseline for ≥ 10 seconds in combination with either desaturation by ≥ 3% or 
- Respiratory effort-related arousal (RERA): due to increased respiratory effort or reduced airflow for ≥ 10 seconds without significant hypopnea or apnea 
- Obstruction of the upper airways due to the collapse of the pharyngeal muscles during sleep
Risk factors for obstructive sleep apnea
- Obesity, especially around the neck (short, wide “bull neck”)
- Structural abnormalities that impair respiratory flow, including:
- Alcohol consumption before sleep
- Intake of sedatives and/or beta blockers before sleep
- Family history
An increased neck circumference (> 40 cm) is the most important risk factor for OSA.
- Obstruction of the upper airways → apnea → ↓ partial pressure of oxygen in arterial blood (PaO2), ↑ partial pressure of carbon dioxide in arterial blood (PaCO2, also known as hypercapnia), which leads to:
Typical symptoms 
- Restless sleep with waking, gasping, or choking
- Loud, irregular snoring with apneic episodes (third-party reports)
- Excessive daytime sleepiness (e.g., patient falls asleep, microsleep while seated)
- Morning headaches
- Signs of complications, including:
General principles 
- A detailed evaluation should include:
- Sleep history, including third-party reports (e.g., interviewing the sleep partner about snoring and witnessed apneas)
- Evaluation for comorbidities (including ) and
Screening for OSA
- Standardized screening questionnaires may be used to assess risk for OSA in certain clinical settings (e.g., STOP-BANG questionnaire for preoperative evaluation).
- Screening asymptomatic patients is not routinely recommended. 
- Sleep studies are required to confirm the diagnosis and determine the severity of OSA (e.g., using the apnea-hypopnea index).
STOP-BANG questionnaire: S – Snoring loudly, T – feeling Tired or fatigued, O – Observed apneas during sleep, P – high blood Pressure, B – BMI > 35, A – Age > 50 years, N – Neck circumference > 40 cm, G – male Gender. 
Laboratory tests are not usually considered useful in the diagnosis of OSA but can help identify physiological consequences of OSA and detect associated conditions.
- CBC may show polycythemia (↑ Hct, ↑ Hb): Hypoxia induces erythropoietin secretion by the kidneys, which stimulates the blood marrow, leading to increased RBC production. 
- Arterial blood gas
Sleep studies 
- Indicated in all patients with excessive daytime sleepiness and at least two of the following:
- Consider in patients with comorbidities (including ) and .
In-laboratory polysomnography (PSG)
- Description: Physiologic variables are recorded during sleep to diagnose sleep-related disorders.
- Patients with significant cardiovascular or respiratory disease
- Suspicion of other types of sleep-related disorders
- Circumstances precluding a home assessment 
- Home sleep apnea testing is inconclusive or negative.
- Consider repeated testing if the initial test is negative and clinical suspicion remains (first night effect). 
- Consider split-night testing. 
Home sleep apnea testing (HSAT)
- Description: an ambulatory screening method for sleep-related breathing disorders that assesses ventilation and oxygenation parameters but not sleep stages or arousal events
- Patients with a high pretest probability for OSA and no significant comorbidities
- In-laboratory testing is not feasible.
- Findings: cardiorespiratory findings similar to those in PSG
Due to its lower sensitivity, HSAT cannot be used to rule out the diagnosis of OSA. 
Interpretation of sleep study findings 
Scores are calculated based on sleep study findings and are then used to diagnose OSA and determine its severity.
- Apnea-hypopnea index (AHI): number of apneas plus hypopneas per hour of sleep
- Respiratory disturbance index (RDI): number of apneas plus hypopneas plus RERAs per hour of sleep 
- Respiratory event index (REI): number of apneas plus hypopneas with desaturation of ≥ 4% per hour of recorded time
Diagnostic criteria for OSA 
Depending on the type of sleep study used, different scores can be calculated. Any of them can be used to diagnose OSA.
- AHI/RDI/REI ≥ 5 in patients with symptoms of OSA and/or associated comorbidities
- OR AHI/RDI/REI ≥ 15 in patients without symptoms
Classification of OSA by severity 
Central sleep apnea (CSA) syndromes 
|Types of CSA |
|Nonhypercapnic CSA||Hypercapnic CSA|
- Clinical features 
- Optimize treatment of the underlying condition.
- Ventilation support
- Further treatment may be considered based on the underlying cause. 
Obesity hypoventilation syndrome (Pickwickian syndrome) 
- Definition: a type of sleep-related hypoventilation disorder defined by a BMI of ≥ 30 kg/m2, diurnal hypercapnia, and disordered breathing during sleep 
- Risk factors: same as those for obesity 
Pathophysiology: Multiple mechanisms caused by obesity contribute to the development of OHS.
- Structural component: reduction in inspiratory muscle strength and restriction of respiratory excursions → reduction; in lung volume → alveolar hypoventilation
- Central component: increased work of breathing → increased respiratory drive → inability to maintain during REM sleep → hypoventilation (↓ PaO2,↑ PaCO2) during sleep → repetitive hypoventilation causes depression of central respiratory centers → diurnal hypercapnia
- Obstructive component: ∼ 90% of OHS patients have concurrent OSA. 
- Clinical features
Other sleep-related hypoventilation disorders
- Sleep-related hypoventilation due to a medical condition 
- Sleep-related hypoventilation due to medication 
- Congenital central hypoventilation syndrome (Ondine's curse): a dysfunction of automatic central breathing control that is typically seen in newborns and is characterized by shallow breathing or complete lack of spontaneous breathing during sleep 
- Late-onset central hypoventilation with hypothalamic dysfunction
- Idiopathic central alveolar hypoventilation: Diagnosis requires exclusion of lung parenchyma disease, airway or pulmonary vessel disease, neuromuscular disease, drug-induced hypoventilation, or congenital hypoventilation. 
The differential diagnoses listed here are not exhaustive.
- Treat all patients with diagnosed OSA.
- First-line treatment: positive airway pressure (PAP)
Consider alternative treatment in patients who are unable to tolerate or decline PAP: 
- Oral appliances
- Upper airway modifications
- Positional therapy
- Supportive care should include management of risk factors, e.g., weight loss and sleep hygiene.
Nocturnal positive pressure therapy is the therapy of choice in OSA. The success of therapy is highly dependent on patient adherence.
- Description: Pressure is used to pneumatically splint collapsible airways open to reduce the frequency of respiratory events. 
Alternative treatment options 
Conservative treatment options are usually only appropriate for mild to moderate disease.
Oral appliances 
- Devices are worn during sleep to maintain mandibular advancement and prevent airway collapse.
- Custom-fitted titratable devices are preferred.
- Positional therapy: : devices to keep patients in a lateral as opposed to supine sleeping position 
Upper airway modification 
- Description: surgical dilatation of the upper airway or neurostimulation of upper airway muscles
- Approach: single-stage, multilevel, or stepwise surgery
- Maxillomandibular advancement: advancement and fixation of the maxillary and mandibular bones, increasing the retrolingual and retropalatal airway space
- Uvulopalatopharyngoplasty: resection of the uvula and redundant retrolingual, soft palate, and tonsillar tissue
- Tracheostomy: may be considered in the case of clinical urgency or as a last resort after failure of other treatment options
- Other procedures include hypoglossal nerve stimulation, radiofrequency ablation of tongue and/or soft palate tissue, and palatal implants. 
Supportive treatment 
- Lifestyle interventions
- Treatment of associated conditions and , e.g., blood pressure control 
- Patient counseling regarding risks of drowsy driving
- Systemic hypertension
- Hypoxia-induced cardiac arrhythmia (e.g., (atrial fibrillation, atrial flutter) 
- Pulmonary hypertension and cor pulmonale
- Global respiratory insufficiency
- Cardiac infarction, stroke, and sudden cardiac death (the risk of sudden death is high in infants and the elderly)
- Risk of accidents (e.g., car crashes, occupational accidents) due to microsleep
- Increased risk of developing vascular dementia
- Poor sleep leads to increased appetite and obesity.
We list the most important complications. The selection is not exhaustive.