WBR0949

Author	[[PageAuthor::William J Gibson (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry, MainCategory::Physiology
Sub Category	SubCategory::Pulmonology
Prompt	[[Prompt::A 22-year-old woman is brought to the emergency department (ED) after several members of her family witnessed her suffering a seizure. On the way to the hospital, she admitted to swallowing 50 aspirin pills in a suicide attempt. She is unconscious but responds to painful stimuli. In the ED, results from arterial blood gas on room air demonstrate the following: pH=7.32, pCO2=18 mmHg, pO2=111 mmHg, Bicarbonate=15 mEq/L. Blood samples are withdrawn, and electrolytes are as follows: Sodium=140 mEq/L, Chloride=100 mEq/L. Which of the following would have a similar effect on the oxygen-hemoglobin dissociation curve as this patient’s condition?]]
Answer A	AnswerA::Decrease in altitude
Answer A Explanation	AnswerAExp::A decrease in altitude would left-shift the oxygen-hemoglobin dissociation curve.
Answer B	AnswerB::Decrease in temperature
Answer B Explanation	AnswerBExp::A decrease in temperature would left-shift the oxygen-hemoglobin dissociation curve.
Answer C	AnswerC::Decrease in CO2
Answer C Explanation	AnswerCExp::A decrease in CO2 would left-shift the oxygen-hemoglobin dissociation curve.
Answer D	AnswerD::Increase in 2,3-bisphosphoglycerate (2,3-BPG)
Answer D Explanation	AnswerDExp::An increase in 2,3-BPG would right-shift the oxygen-hemoglobin dissociation curve.
Answer E	AnswerE::Increase in carbon monoxide (CO)
Answer E Explanation	AnswerEExp::Because carbon monoxide (CO) has a 200x higher affinity for hemoglobin than does oxygen, an increase in CO would cause a non-competitive decrease in the oxygen binding capacity of hemoglobin.
Right Answer	RightAnswer::D
Explanation	[[Explanation::This patient has a high anion gap metabolic acidosis due to salicylate toxicity. The criteria for high anion gap metabolic acidosis is pH < 7.35 and an anion gap >16 (anion gap limit differs with age). The anion gap is defined by the following equation: Anion Gap = Na - Cl - Bicarbonate In this case, the anion gap equals 140-100-15= 25. The oxygen-hemoglobin dissociation curve is right shifted by a decrease in pH (increasing acidity). The following factors result in a right shift of the oxygen-hemoglobin dissociation curve: CO2 BPG (2,3-BPG) Exercise Acidic pH High altitude High temperature Educational Objective: The following factors result in a right shift of the oxygen-hemoglobin dissociation curve: CO2 BPG (2,3-BPG) Exercise Acidic pH High altitude High temperature References: First Aid 2013 page 548]]
Approved	Approved::Yes
Keyword	WBRKeyword::Oxygen, WBRKeyword::Hemoglobin, WBRKeyword::Curve, WBRKeyword::Metabolic acidosis, WBRKeyword::Aspirin, WBRKeyword::Toxicity, WBRKeyword::Overdose, WBRKeyword::BPG, WBRKeyword::High anion gap
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