Presented at the Neonatal Society 2002 Spring Meeting.
Narendra A1, Leung T2, Elwell C2, Costeloe K1 and Delpy D2
1 Department of Child Health, Bart’s and the London School of Medicine and Dentistry, Homerton University Hospital, London, UK
2 Department of Medical Physics, University College of London, London, UK
Background: Routine clinical assessment of the total circulating blood volume (TCV) is inaccurate (1). The availability of a method to measure TCV at the cotside soon after birth would help the assessment of critically ill babies.
Objective: The objective of this study was to develop a method to measure TCV using Indocyanine Green (ICG) and Near Infrared Spectroscopy (NIRS).
Methods: Using a commercially available spectrometer with NIRS capability (NIRO-300, Hamamatsu KK), the ICG blood concentration was determined non-invasively after a bolus injection of 0.2mg/kg. The TCV (ml) was calculated by the equation: TCV= Injected ICG dose (mg)/Initial ICG equilibrium concentration (mg/ml) in blood. Paired measurements of TCV were made using the new method and using the HbF dilution technique in newborn infants in clinical need of a blood transfusion as described by Phillips et al (2). The study was approved by the Local Research Ethics Committee and informed written parental consent obtained. The agreement between the two methods was analysed by correlation coefficient and the method of Bland and Altman.
Results: Data from 8 of 25 infants studied were excluded because of poor signal quality or ICG injection error. The median weight of the 17 infants whose data were analysed was 1030 g (range 640-3400 g), 12 (70.6%) were receiving either mechanical ventilation or nasal CPAP and 5 (29.4%) needed supplementary oxygen. There were no ICG related complications.
The mean TCV measured by HbF dilution was 103.6 ml (range 37.7 to 294.0 ml) and by the ICG and NIRS method was 102.8 ml (range 9.3 to 296.1 ml). The mean TCV per kg body weight was 70.2 ml (range 51.2-97.8 ml/kg) and 71.3 ml (range: 13.9-147.9 ml/kg) using HbF dilution and ICG-NIRS method respectively. The correlation coefficient between the two methods was 0.83 (p=<0.001) and the bias was -0.78 ml (SD 42.9 ml).
Conclusion: The TCV can be measured at cot side non-invasively with reasonable accuracy by ICG and NIRS.
References
1. Narendra et al Proceedings of RCPCH Annual Spring Meeting 1998
2. Phillips et al Lancet 1986