Effect of the pressure ramp on the breathing pattern and respiratory drive in pressure support ventilation

Introduction

Assisted ventilation with pressure support (PS) is one of the most commonly used ventilation modes; however, there is no agreement about the most adequate method to set an optimal level of PS. The aim of our study is to analyze the effect of different pressurization ramps on the work of breathing. This was estimated by the airway occlusion pressure in the first 100 ms of inspiration (P0.1) and by the breathing pattern: the respiratory rate (RR) and tidal volume (TV).

Methods

We carried out an interventional prospective study in a group of 15 patients mechanically ventilated after acute respiratory failure (ARF), with different initial causes at the beginning of assisted ventilation. The initial PS level was equal to the plateau pressure, and this was decreased in order to keep the patient comfortable and the P0.1 lower than 3 cmH₂O. The PEEP level used in controlled ventilation was maintained and subsequently we changed the inspiratory rise time in three ranks: 0.0, 0.2 and 0.4 seconds. After keeping the patient respiratorily and haemodynamically stable we measure the RR, TV and P0.1. We compare data using statistical analysis with nonparametric tests. Results are presented as the mean ± standard deviation at 0.0, 0.2 and 0.4 seconds.

Results

The cause of ARF was acute respiratory distress syndrome (ARDS) in nine patients and acute on chronic respiratory failure in six patients. Mean age: 61.2 ± 14.02 years. The mean level of PS and PEEP was 17.93 ± 7.10 and 6 ± 1.69 cmH₂O. Decreasing the inspiratory ramp was associated with the significantly highest P0.1 levels (1.25 ± 0.8, 1.47 ± 1, 1.96 ± 1.24, P = 0.01), whereas the RR and TV did not significantly change (RR: 22.66 ± 9.38, 21.73 ± 7.05, 22 ± 6.67; TV: 534.46 ± 162.59, 541.8 ± 168.5, 522.73 ± 157.09). There were no significant differences in the P0.1 levels between acute respiratory distress syndrome and acute on chronic respiratory failure.

Conclusion

The parameters frequently used to estimate the breathing pattern do not necessarily reflect the changes in the work of breathing. The availability of automatic measurements in some respirators can help to optimize the ventilatory mode used.