Conventional gas ventilation, liquid-assisted high-frequency oscillatory ventilation, and tidal liquid ventilation in surfactant-treated preterm lambs

This study was designed to compare the efficacy and potential protective or injurious effects of tidal liquid ventilation (TLV), liquid-assisted high- frequency oscillatory Ventilation (LA-HFOV), and high PEEP conventional mec hanical ventilation (CMV) in neonatal respiratory distress syndrome. Preter m lambs (124-126 days gestation), prophylactically treated with natural sur factant, were allocated to one of the treatment modalities or to an untreat ed fetal control group (F), euthanised after tracheal ligation. LA-HFOV ani mals received an intratracheal loading dose of 5 mL.kg(-1) followed by a co ntinuous intrapulmonary instillation of 12 mL.kg(-1);h(-1) FC-75 perfluoroc arbon liquid. The ventilation strategies aimed at keeping clinically approp riate arterial blood gases for a study period of 5 hours. A histological lu ng injury score was calculated and semiquantitative morphometry was perform ed on lung tissue fixed by Vascular perfusion. The alveolar-arterial pressure difference for O-2, was significantly lower throughout the study in TLV compared to CMV lambs; at 1, 2 and 5 hours, oxy genation was better in TLV when compared to LA-HFOV. Total lung injury scor es in TLV lambs were significantly lower than in either CMV or LA-HFOV anim als, but higher when compared to F: CMV and LA-HFOV induced an excess of co llapsed and overdistended alveoli, whereas in TLV alveolar expansion was no rmally distributed around predominantly normal alveoli. CMV and LA-HFOV; bu t not TLV; were associated with an excess of dilated airways. Thus, in the ovine neonatal RDS model, TLV compared favourably to either ga s ventilation strategy by its more uniform ventilation, reduced lung injury , and improved gas exchange.