Which conditions could cause cyanosis?

• A. 1 and 3 only
• B. 2 and 4 only
• C. 1 and 2 only
• D. 2 and 3 only

Answer: (C)

Cyanosis happens when arterial blood carries less oxygen than normal, so deoxygenated hemoglobin rises enough to turn the skin and mucous membranes blue. This most often reflects true central hypoxemia or a dyshemoglobinemia, not just a superficial change in color. In practice, that means conditions that markedly reduce oxygenation of the blood (such as significant lung disease or pulmonary hypertension) or that create mixing of oxygenated and deoxygenated blood (a congenital heart lesion with abnormal blood flow) can cause cyanosis. Absent such changes in arterial oxygen content or hemoglobin’s ability to carry oxygen, cyanosis is less likely to appear.

So the two conditions described in the options that would lead to visible cyanosis are the ones that directly lower arterial oxygen content or alter hemoglobin’s oxygen-carrying capacity. The other two described items would not typically produce cyanosis.