Method for early and repeated measurement of blood volume in newborn piglets

There are limited studies of changes in blood volume after birth in preterm infants. This study aimed to develop a method to measure blood volume in preterm piglets that could potentially be adapted for use in a clinical setting. A tracer dilution method using fluorescent-labeled dextran was optimized and tested in vitro and in vivo in preterm (98/115 days gestation) and term piglets. In vitro, the dextran method had an error of individual samples ranging from -14.2% to +15.9% with a mean bias of +0.1%. Smaller tracer size (150 kDa) significantly overestimated volume with a bias of >20%, compared with the 500 kDa tracer. Using three or four sampling time points fitted with a linear or log-linear curve had only small bias for all groups (<2.3 mL/kg), despite significant differences compared with using a one-phase decay curve fitted to 2 h of sampling (14 time points). Single samples at 10 or 20 min after injection had biases of +4 ± 4mL/kg (range: -7 to +14 mL/kg) and +8 ± 4 mL/kg (range: -5 to +19 mL/kg), respectively. Repeated measures are feasible from birth with minimal blood sample losses (0.5 mL). In neonates, the dextran tracer method requires use of a large tracer size (500 kDa) with multiple, timed samples (minimum 3 samples over the first 40 min after injection). This simple fluorescent-labeled dextran method prevents overestimation of blood volume in neonates and allows for repeat measurements from birth. This method can be adapted for use in preterm infants, which is critical to testing the efficacy of interventions designed to support preterm blood volume.NEW & NOTEWORTHY There are very limited studies on blood volume in preterm babies. Early, repeated measurements of blood volume are essential to understand rapid changes that occur after birth and test interventions to manage cardiovascular function. This study found that blood volume in neonates is overestimated unless large tracers with multiple, timed samples are used to overcome rapid tracer loss from the circulation. This simple method can be adapted for use in preterm infants.