Arteriovenous carboxyhemoglobin gradient is a technical artifact that is eliminated by special calibration (SAT 100)

Pulmonary enzyme heme oxygenase, which catalyses carbon monoxide production , may be responsible for arteriovenous carboxyhemoglobin (COHb) differences measured in humans. Unspecific inflammatory stimuli have been shown to ind uce pulmonary heme oxygenase possibly leading to increased pulmonary carbon monoxide production and elevated arterial COHb. Arteriovenous COHb gradien ts may therefore be a measurable parameter of lung injury severity. To excl ude a technical artefact, we repeated measurements of central venous COHb a nd arterial COHb in healthy humans (ASA I-II) undergoing elective surgery w ith the ABL 625 and the updated version, ABL 725 (Radiometer, Copenhagen). In addition to the standard calibration, an especially accurate adjustment of the spectrophotometer wavelengths (SAT100) was performed. This adjustmen t eliminates the FCOHb dependency on the oxygen saturation. No significant differences were detectable between central venous and arterial COHb concen trations with either blood gas analyzer. The difference between central ven ous COHb and arterial COHb was 0.09 with the ABL 625 and -0.03 with the ABL 725. Therefore, we conclude that previously reported arteriovenous COHb di fferences are artifactual and may be eliminated by SAT 100 adjustment, as i s possible with the ABL 725. (C) 2000 Academic Press.