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J Thorac Cardiovasc Surg 1999;118:771
© 1999 Mosby, Inc.

LETTERS TO THE EDITOR

A word of caution in extrapolating the spinal cord protective effects of memantine obtained in a rabbit model under ketamine anesthesia

Department of Cardiothoracic Surgery
Mount Sinai Medical Center
One Gustave Levy Place
Box 1028
New York City, NY 10029

Reply to the Editor:

My colleagues and I thank Miyamoto and Miyamoto for their interest and comments on our recent article regarding the N-methyl-D-aspartate (NMDA) blocker memantine. ¹

As we are aware of the protective effect of hypothermia on the release of excitatory amino acids, we have tried to keep the rectal temperature in a normothermic range assuming that the rectal temperature will reflect more accurate spinal cord temperature than esophageal temperature. However, we will additionally monitor esophageal temperature in future experiments.

With respect to our anesthesia protocol, a comparable experiment investigating the influence of anesthetics on neurologic recovery showed that ketamine treatment reduced acute paraplegia but increased delayed paraplegia. ² In our study, the control group did not show a protective effect of ketamine compared with the groups treated with memantine. Volatile anesthetics and nitrous oxide are suppressive to myogenic motor-evoked responses, ³ but ketamine is recommended as a suitable supplement to opioid/nitrous oxide anesthesia in men. ⁴ In our experiments we used ketamine to keep the experimental conditions constant and to avoid false positive depression of motor-evoked potentials due to the influence of an anesthetic.

In regard to the different applications of memantine, we assumed that intra-arterial infusion of memantine into the clamped aortic segment would result in better protection than administering the drug systematically. We were surprised by the fact that the systemic group did better than the intra-aortic group. We concur that this phenomenon was due to the slow crossing of memantine through the blood-brain barrier.

References

1. Ehrlich M, Knolle E, Ciovica R, Boeck P, Turkof E, Konetschny R, et al. Memantine for prevention of spinal cord injury in a rabbit model. J Thorac Cardiovasc Surg 1999;117:285-91.[Abstract/Free Full Text]
   
2. Naslund T, Hollier LH, Money SR, Facundus EC, Skenderis BS. Protecting the ischemic spinal cord: the influence of anesthetics and hypothermia. Ann Surg 1992;215:409-16.[Medline]
   
3. Zentner J, Thees C, Pechstein U, Scheufler KM, Würkler J, Nadstawek J. Influence of nitrous oxide on motor-evoked potentials. Spine 1997;22:1002-6.[Medline]
   
4. Kalkman CJ, Drummond JC, Patel PM, Takanobu S, Randall MC. Effects of droperidol, pentobarbital, and ketamine on myogenic transcranial magnetic motor-evoked responses in humans. Neurosurgery 1994;35:1066-71. [Medline]
   

This Article Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Marek Ehrlich Permission Requests Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Ehrlich, M. Search for Related Content PubMed PubMed Citation Articles by Ehrlich, M.