Evaluation of haemolysis and its impact on renal dysfunction during Impella CP support using plasma-free haemoglobin (PFHb) - a single cntre retrospective cohort study-

Background Impella is a micro-axial-flow pump that is effective in the treatment of cardiogenic shock. However, its high-speed rotation increases the risk of haemolysis and subsequent renal failure. Previous studies have defined haemolysis based on elevated LDH levels or the presence of haemoglobinuria, but these criteria may underestimate the incidence of haemolysis. Haemolysis is generally evaluated using the haemolysis index, which is determined by biochemical auto-analysis based on the red colour change measured by absorbance. However, because of its low sensitivity, PFHb measurement is recommended for accurate diagnosis of haemolysis. Purpose This study aimed to investigate the incidence of haemolysis in Impella CP support, its determinants, and its association with renal dysfunction using PFHb measurements. Method A survey was conducted between Dec 2019 and Jan 2025 on 178 patients who had received an Impella CP implant at our facility. During the Impella support period (up to 10 days), PFHb was measured twice daily using the AMCO Plasma/Low Hemoglobin HemoCue® device. Haemolysis was defined as a PFHb level of 0.06 g/dL or greater, at which point 4,000 units of haptoglobin were administered. The incidence of haemolysis based on PFHb was compared with the incidence of haemolysis determined by the conventional haemolysis index threshold of 41 mg/dL measured by the TBA-FX8 analyser. The relationship between the Impella support setting for each patient and the PFHb level was analysed. In addition, we also investigated the risk factors for acute kidney injury (AKI) requiring renal replacement therapy (RRT). Results The mean age of the patients was 70 ± 13 years. 64% underwent ECPELLA, and 16% developed AKI requiring RRT. During Impella support, haemolysis was diagnosed in 28% of the patients based on PFHb levels, whereas only 20% were diagnosed using the hemolysis index. We analyzed 1,265 data points from patients receiving Impella or ECPELLA to assess the relationship between PFHb levels and Impella support levels. Impella support levels were categorized as low (P1–3), middle (P4–6), and high (P7–9). PFHb levels were significantly higher at high support levels than at low and medium support levels, with similar trends observed in both the Impella and ECPELLA groups. Patients requiring RRT had significantly higher maximum PFHb levels than those who did not (0.19 vs. 0.07 g/dL, p < 0.001). Multivariate Cox proportional hazards analysis identified maximum PFHb levels and red blood cell transfusion volume as independent predictors of AKI requiring RRT. Conclusions Haemolysis was significantly increased at higher Impella support levels (≥P7) in both the Impella and ECPELLA groups. Additionally, elevated PFHb levels and greater transfusion volumes are significantly associated with severe renal dysfunction. Further prospective studies are needed to clarify the extent of renal protection provided by early administration of haptoglobin.