Acute kidney injury (AKI) is common in patients treated with microaxial flow pumps (mAFP). Plasma-free haemoglobin (PFHb) due to haemolysis is known to increase kidney injury in a dose-dependent manner. Therefore, we aimed to identify the association between flow pump level, cumulative PFHb exposure, and AKI.

In this retrospective observational study, we analysed consecutive patients aged ≥18 years with cardiogenic shock who underwent mAFP between December 2019 and March 2025 at Saiseikai Kumamoto Hospital, Japan. The primary outcome was AKI. A total of 160 patients were analysed separately: mAFP alone (n = 49) and veno-arterial extracorporeal membrane oxygenation (V-A ECMO) plus mAFP (n = 111). Among patients treated with mAFP alone, higher mAFP pump levels were significantly associated with higher PFHb levels (adjusted P for spline < 0.001). Higher cumulative PFHb exposure was significantly associated with an increased risk of AKI in the mAFP-alone subgroup (adjusted P for spline = 0.03). In contrast, these associations were not observed in patients treated with V-A ECMO plus mAFP. Multivariable analysis demonstrated that a high flow pump level ≥ P8 for 24 h or longer (adjusted risk ratio 3.31; 95% confidence interval 1.67–6.58; P < 0.001), higher peak PFHb, longer duration of mAFP support, higher serum creatinine levels at mAFP initiation, and more severe shock status were significantly associated with an increased risk of AKI occurrence.

Higher mAFP levels are significantly associated with higher PFHb levels, which may increase the risk of AKI in patients treated with mAFP alone.