WBR0267

Author	PageAuthor::Vendhan Ramanujam
Exam Type	ExamType::USMLE Step 3
Main Category	MainCategory::Emergency Room
Sub Category	SubCategory::Endocrine, SubCategory::Electrolytes
Prompt	[[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]]
Answer A	AnswerA::The patient most likely has type A lactic acidosis
Answer A Explanation	[[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.]]
Answer B	AnswerB::Impaired myocardial contractility and hypotension may occur due to this acidosis
Answer B Explanation	AnswerBExp::'''Incorrect'''-Impaired myocardial contractility and hypotension usually occurs at a pH of 7.1 or lower.
Answer C	AnswerC::Sodium bicarbonate should not be administered
Answer C Explanation	[[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.]]
Answer D	AnswerD::Metformin is not actively used in the U.S. market
Answer D Explanation	AnswerDExp::'''Incorrect'''-Metformin is actively used in United States.
Answer E	AnswerE::Ethanol will not cause a similar presentation
Answer E Explanation	AnswerEExp::'''Incorrect'''-Ethanol, methanol, and anti retrovirals are other drugs that cause type B lactic acidosis.
Right Answer	RightAnswer::C
Explanation	[[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. Educational Objective: References: ]]
Approved	Approved::Yes
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