Lactate production and measurement in critically ill horses

Blood lactate concentration can be easily measured by practitioners using inexpensive point-of-care meters. Anaerobic tissue metabolism resulting from inadequate oxygen delivery (DO2) is the most important cause of an increase in blood lactate concentration in equine patients. However,hyperlactatemia also occurs under conditions of apparently adequate DO2, usually in association with sepsis and an intense inflammatory reaction. Numerous mechanisms have been proposed for aerobic hyperlactatemia, including increased Na+/K+-ATPase activity in response to inflammatory mediators; inhibition of pyruvate dehydrogenase, a key enzyme in glucose metabolism; and increased lactate production by activated inflammatory cells. The liver is responsible for most lactate metabolism, and liver disease might contribute to an increase in blood lactate concentration in some patients. Skeletal muscle is usually considered the most important source of lactate during sepsis. The roles of the lungs and the gastrointestinal tract in lactate production have been investigated but remain uncertain.