Abstract
OBJECTIVE
The purpose of this study was to determine whether variations in the delivery systems of continuous positive airway pressure between two ventilators would lead to differences in patient work of breathing (WOBp).
DESIGN
Comparison of two neonatal ventilators with a neonatal pig model.
SETTING
Animal laboratory.
SUBJECTS
Thirty healthy, intubated, sedated, spontaneously breathing neonatal piglets weighing 1.0-2.0 kg.
INTERVENTIONS
Patient work of breathing (WOBp) (gm cm/kg) was measured by using measurements based on an esophageal balloon and a flow transducer. Each breath was analyzed for ventilator response times (in msecs) and negative deflection of pressure. Each animal was studied with the Siemens SV300 and Drager Babylog 8000, on continuous positive airway pressure settings of 0, 3, and 5 cm H2O. Data were analyzed by using Wilcoxon's Signed Rank Test with significance of p <or=.05.
MEASUREMENTS AND MAIN RESULTS
Comparing ventilators, WOBp was on average 29% higher in the Babylog. Analysis of individual breaths showed that disparity in WOBp was probably related to the automatic availability of 2 cm H2O pressure support ventilation in the SV300. This may also explain the differences in delay time during the start of the inspiratory phase before initiation of gas flow. The mean duration of inspiratory effort was 394 (+/- 157) msecs in the Babylog and 138 (+/- 35) msecs in the SV300, a 174% increase in time delay for the Babylog (p =.005). During inspiratory effort, there was >1 cm H2O negative pressure before flow was available with the Babylog.
CONCLUSIONS
In intubated patients, maximum energy expenditure occurs at the initiation of ventilator breaths. WOBp in neonatal pigs was significantly increased. The response time of the ventilators may explain the differences in initiation of flow times and patient work. These differences may have important implications for energy kinetics, weight gain, and duration of mechanical ventilation in preterm neonates.
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