Simple and reliable method for predicting extracorporeal membrane oxygenation flow rates and circuit pressures.

BACKGROUND: Venovenous extracorporeal membrane oxygenation (ECMO) is essential for patients with severe respiratory failure who do not respond to conventional mechanical ventilation. Adequate ECMO flow and safe circuit pressure are critical; however, cannula selection, which has a great impact on these factors, is often based on empirical judgment. This study aimed to develop a simple predictive method based on fluid dynamics for estimating ECMO flow rate and circuit pressures (P1: pre-pump, P2: pre-oxygenator, and P3: post-oxygenator). This experimental predictive model study compared the calculated and measured ECMO parameters across 36 combinations of cannula sizes, pump speeds, and bed heights. A laboratory-based ECMO circuit model was assembled with various drainage and return cannulas, an oxygenator, tubing, and a centrifugal pump. The circuit was primed with a 33% glycerin solution and tested across the 36 combinations. A four-step prediction method was applied: (1) modeling the pressure-flow relationships of ECMO components and the pump using manufacturer data; (2) identifying the expected flow rate by locating the intersection of the total circuit resistance and pump output curves; (3) sequentially calculating pressure drops across the circuit; and (4) adjusting pressures based on bed height.

RESULTS: The predicted flow rate and circuit pressure values were compared to experimental measurements across the 36 combinations. The calculated and measured values showed strong agreement (R2 = 0.96-0.97), and predictions were significant. Notably, bed height alterations were confirmed to affect circuit pressure but not flow rate.

CONCLUSIONS: Our newly developed method reliably predicts the ECMO flow rate and circuit pressure. Hence, it can be considered a valuable tool for preemptively selecting the optimal cannula size for ECMO, thus improving patient safety and circuit management. Furthermore, it may be a valuable educational tool, making complex hemodynamic concepts more intuitive for trainees.