In Reply:—

We appreciate the interest of Drs. Lam and Artru with respect to our article. 1We agree that there may be several interpretations to their findings that intracranial pressure did not increase when nitrous oxide was replaced by sevoflurane. 2However, we are not aware of studies showing that intraparenchymal fiberoptic catheters provide a more accurate measurement of intracranial pressure than lumbar cerebrospinal fluid pressure (LCSFP) in patients with unobstructed fluid pathway between the intracranial and spinal CSF fluid spaces. Furthermore, any obstruction of the fluid pathway in our study should have caused us to underestimate the increase in intracranial pressure caused by sevoflurane. We disagree with Drs. Lam and Artru’s reinterpretation of our results that LCSFP is higher during sevoflurane anesthesia compared with propofol–nitrous oxide anesthesia. Because we added sevoflurane to propofol–nitrous oxide anesthesia, a more accurate interpretation of our results is that addition of sevoflurane to propofol–nitrous oxide anesthesia increased LCSFP. We also agree that the choice of the control group is critically important in interpretation of the observations. In our study, the only variable part of anesthesia was sevoflurane, whereas Drs. Lam and Artru varied two anesthetics with known effects on intracranial pressure (sevoflurane and nitrous oxide) compared with the respective control groups.

Talke P, Caldwell JE, Richardson CA: Sevoflurane increases lumbar cerebrospinal fluid pressure in normocapnic patients undergoing transsphenoidal hypophysectomy. A NESTHESIOLOGY 1999; 91:127–30
Artru AA, Lam AM, Johnson JO, Sperry RJ: Intracranial pressure, middle cerebral artery flow velocity, and plasma inorganic fluoride concentrations in neurosurgical patients receiving sevoflurane and isoflurane. Anesth Analg 1997; 85:587–92