A patient with salicylic acid poisoning has the following aerial blood gas analysis repo: pH= 7.1, pCO2 = 18mmHg, HCO3- = 12 mmol/L. The acid-base disorder here is ________

The acid-base disorder here is a mixed disorder of metabolic acidosis and respiratory alkalosis. It should not be confused with metabolic acidosis with uncompensated respiratory alkalosis. This can be understand by the following calculation: Step 1: The pH in this patient is 7.1 (pH < 7.35) which indicates acidosis Step 2: HCO3- is 12mmol/L (Normal HCO3- : 22-30 mmol/L). In metabolic acidosis, HCO3- levels decrease. Hence, this is a case of metabolic acidosis. Step 3: As per Winter&;s formula , the expected respiratory compensation in metabolic acidosis can be calculated using, pCO2= (1.5*) + 8 +/- 2 = 26+/- 2 = 24-28 mmHg. The pCO2 in this patient is 18 mmHg, which implies there is an overcompensation of pCO2. This overcompensation can happen only if there is an additional component of respiratory alkalosis contributing to reduce pCO2. Hence, this patient has a mixed disorder- metabolic acidosis and respiratory alkalosis Ref: Harrison&;s Principles Of Internal Medicine 20th edition Pgno: 315