Abstract
BackgroundDuring spontaneous breathing trial, low-pressure support is thought to compensate for endotracheal tube resistance, but it actually should provide overassistance. Automatic tube compensation is an option available in the ventilator to compensate for flow-resistance of endotracheal tube. Its effects on patient effort have been poorly investigated. We aimed to compare the effects of low-pressure support and automatic tube compensation during spontaneous breathing trial on breathing power and lung ventilation distribution.ResultsWe performed a randomized crossover study in 20 patients ready to wean. Each patient received both methods for 30 min separated by baseline ventilation: pressure support 0 cmH2O and automatic tube compensation 100% in one period and pressure support 7 cmH2O without automatic tube compensation in the other period, a 4 cmH2O positive end-expiratory pressure being applied in each. Same ventilator brand (Evita XL, Draeger, Germany) was used. Breathing power was assessed from Campbell diagram with esophageal pressure, airway pressure, flow and volume recorded by a data logger. Lung ventilation distribution was assessed by using electrical impedance tomography (Pulmovista, Draeger, Germany). During the last 2 min of low-pressure support and automatic compensation period breathing power and lung ventilation distribution were measured on each breath. Breathing power generated by the patient’s respiratory muscles was 7.2 (4.4–9.6) and 9.7 (5.7–21.9) J/min in low-pressure support and automatic tube compensation periods, respectively (P = 0.011). Lung ventilation distribution was not different between the two methods.ConclusionsWe found that ATC was associated with higher breathing power than low PS during SBT without altering the distribution of lung ventilation.
Highlights
During spontaneous breathing trial, low-pressure support is thought to compensate for endotracheal tube resistance, but it should provide overassistance
Weaning intensive care unit (ICU) patients from invasive mechanical ventilation relies on a daily screening for eligibility, and if present, a spontaneous breathing trial (SBT) testing patient capacity to breathe without respiratory assistance [1]
We reasoned that the only way to provide a support that would just compensate for RET is the automatic tube compensation (ATC) option available in many ICU ventilators [11]
Summary
Low-pressure support is thought to compensate for endotracheal tube resistance, but it should provide overassistance. We aimed to compare the effects of low-pressure support and automatic tube compensation during spontaneous breathing trial on breathing power and lung ventilation distribution. Low PS level was thought as a mean to compensate for the endotracheal tube airflow resistance (RET) [6]. The fact that low PS reduced work of Guérin et al Ann. Intensive Care (2019) 9:137 breathing (WOB) as compared to T-piece [7] questioned this concept. We reasoned that the only way to provide a support that would just compensate for RET is the automatic tube compensation (ATC) option available in many ICU ventilators [11]. ATC works as a closed-loop during insufflation (and/or exsufflation) to compensate for the non-linear pressure– flow relationship across endotracheal tube or tracheostomy canula [12]
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