Amperometric enzyme electrode system for extracorporeal lactate monitoring based on lactate dehydrogenase

Abstract

A lactate electrode for practical extracorporeal monitoring has been produced, using lactate dehydrogenase retained over an H₂O₂ sensor. Soluble NAD⁺ cofactor was used, and phenazine ethosulphate (PES⁺) in solution permitted electron transfer from NADH to O₂ to generate H₂O₂. The system was optimised using O₂ electrodes, but was employed for blood with H₂O₂ detection to avoid effects due to variations in background pO₂. At pH 9.8 in carbonate buffer containing 0.5 mM NAD⁺ and 1 mM PES⁺, the electrodes had sufficient stability and sensitivity to allow measurement of diluted whole blood. Calibration graphs were linearised over the range 0.01–0.5 mM lactate either by means of a square root concentration scale or by use of inverse coordinates. The response time in the extracorporeal flow system was slow (6–10 min), but this was found to be adequate to follow lactate rises during mild exercise.