Figure 36-9 Quantity of deoxygenated hemoglobin (Hb) in arterial blood as a function of the degree of cyanosis. Traditionally, it has been assumed that 5 g/dL of deoxygenated hemoglobin is required for the detection of cyanosis, but mild cyanosis can be observed at lower values. (Data from Stadie WC: The oxygen of the arterial and venous blood in pneumonia and its relation to sepsis. J Exp Med 30:215, 1919.)