6.2 Intra-operative
There is increasing evidence that a low CPB target temperature and a prolonged CPB duration are associated with post-operative KDIGO-3 development, particularly among patients with raised pre-operative serum creatinine levels. Recent studies have suggested that rewarming, rather than cooling, can lead to higher metabolic demand. Longer duration required for the rewarming process further subjects the kidney to ischaemia thereby resulting in renal injury. By raising the target temperature, the risk of KDIGO-3 development can be reduced by 16% per degree Celsius increase.43
Furthermore, findings from a prospective randomized controlled trial reported a 22% relative risk reduction in the rate of perioperative AKI, after using nitric oxide (NO) instead of nitrogen in patients undergoing multiple valves cardiac surgery. NO is a potent vasodilator and promotes tissue perfusion in the body. Based on this study, prolonged CPB leads to haemolysis, increased plasma Hb concentration, and NO consumption compared to before surgery. By exposing the plasma to 80 parts per million NO gas during and after surgery for an additional 24hrs, plasma NO depletion can be prevented, therefore reducing AKI risk and transition to stage 3 CKD at 1 year and 90 days post-surgery. This occurs due to the oxidization of plasma Oxy-Hb to Met-Hb by NO gas, thus preventing systemic and pulmonary vasoconstriction and kidney injury.43
Based on reports from animal and human trials, the accumulation of leukocytes and neutrophils in the kidneys have a protective role in tubular injury in the setting of AKI. Results from a recent meta-analysis of 6 RCTs (n=374) determined that leukocyte filters can reduce the incidence of CS-AKI (OR: 0.18; 95% CI: 0.05-0.64). However, a possible weakness of this study was the small sample size used in the RCTs. Further research is required to validate the efficacy of leukocyte filters in preventing CS-AKI.45 Similarly, the administration of intraoperative natriuretic peptides to prevent renal ischemia-reperfusion injury, seem to lower the incidence of postoperative AKI in various trials. However, large RCTs are still needed to confirm these findings.41