Diurnal and other variations in blood glucose in intensive care unit patients receiving insulin infusions

Introduction

Treatment of hyperglycemia in ICU patients using an insulin infusion protocol was shown by van den Berghe and colleagues to reduce mortality and morbidity in ICU patients. Consequently, many healthcare bodies proposed guidelines for the control of hyperglycemia in the ICU. However, the patchy evidence underpinning these guidelines and a high rate of complications lead to controversy about the optimal glucose target range. Studies showing insulin infusions are effective have reported average glucose values at single time points. However, single time points are difficult to interpret as they do not provide information about the proportion of glucose measurements that need to be in range for benefit. We hypothesized that blood glucose variance was greater if all glucose measurements were considered and asked whether there was a diurnal pattern that accounted for some of the variance.

Methods

Prospective collection of all glucose measurements for ICU patients receiving an insulin infusion protocol between 20 May 2006 and 6 August 2006 in 64 ICU beds at a teaching hospital. We report glucose values from all ICU patients, ≥ 8 hours after infusion initiation.

Results

We compared the 6:00 a.m. glucose value with those collected at all other times in 149 consecutive patients. The 6:00 a.m. values were lower than the remaining values (mean ± SD: 112 ± 30 mg/dl (n = 477) vs 119 ± 35 mg/dl (n = 10,364); P < 0.0001) and as hypothesized had a smaller variance by F test (P < 0.0001). Inspection of the time-averaged data (± SE) revealed a diurnal variation in the blood glucose with peaks occurring at 11:00 a.m. and 10:00 p.m. (Figure 1). This diurnal pattern may account for some of the observed variation in insulin requirements and contribute to episodes of hypoglycemia in the critically ill.

Figure 1

Conclusion

Glucose variance is increased if all time values are considered rather than a single time point and there is a diurnal pattern to glucose in ICU patients receiving insulin. Consideration of this diurnal variation when treating hyperglycemia in the ICU may avoid hypoglycemia and so facilitate better glucose control with insulin infusions.