Muscle Tissue Saturation Compared With Muscle Tissue Perfusion During Low Blood Flows: An Experimental Study

To investigate whether changes in muscle tissue perfusion measured with positron emission tomography would be reflected by parallel changes in muscle tissue oxygen saturation (StO₂) measured using near-infrared spectroscopy during high and low blood flow levels achieved using cardiopulmonary bypass (CPB) in an animal model.

A prospective, randomized study.

Research laboratory, single institution.

Eight pigs (69-71 kg).

In anesthetized pigs, normothermic CPB was established with a blood flow of 60 mL/kg/min for 1 hour. Thereafter, a low blood flow of either 47.5 or 35 mL/kg/min was applied for 1 hour followed by a blood flow of 60 mL/kg/min for an additional hour. Regional StO₂ was measured continuously by placing a near-infrared spectroscopy electrode on the skin above the gracilis muscle of the noncannulated back leg. Muscle tissue perfusion was measured using positron emission tomography with ¹⁵O-labeled water during spontaneous circulation and the different CPB blood flows. Systemic oxygen consumption was estimated by measurement of venous saturation and lactate levels.

The results showed profound systemic ischemia during low CPB blood flow. StO₂ remained high until muscle tissue perfusion decreased to about 50%, after which StO₂ paralleled the linear decrease in muscle tissue perfusion.

In an experimental CPB animal model, StO₂ was stable until muscle tissue perfusion was reduced by about 50%, and at lower blood flow levels, there was almost a linear relationship between StO₂ and muscle tissue perfusion.