Adjuvants in Spinal Anesthesia

Opioid Adjuvants

The American Society of Anesthesiologists recommends morphine 50-100 μg for prolonged postoperative analgesia, with optimal dosing providing effective analgesia and lower side effect profile 1
The American Society of Anesthesiologists suggests dosing morphine by procedure, with standard dose of 50-100 μg providing effective analgesia, high-intensity pain procedures requiring 150-300 μg, and pediatric dosing of 30-50 μg/kg with appropriate monitoring 1, 2
Morphine is associated with side effects including pruritus, nausea, and vomiting, with increased risk at higher doses 1
Fentanyl 25 μg provides rapid onset sensory enhancement with moderate duration, but may lead to acute opioid tolerance when combined with morphine 1

Clonidine 1-2 μg/kg prolongs block duration and enhances analgesia, but carries significant hemodynamic risks, including hypotension and bradycardia 2, 3
The American Society of Anesthesiologists recommends against routine use of clonidine in total knee arthroplasty due to limited and inconsistent evidence 5
Dexmedetomidine 0.5 μg/kg IV provides prolonged sensory block with better postoperative analgesia than fentanyl, but requires cardiac monitoring due to risk of bradycardia and arrhythmias 1

Magnesium sulphate potentiates intrathecal opioid analgesia without significant independent side effects, and enhances effect when combined with dexmedetomidine or morphine 1
Neostigmine is not recommended due to significant side effects, including nausea and vomiting, despite analgesic efficacy 5
Ketamine is not routinely recommended due to neurotoxicity concerns, despite prolonging analgesia compared to fentanyl 1, 6
Midazolam is not recommended due to inferior efficacy compared to other adjuvants and neurotoxicity concerns 1

For procedures requiring prolonged postoperative analgesia, the first choice is intrathecal morphine 50-100 μg, with monitoring for respiratory depression for 24 hours 1
For shorter procedures or when rapid onset is needed, the first choice is intrathecal fentanyl 25 μg, with alternative options including intrathecal sufentanil 10 μg or IV dexmedetomidine 0.5 μg/kg 1, 2

Respiratory monitoring is required for morphine, fentanyl, sufentanil, and dexmedetomidine, with varying durations and intensities of monitoring 1, 2
Hemodynamic monitoring is required for clonidine and dexmedetomidine, with frequent blood pressure monitoring and treatment of hypotension and bradycardia as needed 2, 3