To better understand the pathogenesis of GM-IVH in premature babies, we prospectively studied cerebral and systemic hemodynamics daily for the first four postnatal days in the highest risk group--gestational age (GA) ≤25 weeks. Inclusion criteria were: inborn, AGA, required mechanical ventilation for the first four days, and parental consent. Using Doppler ultrasound we measured systolic (S) and diastolic (D) blood flow velocity (BFV) in the anterior cerebral artery, cardiac output (CO), and ductal shunting. We also measured systemic blood pressure (BP), arterial blood gases, hematocrit (Hct), recorded ventilator parameters, and calculated cerebral vascular resistance(CVR = BP/BFV). Of the 30 babies, 6 had active bleeding during the study period and were designated the hemorrhage group (H) while 24 had persistently negative scans (no H). There were no differences between groups in birthweight, GA, Apgars, cord gases or C-section rate. There also were no differences in daily arterial blood gases, ventilator settings, CO, or the incidence of PDA. On day #1, the Hct was lower in the H group (38±4 vs 45±5, P<.05). Data (mean ±SD) for BP, BFV and CVR are as follows: Table

Table 1
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On day #1, BFV-D was higher and CVR lower in the H group. In the no H group BFV-S and BFV-D both increased and CVR significantly decreased from day 1 to day 4 whereas there were no such changes in the H group. Our data suggests that at ≤25 weeks, babies destined to have active bleeding during the first 4 postnatal days initially have a decreased cerebral vascular resistance which does not appear to be related to asphyxia or arterial blood gases.