Transcutaneous and arterial carbon dioxide tension at various conditions of fetal stress in lambs

In an acute fetal lamb model the relation between arterial PCO2 (PaCO2), transcutaneous PCO2 (tcPCO(2)) and pH was studied at different conditions of stress. Occlusion of the maternal common iliac artery for 8 min, umbilical cord obstruction for 5 min and placental embolization were performed subsequently, every time with an interval of 1 h for fetal recuperation. During the first 2 experiments arterial values changed rapidly after occlusion and returned nearly to normal within 30-60 min after the end of occlusion. TcPCO2 started to increase several minutes after occlusion and reached its maximum about 5 min after the end of occlusion. Afterwards a gradual decrease towards the onset value was observed. During placental embolization tcPCO(2) did not increase until 15 min before fetal death. It is concluded that tcPCO(2) can follow a gradual trend, but not quick changes in PaCO2.