EFFECT OF HCO₃^- THERAPY ON ACID-BASE HOMEOSTASIS IN NEWBORN DOGS WITH AND WITHOUT VENTILATORY RESTRICTION

Abstract

We have previously reported in 36 newborn dogs-with mechanically fixed ventilation that when HCO₃⁻ is infused, PaCO₂ increases, pH is not affected and PaO₂ decreases significantly, in this study, HCO₃⁻ was infused in 71 spontaneously breathing newborn dogs 0 to 22 days of age. Group A dogs (n=39) were breathing against an air way resistance and large dead space resulting in respiratory and metabolic acidosis. Group B dogs (n=32) were normally ventilating. Each group was subdivided into three subgroups. Groups AI (n=11) & BI (n=9) received 2 meq/kg of HCO₃⁻ rapidly over 3 min, Groups AII (n=19) & BII (n=13) received the same dosage slowly over 3 hrs, and Groups AIII (n=9) & BIII (n=10) served as controls and received no treatment. Within 1-3 minutes following HCO₃⁻ Group BI raised their blood pH by .07±.006 units and the pH remained elevated for 90 min. The restricted Group (AI) had a smaller (p<.05) rise in pH (.04±.007 units) and this rise was dissipated in 30 min. PaCO₂ rose by 10±2 Torr in AI pups (p<.01) but not in BI dogs. Base excess rose similarly in both groups. Slow infusion of bicarbonate (subgroup II) had negligible effects on pH and PCO₂ in both groups of animals similar to that for the control experiments (subgroup III). Thus, when ventilation is restricted rapid infusion of bicarbonate does not increase pH as much as when ventilation is normal since the CO₂ produced by the dehydration of HCO₃⁻ cannot be eliminated. These results question the use and efficacy of rapid HCO₃⁻ infusion in infants whose ventilation is restricted.

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