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Relationship between blood pressure and blood flow in the first postnatal day in preterm infants

Presented at the Neonatal Society 2004 Autumn Meeting (programme).

Groves AM1, Kuschel CA1, Knight DB1, Skinner JR2

1 Newborn Services, National Women's Health, Auckland City Hospital, Auckland, New Zealand
2 Paediatric Cardiology, Starship Children's Hospital, Auckland, New Zealand

Background: Low cerebral blood flow has been linked to cerebral injury in preterm infants. Infants are especially at risk in the first 24 hours. Arterial blood pressure (BP) remains the most frequently monitored indicator of neonatal circulatory status - a normal or high BP being taken to indicate a normal systemic blood flow. The relationship between BP and systemic blood flow in the first postnatal day is unclear.

Aims: To examine the relationship between invasively monitored arterial blood pressure and systemic perfusion as assessed by left ventricular output (LVO) and superior vena cava (SVC) blood flow in the first day of postnatal life in preterm infants.

Methods: Infants <31 weeks gestation were part of a cohort examined by echocardiography at 5, 12, 24 and 48 hours postnatal age. LVO was assessed by standard methods. SVC flow was assessed as described previously (1). Infants in whom invasive arterial blood pressure monitoring was requested by the attending clinician had measures of arterial blood pressure downloaded every 60 seconds, and averaged over the period of echocardiography. The relationships between measures of blood flow and blood pressure were examined using univariate regression analysis. The local regional ethics committee approved the study and informed parental consent was obtained in all cases.

Results: Eighty infants were studied, of whom 34 (43%) had readings of invasively monitored BP downloaded every 60 seconds during echocardiography. These 34 infants had a median (range) gestation of 27 (24-29) weeks and birth weight 880 (510-1430) grams. LVO was not associated with blood pressure at 5 hours (p=0.27), 12 hours (p=0.12) or 24 hours (p=0.75) postnatal age. Low SVC flow volume was associated with high BP at 5 hours (p=0.04, figure) and at 12 hours (p=0.06, figure), but not at 24 hours postnatal age.

Figures: Relationship between invasively monitored arterial blood pressure and
volume of SVC blood flow at 5 and 12 hours postnatal age in 34 preterm infants

Conclusion: Invasively monitored arterial blood pressure is not predictive of left ventricular output in the first postnatal day in preterm infants. Volume of SVC flow may be inversely related to BP at this time. Neither left ventricular output nor SVC flow volume are positively related to arterial blood pressure in the first 24 hours of postnatal life in preterm infants.

Acknowledgements: Supported by the Starship Foundation and The Southern Trust

1. Kluckow M, Evans N. Superior vena cava flow in newborn infants: a novel marker of systemic blood flow. Arch Dis Child Fetal Neonatal Ed 2000;82(3):F182-7

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