Question 19.3

With references to intoxications, what do you understand by the term “oxygen saturation gap”?

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College Answer

When there is a difference in the oxygen saturation between a pulse oximeter reading and a co- oximeter reading, seen with CO poisoning and other drugs which result in a methemoglobinemia.


Though not a formally accepted term to describe this phenomenon, the "gap" is a well recognised feature of dyshemoglobinaemia. It develops when the pulse oximeter reads a certain saturation, and the ABG machine or CO-oximeter returns a different reading. The "gap" in saturation readings is vaguely representative of the concentration of the abnormal haemoglobin in the blood.


Akhtar, Jawaid, Bradford D. Johnston, and Edward P. Krenzelok. "Mind the gap."The Journal of emergency medicine 33.2 (2007): 131-132.

Mokhlesi, Babak, et al. "Adult Toxicology in Critical CarePart I: General Approach to the Intoxicated Patient." CHEST Journal 123.2 (2003): 577-592.