The Science Journal of the American Association for Respiratory Care

2000 OPEN FORUM Abstracts

EVALUATION OF PROTOTYPE "ADULT" CIRCUIT FOR PEDIATRIC MECHANICAL VENTILATION

Timothy R. Myers BS, RRT, Michael Tracy RRT and Robert Chatburn RRT, FAARC. Rainbow Babies & Children's Hospital. Cleveland, OH

Introduction. The goal of mechanical ventilation is adequate gas exchange with minimal lung tissue damage and minimal circulatory disturbance. Tidal volume (Vt) selection in pediatric volume ventilation is dependent on disease. Set ventilator volumes never equal delivered volumes at the patient airway, due to the fact that the ventilator circuit has its own compliance (compliance of tubing material plus compressibility of gas) and resistance. This results in set volumes being higher than delivered volumes due to the effective circuit compliance. Circuit manufacturers have traditionally produced three circuits (neonatal, pediatric and adult) to offset for compressible volume loss. Fisher-Paykel has developed a prototype, "adult" ventilator circuit that purportedly delivers safe pediatric Vt. We hypothesized minimal difference in circuit compliance between the Fisher-Paykel and our standard Baxter pediatric circuit prior to use; and with simulated ventilation conditions, no clinical difference in delivered Vt under high (high resistance; low compliance) and normal load (high compliance; low resistance). Methods: Circuit compliance was measured by connecting 4 circuits of each brand to a pressure manometer and injected calibrated volumes (20-100 ml at 20 ml increments). To test our hypothesis of no clinical difference in the delivered pediatric Vt, 5 circuits of each brand were tested under simulated ventilation using an Ingmar Lung Simulator as our patient. A Hamilton Galileo and a Fisher-Paykel humidifier served as our ventilator system. Randomly set Vt (80 to 300 ml at 10-20 ml increments) were tested with resulting exhaled volumes measured by the Galileo's flow sensor software. We tested Vt under normal (high compliance; low resistance) and high (high resistance; low compliance) load conditions. Results: Pressure volume plots yielded circuit compliances of 1.59(± 0.52) cmH20/ml (Fisher-Paykel) and 0.98 (± 0.07) cmH20/ml (Baxter). Volume delivery was not different between the two circuits under normal load (p > 0.05). Under high load, the Fisher-Paykel circuit delivered less volume (p < 0.05). Data below are mean Vt difference (± 1 SD) under normal and high load conditions.
Conclusion: The Fisher-Paykel circuit demonstrated comparable pediatric tidal volumes under normal work conditions. Due to a slighter higher circuit compliance, pediatric tidal volumes under high work conditions was 2-6 ml lower, but the difference is not expected to be clinically important. The new Fisher-Paykel circuit can be considered a universally applicable for all patients. (See Original for Figure)

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