Journal of Neurosurgical Anesthesiology Vol. 4, No. 4, pp. 290-294 0 1992 Raven Press, Ltd., New York

Points of View Place of Nitrous Oxide in Neuroanesthesia: Still a Valuable Drug

Satwant K. Samra

Department of Anesthesiology, University Hospital, Ann Arbor, Michigan, U.S.A.

Nitrous oxide (N20)has been used as anesthetic traditionally been highly recommended, is patient drug since 1863. Its introduction to clinical anesthe- with intracranial pathology, undergoing cranioto sia was surrounded by controversy (1). During its my. In recent years, several clinical investigation. history of nearly 130 years of clinical use it has of effects of N20 on cerebral. blood flow (CBF) outlived many inhalation anesthetic drugs such as intracranial pressure (ICP), cerebrospinal fluic ether, cyclopropane chloroform, fluroxene, trichlo- (CSF) dynamics, sensory evoked potentials (SEPs). roethylene, and methoxyflurane, to name a few. and pneumocephalus have been published. Results This longevity of N20 is attributed to some.of its of these studies have mised the question: Should we physical properties such as nonidlammability, low continue to use N20in neuroanesthesia? To answer solubility, and relative inertness and odorlessness. this question, one first needs to examine the prin- These characteristics, combined with low cost, ciples on which anesthetic management of patients compared with other currently av'ailable inhalation with intracranial pathology should be based. anesthetic drugs, make N20 a valuable tool in an Broadly speaking, these principles are as follows. anesthesiologist's armamentarium. It can provide a 1. Prevent a rise of ICP during induction, because rapid induction of anesthesia with minimal cardio- many of these patients have decreased intracranial vascular depression and a quick emergence from compliance. general anesthesia. It is true that N20 was intro- 2. Provide a "shrunken brain" to facilitate surgi- duced and well accepted in clinical practice without cal exposure, thus avoiding undue pressure during rigorous testing for side effects and toxicity, which retraction, which may result in ischemic injury of modem inhalation anesthetic drugs have to undergo underlying vital brain structures. before being approved by the Food and Drug Ad- 3. If electrophysiological monitoring (electroen- ministration. Recent methodological advances in cephalogram/SEPs/facial nerve recordings) is being drug testing have revealed that indeed, N20 is nei- used, an anesthetic technique that causes the least ther as inert nor totally free of toxicity as was once interference with monitoring should be used. believed. This has led to some controversy about 4. Rapid emergence-thus allowing adequate the appropriateness of its continued use in clinical neurological evaluation in the immediate postoper- anesthesia (2-4). ative period. It also allows early detection of neu- One subset of surgical patient population, in rological deterioration in the recovery room. which nitrous-narcotic or balanced anesthesia had Next, one can make a decision about the place of N20 in achieving these goals in clinical practice based on the current knowledge of the effects of Address comspondence and reprint requests to Dr. S. K. N20 in comparison to alternative choices. For the Samra at Department of Anesthesiology, 1G323 University Hos- pital, 1500 East Medid Center Drive, Ann Arbor, MI 48109- sake of. brevity we .will concentrate on published 0048, U.S.A. clinical studies only.