Prolonged interference of blue dye "patent blue" with pulse oximetry readings.

Several blue dyes were reported to interfere with the accurate determination of oxygen saturation by pulse oximetry. However, in previous reports the interferences were observed only for a short duration. We have experienced a case in which the interference by a blue dye, "patent blue" continued for a long time. It was suggested that the blue dye, when it was injected intra-arterially and in an anaemic patient, interfered with the pulse oximetry measurement to a greater extent.