Effects of high PCO2 on ventilated preterm lamb lungs

Abstract

High PCO2 levels attenuate reperfusion injury and ventilation-induced injury in isolated and perfused lungs. We asked whether premature lambs could tolerate 6 h of ventilation with a PCO2 >80 mm Hg and whether the high PCO2 modulated the ventilator-induced injury. Preterm surfactant-treated lambs were ventilated for 30 min with a high tidal volume (VT) to induce lung injury. The lambs then were ventilated for 5.5 h with a VT of 6-9 mL/kg to achieve a PCO2 of 40-50 mm Hg in the control group. CO2 was added to the ventilator circuit of a high PCO2 group to maintain an average PCO2 of 95 ± 5 mm Hg. The high PCO2 lambs had heart rates, blood pressures, plasma cortisol values, and oxygenation equivalent to the control lambs. The lungs of the high PCO2 group had significantly higher gas volumes and had less lung injury by histopathology. Indicators of inflammation (white blood cells, hydrogen peroxide production, and lL-1β and IL-8 cytokine mRNA expression in cells from the alveolar wash) qualitatively indicated less injury in the high PCO2 group, although the differences were not significant. Preterm lambs tolerated a very high PCO2 without physiologic compromise for 6 h. The high PCO2 may attenuate ventilator-induced lung injury in the preterm.