Microvascular flow, clinical illness severity and cardiovascular function in the preterm infant

Objectives: To characterise the relationships between peripheral microvascular blood flow and measures of physiological and cardiovascular function in preterm infants in the immediate newborn period. Design: Prospective observational cohort study. Setting: Tertiary neonatal intensive care unit, New South Wales, Australia. Patients: Ninety-six preterm neonates (24-36 weeks' gestation) admitted to the neonatal intensive care unit. Main outcome measure: Relationship between laser Doppler-derived basal microvascular blood flow, functional echocardiographic measurements of cardiovascular status, mean arterial blood pressure and clinical illness severity at 24, 72 and 120 h of age. Results: At 24 h of age, multiple linear regression revealed a significant positive relationship, independent of gestational age, between baseline microvascular blood flow and clinical risk index for babies (CRIB II) score (r² = 0.442). Microvascular blood flow was inversely related to mean arterial blood pressure (r² = -0.563), and correlated positively with left ventricular output (r² = 0.435). Microvascular blood flow continued to exhibit a significant inverse relationship with mean arterial blood pressure (r² = -0.4) at 72 h of age, but by 120 h no significant relationships were evident. Conclusions: This is the first study to show that baseline microvascular blood flow in premature infants exhibits significant relationships with clinical illness severity and cardiovascular function in the immediate postnatal period. The effects of temporal and functional changes in the microvasculature on cardiovascular adaptation warrant further detailed study.