Different Target-controlled Concentrations (1 And 2ng/ml) Of Remifentanil Reduce The MAC_BAR Of Sevoflurane

BackgroundMAC (minimal alveolar concentration) is the alveolar concentration of one anesthetic agent that prevents movement in 50% of subjects in response to a noxious stimulus under an atmospheric pressure. with the routine use of muscle relaxants during general anesthesia, assessing of anesthesia depth and MAC don't rely on body-movement or escaping reflex but other clinic signs, for examples, changes of blood pressure and heart rate. It is related to MAC_bar. MAC_bar is the minimum alveolar concentration that blocks the adrenergic response to a noxious stimulus and used to assess the potency of an inhaled anesthetic during operation.There are many effect factors of MAC as age, temperature and observation mathod. Opioid agents also have the same effect. It has beenclearly demonstrated that opioid agents significantly reduce the minimal alveolar concentration (MAC) of potent inhaled anesthetics required to abolish consciousness, intubate, and blunt the sympathetic response to skin incision, for examples, effect offentanil on MAC of isoflurane, sevofiurane and desflurane. There is no research report about effect of remifentanil on MAC of sevofiurane in our country. Both remifentanil and sevofiurane are the new clinic agents. The usage about them is at the beginning stage and need to improve. Our research about remifentanil and sevofiurane will help us understand their pharmacology character, find better combined methods, reduce complication and keep anesthesia process stable. On the other hand, the research will help to reduce economic cost and waste gas pollution. All these have impotant practical clinic value.ObjectiveTo compare effects of different target-controlled concentrations (1 and 2ng/ml) of remifentanil on the sevofiurane MAC which blocks the adrenergic response to surgical incision (MACbar) and to find better combined methods for these two anesthetic agents.Methods75 patients, aged 20-50 yr, with American Society of Anesthesiologists physical status I, were randomly allocated to three groups after induction anesthesia and tracheal intubationwith intravenous propofol(0.2mg/kg), vecuronium(0.1mg/kg) and remifentanil target-controlled infusion(plasmaconcentration of 2 ng/ml). Group Ro (n = 25) received sevoflurane alone, group Ri(n = 25) received sevoflurane plus remifentanil (a target-controlled plasma concentration of 1 ng/ml), and group R2(n = 25) received sevoflurane plus remifentanil (a target-controlled plasma concentration of 2 ng/ml). MACbar determination, in response (changes of MAP or heart rate) to the stimulus of skin incision, was made using the "up and down " method after a 20-min period of stable end-tidal sevoflurane and target-controlled remifentanil concentrations..Results1. No differences in patient characteristics, preoperative heart rate and MAP, or operation area were reported among the three groups.2. Heart rate and MAP decreased significantly after induction of general anesthesia in each group;however, no differences were reported among the three groups.3. The MACbar of sevoflurane was 3.1% in the group Ro, 1.5% in the group Ri and 0.8% in the group R2. The MACbar values were 1.8MAC, 0.88MAC, and 0.47MAC, in the three groups, respectively. The difference in the three groups was very significant (P<0.01).4. At the postoperative visit 24 h after surgery, no patient reported explicit recall of any intraoperative event.ConclusionThere were different effects of two target-controlled concentratios of remifentanil on MACbar of sevoflurane. MACbar of sevoflurane decreased gradually with target-controlled concentratios increasing of remifentanil. Atarget-controlled concentration of 1 ng/ml remifentanil reduce the MACbar of sevoflurane by 51% and the target concentration of remifentanil to 2ng/ml reduce the MACbar of sevoflurane by 74%.