Effects of pressure support during an acute reduction of synchronized intermittent mandatory ventilation in preterm infants

Background: 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. Objective: 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. Methods: 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) 16.6±1.3 cmH₂O, positive end-expiratory pressure (PEEP) 4.3±0.6 cmH₂O, and fraction of inspired oxygen (FiO₂) 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 cmH₂O (SIMV + PS3 and SIMV + PS6, respectively). Results: SIMV rate was reduced during SIMV + PS from 21.4±6.6 to 11.4±6.6b/minute. Arterial oxygen saturation, transcutaneous carbon dioxide tension and FiO₂ 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. Conclusion: Assistance of the spontaneous breaths with pressure support maintained gas exchange. PS of 6 cm H₂O prevented an increase in breathing effort during an acute 50% reduction in SIMV rate.