Parameters:
(1) number of hours in the ICU
(2) cumulative area under the glucose curve when hyperglycemic
(3) cumulative area above the glucose curve when hypoglycemic
The area under the glucose curve while hyperglycemic is based on the time above the upper limit of normal. The units are based on mmol•hours/L or mg•hours/dL.
The area above the glucose curve while hypoglycemic is based on the time below the lower limit of normal. The units are based on mmol•hours/L or mg•hours/dL.
In many situations the areas above or below the reference limit are triangular, in which case the area = 0.5 * (duration in hours) * ((peak glucose) - (upper limit of reference range)).
hyperglycemic index = HGI =
= SUM(areas for all episodes above the upper limit of normal) / (hours in the ICU)
The units are in mmol/L or mg/dL.
hypoglycemic index = HGI =
= SUM(areas for all episodes below the lower limit of normal) / (hours in the ICU)
Vogelzang et al showed that a person with poor glucose control (HGI > 2.4 mmol/L) had a 30 day mortality rate of 25% while those with tight control (HGI < 0.4 mmol/L) had a mortality rate of around 8%.
Performance:
• Vogelzang et al show a ROC curve in Figure 2 page R125 that indicates that the HGI is better than other measures of glucose control but that it is relatively mediocre.
