Cheyne-Stokes respiration

**Definition/Pattern:** Waxing-and-waning tidal volume (crescendo-decrescendo) followed by a central apnea or hypopnea, repeating in cycles (typically ~30-100 sec cycle length). Apneas are CENTRAL (no respiratory effort), unlike obstructive sleep apnea. Often worse during sleep (especially NREM), and may be improved in REM.

**Pathophysiology (unstable negative feedback loop):** 1. Chemoreceptors (central and peripheral) are hypersensitive to PaCO2 (high loop gain), and patients often have chronic mild hyperventilation with PaCO2 near the apneic threshold. 2. Hyperventilation lowers PaCO2 below the apneic threshold, causing central apnea. 3. During apnea, PaCO2 rises and PaO2 falls, eventually stimulating ventilation again. 4. Delayed sensing due to prolonged circulation time (low cardiac output) between the lungs and chemoreceptors causes overshoot, with hyperventilation, then undershoot, with apnea, so the cycle repeats. 5. Arousals and sympathetic surges perpetuate the instability.

**Key associations/causes:** - **Heart failure** (especially systolic HF with low EF; the most common association; poor prognostic marker). Also atrial fibrillation. - **Stroke**, intracranial hemorrhage, raised ICP, brain tumors, traumatic brain injury (bilateral cerebral or diencephalic dysfunction). - **High altitude** (hypoxia-driven hyperventilation with respiratory alkalosis), usually during sleep and resolves with acclimatization. - **Opioids** and other CNS depressants (can cause central apnea patterns), uremia, and end-of-life/terminal illness (can be seen in dying patients). - Chronic kidney disease may also contribute.

**Clinical significance:** Patients may have witnessed apneas, daytime sleepiness, insomnia, paroxysmal nocturnal dyspnea, and fatigue. In HF it is associated with increased mortality and arrhythmias. In neurologic patients it signals bilateral hemispheric or diencephalic dysfunction (and may precede herniation).

**Differentiation from other abnormal breathing patterns (high-yield):** - **Kussmaul:** deep, rapid, regular breathing in metabolic acidosis (DKA, uremia). - **Biot (ataxic) breathing:** irregular, unpredictable clusters of breaths with apneas of variable length, associated with medullary/pontine damage (higher brainstem lesions are more severe). - **Apneustic breathing:** prolonged inspiratory pauses from pontine lesions. - **Central neurogenic hyperventilation:** sustained rapid, deep breathing from midbrain/pons lesions. - **Cheyne-Stokes:** gradual crescendo-decrescendo with a central apnea; bilateral cerebral/diencephalic lesions or HF.

**Management:** - Treat the underlying cause (optimize HF therapy: diuretics, ACEi/ARB/ARNI, beta-blockers, etc.). - Nocturnal oxygen; CPAP may help in some HF patients. - Adaptive servo-ventilation (ASV) is generally AVOIDED in HFrEF (EF ≤45%) with predominant central sleep apnea, since the SERVE-HF trial showed increased cardiovascular mortality. - At altitude: acetazolamide (induces metabolic acidosis to drive ventilation and stabilize CO2 levels) and descent. - Phrenic nerve stimulation is an emerging option.

**Board pearl:** "Crescendo-decrescendo breathing with central apnea in a patient with heart failure or stroke" = Cheyne-Stokes. Mechanism = increased chemosensitivity plus delayed feedback from low cardiac output.