Acidosis and hypocalcemia commonly develop in many critically ill dogs1–3 and also in some dogs undergoing general anesthesia.4–6 In these dogs, it is important to tightly control PaO2 to ensure normal blood oxygenation. In studies7,8 in dogs, our research group determined that metabolic acidosis directly stimulates PTH secretion, that the acidosis-induced increase in arterial Ca2+ concentration reduces the magnitude of PTH stimulation during metabolic acidosis, and that metabolic acidosis enhances the stimulation of PTH secretion during the induction of hypocalcemia. In those studies, arterial blood gases were measured, and as a result, we became aware that both metabolic acidosis and changes in arterial Ca2+ concentration affected PaO2 values.
Metabolic acidosis is known to increase PaO2 values in dogs. The prevailing opinion is that the increase in PaO2 results from a reduction in the alveolar-to-arterial O2 difference caused by a shift in the oxygen-hemoglobin dissociation curve (Bohr effect).9,10 In an earlier study,11 it was suggested that the metabolic acidosis-induced increase in PaO2 might result from a more homogeneous distribution between ventilation and perfusion in the lungs. However, none of those studies evaluated the effect of the increase in arterial Ca2+ concentration that occurs during metabolic acidosis. The purpose of the study reported here was to evaluate the effects of metabolic acidosis and changes in arterial blood Ca2+ concentration on PaO2 values in anesthetized dogs.
Arterial blood pH
Ketolar 50 mg, Parke-Davis SL, Barcelona, Spain.
Fentanest, Productos Roche SA, Madrid, Spain.
Thalamonal, Productos Roche SA, Madrid, Spain.
Pentotal sodico 1 g, Abbot Laboratories, Madrid, Spain.
Servoventilador, Siemens-Elema 900, Lycksele, Sweden.
Dormicum, Productos Roche SA, Madrid, Spain.
Pavulon, Organon Teknika Española, Barcelona, Spain.
Hewlett Packard 7754B system, Houston, Tex.
HCl 37%, Merck KgaA, Darmstadt, Germany.
Na2EDTA, Sigma-Aldrich Chemie Gmbh, Steinheim, Germany.
Na2SO4, Panreac, Barcelona, Spain.
Ciba-Corning Model 850, Bayer Diagnostics, Barcelona, Spain.
Nichols Institute Diagnostics, San Juan Capistrano, Calif.
Phosphorus inorganic, Sigma Diagnostics, St Louis, Mo.
Magnesium, Sigma Diagnostics, St Louis, Mo.
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