Perioperative Versus Postoperative Glycemia Control in Cardiac Surgery Patients

It has been for a long time a well known phenomenon that the acute stress of organism induced for instance by an extensive surgery often leads to hyperglycemia, even in patients without a previous history of diabetes. Also well known are the common pathophysiological mechanisms, which are responsible for this, such as enhanced hepatic gluconeogenesis, impaired insulin secretion and decreased insulin sensitivity due to anti-insulin effect of stress hormones and proinflammatory cytokines, or a change of glucose excretion and higher renal tubular resorption.

Many studies proved the negative effect of the elevated blood glucose level to different tissues and organs. Even short-term hyperglycemia has been found to markedly impair cardiovascular function in ischemic heart, increasing size of myocardial necrosis, reducing coronary collateral blood flow, exaggerating ischemia-reperfusion cellular injury and/or impairing ischemic preconditioning.

Also other studies have identified numerous hyperglycemia-induced abnormalities such as increased risk of thrombosis, endothelial disfunction or activation of systemic inflammation, with possible destabilization of atherosclerotic plaques leading to acute ischemic syndromes. Hyperglycemia also has effect to the extent of renal injury, e.g. in patients after cardiac surgery, and last but not least, hyperglycemia has been associated with increased postoperative infectious complications.

Despite all those facts hyperglycemia has been until recently considered as a "protective" mechanism for patients in critical condition, when the cells are offered a supranormal amount of easily accessible energy. This approach has been radically changed thanks to Leuven study published by prof.Van den Berghe and her colleagues in 2001 in New England Journal of Medicine. This fundamental study proved that a higher levels of blood glucose in intensive care patients significantly increase the risk of organ complications as well as an overall death rate, and that, on the contrary, we can significantly decrease both mortality, as well as the amount of organ complications connected with the critical state by an intensive insulin therapy aimed to keep normoglycemia. Such results were confirmed also by another study of prof.Van den Berghe and her colleagues (published in NEJM 2006), this time performed on non-surgery patients. This fact was quickly accepted by the intensivists and therefore it is nowadays commonplace for us to carefully monitor blood glucose levels in postoperative ICU, and keep it at normal levels.

Both the above-mentioned studies are even more significant for cardiac surgery patients, since the population of the patients in the first Leuven study (2001), where the results of intensive insulinotherapy were more distinct in comparison with non-surgery population (2006) mostly thanks to a 40% reduced mortality, consisted up to 63% from patients following cardiac surgery.