TITLE: DOES CITRATE PROTECT RECIPIENT FROM TRANSFUSION HYPERKALEMIA?

AUTHORS: John M. Watkins-Pitchford, MB BS, FRCA
AFFILIATION: Yale Univ School of Medicine, New Haven, CT.

INTRODUCTION: Packed Red Blood Cells (PRBC) from refrigerated storage have high extra-cellular potassium levels, which only rarely cause significant hyperkalemia in the recipient. A fast potassium ion-selective electrode was used to investigate a possible clinical mechanism, the specific effect of citrate.
METHODS: 20ml samples of the author's blood were mixed with ACD (Na citrate, Citric Acid, Dextrose in 5.26ml water) to mimic ACD stored blood. After two weeks storage at 2°C, the samples were agitated to re-suspend the cells, before 1ml aliquots were withdrawn for testing. Test A: 1ml blood was incubated, and magnetically stirred, open to air at 37°C for 1 hour. A calibrated potassium ion-selective electrode (ISE) continuously monitored K+. Test B: 0.1ml of ACD were added to the sample from Test A, while the K+ was recorded continuously. Test C: 0.1N NaOH was added to raise the pH of freshly citrated blood to 7.5, while the K+ was recorded as before. Test D: 0.18mg NaCitrate were added to 2-day stored acid blood.
RESULTS: Each test was performed in triplicate. Test A: Before incubation K+ 12.4mmol/l, after 60 mins @ 37°C, 12.0, a fall of 0.4mmol/l. Test B: Before citrate addition, 12.0mmol/l, after, 9.1mmol/l, a fall of 2.9mmol/l. Test C: Before NaOH addition 3.31mmol/l, after 3.17mmol/l, a fall of 0.14mmol/l. Test D: Before Na Citrate addition, 3.53mmol/l, after 2.10mmol/l, a fall of 1.43mmol/l.
DISCUSSION: The addition of citrate to both stored and fresh blood caused large fall in extracellular potassium, whereas the alkalinization of an acid sample by NaOH, produced very little change, as did incubation at 37°C. Thus simple pH and temp- erature changes seem insufficient to explain the potassium shift observed. The addition of citrate thus appears central to the mechanism of the change. Is it possible that citrate protects the transfusion recipient from hyperkalemia by this mechanism? The K+ changes were complete in a few milliseconds, so the mecha- nism would be speedy enough even for blood transfused through central lines.
REFERENCE:

1. Howland WS in Nusbacher J, Ed, Massive Transfusion, Amer Assoc Blood Banks, 1978:17.