Comparative addition of dexmedetomidine and fentanyl to intrathecal bupivacaine in orthopaedic procedure in lower limbs

The use of adjuvants may reduce the nature of complications and improve the duration of the anesthetic effect. Some commonly used adjuvants are opioids, ketamine, neostigmine, clonidine, and dexmedetomidine.

Lower limb surgeries could be performed under local, neuroaxial and general anesthesia, but neuroaxial block is the preferred method. Spinal block/ subarachnoid block is a relatively safe anesthetic method, it has rapid onset, deep block, lower risk of infection, preservation of mental status, normal airway reflexes and is cost effective. However, post-operative pain is an important problem as the used drugs have limited duration of effect; so the post-operative analgesic administration is necessary.

Administrating the combinations of other classes of analgesics with local anesthetics has used to increase the duration and reduce side effects of analgesia [3]. Clonidine and dexmedetomidine are two α2 agonists affecting via pre- and post-synaptic α2 receptors [4].

Dexmedetomidine is an α2-adrenergic receptor (α2-AR) agonist. When administered intrathecaly, the time of onset of its action 5-10min peak effect at 15-30 min, duration of action is 2 hours after bolus injection. It prolongs the duration of both sensory and motor blockade induced by local anesthetics irrespective of the route of administration (e.g., epidural [3], caudal [4], or spinal [5]). When given intrathecally, it acts at the spinal and supraspinal levels. It activates α2-AR in the spinal cord, reducing transmission of nociceptive signals, inhibiting substance P’s release, and contributing to their analgesic action, and has a significant opioid-sparing effect [6].

At the supraspinal level, it binds to the presynaptic α2-ARs in locus ceruleus, producing sedation and anxiolysis; postsynaptic activation in CNS inhibits sympathetic activity leading to a decrease in heart rate and blood pressure. Rapid administration of dexmedetomidine infusion(loading Dose) may cause transient hypertension mediated by peripheral α2B-adrenoreceptor vasoconstriction [7].

Fentanyl is primarily a μ-receptor agonist. When administered intrathecally, the time to onset of its action is 1-3 minutes and the duration of action is 30-60 min. The significant advantage of "selective spinal analgesia" by fentanyl lies in the absence of sympathetic blockade and postural hypotension, potentially allowing early ambulation of the patient and avoidance of cardiovascular collapse or convulsions, which are major complications of a spinal anesthetic blockade. It has improved spinal anesthesia and reduced the anesthetic drug related side effects including pruritus, nausea and vomiting [8].

Dexmedetomidine and fentanyl have been used as adjuvant to local anesthetics in different surgeries to provide superior analgesia and to improve the duration of the block [9,10,11]. One study on lower limbs surgery showed a better efficacy with dexmedetomidine [12].

In this study, we aim to compare the efficacy of dexmedetomidine and fentanyl added to intrathecal bupivacaine in orthopedic procedures in lower limbs in terms of onset and duration of Motor Block.

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