LAUSR

The supine position is still the most frequently used type of positioning during surgical procedures. Positions other than the supine position lead to physiological alterations that have a relevant influence on the course of anesthesia and surgery. As a matter of principle, hemodynamic stability is at risk because venous blood is pooled in the lower positioned body parts. In addition, head down positions (Trendelenburg position) may lead to an impairment of respiratory function by reducing lung volumes as well as lung compliance. Upright positions (beach chair position) are characterized by a relative hypovolemia accompanied by a reduction of mean arterial pressure, cardiac output and stroke volume, whereas pulmonary functions remain unchanged. Some severe adverse events have been described in the literature (e.g. intraoperative apoplexy, postoperative blindness). The pathophysiological principles and effects of hemodynamic alterations as well as potential strategies to avoid complications are presented and discussed in this lead article. Head down positions, especially the Trendelenburg position, cause a relative (intrathoracic) hypervolemia and an increase in cardiac preload that is usually well-tolerated in patients without heart problems; however, the Trendelenburg position, especially if combined with a capnoperitoneum, significantly impairs pulmonary function, can have a negative effect on intracerebral pressure and may reduce blood flow of intra-abdominal organs. The pathophysiological intraoperative changes caused by Trendelenburg positioning are described and approaches suitable for risk reduction are discussed. The prone position and lateral decubitus position have little influence on the intraoperative homeostasis. Nevertheless, there is an ongoing discussion concerning the efficacy of a 15° left lateral position during caesarean section, which is also discussed in a separate section of this review.