OBJECTIVETo determine the 50% effective concentration (EC(50) ) of dexmedetomidine (DEX) as an adjuvant for achieving the minimal effect in combined spinal-epidural anesthesia (CSEA) with Narcotrend.

METHODSThirty ASA class I-II patients undergoing CSEA were allocated to receive 0.5% bupivacaine injection (2 ml) in the subarachnoid space, followed by a target-controlled infusion of DEX for at least 60 min. The target concentration of DEX was adjusted according to the response of the previous patient using a double-blind, up-and-down sequential method. The initial DEX concentration of the first patient was 0.5 ng/ml. An Observers Assessment of Alertness/Sedation Scale (OAA/S) score of no more than 3 within 30 min defined an effective sedation. The Narcotrend index (NTI) related to the OAA/S score was recorded as well. The correlation between Narcotrend and OAA/S score was analyzed.

RESULTSThe EC(50) of DEX as an adjuvant in CSEA was 0.35∓0.07 ng/ml. The NTI was positively correlated to the OAA/S score (r=0.967, P=0.000). The regression equation was OAA/S =-3.922+0.094NTI (F=401.710, P=0.000).

CONCLUSIONWe suggest a novel protocol using DEX as a adjunct in CSEA. The EC(50) % of DEX to result in ideal sedation (OAA/S≤3) was 0.35∓0.07 ng/ml. NTI may serve as an objective index for sedation assessment in CSEA.