Glycemic control in critically III patients before and after institution of an intensive insulin infusion protocol: Circadian rhythm and the quality duration calculator

Introduction: A circadian rhythm of blood glucose values has been recently reported in critically ill patients, but there are no reports of how this rhythm is altered by a continuous intensive insulin infusion therapy protocol (IIT). We wished to examine the effect of IIT on this rhythm as well as to describe the use of the quality duration calculator (QDC) for the evaluation of glycemic control before and after IIT. Methods: This was a retrospective multihospital observational study that took place in the medical and surgical intensive care units (ICUs) of 2 tertiary care hospitals. Cohorts of consecutively admitted critically ill patients from 2-year periods before and after institution of an IIT protocol were examined. Laboratory, demographic, and outcome data were extracted from hospital databases. Results: We studied 167,645 blood glucose measurements from 8,327 patients. We observed a circadian rhythm of blood glucose control in the pre-IIT cohort that was greatly attenuated in the post-IIT cohort. The difference between the morning and the average daily blood glucose in the pre-IIT cohort was 3.53 mg/dL (P <.001), and the difference between these values in the post-IIT cohort was 1.10 mg/dL (P =.031). In addition, the circadian nature of hyperglycemia incidence observed in the pre-IIT cohort was not seen in the post-IIT cohort. The amount of time spent in goal glycemic range increased from 23.69% (95% CI 23.01-24.38) in the pre-IIT cohort to 29.67% (95% CI 29.04-30.31) in the post-IIT cohort as estimated by the QDC. The amount of time spent in the hyperglycemic decreased from 20.17% (95% CI 19.33-20.99) in the pre-IIT cohort to 14.80% (95% CI 14.15-15.39) in the post-IIT cohort. Conclusions: The circadian rhythm of blood glucose control confirmed in our pre-IIT cohort was lost after institution of IIT. The morning blood glucose value appears to be a reasonable surrogate of overall glycemic control in a critically ill population on IIT, although this may vary based on the degree of control achieved. The QDC method is useful for analyzing glycemic control in patients on IIT.