RESPONSE TO SYSTEMIC ACIDOSIS IN FETAL PRIMATES

Abstract

The response of the fetus to systemic acidosis has been studied in 8 fetal baboons age 160 gestation. Lactic acid 4meq/kg fetal weight) was infused over a 15 min. period. pH, pCO2, HCO3, base excess and lactate were measured in fetal blood and urine, amniotic fluid and maternal blood and urine. TA and NH4 were measured in amniotic fluid and in fetal and maternal urine Fetal femoral artery blood pH fell from 7.22 to 7.16 after lactic acid infusion. After 18 min., the fetal blood pH had returned to control values. Fetal UpH did not significantly change from the mean control value and there was no increase in TA or NH4. The infused acid was distributed as follows during 75 min. following the infusion. These data support our hypothesis that fetal acid-base balance is primarily maintained by placental clearance of H+ as more than 82% of the infused acid is rapidly cleared by this organ. Fetal-amniotic fluid exchange is also an important homeostatic mechanism. The clearance of only 0.2% of the infused acid by the kidneys indicates no significant participation in acid-base homeostasis in utero by these organs. This is not inconsistent with our previous demonstration of a mature H+ secretory capacity for the fetal kidney.