ST waveform changes during repeated umbilical cord occlusions in near-term fetal sheep.
OBJECTIVE
This study was undertaken to determine whether changes in the fetal ST waveform during repeated umbilical occlusion reflect the development of hypotension and acidosis.


METHODS
Chronically instrumented, near-term fetal sheep received 1-minute total umbilical cord occlusion either every 5 minutes for 4 hours (1:5 group, n = 8), or every 2.5 minutes until blood pressure fell <20 mm Hg on 2 successive occlusions (1:2.5 group, n = 8).


RESULTS
Umbilical cord occlusion caused variable decelerations, with sustained hypertension in the 1:5 group and little change in acid-base status (pH = 7.34 +/- 0.07 after 4 hours). In contrast, the 1:2.5 group showed progressive hypotension and metabolic acidemia (pH 6.92 +/- 0.1 after the final occlusion). There was a marked increase in ST waveform height during occlusions; this increase was greater in the 1:2.5 group (P <.001), but there was overlap between the groups. ST waveform height between occlusions was significantly higher in the 1:2.5 group (P <.001) until negative and biphasic ST waveforms developed in these fetuses between occlusions in the final 30 minutes.


CONCLUSIONS
ST waveform elevation occurs during umbilical cord occlusions but only crudely reflects the severity of hypoxia. Interocclusion waveform height may be a better reflection of the severity of hypoxia. The appearance of biphasic and negative waveforms between occlusions may be a useful marker for severe decompensation.
Department of Obstetrics and Gynecology and the Research Centre for Developmental Medicine and Biology, University of Auckland, New Zealand.
J A
JA
Westgate
L
L
Bennet
C
C
Brabyn
C E
CE
Williams
A J
AJ
Gunn
D000138:Acidosis / Q000209:etiology / Q000503:physiopathology; D000818:Animals; D001794:Blood Pressure; D003250:Constriction; D004562:Electrocardiography; D005260:Female; D005311:Fetal Hypoxia / Q000150:complications / Q000209:etiology / Q000503:physiopathology*; D005333:Fetus / Q000098:blood supply; D005865:Gestational Age; D006340:Heart Rate, Fetal; D006863:Hydrogen-Ion Concentration; D007022:Hypotension / Q000209:etiology / Q000503:physiopathology; D011247:Pregnancy; D012756:Sheep; D014470:Umbilical Cord