Obstructive Sleep Apnea

Epidemiology and Classification

Epidemiology

• Most common sleep-related breathing disorder
• Incidence of approximately 20%–30% in men and 10%–15% in women (note that rates are similar between men and post-menopausal women)
• Prevalence increases with age with a plateau after the seventh decade.
• Obesity (body mass index [BMI] > 30) correlates strongly with obstructive sleep apnea (OSA).
• African Americans are more likely to develop OSA independent of age and BMI.
• Global prevalence more than doubled from 1990 to 2010 (may relate to increased detection and/or increased rates of obesity)

Classification

• Sleep apnea:
  • Repeated cessation of breathing for > 10 seconds during sleep
  • Results in sleep interruption, fatigue, and daytime sleepiness 
• Obstructive sleep apnea:
  • Flaccid soft tissues obstruct airway, leading to hypoventilation during sleep
• Central sleep apnea (CSA):
  • Airflow limitation and/or ventilation problem mediated by aberrant central nervous system
  • May be hyper- or hypoventilation 
• Mixed sleep apnea:
  • Combination of both OSA and CSA
• Obesity hypoventilation syndrome (OHS):
  • Extra adipose tissue in obese individuals leads to hypoventilation while awake.
  • Also known as Pickwickian syndrome

Risk Factors and Pathophysiology

Risk factors

• Obesity:
  • Condition of metabolic or nutritional nature
  • Characterized by accumulation of excess body fat
  • Assessed by BMI, ≥ 30 is considered obese
• Congenital or acquired craniofacial abnormalities: 
  • Abnormalities of the jaw (micrognathia or retrognathia)
  • Tonsillar hyperplasia
  • Macroglossia
  • Neck circumference > 43 cm (17 in.)
  • Previous airway surgery
  • Nasal polyps (benign lesions of the nasal mucosa that typically present with postnasal drip and nasal obstruction; usually due to chronic inflammation) or septal deviation
  • Hypertrophied pharyngeal muscles
• Advanced age: increased incidence > 65 years
• Alcohol consumption before sleep
• Use of sedatives
• Acromegaly: excess production of growth hormone by the pituitary gland
• Hypothyroidism:
  • Deficiency of T3 and T4 hormones
  • Clinical features of hypothyroidism are primarily due to the accumulation of matrix substances and a decreased metabolic rate.
• Poor muscle tone due to brain injury or neuromuscular disease

Pathophysiology

• Sleep results in loss of the wakefulness drive to breathe, decreased motor output to respiratory muscles, decreased upper airway (UA) size, increased UA resistance. 
  • Leads to apneic and hypopneic episodes in susceptible individuals
• Apneic and hypopneic episodes → increased arterial carbon dioxide (CO₂) levels (hypercapnia) → stimulates respiratory efforts against the narrowed upper airway until the individual is awakened
  • Hypercapnia → respiratory acidosis
  • Increased respiratory efforts are achieved by sympathetic effects → secondary tachycardia and hypertension
  • Reduced airflow results in pulmonary hypoxia which triggers pulmonary vasoconstriction (Euler-Liljestrand mechanism) → pulmonary hypertension → cor pulmonale

Clinical Presentation

• Often, the patient is unaware of their symptoms and is brought in by their spouse or sleep partner.
• Symptoms may include:
  • Nocturnal restlessness 
  • Vivid, strange, or threatening dreams 
  • Interrupted sleep, frequent awakenings
  • Snoring, choking, or gasping while asleep
  • Nocturia
  • Diminished ability to concentrate
  • Cognitive deficits
  • Irritability and other changes in mood
  • Morning headaches
  • Daytime sleepiness

Diagnosis

• Suspicion is raised based on a thorough history, including information from bed partner/spouse. A common questionnaire to estimate pretest probability of OSA is:
  • STOP-BANG
    • Do you Snore loud enough to be heard through closed doors, or your bed partner elbows you for snoring at night?
    • Do you often feel Tired, fatigued, or sleepy during the day?
    • Has anyone Observed you stop breathing, or choking/gasping during your sleep?
    • Do you have or are you being treated for high blood Pressure?
    • BMI > 35 kg/m²
    • Age older than 50 years?
    • Neck size large: male > 17 inch shirt collar and female > 16 inch shirt collar
    • Gender: male?
  • Low risk of OSA: Yes to 0–2 questions
  • Intermediate risk of OSA: Yes to 3–4 questions
  • High risk of OSA: Yes to 5–8 questions
• Polysomnography (PSG): gold-standard diagnostic test for OSA
  • Patient is monitored on video overnight while hooked up to electrocardiogram (ECG), electroencephalogram (EEG), pulse oximetry, and nasal prongs to assess snoring, sleep architecture, and physiologic changes during sleep. 
  • The severity of OSA can be determined from the Apnea/Hypopnea index (AHI), which is calculated as the number of apneic episodes per hour of sleep during a sleep study.
    • AHI > 5 = mild OSA
    • AHI > 15 = moderate OSA
    • AHI > 30 = severe OSA
  • If EEG monitoring is used, then the arousal index (AI) can be calculated as the number of arousals per hour of sleep.

Management

Conservative management

Improving modifiable risk factors:

• Weight loss 
• Cessation of consumption of sedatives/alcohol
• Oral appliances or splints during sleep to prevent airway collapse/obstruction

Positive airway pressure devices

• Continuous positive airway pressure (CPAP): most effective treatment method
  • Noninvasive ventilation that uses positive air pressure to keep airways open
  • Improves restlessness, snoring, cognition, daytime somnolence and quality of life
  • Low adherence rate
• Bilevel positive airway pressure (BiPAP): provides a higher pressure during inhalation and a lower one during exhalation

Surgery

• Resection of nasal polyps 
• Nasal septal deviation correction
• Reduction of enlarged tonsils or hypertrophied inferior turbinates
• Uvulopalatopharyngoplasty: resection of uvula, soft palate, tonsils, and excess oropharyngeal tissue
• Maxillomandibular advancement for patients with retrognathia or micrognathia
• Tracheotomy: only used in severe refractory life-threatening OSA
• Bariatric surgery

Clinical Relevance

Possible complications of obstructive sleep apnea:

• Hypertension: condition defined as a systolic blood pressure ≥ 130 mm Hg and/or a diastolic blood pressure ≥ 80 mm Hg
• Stroke: acute neurological condition characterized by an impairment in the arterial blood supply to brain tissue. Usually due to a focal vascular cause, such as an embolism or the rupture of an aneurysm 
• Dementia: term used to group diseases and conditions characterized by a decline in memory, language, problem-solving, and other executive functioning skills
• Pulmonary hypertension: condition of chronically elevated mean pulmonary arterial pressure ≥ 20 mm Hg
• Cor pulmonale: also known as right-sided heart failure, a condition characterized by an alteration in the structure and function of the right ventricle of the heart due to a primary disorder of the respiratory system
• Respiratory failure: insufficient levels of oxygen in the systemic bloodstream, due to inadequate oxygenation of blood or inadequate ventilation or both
• Cardiac disorders:
  • Arrhythmia: abnormality in the rate or rhythm of the heartbeat
  • Myocardial infarction: ischemic damage to the myocardium, which occurs when blood flow is reduced or completely obstructed to a part of the heart
  • Sudden cardiac death: sudden, unexpected death as a result of cardiac arrest. This occurs within 1 hour of symptom onset. Usually caused by acute coronary syndrome