MedWire News: Unilateral spinal anesthesia can be achieved when bupivacaine is combined with clonidine, but clonidine does prolong the motor block and increase the need for vasopressors, researchers report.
“Hyperbaric bupivacaine in small doses effectively produces unilateral spinal anesthesia for outpatient surgery,” Riika Merivirta (Turku University Hospital, Surgical Hospital, Finland) and colleagues point out. But “when the dose of bupivacaine is reduced, the frequency of failed blocks increases,” they add.
While combining bupivacaine with clonidine intensifies the block, the effect of this combination on unilaterality has not been established.
Merivirta and team investigated the effect of adding 15 µg of clonidine to 5 mg hyperbaric bupivaciane on unilaterality in 60 patients undergoing outpatient knee arthroscopy. The patients were randomly assigned to receive either 1.2 ml (6 mg) of hyperbaric bupivacaine or a 1.2 ml solution containing 1.0 ml (5 mg) hyperbaric bupivacaine, 0.1 ml (15 µg) clonidine, and 0.1 ml sterile water.
Unilaterality when the patients were in the lateral position for 10 minutes was similar in the two groups, with completely unilateral block achieved in 77% of patients receiving bupivacaine alone and 73% of patients receiving bupivacaine and clonidine combined.
The addition of clonidine prolonged the motor block, and time-to-walking was significantly longer, at 44 minutes, than in those receiving bupivacaine alone. However, the two groups were similar with regard to voiding times and home-readiness.
The researchers report in the journal Acta Anesthesiologica Scandinavica that patients who received bupivacaine and clonidine combined needed more vasopressors at the beginning of anesthesia than those receiving bupivacaine alone. Also, despite the unilateral block, blood pressure values started to differ between the two groups after 1 hour and 45 minutes, being significantly lower in patients receiving bupivacaine and clonidine combined. However, there was no need for vasopressors at this time.
Patients receiving bupivacaine and clonidine experienced less pain postoperatively both at rest and when moving than those receiving bupivacaine alone, but the difference was not significant.
Merivirta and co-workers conclude that the unilateral spinal block can be achieved by combining clonidine with bupivacaine.
There was a small improvement in the quality of anesthesia, but, in contrast, clonidine prolonged the motor block and increased the need for vasopressors,” they write.
“Therefore the benefits of the use of clonidine as an adjuvant for spinal anesthesia for ambulatory surgery are limited.”
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