The effect of asphyxia on superior mesenteric artery blood flow in the premature sheep fetus

Background/Purpose: The aim of this study was to determine superior mesente ric artery blood flow changes during and after an asphyxial insult in utero in chronically instrumented unanaesthetised premature fetal sheep. Methods: Fetal sheep at 0.7 gestation (103 to 104 days) underwent 25 minute s of complete umbilical cord occlusion (n = 6) or sham occlusion (n = 6). F etal heart rate, blood pressure, superior mesenteric artery (SMA) blood flo w and vascular resistance, electroencephalographic activity, and nuchal ele ctromyographic activity were measured from 6 hours before occlusion until 3 days after occlusion. Fetal gastrointestinal tissue was taken for histolog ical assessment. Results: During occlusion, cardiovascular response was characterised by 3 p hases: initial redistribution of blood flow away from the gut to maintain v ital organ function, subsequently partial failure of this redistribution, a nd finally near terminal cardiovascular collapse with profound hypotension and gastrointestinal hypoperfusion. Postasphyxia there was a secondary peri od of hypoperfusion that was mediated by increased vascular resistance, not hypotension. There was no evidence of injury on standard histological asse ssment after 3 days of recovery. Conclusions: SMA blood flow is not only significantly reduced during asphyx ia, but also for several hours after an asphyxial insult. The authors specu late that these perturbations of gastrointestinal blood flow could compromi se gut wall integrity potentially leading to increased vulnerability to nec rotising enterocolitis. Copyright (C) 2000 by W.B. Saunders Company.