A 28-year-old man with a history of asthma presents to the emergency department with worsening dyspnea. Yesterday, he was diagnosed with influenza by an urgent care provider. He ran out of his Advair inhaler a month ago and also ran out of his albuterol MDI two weeks ago due to inability to afford the medication. He did not fill the same prescriptions given to him by the urgent care provider.
The arterial blood gas analysis reveals a pH of 7.48, pCO2 of 32 mmHg, and HCO3- of 25 mEq/L.
Which of the following is the most likely primary acid-base disorder?
A) Respiratory alkalosis
B) Respiratory acidosis
C) Metabolic alkalosis
D) Metabolic acidosis
Answer and Rationale:
Acid-base disorders are commonly seen in clinical practice and associated with a number of conditions. Respiratory processes and compensation are due to pulmonary diseases while metabolic processes and compensation are accomplished by the kidneys. A full chapter on this topic can be found on Access Pharmacy in the Naplex Review Guide 4th edition here: https://accesspharmacy.mhmedical.com/content.aspx?bookid=3025§ionid=254094831.
Answer A is correct. In respiratory alkalosis, there is an excessive loss of carbon dioxide, either due to hyperventilation or a primary cause such as anxiety or pain. This leads to a decrease in carbonic acid (H2CO3) formation and a subsequent increase in blood pH. The kidneys have not had time to compensate yet and therefore the bicarbonate is essentially normal. In this case the patient has asthma not controlled by any medication and influenza and therefore together is experiencing shortness of breath from both of these factors.
Answer B is incorrect. Respiratory acidosis is characterized by an elevated pCO2 and a decrease in blood pH due to hypoventilation and retention of carbon dioxide. COPD patients often can present with this disorder.
Answer C is incorrect. Metabolic alkalosis is characterized by an elevation in HCO3- and a rise in blood pH, often seen in conditions such as vomiting or excessive bicarbonate intake.
Answer D is incorrect. Metabolic acidosis is characterized by a decrease in HCO3- and a decrease in blood pH, often seen in conditions such as diabetic ketoacidosis or renal failure.
NAPLEX competencies covered:
4.1 – Patient parameters or laboratory measures
Create a Free MyAccess Profile
AccessMedicine Network is the place to keep up on new releases for the Access products, get short form didactic content, read up on practice impacting highlights, and watch video featuring authors of your favorite books in medicine. Create a MyAccess profile and follow our contributors to stay informed via email updates.