Oxygen transport in newborn piglets with pulmonary hypertension

Because of the neonate's susceptibility to pulmonary hypertension (PHN) and his inefficiency in invoking the compensatory mechanisms often used by adults to maintain stable levels of O2 consumption (VO2) in the face of changes in O2 delivery (DO2) and metabolic demand, we have attempted to define the O2 handling capabilities of the newborn piglet affected with various types of pulmonary vasoconstriction. Hemodynamically similar levels of PHN were generated in 18 newborn piglets (six through group B beta-hemolytic Streptococci infusion; six through hypoxia; six through hypercarbia) and O2 transport was studied. At 60 min VO2 was similar in all groups, although DO2 was different (10.7 +/- 6.7, 7.2 +/- 1.6, and 21.7 +/- 8.9 ml/kg.min, in the septic, hypoxic, and hypercarbic groups, respectively). Extraction efficiency varied in an inverse fashion (43 +/- 12%, 72 +/- 12%, and 27 +/- 16%, in the septic, hypoxic, and hypercarbic groups, respectively). Supply dependency and a critical DO2 were observed in the septic and hypoxic PHN groups (18.4 and 12.2 ml/kg.min, respectively). Both of these were elevated as compared to healthy adult levels. Hypercarbic pulmonary hypertension was supply independent at the levels studied; however, DO2 remained elevated in these animals and may never have reached the critical DO2 level.