Cerebrospinal fluid pressure during O2 encephalography and N2O inhalation.

Cerebrospinal fluid (CSF) pressure was studied in 8 patients and 5 dogs during pneumoencephalography (PEG) or ventriculography in which either O2 or N2O was used as the contrast gas prior to and during N2O inhalation. In 7 patients, the use of O2 as the contrast gas increased CSF pressure 8.7 torr (range 4 to 12 torr) following N2O inhalation. In 1 patient, when N2O was used as the contrast gas, CSF pressure did not change after N2O inhalation. These findings were confirmed in anesthetized animals ventilated at a constant PaCO2. The authors conclude that if N2O inhalation is required during PEG, maximum patient safety can be achieved if the contrast gas is also N2O.