The effects of pressurization rate on breathing pattern, work of breathing, gas exchange and patient comfort in pressure support ventilation

The aim of this study was to investigate the effects of different pressurization rates during pressure support ventilation on breathing pattern, work of breathing, gas exchange and patient comfort in patients with acute lung injury. The pressurization rate modifies the initial pressure ramp by changing the initial peak flow rate: the increase in pressurization rate is associated with a decrease in the time to reach the level of pressure support ventilation by increasing the peak flow rate. Ten intubated patients (age 64 +/- 17 yrs, body mass index 24 +/- 17 Kg.m(-2), arterial oxygen tension/inspired oxygen fraction 214 +/- 59) were studied in random order varying the pressurization rate at 5 and 15 cmH(2)O of pressure support ventilation. Breathing comfort was evaluated by a visual analogue scale. Increasing the pressurization rate caused an increase of peak flow rate from 473 +/- 141 mL.s(-1) to 758 +/- 302 mL.s(-1) at pressure support ventilation 5 (p <0.05) and from 481 +/- 126 mL.s(-1) to 1,121 +/- 175 mL.s(-1) at pressure support ventilation 15 (p <0.05). At the lowest pressurization rate the tidal volume was the lowest, the respiratory rate and the work of breathing were the highest (p <0.05) compared with other pressurisation rates. Excluding the lowest pressurization rate, in all the other pressurization rates tested the breathing pattern and the work of breathing did not change. The lowest and the highest pressurization rates caused the worst patient comfort (p <0.05). The gas exchange was stable throughout the study. The presented results suggest: 1) the lowest pressurization rate caused the lowest tidal volume, highest respiratory rate and highest work of breathing; 2) at the other pressurization rates no differences in breathing pattern and work of breathing were observed; and 3) the patient's comfort was worse at the lowest and highest pressurization rates.