Warning about potential incidents of critical hyperkalemia during massive transfusion protocol after the preservation period of red blood cell products was extended in Japan

BACKGROUND: Recently, the Japanese Red Cross Society approved extension of the preservation period of red blood cell products. Since then, we have already experienced two cases of critical hyperkalemia during massive transfusion protocol (MTP). CASE PRESENTATION: Case 1, a 24‐year‐old man was stabbed in his right posterior chest. Although quick hemorrhage control was completed 35 min after arrival, his potassium level increased from 3.5 to 8.9 mEq/L within 40 min. Case 2, a 44‐year‐old man was transferred to our hospital after a car hit him. We immediately started resuscitation including MTP and opened his abdomen 24 min after arrival. His potassium level increased from 3.5 to 7.8 mEq/L within 38 min. CONCLUSION: Although several other factors might be causing this rise in potassium, we consider the extended preservation periods of red blood cell products to be one cause of these unexpectedly rapid rises in potassium during MTP.