“EVer since the discovery that incomplete oxygenation of arterial blood is the cause of central cyanosis, the question has been asked: How much reduced (deoxygenated or unsaturated) hemoglobin (RHB) is needed to generate central cyanosis? The amount commonly quoted, 5 g of RHB/dl of blood, comes from the classic 1923 monograph by Lunds- gaard and Van Slyke (emphasis added):
About 5 grams of reduced hemoglobin per 100 c.c. of capillary blood appear necessary to cause cyanosis, the amount of oxygenated hemoglobin also present having relatively little effect. An anemic with less than 5 grams of hemoglobin per 100 c.c. of blood cannot usually become cyanotic. It is the blood in the capillaries, and possibly in the arterioles and venules of the subpapillary plexus as well, which produces the cyanotic skin color. The arteries and most of the veins are so far away from the skin that their content cannot influence the skin color. Viagra Professional
Unfortunately, the location of the 5 g/dl RHB, so clearly stated by Lundsgaard and Van Slyke, is often overlooked by modern authors. As a result, the medical literature reflects confusion over the difference between what is measured (arterial levels of oxygenated and reduced hemoglobin) and what actually generates cyanosis (quantity of reduced hemoglobin in the capillaries). Several authors have mistakenly compared arterial levels of RHB with the capillary value of Lundsgaard and Van Slyke and as a result found the Lundsgaard and Van Slyke value too high. To clarify this confused state of affairs we searched for all original articles that provide data on the oxygen levels at which cyanosis is detectable (Table l). We also examined all review papers and letters on the subject that are either indexed in Medline (1966 to present) or referenced in other articles, as well as 24 textbooks (12 pulmonary medicine, seven internal medicine, and five emergency medicine) for their discussions of cyanosis.