The blood glucose concentration can be measured in vitro by sensors that sit in the vascular or interstitial space or ex vivo by drawing blood samples or a dialysate to a sensor from an indwelling vascular catheter never or dialysis membrane. Systems that intermittently draw blood to an externally based sensor may be described as automated intermittent monitors rather than continuous glucose monitors. Potential advantages of continuous glucose monitors include the ability to observe trends in blood glucose concentration and to intervene before the blood glucose concentration enters an unacceptable range, and removal of operator error both in the timing of blood glucose measurements and in the sampling and analysis of blood.

Can we use the same measures for assessment of glucose control with continuous and intermittent monitoring?As noted in the first section of this paper, almost all monitoring of the blood glucose concentration in critically ill patients is by intermittent measurement. Although intermittent measurement is current standard practice, there is no agreed metric for reporting glycemic control and many of the metrics currently reported are affected by the frequency of measurement. Current systems for continuous or automated intermittent monitoring may measure the blood glucose concentration at a frequency varying from every minute to every 15 minutes. Such monitors will not only increase the number of measurements, but will also standardize the frequency of measurements amongst patients monitored with each device.

This may allow for a better reporting of glucose control metrics, and if sufficiently accurate may offer a better understanding of the association between those metrics and outcomes.Possible metrics available from continuous glucose monitoring systems include the following (Figure (Figure22 and Table Table22):Figure 2Schematic representation of the performance of continuous blood glucose concentration. Area A, possible measure of hyperglycemia (when defined as blood glucose concentration >10.0 mmol/l). Area B, possible measure of moderate hypoglycemia (when …Table 2Metrics to report glycemic control using continuous glucose monitoring systems1. Measures of central tendency:a. The mean and Batimastat median blood glucose per patient, per day and during stay in the ICU.2. Measures of dispersion and variability:a. The standard deviation and coefficient of variation of blood glucose.b. Analysis of the rate of change of the blood glucose concentration.c. The peak blood glucose concentration reached within a set time period after correction of hypoglycemia.3. Hypoglycemia and lowest blood glucose concentration:a. The lowest blood glucose concentration recorded.b.