Effects Of Dexmedetomidine On Pressor Response To Ephedrine In Aged Patients Undergoing Intravertebral Anesthesia

Objective:With the accelerated development of aging process in our country, there are 10 % people over 65 years old and aged patients with femoral neck fractures and need operations are increasing. Aged patients undergoing intravertebral anaesthesia usually have a decrease in blood pressure and a poor effect to vasoactive drugs. In general anaesthesia, dexmedetomide could enhance the pressor effect of ephedrine, but its enhanced pressor effects to dexmedtomidine in spinal anaesthesia are still unknown. In this study, we will observe the effects of dexmedetomidine on pressor response to ephedrine and its safety in aged patients undergoing artificial femoral head arthroplasty(FHA) or total hip arthroplasty(THA) after intravertebral anesthesia. Methods:This clinical trial was approved by Ethics Committee of Shanxi Dayi Hospital. After obtained informed consent, 64 aged patients undergoing artificial femoral head replacement or total hip replacement were recruited and grouped to two parts randomly. They were group control(group C, n=34) and group dexmedetomidine(group D, n=30). All the patients in position on uninjured side were received combined spinal-epidural anesthesia in L2~L3. After disinfection and draped, the epidural needle was placed in epidural space and then the spinal needle was put through the epidural needle. When clear cerebrospinal fluid outflowed, 1% ropivacaine 2 ml and fentanyl 0.05 mg(in total 3 ml) were intrathecal injected and then ephedrine 6 mg was injected intravenously. Dexmedetomidine was administrated in group D, loading dose 0.5μg·kg-1 was given in 10 min and followed by micro pump injection in 0.3μg·kg-1·h-1, patients in group C received isodose 0.9% sodium chloride injection.The systolic blood pressure(S B P). diastolic blood pressure(D B P). mean arterial pressure(M A P). heart rate(H R) and S p O2 of patients were recorded when patients entering operation room(T0), before intrathecal injection with drugs(T1), 2 min after ephedrine injection(T2), at intravenous infusion dexmedetomidine 10 min(T3), 30 min(T4) and 60 min(T5).Statistical analyses were performed using SPSS 22.0. Mean and standard deviation(S D) were used to express measurement data. The comparison of age and body mass index(B M I) between two groups were analyzed with independent sample t-test, the hemodynamic parameters in different time points were compared with repetitive measurement and analysis of variance and the comparisons of discrete variables such as gender, ASA and operating methods between the groups were analyzed with chi-square test. A P-value < 0.05 was been thought no influence. Results:1. Comparison of hemodynamic between two groupsS B P. D B P and M A P in group D were taller at T2(P<0.05), reached the highest at T3(P<0.05) and lasted until T4(P<0.05); however in group C, S B P. D B P and M A P were bigger at T2(P<0.05), become the biggest at T3(P<0.05), began to decrease at T4(P<0.05), these results indicated that the combined administration of dexmedetomidine and ephedrine could prolong the pressor action time of ephedrine. There was no significant difference of HR in group D at different time points. However in group C, H R at T2 were faster than others(P<0.05). These results proved that the administration of ephedrine alone may induce transient increase of HR. Compared to group C. S B P, D B P and M A P at T3 and T4 in group D were higher(P<0.05), which reflected that dexmedtomidine could improve the pressor effect of ephedrine; HR at T2 in group D was lower(P<0.05), which demonstrated that the combined administration of dexmedetomidine and ephedrine could reduce the fluctuation of HR.2. Comparison of Sp O2 between two groupsThere was no significant difference in Sp O2 between two groups, which indicated that dexmedetomide had no respiratory depression. Conclusion:1. Low dose dexmedetomidine could enhance the pressor response and action time of ephedrine in aged patients undergoing artificial femoral head replacement or total hip replacement after intravertebral anesthesia, which maintain the intraoperative hemodynamics more stable.2. Intravenous injection of low dose dexmedetomidine has no respiratory depression which could be safely used in aged patients undergoing intravertebral anesthesia.