To the Editor: Dr Soylemez Wiener and colleagues1 reported the results of a meta-analysis that included 29 studies on tight glucose control in critically ill adults. Several methodological issues limit the conclusions to be drawn from this study.
First, the included studies have substantial differences, most importantly concerning the type of intervention (fixed vs titrated insulin dose) and the glucose levels actually achieved. The proof-of-concept study on tight glucose control in the intensive care unit (ICU)2 hypothesized that normalization of blood glucose (80-110 mg/dL) with insulin protects against complications (eg, severe infections, organ failure, death). (To convert glucose values to mmol/L, multiply by 0.0555.) The scientific concept was that any degree of hyperglycemia above normal (≥110 mg/dL) in a condition of ischemia/reperfusion additionally damages those cells that take up glucose passively. The study by Soylemez Wiener et al pooled all published studies on insulin therapy (including glucose-insulin-potassium) and those that targeted glucose of 150 mg/dL or lower. Studies not achieving normoglycemia in the majority of patients should not be expected to provide the same benefit as in the original Leuven study.2 Methodological quality assessment in the meta-analysis should have addressed this issue of achievement of normoglycemia, as well as the varying blood glucose levels in the different control groups. Overlap of glucose levels in controls and the intervention groups should not exceed 20%.2,3 Achieving a glycemic target cannot be assessed using mean glycemia levels; high and low values may cancel out and falsely suggest goal achievement. The number of patients on average within the target would have been a better parameter.
Hermans G, Schetz M, van den Berghe G. Tight Glucose Control in Critically Ill Adults. JAMA. 2008;300(23):2725-2728. doi:10.1001/jama.2008.815