Discussion
The accuracy of glucose POCT in the critical care setting has been called into question.4,5 The clinical demands of glucose management using CII include timely and accurate guidance in postoperaptive cardiac surgery, in this case, CABG. A previous study compared POCT and central laboratory blood glucose values in medical intensive care unit patients,8 but not in patients who have had CABG surgery. Another study has reviewed the difference in glucose values from POCT and central lab analysis in the critically ill population, but not in the post cardiac surgical population.9 We have shown that the POCT blood glucose values correlate well with the clinical lab values, but the values are statistically different. Our study adds an additional observation in that, although the POCT inconsistencies were statistically significant, they were not clinically significant. That is, POCT of blood glucose was inaccurate, but it still helped guide care by providing enough information to keep the blood glucose in range (most of the time) and allowing the bedside nurse to detect trends and make appropriate adjustments to the infusion. However, given these inconsistencies, we recommend a low threshold for sending additional samples to the central lab to double-check the glucose values, especially when they are outside the prescribed range. Our analysis provides some measure of reassurance with regard to current postoperative CABG glucose management by showing that the limitations of the blood glucose meter do not jeopardize the safety of patients. Nonetheless, we look forward to advances in the accuracy of POCT blood glucose technology so that critical care patients can be better managed when blood glucose is outside the prescribed range.
This analysis of 116 CABG patients points out both the inaccuracy and the utility of a representative POCT glucometer (in this case, the FreeStyle Precision Pro) used at the bedside to manage CIIs in postoperative CABG patients, keeping the blood glucose level in the moderate control range (110-150 mg/dL). The correlation plot shows that in this population the bedside nurses were able to keep blood glucose in range most of the time, in spite of the inaccuracy of POCT of blood glucose, given that the error of the test fits in the wide margin of 40 mg/dL. The fact that the 6-hour values were slightly less variable than the admission values indicates that sequential determinations of blood glucose over the 6-hour period to detect trends allowed good clinical management even in the face of such inaccuracy. The correlation allows the inaccurate number (blood glucose value) to indicate direction, and frequent determinations allow the bedside nurse to keep that number in the prescribed range most of the time in this population of patients.
Conclusion
We have found that glucometer blood glucose determinations in our center used on a homogenous population (CABG surgery) utilizing a single type of glucometer correlated well with those of the central lab, but were not always accurate. In spite of the inaccuracies, experienced bedside nurses were able to use the instrument successfully and safely, as it informed them if the blood glucose was in or out of a predetermined range and in which direction it was going.
Acknowledgment: The authors are indebted to the nurses of the Cardiothoracic Surgery Intensive Care Unit at Maine Medical Center for their support and assistance, without which this analysis would not have been possible.
Corresponding author: Robert S. Kramer, MD, Division of Cardiothoracic Surgery, Maine Medical Center Cardiovascular Institute, 22 Bramhall St., Portland ME 04102; kramer@mmc.org.
Financial disclosures: None.