Does a triggered percentage of 95% on a BiPAP (Bilevel Positive Airway Pressure) ST machine correlate with a low central Apnea-Hypopnea Index (AHI)?

Relationship Between Triggered Percentage on BiPAP ST and Central AHI

A high triggered percentage of 95% on a BiPAP ST machine strongly correlates with a low central apnea-hypopnea index (AHI), indicating effective spontaneous breathing with minimal need for machine-triggered breaths. 1

Understanding Triggered Percentage on BiPAP ST

BiPAP ST (Spontaneous/Timed) mode provides two key mechanisms for breath delivery:

• Patient-triggered breaths: When the patient initiates a breath independently
• Machine-triggered breaths: When the backup rate delivers a breath because the patient failed to trigger one within the set time interval

The triggered percentage represents the proportion of breaths that are patient-initiated rather than machine-delivered. A high triggered percentage (95%) indicates:

• The patient is initiating most breaths spontaneously
• The backup rate is rarely needed to initiate breaths
• The patient's respiratory drive is functioning effectively

Correlation with Central AHI

A high triggered percentage correlates with low central AHI for several reasons:

1. Respiratory drive indication: Central sleep apnea events occur when the brain fails to send proper signals to the breathing muscles. A high triggered percentage (95%) demonstrates intact respiratory drive, which is inconsistent with significant central apnea 1.

2. Backup rate function: The backup rate on BiPAP ST is specifically designed to prevent central apneas by triggering breaths when the patient fails to do so. When the triggered percentage is high (95%), it means the backup rate is rarely needed, suggesting minimal central events 2.

3. Ventilation stability: According to AASM guidelines, effective BiPAP ST therapy stabilizes breathing patterns in patients with central sleep apnea, reducing central events and maintaining spontaneous breathing 1.

Clinical Implications

When evaluating a patient with a 95% triggered percentage on BiPAP ST:

• Low central AHI likely: This high percentage strongly suggests minimal central events are occurring
• Appropriate backup rate setting: The backup rate is likely appropriately set - high enough to prevent central events but low enough to allow spontaneous breathing 1
• Effective therapy: The BiPAP ST therapy is effectively supporting the patient's breathing without over-controlling it

Potential Pitfalls and Considerations

Despite the strong correlation, several factors should be considered:

• Obstructive events: A high triggered percentage doesn't necessarily indicate absence of obstructive events, which require different management strategies 2

• Mask leaks: Excessive mask leaks can falsely increase the triggered percentage by causing the machine to misinterpret leak-related pressure changes as patient effort 1

• Backup rate setting: If the backup rate is set too low relative to the patient's needs, the triggered percentage may be artificially high while still allowing central events to occur 1

• Mixed apneas: In patients with mixed apneas (central followed by obstructive components), a high triggered percentage may not fully reflect the complexity of their sleep-disordered breathing 2

Monitoring Recommendations

For patients showing a high triggered percentage (95%) on BiPAP ST:

• Review downloaded data for residual AHI, particularly central events
• Ensure the backup rate is set appropriately based on the patient's spontaneous respiratory rate
• Consider a follow-up sleep study if symptoms persist despite favorable machine data
• Evaluate for mask leaks that might affect data accuracy

In conclusion, a 95% triggered percentage on BiPAP ST strongly correlates with a low central AHI, indicating effective spontaneous breathing with minimal central respiratory events.