Effects of Pressure Support during an Acute Reduction of Synchronized Intermittent Mandatory Ventilation in Preterm Infants

Abstract

During weaning of synchronized intermittent mandatory rate in preterm infants, the spontaneous breaths must overcome the resistance of the endotracheal tube and the disease-induced respiratory loads. Pressure Support (PS) can be used as an adjunct to synchronized intermittent mandatory ventilation (SIMV) to partially unload the spontaneous breaths. To evaluate the effects of two levels of PS as an adjunct to SIMV on gas exchange and breathing effort during an acute reduction in SIMV rate in preterm infants. In all, 15 infants (birth weight 793 +/- 217 g, gestational age 26.4 +/- 1.5 weeks, postnatal age 15 +/- 16 days). Ventilatory support consisted of SIMV with peak inspiratory pressure (PTP) 16.3 +/- 1.3 cmH(2)O, positive end-expiratory pressure (PEEP) 4.3 +/- 0.6 cmH(2)O, and fraction of inspired oxygen (FiO(2)) 0.26 +/- 0.06. Infants were studied during four 30-minute periods: Two baseline SIMV periods and two periods of SIMV plus PS, in random order. During SIMV + PS, SIMV rate was lowered by 10 breaths per minute (b/minute) and PS was set at 3 and 6 cmH(2)O (SIMV+PS3 and SIMV + PS6, respectively). SIMV rate was reduced during SIMV + PS from 21.4 +/- 6.6 to 11.4 +/- 6.6 b/minute. Arterial oxygen saturation, transcutaneous carbon dioxide tension and FiO(2) remained unchanged. Minute ventilation, total respiratory rate and mean airway pressure were higher during SIMV + PS. Per-breath inspiratory effort was lower during SIMV + PS and this was more striking during SIMV + PS6. Spontaneous inspiratory effort per minute increased during SIMV + PS3, but this increase was averted during SIMV + PS6. Assistance of the spontaneous breaths with pressure support maintained gas exchange. PS of 6 cm H(2)O prevented an increase in breathing effort during an acute 50% reduction in SIMV rate.