Comparative Study Between Intrathecal Magnesium Sulfate, Neostigmine and Fentanyl As Adjuvant for Bubivacaine in Postoperative Analgesia in Lower Abdominal Surgeries

Effective analgesia aims to minimize patients stress response, pain intensity and distress, and side-effects of large single drug doses (typically an opioid). Numerous analgesic options exist for postoperative analgesia after abdominal surgery, including multiple classes of drugs and routes of administration e.g. parenteral, regional, neuraxial analgesia which include (epidural/intrathecal) techniques, truncal nerve blocks, and systemic drugs infusions.

Spinal anesthesia is a widely used technique in lower abdominal surgeries, offering several benefits such as allowing the patient to remain awake during the procedure, quick onset of action, high success rate, minimal drug dosage, effective sensory and motor blocks, and cost-effectiveness. However, despite these advantages, it can also cause side effects like hypotension, bradycardia, nausea, vomiting, and shivering.

Bupivacaine, is a commonly used local anesthetic, but its use can be limited by the duration of action and potential side effects. To enhance the analgesic effects and prolong the duration of bupivacaine, various adjuvants such as magnesium sulfate, neostigmine, and fentanyl are added intrathecally. Each adjuvant offers unique pharmacological properties that can influence spinal anesthesia's efficacy.

Magnesium sulfate, known for its N-methyl-D-aspartate (NMDA) receptor antagonist properties, decreases sensitivity to both central and peripheral pain stimuli by blocking calcium influx and reducing the excitability of NMDA receptors. Several studies have evaluated the role of magnesium sulfate (MgSO4) as an agent for pain control and reduction of analgesia requirement intra-and post-operatively. In some of these studies, researchers concluded that MgSO4 may reduce the need for opioid analgesic agents.

Neostigmine is a water-soluble, ionized compound that inhibits acetylcholinesterase (AChE). Its indication in FDA is to reverse the effect of non-depolarizing neuromuscular blockers after surgery. The drug is usually administered by intravenous injection, and the main route of excretion is the kidney. Neostigmine should be used with caution in patients with coronary heart disease, arrhythmia, recent acute coronary syndrome and myasthenia gravis. Neostigmine works by preventing the breakdown of the neurotransmitter acetylcholine. Recent studies suggest that this inhibition of acetylcholine degradation strengthens the descending modulation of afferent pain signals, offering a novel method for improving analgesia with minimal dose-related side effects. It enhances spinal cholinergic transmission, potentially increasing the analgesic effects without causing respiratory depression.