Blood gas studies during labaroscopy under general anesthesia.

Abstract

The effects of the laparoscopy procedure on the arterial blood gases were studied. In particular, the authors were interested in 1) what the effect of carbon dioxide is in the peritoneal cavity on arterial carbon dioxide partial pressure and pH and 2) whether the head down position together with an elevated immobile diaphragm can cause a significant change in arterial oxygen pressure or oxygen saturation. The subjects of the study were 20 patients hospitalized for laparoscopy. The patients were divided into 3 groups: 1) controlled respiration, 1-2% halothane in oxygen, 2) spontaneous respiration, 1-2% halothane in oxygen, and 3) controlled respiration, 1% halothane, 74% nitrous oxide, 25% oxygen. Blood gases were analyzed with the Clark electrode for oxygen tension and with the Severinghaus electrode for carbon dioxide tension at 37 degrees centigrade. Samples were obtained in each group of patients just before laparoscopy, after 15 minutes of carbon dioxide insufflation, and 15 minutes after the carbon dioxide was removed. In group 1, mean arterial carbon dioxide was maintained at about 25 mm mercury before, during, and after carbon dioxide insufflation. The mean arterial oxygen fell during laparoscopy, but the change was not statistically significant. In group 2, mean arterial carbon dioxide rose from 44.4 to 49.2 mm mercury during the procedure (p less than .05) and fell to 45.9 mm mercury after removal of carbon dioxide. Arterial oxygen was consistently lower as compared with those in group 1, but did not change significantly during laparoscopy. In group 3, mean arterial carbon dioxide rose from 30.5 to 37.3 mm mercury after insufflation of carbon dioxide. It fell to 31.8 mm after the procedure. Mean arterial oxygen decreased from 92.2 mm to 81.4 mm mercury during laparoscopy and returned to 87.2 mm mercury afterwards. The data indicated that with adequate controlled respiration the arterial carbon dioxide does not rise significantly in spite of the presence of carbon dioxide in the peritoneal cavity at the pressure of 50 cm water. In the patients breathing spontaneously, the arterial carbon dioxide rose during laparoscopy despite an increased minute volume. This and further interpretation of the data led the authors to recommend that patients undergoing laparoscopy breathe a gas mixture containing at least 50% oxygen, while ventilation is controlled with an endotracheal airway in place.