In this episode, I’ll discuss an article about relative hypoglycemia in the ICU.
Relative Hypoglycemia in Diabetic Patients With Critical Illness
Lead author: Timothy Kwan
Published in Critical Care Medicine online January 2020
Relative hypoglycemia is most commonly a term used in outpatient care of diabetic patients. Previous to this study, it had not been looked at in a critically ill population. The authors examined the frequency, characteristics, and outcome associations of relative hypoglycemia in diabetic patients with critical illness.
This was a retrospective cohort study in a single-center ICU. Over 1500 patients were examined. Patients were divided into subgroups according to their first hemoglobin A1C in the past 3 months: hemoglobin A1C less than 6.5%, 6.5–7.4%, and greater than or equal to 7.5%. This particular split was decided upon because, for patients with hemoglobin A1C in the diabetic range (≥ 6.5%), the median hemoglobin A1C was 7.5% and so 2 categories were made to better analyze the data.
Fully one-third of patients with diabetes experienced relative hypoglycemia during their ICU admission. Thesse patients had higher glycemic lability, hemoglobin A1C levels, and APACHE III scores. Mortality was significantly higher in this group of patients with a hazard ratio of 1.9 for 28-day mortality. This hazard ratio was essentially unchanged after adjustment for episodes of absolute hypoglycemia. In patients who did experience an episode of relative hypoglycemia, the hazard ratio for subsequently developing absolute hypoglycemia in the ICU was 3.5, and this was statistically significant.
The authors concluded:
In ICU patients with diabetes, relative hypoglycemia is common, increases with higher hemoglobin A1C levels, and is a modifiable risk factor for both mortality and subsequent absolute hypoglycemia. These findings provide the rationale for future interventional studies to explore new blood glucose management strategies and to substantiate the clinical relevance of relative hypoglycemia.
In this study, relative hypoglycemia was defined as a single episode of glucose greater than or equal to 30% below the average glucose level but not less than or equal to 70mg/dL.
The study ICU used a liberal glucose target between 180 and 250mg/dL in diabetic patients and 100 to 180mg/dL in nondiabetics.
Perhaps the most significant finding is that among patients with hemoglobin A1C greater than or equal to 6.5% who experienced absolute hypoglycemia, two-thirds had a preceding episode of relative hypoglycemia. This suggests that absolute hypoglycemia could be predicted and possibly avoided with increased vigilance after the development of relative hypoglycemia.
Some measure of computer support would be required to first calculate an average glucose level for a patient that could then be compared to ongoing glucose values to identify and alert staff to the onset of relative hypoglycemia.
Since this study was retrospective, ideally a prospective and multicenter study would be conducted to confirm the results.
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