Increased energy expenditure after dilutional exchange transfusion for neonatal polycythemia

OBJECTIVE: Hypothermia is a known symptom of neonatal polycythemia (NP) and its pathophysiology is unclear. The effect of partial dilutional exchange transfusion (PET) upon resting energy expenditure (REE) is unknown. We aimed to test the hypothesis that PET leads to an increase in REE. STUDY DESIGN: 11 patients with NP who underwent PET and 10 controls without polycythemia were studied. NP was defined as a venous HCT >/=0.65. Per protocol, symptomatic infants and/or those with venous HCT > or =0.70 underwent PET. REE was measured just prior and 23 hours after PET in patients with NP and at identical ages in the control group. Infants were studied in a skin servo controlled radiant warmer, while clinically and thermally stable, prone and asleep. Measurements were stopped during body movements (less than 5% of the time of measurement). Metabolic measurements were performed by indirect calorimetry, using the Deltatrac II Metabolic monitor (Datex-Ohmeda, Helsinki, Finland). This instrument uses the principle of the open circuit system that allows continuous measurements of oxygen consumption (Vo(2)) and carbon dioxide production (Vco(2)) using a constant flow generator. REE measurements were corrected for the infant weight (Kcal/kg/d). Comparison of REE values between groups was performed using paired Wilcoxon ranked test. RESULTS: Patients with and without NP had nearly identical baseline REE. In patients with NP, REE increased from 44.0 +/- 6.6 Kcal/Kg/d to 48.3 +/- 5.1 Kcal/Kg/d after PET (P<0.05). Furthermore, the increase in REE following PET correlated inversely with the decrease in hematocrit. There was no significant change in REE over time in the control group. In the NP group, symptomatic infants (n=5) had a significantly greater increase in REE following PET than non-symptomatic ones (1.4 +/- 6.3 vs. 7.8 +/- 4.9 Kcal/Kg/d, p<0.05). CONCLUSIONS: Energy expenditure of polycythemic infants increases following PET, in a manner proportional to the decrease in hematocrit. Symptomatic polycythemic infants have a greater rise in REE following PET than non-symptomatic ones. We speculate that polycythemia leads to a decreased REE that might be remedied by PET.