ACID-BASE, METABOLIC, AND HEMODYNAMIC-EFFECTS OF SODIUM-BICARBONATE OR TROMETHAMINE ADMINISTRATION IN ANESTHETIZED DOGS WITH EXPERIMENTALLY-INDUCED METABOLIC-ACIDOSIS

Objective-To evaluate buffering capacity and side effects of equivalen t doses of tromethamine (THAM) and sodium bicarbonate (BIG). Animals-1 8 purebred dogs. Procedure-Acidosis was induced by having dogs breathe a hypoxic gas mixture (F-IO2 = 0.10) until arterial base balance less than or equal to -7.5 mEq/L was reached. Dogs then received a 30-minu te infusion of 5% BIC (n = 6) or 0.3M THAM (n = 8), and F-IO2 increase d to 0.30. Drug doses were calculated to correct base balance to zero. Results-During hypoxia, for BIG- and THAM-treated groups, median (int erquartile range [Q(1), Q(3)]) pHa and arterial base balance decreased to 7.16 (7.07, 7.38) and 7.19 (7.11, 7.31), -14 (-16, 9) and -12 (-16 , -11) mEq/L, respectively, and mixed venous lactate concentration inc reased to 7 (2, 15) and 6 (3, 13) mmol/L, respectively. Immediately af ter each infusion, acid-base and cardiopulmonary variables returned to ward baseline. For respective BIG- and THAM-treated groups, pHa increa sed to 7.37 (7.26, 7.44) and 7.40 (7.33, 7.49) and base balance increa sed to 0 (-4, 7) and 0 (-4, 2) mEq/L. Lactate concentration decreased only slightly to 5 (2, 6) and 5 (2, 9) mmol/L, but continued to decrea se throughout the study. The only significant (P less than or equal to 0.05) difference between groups was hypernatremia after BIG administr ation that persisted for 60 minutes. The Pace, in BIG-treated dogs inc reased immediately after infusion, compared with values during hypoxia . Standardized ionized calcium values initially decreased in both grou ps, but returned to baseline by 60 minutes.Conclusion-The buffering ca pacity of THAM is equal to that of BIG, although THAM does not cause t he transient hypernatremia or hypercapnia observed after BIC administr ation. Hypocalcemia may be transient after administration of either so lution. Thus, THAM is an acceptable alternative to BIC for treatment o f metabolic acidosis in selected anesthetized dogs.