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 cmH2O 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 cmH2O 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 cmH2O 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 cmH2O s−1 min−1, 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 cmH2O, whereas the workload during automatic tube compensation corresponded closely to the values during trials of breathing through a T-piece.(Accepted December 2001)
Key Words: RESPIRATION, ARTIFICIAL, ventilator weaning; RESPIRATION, respiratory mechanics, pulmonary ventilation; RESPIRATORY DISORDERS, respiratory insufficiency.
c1 Correspondence to: Ralf Kuhlen, Klinik für Anaesthesiologie, Medizinische Einrichtungen der RWTH Aachen, Pauwelsstrasse 30, D–52074 Aachen, Germany. E-mail: Ralf.Kuhlen@post.rwth-aachen.de; Tel: +49 241 8088179; Fax: +49 241 8888406