Intrathecal Morphine Versus Intrathecal Dexmedetomidine Compared to Placebo for Postoperative Pain Relief After Spine Fixation Surgeries

Spine surgeries represent a challenge to the anesthetists, as they are accompanied by multiple perioperative problems, including significant intraoperative blood loss and severe postoperative pain.

Morphine is a prototypical opioid analgesic that acts mainly on mu-opioid receptors in the central nervous system. It exerts its analgesic effects by binding to these receptors, inhibiting the release of a neurotransmitter known as substance P, thereby diminishing pain perception.

Dexmedetomidine (DEX) is a highly selective and potent α-2 adrenoceptor agonist. Its intrathecal administration leads to anti-nociceptive effects, although it has some undesired side effects (e.g., hypotension, bradycardia, and sedation).

• Intrathecal Morphine (Drug): Patients will receive intrathecal morphine (0,3 mg) in 2 ml normal saline at the end of the operation through a 25G spinal needle through the lumbar intervertebral space (L3-L4 or L4-L5).
• Intrathecal Dexmedetomidine (Drug): Patients will receive intrathecal 2 ml normal saline at the end of the operation through a 25G spinal needle through the lumbar intervertebral space (L3-L4 or L4-L5).
• Normal Saline (Drug): Patients will receive intrathecal 2 ml normal saline at the end of the operation through a 25G spinal needle through the lumbar intervertebral space (L3-L4 or L4-L5).

Primary outcomes

• Time to the first rescue analgesia [24 hours postoperatively]: Time to the first rescue analgesia will be recorded from the end of surgery till the first dose of pethidine adminstrated.

Secondary outcomes

• Heart rate [24 hours postoperatively]: Heart rate will be recorded at rest (static) and on movement (dynamic), evaluated at 30 minutes, 1, 2, 4, 8, 12, and 24 h after surgery.
• Mean arterial pressure [24 hours postoperatively]: Mean arterial pressure will be recorded at rest (static) and on movement (dynamic), evaluated at 30 minutes, 1, 2, 4, 8, 12, and 24 h after surgery.
• Degree of pain [24 hours postoperatively]: Postoperative pain will be assessed using visual analog scale (VAS) scores where (0 = no pain, 10 = the worst possible pain), postoperative pain will be assessed at rest (static) and on movement (dynamic), evaluated at 30 minutes, 1, 2, 4, 8, 12, and 24 h after surgery
• Postoperative sedation score [24 hours postoperatively]: The Sedation Scale (modified Observer's Assessment of Alertness/Sedation (OAA/S) scale). (6 = Agitated, 5 = Responds readily to name spoken in normal tone, 4 = Lethargic response to name spoken in normal tone, 3 = Responds only after name is called loudly and/or repeatedly, 2 = Responds only after mild prodding or shaking, 1 = Does not respond to mild prodding or shaking, 0 = Does not respond to deep stimulus)
• Total pethidine consumption [24 hours postoperatively]: After assessment of pain scores, when visual analog scale (VAS) score measures ≥3, patients will receive 25 mg pethidine, which can be repeated.
• Incidence of adverse effect [24 hours postoperatively]: Incidence of adverse effect such as pruritus, nausea/vomiting, bradycardia, hypotension, and respiratory depression will be recorded.

Sex: All, ages: 21 Years to 60 Years

Inclusion Criteria:

* Aged between 21 and 60 years.
* Both sexes.
* American Society of Anesthesiologists (ASA) Physical Status I or II.
* Scheduled for elective lumbar spine fixation surgery under general anesthesia.

Exclusion Criteria:

* Patients' refusal.
* Decompensated hepatic or renal or cardiac disease.
* Coagulation disorder.
* Pregnancy and lactation.
* Body mass index above 30 kg/m2.
* Severe pulmonary disorders.
* Patients on opioid, alcohol or allergy to any of the study drugs.