Optimal Single Dose Intrathecal Dexmedetomidine for Postoperative Analgesia

Optimal Single-dose Intrathecal Dexmedetomidine for Postoperative Analgesia After Lower Limb Surgery

Spinal anesthesia is a commonly used technique for lower limb surgeries offering better quality of postoperative analgesia, lower incidence of side effects, and shorter post-anesthesia care unit stay than general anesthesia. However, the relatively short duration of action of the currently available local anesthetics (LAs) make these advantages short-lived.

The risk for local anesthetic toxicity (LAST) increases with the trials to use higher concentrations or volumes of intrathecal local anesthetics to increase the duration of analgesia.

Dexmedetomidine has the potential to prolong the duration of perioperative analgesia without the need for using high doses of local anesthetics and hence with decreasing the potential risk of local anesthetic, but the increased likelihood adverse effects such as short term bradycardia and prolonged duration of motor block may offset these benefits.

The aim of this study is to determine the optimal single-dose of intrathecal dexmedetomidine that prolongs the analgesic duration with the least possible side effects.

With the patients in the sitting position and the use of complete aseptic technique, 25G Whitacre spinal needles will be introduced through L2-L4 interspaces and after observing free flow of the CSF, a 3ml volume including bupivacaine 12.5mg in conjunction with dexmedetomidine (3 µg) will be injected in the first case, then the patient will be turned supine.

The dose of intrathecal DEX given to the next patient will be guided by modified Dixon's up-and-down method using 1.5 mg as a step size, which assumed to be of clinical importance.

Inclusion Criteria:

• American Society of Anesthesiologists physical class I to II.
• Patients scheduled for elective lower limb surgeries.

Exclusion Criteria:

• Morbid obese patients.
• Severe or uncompensated cardiovascular disease.
• Significant renal disease.
• Significant hepatic disease.
• Pregnancy.
• Lactating .
• Heart block.
• Bradyarrhythmias.
• Receiving adrenergic receptor antagonist medications.
• Receiving calcium channel blockers.
• Patients with pacemakers.
• Patients with implanted cardioverter defibrillator.
• Allergy to the study medications.
• Psychological disease.
• Neurological disorders.
• Communication barrier.
• Mental disorders.
• Epilepsy.
• Drug or alcohol abuse.
• Contraindications to spinal anaesthesia.
• Receiving opioid analgesic medications within 24 h before the operation.