View source for WBR0267

 {{WBRQuestion
|QuestionAuthor=Vendhan Ramanujam
|ExamType=USMLE Step 3
|MainCategory=Emergency Room
|SubCategory=Endocrine, Electrolytes
|MainCategory=Emergency Room
|SubCategory=Endocrine, Electrolytes
|MainCategory=Emergency Room
|SubCategory=Endocrine, Electrolytes
|MainCategory=Emergency Room
|MainCategory=Emergency Room
|SubCategory=Endocrine, Electrolytes
|MainCategory=Emergency Room
|SubCategory=Endocrine, Electrolytes
|MainCategory=Emergency Room
|SubCategory=Endocrine, Electrolytes
|MainCategory=Emergency Room
|SubCategory=Endocrine, Electrolytes
|MainCategory=Emergency Room
|MainCategory=Emergency Room
|SubCategory=Endocrine, Electrolytes
|Prompt=An ill appearing 52 year old European female presents to the ED with nonspecific complaints like dizziness, nausea and fatigue.  Laboratory tests show an anion gap of 13 mEq/L, lactate level of 15.0, pH 7.30 and a normal glucose level, HCO3 17.  Detailed history reveals that she is taking oral metformin.  Which of the following will apply to this patient’s lactic acidosis 
|Explanation=This patient suffers from [[metformin]] induced [[lactic acidosis]].  The clinical findings of lactic acidosis are nonspecific.  Administration of [[sodium bicarbonate]] solution is controversial.  Current recommendations suggest withholding alkali therapy if the [[pH]] is above 7.1.  The infused bicarbonate combines with a hydrogen ion to form H2CO3 (carbonic acid), which dissociates into CO2 and H2O.  The generated CO2 is usually not efficiently removed from the body even with adequate circulation and ventilation thus resulting in the increase of PCO2, which will prevent carbonic acid dissociation and continues to keep the pH low.  PCO2 can also readily penetrate cell membranes and worsen intracellular acidosis even as arterial blood pH increases.  Following this hypokalemia occurs.  An increase in pH can decrease the ionized calcium concentration also. Sodium bicarbonate is usually infused as a hypertonic solution, which will raise the serum sodium concentration. 

'''Educational Objective:'''
Sodium bicarbonate therapy for treating metabolic acidosis is withheld until the pH is below 7.1 to prevent sodium bicarbonate infusion induced further lowering of pH, hypokalemia and hypocalcemia. 
|AnswerA=The patient most likely has type A lactic acidosis
	
|AnswerAExp='''Incorrect'''-Metformin induced lactic acidosis is a type B lactic acidosis that occurs without any clinical evidence of poor tissue perfusion or oxygenation.  Type A lactic acidosis occurs in association of clinical evidence of poor tissue perfusion or oxygenation.
|AnswerB=Impaired myocardial contractility and hypotension may occur due to this acidosis 
|AnswerBExp='''Incorrect'''-Impaired myocardial contractility and hypotension usually occurs at a pH of 7.1 or lower. 
|AnswerC=Sodium bicarbonate should not be administered
|AnswerCExp='''Correct'''-This patient suffers from [[metformin]] induced [[lactic acidosis]].  The clinical findings of lactic acidosis are nonspecific.  Administration of [[sodium bicarbonate]] solution is controversial.  Current recommendations suggest withholding alkali therapy if the [[pH]] is above 7.1.  The infused bicarbonate combines with a hydrogen ion to form H2CO3 (carbonic acid), which dissociates into CO2 and H2O.  The generated CO2 is usually not efficiently removed from the body even with adequate circulation and ventilation thus resulting in the increase of PCO2, which will prevent carbonic acid dissociation and continues to keep the pH low.  PCO2 can also readily penetrate cell membranes and worsen intracellular acidosis even as arterial blood pH increases.  Following this hypokalemia occurs.  An increase in pH can decrease the ionized calcium concentration also. Sodium bicarbonate is usually infused as a hypertonic solution, which will raise the serum sodium concentration. 

|AnswerD=Metformin is not actively used in the U.S. market
|AnswerDExp='''Incorrect'''-Metformin is actively used in United States.
|AnswerE=Ethanol will not cause a similar presentation

|AnswerEExp='''Incorrect'''-Ethanol, methanol, and anti retrovirals are other drugs that cause type B lactic acidosis.
|RightAnswer=C
|Approved=Yes
}}