tissue perfusion and oxygenation refer to what happens at the cellular level.
Tissue perfusion refers to arterial blood flowing through all tissues in the body: brain, heart, lungs, muscles, skin, liver, kidneys, GI tract, bones, etc. Oxygenation refers to the oxygen that is off-loaded from the hemoglobin molecules on RBCs in arterial blood as it passes through these tissues, and the reverse process when venous blood travels through the lungs, exchanging the carbon dioxide on hemoglobin for oxygen molecules.