Abstracts

Animal studies have demonstrated a decrease in seizure thresholds with the administration of dexmedetomidine (DEX), suggesting facilitation of seizure expression by inhibition of central noradrenergic transmission (Anesthesiol 1994; 81:1422). Alpha-2 adrenergic agonists have been used to reduce the dose requirement of intravenous and volatile anesthetics with excellent hemodynamic stability in patients undergoing craniotomy (Anesthesiol 2002; 96:A310). However, no study has evaluated the effect of DEX on the electrocorticograph of seizure focus in humans.
After IRB approval, 8 consecutive patients undergoing craniotomy for seizure focus resection were studied. General anesthesia (GA) was induced with etomidate (0.2mg/kg), sufentanil (0.5 mcg/kg) and DEX (1 mcg/kg loading dose) and maintained with sufentanil (0.3-0.5 mcg/kg/hr) and DEX (0.5-0.7 mcg/kg/hr) infusions and air/oxygen, until lobectomy was complete. During closure, Desflurane was added and intravenous drugs tapered to achieve immediate awakening. Surgical field blocks were performed in all patients. Electrocorticographs (ECOG) were recorded using electrode grids placed over the lateral surface of the cortex as well as 4-electrode strips placed subtemporally.
Pre-operative EEG recordings performed with subdural implanted electrode grids revealed average background activity frequencies of 4-7 Hz with variability depending on patient level of wakefulness and activity. In comparison, under GA with DEX infusion, ECOG revealed marked alterations in background activity consisting of monotonous semi-rhythmic 4-5 Hz theta activity in 20% of patients, and diffuse high amplitude delta activity in the remainder of the patients. Sharp waves and spike activity were 50-75% suppressed compared to pre-op EEG recordings. Bolus doses (4 mg) of etomidate elicited epileptiform activity over suspected epileptogenic cortex in most patients, but 3-6 boluses were often required. Satisfactory neuro-operative conditions were achieved in all patients, typified by cardiovascular stability (MAP [plusmn] 20% and HR [plusmn] 30% of pre-induction baseline) and no supplemental vasoactive drug requirement at any point during the procedures. Five patients initiated movement during surgery despite prior administration of paralytic agents, yet without intraoperative recall or other adverse sequelae.
Craniotomy for seizure foci resection under GA requires a balance between provision of adequate analgesia, amnesia and immobility with achievement of valid interpretation of the ECOG. Combined DEX and sufentanil infusions allowed adequate neuro-operative conditions, yet despite a lightly anesthetized state, marked alterations in ECOG background activity, compared to pre-op subdural grid EEG recordings, were noted and epileptiform activity was suppressed. Therefore, DEX infusion appears to limit the efficacy of ECOG during asleep seizure focus resective surgery under the conditions studied.