Explore The Optimal Dose Of Dexmedetomidine When Combined Spinal-epidural Anesthesia

Objective: Diseases encountered in clinical work is often accompanied by varying degrees of obesity, it is largely leading by illness that caused by the obesity itself, they often requiring surgery therapy, obese patients anesthesia implement gradually increased, but obesity has changed the original body normal physiological mechanisms, such as many parts of the body composition changes, an increase in the proportion of fat, compared to skeletal muscle, the proportion of inorganic salts and water were cut down, have different effects on drug metabolism, drug metabolism and therefore obese patients with normal-weight on drug using method are different. To evaluate the effect of obesity factor act on dexmedetomidine optimal dose during combined spinal-epidural anesthesia according to sequential method, when these obese patients were on orthopedic surgery whose BMI were between 30~34kg/m2.Methods: Elective lower limb orthopedic surgery patients 28 cases, ASA grade Ⅰ or Ⅱ, divided into two groups, the normal weight group(group C) and obese group(group O), mean operation time was 2h, aged 20 to 50 yr, both sexes, BMI18~22.9kg/m2, BMI30~34kg/m2 combined spinal-epidural anesthesia was performed at L2-3 interspace. Anesthesia level control in under T10, when anesthesia effect was exact, groups O and C were given the same loading dose of 1μg/kg dexmedetomidine iv infusion(200μg: 2ml diluted to 48 ml saline) 10 min, after 10 min and the 0.5μg/(kg·h) to maintain dose infusion. When at the 30 min time point,Ramsay sedation score criteria for assessing the depth of sedation, the first patient given dexmedetomidine maintenance dose was 0.5μg/(kg·h), the dose was increased decreased by 0.05μg/(kg·h) in the next patient,calcuated by up-and down method.ED50 and 95% CI of two groups were calculated in returning of probability method. To observe and record hemodynamic level, change and BIS value of the two groups on T1(base line value),T2(10 minutes after dexmedetomidine infusion),T3(when dexmedetomidine infusion at 0.5μg(kg·h) after 30 minutes and T4(when operation ended).Results:1 There was no difference between the groups in general situation(P> 0.05).2 The two groups at T1, T2, T3,T4 time point hemodynamic changes: Compared with group C, group O at various time points BP, Sp O2, HR was in no significant difference(P> 0.05).3 The two groups BIS value comparison: Compared with group C, group O at T1, T2, T3,T4 moment BIS value in no significant difference(P> 0.05).4 Normal weight group given dexmedetomidine optimal dose was 0.47μg/(kg·h), 95%CI 0.32~0.63μg/(kg·h); the obese group 0.40μg(kg·h),95%CI 0.29~0.58μg/(kg·h), the difference between two groups was statistically significant(P> 0.05), Table 1.Conclusion:The obesity factors leads the dexmedetomidine pharmacodynamic effect increasing in spinal-epidural anesthesia, ED50 is 0.40μg /( kg·h).