EFFECTS OF EXAGGERATED LITHOTOMY POSITION ON VENTILATION AND HEMODYNAMICS DURING RADICAL PERINEAL PROSTATECTOMY

Ventilation and haemodynamics were studied in nine anaesthetized male patients undergoing perineal prostatectomy in the exaggerated lithotom y position (flexed, head-down position). In the flexed head-down posit ion, as compared to the supine position, there was a significant decre ase 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 pre ssures (11.3 +/- 2.9 to 17.9 +/- 2.9 mmHg, p < 0.01), mean pulmonary a rtery pressures (17.6 +/- 3.8 to 25.2 +/- 3.5 mmHg, p < 0.001) and cen tral venous pressures (11.9 +/- 2.1 to 14.7 +/- 2.8, p < 0.05). Mean a rterial pressure fell from 92 +/- 14 to 75 +/- 10 mmHg (p < 0.05). Hea rt rate and cardiac output were unchanged. All these changes had alrea dy 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 returne d 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 a cceptable levels in healthy anaesthetized patients. All values returne d to normal when patient position was normalized after surgery.