Fetal heart rate and tissue pH changes associated with repetitive aortic occlusion in the pregnant dog.

Variations in fetal heart rate (FHR) and tissue pH (tpH) were studied simultaneously in 10 pregnant dogs at term during experimental fetal distress produced by subjecting the fetuses to short episodes of acute anoxia, which was produced by occlusion of thr maternal aorta. The fetal response to these anoxic episodes dependent on the initial value of the tpH. With tpH higher than or equal to 7.20, the tpH and FHR showed minimal or no response. With tpH between 7.20 and 7.10, the FHR showed a "delayed" deceleration and there was a sharp decline in tpH. With lower tpH, the variations in FHR and tpH were less accentuated. Also noted were unusual variations, such as "transient" or "irregular" FHR decelerations, and tpH "reactive alkalosis." In this acute experimental situation, tpH seemed to be a very sensitive indicator of fetal anoxia. The combined continuous monitoring of FHR and tpH for the diagnosis of fetal distress deserves further investigation.