A 43-year-old woman with borderline personality disorder is brought to the emergency department after taking an undetermined number of pills. She is lethargic but arousable. She refuses to answer questions. Blood pressure is 110/60 mm Hg and heart rate is 120/min and regular. Laboratory results are as follows: Which of the following best describes this patient's acid-base disturbance?

Question

A 43-year-old woman with borderline personality disorder is brought to the emergency department after taking an undetermined number of pills.  She is lethargic but arousable.  She refuses to answer questions.  Blood pressure is 110/60 mm Hg and heart rate is 120/min and regular.  Laboratory results are as follows:  Which of the following best describes this patient's acid-base disturbance?

Quizplus · Accepted Answer

11ec160b_3cff_c8ea_9249_91b3d620300d_MD0001_00 This patient's elevated pH and low PaCO₂ (<40 mm Hg) are suggestive of primary respiratory alkalosis. Normally, serum bicarbonate is expected to drop in response. However, a bicarbonate of 13 mEq/L is much lower than the expected secondary compensation, which indicates a second primary acid-base disorder. The lower-than-expected serum bicarbonate with a high anion gap [139 − (98 + 13) = 28] is consistent with a concomitant primary anion gap metabolic acidosis. This mixed respiratory alkalosis and anion gap metabolic acidosis is most likely the result of salicylate poisoning: The pH is typically near or within normal range in patients with salicylate poisoning because of the opposing influences of the respiratory alkalosis and metabolic acidosis. (Choice A) Primary metabolic acidosis and primary metabolic alkalosis can simultaneously develop in the setting of 2 disparate pathologic processes (eg, renal failure and vomiting). The pH and bicarbonate levels can be increased, normal, or decreased, depending on the severity of the metabolic acidosis compared with the metabolic alkalosis. (Choice B) Primary metabolic acidosis with primary respiratory acidosis (eg, sepsis and hypoventilatory respiratory failure) typically leads to significant acidemia (very low pH) with low bicarbonate and high PaCO₂. (Choice D) Primary metabolic alkalosis with primary respiratory acidosis (eg, vomiting and hypoventilation due to opioid overdose) is expected to show elevated bicarbonate and PaCO₂; the pH can reflect alkalemia or acidemia, depending on the relative severity of the 2 disturbances. (Choice E) Primary metabolic alkalosis with primary respiratory alkalosis (eg, vomiting and hyperventilation due to anxiety) is expected to cause significant alkalemia (very high pH) with high bicarbonate and low PaCO₂. Educational objective: Salicylate poisoning causes mixed primary respiratory alkalosis and primary anion gap metabolic acidosis. Mixed acid-base disturbances can be recognized by inappropriate secondary compensation for one of the primary disturbances, indicating that an additional primary disturbance must be present.

A 43-Year-Old Woman with Borderline Personality Disorder Is Brought to the Emergency