USE OF ARTERIAL BLOOD WITH BEDSIDE GLUCOSE REFLECTANCE METERS IN AN INTENSIVE-CARE UNIT - ARE THEY ACCURATE

Objective: To compare blood glucose values obtained from two different sampling sites (arterial catheter and capillary from finger puncture) , which were analyzed by a bedside reflectance meter. A sample was als o analyzed by standard methods (oxygen electrode oxidation in the labo ratory). Design: Prospective, cross-sectional clinical study. Setting: Cardiovascular intensive care unit (ICU) designed for postoperative o pen-heart surgery patients in a 1,100-bed medical center. Patients: Se quential sample of 50 patients immediately after open-heart surgery. M easurements and Main Results: The blood glucose concentration of each patient was analyzed on the patient's arrival to the ICU (immediately postoperatively) by three methods: one blood specimen was obtained fro m an arterial catheter, divided and analyzed either at the bedside by a reflectance meter (glucose method 1) or in the hospital laboratory ( glucose method 2); another sample was obtained by lancing the fingerti p and the glucose concentration was analyzed at the bedside in the sam e reflectance meter (glucose method 3). Using paired analyses to compa re the mean glucose values of the bedside arterial whole blood sample (method 1) with the arterial, serum sample (method 2) demonstrated tha t the glucose concentration in the arterial whole blood sample (method 1) was significantly (p <.001) higher. For 46 of 50 comparisons, the glucose value in the arterial whole blood sample (method 1) was higher , with a mean difference of 30 mg/dL (1.7 mmol/L). Although the mean d ifference was reduced to 10 mg/dL, (0.6 mmol/L) when the arterial whol e blood sample (method 1) was corrected for the hematocrit (i.e., <35% [<0.35]), the mean glucose concentration in the arterial whole blood samples (method 1) remained statistically higher (p <.05). The glucose concentration in the arterial serum sample (method 2) was significant ly higher than the value determined from the bedside capillary sample (method 3) before (p <.05) and after (p <.001) correction for hematocr it. The difference in mean glucose concentrations between the arterial serum sample (method 2) and bedside capillary sample (method 3) was 9 mg/dL (0.5 mmo/L) when the capillary specimen (method 3) was not corr ected for hematocrit. This difference increased to 21 mg/dL (1.2 mmol/ L) when low hematocrit values were considered and appropriate adjustme nts of the glucose values were made. At the bedside, one can accuratel y correct arterial whole blood glucose values to correspond to laborat ory values by the following formula: (0.94 x arterial whole blood gluc ose) + (4.6 x hematocrit) + (-16.5 x [37 degrees C patient's temperatu re]) - 132 = laboratory glucose value. Conclusions: Since arterial who le blood samples give higher glucose results than arterial serum, the use of arterial whole blood in combination with reflectance meters mus t be recommended with caution. This caution is especially advised if t he glucose values obtained with arterial whole blood are used in conju nction with a sliding scale of insuIin, which depends on threshold con centrations of glucose. In our hospital, use of arterial whole blood i n combination with reflectance meters could have resulted in an incorr ect dose of insulin in 31 of 50 patients.