PATIENT TRIGGER TO RESPONSE TIME OF THE DRÄGER BABYLOG AND THE BIRD GOLD INFANT VENTILATORS IN A NEONATAL BENCH STUDY

Introduction: When ventilating spontaneously breathing neonates it is extremely important for patient comfort and synchrony for ventilator breaths to be delivered as quickly as possible. Ventilator manufacturers refer to this as response time and many have different ways of calculating and reporting it. For our purpose, we defined response time as how quickly a ventilator begins to deliver flow at the endotracheal tube after a patient?s spontaneous breath effort is detected by the ventilator. We sought to measure response time of the Bird Gold and the Dräger Babylog.

Method: The Vitaltrends plethysmograph isolette is a closed system that measures volumes and pressures displaced within the system. The Vitaltrends uses a differential pressure transducer to measure pressures and uses a single screen (300 mesh stainless steel) low resistance pneumotachometer to measure volume. The plethysmograph?s pressure transducer is wyed into the ventilator circuit?s proximal pressure line distal to the wye piece. This allows graphic and waveform analysis on ventilated infants <3Kg. The Vitaltrends computer package has the ability to measure and analyze graphic waveforms in milliseconds. The Bird Gold and Dräger Babylog ventilators were used with neonatal circuits ventilating an Ingmar neonatal test lung in separate tests. New flow sensors were used for each experiment. The ventilator settings used were: time cycled, pressure limited AC, Pressure 25 cm H2O, rate 20, flow 6 LPM, Ti 0.35 sec, and a trigger sensitivity of 0.3 LPM. A small plastic t-piece was inserted between a 3.0 mm endotracheal tube?s connector and the tube itself. The t-piece was connected to a 10 cc Hans Rudolph syringe. Fish line was attached to the syringe plunger and was run out of the closed plethysmograph. The plethysmograph was calibrated before each test as per the manufacturer?s specifications. A spontaneous breath was simulated when the line attached to the syringe plunger was pulled. Twenty spontaneous breaths were recorded and analyzed for both ventilators.

Results: To determine response time we measured from the Vitaltrends graphics at the point of negative pressure deflection, caused by our spontaneous trigger, to the first rise detected in flow. Response time results are reported in the table.

Conclusion: Response time is an important component for patient comfort and synchrony when choosing a ventilator for neonates. The % difference indicates that the Dräger response time is 0.28 shorter than Bird Gold, however, the actual time difference is 0.015 sec. Two questions that require further investigation are: 1) is a difference of 0.015 sec. clinically significant between two devices? 2) What are appropriate response times of ventilators for spontaneously breathing neonates?

P<0.008 Mann-Whitney U