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The intensity of the response to acid-base parameters in relation to the age after a defined acid load was studied in calves.
32 clinically healthy calves (age: 4-104days) were infused with 5M NH4Cl solution (dose: 1.0ml/kg) through a permanent intravenous catheter. Before (0 hrs) and after starting the infusion (2, 4, 6, 8 and 24hrs) venous blood samples were collected for the determination of the various acid-base parameters. The intensity of the response of the acid-base parameters was estimated by using the ?area under curve (AUC)? procedure.
By 2-6hrs after the infusion of the NH4Cl solution, the Henderson-Hasselbalch parameters decreased significantly (pH,[HCO3-]) as did Stewart?s variables ([Strong ion difference=SID3],[Acid total=Atot or A-]). A transient moderate hyperchloraemic acidosis with a slight hypoproteinaemic alkalosis was observed in all calves in association with a respiratory compensation (PCO2). The younger calves (1st-3rdweek) showed a similar pattern of response to the same dose per kg0.75 acid load with significantly greater acid-base parameters response (higher AUC values) than the older animals. The calculated pH was determined by using the three Stewart variables PvCO2, serum-[SID3] and serum-[Atot]. The mean difference was
-0.03 to -0.09 compared with the measured pH (7.32-7.40).
Conclusion: The Stewart model appears to be more successful in providing a comprehensive evaluation of acid-base status compared with the traditional Henderson-Hasselbalch model. The younger calves during the first few weeks of life reacted more sensitively to an equal acidotic condition than the older animals.