Sequential plasma lactate concentrations as prognostic indicators in adult equine emergencies

Background: Sequential lactate concentration ([LAC]) measurements have prognostic value in that hospitalized humans and neonatal foals that have a delayed return to normolactatemia have greater morbidity and case fatality rate. Hypothesis: Prognosis for survival is decreased in horses with a delayed return to normal [LAC]. Animals: Two hundred and fifty adult horses presented for emergency evaluation excepting horses evaluated because of only ophthalmologic conditions, superficial wounds, and septic synovitis without systemic involvement. Methods: Prospective observational study. [LAC] was measured at admission and then at 6, 12, 24, 48, and 72 hours after admission. The change in [LAC] over time ([LAC]ΔDT) was calculated from changes in [LAC] between sampling points. Results: Median [LAC] was significantly (P <.001) higher at admission in nonsurvivors (4.10mmol/L [range, 0.60-18.20mmol/L]) when compared with survivors (1.30mmol/L [range, 0.30-13.90mmol/L]) and this difference remained at all subsequent time points. The odds ratio for nonsurvival increased from 1.29 (95% confidence interval 1.17-1.43) at admission to 49.90 (6.47-384) at 72 hours after admission for every 1mmol/L increase in [LAC]. [LAC]ΔT was initially positive in all horses but became negative and significantly lower in nonsurvivors for the time periods between 24-72 hours (-0.47, P =.001) and 48-72 hours (-0.07, P =.032) when compared with survivors (0.00 at both time periods) consistent with lactate accumulation in nonsurvivors. Conclusions and Clinical Importance: These results indicate that lactate metabolism is impaired in critically ill horses and [LAC]ΔT can be a useful prognostic indicator in horses.