CEREBRAL AUTOREGULATION DYNAMICS IN PREMATURE NEWBORNS

Background and Purpose Autoregulation of cerebral blood flow is easily disrupted, and loss of this normal physiological reflex may worsen th e neurological outcome for patients undergoing intensive care. We stud ied the response of cerebral blood flow velocity to changes in mean ar terial blood pressure. Methods Cerebral blood flow velocity was measur ed with Doppler ultrasonography in one middle cerebral artery for 5-mi nute periods in 33 babies of gestational age <33 weeks admitted to a n eonatal intensive care unit. Two methods of evaluating autoregulation were developed. The first used linear regression analysis of blood flo w velocity on blood pressure. Records were classified as showing loss of autoregulation if the regression slope was greater than a critical value. A minimum change in mean arterial blood pressure of 5 mm Hg and a critical slope of 1.5 %/mm Hg were found to be adequate criteria fo r the classification of records by the regression method. The second m ethod used coherent averaging, a technique similar to that used in rec ording evoked potentials. Spontaneous transient increases in blood pre ssure were automatically detected, and the instant corresponding to it s maximum rate of rise was used to synchronize averages of the blood p ressure and blood velocity transients. The resulting coherent averages were classified into two groups based on the morphology of the cerebr al blood flow velocity average. Results Whereas the regression method allowed the classification of only 51 of 106 records, the coherent ave rage method classified 101 of 106 (95.3%) of the records available. Fo r 51 records that were classified by both methods, there was agreement in 42 cases (82.3%). The coherent average of all records classified a s having an active autoregulation showed cerebral blood flow velocity returning to baseline much earlier than blood pressure, suggesting tha t autoregulation was taking place within 1 to 2 seconds. This pattern was absent in records in which autoregulation was classified as absent . Conclusions Computerized coherent averaging of the cerebral blood ho w velocity response to spontaneous blood pressure transients offers a promising new method for noninvasive bedside assessment of autoregulat ion in patients undergoing intensive care. The time course for autoreg ulation, when present, is in agreement with that reported in adults.