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