Hypoglycemia in the critically ill

Raised blood glucose (hyperglycemia) is a common feature of critical illness, irrespective of diabetes status. A landmark Belgian study conducted in 2001 demonstrated that this hyperglycemia is associated with increased morbidity and mortality. As a result of that study maintenance of normal blood glucose, with insulin therapy if necessary, has become a standard of critical care in intensive care units around the world. 

It has always been acknowledged that striving to avoid hyperglycemia artificially is associated with risk of reduced blood glucose (hypoglycemia), and that severe hypoglycemia (usually defined as blood glucose <2.0 mmol/L) can be lethal if not treated quickly. It is not clear, however, whether a lesser degree of hypoglycemia (mild to moderate hypoglycemia) affects survival from critical illness. 

This is the issue addressed by the largest and most comprehensive study ever conducted of hypoglycemia in the critically ill, which is recently published. The focus of this retrospective study was all patients admitted to two Australian intensive care units during a 4-year period (2000-2004) who had at least one episode of hypoglycemia (defined as blood glucose <4.5 mmol/L). 

During the study period a total of 4946 patients were admitted to the two units and 1109 (22.4 %) suffered at least one hypoglycemic episode; 103 (2.1 %) suffered an episode of severe hypoglycemia (blood glucose <2.0 mmol/L). 

This study provides a wealth of data on the epidemiology, cause, duration, severity and outcome of hypoglycemia in the critically ill, but the headline finding is that hypoglycemia is associated with increased mortality. Unadjusted mortality was 36.6 % in those who suffered hypoglycemia compared with 19.7 % who did not. 

Although there was a clear relationship demonstrating that the more severe the hypoglycemia the greater the risk of death, even mild hypoglycemia (blood glucose in the range of 4.0-4.5 mmol/L) was associated with increased risk of death. Since 2001 the focus has been on avoiding hyperglycemia in the critically ill. 

The results of this important study suggest tha avoidance of hypoglycemia (not just severe hypoglycemia) is as important.