Authors

1. Higgs, Megan BN, MN, PhD Candidate
2. Fernandez, Ritin BSc (Nursing), MN (Critical Care), PhD

Abstract

Review question/objective: The objective of this review is to determine the best available evidence related to the effect of insulin therapy algorithms on blood glucose levels in patients in critical care environments following cardiac surgery.

More specifically, the review question to be answered is:

Among adults within critical care environments who are in the acute postoperative phase (5 days) following cardiac surgery, what is the effect of insulin therapy algorithms for the control of blood glucose levels?

Background: Hyperglycemia, a condition characterized by elevated blood glucose levels (BGLs), is most commonly associated with diabetic illness.1 However, hyperglycemia has also been found to have a high incidence after cardiac surgery. Current literature surrounding this topic suggests that hyperglycemia occurs almost universally after cardiac surgery; irrespective of whether a person has a pre-existing diagnosis of diabetes mellitus or not.1-3 Conventionally, post-operative hyperglycemia following cardiac surgery was viewed purely as a natural adaptive physiological response of the body that was treated only when BGLs rose to what was considered excessively high levels;2 generally greater than 12.2 mmol/L [220mg/dl].4 This view has since changed and hyperglycemia following cardiac surgery is now viewed as an adverse effect of surgery, occurring as a result of multiple factors that include: the intraoperative hypothermic state, surgical stress, hypokalemia, adverse effects from pharmacological agents and the commonly occurring post-operative systemic inflammatory response.5-7

While generally only transient, an incidence of hyperglycemia during the initial post-operative period can have serious detrimental side effects following cardiac surgery such as deep sternal wound infection and an increased risk of mortality.8 Current evidence suggests that within critical care environments, the early recognition and treatment of post-operative hyperglycemia is imperative. This is achieved through the utilization of continuous intravenous insulin infusion algorithms, with the aim of maintaining BGLs within normal to near normal ranges, in order to prevent the adverse outcomes associated with hyperglycemia in post-operative patients.9

The practice of maintaining BGLs within strict pre-defined levels, via the administration and titration of a continuous insulin infusion, has become common practice within critical care environments over the past decade.10 Results from a study by Van Den Berghe et al., which included 970 cardiac surgery patients [63%] showed that the maintenance of BGLs below 110 mg/dl [6.1 mmol/L], using continuous insulin therapy lead to decreases in both mortality and morbidity rates among critically ill surgical patients.3 Since this time, multiple studies investigating the effects of continuous insulin infusion algorithms have concluded that the use of such algorithms for the management of BGLs in cardiac surgery patients has favorable effects, decreasing the incidence of post-operative complications and reducing the length of time patients are required to remain in hospital.11

The use of continuous intravenous infusion algorithms for controlling BGLs in critically ill patients is further supported by the American Diabetes Association [ADA] who recommend the use of tried and tested insulin infusion protocols that demonstrate a low incidence of hypoglycemia.12 The ADA go on to state that BGLs of critically ill patients, including postoperative patients who have undergone a cardiac procedure, should be maintained between 7.8 and 10 mmol/L [140 and 180mg/dl] with insulin therapy commenced at a threshold no higher than 10 mmol/L [180mg/dl].12 While it is acknowledged that greater benefits may be achieved by the maintenance of BGLs at the lower ends of the range, the American Diabetes Association do not recommend targets less than 6.1mmol/l [110mg/l] due the high risk of causing significant hypoglycemia.12

A review of the literature shows that a number of insulin infusion algorithms, with varying methods and effects, have been developed for utilization by clinicians in critical care environments to guide the management of hyperglycemia. Due to the conflicting evidence that currently exists, the critical care clinician responsible for the provision of care to post-operative cardiac surgery patients needs to determine the best evidence in relation to the management of hyperglycemia, to maintain patient safety and ensure good surgical outcomes, free from complications. However, a review of the outcomes of these protocols for cardiac patients has not been published to inform the development of best evidence based practice guidelines. This systematic review therefore aims to review the various protocols to ascertain the best available evidence related to the effect of intensive insulin therapy algorithms on BGLs in post-operative patients in critical care environments following cardiac surgery.