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Non-invasive measurements in the assessment of normal cardiovascular adaptation in term & near term infants

Presented at the Neonatal Society 2015 Autumn Meeting.

Mahoney L1,2, Seddon P1,2, Wertheim D3, Alvarez JRF1,2, Aiton N1, Rojas-Anaya H1, Rabe H1,2

1 Trevor Mann Baby Unit, Brighton and Sussex University Hospital NHS Trust, Brighton, UK 
2 Brighton & Sussex Medical School, Brighton, UK
3 Kingston University, Kingston, UK

Background: Assessing the adequacy of the circulation in neonates is controversial, with concerns that traditional measures such as blood pressure may not reliably reflect a neonate’s perfusion. Advanced techniques such as near infrared spectroscopy show promise but require specialist interpretation and are not readily available. There is increasing recognition of the potential of functional echocardiography, and emerging evidence for indices derived from pulse oximeter plethysmographic traces in monitoring cardiovascular status in the neonate. This study aims to establish normal values and observe trends for these non-invasive bedside measures in healthy neonates.

Methods: A prospective cohort study of healthy infants <72 hours of age and >33 weeks gestational age (w) admitted to a tertiary NICU for special care. For the first three days of life daily consecutive clinical cardiovascular assessments including capillary refill time and blood pressure were performed. These were combined with daily echocardiographic examinations of superior vena cava flow (SVC), right ventricular outflow (RVO) and ductal patency (1). Measurements of modified plethysmography variability index (mPVI) and pulse transit time (mPTT) were also derived from oxygen saturation probes placed in the post-ductal position. Data are displayed as median and interquartile range (IQR); statistical analysis was performed by Kruskal Wallis and Spearman’s Correlation Coefficient with a p-value <0.05 considered significant. Ethical approval for the study was provided by the London City East NRES committee. Research funding was provided by The Rockinghorse Charity and an EU FP 7-Health grant.

Results: 51 infants with a median gestational age of 34 weeks (IQR 33-39 weeks) and birth weight of 2294 grams (IQR 2035-3173 grams) were included. Median SVC flow decreased significantly from day 1 to day 3 (139 to 106 mls/kg/min, p=0.01). There were trends noted for increases in median RVO (257 to 267mls/kg/min). Furthermore trends for decreases in median mPVI (21.9 to 14.3%) and mPTT values (0.29 to 0.28 seconds) were also found from day 1 to day 3. Mean BP was significantly negatively correlated with RVO & SVCF (r= -0.32, -0.48 respectively, p<0.05).

Conclusion: As well as providing reference values for mPVI and mPTT in term and near term infants, these non-invasive biomarkers appear to reflect the changes involved in neonatal cardiovascular adaptation; namely a decrease in pulmonary and increase in systemic vascular resistance. We are currently investigating the potential role of mPVI and mPTT in the management of the cardiovascularly compromised term and near term infant.

Corresponding author: liam.mahoney@bsuh.nhs.uk

1. Osborn et al. Randomized trial of dobutamine versus dopamine in preterm infants with low systemic blood flow. Journal of Pediatrics 2002; 140: 183-191

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