Expert: Ronald Levy, M.D. - 12/4/2009

Question
I'm a night nurse on a med-surg floor (I'm a new grad).  Recently, I had an epileptic patient with a serum phenytoin level of only 5.7 who was scheduled to have a hip replacement surgery the next morning at 0730.  MD was aware of the patient's phenytoin level, but had ordered no phenytoin beyond the dose the patient had already been taking (the dose that had resulted in this low serum level).  
As I passed the patient and his information on to the day shift nurse, we asked ourselves the question, "What if the patient were to have a seizure while under general anesthesia?"  If a neuromuscular blocking agent were used, and the patient ventilated, what, if any, would be the effects of a seizure while under general anesthesia?  Also, do inhalation anesthetics and their adjuncts raise the seizure threshold?  Enough so that low serum levels of anticonvulsants are not a deterrent to surgery?

Thank you so much for being available to answer these questions.
Sincerely,
Rebecca

Answer
Here are the answers to your questions:


What if the patient were to have a seizure while under general anesthesia?

While it is rare, it can happen. The main problem with seizures (in awake patients) is potential aspiration and airway issues. These would be no problem under general anesthesia as the patient is intubated.


If a neuromuscular blocking agent were used, and the patient ventilated, what, if any, would be the effects of a seizure while under general anesthesia?

They would still have a seizure but the effects would be minimal (for reasons mentioned above). The main problem would occur if the patient had ICP or IOP issues. In these cases, a seizure could be a serious problem.


Also, do inhalation anesthetics and their adjuncts raise the seizure threshold?  Enough so that low serum levels of anticonvulsants are not a deterrent to surgery?

Most anesthetics do raise the seixzure threshold (in fact some are used for status epilepticus) although there are some agents that actually lower the threshold.


In any case, when the anesthesiologist saw your patient preoperatively, if he was concerned with the levels, he would have either cancelled the case or had the level corrected prior to surgery.

Ronald Levy, MD
Professor of Anesthesiology
UTMB-Galveston