Lactate biosensors for continuous monitoring

Blood lactate concentration is a highly sensitive measure of tissue oxygen deprivation from ischemia, trauma, and hemorrhage, which can produce life-threatening shock. Significantly, blood lactate is the most reliable end point indicator of resuscitation and predictor of survivability. The need for continuous measurement of blood lactate, and the slowness of discrete conventional photometric assays, is leading to the development of monitoring systems based on electrochemical lactate biosensors. Research and development of both in vivo and ex vivo biosensor systems is ongoing. Ex vivo biosensors are used with implanted microdialysis or ultrafiltration probes. Lactate from the blood diffuses into the dialysate/filtrate is transported outside of the body for measurement. The external biosensors are protected from fouling or contamination from unwanted blood constituents, but at the cost of an inherent delay in response despite system miniaturization. In vivo biosensors provide a direct measurement of blood lactate concentration, providing rapid response to changes in lactate levels. In vivo sensors are placed in the skin or implanted subcutaneously. Response to changes in lactate concentration is rapid, but biocompatibility requirements are more stringent than for ex vivo sensors. As is the case with all microdialysis systems, some in vivo biosensors must be implanted into the body using an insertion needle or surgical means, limiting their use. However, small, inexpensive, disposable in vivo sensors are also being developed which can emplaced and removed by the user.