WBR0383
| Author | [[PageAuthor::Rim Halaby, M.D. [1], Alison Leibowitz [2] (Reviewed by Alison Leibowitz)]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Physiology |
| Sub Category | SubCategory::Renal |
| Prompt | [[Prompt::A 54-year-old male is brought to the ER for confusion and altered consciousness. The patient’s arterial blood gas (ABG) and blood lab tests reveal the values displayed in the table below. Which of the following causes most likely led to this patient’s condition?]] |
| Answer A | AnswerA::Narcotics abuse |
| Answer A Explanation | [[AnswerAExp::Narcotic abuse can cause hypoventilation. A respiratory acidosis with elevated pCO2 is characteristic in narcotic abusing patients.]] |
| Answer B | AnswerB::Methanol intoxication |
| Answer B Explanation | [[AnswerBExp::Methanol intoxication can cause a high anion metabolic acidosis clinical picture.]] |
| Answer C | AnswerC::Renal tubular acidosis |
| Answer C Explanation | [[AnswerCExp::Renal tubular acidosis presents with a normal anion gap metabolic acidosis.]] |
| Answer D | AnswerD::Acetazolamide intoxication |
| Answer D Explanation | [[AnswerDExp::Acetazolamide intoxication typically causes a normal anion gap metabolic acidosis. Acetazolamide is often used to treat metabolic alkalosis.]] |
| Answer E | AnswerE::Severe vomiting |
| Answer E Explanation | [[AnswerEExp::Severe vomiting typically causes metabolic alkalosis due to a loss of gastric acid while vomiting. Likely, pH would have been > 7.4 with elevated bicarbonate levels.]] |
| Right Answer | RightAnswer::B |
| Explanation | [[Explanation::The patient likely has a high anion-gap metabolic acidosis. The approach to acid-base disturbances begins with assessment of blood pH. Since the patient's blood pH is 7.26, he is in a state of acidosis. Because acidosis can be metabolic or respiratory, bicarbonate and pCO2 are helpful in the distinguishing between the two. In this scenario, the patient has metabolic acidosis, manifesting with low bicarbonate levels. With respiratory acidosis, the pCO2 level is elevated.
There are two types of metabolic acidosis: Normal anion gap (hyperchloremic) and high anion gap (normochloremic). To differentiate between them, the equation, Anion Gap = Sodium - (Chloride + Bicarbonate) is used. A normal anion-gap ranges btween 8-12 mEq/L. The patient in this scenario exemplifies a high anion gap metabolic acidosis. Anion gap = 140 - (100 + 12) = 30 mEq/L. Identification of the type of acid-base abnormality is crucial because it aids in the diagnosis. Among the possible diagnoses, only methanol intoxication manifests with a high anion gap metabolic acidosis. Other causes of high anion gap metabolic acidosis can be remembered with the mnemonic KARMEL: Ketoacidosis, Aspirin intoxication, Renal failure, Methanol, Ethanol, Lactic acidosis. |
| Approved | Approved::Yes |
| Keyword | |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |