57 Use of Nirs to Detect Cerebral Autoregulation: A Validation Study in Piglets

Abstract

BACKGROUND AND Aims: Impaired cerebral autoregulation (CA) is common and associated with brain damage in sick neonates. Frequency analysis between spontaneous changes in arterial blood pressure (ABP) and cerebral NIRS has been used to detect the presence and estimate the magnitude of this impairment. Coherence (i.e. correlation in the frequency-domain) detects its presence. Gain estimates its magnitude by analysing the magnitude of ABP-variability passing from systemic to cerebral circulation. We aimed to validate this dynamic method by comparing it with a static measurement of CA-capacity in piglets. Methods: Piglets (n=7, age 1-2 days) were anaesthetized and monitored during normo- and hypovolaemia. In both states, dynamic CA was estimated with analysis of coherence and gain between spontaneous changes in ABP and cerebral oxygenation (NIRS) in four 10-minutes epochs. Both before and after this dynamic period, static CA-capacity was estimated from changes in cortical flux (laser-Doppler probe) to induced rises in ABP by repeated inflations of a thoracic aorta balloon for 30 seconds. Subsequently, CA-capacity was calculated as %ΔCVR/%ΔABP (i.e. percentage of full autoregulatory capacity), where CVR (i.e. cerebral vascular resistance) was estimated as ABP/Doppler flux. Results: Linear regression demonstrated an inverse relationship between coherence and static CA-capacity (R2=38%, P=0.02). Likewise, linear regression indicated an inverse, however weak, relationship between gain and static CA-capacity, with R2 increasing from 1% (P=0.72) to 55% (P=0.09) when measurements with insignificant coherence were excluded. Conclusions: Frequency analysis of spontaneous changes in ABP and cerebral NIRS is associated with cerebral autoregulation as measured with laser-Doppler during ABP-challenge.