RESUMEN
Ventilation and haemodynamics were studied in nine anaesthetized male patients undergoing perineal prostatectomy in the exaggerated lithotomy position (flexed, head-down position). In the flexed head-down position, as compared to the supine position, there was a significant decrease in arterial oxygen tension (13.1 +/- 2.1 to 11.2 +/- 1.1 kPa, p < 0.001), a significant increase in carbon dioxide tension (4.6 +/- 5.7 to 5.7 +/- 0.2 kPa, p < 0.001) and shunt fraction (7.8 +/- 2.3 to 14.0 +/- 3.0%, p < 0.01). There were also increases in pulmonary wedge pressures (11.3 +/- 2.9 to 17.9 +/- 2.9 mmHg, p < 0.01), mean pulmonary artery pressures (17.6 +/- 3.8 to 25.2 +/- 3.5 mmHg, p < 0.001) and central venous pressures (11.9 +/- 2.1 to 14.7 +/- 2.8, p < 0.05). Mean arterial pressure fell from 92 +/- 14 to 75 +/- 10 mmHg (p < 0.05). Heart rate and cardiac output were unchanged. All these changes had already been seen but to a lesser extent when the patients were positioned in the flexed supine position. When the patients were returned to the supine position following surgery, arterial oxygen tension was returned to baseline values. Mean pulmonary artery, pulmonary capillary wedge and central venous pressures also fell significantly. It is concluded that the extreme exaggerated lithotomy used during surgery results in impaired oxygenation and increased cardiac filling pressures but to acceptable levels in healthy anaesthetized patients. All values returned to normal when patient position was normalized after surgery.
