Possible mechanism of how anesthetic concentration may affect outcomes. Anesthetic concentration increase along the x axis. If the concentration is too low then there is a risk of awareness and lack of neuronal protection (left y axis). If the concentration is too high then there is a risk of cardiovascular depression with hypotension and decreased oxygen delivery (DO2) and a risk of neuronal toxicity (right y axis). The red arc indicates a low-risk patient where the risk of problems is small despite big changes in anesthetic concentration. The blue curves indicate the various likely responses of a high-risk patient where the response to anesthesia is, and the implications for getting it wrong, are much greater as indicated by the much steeper dose–response curves. CV: cardiovascular; DO2: oxygen delivery.