INSPIRATORY WORK OF BREATHING IN VENTILATED PRETERM INFANTS

In ventilated newborns, part of the inspiratory work of breathing (WOB ) may be due to the inspiratory efforts preceding inspiratory ventilat or flow. This study was designed to quantify the contribution of these efforts to WOB. WOB was evaluated in six intubated preterm infants ve ntilated by the Drager Babylog 8000. The ventilatory modes studied wer e intermittent manda tory ventilation (IMV), continuous positive airwa y pressure (CPAP), and assist-control ventilation at 10 (ACV(10)) and 15 (ACV(15)) cm H2O peak pressure. Mouth flow (V) and esophageal press ure (Pe) were recorded, and WOB was estimated from the area delineated by the esophageal pressure-volume curve, where volume is the time int egral of V. Calculation of WOB started either at the onset of the infa nt's inspiratory flow (WOBf), or at the beginning of the infant's insp iratory muscle efforts, detected on Pe and confirmed on the V tracing (WOBm). WOBm was found to be significantly higher than WOBf under all ventilatory conditions studied. The difference in work of breathing (D elta W) between WOBm and WOBf did not depend on the type of ventilator y mode. When Delta W was related to WOBm, it amounted to about 30% of WOBf in IMV and CPAP, and 60% in ACV (P < 0.05, ACV(15) vs. IMV). Thes e results suggest that, in preterm infants connected to a ventilator, inspiratory efforts preceding flow inspiration might account for a lar ge fraction of the inspiratory work of breathing. (C) 1996 Wiley-Liss. Inc.