A 34-year-old man is brought to the emergency department with new-onset confusion and lethargy. Laboratory studies, including an arterial blood gas, are obtained. The changes in his blood gas parameters are shown in the graph below. Point A represents these parameters at the patient's physiologic baseline, and point B indicates his state on arrival in the emergency department. Which of the following is the most likely diagnosis?

Question

A 34-year-old man is brought to the emergency department with new-onset confusion and lethargy.  Laboratory studies, including an arterial blood gas, are obtained.  The changes in his blood gas parameters are shown in the graph below.  Point A represents these parameters at the patient's physiologic baseline, and point B indicates his state on arrival in the emergency department.   Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

11ec160b_3a31_66d1_9249_fd3a11429a1a_MD0001_00 Point B on the graph above shows that this patient has a decreased pH compared to his baseline physiologic state, which indicates acidosis. The next step is to determine whether the acidosis is driven by a metabolic or respiratory disturbance. Acidosis can be caused by either a decrease in serum bicarbonate (metabolic) or an increase in PaCO₂ (respiratory). This patient demonstrates decreased serum bicarbonate, indicating metabolic acidosis as the primary disturbance. The decreased PaCO₂ represents respiratory compensation (via hyperventilation to breathe off CO₂) to help normalize the pH. (Choice B) Metabolic alkalosis would be characterized by increased pH and serum bicarbonate. The PaCO₂ would also increase due to respiratory compensation. (Choices C and D) Respiratory acidosis involves decreased pH and increased PaCO₂. Respiratory alkalosis is recognized by increased pH and decreased PaCO₂. Plasma bicarbonate gradually increases or decreases to compensate for the primary respiratory disturbance (renal compensation). However, unlike respiratory compensation, these responses are delayed and take place over ~72 hours. Educational objective: Metabolic acidosis is characterized by a decrease in serum pH and serum bicarbonate. PaCO₂ will also decrease due to respiratory compensation for the primary metabolic acidosis.

A 34-Year-Old Man Is Brought to the Emergency Department with New-Onset