Contribution of unmeasured anions to acid-base disorders and its association with altered demeanor in 264 calves with neonatal diarrhea

Abstract

Background: The quantitative effect of strong electrolytes, unmeasured anions (UAs), pCO2, and plasma protein concentrations in determining plasma pH and bicarbonate (HCO3-) can be demonstrated using the physicochemical approach. Demeanor of calves with diarrhea is associated with acidemia, dehydration, and hyper-d-lactatemia. Hypothesis: Unmeasured anions are a major factor influencing changes in plasma pH and HCO3- of calves with diarrhea and UAs and strong UAs, estimated by anion gap (AG) and strong ion gap (SIG), respectively, are more strongly associated with alteration of demeanor compared to other acid-base variables. Animals: A total of 264 calves with diarrhea from two data sets (DS1 and DS2). Methods: Retrospective study. Forward stepwise regression was performed to determine the relationship between measured pH or HCO3-, and physicochemical variables. A two-way ANOVA was performed to investigate the association between acid-base variables and attitude (bright, obtunded, and stuporous), posture (standing, sternal or lateral recumbency), and strength of suckling reflex (strong, weak, or absent). Results: Increased strong UAs estimated by SIG was the most important contributor to changes in measured pH and HCO3- (DS1: r2 66 and 59%, DS2: 39 and 42%, P < .0001). SIG and AG were correlated to deteriorating calf demeanor for all three clinical scoring categories: attitude, posture, and suckle reflex (P < .0001). Conclusion and Clinical Relevance: Elevated concentrations of strong UAs were the primary cause of acidemia and had an important influence on the demeanor of calves with diarrhea. These findings emphasize the importance of the calculation of UAs when evaluating acid-base abnormalities in calves. © 2013 by the American College of Veterinary Internal Medicine.