title: Age-dependent response of the acid-base parameters (Henderson-Hasselbalch, Stewart) in healthy calves with experimentally induced metabolic acidosis.
abstract: 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: 4-104 days) were infused with 5M NH4Cl solution (dose: 1.0 ml/kg) through a permanent intravenous catheter. Before (0 hrs) and after starting the infusion (2, 4, 6, 8 and 24 hrs) 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 2-6 hrs after the infusion of the NH4Cl solution, the Henderson-Hasselbalch parameters decreased significantly (decrease pH, decrease [HCO3-]) as did Stewart's variables (decrease [Strong ion difference=SID3], decrease [Acid total = A(tot) or A-]). A transient moderate hyperchloraemic acidosis with a slight hypoproteinaemic alkalosis was observed in all calves in association with a respiratory compensation (decrease PCO2). The younger calves (1st-3rd week) showed a similar pattern of response to the same dose per kg 0.75 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-[A(tot)]. The mean difference was -0.03 to -0.09 compared with the measured pH (7.32-7.40).
  
  
  CONCLUSIONS
  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 week of life reacted more sensitively to an equal acidotic condition than the older animals.
authors.affiliation: Department of Physiology, Faculty of Veterinary Medicine, University of Khartoum, Sudan.
authors.forename: Nawal M
authors.initials: NM
authors.lastname: Elkhair
authors.forename: Christiane
authors.initials: C
authors.lastname: Siegling-Vlitakis
authors.forename: Eva
authors.initials: E
authors.lastname: Radtke
authors.forename: Antje
authors.initials: A
authors.lastname: Willing
authors.forename: Helmut
authors.initials: H
authors.lastname: Hartmann
mesh_terms: D000136:Acid-Base Equilibrium / Q000502:physiology*; D000137:Acid-Base Imbalance / Q000175:diagnosis / Q000378:metabolism; D000138:Acidosis / Q000139:chemically induced / Q000378:metabolism / Q000662:veterinary*; D000367:Age Factors; D000375:Aging / Q000378:metabolism; D000643:Ammonium Chloride / Q000493:pharmacokinetics*; D000818:Animals; D019540:Area Under Curve; D002417:Cattle; D002418:Cattle Diseases / Q000175:diagnosis / Q000378:metabolism*; D007263:Infusions, Parenteral / Q000379:methods / Q000662:veterinary*; D011897:Random Allocation
chemical_list: D000643:Ammonium Chloride