LISBON – Although microcirculation in cardiac surgery patients is impaired during the first few hours of admission to the intensive care unit, the degree of impairment was not great enough to affect the accuracy of continuous glucose monitors in a prospective, observational study of 60 patients.
Hyperglycemia, hypoglycemia, and glucose hypervariability are all associated with increased mortality in critically ill patients following cardiac surgery. Continuous glucose monitoring (CGM) is a potential alternative to frequent, time-consuming fingerstick glucose measurements, and can provide more information about glucose trends. However, the accuracy of these systems in critically ill patients has been uncertain, said Dr. J. Hans DeVries, an endocrinologist at the University of Amsterdam.
Dr. J. Hans DeVries
Now, "these results support CGM use in cardiac surgery patients, with quite good sensor accuracy in patients with a low severity of illness," he said at the annual meeting of the European Association for the Study of Diabetes (EASD).
The patients had a mean age of 65 years, and 48 of the 60 were male. Nearly a third (27%) had diabetes. Thirty-two (53%) of the patients were undergoing only coronary artery bypass surgery, 16 (27%) were having just valve surgery, and 12 (20%) had both procedures. Their APACHE score predicting mortality was low, 0.01. Total ICU stay was 23 hours. Hemodynamic parameters were fairly good, with a microcirculatory function index of 2.8 (out of 3.0). The proportion of perfused vessels was high, 0.97. However, the patients’ peripheral temperature was low, 32.8 °C.
Two sensors – the Medtronic Guardian REAL-Time and the Abbott FreeStyle Navigator – were placed subcutaneously in the abdominal wall of each patient prior to surgery. The Navigator performed slightly better than did the Guardian. Microcirculation was measured by microvascular flow index (MFI), perfused vessel density (PVD), and proportion of perfused vessels (PPV) using sublingual sidestream dark-field (SDF) imaging; and tissue oxygenation (StO2) was obtained with near-infrared spectroscopy.
While StO2 and PVD were impaired in the first hours after surgery, at no point were any microcirculatory parameters significantly associated with sensor accuracy. For the Navigator CGM, lower peripheral temperature and higher APACHE IV scores were significantly associated with decreased sensor accuracy (P values of .003 and less than .001, respectively). For the Guardian, lower peripheral temperature was significantly associated with decreased sensor accuracy (P = .048).
"Further studies are needed to assess the influence of microcirculation on sensor accuracy in more severely ill patients, such as those with sepsis," Dr. DeVries concluded.
The study was supported by the EASD’s European Foundation for the Study of Diabetes. Dr. DeVries has received research support from, and is on the speakers’ bureau for Dexcom, Abbott, and Medtronic.