Cerebral blood flow velocity variability after cardiovascular support in premature babies.

The variability of cerebral blood flow velocity was measured in 20 very low birthweight infants. The area under the curve of the Doppler frequency spectrum was used and was obtained from the anterior cerebral artery in the infants before and after infusions of plasma or dopamine. Both interventions significantly reduced the variability without a demonstrable effect on cardiac output, heart rate, or cerebral blood flow velocity. The reduction was from a median of 13% to 5% after plasma and from 13% to 4% after dopamine. The effect was probably due to an increase in circulating blood volume. It is proposed that appreciable variations in systolic blood pressure occurring in phase with respiration indicate a low central venous pressure in infants, as in adults and animals. The variations could be transmitted to the cerebral circulation in the absence of autoregulation, and their detection in either the aorta or a cerebral artery may prove a useful index of hypovolaemia.