Perry DA, et al. - Researchers determined how hyperoxemia (arterial oxygen tension >100 mm Hg) influences venous saturation (SvO₂) and assessments of cardiac output (CO) using the Fick equation. They measured SvO₂ and tissue oxygen tension (tPO₂) in brain and myocardium during systematic manipulation of arterial oxygen tension (PaO₂) using graded hyperoxia in anesthetized, intubated Yorkshire swine (n = 14) paralyzed for instrumentation. Thereafter, they compared oxygen- and carbon dioxide-based estimates of CO (Fick_O2 and Fick_CO2, respectively) with measurements from a flow probe placed on the aortic root. They noted that changes in PaO₂ were followed by acute changes in SvO₂ even when there were absent changes in measured DO₂. This could give rise to errors in Fick_O2 estimates of CI.