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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor={{Rim}}, {{AJL}} {{Alison}}
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Physiology
|MainCategory=Physiology
Line 20: Line 20:
|MainCategory=Physiology
|MainCategory=Physiology
|SubCategory=Renal
|SubCategory=Renal
|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 as shown in the table below.  Which of the following causes most likely led to this patient’s condition?
|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?
|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.
|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 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.  
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.  
 
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


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.


|EducationalObjectives= Measurement of anion-gap in metabolic acidosis is essential to identify the likely diagnosis.  Anion Gap = Sodium - (Chloride + Bicarbonate).  A normal anion-gap ranges btween 8-12 mEq/L.  Common causes of high anion gap metabolic acidosis are KARMEL = Ketoacidosis - Aspirin toxicity – Renal failure – Methanol intoxication – Ethanol intoxication – Lactic acidosis
|References=First Aid 2014 page 328


|AnswerA=Narcotics abuse
|AnswerA=Narcotics abuse
|AnswerAExp=Narcotic abuse causes hypoventilation.  A respiratory acidosis with elevated pCO2 would have been present.
|AnswerAExp=[[Narcotic abuse]] can cause hypoventilation.  A respiratory acidosis with elevated pCO2 is characteristic in narcotic abusing patients.
|AnswerB=Methanol intoxication
|AnswerB=Methanol intoxication
|AnswerBExp=Methanol intoxication can cause a high anion metabolic acidosis clinical picture.
|AnswerBExp=[[Methanol intoxication]] can cause a high anion metabolic acidosis clinical picture.
|AnswerC=Renal tubular acidosis
|AnswerC=Renal tubular acidosis
|AnswerCExp=Renal tubular acidosis presents with a normal anion gap metabolic acidosis.  
|AnswerCExp=[[Renal tubular acidosis]] presents with a normal anion gap metabolic acidosis.  
|AnswerD=Acetazolamide intoxication
|AnswerD=Acetazolamide intoxication
|AnswerDExp=Acetazolamide intoxication causes a normal anion gap metabolic acidosis.  Acetazolamide is used to treat metabolic alkalosis
|AnswerDExp=[[Acetazolamide intoxication]] typically causes a normal anion gap metabolic acidosis.  Acetazolamide is often used to treat [[metabolic alkalosis]].
|AnswerE=Severe vomiting
|AnswerE=Severe vomiting
|AnswerEExp=Severe vomiting causes metabolic alkalosis due to loss of gastric acid while vomiting.  pH would have been > 7.4 with elevated bicarbonate.
|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.
|RightAnswer=B
|RightAnswer=B
|Approved=No
|Approved=Yes
}}
}}

Revision as of 19:10, 16 July 2014
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.
Educational Objective: Measurement of anion-gap in metabolic acidosis is essential to identify the likely diagnosis. Anion Gap = Sodium - (Chloride + Bicarbonate). A normal anion-gap ranges btween 8-12 mEq/L. Common causes of high anion gap metabolic acidosis are KARMEL = Ketoacidosis - Aspirin toxicity – Renal failure – Methanol intoxication – Ethanol intoxication – Lactic acidosis
References: First Aid 2014 page 328]]

Approved Approved::Yes
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