Comparison of the measurement of total carbon dioxide and strong ion difference for the evaluation of metabolic acidosis in diarrhoeic calves

Eighty-four calves with diarrhoea were treated with fluids and 13 apparentl y healthy calves of similar ages were sampled as controls. Their total bloo d carbon dioxide (TCO2) was measured with a Harleco apparatus and 31 of the calves were treated with oral fluids and 53 with parenteral fluids. The or al fluid contained 118 mmol/litre Na+, 25 mmol/litre K+, 110 mmol/litre glu cose, 108 mmol/litre bicarbonate (HCO3- as citrate), 43 mmol/litre Cl-, 4 m mol/litre Ca++, 4 mmol/litre Mg++ and 20 mmol/litre glycine, and the parent eral fluid contained 144 mmol/litre Na+, 4 mmol/litre K+, 35 mmol/litre HCO 3- and 113 mmol/litre Cl-. Both treatments resulted in significant improvem ents in acid-base status as demonstrated by an increase in TCO2, and the tr eatment was successful in 27 of the 31 calves receiving oral fluids and in 45 of the 53 calves receiving parenteral fluids. Thirty-seven of the calves treated parenterally were very severely acidotic (TCO2 <8 mmol/litre) init ially and they received an additional 400 mmol HCO3- added to the first 5 l itres of infusion. Treatment was successful in 33 of these calves. The deci sion to administer additional bicarbonate was made on the basis of their ac id-base status as measured with a Harleco apparatus. The strong ion differe nce (Na+ +K+-Cl-) (SID) of the calves was calculated retrospectively. There was a significant correlation between the SID and TCO2 of the calves treat ed with oral fluids but not among the control calves or the calves treated parenterally. Furthermore, measurements of the change in SID during therapy gave little indication of the change in acid-base status as measured by th e Harleco apparatus, with the SID decreasing (suggesting a worsening of aci d-base status) in 16 calves in which the TCO2 increased (suggesting an impr ovement in acid-base status). There was a significant correlation between t he change in SID and the change in TCO2 during treatment in the calves rece iving oral fluids but not in the calves treated parenterally.