The effect of two levels of pressure support ventilation on tidal volume delivery and minute ventilation in preterm infants.

Objective: To study the effect of different levels of pressure support ventilation (PSV) on respiratory parameters in preterm infants during the weaning phase of mechanical ventilation.
Design/methods: In this quasi-experimental crossover study, a total of 19 154 breaths were analysed from 10 ventilated infants of <32 weeks' gestation. Breath-to-breath data on minute ventilation, tidal volume, respiratory rate, peak inspiratory pressure and mean airway pressure were collected during three study epochs: synchronised intermittent mandatory ventilation (SIMV) alone, SIMV with partial PSV (PS(min)), and SIMV with full PSV (PS(max)). PS(min) was set to provide an exhaled tidal volume (V(Te)) between 2.5-4 ml/kg and PS(max) 5-8 ml/kg V(Te). Statistical analyses were performed using analysis of variance (ANOVA) for repeated measures.
Results: The addition of full PSV (PS(max)) was associated with a significant increase in total minute ventilation as compared with SIMV alone (392 ml/kg/min vs 270 ml/kg/min, respectively; p<0.05). This difference in minute ventilation was still present when PS(min) was used (332 ml/kg/min as compared with 270 ml/kg/min in SIMV; p<0.05). There was also a concomitant decrease in the respiratory rate with both PS(max) (59 breaths per minute) and PS(min) (65 breaths per minute) compared with SIMV alone (72 breaths per min) (p<0.05).
Conclusions: Pressure support ventilation increases total minute ventilation and stabilises breathing in proportion to the level of pressure support used. This may be advantageous and provide a useful ventilation strategy for use during weaning stages of mechanical ventilation in preterm infants.