BREATHING PATTERN AND ADDITIONAL WORK OF BREATHING IN SPONTANEOUSLY BREATHING PATIENTS WITH DIFFERENT VENTILATORY DEMANDS DURING INSPIRATORY PRESSURE SUPPORT AND AUTOMATIC TUBE COMPENSATION

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), compe nsates for the flow-dependent pressure drop across the endotracheal tu be (ETT) and controls tracheal pressure to a constant value. In this s tudy, we compared ATC with conventional patient-triggered inspiratory pressure support (IFS). Design: A prospective, interventional study. S etting: A medical intensive care unit (ICU) and an ICU for heart and t horacic surgery in a university hospital. Patients: We investigated tw o groups of intubated, spontaneously breathing patients: ten postopera tive 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 showe d increased ventilatory demand (V-E = 16.8 +/- 3.0 l/min). Interventio ns: We measured the breathing pattern [V-E, tidal volume (V-T), and re spiratory rate (RR)] and additional work of breathing (WOBadd) due to ETT resistance and demand valve resistance. Measurements were performe d under IFS of 5, 10, and 15 mbar and under ATC. Results: The response of V-T, RR, and WOBadd to different ventilatory modes was different i n both patient groups, whereas V-E remained unchanged. In postoperativ e patients, ATC, IFS of 10 mbar, and IFS of 15 mbar were sufficient to compensate for WOBadd. In contrast, WOBadd under IFS was greatly incr eased in patients with increased ventilatory demand, and only ATC was able to compensate for WOBadd. Conclusions: The breathing pattern resp onse to IFS and ATC is different in patients with differing ventilator y demand. ATC, in contrast to IPS, is a suitable mode to compensate fo r WOBadd in patients with increased ventilatory demand. When WOBadd wa s avoided using ATC, the patients did not need additional pressure sup port.