Perfusion index in preterm newborns: predictive value for morbimortality and association with Apgar score at five minutes and CRIB-II score

Introduction: Perfusion index (PI) is a noninvasive indirect method of microcirculation measurement that might have a potential to predict morbimortality in preterm newborns. This study aims: 1) to define a critical value for post-ductal PI related to the morbimortality in preterm newborns under 32 weeks; 2) to define a prognostic value for post-ductal PI to predict that risk of morbimortality; and 3) to associate post-ductal PI values with the Apgar score at five minutes and the Clinical Risk Index for Babies II (CRIB-II) score. Material and methods: This is an observational study, with a prospective character, performed in a Neonatal Intensive Care Unit that enrolled 34 preterm newborns with less than 32 weeks admitted between 1st February 2016 and 1st February 2017. Post-ductal PI values were evaluated in the newborns' feet at 24 hours of life. The Apgar score was registered at birth and CRIB-II score was calculated. The other clinical variables, including the presence of an adverse outcome and/or death, was assessed in clinical records. Measurements and main results: We found significant correlations between post-ductal PI values, Apgar score at five minutes and CRIB-II score. The area under ROC curve was higher for CRIB-II score and lower for Apgar score at five minutes. The best cut-off points were: 1) post-ductal PI value <= 0.72; 2) Apgar score at five minutes < 6; and 3) CRIB-II score > 9. Preterms within these cohorts have higher rates of morbimortality. Post-ductal PI values <= 0.72 were an independent predictor of mortality in preterm newborns (p-value = 0.047). Conclusions: This study suggests that post-ductal PI value <= 0.72 at 24 hours of life might be a potential predictor of morbimortality in preterm newborns. However, it is important to clarify that this study has a small representative population which can reduce the accuracy of the results. The very high morbimortality rate in this cohort is another strong limitation for the quality of the results.