Comparison of electrical impedance and 133xenon clearance for the assessment of cerebral blood flow in the newborn infant.

The peak amplitude of pulsatile cerebral electrical impedance (delta Zp) was compared with simultaneous 133xenon clearance estimations of cerebral blood flow (CBF infinity) on 28 occasions in nine infants receiving assisted ventilation who had changes in PaCO2 and thereby presumably in cerebral blood flow. Percentage changes from one measurement to the next in each infant were compared. Using linear regression the relationship was delta Zp = 0.5 CBF infinity-1.5 with r = 0.67. The 95% confidence interval for the regression coefficient was 0.2-0.8 and the mean residual was 28%. Changes in cerebral blood flow in these clinical conditions were similarly detected by the two methods but delta Zp underestimated the magnitude of the change in comparison with CBF infinity and its accuracy was insufficient to allow conclusions about the magnitude of small changes in cerebral blood flow in individual infants.