IN-LINE MICROWAVE BLOOD WARMING OF IN-DATE HUMAN PACKED RED-BLOOD-CELLS

Objective: To verify two hypotheses: a) Inline microwave warming of co ld in-date packed red blood cells (RBCs) does not produce significant hemolysis; and b) in-line microwave warming achieves higher outlet tem peratures as compared with current blood warming technology at high fl ow rates (>250 mL/min), Design: Multiple part, randomized, controlled study, Setting: Surgical research laboratory of a large university med ical center. Subjects: Twenty-four units of cold, ready for transfusio n in-date packed RBCs ranging in storage age from 6 to 16 days. Interv entions: Part I: Microwave apparatus outlet, warmed vs. unwarmed. Six units of cold packed RBCs was split into paired samples and infused at 13 mL/min through a 700-watt in-line microwave test apparatus. One pa ired specimen was warmed to 37 degrees C; the other was infused withou t warming (control). Blood was analyzed at the outlet, Part II: Microw ave and countercurrent warming, inlet vs, outlet. Twelve units of cold packed RBCs was analyzed biochemically both before (inlet) and after (outlet) simulated transfusions, Six units was infused through a 900-w att in-line microwave test apparatus at >500 mL/min, Six separate cold units were warmed at this rate using single channel countercurrent wa ter bath warming, Part III: Microwave and counter-current technology, inlet vs. outlet, warmed vs. unwarmed. a) Six units of cold packed RBC s was also analyzed biochemically and infused at 5 mL/min through eith er a microwave or countercurrent water bath warmer. b) Packed RBCs fro m the units used in part a) were allowed to remain stationary in the m icrowave heating cartridge for 15 mins with an activated heating eleme nt, Parallel stationary flow studies were done using the countercurren t blood warmer. Control unwarmed samples were also tested. Measurement s and Main Results: Part I: No statistical differences in hemolysis pa rameters were observed between microwave warmed and unwarmed packed RB Cs. Part II: At high-flow rates, no statistical increases in hemolysis parameters were seen after in-line microwave or countercurrent water bath warming as compared with prewarmed cold controls, Part III: At sl ow-flow rates, nonstatistically significant increases were seen by pas sing the packed RBCs through either test apparatus unwarmed, Packed RB Cs remaining stationary within microwave and countercurrent heating ca rtridges for 15 mins did show biochemical evidence of hemolysis, Mean plasma hemoglobin increased from 14 +/- 1.7 mg/dL in cold prewarmed un its to 57.7 +/- 5.8 mg/dL (p < .05), when warmed in the microwave heat ing cartridge, and to 55.2 +/- 25 mg/dL (p < .05), when warmed in the countercurrent heat exchanger. Outlet Temperature Studies. Part II: Th e in-line 900-watt microwave device warmed cold units from a mean inle t temperature of 8.3 +/- 0.3 degrees C to a mean outlet temperature of 31.8 +/- 0.5 degrees C within 5 sees at a mean flow rate of 556 mL/mi n, At 30 sees, the mean outlet temperature was 33.9 +/- 0.4 degrees C (mean inlet temperature = 9.6 +/- 0.2 degrees C) for microwave warmed packed RBCs as compared with 32.1 +/- 0.5 degrees C (mean inlet temper ature = 9.6 +/- 0.3 degrees C) in countercurrent water bath warmed blo od (p < .05). From 20 to 30 sees, the packed RBCs warmed by microwave were statistically warmer than the countercurrent water bath warmed pa cked RBCs. Conclusions: a) Both in-line countercurrent warming and in- line microwave warming were associated with small increases in paramet ers of red cell damage representing statistically and clinically insig nificant hemolysis. b) Blood sitting in any blood warming device is su bject to statistically significant but clinically irrelevant increases in those parameters. c) At high-flow rates, the in-line microwave dev ice warmed blood to higher outlet temperatures than the single channel countercurrent water bath warmer. This method may represent a clinica l blood warming modality of the near future.