Acid–Base And Electrolyte Regulation Practice Test

A 65-year-old man with a 40-pack-year smoking history and recently diagnosed small cell lung cancer presents to the emergency department with increasing confusion and lethargy over the past 3 days. He has no history of head trauma or neurologic disease. His temperature is 37.1°C (98.8°F), blood pressure is 130/80 mm Hg, pulse is 88/min, and respirations are 16/min. Physical examination reveals a lethargic man who is oriented only to person. He has no focal neurologic deficits. Laboratory studies show a serum sodium of 118 mEq/L, serum osmolality of 245 mOsm/kg, and urine osmolality of 450 mOsm/kg.

A 19-year-old woman with type 1 diabetes mellitus is brought to the emergency department by her roommate due to altered mental status. For the past two days, she has had nausea, vomiting, and abdominal pain. She has not taken her insulin. On examination, she is breathing rapidly and deeply. Her breath has a fruity odor. An arterial blood gas analysis shows: pH 7.15, PaCO2 20 mm Hg, and HCO3- 8 mEq/L.