Dyshemoglobinemia

Pulse oximetry has the advantage of being a noninvasive and cost-effective method of providing continuous measurements of arterial oxygen saturation. […] However, pulse oximetry does not measure arterial carbon dioxide tension or pH; it is not a reliable indicator of hyperoxemia; and it can be unreliable in certain patients, such as those with dyshemoglobinemia or sickle cell anemia.

Pulse oximetry is universally used for monitoring respiratory status of patients in the ICU. […] Multiwavelength oximeters may prove to be useful in detecting dyshemoglobinemia.

A possible dyshemoglobinemia should be suspected when discordance exists between pulse oximetry readings and physical examination findings.