Estimation of femoral arterial blood flow from femoral venous oxygen saturation.

In six patients in whom a femoro-popliteal vein bypass graft was performed for intermittent claudication, the relationship between the haemodynamic state of the leg and the femoral venous oxygen saturation before and after local vasodilatation was investigated. The study was undertaken with special reference to the known influence of hypovolaemia on the leg blood flow. It is concluded that a femoral venous oxygen saturation below 70%indicates that the leg blood flow is less than 200 ml/min and that the bypass flow is less than 100 ml/min and thus within a range in which the incidence of early thrombosis is high. Furthermore, an increase in femoral venous oxygen saturation of 10% or more on local vasodilatation indicates a state of hypovolaemia, necessitating further blood substitution.