PhysicalDiagnosisCyanosis課件.pptVIP

DefinitionCyanosis refers to a bluish(带蓝色的；带青色的)color of the skin and mucous membranes resulting from an increased quantity of reduced hemoglobin(亚铁血红蛋白；还原血红蛋白), or of hemoglobin derivatives, in the small blood vessels of those areas. It is usually most marked in the lips, nail beds(甲床), ears, and malar(颧骨的；颊的)eminences(隆起).  Mechanism of Cyanosis Cyanosis, especially if developed recently, is more commonly detected by a family member than the patient. The florid(鲜红色的；气色好的) skin characteristic of polycythemia vera(真性红细胞增多症) must be distinguished from the true cyanosis discussed here. A cherry(樱桃)-colored flush(潮红), rather than cyanosis, is caused by COHb(Carboxyhemoglobin 碳氧血红蛋白). The degree of cyanosis is modified by the color of the cutaneous(皮肤的) pigment and the thickness of the skin, as well as by the state of the cutaneous capillaries. The accurate clinical detection of the presence and degree of cyanosis is difficult, as proved by oximetric(血氧定量法的)studies. In some instances, central cyanosis can be detected reliably when the SaO2 has fallen to 85%; in others, particularly in dark-skinned persons, it may not be detected until it has declined to 75%. In the latter case, examination of the mucous membranes in the oral cavity and the conjunctivae(结膜)rather than examination of the skin is more helpful in the detection of cyanosis. The increase in the quantity of reduced hemoglobin in the mucocutaneous(皮肤粘膜的) vessels that produces cyanosis may be brought about either by an increase in the quantity of venous blood as the result of dilatation of the venules(小静脉) and venous ends of the capillaries or by a reduction in the SaO2 in the capillary blood. In general, cyanosis becomes apparent when the mean capillary concentration of reduced hemoglobin exceeds 50 g/L (5g/dL). It is the absolute rather than the relative quantity of reduced hemoglobin that is important in producing cyanosis. Thus, in a patient with severe anemia, the relative amount of reduced hemogl