Breathing pattern and workload during automatic tube compensation, pressure support and T-piece trials in weaning patients

Background and objective: Automatic tube compensation has been designed as a new ventilatory mode to compensate for the non-linear resistance of the endotracheal tube. The study investigated the effects of automatic tube compensation compared with breathing through a T-piece or pressure support during a trial of spontaneous breathing used for weaning patients from mechanical ventilation of the lungs. Methods: Twelve patients were studied who were ready for weaning after prolonged mechanical ventilation (10.2 +/- 8.4 days) due to acute respiratory failure. Patients with chronic obstructive pulmonary disease were excluded. Thirty minutes of automatic tube compensation were compared with 30 min periods of 7 cmH(2)O pressure support and T-piece breathing. Breathing patterns and workload indices were measured at the end of each study period. Results: During T-piece breathing, the peak inspiratory flow rate (0.65 +/- 0.20 L s(-1)) and minute ventilation (8.9 +/- 2.7 L min(-1)) were lower than during either pressure support (peak inspiratory flow rate 0.81 +/- 0.25 L s(-1); minute ventilation 10.2 +/- 2.3 L min(-1), respectively) or automatic tube compensation (peak inspiratory flow rate 0.75 +/- 0.26 L s(-1); minute ventilation 10.8 +/- 2.7 L min(-1)). The pressure-time product as well as patients' work of breathing were comparable during automatic tube compensation (pressure-time product 214.5 +/- 104.6 cmH(2)O s(-1) min(-1), patient work of breathing 1.1 +/- 0.4 J L-1), and T-piece breathing (pressure-time product 208.3 +/- 121.6 cmH(2)O s(-1) min(-1), patient work of breathing 1.1 +/- 0.4 J L-1), whereas pressure support resulted in a significant decrease in workload indices (pressure-time product 121.2 +/- 64.1 cmH(2)O s(-1) min', patient work of breathing 0.7 +/- 0.4 J L(-)1). Conclusions: In weaning from mechanical lung ventilation, patients' work of breathing during spontaneous breathing trials is clearly reduced by the application of pressure support 7 cmH(2)O, whereas the workload during automatic tube compensation corresponded closely to the values during trials of breathing through a T-plece.