Blood passage through medical devices can cause hemolysis and increased levels of plasma free hemoglobin (pfH) that may lead to adverse effects such as vasoconstriction and renal tubule injury. Although the hemolytic potential of devices is typically characterized in vitro using animal blood, the results can be impacted by various blood parameters, such as donor species. Moreover, it is unclear how to relate measured in vitro hemolysis levels to clinical performance because pfH accumulation in vivo depends on both hemolysis rate and availability of plasma haptoglobin (Hpt) that can bind and safely eliminate pfH. To help to address these uncertainties, we developed a biokinetic model linking in vivo hemolysis rates to time-dependent pfH and Hpt concentrations. The model was initially parameterized using studies that characterized baseline levels and evolution of pfH and Hpt after introduction of excess pfH in humans. With the biokinetic parameters specified, the model was applied to predict hemolysis rates in three patient groups undergoing cardiopulmonary bypass surgery. The congruity of the model with these clinical data suggests that it can infer in vivo hemolysis rates and provide insight into pfH levels that may cause concern. The model was subsequently used to evaluate acceptance threshold hemolysis values proposed in the literature for chronic circulatory assist blood pumps and to assess the impact of patient weight on pfH accumulation using simple scaling arguments, which suggested that identical hemolysis index values may increase pfH levels nearly threefold in 10 kg pediatric patients compared with 80 kg adults.
From the *Center for Devices and Radiological Health, Silver Spring, Maryland
†Center for Biologics Evaluation and Research, Food and Drug Administration, Silver Spring, Maryland.
Submitted for consideration October 2017; accepted for publication in revised form March 2018.
Disclosure: The authors have no conflicts of interest to report.
Funding for this project was provided by the U.S. Food & Drug Administration.
The findings and conclusions reported herein have not been formally disseminated by the Food and Drug Administration and should not be construed to represent any agency determination or policy. The mention of commercial products, their sources, or their use in connection with material reported herein is not to be construed as either an actual or implied endorsement of such products by Department of Health and Human Services.
Correspondence: Richard A. Malinauskas, Center for Devices and Radiological Health, U.S. Food & Drug Administration, Building 62, Room 2108, 10903 New Hampshire Ave., Silver Spring, MD 20993. Email: Richard.Malinauskas@FDA.HHS.GOV.