In general, decisions about anesthetic techniques and agents, intraoperative monitoring, and other aspects of care within the operating room should be left to the anesthesiologist. However, the medical consultant should understand the physiologic effects of anesthesia and surgery. Both general and neuraxial (spinal or epidural) anesthetic agents usually cause peripheral vasodilatation, and many of the commonly used general anesthetic regimens also decrease myocardial contractility. These effects often result in transient mild hypotension or, less frequently, prolonged or more severe hypotension. The decrease in tidal volume and functional residual capacity caused by general and regional anesthesia can close small airways and lead to atelectasis. Epinephrine, norepinephrine, and cortisol levels increase during surgery and remain elevated for 1–3 days. Serum antidiuretic hormone levels may be elevated for up to 1 week postoperatively, which can lead to hyponatremia. Anesthesia and surgery may be associated with both hypercoagulability, mediated by increases in plasminogen activator-1, factor VIII, and platelet reactivity, as well as inflammation due to increased levels of tumor necrosis factor, interleukins 1 and 6, and C-reactive protein.