A 19-year-old man comes to the emergency department with a daylong history of nausea and abdominal pain. Temperature is 37.6 C (99.7 F) , blood pressure is 122/86 mm Hg, pulse is 88/min, and respirations are 25/min and deep. BMI is 18 kg/m². Pulse oximetry is 98% on room air. On physical examination, the mucous membranes are dry and skin turgor is decreased. The lungs are clear to auscultation. There is diffuse tenderness to palpation over the abdomen without rebound or guarding. Laboratory results are as follows: Which of the following arterial blood gas findings are most likely to be found in this patient?

Question

A 19-year-old man comes to the emergency department with a daylong history of nausea and abdominal pain. Temperature is 37.6 C (99.7 F) , blood pressure is 122/86 mm Hg, pulse is 88/min, and respirations are 25/min and deep. BMI is 18 kg/m². Pulse oximetry is 98% on room air. On physical examination, the mucous membranes are dry and skin turgor is decreased. The lungs are clear to auscultation. There is diffuse tenderness to palpation over the abdomen without rebound or guarding. Laboratory results are as follows:

Which of the following arterial blood gas findings are most likely to be found in this patient?

Quizplus · Accepted Answer

Explanation: This patient with abdominal pain, dehydration, hyperventilation (fast and deep respirations), and markedly elevated glucose has classic symptoms of diabetic ketoacidosis (DKA), which is associated with type 1 diabetes mellitus (T1DM). Key features consistent with DKA and T1DM in this patient include acute symptom onset, lean body habitus (BMI <25 kg/m²), and young age. DKA is often the initial presenting finding of T1DM. ² Expected acid-base findings in DKA with hyperventilation include decreased pH, PaCO₂, and bicarbonate: ₂ DKA causes an anion gap metabolic acidosis due to the rapid accumulation of ketoacids (beta-hydroxybutyrate, acetoacetate). Serum bicarbonate and pH are therefore decreased. Chemoreceptors sense decreased serum bicarbonate and trigger hyperventilation, resulting in decreased PaCO₂ and representing compensatory respiratory alkalosis. Compensatory responses (whether correcting for acidosis or alkalosis) are unable to completely return the pH to normal. Therefore, although hyperventilation slightly elevates the pH (as the PaCO₂ decreases), the pH still remains acidic, reflecting metabolic acidosis as the primary acid-base disturbance (Choices D and E). (Choice B) Low pH with a high PaCO₂ suggests primary respiratory acidosis; a concurrent elevation in serum bicarbonate suggests compensatory metabolic alkalosis. This can be seen in patients with long-standing chronic obstructive pulmonary disease due to chronic CO₂ retention. ₂ ₂ (Choice C) Low pH and bicarbonate suggest primary metabolic acidosis; the normal PaCO₂ suggests absence of a compensatory respiratory response. This can be seen in the very early stages of metabolic acidosis; however, a normal PaCO₂ would be unexpected in this patient, given his high respiratory rate and daylong history of symptoms. ₂ ₂ (Choice F) Normal bicarbonate and PaCO₂ levels are not expected in this acutely ill patient with hyperventilation and markedly elevated blood glucose. ₂ Educational objective: Diabetic ketoacidosis commonly occurs as a presenting symptom of type 1 diabetes mellitus. It generates anion gap metabolic acidosis (low pH, low bicarbonate) and can be accompanied by compensatory respiratory alkalosis (signified by increased respiratory rate and deep breathing) leading to decreased PaCO₂. The pH can be restored to near-normal levels but never fully corrects. ₂

A 19-Year-Old Man Comes to the Emergency Department with a Daylong