What is the workup for central sleep apnea (CSA)?

Workup for Central Sleep Apnea

Polysomnography is the standard diagnostic test for central sleep apnea (CSA) and should be performed in all patients with suspected CSA to confirm the diagnosis and determine its severity. 1

Initial Assessment

• Obtain a detailed sleep history, including symptoms such as gasping for breath during sleep, daytime sleepiness, irritability, forgetfulness, fatigue, and recurrent headaches 2
• Inquire about alcohol use and obtain a detailed medication list, particularly focusing on sedative-hypnotics and opiate analgesics, which can contribute to CSA 1
• Assess for underlying medical conditions associated with CSA, including:
  • Heart failure (most common cause of CSA) 1, 3
  • Neurological disorders (stroke) 3
  • Atrial fibrillation 3
  • Pulmonary hypertension 3
  • Renal failure 3
  • Chronic opioid use 3, 4

Diagnostic Testing

Polysomnography (PSG)

• In-laboratory polysomnography is the gold standard for diagnosing CSA 1
• PSG should include measurement of:
  • Oxygen saturation
  • Rib cage and abdominal movement (to document absence of respiratory effort during apneas)
  • Nasal and oral airflow
  • Sleep staging via electroencephalography, electrooculography, and electromyography
  • Electrocardiogram 1, 3

Diagnostic Criteria

• CSA is diagnosed when the apnea-hypopnea index (AHI) is ≥5 events/hour with central events predominating 1
• Central apneas are characterized by absence of airflow without respiratory effort 3, 4
• Assess cycle length pattern:
  • Long cycle length (45-75 seconds) suggests heart failure-associated CSA with Cheyne-Stokes respiration
  • Short cycle length (<45 seconds) suggests other etiologies such as atrial fibrillation, narcotics, or stroke 3

Additional Testing Based on Suspected Etiology

• For suspected heart failure: Echocardiography to assess ejection fraction 1
• For suspected neurological causes: Brain imaging (CT or MRI) 3
• For suspected medication-induced CSA: Medication review with temporal relationship to symptom onset 3
• Arterial blood gas analysis to assess for hypercapnia (suggests hypoventilation syndromes) 4

Differential Diagnosis

• Distinguish between different types of sleep apnea:
  • Obstructive sleep apnea (OSA): Characterized by continued respiratory effort during apneas 1
  • Central sleep apnea (CSA): Characterized by absence of respiratory effort during apneas 3
  • Complex sleep apnea: Exhibits characteristics of both OSA and CSA 2
  • Treatment-emergent CSA: Occurs in approximately 1% of patients starting CPAP therapy for OSA 3

Severity Assessment

• Mild CSA: AHI 5-14/hour with no or mild symptoms
• Moderate CSA: AHI 15-30/hour with occasional daytime sleepiness
• Severe CSA: AHI >30/hour with frequent daytime sleepiness that interferes with normal activities 2

Common Pitfalls to Avoid

• Do not rely solely on clinical tools, questionnaires, or prediction algorithms to diagnose CSA without polysomnography 1
• Do not miss evaluating for underlying medical conditions that could be causing or exacerbating CSA 3
• Recognize that patients with CSA may present with insomnia and depression rather than classic hypersomnolence 5
• Do not assume all sleep apnea is obstructive; carefully evaluate respiratory effort patterns during polysomnography 3, 4
• Patients with heart failure may require referral to sleep specialists for proper management 1

By following this systematic approach to the workup of central sleep apnea, clinicians can accurately diagnose the condition and identify underlying causes, which is essential for determining appropriate treatment strategies.