Novel system for real-time ex vivo lactate monitoring in human whole blood.

The objective of the study was to evaluate the performance of an amperometric enzyme based lactate sensor and to investigate the possibility of replacing a double lumen catheter based blood withdrawal system with a heparin coated single lumen system. The inner lumen of a double lumen catheter which was placed in a peripheral vein was perfused with heparin solution. The outer lumen was used to collect heparinized blood samples at a defined flow rate. The single lumen system was attached to a heparinized catheter which was also placed in a peripheral vein. The undiluted blood samples were collected at a specified flow rate. A sensor flow chamber incorporating an amperometric thin-film lactate microbiosensor was placed in the sampling line for real-time lactate monitoring. Plasma lactate concentrations were measured during frequently performed hyperlactatemia bicycle ergometer experiments in six healthy volunteers (age 25.8 +/- 2.8 years, BMI 22.7 +/- 1 kg/m2). Additionally, plasma lactate was measured in real-time using the lactate sensors. The first three experiments were performed with a double lumen based catheter system whereas the following three experiments were performed with a heparin coated catheter system. The correlation coefficients of sensor readings and laboratory analyzer results in all six experiments were between 0.93 and 0.99, respectively (P < 0.001). The miniaturized lactate sensors showed a linear range up to 25 mmol/l lactate concentration and 95% response times < 30 s in undiluted serum. During the experiments maximum lactate concentrations of 14 mmol/l were achieved. Improvements of system performance using heparin coated catheter systems could be shown. The overall SD of the sensor readings compared to laboratory results using three double lumen catheter based systems was 0.91 mmol/l whereas the SD using three heparin coated systems was 0.65 mmol/l. In summary, real-time monitoring of lactate in human whole blood is feasible with such a device and can be improved by using heparin coated catheter systems.

Accuracy of home blood glucose meters during hypoglycemia.

OBJECTIVE: To evaluate the accuracy of home blood glucose meters during hypoglycemia. METHODS: Six blood glucose meters-One Touch II (LifeScan, Milpitas, CA), Companion II (Medisense, Cambridge, U.K.), Reflolux (Boehringer Mannheim, Mannheim, Germany), Accutrend (Boehringer Mannheim), Elite (Bayer, Munich, Germany), and HemoCue (HemoCue, Angelholm, Sweden)-were compared with a reference method (Beckman Glucose Analyzer 2). Glucose concentrations from arterialized venous blood samples were measured using all glucose meters (whole blood) and the reference method (plasma) during hypoglycemic-hyperinsulinemic clamps in 15 subjects. RESULTS: In total, 663 blood glucose monitor readings and 119 reference values ranging from 2.28 to 3.89 mmol/l were analyzed. The correlation coefficients and the percentage of measurements within 20% and outside 40% of the reference values for each glucose meter were as follows: One Touch II: 0.91, 99.2% and 0%; Companion II: 0.81, 88.2% and 2.5%; Reflolux: 0.78, 85.0% and 0.9%; Accutrend: 0.88, 46.0% and 6.6%; Elite: 0.78, 75.6% and 4.2%; and HemoCue: 0.93, 96.6% and 0% (P < 0.001). CONCLUSIONS: There were substantial differences between the blood glucose meters during hypoglycemia, and none of the devices met the latest criteria recommended by the American Diabetes Association.