Heparin-Free Purge: Bicarbonate-Based Purge Solution

Jeremy Moretz, PharmD, BCCP, describes the Impella® heart pump purge system and explains that while Impella has historically required a heparin-based purge solution, a bicarbonate-based purge solution is now a viable alternative.

Heparin-based dextrose purge solution creates a pressure barrier to prevent blood from entering critical components of the Impella heart pump. It also prevents deposition of biomaterial in critical purge gaps. However, Dr. Moretz explains that heparin in the purge solution, in conjunction with systemic heparin requirements, has created a wide distribution in anticoagulation practices. A 2019 study by Reed et al. revealed that centers use a variety of initial heparin purge concentrations (ranging from 0 units/mL to 50 units/mL) and that 41% of high-volume centers do not adjust systemic heparin dose calculation for the dose included in the purge. This heterogeneous practice in Impella patients increases the risk of bleeding and complicates anticoagulation management.

Dr. Moretz shows how purge fluid flows through the Impella pump, explaining that some blood components may potentially reach a small radial purge gap. Without heparin in the purge fluid, biologic material may be deposited, resulting in rising purge pressures and friction leading to high motor current. He explains that this may occur because blood proteins require a certain pH to remain stable. Exposing blood proteins to the acidic environment of dextrose-only purge solution can destabilize the proteins leading to potential deposits on the surface of the purge gaps.

“So, what we actually feel heparin is doing,” Dr. Moretz explains, “is conferring a biochemical protection, by increasing the pH of the purge fluid, stabilizing blood proteins, and increasing charge dissipation providing a repelling force to prevent proteins from depositing and aggregating onto these purge gaps.” He also emphasizes that the heparin in the purge solution is not intended to prevent thrombus formation on other locations of the pump—that’s the job of systemic anticoagulation.

So, what should clinicians do in a setting where they cannot use heparin? The direct thrombin inhibitor (DTI) bivalirudin is often used in the setting of heparin-induced thrombocytopenia (HIT). However, Hohlfelder et al. demonstrated that when bivalirudin was used in the Impella purge solution, 7 of the 9 patients in the study experienced decreases in purge flow and increases in purge pressure, leading to the conclusion that DTIs may be suboptimal in the purge.

Dr. Moretz explains that a bicarbonate-based purge solution (sodium bicarbonate 8.4% 25 mEq in 1L D5W) has been approved by the United States FDA as an alternative to heparin in the Impella purge solution when the patient is intolerant to heparin or when heparin is contraindicated. Bicarbonate may be a viable alternative to heparin because it both neutralizes the acidic pH of dextrose and reduces denaturation and adsorption of blood proteins in the radial gap. Therefore, it promotes adequate pump purge reliability without contributing to the overall systemic heparin exposure. “Collectively this supports purge reliability, it simplifies anticoagulation management, and reduces the risk of bleeding,” Dr. Moretz concludes.