Evaluation of the association between strong ion acid–base disturbances and mortality in dogs: a retrospective study

Acid–base abnormalities are frequently encountered in veterinary emergency and critical care, but information regarding the prognostic value of these findings is limited. Several systems for analysing acid–base disturbances have been reported, but the prognostic abilities of these systems have not been compared in dogs. The objectives of this retrospective study were to determine if the commonly used acid–base interpretation methods (Henderson–Hasselbalch, Stewart and semi‐quantitative) have prognostic value, and to compare the performance of the three methods. Electronic medical records were searched to create a database containing point‐of‐care blood‐gas, electrolyte and serum chemistry values for 1024 dogs assessed at a university teaching hospital. Dogs with contemporaneous blood‐gas analysis, blood lactate and serum biochemistry samples were eligible for study, and only the first recorded analyses for each patient visit were included. Components of the Henderson–Hasselbalch, Stewart and semi‐quantitative methods were calculated. To assess prognostic ability and to compare analysis system performance, receiver‐operating characteristic (ROC) curves for survival to hospital discharge were created. Of the 1024 dogs identified, case fatality rate was 23.8%. Area under the ROC curve did not exceed 0.63 for any calculated variable. Performance of all three analysis systems was similar. While some acid–base abnormalities identified were associated with mortality, no individual abnormality or system output yielded sensitive and specific cut‐off values for mortality prediction, and no interpretation method outperformed the others. This study suggests that initial acid–base abnormalities have limited prognostic utility and that various analysis systems can be used to assess acid–base disturbances in critically ill dogs.