Quantification of lipid and leucocyte filtration and the effects on cerebral and renal injury markers and pulmonary function during cardiopulmonary bypass

Abstract

Background: Despite the extremely low mortality and morbidity rates of coronary artery bypass graft (CABG) surgery involving cardiopulmonary bypass (CPB), there are a number of pathological injuries believed to be due to the CPB circuit. Lipid Microemboli (LME) are produced when fats are released from bone marrow during a sternotomy, which then mix with blood in the pericardium during surgery. This blood is passed into the CPB circuit and reintroduced into the systemic circulation and is thought to promote an increased inflammatory response and ischaemia-inducing blockages. There are at present no adequate methods of dealing with this problem.

Methods: A randomised controlled trial was undertaken to determine if a new Oxygenator, the RemoweLL, which contains a lipid and leucocyte filter, can effectively remove LME from the patient’s circulation compared with current gold standard CPB technologies and examine the effects on markers of cerebral, renal injury; neuron specific enolase, Cystatin C and pulmonary function. The Null hypothesis was that there would be no difference in peak neuron specific enolase concentrations.

Results: The data presented in this Thesis provide the first biochemical evidence for a direct effect of LME upon neuron specific enolase release, which correlates in a linear fashion with increasing numbers of LME. The filtration of LME does not appear to significantly reduce systemic levels of activated leucocytes, which is reflected in similar pulmonary functions of those patients with and without LME filtration. However, there is evidence of a weak association towards renal protection with LME, with peak Cystatin C clearance lower than non-filtered patients. This met statistical trial stopping criteria.

Conclusions: The RemoweLL CPB system removes significant numbers of LME compared to current CPB technology. Significant differences in the release of neuron specific enolase in the immediate postoperative period have been demonstrated. Furthermore, there is weak evidence towards improved clearance of Cystatin C. Further work is now planned to determine if LME filtration translates into longer-term neurocognitive and renal protection. The statistical differences between groups were so great from neuron specific enolase that the Ethics Committee advised early termination of the trial.

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Identifiers

ORCID for David Voegeli: orcid.org/0000-0003-3457-7177

ORCID for Bronagh Walsh: orcid.org/0000-0003-1008-0545

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