Increased contractility means your CO should go up. Increased CO means more blood circulates which means more blood (hgb and all of it's oxygens) are available. More availability means the cells have more to grab and use which hopefully will help decrease your serum lactate (because you've got more oxygen to use during metabolism) which will hopefully also help with any acidosis you may be dealing with. We use ScVO2 in our septic patients because of the surviving sepsis guidelines. According to the guidelines, for a low ScVO2 with a low hgb, you'd give blood in place of the milrinone (some places use dobutamine) to increase your ScVO2 (more blood means more hgb which means more oxygens to go around and around). Other patients with cardiac issues we will titrate to a CI, so you're definitely not wrong there.