A 36-year-old man is brought to the emergency department due to confusion, nausea, and decreased arousal. He is unable to answer questions, and no other history is available. Temperature is 36.7 C (98.2 F), pulse is 86/min, and respirations are 22/min. His arterial blood gas and serum electrolyte results are shown below: What is the most likely primary acid-base disorder in this patient?

Question

A 36-year-old man is brought to the emergency department due to confusion, nausea, and decreased arousal.  He is unable to answer questions, and no other history is available.  Temperature is 36.7 C (98.2 F), pulse is 86/min, and respirations are 22/min.  His arterial blood gas and serum electrolyte results are shown below:  What is the most likely primary acid-base disorder in this patient?

Quizplus · Accepted Answer

Explanation: This patient's primary acid-base disorder is anion gap metabolic acidosis. This is evidenced by his acidic pH (< 7.35) and his severe primary decrease in HCO3 (< 24 mEq/L). Normally, the anion gap (AG) is made up of negatively charged molecules (eg, protein, citrate, phosphate, sulfate) that are normally present in serum. These molecules account for the normal anion gap value of 10-14 mEq/L. The AG can be calculated using the following formula: AG = Measured cations (positive charge) − Measured anions (negative charge) Because the major cation in the serum is Na⁺, and the major anions in the serum are Cl^- and HCO₃^-, the formula for plasma AG can be simplified as follows: ⁺ ^- ₃^- AG = Na⁺ − (HCO₃^- + Cl^-) ⁺ ₃^- ^- This patient's calculated AG = 136 − (90 + 12) = 136 − 102 = 34 mEq/L, an abnormally elevated value. An increase in the AG indicates the presence of nonchloride acids that contain inorganic (phosphate, sulfate), organic (ketoacids, lactate, uremic organic anions), exogenous (salicylate or ingested toxins with organic acid production), or unidentified anions. The most common causes of anionic gap metabolic acidosis and their corresponding unmeasured anions that compose the anion gap are: Lactic acidosis (lactate) Ketoacidosis (beta-hydroxy butyrate, acetoacetic acid) Methanol / formaldehyde ingestion (formic acid) Ethylene glycol ingestion (glycolic acid, oxalic acid) Salicylate poisoning (salicylic, lactic, sulfuric and phosphoric acids) Uremia (eg, endstage renal disease) (impaired excretion of H⁺) Educational objective: The anion gap (AG) represents the concentration of unmeasured serum anions. In anion gap metabolic acidosis, the AG is increased by the abnormal presence of non-chlorinated acids in the serum.

A 36-Year-Old Man Is Brought to the Emergency Department Due