Acid-base, metabolic, and hemodynamic effects of sodium bicarbonate or tromethamine administration in anesthetized dogs with experimentally induced metabolic acidosis

P. F. Moon From the Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, 14853 (Moon, Gleed, Erb) and the College of Veterinary Medicine, University of Sydney, Sydney, Australia (Gabor).

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L. Gabor From the Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, 14853 (Moon, Gleed, Erb) and the College of Veterinary Medicine, University of Sydney, Sydney, Australia (Gabor).

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R. D. Gleed From the Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, 14853 (Moon, Gleed, Erb) and the College of Veterinary Medicine, University of Sydney, Sydney, Australia (Gabor).

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H. N. Erb From the Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, 14853 (Moon, Gleed, Erb) and the College of Veterinary Medicine, University of Sydney, Sydney, Australia (Gabor).

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Abstract

Objective

To evaluate buffering capacity and side effects of equivalent doses of tromethamine (THAM) and sodium bicarbonate (BIC).

Animals

18 purebred dogs.

Procedure

Acidosis was induced by having dogs breathe a hypoxic gas mixture (FIO2 = 0.10) until arterial base balance ≤ −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 Fio2 increased to 0.30. Drug doses were calculated to correct base balance to zero.

Results

During hypoxia, for BIC- and THAM-treated groups, median (interquartile range [Q1, Q3]) 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 BIC- 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 ≤ 0.05) difference between groups was hypernatremia after BIC administration that persisted for 60 minutes. The PaCO2 in BIC-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 BIC, 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. (Am J Vet Res 1997;58:771–776)

Abstract

Objective

To evaluate buffering capacity and side effects of equivalent doses of tromethamine (THAM) and sodium bicarbonate (BIC).

Animals

18 purebred dogs.

Procedure

Acidosis was induced by having dogs breathe a hypoxic gas mixture (FIO2 = 0.10) until arterial base balance ≤ −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 Fio2 increased to 0.30. Drug doses were calculated to correct base balance to zero.

Results

During hypoxia, for BIC- and THAM-treated groups, median (interquartile range [Q1, Q3]) 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 BIC- 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 ≤ 0.05) difference between groups was hypernatremia after BIC administration that persisted for 60 minutes. The PaCO2 in BIC-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 BIC, 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. (Am J Vet Res 1997;58:771–776)

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