To the Editor:—
We read with interest the article by Vachon et al. 1entitled “Succinylcholine and the Open Globe,” which was published in the July 2003 issue of Anesthesiology. Although it is true that the risk of using succinylcholine in anesthesia for open globe injuries is still an open question, we would like to clear up a misconception in the article regarding why there might be such a risk. In their excellent article, Vachon et al. emphasized that succinylcholine has been shown to increase intraocular pressure. Although this is absolutely correct, it is irrelevant when it comes to injuries involving an open globe because, by definition, as soon as the globe is open, the intraocular pressure is zero. Because the globe is open, any medication that might be shown to increase the intraocular pressure in a closed globe will be unable to do so.
What is important in an open globe injury is the extraocular pressure. This is why it is critical that an open globe be handled with extreme dexterity and care by the surgeon, so as not to put any pressure on the tissues with the surgical instruments. Obviously, compressing an open globe from the outside leads to the possibility of extravasating the intraocular contents. This is why these cases are performed under general anesthesia, rather than injecting local anesthetic into the retrobulbar space. Cocontraction of the recti muscles could theoretically place pressure on the globe from the outside (i.e. , increase the extraocular pressure), leading to extrusion of the intraocular contents.
Therefore, the issue with succinylcholine is not that it increases the intraocular pressure but that it causes cocontraction of the four recti muscles, as was shown in electrophysiologic studies by Macri and Grimes 2and clinically by Kornblueth et al. 3Vachon et al. correctly point out that although it has been clearly demonstrated that cocontraction of the recti muscles does occur in response to succinylcholine administration, it has not been clearly shown that this is of a magnitude to produce extrusion of the intraocular contents in the clinical setting of an open globe injury.
Because the traditional teaching is that succinylcholine should be avoided in such cases but in practice many anesthesiologists use succinylcholine, only a prospective randomized clinical trial will settle the question. Assuming that an institutional review board would approve such a trial (and we think it would, given the fact that both the use of succinylcholine and the avoidance of succinylcholine are routinely practiced in such cases), we believe that such a study is feasible. There are many city and county hospitals that have well over 100 cases of open globe injuries per year, and therefore, such a study would be practical.
To reiterate, the main point we wish to convey is that if succinylcholine use in open globe injuries is dangerous, it is because of the cocontraction of the recti muscles increasing the extraocular pressure rather than any increase in intraocular pressure that may occur in studies performed with an intact globe.