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

OBJECTIVES

To determine which mechanical ventilation settings influence the attainment of expiratory flow rate characteristics that may promote secretion mobilisation during ventilator hyperinflation (VHI).

DESIGN

Prospective, single centre study.

SETTING

Intensive care unit, tertiary metropolitan hospital.

PARTICIPANTS

Twenty-four patients receiving mechanical ventilation.

INTERVENTIONS

Patients were recruited to either a low PEEP or high PEEP group (5-9 cmHO or 10-15 cmHO PEEP respectively). Each group had three hyperinflation protocols applied.

MAIN OUTCOME MEASURES

Peak 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.

RESULTS

In 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 cmHO or a driving pressure of 20 cmHO. Median heart rate and blood pressure values did not change during VHI, but transient reductions in blood pressure were present in six participants (25%).

CONCLUSIONS

VHI 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 PAPER

Mechanical 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.