Griffin, Steven Charles; (1995) The effect of cerebral substrate load and glucose management on cerebral dysfunction after cardiac surgery. Masters thesis (M.Surg), UCL (University College London).

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Abstract

Over the last decade there has been a general improvement in results of coronary artery bypass graft surgery. This procedure is being offered to a greater number of patients each year. It has been known for some time that subtle neuropsychological changes can occur after cardiac surgery. The aetiology of these neuropsychological changes is thought to be diffuse cerebral damage caused by multiple microemboli entering the circulation during cardiopulmonary bypass. There is evidence from animal experiments and further evidence from clinical stroke literature that hyperglycaemia during an ischaemic cerebral insult may exacerbate that injury. We set out to test the hypothesis that hyperglycaemia during cardiopulmonary bypass may be harmful. 70 patients undergoing elective coronary revascularisation were prospectively randomised into either of two bypass primes, 5% dextrose or Hartmann's solution. The groups were comparable. Neuropsychological assessment was performed before surgery and eight weeks after surgery. Glucose and lactate levels were measured in arterial blood and cerebral effluent blood. During bypass glucose concentrations rose to a mean of 26 mmol/l in the 5% dextrose group and 6 mmol/1 in the Hartmann's group. There were no deaths in either group, there were two clinically evident neurological events, both occurring in the hyperglycaemic group. We found an overall deterioration in neuropsychological performance in both groups at post operative testing compared with pre operative testing. Detailed analysis of the results showed little differences between the groups. When score changes between tests were assessed it was found that in all but one version of the tests more patients in the hyperglycaemic group deteriorated than did the normoglycaemic controls. Analysis of variance however showed no conclusive relationship between prime and neuropsychological outcome. Learning ability was possibly reduced in the hyperglycaemic group after surgery. Hyperglycaemia may be a detrimental factor in the development of post cardiac surgical intellectual dysfunction.

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