Comparative Study on Measured Volumes and Pressures for Two Pediatric Ventilator Circuits

Abstract

Background:

This study was undertaken to determine if there were any functional differences between two pediatric ventilator circuits. An in vitro study was performed to examine compressible volumes and volume accuracy in 2 pediatric ventilator circuits, looking at differences in measured peak inspiratory pressure (PIP), and inspiratory and expiratory tidal volumes (VTI and VTE).

Methods:

Two pediatric ventilator circuits: Fisher & Paykel (F&P) and Intersurgical (IS) were studied comparing compressible volume variances and the effect the different circuits had on PIP, VTI, and VTE. Four of each ventilator circuit types were used. The Servo-i (PRVC, rate-20, PEEP-8, circuit compliance-on, I-time-0.75, IRT-0.15, and FIO₂-. 21) was used to ventilate a test lung in both a normal lung model (resistance = 5 cm H₂O; compliance = 20 mL/cm H₂O) and an injured lung model (resistance = 20 cm H₂O; compliance = 10 mL/cm H₂O) with set V_T of 20mL, 50mL, 100mL, and 150mL. Flow and pressure waveforms were acquired utilizing a pneumotachograph (PNT) and a computerized digital recorder over 30 seconds. Five breaths were analyzed for each circuit and PIP, VTI, and VTE for both normal and injured lung models. Results are shown as mean ± SD. The circuit types were compared using t-tests with significance set at p <.05.

Results:

The measured mean compressible volumes for each circuit type were different: F&P (0.935 ± 0.005 mL/cm H₂O) and IS (1.003 ± 0.023 mL/cm H₂O) ; p < .001. Overall, there were no significant differences in PNT measured PIP, VTI and VTE in either the normal lung model (P= .98, >.99, and .82; respectively) or the injured lung model (P= .88, .81, and .94; respectively).

Conclusions:

The compressible volumes for each circuit type were significantly different, although there would be a small difference clinically. With the circuit compensation mode engaged, no significant differences were noted in PIP, VTI, or VTE between the circuit types. This reinforces the practice of utilizing the circuit compensation mode and translates to accurate volumes being delivered even with small V_T utilized in the pediatric population. Although this in vitro study provides valuable information showing little difference between the circuit types, a thorough clinical evaluation in patients should also be conducted to validate overall performance.