Respiratory effects of prolonged Trendelenburg position.

The Trendelenburg position has been severely criticized (Inglis and Brooke, 1956; Swain, 1960) but is still popular for pelvic surgery. One of the main complaints about this position is that it reduces ventilation as a result of pressure by the abdominal contents upon the diaphragm. This, of course, applies only to patients breaching spontaneously, because, if artificial ventilation is used, there should be little difficulty in performing the small amount of extra work entailed. During epidural blockade, spontaneous respiration continues, and this form of analgesia is widely used for pelvic surgery. A study carried out to measure the effects of steep head-down tilt upon the blood gases showed that no significant hypoventilation occurred under nitrous oxide/oxygen/halothane anaesthesia (Scott, Lees and Taylor, 1966), but the duration of the tilt used in these experiments was short (10 minutes). The following study was carried out to examine the effects of more prolonged tilting during epidural analgesia combined with general anaesthesia.