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Proportional Assist Ventilation in Very Prematurely Born Infants with Evolving Bronchopulmonary Dysplasia

Presented at the Neonatal Society 2013 Summer Meeting.

Bhat P, Rafferty GF, Hannam S, Milner AD, Greenough A

Division of Asthma, Allergy and Lung Biology, King’s College London, London, United Kingdom

Background: During assist control ventilation (ACV), ventilator inflations are triggered by the onset of the infant’s respiratory efforts. Proportional assist ventilation (PAV) offers additional advantages as the ventilator pressure is servo controlled throughout each respiratory cycle and the ventilator can reduce the resistive and the elastic load (work of breathing) of the infant (“unloading”). Infants with evolving bronchopulmonary dysplasia (BPD) frequently have severe lung function abnormalities and hence may benefit more from PAV than ACV.

Methods: A randomised crossover study in prematurely born infants was undertaken. Prior to the start of the study, each infant’s compliance and resistance were determined using the ventilator (Stephanie paediatric ventilator, F Stephan, Gackenback Germany). During PAV, a median elastic unloading was used that compensated for 100% of the infant’s baseline compliance. Resistive unloading was not used as this may result in abnormal airway pressure oscillations. At the end of an hour on each ventilator mode, the oxygenation index (OI) was calculated and measurements were made of the PaCO2 levels, the work of breathing (assessed using the pressure time product, PTP) and respiratory muscle strength (by assessment of the maximum diaphragmatic (Pdimax) and the inspiratory (Pimax) and expiratory (Pemax) pressures during brief airway occlusions).

Results: Ten infants with a median gestational age of 25 (range 24-28) weeks have been studied at a median of 43 (range 08-86) days. Their median baseline compliance was 0.6 (range 0.3-0.7) mls/cm H2O and resistance was 86.5 (range 50-102) cmH2O/l/sec. The median OI following one hour on PAV was significantly lower than that following one hour on ACV (5.55 (range 5-11) versus 10.16 (range 7-16) respectively), p=0.005. There were no significant differences in Pimax between PAV and ACV (20.33 (range 11.24 – 37.3) cm H20 versus 21.72 (range 13.61 – 38.6) cm H20 respectively), p=0.445 nor in the PaCO2 levels (7.98 (5.72 – 10) kpa versus 7.65 (5.7 – 12.1) kpa respectively), p=0.799. Following an hour on PAV compared to following an hour on ACV, however, the PTP levels were lower (253 (range 59-556) cm H20/s/min versus 344 (range 55-544) cm/H20/s/min), p=0.013, Pdimax levels were higher (44.26 (range 21-66) cm H20 versus 35 (range 19-45) cm H20), p=0.005 and Pemax levels were higher (25.67(range 6.5-42)cm H20 versus 15(range 3-35)cm H20), p=0.005.

Conclusion: These results suggest that PAV compared to ACV may be advantageous for infants with evolving BPD.

Corresponding author: anne.greenough@kcl.ac.uk

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