Comparative study between magnesium sulfate and ketamine added to lidocaine in ultrasound-guided supraclavicular brachial plexus block in upper limb surgery

Introduction
Supraclavicular brachial plexus (SBP) block is an excellent substitute for general anesthesia during upper limb operations. It prevents undesirable effects of using general anesthesia and upper airway instruments. Moreover, it reduces the duration of hospitalization and costs and provides complete muscle relaxation. The ultrasound-guided technique requires a lower anesthetic volume to provide an efficient block and decreases the risk associated with intravascular injections and trauma to the surrounding tissues.
Aim
We conducted this study to compare the effect of ketamine versus magnesium sulfate as additives to lidocaine on onset and duration of sensory and motor block and duration of analgesia time, postoperative visual analog scale (VAS), total analgesic need, stress response (cortisol and blood glucose), and adverse effects in ultrasound-guided supraclavicular brachial plexus (SBP) block for patients who electively underwent upper limb surgeries.
Patients and methods
A total of 90 patients aged 21–65 years, with American Society of Anesthesiologists status I, II, and III, scheduled for elective upper limb surgeries under SBP block, were divided into three equal groups in a randomized controlled fashion: group C (=30) received 25 ml 2% lidocaine plus 5 cm saline, group K (=30) received 25 ml 2% lidocaine plus 2 mg/kg ketamine, and group M (=30) received 25 ml 2% lidocaine plus 250 mg magnesium sulfate (total volume in all groups 30 ml). Hemodynamic variables such as mean arterial blood pressure and heart rate, onset and duration of sensory and motor block, postoperative VAS, time to first analgesic request, total analgesic need, stress response (cortisol and blood glucose), and adverse effects were recorded for each patient.
Results
The sensory block duration was 438.0±80.4 min in group K, 280.2±42.6 min in group M, and 132.0±24.6 min in group C, with a value less than 0.001, which was statistically significant, whereas the motor block duration was 500±79 min in the group K, 342±50 min in group M, and 200±35 min in group C, with a value less than 0.001, which was statistically significant, indicating a prolongation in block duration in the ketamine group followed by magnesium group and then control group. The most significant and highest VAS pain scores were found in the control group at all time points (<0.001), whereas the K group had the lowest VAS. Postoperative analgesic requirement was less in K group when compared with other groups (<0.001).
Conclusion
Both ketamine and magnesium sulfate prolong the duration of analgesia without any major adverse effects. Ketamine is a better adjuvant to lidocaine for SBP than magnesium sulfate, as it has lower VAS and less postoperative analgesic requirement in upper limb surgeries.