The influence of cycling-off criteria and pressure support slope on the respiratory and hemodynamic variables in intensive care unit patients

Introduction

Modern mechanical ventilators allow changes in the flow cycling-off criteria and the pressure slope during pressure support ventilation (PSV). Changes in the cycling-off flow criteria of PSV can modify the expiratory synchrony between the mechanical and neural inspiration termination. The influences of the slope changes on the respiratory parameters in ICU patients are still under investigation.

Objectives

To compare the effects of two different flow cycling-off criteria and the effects of two different pressure slopes (150 ms or 300 ms) of PSV on the respiratory parameters of ICU mechanically ventilated patients.

Methods

We prospectively evaluated 20 intubated and mechanically ventilated adult ICU patients recovering from acute respiratory failure who could be comfortably ventilated on pressure support mode (PSV) with pressure support of 15 cmH₂O, PEEP of 5 cmH₂O and FIO₂ of 40%. Patients were ventilated on PSV, with 25% and 40% of peak expiratory flow cycling criteria, and were submitted to 150 ms and 300 ms pressure slope delay. We evaluated the respiratory rate, expiratory tidal volume, minute ventilation, VCO₂, VTCO₂, ETCO₂, mean arterial pressure (MAP), heart rate and SpO₂.

Results

Comparisons between different slope and cycling-off values did not result in any statistically significant changes for the evaluated variables (Table 1).

Table 1 (abstract P165)

Conclusion

Changes in cycling-off criteria from 25% to 40% of the peak flow and on the pressure slope from 150 ms to 300 ms do not affect other respiratory and hemodynamic variables in mechanically ventilated patients.