Interpreting lactate measurement in critically ill horses: diagnosis, treatment, and prognosis

In hospitalized horses, hypovolemia and the resulting decrease in tissue perfusion is the most common cause of hyperlactatemia. Therefore, measurement of blood lactate concentration can be a useful tool for guiding fluid therapy. Similarly, measuring blood lactate concentration can be used to assess the need for and adequacy of transfusions in horses receiving whole blood. Inflammatory leukocytes within closed body cavities consume glucose and produce lactate. Simultaneous measurement of blood lactate concentration and lactate concentration of peritoneal, pleural, or synovial fluid has been used to help differentiate septic from nonseptic effusions. A fluid lactate concentration higher than the blood lactate concentration provides evidence for a bacterial cause of the effusion. In horses evaluated for colic, a peritoneal lactate concentration higher than the simultaneously measured blood lactate concentration is indicative of intestinal strangulation and ischemia. Veterinary studies have suggested that serial blood lactate measurements might be a more useful prognostic indicator than a single lactate measurement. In hospitalized adult horses and foals, blood lactate concentration is higher at all time points in nonsurvivors compared with survivors, although the differences tend to be subtle. Measuring the rate at which lactate concentrations return to normal might also prove useful in equine medicine, but this requires further investigation.