The relation between inferior vena cava oxygen saturation, superior vena cava flow, fractional oxygen extraction and haemoglobin affinity in sick newborns: a pilot study.

Aim: To determine whether inferior vena cava oxygen saturation (UvO2) or lower-body fractional oxygen extraction (FOE) could detect poor cardiac output in newborns.

Methods: UvO2 and arterial oxygen saturation (SaO2) were measured simultaneously with echocardiographic determination of superior vena cava blood flow (SVC flow) at <12, 12-24 and >24 h. Haemoglobin concentration ([Hb]), haemoglobin oxygen affinity (HOA) and lactate were measured and FOE calculated.

Results: 56 studies in 17 infants, gestational age (median (range)) 26 wk 4 d (23 wk 2 d-42 wk 3 d): UvO2 (mean (SD)) was 84.9% (5.0), 77.6% (9.2) and 81.7% (12.9) at <12, 12-24 and >24 h, respectively; SVC flow (mean (SD)) increased from 71.7 (33) to 85 (66) and 123 (88) ml/kg/min at <12, 12-24 and >24 h, respectively. Despite a fall in mean [Hb], mean upper-body oxygen delivery increased due to increases in both SVC flow and arteriovenous content difference. There was a negative correlation between [Hb] and FOE. Infants with high HOA had significantly lower FOE.

Conclusion: Measurement of UvO2 is feasible in newborns. Changes to SVC flow and arteriovenous content difference lead to improvements in oxygen delivery. The interaction of HOA warrants further study.