Intra-operative positioning considerations are more important for the obese patient. The supine position causes a marked increase in intra-abdominal pressure, which results in a splinting effect of abdominal contents on the diaphragm. Awake, spontaneously breathing obese patients should be in a head-up position. The Trendelenburg position can be used to engorge neck veins to facilitate central venous cannulation. Spontaneously breathing obese patients generally do not tolerate the Trendelenburg position. In mild to moderately obese patients, respiratory mechanics, lung volumes, and oxygenation all increase when changing from the supine to prone position. Due to the difficulties moving and positioning mobidly obese (MO) patients, procedures routinely performed prone are often done in the lateral decubitus position. In the lithotomy position the patient is on their back with their legs and thighs flexed at right angles. MO patients are at special risk for rhabdomyolysis (RML), a potentially fatal post-operative complication.