The influence of increasing concentrations of nitrous oxide on cerebral blood flow velocity in hypocapnic patients with brain tumours

An increase of more than 50% in cerebral blood flow velocity in the middle cerebral artery was recently reported in hypocapnic volunteers, while inhal ing 50% nitrous oxide. We measured cerebral blood flow velocity in the midd le cerebral artery in 10 anaesthetized hypocapnic (ETCO2=25 mmHg) patients with brain tumours while administering increasing concentrations of nitrous oxide. At an end-tidal concentration of 50% and 70% nitrous oxide in oxyge n, neither mean arterial pressure (base-line: 84+/-8 mmHg vs. (50% nitrous oxide): 82+/-9 mmHg and (70% nitrous oxide): 80+/-8 mmHg) nor cerebral bloo d flow velocity in the middle cerebral artery (base-line: 32+/-7 cm s(-1) v s. (50% nitrous oxide): 34+/-8 cm s(-1) and (70% nitrous oxide): 34+/-9 cm s(-1)) changed significantly. The data from our clinical investigation indi cate that administration of increasing concentrations of nitrous oxide to a lready anaesthetized and hypocapnic patients does not change cerebral blood flow velocity in the middle cerebral artery.