WBR0383
| Author | [[PageAuthor::Rim Halaby, M.D. [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Physiology |
| Sub Category | SubCategory::Renal |
| Prompt | [[Prompt::A 54 year old male patient is brought to the emergency department with confusion and altered consciousness. Appropriate history could not be taken due to the patient’s clinical status. Patient’s arterial blood gas (ABG) and blood lab tests are withdrawn and reveal the values as shown in the table below. What is the most likely cause of this patient’s condition?]] |
| Answer A | AnswerA::Narcotics abuse |
| Answer A Explanation | AnswerAExp::Narcotic abuse causes hypoventilation. A respiratory acidosis with elevated pCO2 would have been present. |
| 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 causes a normal anion gap metabolic acidosis. Acetazolamide is used to treat metabolic alkalosis |
| Answer E | AnswerE::Severe vomiting |
| Answer E Explanation | [[AnswerEExp::Severe vomiting causes metabolic alkalosis due to loss of gastric acid while vomiting. pH would have been > 7.4 with elevated bicarbonate.]] |
| Right Answer | RightAnswer::B |
| Explanation | [[Explanation::The patient presents with a high anion-gap metabolic acidosis. The approach to acid-base disturbances starts with assessment of pH. Since pH = 7.26, the patient is in a state of acidosis. Since acidosis could either be metabolic or respiratory, bicarbonate and pCO2 are both helpful in the distinguishing between the two. In this vignette, the patient has metabolic acidosis, as demonstrated by low bicarbonate. Had the patient had respiratory acidosis, his pCO2 would have been elevated, which is not the case.
There are 2 types of metabolic acidosis: Normal anion gap (hyperchloremic) or high anion gap (normochloremic). To differentiate them, the equation: Anion Gap = Sodium – (Chloride + Bicarbonate) is used. A normal anion-gap is in the range of 8-12 mEq/L. This case is an example of high anion gap metabolic acidosis. Anion gap = 140 – (100 + 12) = 30 mEq/L. Identification of the type of acid-base abnormality is sometimes crucial because it can be very helpful in the diagnosis. Among the list of options, only methanol intoxication reveals a high anion gap metabolic acidosis. Other causes of high anion gap metabolic acidosis can be remembered by KARMEL: Ketoacidosis – Aspirin intoxication - Renal failure – Methanol – Ethanol - Lactic acidosis. Educational Objective:
Measurement of anion-gap in metabolic acidosis is important to identify possible diagnoses. Anion-gap = Sodium – (Chloride + Bicarbonate). Common causes of high anion gap metabolic acidosis are KARMEL = Ketoacidosis - Aspirin toxicity – Renal failure – Methanol intoxication – Ethanol intoxication – Lactic acidosis |
| Approved | Approved::No |
| Keyword | |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |