Influence of blood haemoglobin concentration on renal haemodynamics and oxygenation during experimental cardiopulmonary bypass in sheep

Abstract

Aim Blood transfusion may improve renal oxygenation during cardiopulmonary bypass (CPB). In an ovine model of experimental CPB, we tested whether increasing blood haemoglobin concentration [Hb] from ~7 g dL−1 to ~9 g dL−1 improves renal tissue oxygenation. Methods Ten sheep were studied while conscious, under stable isoflurane anaesthesia, and during 3 hours of CPB. In a randomized cross‐over design, 5 sheep commenced bypass at a high target [Hb], achieved by adding 600 mL donor blood to the priming solution. After 90 minutes of CPB, PlasmaLyte® was added to the blood reservoir to achieve low target [Hb]. For the other 5 sheep, no blood was added to the prime, but after 90 minutes of CPB, 800‐900 mL of donor blood was given to achieve a high target [Hb]. Results Overall, CPB was associated with marked reductions in renal oxygen delivery (−50 ± 12%, mean ± 95% confidence interval) and medullary tissue oxygen tension (PO2, −54 ± 29%). Renal fractional oxygen extraction was 17 ± 10% less during CPB at high [Hb] than low [Hb] (P = .04). Nevertheless, no increase in tissue PO2 in either the renal medulla (0 ± 6 mmHg change, P > .99) or cortex (−19 ± 13 mmHg change, P = .08) was detected with high [Hb]. Conclusions In experimental CPB blood transfusion to increase Hb concentration from ~7 g dL−1 to ~9 g dL−1 did not improve renal cortical or medullary tissue PO2 even though it decreased whole kidney oxygen extraction.

Reversal of renal tissue hypoxia during experimental cardiopulmonary bypass in sheep by increased pump flow and arterial pressure

“…The best available evidence, from the recently completed Transfusion Requirements in Cardiac Surgery III (TRICS III) trial, provided no evidence that a liberal transfusion protocol resulted in reduced incidence of AKI compared with a more conservative protocol 32 . Furthermore, we recently found that varying blood haemoglobin concentration across a similar range to that applied in the TRICS III trial did not alter renal cortical or medullary tissue pO 2 in our ovine model of CPB 33 . Taking these recent clinical and experimental observations together, it seems reasonable to conclude that a simple change in standard practice, to simultaneously increase target pump flow and arterial pressure, has the potential to alleviate renal tissue hypoxia and mitigate the risk of post‐operative AKI.…”

“…32 Furthermore, we recently found that varying blood haemoglobin concentration across a similar range to that applied in the TRICS III trial did not alter renal cortical or medullary tissue pO 2 in our ovine model of CPB. 33 Taking these recent clinical and experimental observations together, it seems reasonable to conclude that a simple change in standard practice, to simultaneously increase target pump flow and arterial pressure, has the potential to alleviate renal tissue hypoxia and mitigate the risk of post-operative AKI. The design of our current experimental protocol is comparable to that of two ongoing clinical trials to determine whether increasing target pump flow and MAP during CPB can reduce the incidence of post-operative AKI (ACTRN12619000128190; NCT04084301).…”

Role of Renal Sympathetic Nerve Activity in Volatile Anesthesia's Effect on Renal Excretory Function

“…Renal denervation normalized RBF indicating that at least part of the reduction in RBF during sevoflurane anesthesia is due to RSNA-induced renal vasoconstriction. Anesthesia with isoflurane 57 or propofol 58 reduce renal oxygen consumption in sheep. In theory an elevation in RSNA by sevoflurane may increase renal oxygen consumption by stimulating excessive renal tubular sodium reabsorption and reduce renal oxygen delivery by renal vasoconstriction.…”

Emerging benefits and drawbacks of α2‐adrenoceptor agonists in the management of sepsis and critical illness

“…Therefore, it is conceivable that that intra‐operative neuroinflammation (i.e., activated microglia) may be a contributing factor for post‐operative cognitive dysfunction (Safavynia & Goldstein, 2019). There is also extensive experimental evidence that intraoperative overstimulation of renal SNA during CPB leads to tissue hypoperfusion and hypoxia, particularly within the renal medulla (Evans et al, 2020; Iguchi et al, 2019, 2020; Lankadeva et al, 2019; Lankadeva et al, 2020, 2021). Thus, renal medullary hypoxia, as indirectly assessed by the progressive development of a greater degree of bladder urinary hypoxia during CPB, has been reported in the subgroup of patients that developed post‐operative AKI (Zhu et al, 2018).…”