[Lithotomy position: respiratory resistance with thiopental and propofol anesthesia]

To study airway resistance changes induced by placement in lithotomy position under thiopentone and propofol anaesthesia.

Prospective, randomised study.

OR of a university hospital.

Consecutive sample of 36 patients without bronchopulmonary disease (ASA 1-2; 18-78 yr.; 45-100 kg) scheduled for elective surgery in lithotomy position under general (mask) anaesthesia; oral premedication with 0.3 mg.kg-1 dipotassium chloroazeptate on the evening before and in the morning of surgery.

Injection of either 4-6 mg.kg-1 thiopentone or 2-2.5 mg.kg-1 propofol into a fast running peripheral infusion until loss of eyelash reflex. Placement of an oropharyngeal airway and assisted ventilation via anatomic mask until recovery of spontaneous respiration. Oscilloresistometric determination (Siregnost FD 5; Siemens AG, Erlangen) of airway impedance (ROS) before and after placement in lithotomy position.

Before positioning ROS was 3.5 +/- 1.3 mbar.l-1.s-1 and 3.7 +/- 1.1 mbar.l-1.s-1 in the propofol and thiopentone group respectively. After positioning ROS was unchanged in the propofol group (3.8 +/- 1.8 mbar.l-1.s-1) and increased to 4.5 +/- 1.5 mbar.l-1.s-1 (p < 0.05) in the thiopentone group.

Lithotomy positioning induces an increase in airway impedance under thiopentone but not under propofol anaesthesia.