Flat electroencephalogram caused by carbon dioxide pneumoperitoneum.

Hypercapnia during laparoscopy with CO2 is predicted in the following situations: compromised pulmonary function, retroperitoneal insufflation, and subcutaneous emphysema. We present a case of sudden electroencephalogram (EEG) depression in response to severe hypercapnia during laparoscopic ureteronephrectomy in a 77-yr-old patient with chronic pulmonary emphysema. During intraperitoneal and retroperitoneal insufflation, subcutaneous emphysema and difficult ventilation occurred. Severe hypercapnia ensued, with pH = 6.94, and Paco2 = 137 mm Hg. Subsequent EEG activity was markedly depressed with a minimum Bispectral Index of 4, accompanied by an increase in arterial blood pressure and heart rate. Termination of the laparoscopic procedure improved ventilation, EEG, and hemodynamics. These EEG changes may result from the narcotic properties of CO2 or hypercapnia-induced neurological abnormalities.