Cerebral Resistance Index is less predictive in hypothermic encephalopathic newborns

Abstract

Aim: Neonatal hypoxic-ischaemic encephalopathy (HIE), if severe, may involve cerebral vasoparalysis. In HIE, Pourcelot's cerebral vascular resistance index (RI) below 0.55 (by Doppler ultrasound) from published literature at normothermia predicted poor outcome with a positive predictive value (PPV) of 84%. The aim of this study was to re-assess RI as a predictor of outcome in HIE during hypothermia.

Methods: One hundred and twenty-five infants with HIE treated with hypothermia with outcome data and at least one measurement of RI at 24 h or later were included. Poor outcome was defined as death or severe disability.

Results: Positive predictive value of low RI (≤ 0.55) was 60% (95% CI 45%, 74%), while the negative predictive value (NPV) was 78% (95% CI: 67%, 86%). The PPV during hypothermia is significantly lower than the pooled PPV of 84% (95% CI 73%, 91%) from all published studies of RI at normothermia. NPV during hypothermia and normothermia was similar [76%, (95% CI 69%, 82%)].

Conclusion: Low RI is significantly less predictive of poor outcome during hypothermia than normothermia. The lower PPV may be because hypothermia affects cerebral vasculature or protects the brain solely at a molecular and cellular level. Infants, who would have been predicted from their RI to have poorer outcome at normothermia, have better outcome when cooled.