VALIDITY OF NORMALIZED INDEX OF HEMOLYSIS IN PEDIATRIC MECHANICAL CIRCULATORY ASSIST DEVICES

Abstract

Mechanical blood trauma is one of the major concerns in development and clinical use of mechanical circulatory assist devices (MCAD). Even moderate hemolysis, which is not an immediate threat to renal function, is an important warning sign of other blood cell potential damage which can cause serious complications (platelet activation, WBC dysfunction, etc.). The common parameter used to assess the hemolytic potential of MCADs in vitro is plasma free hemoglobin (plfHb) released from overstretched or fragmented RBCs. It is often represented by a Normalized Index of Hemolysis (NIH) which is proportional to the rate of plfHb, volume of circulating blood, hematocrit, and inversely proportional to flow rate. We hypothesized that due to complex nature of cellular hemodynamics inside a MCAD, this index might not be scalable to the small MCADs required for pediatric applications, which exhibit flow rates as low as 0.2 - 0.5 L/min. We tested this hypothesis in vitro using a BioMedicus pediatric pump and bovine blood. We found that while an increase in plfHb during a given time was much lower at a flow rate of 0.3 L/min then at flow rate of 2.0 L/min, the computed NIH was several times greater for the lowest flow rate compared to the highest. In general, while the plfHb level linearly increased with an increase in flow rate, NIH increased exponentially with decreasing flow rates. This study motivates the development of revised normalization formulae that may account for small scale devices.