What is the primary treatment for severe metabolic acidosis due to ASA overdose?

Sodium bicarbonate is the primary treatment for severe metabolic acidosis resulting from acetylsalicylic acid (ASA) overdose because it helps to correct the acid-base balance in the patient's body. Aspirin (ASA) overdose can lead to metabolic acidosis due to the acidic nature of salicylates and their effects on the body's metabolism, including increased production of lactic acid and decoupling of oxidative phosphorylation.

Administering sodium bicarbonate helps to neutralize the excess acid in the bloodstream and increase the pH, thus addressing the acute complications associated with severe acidemia. Additionally, it may help to enhance the renal excretion of salicylate, further aiding recovery from overdose.

Other treatments, such as activated charcoal, can be effective if given shortly after ingestion but are not the primary treatment for established metabolic acidosis. Fluid replacement could be important for overall management and rehydration but does not directly address the acidosis. Insulin therapy is typically used in cases of hyperglycemic emergencies, such as diabetic ketoacidosis, and is not relevant for treating metabolic acidosis due to ASA overdose. Thus, sodium bicarbonate stands out as the most directed approach to manage the acid-base derangement in this scenario.