Ventilator hyperinflation – what settings generate an expiratory flow rate bias?

Abstract

ObjectivesTo determine which mechanical ventilation settings influence the attainment of expiratory flow rate characteristics that may promote secretion mobilisation during ventilator hyperinflation (VHI). DesignProspective, single centre study. SettingIntensive care unit, tertiary metropolitan hospital. ParticipantsTwenty-four patients receiving mechanical ventilation. InterventionsPatients were recruited to either a low PEEP or high PEEP group (5–9 cmH2O or 10–15 cmH2O PEEP respectively). Each group had three hyperinflation protocols applied. Main outcome measuresPeak inspiratory flow rates (PIFR) and peak expiratory flow rates (PEFR) were measured and reported as PIFR/PEFR of less than or equal to 0.9; a PEFR-PIFR greater than or equal to 33 L/min; and PEFR greater than or equal to 40 L/min. ResultsIn both the low and high PEEP groups, VHI protocols using volume-controlled ventilation were significantly better at generating expiratory flow rate bias compared to pressure-controlled or Pressure Support ventilation. An expiratory flow rate bias was also achieved when VHI was performed in volume-controlled ventilation with either a peak inspiratory pressure target of 35 cmH2O or a driving pressure of 20 cmH2O. Median heart rate and blood pressure values did not change during VHI, but transient reductions in blood pressure were present in six participants (25%). ConclusionsVHI performed using volume-controlled ventilation was more effective than pressure-controlled or Pressure Support ventilation to generate an expiratory flow rate bias. Contribution of the PaperMechanical ventilator settings can be altered to perform hyperinflation and achieve expiratory flow rate properties that may increase the mobilisation of airway secretions. The results demonstrate that to achieve these properties:•Volume-controlled ventilation appears superior to pressure-controlled and Pressure Support ventilation.•Delivering volume-controlled breaths to a volume that result in a peak pressure of 35 cmH2O or using a driving pressure of 20 cmH2O appear to be equally effective.•Limiting the change in pressure to 20 cmH2O results in significantly lower tidal volumes and may still be effective for airway clearance in people on mechanical ventilation with either high or low PEEP.