Monitoring Airway Pressure at Different Locations During High Frequency Percussive Ventilation

Abstract

Background:

High frequency percussive ventilation (HFPV) is utilized for airway clearance in the setting of retained secretions and persistently increased PaCO₂ levels. The VDR displays two measurements of PIP, PEEP, and MAP. The Multimeter displays average inhalation pressure, average exhalation pressure, and MAP. This average pressure is not in line with the Monitron values or absolute PIP and PEEP as clinicians are accustomed to with conventional ventilation. We aimed to compare pressure measured by the ventilator to pressure delivered to the simulated patient in two circuit configurations.

Methods:

A healthy 5yo passive patient with C = 20mL/cm H₂O, R = 15cm H₂O/L/s, and URC = 0.4L was simulated with the ASL 5000 with an additional pneumotachometer inline at the patient Y-piece with waveform capture in PowerLab software. Six different settings were used with both Distal Phasitron (ie, HUB) and Traditional circuits (Table 1). Five complete breaths for each condition were analyzed. Absolute PIP, average PIP, MAP, absolute PEEP, and average PEEP were measured at the Monitron, Multimeter, PowerLab Y-piece, ASL mouth, and ASL trachea where applicable. A one-way ANOVA was performed to assess differences between pressures measured at different locations.

Results:

All pressures differed significantly between locations (P <.001 for PIP and PEEP for both circuits, P = .012 for Distal Phasitron MAP, P = .006 for Traditional MAP)(Figure 1). The Multimeter measure of median PIP/PEEP was 32.5/10 cm H₂O for both circuits and most closely resembled ASL tracheal pressure of 32.8/10.1 and 34.0/9.6 cm H₂O for the Distal Phasitron and Traditional circuits, respectively. The variation between PIP and PEEP at these locations did not exceed more than 1.5 cm H₂O for PIP and 0.4 cm H₂O for PEEP. The difference in pressures between the Multimeter and ASL tracheal pressure were not clinically significant.

Conclusions:

Although the difference between pressures at different points reached statistical significance, the difference in recommended monitoring and what is estimated to be delivered to the lung was not clinically meaningful. The Multimeter can be used to monitor delivered pressure by the bedside clinician using either circuit with the limitation that it may under report PIP and over report PEEP. More research is needed in human, animal, and anatomical models to better describe the behavior of pressure, volume, and high frequency breaths during HFPV.

Settings on the VDR for Two Circuit Configurations

Circuit	PIP (cmH2O)	Oscillatory PEEP (cmH2O)	Demand PEEP (cmH2O)	Convective Rate (bpm)	Percussive Rate (bpm)
Distal Phasitron 1	35	8	2	20	600
Traditional 1	35	8	2	20	600
Distal Phasitron 2	35	13	2	20	600
Traditional 2	35	13	2	20	600
Distal Phasitron 3	30	3	2	20	600
Traditional 3	30	3	2	20	600
Distal Phasitron 4	30	8	2	20	600
Traditional 4	30	8	2	20	600
Distal Phasitron 5	35	8	2	20	450
Traditional 5	35	8	2	20	450
Distal Phasitron 6	30	8	2	20	450
Traditional 6	30	8	2	20	450

Figure 1. One-way ANOVA results comparing PIP, PEEP, and MAP at different locations in the Distal Phasitron and Traditional circuit configurations.