WBR0949

Author	PageAuthor::William J Gibson
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 room 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. An arterial blood gas reveals the following: pH: 7.32 CO2: 18 O2: 111 Bicarbonate: 15 Sodium: 140 Chloride: 100 Which of the following would have a similar effect on the oxygen-hemaglobin 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-BPG
Answer D Explanation	AnswerDExp::An increase in 2,3-BPG would right-shift the oxygen-hemoglobin dissociation curve.
Answer E	AnswerE::Increase in 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 noncompetitive decrease in the oxygen binding capacity of hemoglobin.
Right Answer	RightAnswer::D
Explanation	[[Explanation::This patient has an anion gap metabolic acidosis due to salicylate toxicity. The criteria for anion gap metabolic acidosis is pH < 7.35 and an anion gap >16. 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. Recall that the oxygen-hemoglobin dissociation curve is right shifted by a decrease in pH (increasing acidity). Therefore, the question is asking: “Which of the following changes would cause a right-shift of the oxygen hemoglobin dissociation curve?” Recall that an increase of everything except pH causes a right shift of the curve. A useful way to remember the effects of various substances on the oxygen-hemoglobin dissociation curve is the following mnemonic: C-BEAT CO2 BPG (2,3-BPG) Exercise Acid/Altitute Temperature Educational Objective: An increase of both 2,3-BPG and acidity will cause a rightward shift of the oxygen-hemoglobin dissociation curve. References: First Aid 2013 page 548]]
Approved	Approved::Yes
Keyword	WBRKeyword::Oxygen, WBRKeyword::Hemoglobin, WBRKeyword::Metabolic Acidosis, WBRKeyword::Aspirin, WBRKeyword::Toxicity, WBRKeyword::Overdose
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