Quantifying unintended exposure to high tidal volumes from breath stacking dyssynchrony in ARDS: the BREATHE criteria

Abstract

Purpose: Breath stacking dyssynchrony generates higher tidal volumes than intended, potentially increasing lung injury risk in acute respiratory distress syndrome (ARDS). Lack of validated criteria to quantify breath stacking dyssynchrony contributes to its under-recognition. This study evaluates performance of novel, objective criteria for quantifying breath stacking dyssynchrony (BREATHE criteria) compared to existing definitions and tests if neuromuscular blockade eliminates high-volume breath stacking dyssynchrony in ARDS.

Methods: Airway flow and pressure were recorded continuously for up to 72 h in 33 patients with ARDS receiving volume-preset assist-control ventilation. The flow-time waveform was integrated to calculate tidal volume breath-by-breath. The BREATHE criteria considered five domains in evaluating for breath stacking dyssynchrony: ventilator cycling, interval expiratory volume, cumulative inspiratory volume, expiratory time, and inspiratory time.

Results: The observed tidal volume of BREATHE stacked breaths was 11.3 (9.7-13.3) mL/kg predicted body weight, significantly higher than the preset volume [6.3 (6.0-6.8) mL/kg; p < 0.001]. BREATHE identified more high-volume breaths (≥2 mL/kg above intended volume) than the other existing objective criteria for breath stacking [27 (7-59) vs 19 (5-46) breaths/h; p < 0.001]. Agreement between BREATHE and visual waveform inspection was high (raw agreement 96.4-98.1 %; phi 0.80-0.92). Breath stacking dyssynchrony was near-completely eliminated during neuromuscular blockade [0 (0-1) breaths/h; p < 0.001].

Conclusions: The BREATHE criteria provide an objective definition of breath stacking dyssynchrony emphasizing occult exposure to high tidal volumes. BREATHE identified high-volume breaths missed by other methods for quantifying this dyssynchrony. Neuromuscular blockade prevented breath stacking dyssynchrony, assuring provision of the intended lung-protective strategy.

Keywords: Acute lung injury; Acute respiratory distress syndrome; Mechanical ventilation; Patient–ventilator dyssynchrony; Respiratory mechanics; Ventilator-induced lung injury.

Fig. 1

Tidal volume delivered during breath stacking dyssynchrony. A: Integration of the flow-time waveform during consecutive inspiratory cycles with incomplete interval exhalation (shaded area under the flow-time curve) was used to calculate the true tidal volume delivered. B: Comparison of preset tidal volume with actual volume delivered during breath stacking dyssynchrony according to the Thille and BREATHE Criteria. Box plots illustrate median and interquartile range (boxes), mean (diamond), and maximum and minimum values (whiskers). Abbreviations: BSD, breath stacking dyssynchrony; PBW, predicted body weight; V_T, tidal volume.

Fig. 2

Frequency of BREATHE breath stacking dyssynchrony in early ARDS. A: Cumulative relative frequency distributions for BREATHE BSD frequency absent neuromuscular blockade among all study patients. B and C: Evolution of BREATHE breath stacking dyssynchrony frequency (black line) and minute-volume (gray bars) over time from representative study participants. B: Breath stacking occurred regularly during the first 31 hours and was eliminated upon initiation of neuromuscular blockade at hour 32. Ventilator mode was volume-targeted pressure control throughout the recording. C: Breath stacking was rare during the first 24 hours of enrollment before occurring with increasing frequency, up to 418 breaths/hour at hour 56. Ventilator mode was volume-targeted pressure control unless otherwise noted. PSV mode excluded from BREATHE analysis. Abbreviations: BSD, breath stacking dyssynchrony; NMB, neuromuscular blockade; PSV, pressure support ventilation mode.