Volume-targeted modes of modern neonatal ventilators: how stable is the delivered tidal volume?

OBJECTIVE: Volume-targeted modes are designed to deliver a constant tidal volume (V(t)) at lowest possible pressure independently of changes in compliance, resistance, and leak of the respiratory system. We examined whether these volume-targeted modes respond rapidly enough to sudden changes in respiratory mechanics (e.g., selective intubation, surfactant administration, endotracheal tube kinking, de-kinking, obstruction), resulting in insufficient or excessive V(t) delivery. DESIGN AND
SETTING: Bench study of six neonatal ventilators in the volume-targeted mode simulating preterm and full-term infant settings on a test lung. MEASUREMENTS AND
RESULTS: Breath-to-breath expiratory V(t) were measured after rapid compliance, resistance, and leak changes. Under our test settings all ventilators showed important volume overshooting following rapid increase in compliance or decrease in resistance. Between one and 16 inflations were required to return to the set V(t). Some ventilators delivered inaccurate V(t) under steady state condition while others showed considerable breath-to-breath V(t) variability.
CONCLUSIONS: We observed inaccurate V(t) delivery under specific conditions as well as immediate and sometimes prolonged volume overshooting after a rapid respiratory system compliance increase or resistance decrease in volume-targeted modes of modern neonatal ventilators. Similar discrepancies between the set V(t) and the delivered inflations can be harmful in clinical situations, especially in newborns. Their clinical relevance needs to be clarified with safety studies in the neonatal population and we encourage manufacturers to further improve the ventilators algorithms.