Hemifacial Spasm and Desflurane
Hemifacial Spasm and Desflurane
Patients are chosen to participate in this study because they will undergo a particular type
 of brain surgery to treat their hemifacial spasm. This surgery is called microvascular
 decompression (MVD) and involves the facial nerve. The facial nerve is being compressed by
 one or more blood vessels and this contact produces the facial twitches. The investigators do
 not know why a blood vessel that touches the facial nerve produces facial twitches. The
 investigators are interested in investigating this during your surgery. A total of 25
 participants are expected to participate in this study.
"Intra Operative Monitoring" (IOM) is a standard and routine medical practice for patients
 having MVD surgery. IOM is done to make sure that the hearing and face nerves are not
 accidentally bumped or damaged during surgery. After anesthetic induction, the
 neurophysiologist places electrodes for the nerves, on the scalp and muscles. Stimulation and
 monitoring of muscle twitches are all common, safe and painless medical procedures.

 In this study, the investigators would like to measure the nerve and muscle function on the
 normal side and compare it to nerve and muscle function on the abnormal side during different
 levels of the anesthetic desflurane. In order to monitor the normal side of the face one
 additional set of electrodes will be placed in the facial muscles. The investigators will
 compare responses to three different levels of anesthetic. The technique used will be motor
 evoked potentials. The effect of the anesthesia on the lateral spread response will also be
 examined. This response is evident only on the symptomatic side. These observations will take
 approximately 10 to 15 minutes and will not delay or lengthen the surgery.
Inclusion Criteria:

 -  patients referred to the neurosurgical service for microvascular decompression surgery
 for HFS

 -  males and females 18 to 75 years of age

 -  otherwise normal neurological exam

 -  signed informed consent

 Exclusion Criteria:

 -  Botox treatment within the last three months