EFFECTS OF NORMOCAPNIC AND HYPOCAPNIC NITROUS-OXIDE-INHALATION ON CEREBRAL BLOOD-FLOW VELOCITY IN PATIENTS WITH BRAIN-TUMORS

Nitrous oxide (N2O) use during anesthesia for intracranial procedures has been a subject of controversy in the past. To date, the isolated i nfluence of N2O on mean cerebral blood flow velocity in the middle cer ebral artery (V-MCA) has not been investigated during hypocapnia in pa tients with brain tumors. We compared V-MCA during normocapnic (ETCO(2 ): 40 mm Hg) and hypnocapnic (ETCO(2): 25 mm Hg) inhalation of air and 50% nitrous oxide in oxygen N2O/O-2 in eight patients with unilateral brain tumors on both the tumor side and the healthy side. Six patient s completed the study. Mean V-MCA increased during normocapnic inhalat ion of N2O/O-2 (tumor side: 86 +/- 16 cm sec(-1); healthy side: 74 +/- 17 cm sec(-1)) when compared with air (tumor side: 72 +/- 18 cm sec(- 1); healthy side: 62 +/- 14 cm sec(-1), p < 0.01), whereas during hype rventilation V-MCA decreased on both sides (p < 0.001). Mean V-MCA val ues were quite similar during hypocapnic inhalation of 50% N2O/O-2 (tu mor side: 50 +/- 12 cm sec(-1); healthy side: 45 +/- 13 cm sec(-1)) an d air (tumor side: 51 +/- 14 cm sec(-1); healthy side: 45 +/- 12 cm se c(-1)). The data of our study suggest that in patients with cerebral t umors the N2O-induced increase in mean V-MCA can be completely reverse d by hyperventilation.