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 equivalent doses of tromethamine (THAM) and sodium bicarbonate (BIG). Animals-18 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-minute infusion of 5% BIC (n = 6) or 0.3M THAM (n = 8), and F-IO2 increased to 0.30. Drug doses were calculated to correct base balance to zero. Results-During hypoxia, for BIG- and THAM-treated groups, median (interquartile 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 increased to 7 (2, 15) and 6 (3, 13) mmol/L, respectively. Immediately after each infusion, acid-base and cardiopulmonary variables returned toward baseline. For respective BIG- and THAM-treated groups, pHa increased to 7.37 (7.26, 7.44) and 7.40 (7.33, 7.49) and base balance increased 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 decrease throughout the study. The only significant (P less than or equal to 0.05) difference between groups was hypernatremia after BIG administration that persisted for 60 minutes. The Pace, in BIG-treated dogs increased immediately after infusion, compared with values during hypoxia. Standardized ionized calcium values initially decreased in both groups, but returned to baseline by 60 minutes. Conclusion-The buffering capacity of THAM is equal to that of BIG, although THAM does not cause the transient hypernatremia or hypercapnia observed after BIC administration. Hypocalcemia may be transient after administration of either solution. Thus, THAM is an acceptable alternative to BIC for treatment of metabolic acidosis in selected anesthetized dogs.