Summary Nerve blocks improve postoperative analgesia, but their benefits may be short-lived. This quantitative review examines whether perineural dexmedetomidine as a local anaesthetic (LA) adjuvant for neuraxial and peripheral nerve blocks can prolong the duration of analgesia compared with LA alone. All randomized controlled trials (RCTs) comparing the effect of dexmedetomidine as an LA adjuvant to LA alone on neuraxial and peripheral nerve blocks were reviewed. Sensory block duration, motor block duration, block onset times, analgesic consumption, time to first analgesic request, and side-effects were analysed. Results were combined using random-effects modelling. A total of 516 patients were analysed from nine RCTs. Five trials investigated dexmedetomidine as part of spinal anaesthesia and four as part of a brachial plexus (BP) block. Sensory block duration was prolonged by 150 min [95% confidence interval (CI): 96, 205, P

Facilitatory effects of perineural dexmedetomidine on neuraxial and peripheral nerve block: a systematic review and meta-analysis

Dexmedetomidine: New avenues

Although beneficial in acute and chronic pain management, the use of local anaesthetics is limited by its duration of action and the dose dependent adverse effects on the cardiac and central nervous system. Adjuvants or additives are often used with local anaesthetics for its synergistic effect by prolonging the duration of sensory-motor block and limiting the cumulative dose requirement of local anaesthetics. The armamentarium of local anesthetic adjuvants have evolved over time from classical opioids to a wide array of drugs spanning several groups and varying mechanisms of action. A large array of opioids ranging from morphine, fentanyl and sufentanyl to hydromorphone, buprenorphine and tramadol has been used with varying success. However, their use has been limited by their adverse effect like respiratory depression, nausea, vomiting and pruritus, especially with its neuraxial use. Epinephrine potentiates the local anesthetics by its antinociceptive properties mediated by alpha-2 adrenoreceptor activation along with its vasoconstrictive properties limiting the systemic absorption of local anesthetics. Alpha 2 adrenoreceptor antagonists like clonidine and dexmedetomidine are one of the most widely used class of local anesthetic adjuvants. Other drugs like steroids (dexamethasone), anti-inflammatory agents (parecoxib and lornoxicam), midazolam, ketamine, magnesium sulfate and neostigmine have also been used with mixed success. The concern regarding the safety profile of these adjuvants is due to its potential neurotoxicity and neurological complications which necessitate further research in this direction. Current research is directed towards a search for agents and techniques which would prolong local anaesthetic action without its deleterious effects. This includes novel approaches like use of charged molecules to produce local anaesthetic action (tonicaine and n butyl tetracaine), new age delivery mechanisms for prolonged bioavailability (liposomal, microspheres and cyclodextrin systems) and further studies with other drugs (adenosine, neuromuscular blockers, dextrans).

Adjuvants to local anesthetics: Current understanding and future trends

Background: Various adjuvants have been used with local anesthetics in spinal anesthesia to avoid intraoperative visceral and somatic pain and to provide prolonged postoperative analgesia. Dexmedetomidine, the new highly selective α2-agonist drug, is now being used as a neuraxial adjuvant. The aim of this study was to evaluate the onset and duration of sensory and motor block, hemodynamic effect, postoperative analgesia, and adverse effects of dexmedetomidine or fentanyl given intrathecally with hyperbaric 0.5% bupivacaine. Materials and Methods: Sixty patients classified in American Society of Anesthesiologists classes I and II scheduled for lower abdominal surgeries were studied. Patients were randomly allocated to receive either 12.5 mg hyperbaric bupivacaine plus 5 μg dexmedetomidine (group D, n=30) or 12.5 mg hyperbaric bupivacaine plus 25 μg fentanyl (group F, n=30) intrathecal. Results: Patients in dexmedetomidine group (D) had a significantly longer sensory and motor block time than patients in fentanyl group (F). The mean time of sensory regression to S1 was 476±23 min in group D and 187±12 min in group F (P Conclusions: Intrathecal dexmedetomidine is associated with prolonged motor and sensory block, hemodynamic stability, and reduced demand for rescue analgesics in 24 h as compared to fentanyl.

A Comparative study of intrathecal dexmedetomidine and fentanyl as adjuvants to Bupivacaine.

Background: Spinal anaesthesia is the most common approach which is used for lower limb surgery. Dexmedetomidine is the recent drug which acts on α2-adrenergic receptors in the dorsal horn of the spinal cord to produce analgesic effects. Aim: Efficacy and safety of intrathecal dexmedetomidine added to ropivacaine. Setting and Design: Randomised double blind trial. Methods: Sixty patients were randomly allocated to receive intrathecally either 3 ml of 0.75% isobaric ropivacaine + 0.5 ml normal saline (Group R) or 3 ml of 0.75% isobaric ropivacaine + 5 μg dexmedetomidine in 0.5 ml of normal saline (Group D). Results: The mean time of sensory regression to S2 was 468.3±36.78 minutes in group D and 239.33±16.8 minutes in group R. Duration of analgesia (time to requirement of first rescue analgesic) was significantly prolonged in group D (478.4±20.9 minutes) as compared to group R (241.67±21.67 minutes). The maximum visual analogue scale score for pain was less in group D (4.4±1.4) as compared to group R (6.8±2.2). Conclusion: The addition of dexmedetomidine to ropivacaine intrathecally produces a prolongation in the duration of the motor and sensory block.

Dexmedetomidine as an intrathecal adjuvant for postoperative analgesia.

OBJECTIVES 
To determine the effect of adding dexmedetomidine to bupivacaine for neuraxial anesthesia.
 METHODS 
Sixty-six patients were studied between April and May 2008 in the University of Jordan, Amman Jordan. They were randomly assigned into 3 groups, each receiving spinal bupivacaine 12.5mg combined with normal saline (group N) Dexmedetomidine 5 microg (group D5), or dexmedetomidine 10 microg (group D10). The onset times to reach T10 sensory and Bromage 3 motor block, and the regression times to reach S1 sensory level and Bromage 0 motor scale, were recorded.
 RESULTS 
The mean time of sensory block to reach the T10 dermatome was 4.7 +/- 2.0 minutes in D10 group, 6.3 +/- 2.7 minutes in D5, and 9.5 +/- 3.0 minutes in group N. The mean time to reach Bromage 3 scale was 10.4 +/- 3.4 minutes in group D10, 13.0+/-3.4 minutes in D5, and 18.0 +/- 3.3 minutes in group N. The regression time to reach S1 dermatome was 338.9 +/- 44.8 minutes in group D10, 277.1 +/- 23.2 minutes in D5, and 165.5 +/- 32.9 minutes in group N. The regression to Bromage 0 was 302.9 +/- 36.7 minutes in D10, 246.4 +/- 25.7 minutes in D5, and 140.1 +/- 32.3 minutes in group N. Onset and regression of sensory and motor block were highly significant (N vesus D5, N versus D10, and D5 versus D10, p<0.001).
 CONCLUSIONS 
Dexmedetomidine has a dose dependant effect on the onset and regression of sensory and motor block when used as an adjuvant to bupivacaine in spinal anesthesia.

Micheal A. Ramsay

Papers

Effect of dexmedetomidine added to spinal bupivacaine for urological procedures.