In some instances, central cyanosis can be detected reliably when the sao, has fallen to 85%; in others particularly in dark skinned persons, it may not be detected until it has declined to 75%o. In the latter case examination of the mucous membranes in the oral cavity and the 士上 conjunctivae(结膜) 摸 )rather than examination of the skin is more helpful in the detection of cyanosisIn 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