Shunt and ventilation-perfusion distribution during partial liquid ventilation in healthy piglets.

Replacing gas in the lung with perfluorocarbon fluids (PFC) and periodically ventilating with a gas [partial liquid ventilation (PLV)] has been shown to improve oxygenation in models of respiratory distress syndrome. We hypothesized that the addition of PFC to healthy lungs would result in shunt, diffusion impairment, and increased ventilation-perfusion (VA/Q) heterogeneity. Previously, Mates et al. showed that O2 shunt and arterial-alveolar CO2 difference increased linearly with dose in piglets given graded intratracheal doses of PFC (10, 20, and 30 ml/kg followed by mechanical ventilation with 100% O2) (E.A. Mates, J. C. Jackson, J. Hildebrandt, W. E. Truog, T. A. Standaert, and M. P. Hlastala. In: Oxygen Transport to Tissue XVI, 1994, p. 427-435). Here we report VA/Q distribution in the same animals, showing a 50% increase in VA/Q heterogeneity during PLV independent of PFC dose. Ventilation heterogeneity was the major factor in this increase, and there was no significant change in dead space ventilation. We also report on five animals given a single 20 ml/kg dose of PFC and followed for 3 h. They showed an increase in shunt during PLV but no change in arterial-alveolar CO2 difference.

Effects of exogenous surfactant on lung pressure-volume characteristics during liquid ventilation.

Total liquid ventilation (LV) lowers airway pressures and potentially reduces barotrauma in models of hyaline membrane disease. LV eliminates surface tension by eliminating the air-perfluorochemicals (PFC) interface but does not eliminate interfacial tension (IT) at the lung/PFC interface. We hypothesized that pretreatment with exogenous surfactant before LV would shift the overall pressure-volume (PV) curve to the left, compared with LV without surfactant. Sequential quasi-static PV curves were obtained in 10 excised lungs (saline, air, PFC), with one-half randomized to exogenous surfactant replacement before LV. Analysis revealed that maximal inflation pressures were reduced during LV compared with baseline air curves. Addition of exogenous surfactant to LV further reduced maximal inflation pressures. A novel approach was used to transform these PV curves to estimates of in situ IT-volume curves. Estimated maximal IT at 20 ml/kg in preterm lamb lungs on air inflation after surfactant was 51 mN/m, compared with 40 mN/m for LV alone and with 27 mN/m for the combination of surfactant and LV. We conclude that the IT-reducing properties of the PFC studied (perflubron) can be augmented through the use of exogenous surfactant.