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The pulse oximetry gap in carbon monoxide intoxication
R G Buckley1, S E Aks, J L Eshom
1Department of Emergency Medicine, Cook County Hospital, Chicago, Illinois.
Annals of Emergency Medicine
|August 1, 1994
Summary
Pulse oximetry inaccurately measures oxygen saturation in carbon monoxide (CO) poisoning. Readings remain falsely high, overestimating actual oxygen levels in CO-exposed patients.
Area of Science:
- Medical Devices
- Toxicology
- Respiratory Medicine
Background:
- Pulse oximetry is a common non-invasive method for measuring oxygen saturation.
- Carbon monoxide (CO) exposure can interfere with pulse oximetry readings.
- The extent of this interference, particularly in patients with elevated carboxyhemoglobin (COHb), requires further investigation.
Purpose of the Study:
- To quantify the impact of CO exposure on pulse oximetry readings.
- To determine the relationship between carboxyhemoglobin (COHb) levels and pulse oximetry overestimation of oxyhemoglobin saturation (O2Hb).
Main Methods:
- A prospective case series design was employed.
- 25 pulse oximetry measurements were taken concurrently with arterial blood gas sampling.
- Data were collected from 16 adult patients with documented CO exposure.
Main Results:
- Carboxyhemoglobin (COHb) levels (mean 16.1%) did not significantly correlate with pulse oximetry saturation.
- A significant linear regression model was established for the pulse oximetry gap (pulse oximetry saturation minus O2Hb) and COHb levels (R2 = .90, P < .0001).
- The pulse oximetry gap was found to be approximately equal to the COHb level.
Conclusions:
- Pulse oximetry significantly overestimates oxygen saturation in patients with CO exposure.
- Even with COHb levels as high as 44%, pulse oximetry readings remained above 96%.
- Pulse oximetry is unreliable for assessing oxygen saturation in CO-exposed individuals and should be used with caution, especially in smokers.