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Retired NBME 15 Answers

nbme15/Block 0/Question#0 (reveal difficulty score)
A 50-year-old man comes to the emergency ...
Anemia ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
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submitted by โˆ—lola915(57)
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  • Arterial: Pco2 30 mm Hg, Po2 96 mm Hg
  • Arterial O2 content: 12 vol% (N=17%โ€“21%)
  • Mixed venous Po2 36 mm Hg
  • Mixed venous O2 content 8 vol% (N=10%โ€“16%)

  • A) Anemia - Patient has nl PaO2 and decreased O2 content. Also patient is hyperventilating and CO2 is thus low.

  • B) Drug-induced alveolar hypoventilation - Arterial PO2 would be low&CO2 high
  • C) Residence at a high altitude - Arterial PO2 would be low
  • D) Severe regional mismatching of alveolar ventilation and pulmonary capillary perfusion - Pulmonary Embolus would cause a decrease in arterial PO2 E) Voluntary hyperventilation - Arterial O2% content would be nl

Anemia causes hypoxia without hypoxemia. Meaning low O2 delivery to tissues but not low O2 saturation of the blood. The lungs can adequately deliver O2 to the arterials so PaO2 is normal. Anemia causes low O2 content because you have relatively low amounts of Hb to carry oxygen.

O2 content = (1.34 ร— Hb ร— Sao2) + (0.003 ร— Pao2)

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