Another group demonstrated that when insulin infusion was initiated in patients in the operating room before sternotomy and continued until the third postoperative day that there was improved glucose control. There was a 57% decrease in mortality rate, compared with control groups who were treated with subcutaneous insulin. Patients with diabetes have been shown to have worse outcomes compared to patients without diabetes. There have been no relationship was found between the presence of diabetes and the influence of hyperglycemia on outcomes. Patients who have diabetes, even though they are at increased risk for adverse outcomes because of having diabetes, have been found to have the same risk as patients without diabetes. Based upon these findings it would seem reasonable to say that that Perioperative serum glucose control for patients undergoing Coronary Artery Bypass surgery would be an encouraged best practice.
It has been found that strict glucose control is often difficult to achieve during cardiac procedures requiring cardiopulmonary bypass because of the stress of surgery. Administration of large amounts of insulin during surgery has been associated with an increased risk for postoperative hypoglycemia. Research has shown though, that glucose concentrations if maintained during surgery as close to normal as possible, by the use of carefully monitored intravenous insulation fusion procedure, does not increase the risk for hypoglycemia. Although it has been shown that glucose concentration in groups given insulin treatment during surgery were lower than those in conventional groups, postoperative complications were not any different1. It has also been found that a high glucose level during cardiopulmonary bypass is an autonomous predictor of all major adverse events in patients. It has been found that a high glucose level is not directly correlated to cardiopulmonary bypass. A high serum glucose level during cardiopulmonary bypass has been found to be an independent risk factor adverse outcome in diabetic patients and nondiabetic patients alike.
The findings of the study done by Ascione, Rogers, Rajakaruna and Angelini, (2008), found that insulin infusion practice during surgery was not effectual in maintaining tight blood sugar control in all patients regardless of their diabetic status. It is thought that the stress of cardiac surgery might bring about a borderline diabetic status causing a marked temporary or permanent imbalance in body sugar control leading to hyperglycemia. Because hyperglycemia has been linked with poor outcomes it is thought that insulin infusion protocol should be extended to 48 hours after surgery in all patients regardless of their diabetic status. These findings have been found to contradict these other studies.
Although the results of these studies are intriguing, there are two potentially confounding factors that make their interpretation difficult. Postoperative serum glucose levels in diabetic patients are thought to be an indication of the severity of their disease, which might be an indicator for more co-morbidities and greater insulin resistance. It is also thought that patients with poor outcome are more likely to receive more glycogenic drugs than patients with an uncomplicated course and will therefore most likely have higher postoperative glucose levels3.
Both patients with known diabetes and those without have been found to be at risk for complications following cardiac surgery. Intraoperative and postoperative glucose measurements have been shown to be important predictors of outcomes after cardiac surgery. Even though severe hyperglycemia has been associated with adverse patient outcomes, involvement to normalize glycemia has yielded conflicting results. Whether hyperglycemia is a risk factor for adverse outcomes or merely a marker for severity of illness has yet to be determined. It is unclear whether associated benefits on outcomes result from treatment of hyperglycemia vs. benefits related to insulin therapy. Because insulin is the only clinically effective therapy that is currently available, it has found to be difficult to separate the effects of insulin from those of normalizing blood glucose in hyperglycemic patients.
Some research has found that both intraoperative and postoperative glucose concentrations are important indicators of postoperative morbidity and mortality. Although severe perioperative hyperglycemia is associated with an increased risk of adverse outcomes, incremental decreases in mean glucose concentrations has not shown to consistently moderate the risk during the intraoperative period. Research has shown that mean intraoperative glucose concentrations closest to normoglycemia were not associated with a lower risk for adverse outcomes. Increased postoperative glycemic variability has been associated with increased risk for adverse outcomes. It is thought that beneficial effects on outcomes may come from a higher target range of intraoperative glucose concentrations and lower perioperative glycemic variability.
Currently there is no consensus on what the optimal management of intraoperative hyperglycemia in cardiac surgical patients because of a lack of evidence from randomized trials. Researchers are increasingly extrapolating evidence from studies that assess the role of strict postoperative glycemic controls in patients to advocate for intravenous insulin therapy. An association established between intraoperative hyperglycemia and adverse outcomes based on observational studies does not prove causality. Due to the fact that hyperglycemia can negatively affect immunity, wound healing and vascular function the concept that normoglycemia be maintained during the brief duration of cardiac surgery. On the other hand, the degree of intraoperative may merely be a factor of the underlying stress of the surgery itself.
Although the association between hyperglycemia and Perioperative Serum Glucose Control has been established and agreed upon by most experts, the amount and degree of control during surgery has yet to be established. It has been found that strict glucose control is often difficult to attain during cardiac procedures because of the stress of surgery. Administration of large amounts of insulin during surgery has been associated with an increased risk for postoperative hypoglycemia. Research has shown that glucose concentrations if maintained during surgery as close to normal as possible, by the use of carefully monitored intravenous insulation fusion procedure, does not increase the risk for hypoglycemia.
Obviously there are many factors that must be looked at both preoperatively and postoperatively in regards to hyperglycemia and adverse outcomes. The research that has been conducted to date is very inconsistent in its findings. Most experts agree on the fact that Perioperative serum glucose control is a positive thing that needs to be done during Coronary Artery Bypass surgery. What they don’t agree on is the best way to control glucose during surgery in order to produce the most optimal outcomes. The fact that there is discrepancy in what would be considered best practice; this would be an area in which further research would be needed. These inconsistencies leave a lot of room for further research in this area in order to further pinpoint what factors are important and how each of these factors influences the outcomes of patients who undergo cardiac surgery. Overall Perioperative Serum Glucose Control is a good practice as it has been shown to be effective in patient outcomes during surgery, regardless of whether the patient has diabetes before surgery or not.
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Manjula, Rae, Vivek and Borger, Michael A. Hyperglycemia during cardiopulmonary bypass is an independent risk factor for mortality in patients undergoing cardiac surgery. The Journal of Thoracic and Cardiovascular Surgery. 2005; 130(4)
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