Sleep Disorders — Sleep Apnea

Obstructive mechanisms — anatomic crowding

• Obesity: parapharyngeal fat deposition plus reduced caudal tracheal traction from decreased lung volumes; the single most important modifiable risk factor, and the reason neck circumference outperforms BMI in prediction
• Adenotonsillar hypertrophy: the dominant cause of pediatric OSA; the American Academy of Pediatrics identifies adenotonsillectomy as first-line therapy in otherwise healthy children
• Craniofacial morphology: retrognathia, micrognathia, macroglossia, high-arched narrow palate, nasal septal deviation; classically Pierre Robin sequence, Treacher Collins, and Down syndrome (midface hypoplasia plus hypotonia plus macroglossia)

Obstructive mechanisms — reduced dilator tone or increased loop gain

• Alcohol, benzodiazepines, opioids, and general anesthesia: depress genioglossus activity and blunt arousal, converting snoring into frank apnea — modifiable and frequently the stem's trigger
• Supine sleep and REM sleep: gravity plus REM atonia; REM-predominant events explain a normal-appearing brief nap study
• Endocrine disease: hypothyroidism (macroglossia, myxedematous soft tissue), acromegaly (soft-tissue and mandibular overgrowth), PCOS

Non-modifiable risk factors examiners plant

• Male sex (roughly 2–3× risk), advancing age, postmenopausal status in women, family history, and African American, Hispanic, and Asian ancestry (the last through craniofacial structure at lower BMI)

Central sleep apnea etiologies

• Heart failure with reduced EF: prolonged circulation time and heightened chemoreflex sensitivity produce Cheyne-Stokes respiration
• Chronic opioid use: brainstem mu-receptor suppression of respiratory rhythm — ataxic (Biot) breathing
• Brainstem injury: stroke, tumor, syringobulbia, Chiari malformation; congenital central hypoventilation syndrome (PHOX2B mutation, "Ondine's curse")
• High-altitude periodic breathing and treatment-emergent central apnea appearing after CPAP initiation

Obstructive Sleep Apnea

• Anatomic narrowing of the upper airway during sleep due to collapse of pharyngeal structures (soft palate, tongue, lateral pharyngeal walls); occurs despite intact central respiratory drive
• Loss of neuromuscular tone in the pharyngeal dilator muscles (genioglossus, tensor veli palatini) during sleep, particularly REM sleep, exacerbated by supine positioning
• Increased collapsibility of the airway in predisposed individuals secondary to anatomic factors (adenotonsillar hypertrophy, retrognathia, deviated septum, high Mallampati score) or metabolic factors (obesity causing pharyngeal fat deposition)
• Resulting hypoxemia, hypercapnia, and arousals trigger sympathetic activation, causing micro-awakenings and fragmented sleep architecture; repetitive negative intrathoracic pressure generation further increases afterload

Central Sleep Apnea

• Failure of central respiratory drive from the brainstem respiratory centers during sleep, resulting in cessation of both airflow and respiratory effort
• Common mechanisms include loss of CO₂ responsiveness (particularly during non-REM sleep), instability in the ventilatory control system (periodic breathing), or narcotic-induced respiratory depression
• May involve Cheyne-Stokes respiration: a crescendo-decrescendo breathing pattern with central apneas alternating with hyperpnea, classically seen in heart failure and neurologic conditions

• Loud, habitual snoring with witnessed apneic episodes and gasping/choking awakenings — family members often report the patient "stops breathing" during sleep; hallmark of OSA
• Excessive daytime somnolence (EDS) and unrefreshing sleep despite apparently adequate sleep duration; patients report falling asleep uncontrollably during the day, including during driving ("microsleeps")
• Morning headaches (especially frontal and occipital) due to nocturnal hypercapnia and hypoxemia, often worse with central apnea; may mimic migraine
• Nocturia and erectile dysfunction — both manifestations of increased sympathetic tone and hormonal changes from sleep fragmentation
• Behavioral/cognitive dysfunction including irritability, impaired concentration, memory problems, and personality changes from sleep deprivation
• Hypertension (both resistant and newly diagnosed), particularly diastolic predominant, from sustained sympathetic activation
• Obese body habitus with large neck circumference (>17 inches in men, >16 inches in women); however, OSA also occurs in non-obese patients
• Clinical pearls: Presentation varies widely — some patients present with incidental diagnosis on sleep study without classic symptoms; severe OSA may present with acute decompensated heart failure or new-onset atrial fibrillation before sleep apnea is recognized; central apnea may be subtle, with minimal snoring but prominent EDS or nocturnal desaturation

• Overnight polysomnography (PSG) — gold standard diagnostic test performed in sleep laboratory; measures EEG, EOG, chin electromyography, airflow (nasal pressure), respiratory effort (inductance plethysmography), oxygen saturation, heart rate, and leg movement
• Apnea-Hypopnea Index (AHI) — primary diagnostic metric defined as number of apneas plus hypopneas per hour of sleep; severity grading: mild (AHI 5-14), moderate (15-29), severe (≥30); diagnosis requires AHI ≥5 with compatible symptoms or AHI ≥15 regardless of symptoms
• Home sleep apnea testing (HSAT) — increasingly used for OSA screening in appropriate populations; measures airflow, respiratory effort, and oxygen saturation but lacks EEG data; useful for low-probability patients with typical symptoms but less sensitive than PSG and cannot diagnose central apnea
• Oxygen desaturation index (ODI) — number of oxygen saturation drops ≥3-4% per hour; correlates with severity and cardiovascular risk
• Clinical scoring systems (STOP-BANG, Berlin Questionnaire, EPWORTH Sleepiness Scale) — useful for pretest probability assessment and identifying patients who need sleep testing; high sensitivity but modest specificity
• Diagnostic pearls: Diagnosis requires correlation of objective sleep study findings with clinical symptoms; AHI alone does not determine need for treatment (symptomatic mild OSA may warrant treatment); differentiation between OSA and CSA requires PSG analysis of respiratory effort patterns; atypical presentations (minimal daytime sleepiness but severe desaturation, or prominent behavioral dysfunction) still warrant treatment if AHI is significant

First-Line Treatment

• Positive airway pressure (PAP) therapy — primary treatment for moderate-to-severe OSA; works by providing pneumatic splint preventing airway collapse
• Continuous PAP (CPAP): single fixed pressure; empirically determined or titrated during sleep study; typical pressures 8-15 cm H₂O
• Bilevel PAP (BiPAP): separate inhalation and exhalation pressures, improving comfort and compliance; preferred when patients cannot tolerate CPAP
• Autotitrating PAP (APAP): automatically adjusts pressure based on airway resistance; useful for pressure variation across nights
• Compliance monitoring essential; effective therapy requires ≥4 hours use on ≥5 nights per week
• Lifestyle modifications: weight loss (10% reduction often improves AHI by 25-30%), positional therapy (avoiding supine sleep), sleep hygiene optimization, alcohol cessation, smoking cessation, nasal decongestants if rhinitis present

Second-Line and Alternative Treatments

• Oral appliances (mandibular advancement devices) — advance lower jaw to enlarge airway; effective for mild-to-moderate OSA and in patients intolerant of PAP; typically reduces AHI by 40-50%; requires dental assessment and titration
• Upper airway surgery: indicated when anatomic obstruction identified AND patient fails or cannot tolerate PAP/oral appliance
• Uvulopalatopharyngoplasty (UPPP): removes redundant soft palate and uvula; success rate 40-50% for symptom improvement
• Genioglossus advancement: surgical advancement of tongue insertion; better results than UPPP in selected patients
• Maxillomandibular advancement: most effective surgical option (success rate 70-80%) but extensive surgery; reserved for motivated patients with severe OSA
• Hypoglossal nerve stimulation — FDA-approved implantable device stimulating genioglossus muscle during sleep; effective alternative for patients unable to use PAP; AHI reduction 50% on average; requires intact respiratory drive (excludes central apnea)
• Nasal steroids and antihistamines — adjunctive therapy if allergic rhinitis/nasal obstruction present

Central Sleep Apnea — Specific Treatment

• Treat underlying cause: optimize heart failure management (ACE inhibitors, beta-blockers), manage pain to reduce narcotic dependence, correct neurologic disease
• Adaptive servo-ventilation (ASV) — preferred PAP mode; intelligently adjusts pressure breath-by-breath to maintain consistent ventilation; particularly effective in CSA and Cheyne-Stokes respiration
• Supplemental oxygen and/or CO₂ inhalation — may suppress central apneas by stabilizing ventilatory drive; less effective than ASV
• Pharmacotherapy: acetazolamide (carbonic anhydrase inhibitor) useful for CSA/Cheyne-Stokes (improves CO

Cardiovascular (mechanism: cyclical hypoxemia, arousals, sympathetic surge, negative intrathoracic pressure)

• Resistant hypertension: nondipping or reversed nocturnal blood pressure pattern; the ACC/AHA 2017 hypertension guideline lists OSA among the leading causes of secondary and resistant hypertension — screen before escalating drugs
• Atrial fibrillation: atrial stretch from exaggerated negative intrathoracic pressure plus vagal-sympathetic swings; signaled by high recurrence after cardioversion or ablation in an untreated patient
• Nocturnal bradyarrhythmias and pauses: diving-reflex vagal surge during apnea; often resolve with PAP rather than a pacemaker
• Pulmonary hypertension and cor pulmonale: hypoxic pulmonary vasoconstriction; look for loud P2, elevated JVP, peripheral edema, and RV strain on ECG
• Sudden cardiac death and MI clustering in the midnight-to-early-morning hours — an emergency presentation
• Stroke, independent of hypertension

Metabolic and hematologic

• Insulin resistance and type 2 diabetes; secondary erythrocytosis from hypoxia-driven EPO (distinguish from polycythemia vera: EPO is high here, and JAK2 is negative)

Respiratory emergencies

• Acute-on-chronic hypercapnic respiratory failure in obesity hypoventilation syndrome — somnolence, elevated serum bicarbonate, and an ABG confirming awake hypercapnia; the ATS OHS guideline warns that unmonitored supplemental oxygen without ventilatory support can worsen hypercapnia. Treat with noninvasive ventilation.
• Perioperative and post-sedation respiratory arrest: opioids and benzodiazepines abolish arousal; the American Society of Anesthesiologists recommends heightened monitoring, and difficult mask ventilation/intubation should be anticipated

Treatment complications

• PAP: nasal dryness, epistaxis, aerophagia, conjunctivitis from mask leak, skin breakdown, claustrophobia; rare barotrauma; treatment-emergent central apnea
• Adaptive servo-ventilation: increased cardiovascular mortality in symptomatic HFrEF with predominantly central apnea (SERVE-HF), so AASM advises against ASV when LVEF is significantly reduced
• Oral appliances: TMJ pain, occlusal change. UPPP: velopharyngeal insufficiency, nasopharyngeal stenosis, and postoperative airway edema.

• Obese, snoring, hypertensive, sleepy man → next best step is polysomnography, not a drug. Questionnaires (STOP-BANG, Epworth) only set pretest probability; a high score alone never establishes the diagnosis. Note that the USPSTF issued an I statement — insufficient evidence — on screening asymptomatic adults, so screening is symptom-driven.
• OSA vs. CSA hinges on respiratory effort, not airflow. Both show absent airflow; OSA shows paradoxical thoracoabdominal effort, CSA shows no effort at all. This is the single distinction most often tested.
• "Pickwickian" means obesity hypoventilation syndrome, not OSA. The defining feature is awake hypercapnia with a compensatory elevated serum bicarbonate; an unexplained high HCO₃⁻ in an obese patient is the planted clue. Confirm with ABG.
• The one association examiners love: OSA and resistant hypertension/atrial fibrillation. Nondipping nocturnal BP, AF recurring after ablation, or morning headaches in a snorer should prompt sleep testing rather than a fourth antihypertensive.
• Erythrocytosis with a high EPO points to chronic hypoxemia (OSA), not polycythemia vera — PV has suppressed EPO and a JAK2 V617F mutation.
• In children, think tonsils, not weight, and think hyperactivity, not sleepiness. Pediatric OSA classically presents as inattention and behavioral problems mimicking ADHD; the AAP supports adenotonsillectomy first-line.
• Common distractors to avoid: modafinil treats residual sleepiness on adequate PAP — it is never the initial therapy; home sleep apnea testing cannot diagnose central apnea or exclude OSA when negative; hypoglossal nerve stimulation requires intact central respiratory drive; weight loss is adjunctive and does not replace PAP in moderate-to-severe disease.
• Perioperatively, opioids and benzodiazepines are the danger. Undiagnosed OSA plus sedation is a classic postoperative hypoxemic-arrest vignette.