In Vitro Evaluation of Resistance and Warming Performance of a Small Blood Warmer on a Continuous Renal Replacement Therapy Circuit

Children on extracorporeal devices are at increased risk of hypothermia and require circuits with lower extracorporeal volume to avoid blood priming. We performed an in vitro study of the enFlow blood warmer to assess its warming performance and impact on circuit resistance at a high blood flow rate. The enFlow was added on the return line of a continuous renal replacement therapy circuit in a closed circuit primed with expired packed red blood cells (40% Hct). Return venous pressure and temperature pre- and post- both enFlow and Prismaflo II were measured at varying blood flow with different combination of the two blood warmers. Each variable was recorded eight times over 2 min. Return venous pressure was higher with the enFlow but was still within clinically usable range (127.5 ± 4.6 vs. 45.3 ± 1.4 mm Hg at 200 mL/min, P < 0.05). The enFlow was able to achieve post-warmer temperature between 34.1 and 35.2°C even at 200 mL/min with blood, lower than what was observed with crystalloid, but still more effective than the Prismaflo II (P < 0.05 vs. enFlow post-warmer temperature) achieving between 32.8 and 34.0°C. Combining both warmers achieved a higher post-warmer temperature between 35.1 and 36.5°C. The enFlow can warm blood at high flow rates with minimal extracorporeal volume increase (~5 mL) and improve hypothermia prevention but may have resistance issues at the highest flows. The use of this device could benefit pediatric practice where smaller extracorporeal volumes are needed and patients are at increased risk of hypothermia.