A 17-year-old man is brought to the emergency room with confusion and incoordination. He is uncooperative and refuses to provide further history. Physical examination reveals an RR of 30; the vital signs are otherwise normal as is the general physical examination. Laboratory values are as follows:
Which of the following is the most likely cause of the acid base disorder?
A. GI loss owing to diarrheaThe patient has a metabolic acidosis. Respiratory compensation is appropriate, and the anion gap is normal. Therefore, he has a hyperchloremic (normal anion gap) metabolic acidosis. Common causes include renal tubular acidosis, bicarbonate loss owing to diarrhea, and mineralocorticoid deficiency. In a metabolic acidosis, the urine pH should be low (ie, the patient should be trying to excrete the excess acid). This patient’s high urine pH is therefore diagnostic of renal tubular acidosis (RTA). Proximal RTA is associated with glycosuria, phosphaturia, and aminoaciduria (Fanconi syndrome). Since the serum phosphorus is normal and glycosuria is absent, proximal RTA is unlikely. GI loss of bicarbonate caused by diarrhea would be associated with an appropriately acidic urine (pH < 5.5). Disorders of the renin-angiotensin-aldosterone system are associated with hyperkalemia, not hypokalemia. The low PCO2 excludes respiratory acidosis. So this patient has a distal RTA, probably because of toluene inhalation (glue sniffing). Toluene can lead to life-threatening metabolic acidosis and hypokalemia.