High bias gas flows increase lung injury in the ventilated preterm lamb.
BACKGROUND
Mechanical ventilation of preterm babies increases survival but can also cause ventilator-induced lung injury (VILI), leading to the development of bronchopulmonary dysplasia (BPD). It is not known whether shear stress injury from gases flowing into the preterm lung during ventilation contributes to VILI.


METHODS
Preterm lambs of 131 days' gestation (term = 147 d) were ventilated for 2 hours with a bias gas flow of 8 L/min (n = 13), 18 L/min (n = 12) or 28 L/min (n = 14). Physiological parameters were measured continuously and lung injury was assessed by measuring mRNA expression of early injury response genes and by histological analysis. Control lung tissue was collected from unventilated age-matched fetuses. Data were analysed by ANOVA with a Tukey post-hoc test when appropriate.


RESULTS
High bias gas flows resulted in higher ventilator pressures, shorter inflation times and decreased ventilator efficiency. The rate of rise of inspiratory gas flow was greatest, and pulmonary mRNA levels of the injury markers, EGR1 and CTGF, were highest in lambs ventilated with bias gas flows of 18 L/min. High bias gas flows resulted in increased cellular proliferation and abnormal deposition of elastin, collagen and myofibroblasts in the lung.


CONCLUSIONS
High ventilator bias gas flows resulted in increased lung injury, with up-regulation of acute early response genes and increased histological lung injury. Bias gas flows may, therefore, contribute to VILI and BPD.
Liggins Institute, University of Auckland, New Zealand. kittyb@adhb.govt.nz
Katinka P
KP
Bach
Carl A
CA
Kuschel
Stuart B
SB
Hooper
Jean
J
Bertram
Sue
S
McKnight
Shirley E
SE
Peachey
Valerie A
VA
Zahra
Sharon J
SJ
Flecknoe
Mark H
MH
Oliver
Megan J
MJ
Wallace
Frank H
FH
Bloomfield
D000818:Animals; D000831:Animals, Newborn; D001997:Bronchopulmonary Dysplasia / Q000209:etiology* / Q000378:metabolism; D006801:Humans; D007231:Infant, Newborn; D012756:Sheep; D013314:Stress, Mechanical; D055397:Ventilator-Induced Lung Injury / Q000209:etiology* / Q000378:metabolism