2002 Abstracts

Introduction: Monitoring tidal volumes (Vt) in a time-cycled, pressure-limited mode has greatly improved the management of ventilated neonates, thereby preventing lung injury and possibly BPD. However, increased reliance upon monitoring Vt requires that the accuracy of the flow sensors be assessed. We sought to validate Vt reported on the Bird Gold and Dräger Babylog infant ventilators by comparison with plethysmography, which is the gold standard for Vt measurement.

Methods: The Vitaltrends body plethysmograph isolette is designed for infants <3 kg and uses a single screen (300 mesh stainless steel) low resistance pneumotachometer to measure volume displaced within a closed system. The Bird Gold and Dräger Babylog ventilators were compared using a neonatal circuit, a 3.0-mm endotracheal tube, and an IngMar neonatal test lung. New flow sensors were used for each experiment. Two ventilator conditions were selected: Condition 1) time-cycled, pressure limited AC, rate 25, pressure 20 cm H₂O, Ti 0.3 sec and a flow of 6 LPM; Condition 2) time-cycled, pressure limited AC, rate 20, pressure 30 cm H₂O, Ti 0.4 sec and a flow of 10 LPM. Under each condition, experiments using FiO₂ = 0.21 and 1.0, and relative humidity = 21% and 100% were conducted. The plethysmograph was calibrated prior to each experiment according to manufacturer?s specifications. Each experiment was conducted using 20 ventilator breaths. The Vt reported for each ventilator breath was compared to the corresponding Vt measured by plethysmography. Vt was adjusted for the local altitude of ~5000 ft, according to conversion factors provided by each ventilator manufacturer. Data were compared using Student?s t test or Mann Whitney U test.

Results: Vt for both ventilators and plethysmography are reported and compared in the table.

Conclusion: Ventilator?s accurate measuring and reporting of tidal volumes is extremely important, as it is often an integral part of ventilator management. In this study the Dräger reported the volumes more accurately than the Bird Gold.

* P<0.05, Pleth vs. BIRD ? P< 0.05, % Deviation, BIRD vs. Drager ? P< 0.05, Pleth vs. Drager