Free heme and hemopexin in acute kidney injury after cardiopulmonary bypass and transient renal ischemia

Navigating Hemolysis and the Renal Implications of Hemoglobin Toxicity in Cardiac Surgery

Acute kidney injury (AKI) affects 20% to 30% of patients undergoing cardiac surgery with cardiopulmonary bypass (CPB). This review synthesizes clinical evidence indicating that CPB-induced hemolysis plays a pivotal role in the development of AKI. The pathogenesis involves cell-free hemoglobin, which triggers oxidative stress, depletes nitric oxide, and incites inflammation, culminating in renal damage. We highlight emerging interventions, including haptoglobin administration, nitric oxide supplementation, and antioxidants, which are promising in reducing the toxicity of cell-free hemoglobin and the incidence of AKI. Current clinical data support the potential efficacy of these treatments. Our analysis concludes that sufficient proof of concept exists to further develop and test these targeted therapies for preventing hemoglobin-induced AKI in patients undergoing CPB.

Cardiopulmonary bypass-induced hemolysis is linked to acute kidney injury in cardiac surgery. Emerging therapies targeting cell-free hemoglobin, like haptoglobin, nitric oxide, and antioxidants, show promise in reducing kidney injury, highlighting the need for further research.

Carboxyhemoglobin as Potential Biomarker for Cardiac Surgery Associated Acute Kidney Injury

OBJECTIVES

Carboxyhemoglobin (CO-Hb) is a marker of hemolysis and inflammation, both risk factors for cardiac surgery-associated AKI (CSA-AKI). However, the association between CO-Hb and CSA-AKI remains unknown.

DESIGN

A retrospective cohort study.

SETTING

Tertiary university-affiliated metropolitan hospital: single center.

PARTICIPANTS

Adult on-pump cardiac surgery patients from July 2014 to June 2022 (N = 1,698).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Patients were stratified into quartiles based on CO-Hb levels at intensive care unit (ICU) admission. A progressive increased risk of CSA-AKI was observed with higher CO-Hb levels at ICU admission. On multivariable logistic regression analysis, the highest quartile (CO-Hb ≥ 1.4%) showed an independent association with the occurrence of CSA-AKI (odds ratio 1.45 compared to the lowest quartile [CO-Hb < 1.0%], 95% CI 1.023-2.071; p = 0.038). Compared to patients with CO-Hb <1.4%, patients with CO-Hb ≥ 1.4% at ICU admission had significantly higher postoperative creatinine (135 vs 116 μmol/L, p < 0.001), higher rates of postoperative RRT (6.7% vs 2.3%, p < 0.001) and AKI (p < 0.001) on univariable analysis and shorter time to event for AKI or death (p < 0.001).

CONCLUSIONS

CO-Hb ≥ 1.4% at ICU admission is an independent risk factor for CSA-AKI, which is easily obtainable and available on routine arterial blood gas measurements. Thus, CO-Hb may serve as a practical and biologically logical biomarker for risk stratification and population enrichment in trials of CSA-AKI prevention.

Red blood cells as oxygen carrier during normothermic machine perfusion of kidney grafts: Friend or foe?

Renal ex vivo normothermic machine perfusion (NMP) is under development as an assessment tool for high-risk kidney grafts and as a means of achieving more physiologically accurate organ preservation. On-going hemolysis has been reported during NMP, as this technique relies on red blood cells for oxygen delivery. In this study, we confirm the occurrence of progressive hemolysis during 6-hour kidney NMP. NMP-associated erythrostasis in the glomeruli and in peri-glomerular vascular networks points to an interaction between the red blood cells and the graft. Continuous hemolysis resulted in prooxidative changes in the perfusate, which could be quenched by addition of fresh frozen plasma. In a cell-based system, this hemolysis induced redox stress and exhibited toxic effects at high concentrations. These findings highlight the need for a more refined oxygen carrier in the context of renal NMP.