CBF reactivity in hypotensive and normotensive preterm infants

Perinatal distress in the preterm neonate, and the consequent loss of cerebrovascular autoregulation, has been implicated in the pathogenesis of neonatal cerebral lesions. A component of this distress is thought to be hypotension. We examined the autoregulatory capacity of hypotensive and normotensive infants using the 133Xe technique to measure cerebral blood flow. Global CBF was measured during only normotension in 5 infants, and during both hypotension and normotension in 11 infants. All the infants were ventilated and blood pressure was measured using an intra-arterial catheter. Fourteen CBF measurements were made on the normotensive infants. Forty-seven CBF measurements were made on the hypotensive infants, 34 measurements during hypotension and 13 during normotension. The global CBF of the normotensive and hypotensive infants were 13.3 and 13.6 mL/100 g/min, respectively. The mean arterial blood pressure (MABP)-CBF reactivity (95% CI) of the normotensive and hypotensive infants were 1.9% (-0.8% to 4.7%)/mm Hg and 1.9% (0.8% to 3.0%)/mm Hg, respectively. The CO2-CBF reactivity (95%CI) of the normotensive and hypotensive infants was 11.1% (6.8% to 15.5%)/KPa deltaPaCO2 and 4.1% (-5.0% to 14.1%)/KPa deltaPaCO2. The implications of these calculated CBF reactivities is that normotensive infants may have intact autoregulation but with a diminished response to fluctuations in PaCO2. The hypotensive infants appear to have attenuated or absent autoregulation with little or no response in CBF to changes in PaCO2.