a 1-month - old , 3.1 kg , male infant was scheduled for surgery due to huge hemorrhagic mass in the left posterior fossa , which extended to the left upper neck through the jugular foramen ( fig . the oxygen saturation ( spo2 ) was 98% on fio2 0.4 , under mechanical ventilation . after standard , non - invasive monitoring was applied , anesthesia was induced with atropine 0.06 mg and thiopental 18 mg . manual ventilation was performed with sevoflurane 8 vol% in 100% oxygen , and rocuronium 1.8 mg was injected for muscle relaxation . the initial endotracheal tube was changed to reinforced endotracheal tube i d 3.0 mm and a 24-gauge catheter was placed in the left radial artery . although the amount of bleeding was not small , the patient 's vital signs remained stable for the first two hours of surgery ( systolic bp 70 - 90 mmhg , pulse rate 120 - 140 bpm , spo2 99% , and temperature 36 ) . blood laboratory tests were performed 30 minutes prior to the first cardiac arrest , as presented in table 1 . during this period , volume replacement consisted of 350 ml of 0.9% normal saline and 1 unit of non - irradiated rbcs ( average unit volume 160 ml , hematocrit 70% ) . after 1 pack of non - irradiated rbcs for a hematocrit of 25% , the patient started to receive irradiated rbcs . blood loss was replaced by rapid intravenous administration of the rbcs . shortly after injection of the rbcs the qrs interval was widened , tall peaked t - waves were observed on v1-v6 leads and the ecg became isoelectric . the anesthesiologists commenced external chest compressions with the 2 thumb - encircling technique , because the child was placed in the prone position . an adequate cardiac output was achieved with this technique , as evidenced via oximetry , arterial pressure and capnography readings . before the cardiac arrest , approximately 80 ml of irradiated rbcs had been transfused for 10 minutes . following the cardiac arrest , the hematocrit was 38% , while the serum k was increased to14.2 mm / l . we infused the mixture of 10 units of regular insulin and 50 ml of 50% dextrose . several doses of epinephrine 10 mcg , atropine 0.1 mg , and cacl2 30 mg were administered , with concomitant chest compressions . seven minutes after the cardiac arrest , the cardiac electrical activity was returned and bp was 70/40 mmhg . ten minutes after recovery of spontaneous circulation , an arterial blood sample was tested , and the k level was found significantly decreased to 6.8 mm / l . at this time , other laboratory data were also quite close to the normal limits , as shown in table 1 . further massive transfusion would have resulted in a potentially fatal , further increase in the serum k level . therefore , we decided to wash these rbcs before transfusion by using a cats which was readily available in the operating room . during the operation , the patient received 27 more units of blood bank rbcs ; each was processed with 0.9% normal saline by the cats before transfusion , but the cell saver device was not used to salvage shed blood . the packed rbcs were filtered , washed , and then reinfused to the patient . utilizing a transfusion set , the packed rbcs were prepared and were mixed with an anticoagulation solution ( 25,000 iu of heparin per each 1 l normal saline ) in the reservoir . when a volume has been collected enough to fill the wash bowl , the washing phase removed cellular debris , plasma free hemoglobin , anticoagulant solution , activated clotting factors , any plasma bound antibiotics , intracellular enzymes , plasma , platelets , and white cells . when the washing phase has been terminated , the device pumped the blood into the reinfusion bag and stopped when the bowl is emptied . after using cats , there was no more electrocardiographic abnormality or cardiac arrest due to transfusion - related hyperkalemia . while waiting for non - irradiated rbcs were ready at the blood bank , we started the first washing process with irradiated rbcs . but , transfusion was performed with non - irradiated rbcs after the preparation of non - irradiated rbcs . on the occasion of arrest , esophageal temperature fell to 34. accordingly , level 1 rapid infusion ( sims level 1 , inc . , rockland , ma ) system was installed that ensures blood products are delivered at the proper temperature . the blood biochemistry at this time is shown in table 1 , as results at ' 6 hr ' following the cardiac arrest . after skin closure , the patient was transferred to the pediatric icu and expired at the icu . during operation , infused fluids consisted of normal saline 750 ml , he s 640 ml , rbcs 28 units , fresh frozen plasma 21 units , platelet concentrate 9 units , and cryoprecipitate 1 unit . the pathogenesis of hyperkalemia - induced cardiac arrest during massive rbcs transfusion is complex , and it depends on the quality of rbcs , the patient , and administration factors . the k concentration in the stored rbc unit may be one of the most important factors . serious patient condition , such as low cardiac output , may increase the k level in the coronary artery during rbcs transfusion . it may also be affected by other patient factors , such as hypocalcemia , hypothermia and acidosis . finally , the amount , the speed , and the route of transfusion are all associated with hyperkalemia - induced cardiac arrest . in our case , rapid transfusion of rbcs was urgently required , and 80 ml of blood was injected through the central line . rapid administration through the central venous access may deliver more concentrated k loads to the coronary circulation than the peripheral venous access , and this could have contributed to provoking cardiac arrest . we would like to pay more attention to the quality of the rbcs , which had been irradiated 5 days prior to transfusion . although irradiation policies vary in different hospitals , the time between irradiation and transfusion should be minimized , particularly in neonates or pediatric patients . irradiation is thought to increase the damage to the membrane bound ionic pumps , leading to increased leak of k into the extracellular space . therefore , it has been demonstrated that irradiated rbcs have significantly higher extracellular k levels than non - irradiated units . similarly , it has been shown that the increase in the k level was more significant in rbcs stored for longer periods of time , prior to transfusion . therefore , both the british committee for standards in haematology blood transfusion task force and the australian & new zealand society of blood transfusion suggested the following guidelines : 1 . red cells may be irradiated at any time up to 14 days after collection , and thereafter stored for a further 14 days from irradiation . however , it is unlikely that a unit of rbcs would have a k concentration higher than 5 mm / l after washing , during 6 hours of storage at 4 if the cells were not irradiated , and for 3 hours if the cells were irradiated . in our case , we transfused the post - washing rbcs within 3 hours of the washing process . it has been demonstrated that processing of stored rbcs with cats effectively removes cellular products and metabolites , while maintaining the physiologic electrolyte range . similarly , the washing of the rbcs results in very low levels of residual k . the cats autotransfusion system has been documented for a mean k elimination rate of 97.3% . there are two representative operational modes for this system , depending on the adequate volume to fill the bowl and the speed of processing . compared with the quality mode , the emergency mode is characterized by faster processing , thereby consuming less washing solution . according to a previous article , quality mode cats reduced the median load of k to 92% of the baseline , whereas the emergency mode cats reduced it to only 70% of that . although we followed the guidelines suggested in several previous studies , our case showed a higher level of k than expected . to evaluate the quality of the washed rbcs , we measured the k level after processing with the cats and the concentration was very high , i.e. 19.9 mm / l . we used the gem premier 3000 system to check for the parameters , and the range of k concentration that could be displayed with this device was from 0.1 to 20.0 mm / l . therefore , we did not know the exact value . nevertheless , according to several previous studies , it is assumed that the k level might be , on average , 40 mm / l in non - irradiated rbcs   and 60 mm / l in the irradiated units . in our case , supposing pre - processing value of 60 mm / l , k was reduced only 67% after processing . in this presented case , we could suggested 3 possible reasons which may have contributed to the relatively high level of k in the washed rbcs . first , we used the emergency mode not the quality mode , because we had to install the device immediately after reversing the cardiac arrest . second , we used relatively old blood and there was a delay of 5 days in the use of these units after radiation ; these factors could both lead to high k concentration in the prewashed rbcs unit . it has been shown that , if the blood product was more than 17 days old , the reduction in the k level after washing it was less efficient than after washing fresh rbc units . third , if the rbcs were transfused as soon as processed and not stored in the collecting bottle , the k concentration could be lower , because there might be an increase of hemolysis in the washed rbcs while stored at room temperature , as previously reported . hence , to strengthen the merits of cats , using quality mode rather than emergency mode is recommended , and fresh rbcs are always preferable , especially in infants . washing should be done just before whenever needed , so that the rbcs would not be left at room temperature for a long time . although the packed rbcs were mixed with a large amount of heparin in the reservoir , the ratios of residual heparin in washed red cells transfused to neonatal or pediatric patients are extremely low . therefore , when properly processed , autotransfusion does not provoke bleeding and can be used safely with neonates and pediatric patients , without concern regarding the residual heparin . in conclusion , cats can be used for decreasing the k level of the rbcs before transfusion , particularly when clinically significant hyperkalemia is anticipated in neonates and infants , and the risk of hyperkalemic cardiac arrest is high .
transfusion - induced hyperkalemia can lead to cardiac arrest , especially when the patient rapidly receives a large amount of red blood cells ( rbcs ) , previously stored for a long period of time , irradiated or both . 
 we report on a case of application of the continuous autotransfusion system ( cats ) to wash rbcs , in order to lower the high potassium ( k+ ) level in the packed rbcs unit , during massive transfusion following transfusion - induced hyperkalemic cardiac arrest . after the washing process using cats 
 , there was no more electrocardiographic abnormality or cardiac arrest due to hyperkalemia . 
 this case emphasizes the potential risk to develop transfusion - related hyperkalemic cardiac arrest , during massive transfusion of irradiated , pre - stored rbcs . 
 cats can be effectively used to lower the k+ concentration in the packed rbcs unit , especially when the risk of transfusion - induced hyperkalemia is high .