INCREASED INCIDENCE OF SIGHS (AUGMENTED INSPIRATORY EFFORTS) DURING SYNCHRONIZED INTERMITTENT MANDATORY VENTILATION (SIMV) IN PRETERM NEONATES

A reflex resulting in a deep, sigh-like inspiratory effort (augmented breath) is frequently triggered during synchronized mechanical ventila tion in preterm infants, We studied the incidence of augmented inspira tory efforts and their effect on ventilation and lung compliance durin g conventional IMV and synchronized IMV (SIMV) in 15 preterm neonates (GA 26.7 +/- 1.5 wks (mean +/- SD), BW 925 +/- 222 g, age 1-8 days). A ugmentation of spontaneous inspiratory effort was defined as an esopha geal pressure deflection occurring coincident with a synchronized mech anical breath and exceeding the previous unassisted spontaneous effort by more than 50%. The incidence of augmented breaths was higher durin g SIMV (11.1 +/- 7.7%; P < 0.01) than during conventional IMV (5.1 +/- 6.1%). However, when the synchronized breaths were triggered late (20 0-300 msec) after the onset of inspiration, augmented breaths occurred no more frequently than during conventional IMV (6.0 +/- 4.7%). The i ncidence of augmented breaths correlated inversely with dynamic lung c ompliance (P = 0.014), but was not significantly influenced by a chang e in PEEP. Although inspiratory effort increased nearly three times du ring the augmented breaths, tidal volume increased only 12%. The chang e in tidal volume was limited because the augmented effort reached its maximal negativity only approximately 500 ms after the beginning of t he synchronized, mechanical breath and at a time when the mechanical b reath had already ended. For this reason the augmented effort did not contribute significantly to minute ventilation, but only prolonged ins piration. Dynamic lung compliance did not change significantly after a n augmented breath. The results indicate that augmented inspiratory ef forts are more common in preterm neonates ventilated with SIMV than wi th conventional IMV, but do not contribute significantly to ventilatio n. (C) 1997 Wiley-Liss, Inc.