Association of Sodium Homeostasis with Blood Transfusions During Liver Transplantation (2016)

To the Editor We read with interest the article by Hudcova et al.1 who retrospectively investigated the relation of intraoperative serum sodium changes (ΔNa) with anesthesia management and short-term postoperative outcomes in patients undergoing liver transplantation. They observed that the increase of sodium was significantly related to the amount of red blood cells (RBCs) and fresh frozen plasma (FFP) transfused during surgery. Liver transplantation often requires the need for frequent blood transfusion. Although data on the impact of RBC and FFP administration on electrolytes are limited, the correlation of increasing sodium levels with RBC administration stands in contrast to available data on sodium content of packed RBCs. It has been consistently shown that sodium concentration in RBC units decreases steadily during storage, resulting in a sodium concentration of approximately 120 to 125 mmol L−1 after 14 days.2,3 One of the contributing mechanisms to the decrease in sodium concentration in RBCs during storage is an inoperative membrane sodium–potassium pump at the storage temperature of 4°C, and subsequently potassium and sodium ions equilibrate through the semipermeable cell membrane.4,5 In this context, it takes up to 24 hours to restore the physiologic intracellular and extracellular sodium concentrations of RBC after transfusion.5,6 In contrast, FFP has been shown to contain an unphysiologic high sodium concentration with up to 172 ± 7 mmol L−1 because of the added preservative solution containing a high load of sodium citrate.7 In this context, from a rational view and in case of a causal relationship, transfusion of FFP might be a more important determinant to the observed increase in sodium in the study by Hudcova et al. than transfusion of RBCs. The contrasting findings by Hudcova et al. might be due to the study design comparing only preoperative and postoperative sodium values disregarding the relationship of ΔNa with the variables of interest at different time points during surgery. Furthermore, according to their article, it is unknown whether the classical Spearman rank correlation coefficient without extension or with partial rank correlation was used to assess the relationship of ΔNa with the variables of interest. The latter would have allowed removing the effect of other contributing variables. In our opinion, the association of ΔNa with RBCs and FFP during surgery can only be assessed appropriately if multiple blood gas samples are obtained during the course of surgery and regression analysis for longitudinal data with adjustment for multiple measurements per patient is performed. Oliver Hunsicker, MD Department of Anesthesiology and Intensive Care Medicine Campus Charité Mitte and Campus Virchow-Klinikum, Charité University Medicine Berlin Berlin, Germany Alexander Krannich, BSc Department of Biostatistics Coordination Center for Clinical Trials, Charité University Medicine Berlin Berlin, Germany Claudia Spies, MD, PhD Aarne Feldheiser, MD Department of Anesthesiology and Intensive Care Medicine Campus Charité Mitte and Campus Virchow-Klinikum, Charité University Medicine Berlin Berlin, Germany [email protected]