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Acid Base: Back to the Basics of Henderson-Hasselbalch
LETTER
Acid Base: Back to the Basics of HendersonHasselbalch To the Editor: We thank Correia and Bronander1 for their interesting article, “Metformin-associated Lactic Acidosis Masquerading as Ischemic Bowel” in the May 2012 issue of the Journal. The authors demonstrated a case of wide-anion gap metabolic acidosis secondary to metformin (pH of 6.96, pCO2 of 33 mm Hg, bicarbonate of 19 mmol/L, and anion gap of 19 mmol/L). After careful calculation, however, we find that the degree of acidosis and serum bicarbonate level are incongruent. The patient has a wide-anion gap metabolic acidosis as the primary acid-base disturbance based on the low pH, low bicarbonate, and low PaCO2. The expected PaCO2 should be 34.5-38.5 based on Winters’equation2 [expected PaCO2 ⫽ (1.5 ⫻ HCO3) ⫹8 ⫾2]. His delta anion gap/delta bicarbonFunding: None. Conflict of Interest: None. Authorship: All authors had access to the data and a role in writing the manuscript.
0002-9343/$ -see front matter Published by Elsevier Inc.
ate ratio is also high at 1.4, which suggests that he may have coexistent metabolic alkalosis. From Henderson-Hasselbalch equation,3 the patient should have arterial pH of 6.1 ⫹ log 19/0.03 ⫻ 33 ⫽ 7.38 which is substantially higher than the measured value of 6.96 in the article. There could be multiple explanations for this, including a misprint or arterial blood gas and bicarbonate collected at different times. Wisit Cheungpasitporn, Patompong Ungprasert, Narat Srivali, Edward F. Bischof,
MD MD MD MD
Department of Internal Medicine Bassett Medical Center Cooperstown, NY
http://dx.doi.org/10.1016/j.amjmed.2012.04.046
References 1. Correia CS, Bronander KA. Metformin-associated lactic acidosis masquerading as ischemic bowel. Am J Med. 2012;125:e9. 2. Albert MS, Dell RB, Winters RW. Quantitative displacement of acidbase equilibrium in metabolic acidosis. Ann Intern Med. 1967;66:312. 3. Rose BD, Post TW. Clinical Physiology of Acid-Base and Electrolyte Disorders, 5th ed, McGraw-Hill, New York: 2001; 536.
Acid Base: Back to the Basics of HendersonHasselbalch To the Editor: We thank Correia and Bronander1 for their interesting article, “Metformin-associated Lactic Acidosis Masquerading as Ischemic Bowel” in the May 2012 issue of the Journal. The authors demonstrated a case of wide-anion gap metabolic acidosis secondary to metformin (pH of 6.96, pCO2 of 33 mm Hg, bicarbonate of 19 mmol/L, and anion gap of 19 mmol/L). After careful calculation, however, we find that the degree of acidosis and serum bicarbonate level are incongruent. The patient has a wide-anion gap metabolic acidosis as the primary acid-base disturbance based on the low pH, low bicarbonate, and low PaCO2. The expected PaCO2 should be 34.5-38.5 based on Winters’equation2 [expected PaCO2 ⫽ (1.5 ⫻ HCO3) ⫹8 ⫾2]. His delta anion gap/delta bicarbonFunding: None. Conflict of Interest: None. Authorship: All authors had access to the data and a role in writing the manuscript.
0002-9343/$ -see front matter Published by Elsevier Inc.
ate ratio is also high at 1.4, which suggests that he may have coexistent metabolic alkalosis. From Henderson-Hasselbalch equation,3 the patient should have arterial pH of 6.1 ⫹ log 19/0.03 ⫻ 33 ⫽ 7.38 which is substantially higher than the measured value of 6.96 in the article. There could be multiple explanations for this, including a misprint or arterial blood gas and bicarbonate collected at different times. Wisit Cheungpasitporn, Patompong Ungprasert, Narat Srivali, Edward F. Bischof,
MD MD MD MD
Department of Internal Medicine Bassett Medical Center Cooperstown, NY
http://dx.doi.org/10.1016/j.amjmed.2012.04.046
References 1. Correia CS, Bronander KA. Metformin-associated lactic acidosis masquerading as ischemic bowel. Am J Med. 2012;125:e9. 2. Albert MS, Dell RB, Winters RW. Quantitative displacement of acidbase equilibrium in metabolic acidosis. Ann Intern Med. 1967;66:312. 3. Rose BD, Post TW. Clinical Physiology of Acid-Base and Electrolyte Disorders, 5th ed, McGraw-Hill, New York: 2001; 536.