Changes in arterial oxygen tension correlate with changes in end-expiratory carbon monoxide level.
OBJECTIVE
Carbon monoxide (CO) and oxygen compete for haemoglobin binding sites. While the effects of increased inspiratory oxygen fractions on exhaled carbon monoxide concentrations have been studied previously, the relationships between intravascular oxygen tension, blood carboxyhaemoglobin levels and expiratory CO concentrations remain unclear. We therefore studied the effects of increases in arterial oxygen tension as crucial determinant for the displacement of carbon monoxide from its haemoglobin bond during lung passage.


METHODS
Measurements of end-expiratory CO concentrations (eCO), arterial oxygen tensions and carboxyhaemoglobin concentrations were performed in 19 patients while breathing air and oxygen.


RESULTS
With increasing PaO(2) (from 11.5 +/- 1.9 to 35.2 +/- 10.3 kPa) end-expiratory CO concentrations increased from 8.6 +/- 4.9 to 16.7 +/- 9.4 ppm, p < 0.001, with a mean increase of 0.36 ppm CO per kPa increase in PaO(2) (DeltaeCO [ppm] = 0.36 * DeltaPaO(2 )[kPa]). Increases of arterial oxygen tension correlated with increases of end-expiratory CO concentration (r(2) = 0.33). Arterial carboxyhaemoglobin concentrations decreased from 1.06 +/- 0.37 during air breathing to 0.92 +/- 0.35 % after 5 minutes of oxygen inhalation (p < 0.001).


CONCLUSIONS
Oxygen-induced increases in exhaled CO correlate with increases in arterial oxygen tensions. Furthermore, oxygen inhalation reduces carboxyhaemoglobin levels, supporting the concept of accelerated CO elimination by oxygen via the lungs.
Schober
Patrick
P
Department of Anaesthesiology, VU Medisch Centrum, PO Box 7057, 1007 MB, Amsterdam, The Netherlands. P.Schober@vumc.nl
Kalmanowicz
Melanie
M
Schwarte
Lothar A
LA
Weimann
Joerg
J
Loer
Stephan A
SA
D000368:Aged; D002248:Carbon Monoxide / Q000378:metabolism*; D045853:Exhalation / Q000187:drug effects / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D010100:Oxygen / Q000008:administration & dosage* / Q000378:metabolism*; D011651:Pulmonary Artery / Q000187:drug effects / Q000378:metabolism*; D011659:Pulmonary Gas Exchange / Q000187:drug effects / Q000502:physiology*; D013223:Statistics as Topic
D002248:Carbon Monoxide; D010100:Oxygen