Based on this patients pH of 7.32, either a metabolic or respiratory acidosis is present. The Pco2 is diminished (< 40 mm Hg), which is consistent with the presence of at least a metabolic acidosis. Applying Winters formula (predicted Pco2 = 1.5
[serum bicarbonate] + 8), this patients predicted Pco2 is 23 mm Hg. However, the patients actual Pco2 (12 mm Hg) is less than predicted, which is consistent with respiratory alkalosis. Lastly, this patients anion gap (serum sodium [serum chloride + serum bicarbonate]) is elevated at
30 mEq/L (normal, 8-16 mEq/L).3 Therefore, the patient has a mixed anion gap metabolic acidosis and respiratory alkalosis. A possible etiology of the acid-base disorder in this patient is an acute salicylate overdose. Salicylate toxicity disrupts the oxidative mechanisms within cells, leading to the development of an anion gap metabolic acidosis. Moreover, salicylates in high concentrations stimulate the central respiratory center to cause respiratory alkalosis.
- Anion gap metabolic acidosis and respiratory alkalosis.
3. Fall PJ. A stepwise approach to acid-base disorders. Practical patient evaluation for metabolic acidosis and other conditions. Postgrad Med 2000;107:249-50, 253-4, 257-8 passim.
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