Breathing pattern and additional work of breathing in spontaneously breathing patients with different ventilatory demands during inspiratory pressure support and automatic tube compensation

Abstract

Objective: We designed a new ventilatory mode to support spontaneously breathing, intubated patients and to improve weaning from mechanical ventilation. This mode, named Automatic Tube Compensation (ATC), compensates for the flow-dependent pressure drop across the endotracheal tube (ETT) and controls tracheal pressure to a constant value. In this study, we compared ATC with conventional patient-triggered inspiratory pressure support (IPS). Design: A prospective, interventional study. Setting: A medical intensive care unit (ICU) and an ICU for heart and thoracic surgery in a university hospital. Patients: We investigated two groups of intubated, spontaneously breathing patients: ten postoperative patients without lung injury, who had a normal minute ventilation (V(E)) of 7.6 ± 1.7 l/min, and six critically ill patients who showed increased ventilatory demand (V(E) = 16.8 ± 3.0 l/min). Interventions: We measured the breathing pattern [V(E), tidal volume (V(T)), and respiratory rate (RR)] and additional work of breathing (WOB(add)) due to ETT resistance and demand valve resistance. Measurements were performed under IPS of 5, 10, and 15 mbar and under ATC. Results: The response of V(T), RR, and WOB(add) to different ventilatory modes was different in both patient groups, whereas V(E) remained unchanged. In postoperative patients, ATC, IPS of 10 mbar, and IPS of 15 mbar were sufficient to compen sate for WOB(add). In contrast, WOB(add) under IPS was greatly in creased in patients with increased ventilatory demand, and only ATC was able to compensate for WOB(add). Conclusions: The breathing pattern response to IPS and ATC is different in patients with differing ventilatory demand. ATC, in contrast to IPS, is a suitable mode to compensate for WOB(add) in patients with increased ventilatory demand. When WOB(add) was avoided using ATC, the patients did not need additional pressure support.