To the Editor:—
I read with interest the article “Sedation during Spinal Anesthesia” by Pollock et al. 1During the past 12 yr, while performing local anesthetic blocks for eye surgery without the administration of sedative medication, I have observed a considerable number of patients who become lightly sedated after block insertion. These patients note the sedative effect not infrequently and ask what has been administered to produce it. They do not attribute it to relief that a stressful procedure has been successfully completed. I have not noticed comparable sedation with any other peripheral local anesthetic blocks. The mass of local anesthetic is small, generally between 3–5 ml lignocaine, 2% (60–100 mg), but in excess of the quoted spinal doses in the article. Within its sheath and the layers of dura and arachnoid mater that surround it, the optic nerve is bathed in cerebrospinal fluid.
Brain stem anesthesia by direct injection into the subdural space around the nerve is a well-documented complication of retrobulbar blocks. 2In most regional anesthetic techniques for eye surgery, the deposited local anesthetic gains access to the intraconal space, and there it lies in close contact with the optic nerve. This is particularly true of sub-Tenons and uncomplicated retrobulbar blocks. Is it possible that this unique epidural deposition of local anesthetic may have a similar mechanism of sedative action in these patients as occurs in spinal or classic epidural anesthetics?