Identifying functional autoregulation presents a difficult problem, especially in neonates, in whose care large variations in arterial blood-pressure (ABP) should be avoided. We present the application of a new technique involving the study of the dynamic response to spontaneous, relatively small ABP transients, which is applicable at the bed-side.

Methods: Fourteen babies from neonatal units in Rio de Janeiro, Brazil, were studied (9 term - 3070 +/- 326g Footnote 1 and 5 premature - 990 +/- 377g), whose major diagnosis was neonatal asphyxia. Cerebral blood-flow velocity (CBFV) was measured in the middle cerebral artery using Doppler ultrasound over a period of approximately 10 minutes, at various intervals over the first 48 hours of life. Simultaneously, intra-arterial ABP was recorded. Beat-to-beat mean CBFV (MCBFV) and ABP (MABP) were calculated and spontaneous transients in ABP were identified. Following the technique ofPanerai et al., (1995), the transients in MABP, accompanied by transients in MCBFV were coherently averaged in each patient. Early return of MCBFV to base-line indicates functional cerebral autoregulation.

Results: Of the 13 babies examined, suitable MABP transients were identified in 7 (4 term and 3 preterm) cases. Of the term babies, one showed clear evidence of functional autoregulation and had normal neurological outcome (7 days of life), in the remaining three, the neurological outcome was normal (10 months), abnormal (7 days) and one died (first day of life). All preterms showed impaired autoregulation and died within the first week.

Conclusion: The technique applied requires minimal manipulation of the babies, but the absence of suitable spontaneous transients restricted the analysis to approximately half the sample. In these cases of severe asphyxia examined, most showed impaired autoregulation and poor outcome. A possible link between autoregulatory function and neurological outcome is being investigated further.