In this study, we evaluated the efficacy of three spinal anesthesia methods, bupivacaine alone or with dexmedetomidine or fentanyl in lower limb orthopedic surgeries. Although there was no significant difference between groups in time to onset of Bromage 3 and complete motor block, BD group had lower time to reach the highest sensory level than BF group, with no difference with BN group but it was not statistically significant. (P-value = 0.08).
Similarly, Mahendru et al. found no significant difference in onset of motor block between dexmedetomidine and fentanyl groups. While Yektas and Ravipati reported faster onset of motor block for dexmedetomidine compared to fentanyl. Other studies have also mentioned lower time to reach the highest sensory level in dexmedetomidine compared to fentanyl.[12–19]
The mechanism of how dexmedetomidine prolongs sensory and motor blockade is not known. Dexmedetomidine is a highly-selective α2-adrenergic receptor agonist that causes analgesia by suppression the release of C fiber transmitters and hyperpolarization of post-synaptic neurons.
In our study, the highest sensory level in BD and BF group were T6 and T5 while in BN group was T6 and T7 dermatomes. One study reported the highest sensory level at T5 dermatome and Mahendru reported in T6 dermatome. Other study reported the highest sensory level at T5 dermatome in dexmedetomidine and T6 in fentanyl group.
None of the patients requested analgesic during the surgery. Bromage 3 occurred in all patients before operation. Complete regression of motor block (Bromage 0) was reached in all patients and with the highest duration in BD group. Moreover, time to regression to S1 sensory level and regression of two sensory levels in BD group was significantly longer than the other groups. These patients also experienced lower pain intensity six hours after surgery indicative of the highest postoperative analgesia duration in BD group.
Reduced need for analgesics in the post-operation period, more stable hemodynamics, longer duration of sensory and motor block for dexmedetomidine have been reported in previous studies comparing this drug with other drugs such as clonidine, fentanyl and sufentanil.[16,19,21–24] In orthopedic surgeries of lower limb, better results have also been reported for dexmedetomidine compared to fentanyl.[12,13]
Hemodynamic changes is common in anesthesia medications. We observed that changes in SBP, DBP and HR in BF was higher than BD and BN groups, with no difference between BD and BN patients. The highest decline occurred 5 min after spinal injection and was rather stable afterwards. Unlike our findings, other studies did not report any significant difference between fentanyl and dexmedetomidine regarding hemodynamic status.[12,13,15–18] Decline in HR and blood pressure are common effects of opioids. The difference in hemodynamic findings could be due to the response of each individual to the drug, demographic profile, volume of IT injectate and volume of diluent used.
Side effects may occur by using any anesthesia medications. The best medication is the one with the highest efficacy and lowest side effects. We observed no significant difference in the rate of hypotension, bradycardia, nausea and vomiting and chilling between groups. Previous studies have reported different rate of side effects. Similar to our findings, Ravipati observed pruritus only in fentanyl group while nausea and vomiting was more common in dexmedetomidine, with no significant difference between groups. There is also only one study reporting increase in hemodynamic side effects, bradycardia and hypotension, in dexmedetomidine.
Another important side effect of anesthesia medications is respiratory system suppression. However, we observed no respiratory suppression. First, fentanyl compared to other opioids is less likely to cause respiratory suppression. Second, this complication is not common in dexmedetomidine.
In order to reach better efficacy, we can increase the dose of the used dexmedetomidine. Gupta reported that increasing the dose of dexmedetomidine from 2.5 μg to 10 μg would show better and longer sensory and motor block, with longer duration of anesthesia and comparable hemodynamic and side effects profile.
BMC Anesthesiol. 2018;18(62) © 2018 BioMed Central, Ltd.