View source for WBR0068

 {{WBRQuestion
|QuestionAuthor=Mahmoud Sakr, M.D.
|ExamType=USMLE Step 2 CK
|MainCategory=Internal medicine
|SubCategory=Respiratory
|MainCategory=Internal medicine
|SubCategory=Respiratory
|MainCategory=Internal medicine
|SubCategory=Respiratory
|MainCategory=Internal medicine
|MainCategory=Internal medicine
|SubCategory=Respiratory
|MainCategory=Internal medicine
|SubCategory=Respiratory
|MainCategory=Internal medicine
|SubCategory=Respiratory
|MainCategory=Internal medicine
|SubCategory=Respiratory
|MainCategory=Internal medicine
|MainCategory=Internal medicine
|SubCategory=Respiratory
|Prompt=37 y/o woman was brought to the emergency room after a motor vehicle accident with altered mental status and several crush injuries.  Her blood pressure is 80/40, Pulse 117, RR 32. She was noted to be in severe respiratory distress and was intubated by the emergency room physician. Follow-up chest X-ray revealed diffuse bilateral alveolar infiltrates. She was reported to be previously healthy with no smoking history and on no medications. Which of the following is likely present in this patient?
|Explanation=The correct answer is D.  
This patient has ARDS secondary to multiple crush injuries and her vital signs and chest X-ray are consistent with this diagnosis. In ARDS, patients have decreased lung compliance and increased airway resistance leading to increased requirement of positive pressure ventilation called PEEP. They will have impaired oxygenation (E), not ventilation (B), hyperventilation leading to low CO2 levels (A), and usually they are very hypotensive with poor peripheral perfusion(C).

|AnswerA=High arterial PCO2
|AnswerAExp=Incorrect! This patient is tachypneic and was started on mechanical ventilation, therefore she will have low PCO2 levels in the blood as a result of her tachypnea.
|AnswerB=Impaired ventilation
|AnswerBExp=Incorrect! ARDS patients usually have a problem with oxygenation due to diffuse alveolar infiltrates, however the process of gas exchange between the alveoli and the capillary bed is usually intact.
|AnswerC=Increased peripheral tissue perfusion
|AnswerCExp=Incorrect! This patient is hypotensive and in shock, therefore her peripheral perfusion will be decreased.
|AnswerD=Increased PEEP requirement on mechanical ventilation
|AnswerDExp=Correct! The rationale for delivering a high level of applied PEEP to patients with ARDS is that the applied PEEP opens collapsed alveoli, which decreases alveolar overdistension, therefore improves lung compliance.
|AnswerE=Normal oxygenation
|AnswerEExp=Incorrect! One of the landmarks of ARDS is hypoxemia, not normal oxygenation.
|RightAnswer=D
|Approved=Yes
}}