AVAPS vs BPAP S/T in Hypercapnic Respiratory Failure: What This RCT Teaches Us

 

Written By: Richa Gupta, MD; Edited by: Brian Smith, MD, MA, MMSc-Med

AVAPS vs BPAP S/T in Hypercapnic Respiratory Failure: What This RCT Teaches Us

When patients arrive at the emergency department struggling with hypercapnic respiratory failure, quick action and the right ventilation strategy can make the difference between recovery and decline. A recent randomized controlled trial (PMID: 34462252) explored whether Average Volume-Assured Pressure Support (AVAPS) is as safe and effective as the well-established Bilevel Positive Airway Pressure Spontaneous/Timed (BPAP S/T) mode.

This post breaks down the study’s methods, findings, and what they mean for clinical practice.

Why Compare AVAPS and BPAP S/T?

BPAP S/T has been a mainstay in treating acute hypercapnic respiratory failure, especially in COPD. AVAPS is newer—offering automatic adjustments to keep a consistent tidal volume while still delivering pressure support. In theory, this could improve gas exchange more quickly and reduce the need for intubation, but does the evidence back it?

How Was the Study Conducted?

Study Design

  • Type: Single-center, single-blind randomized controlled trial (ED setting)

  • Period: October 2016 – June 2017

  • Location: Emergency Department, tertiary hospital, Turkey

Who Was Studied?

From 140 ED patients presenting with hypercapnic respiratory failure:

  • Included: 80 patients meeting eligibility (mainly elderly, COPD exacerbations)

  • Excluded: Those needing urgent intubation, with airway instability, pneumothorax, cardiac arrest, trauma, severe arrhythmia, recent MI, or tracheostomy.

Participants were randomized to AVAPS (47 patients) or BPAP S/T (33 patients) before ventilation was initiated.

What Did They Measure?

  • Primary: Arterial blood gas (ABG) changes — PaCO₂ and pH

  • Secondary: Intubation rate, Glasgow Coma Scale scores, response to NIV, need for alternative therapy, disposition (home, ICU, ward, death)

ABGs were tracked at baseline, 30 minutes, and 60 minutes — though exact timing was at the clinicians’ discretion.

What Did They Find?

  • Both groups improved in PaCO₂, pH, and mental status.

  • AVAPS led to a faster drop in PaCO₂ and rise in pH within the first hour (statistically significant for this early timepoint).

  • No significant differences between groups in overall blood gas changes across the treatment period.

  • Intubation rates were lower in AVAPS (6.4% vs 15.2%), but not statistically significant.

  • Length of stay, ICU admissions, and mortality were similar.

Study Strengths

  • Randomization reduced selection bias.

  • Baseline characteristics matched between groups.

  • Intention-to-treat analysis preserved.

Study Limitations

  • Sample size smaller than planned (goal: 102; actual: 80) → reduced statistical power.

  • Single-center → limited generalizability.

  • Blood gas timing not standardized → potential measurement variability.

  • Missing data for 13 transferred patients.

What Does This Mean for Practic

In this ED population:

  • AVAPS is just as safe and effective as BPAP S/T for managing acute hypercapnic respiratory failure.

  • It may improve blood gas parameters a little faster, at least initially, though this didn’t translate into lower intubation rates or shorter stays.

  • Clinicians could consider AVAPS as an alternative to BPAP S/T, especially for patients who might benefit from more consistent tidal volumes.

 
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