What is Adaptive Servo Ventilation (ASV)?

What is Adaptive Servo Ventilation (ASV)?

Adaptive servo-ventilation (ASV) is a form of bilevel positive airway pressure (BPAP) therapy that provides dynamic, breath-by-breath adjustment of inspiratory pressure support and an auto-backup respiratory rate, primarily used to treat central sleep apnea (CSA) and complex sleep-disordered breathing. 1

Mechanism of Action

ASV differs fundamentally from standard CPAP or BPAP by providing:

• Expiratory positive airway pressure (EPAP) that can be adjusted to control obstructive events, similar to CPAP 1
• Dynamic inspiratory pressure support (IPS) that adjusts breath-by-breath based on the patient's ventilatory pattern 1
• Auto-backup respiratory rate to normalize breathing rate relative to a predetermined target 1

The device uses a three-minute moving average to monitor and determine an appropriate target minute ventilation, typically set to 90% of the patient's most recent minute ventilation. 1 This target threshold prevents both under-ventilation and over-ventilation by dynamically increasing IPS during hypopneas or decreasing it during hyperpneas. 1

Technical Operation

ASV functions as a hybrid system that combines:

• A baseline of CPAP (e.g., 8 cmH₂O) 1
• Periodic ventilatory support (e.g., 3-82 cmH₂O) provided during central apneas 1
• The cumulative positive airway pressure during sleep typically ranges from 8 to 16 cmH₂O 1

The aim is to maintain approximately 80% of the prevailing minute ventilation, with the theoretical benefit of reducing minute ventilation through fewer arousals and greater amounts of stage N3 and REM sleep. 1

Clinical Efficacy

ASV has demonstrated superior efficacy compared to other positive airway pressure modalities:

• Versus NPPV: ASV reduces AHI more effectively (0.8 ± 2.4/hr) compared to noninvasive positive pressure ventilation (6.2 ± 7.6/hr) in patients with CSA, mixed apneas, and complex sleep apnea (p < 0.01) 2
• Versus CPAP/Oxygen: One-night studies show ASV reduces thermistor AHI to 6.3 ± 0.9/hr compared to 28.2 ± 3.4/hr with oxygen and 26.8 ± 4.6/h with CPAP (p < 0.001) 3
• ASV produces large increases in slow-wave and REM sleep that are not seen with CPAP or oxygen 3

Critical Safety Contraindication

ASV is absolutely contraindicated in patients with heart failure and ejection fraction ≤ 45% with moderate or severe CSA due to demonstrated increased all-cause and cardiovascular mortality. 4, 5

This contraindication stems from the SERVE-HF trial, which enrolled 1,325 patients with heart failure with reduced ejection fraction (HFrEF) on optimal therapy. 1 The trial failed to show benefit in the primary composite outcome and demonstrated increased all-cause and cardiovascular mortality with ASV, particularly sudden death. 1 This led to a Field Safety Notice in 2015 from the device manufacturer. 1

Appropriate Clinical Applications

ASV may be considered in the following scenarios:

• Treatment-emergent (complex) sleep apnea after CPAP failure, which represents the most common indication in respirology settings (80% of cases) 6
• CSA in heart failure patients with ejection fraction > 45%, with close monitoring and follow-up 4, 5
• Idiopathic CSA and CSA associated with neurological disorders, where long-term compliance averages 5.2-5.9 hours per night with significant AHI reduction (from 47.4 ± 19.8 to 6.9 ± 9.3/hr, p<0.001) 7

Treatment Algorithm

The American Academy of Sleep Medicine recommends the following stepwise approach:

1. Start with standard CPAP as first-line therapy for complex sleep apnea 5
2. Progress to BPAP with backup rate (BPAP-ST) if CPAP fails, before considering ASV 5
3. Obtain ejection fraction before considering ASV, as this is the critical safety determinant 5
4. Consider ASV only if BPAP proves inadequate (AHI remains >10-15/hr) AND ejection fraction is >45% 5

Available Devices

Two manufacturers currently offer ASV devices in North America: ResMed (AirCurve 10 ASV, S9 VPAP Adapt series) and Philips Respironics. 1 Device settings differ between manufacturers, with variations in end-expiratory pressures and minimal pressure support. 1

Common Pitfalls to Avoid

• Never use ASV without knowing the ejection fraction in patients with heart failure 5
• Do not use oxygen as primary therapy for central sleep apnea; it is only appropriate when PAP therapies fail or are contraindicated 5
• Recognize that ASV usage should be monitored with diligence even in appropriate indications, as clinical usage patterns show 9-16% of patients may have been treated despite contraindications 6