Interpret the following ABG values: PaCo2 - 65, HCO3 - 15 mEq/L and pH - 7.21:

pH - 7.21 , HCO3 - 15 mEq/L , PaCo2 - 65, HCO3 - 15 mEq/L = Mixed respiratory and metabolic acidosis The patient has acidosis. The decreased bicarbonate points to metabolic etiology. For compensation in metabolic acidosis, patient will hyperventilate and carbon dioxide washout will occur. There is a linear relationship between PaCO2 and serum HCO3 in metabolic acidosis. Winter's formula: expected PaCO2= + Expected PaCO2= (1.5X15) +8+-2 = 22.5 + 8 +- 2= 28-32 Interpretation from Winter's formula If PaCO2 is lower than normal, there is a concomitant primary respiratory alkalosis If PaCO2 is higher than normal, there is a concomitant primary respiratory acidosis Note : Salicylate poisoning is characterised by Both Metabolic and respiratory acidosis