Pneumoperitoneum for laparoscopic surgery does not increase venous admixture.

Venous admixture as a measure of pulmonary gas exchange was studied before and during laparascopic cholecystectomy in 12 patients with normal healthy cardio-pulmonary function. After induction of anaesthesia the patients were studied by radial and pulmonary arterial catheterization and simultaneous arterial and mixed venous blood gas sampling in the horizontal, 15-20 degrees head-down and 15-20 degrees head-up tilt positions. After establishing the pneumoperitoneum (PP) by insufflation of carbon dioxide to an intraabdominal pressure level of 11-12 mmHg, the measurements were repeated in the same positions. The laparoscopic cholecystectomy then started and measurements were repeated every 30 min during surgery. The venous admixture was 4 +/- 0.6% (range 2-6%) in the horizontal position and was not influenced by altered body position. Immediately after establishment of PP, there was a 31 +/- 5% (P < 0.05) reduction of venous admixture and a 15 +/- 3% (P < 0.01) elevation of PaO2 compared with the control situation without PP. These changes were maintained during pneumoperitoneum and were not influenced by posture. It is suggested that alterations in the distribution of ventilation and/or lung perfusion results in a reduced venous admixture during PP without surgery. In addition, there was no indication that venous admixture is elevated as a result of laparoscopic surgery in the reversed Trendelenburg position.