Suitability of capillary blood glucose analysis in patients receiving vasopressors

Glycemic control in critically ill patients decreases infection and mortality. Patients receiving vasopressors have altered peripheral perfusion, which may affect accuracy of capillary blood glucose values measured with point-of-care devices.

To compare capillary and arterial glucose values measured via point-of-care testing (POCT) with arterial glucose values measured via clinical chemistry laboratory testing (CCLT) in patients after cardiothoracic surgery. To determine if vasopressors or diminished peripheral perfusion influence the accuracy of POCT values.

In a prospective, convenience sample of 50 adult postoperative cardiothoracic patients receiving insulin and vasopressors, 162 samples were obtained simultaneously from capillary and arterial sites during insulin infusion and tested via both POCT and CCLT. Clarke error grid analysis and ISO 15197 were used to analyze level of agreement. Two-way analysis of variance was used to analyze differences in glucose values with respect to vasopressor use and peripheral perfusion.

An unacceptable level of agreement was found between the capillary POCT results and arterial CCLT results (only 88.3% of values fell in zone A, or within the ISO 15197 tolerance bands). Arterial POCT results showed acceptable (94.4%) agreement with CCLT results. Vasopressor use had a significant effect on the accuracy of arterial blood glucose values (F=15.01; P<.001).

Even when the more accurate POCT with arterial blood is used, blood glucose values are significantly less accurate in patients receiving more than 2 vasopressors than in patients receiving fewer vasopressors. CCLT may be safer for titrating insulin doses in these patients.