Comparison of lactate, base excess, bicarbonate, and pH as predictors of mortality after severe trauma in rhesus macaques (Macaca mulatta)

Abstract

Social group housing of rhesus macaques at biomedical facilities is advocated to improve the psychologic wellbeing of these intelligent and social animals. An unintended outcome of social housing in this species is increased intraspecific aggression resulting in cases of severe multiple trauma and posttraumatic shock. The metabolic correlates of oxygen debt are likely important quantifiers of the severity of posttraumatic shock and may serve as useful guides in the treatment of these cases. The purpose of this retrospective study was to evaluate venous blood lactate, base excess, bicarbonate, and pH as predictors of mortality. These 4 variables were assessed in 84 monkeys with severe traumatic injury and shock. Data were available from blood samples collected prior to resuscitation therapy and the day after resuscitation therapy. The pre- and postresuscitation therapy levels of the variables then were tested for association with 6-d survival. When measured prior to resuscitation therapy, all variables were strongly correlated with each other and had a statistically significant association with survival. No single variable had both strong specificity and high sensitivity when measured prior to resuscitation therapy. Survival analysis showed that as the number of categorical indicators of acidosis increased, 6-d survival decreased. Analysis of the 4 variables after resuscitation therapy indicated that lactate was the only variable significantly associated with survival in our study.

Figure 1.

Flow chart of subjects in the study.

Figure 2.

Negative association of increasing numbers of pretreatment indicators of acidosis with 6-d survival in rhesus macaques. The lines indicate probability of survival at the time indicated. Because the study was stopped at 6 d, the probability of survival at 6 days is not estimatable, and the graph lines terminate at the last death prior to 6 d. Categorical indicators of venous acidosis: lactate, greater than 2 mmol/L; pH, less than 7.35; base excess, less than –2 mEq/L; or bicarbonate less than 15 mmol/L. *, Differences from 0 indicators significant at P < 0.02. +, Differences from 4 indicators significant at P < 0.05.

Figure 3.

Negative association of posttreatment indicators of acidosis with survival in rhesus macaques. The lines indicate probability of survival at the post therapy time indicated. Because the study was stopped at 5 d post therapy (6 d post trauma), the probability of survival at 5 d post therapy cannot be estimated, and the graph lines terminate at the last death prior to 5 d. Categorical indicators of venous acidosis: pH, less than 7.35; base excess, less than –2 mEq/L; or bicarbonate less than 15 mmol/L. *, Differences from 0 indicators significant at P < 0.05.