<prompt> A patient with salicylic acid poisoning has the following arterial blood gas analysis report: pH 7.12; PCO2 18 mmHg; HCO3 12 mmolL. The resulting acid-base abnormality can be best labeled as:Metabolic acidosis with respiratory alkalosisMetabolic acidosis with respiratory acidosisRespiratory acidosis with metabolic alkalosisMetabolic acidosis  <response>: Ans. is a i.e. Metabolic acidosis with respiratory alkalosisRef. Harrison 17the p 288 16the p 2591, 266 15the page 284, 286,187Also see June 2000 Q. No. 94.In patients with salicylate poisoning, initially the acidic metabolites of salicylic acid accumulate and cause metabolic acidosis.This causes the following acid base reaction to shift to left because of addition of H CO2 H20 H2CO3 H HCO3-This causes decrease in extracellular HCO3 This in turn stimulates the medullary chemoreceptors to increase ventilation and return the ratio of PaCO2 and thus pH towards normal The formula given to predict the degree of compensation required for simple form of metabolic acidosis is PaCO2 1.5 x 8 or you can say that the PaCO2 is expected to decrease 1.25 mm of Hg for each mmolL decrease in The normal values of PCO2 and HCO3-Arterial PC02 - 40 - 2 mm HgArterial - 24 - mm HgThus a patient with metabolic acidosis and of 12 mmolL would be expected to have a PaCO2 between 24 and 28 mm Hg. to compensate for the acidosisValues of PaCO2 below 24 or greater than 28 mm Hg will mean mixed disturbance.If PaCO2 is 24 it means metabolic acidosis respiratory alkalosis hyperventilation has led to excess CO2 washout causing respiratory alkalosisIf PaCO2 28 it means - metabolic acidosis respiratory acidosisHere is a table giving predictions of compensatory response on simple acid base disturbance. Prediction of Compensatory Responses on Simple Acid-Base DisturbancesDisorderPrediction of CompensationMetabolic acidosisPaCO2 1.5xHCO3- 8 OrPaCO2 will 1.25mmHg per mmolL in OrPaCO22 15Metabolic alkalosisPaCO2 will 0.75 mmHg per mmolL in orPaCO2 will 6 mmHg per 10-mmolL in OrPaCO2 15Respiratory AlkalosisAcute will 2 mmolL per 10-mmHg in PaCO2Chronic will 4 mmolL per 10-mmHg in PaCO2Respiratory acidosisAcute will 1 mmolL per 10-mmHg T in PaCO2Chronic will 4 mmolL per 10-mmHg in PaCO2 