What is complex sleep apnea?

Definition of Complex Sleep Apnea Syndrome

Complex sleep apnea syndrome (CompSAS) is a distinct form of sleep-disordered breathing characterized by the emergence or persistence of central apneas during initial treatment of obstructive sleep apnea (OSA) with continuous positive airway pressure (CPAP) therapy. 1

Key Characteristics

Complex sleep apnea has features of both obstructive and central sleep apnea:

• Initially presents with clinical features similar to obstructive sleep apnea
• When CPAP is applied to treat the obstructive component, central apneas emerge or persist
• Shows instability of both upper airway tone and ventilatory control 2

Diagnostic Criteria

The diagnosis of CompSAS is established when:

• Patient initially presents with predominantly obstructive sleep apnea
• Upon application of CPAP therapy, central apneas emerge or persist
• Central apneas become the predominant form of sleep-disordered breathing during CPAP titration 1, 3

Pathophysiology

The exact mechanisms of CompSAS are not fully understood, but several theories exist:

• High loop gain (increased sensitivity of the respiratory control system)
• Unstable chemosensitive ventilatory control
• Respiratory center dysfunction that becomes unmasked when upper airway obstruction is relieved 1, 4

Clinical Significance

CompSAS is clinically significant because:

• It may lead to poor initial experience with CPAP therapy
• Results in continued sleep fragmentation despite treatment of obstructive events
• Can cause persistent symptoms including excessive daytime sleepiness
• May lead to nonadherence with continued CPAP therapy 1
• Associated with increased cardiovascular morbidity and mortality similar to other forms of sleep apnea 3

Natural History

In many cases, CompSAS is transient:

• Central apneas that appear during initial CPAP titration may disappear after continued CPAP use for 4-8 weeks or longer 1
• Some patients experience adaptation to CPAP therapy over time 2
• However, in other patients, central apneas persist and require specialized treatment approaches

Treatment Approaches

When CompSAS persists, treatment options include:

1. Adaptive servo-ventilation (ASV): Most effective treatment, dramatically improving AHI to a median of 5 events per hour compared to 31 events per hour with CPAP 5

2. Bilevel positive airway pressure (BPAP) with backup rate: Can improve AHI to a median of 15 events per hour 5

3. Other approaches (with limited evidence):

   • Supplemental oxygen
   • Addition of dead space
   • Carbon dioxide manipulation
   • Carbonic anhydrase inhibitors 2, 4

Clinical Implications

CompSAS represents an important clinical entity that:

• May be underdiagnosed in clinical practice
• Requires recognition during CPAP titration
• Often necessitates advanced positive airway pressure modalities beyond standard CPAP
• May benefit from multi-modality therapy for optimal outcomes 4

Understanding CompSAS is essential for proper management of patients with sleep-disordered breathing who do not respond adequately to conventional CPAP therapy.