122. When is cyanosis visible? / What causes a left shift in the hemoglobin-oxygen dissociation curve? October 25th, 2007 by reuben in .cyanosis Back Top Tags: card 121. Cyanosis unresponsive to oxygen in the nondistressed patient: ddx / Criteria to discharge methemaglobinemia patient 123. Describe airway-preserving posture positioning / List upper airway signs Leave a Reply Cancel reply Please post any discussion to the emupdates Reddit page.