Prevention And Comparison Of Different Concentrations Of N₂O On Remifentanil-induced Hyperalgesia

Purpose To explore the preventive effects of Nitrous Oxide（N₂O）of different concentrations on opioid-induced hyperalgesia（OIH）induced by remifentanil.Methods With the approval of the ethics committee of our hospital,75 male patients undergoing elective laparoscopic radical gastrectomy for gastric cancer were randomly divided into 3 groups:Intraoperative inhalation of 0%N2O group（N0 group）,25%N2O group(N₂₅5 group),50%N₂O group(N₅₀ group).All patients were treated with general anesthesia by tracheal intubation.PCA ache pump（PCA）was used after operation.Observation indexes:（1）age,weight,operation time,blood loss,remifentanil dosage,recovery time and Ramsay score.（2）In each group,mean arterial pressure（MAP）and heart rate（HR）were obtained at different time points before and after anesthesia in patients of each group.（3）The mechanical pain threshold around the incision was measured at different time points.（4）Patients were evaluated for pain at 1h,4h,6h,and 24h after extubation.（5）When the VAS Score（Visual Analogue Score）exceeded 4 point,50mg of fluorobulofenate（kavin）was added and the additional kavin dosage was recorded.（6）Postoperative adverse reactions were recorded.Results（1）There was no statistically significant difference in age,weight,operation time,blood loss,remifentanil dosage,recovery time and Ramsay score（P>0.05）among the patients of three groups.（2）Comparison of MAP value groups:There was no statistically significant difference in MAP at three time points（T0,T1 and T2）（P>0.05）among four groups.At T3 time point,MAP values of N50 group were significantly lower than those of N0group（P<0.05）.Comparison within groups:MAPs of N₀ group and N₂₅ group at time points T₂ and T₃ were significantly higher than those at T₀（P<0.05）.There was no statistically significant difference in MAP changed over time N₅₀ group（P>0.05）.HR value comparison between groups:At T₀ time point and T₃ time point,there was no statistically significant difference in HR among four groups（P>0.05）.At T₁ and T₂ time points,HR values of N₅₀ group and N₇₀ group were lower than those of N₀ group and N₂₅ group,with statistically significant differences（P<0.05）.Comparison within groups:All four groups showed that HR values at T₁ and T₂ were higher than those at T₀ and T₃,and the differences were statistically significant（P<0.05）.（3）There was no statistically difference in the basic mechanical pain threshold around the incision in each group.Postoperative pain threshold of N₀ group was significantly lower than that of N₂₅ group and N₅₀ group（P<0.05）.Compared with group N25,the mechanical pain threshold of group N50 was significantly increased after surgery（P<0.05）（4）VAS score comparison between groups:at 1h and 4h of after extubation,VAS score of N₅₀ group was lower than that of N₀ group.At the time of 6h after extubation,VAS scores of N50 group group were lower than those of N0 group and N25 group,and the difference was statistically significant（P<0.05）.No statistically difference in VAS scores was observed between the four groups 24 hours after extubation（P>0.05）.Comparison within groups:At the three experimental concentrations,VAS score decreased with the increase of postoperative time,namely VAS_1h>VAS_4h>VAS_6h>VAS_24h,and the difference was statistically significant（P<0.05）.（5）Postoperative additional analgesic:the amount of additional analgesic drugs in the N₀ group was higher than that in the other two groups,and the difference was statistically significant（P<0.05）.（6）There was no statistically significant difference between the three groups（P>0.05）Conclusion（1）Inhalation of N₂O can effectively prevent OIH induced by remifentanil（2）Inhalation of 50%N₂O was more effective in preventing OIH induced by remifentanil than inhalation of 25%N₂O.