Pressure support ventilation or synchronised intermittent mandatory ventilation for weaning premature babies on mechanical ventilation : a multi centre randomised controlled trial

Abstract

Mechanical ventilation is life saving as a respiratory support for preterm infants with respiratory distress syndrome. There is good evidence now that any form of volume-targeted modality of mechanical ventilation is superior over pressure-targeted modality to reduce chronic lung disease and death. It is perceived by minimising the duration of mechanical ventilation would reduce the exposure to positive pressure breaths and thereby could reduce long term morbidities such as chronic lung disease. An area of lacunae is defining what is weaning on mechanical ventilation. Whilst most clinicians will agree when to commence mechanical ventilation there is paucity of consensus on when to commence weaning on mechanical ventilation and the best way for weaning to prevent extubation failure. Pressure support ventilation (PSV) is pressure-targeted modality of ventilation designed to support spontaneous breathing. It was designed as a weaning mode to facilitate extubation. Pure PSV has no back up rate. Currently, PSV is used in combination with other modes such as SIMV to provide some back up respiratory rate for the unreliable respiratory drive due to apnoea in preterm infants. However, there is inadequate understanding of the appropriate PSV level for weaning preterm infants on mechanical ventilation. Clinicians routinely use 50%-70% of peak inflation pressures used prior to commencing the weaning mode. Use of Pressure support ventilation (PSV) could be variable- with one extreme utilising minimal pressure to just overcome the tube resistance (PSmin) with the aim to prevent fatigue and avoid extubation failure. The other extreme is augmenting spontaneous breathing effort to provide a full tidal volume breath (PSmax). Features of flow triggering and flow cycling aid synchrony at inspiration and expiration and this allows greater autonomy to the infant to control all aspects of its breathing cycle. Addition of some PSV to aid spontaneous breaths has shown to reduce the duration of weaning. A randomised controlled study was designed to compare duration of weaning using PSmax and SIMV. Infants less than 32 weeks gestation at birth with respiratory distress syndrome from surfactant deficiency were eligible to participate. 93 infants stratified in three groups based on their gestation at birth were randomised over 30-month period. Weaning was commenced in the randomised mode when infants reached a set priori of MAP<10 cm H2O, FiO2 <40% and had a reliable respiratory drive for at least 2 consecutive hours. In the control arm (SIMV with PSmin)– clinicians reduced the back up rate to wean. In the intervention arm (PSmax with ten SIMV breaths)- clinicians reduced the PSVmax to PSVmin for weaning. A minute ventilation test was performed to assess readiness to extubation when both arms reached PSmin with ten back up SIMV breaths. Primary outcome for the study was duration of weaning on mechanical ventilation. Our study suggests there is no difference between the two groups but there is a trend towards faster extubation in the PSV arm (the median time to extubate in the SIMV arm was 42 (95%CI, 28.23 to 55.76) hours and the median time to achieve the primary outcome in the PSV arm was 31 (95% CI, 12.59 to 49.40) hours). The survival distribution between the interventions was statistically not significant, Chi-square 0.768, p 0.381. This effect was more evident in bigger infants weighing at least 1500 grams. There was no difference in the secondary outcomes between the two groups and common preterm morbidities were equally balanced. There were no adverse events during the study period to report. Contrary to the general belief, infants are not disadvantaged by weaning on PSVmax. Clinical outcomes were comparable with the traditional SIMV method of weaning on mechanical ventilation.