Background
Unloading ventilatory muscles has been a primary issue with our ventilator population. After analyzing ninety samples, it was revealed that 81% of the failed spontaneous breathing trials (SBT) were related to rapid, shallow breathing. Our original process for resting patients who have failed a SBT was to ventilate the patient utilizing “Volume Control Ventilation plus” (VCV+). One disadvantage of using an assisted mode for resting patients is the inability to properly set the ventilator to provide adequate rest without over resting the ventilatory muscles. Another disadvantage is patient/ventilator asynchrony, which may occur at any phase of breath delivery. A study of “Proportional Assist Ventilation” (PAV) was initiated to explore potential advantages over VCV+.
Method
16 adult patients (age 63 +/- 5yrs. Male gender 50%) who failed a SBT were included in this study. Test conditions consisted of alternating the ventilator (Puritan Bennett 840, Tyco Healthcare, LLC.) between the basal mode of ventilation, VCV+, to PAV with 80% support, PEEP, and a FiO2 to match the basal parameters. Patients were allowed 30 minutes to stabilize after modality changes before obtaining respiratory and hemodynamic measurements (table 1). Patient ventilator asynchrony was detected by visual inspection of the flow and pressure waveforms displayed on the ventilator. The paired two sample t test was used to evaluate differences between the modalities using spreadsheet software (Excel, Microsoft, Redmond, Washington). A p value less than 0.05 was considered statistically significant.
Results
When comparing total PEEP, exhaled tidal volume, minute ventilation, total respiratory rate, heart rate, and asynchronies there was no statistical differences between VCV+ and PAV. However, in regards to Peak Inspiratory Pressure (PIP) PAV ventilated at a lower measured PIP (p < 0.05) and generated a lower mean airway pressure (< 0.01) in comparison to VCV+.
Conclusion
The findings of this study indicate that PAV creates a significantly lower PIP during ventilation in comparison to VCV+ with modest variation in exhaled tidal volume, minute ventilation, and total respiratory rate.
1. Proportional Assist Ventilation: Guidelines & standards for using PAV™*+