The Role of Magnesium in Postoperative Pain Management

What is Central Sensitization?

A lot of noxious inputs come into the brain all at once, during and immediately before and after surgery which may cause central sensitization, a condition when the body’s pain signals are turned up too high. But analgesics given before the noxious stimulus may reduce or block sensitization.

What are the Purposes of Pre-Emptive Analgesia?

Pre-emptive analgesia is a treatment given before surgery to help reduce the intensity of pain after surgery. This pain reduction is done by stopping or reducing the number of pain signals the brain receives. The purposes of pre-emptive analgesia are to decrease pain after tissue injury, prevent pain-related pathologic changes in the central nervous system, and inhibit the development of chronic pain.

Can Magnesium Help in Improving the Efficacy of Analgesics?

A series of experimental data suggests that N-methyl-d-aspartate (NMDA) receptors (ion channels found in nerve cells) play a crucial role in how brain nerves change through growth and reorganization in response to pain. NMDA antagonists have been shown to help reduce acute postoperative pain, analgesic consumption, or both. The presence of a magnesium ion blocks NMDA receptors. Studies concerning different ways to administer magnesium, such as epidurally (injecting through the spine), improve anesthetic and analgesic quality.

This randomized, double-blind, prospective study was designed to assess the analgesic efficacy of adding magnesium to a multimodal treatment plan of patient-controlled epidural analgesia (PCEA) in patients undergoing abdominal hysterectomy.

The Study Method on Magnesium for Postoperative Pain Management

87 patients completed the study. They were randomly and equally assigned to one of the three groups. Before the operation, the patients were instructed on the use of the PCEA device and the visual analog scale [(VAS); 0 = no pain and 10 = worst possible pain].

Pre-magnesium patients received an initial 10 milliliters (ml) bolus of 50 milligrams (mg) magnesium through epidural catheter before induction of anesthesia followed by infusion of 10 mg h−1 during and until the end of the surgery, and a 10 ml bolus of normal saline after surgery.

Post-magnesium patients received 10 ml saline epidurally before the induction of general anesthesia and during surgery, plus a 50 mg bolus epidural magnesium right after surgery.

Patients in the control group received saline epidurally as a placebo before induction of anesthesia, during, and at the end of surgery.

Those in the magnesium groups received PCEA with fentanyl 1 microgram (μg) ml−1, bupivacaine 0.08%, and magnesium 1 mg ml−1 after the surgery. Those in the control group received PCEA with 1 μg ml−1 fentanyl and 0.08% bupivacaine. Data were recorded for the first three days after the operation.

The Results

The pain scores while on rest, on movement (except at 2, 4, and 6 hours after the operation when the scores were lower but not statistically significant), and on the first three days after the operation were significantly lower than the post-magnesium and control groups.

The daily analgesic consumption in the pre-magnesium group was significantly lesser than the other two groups over postoperative days 1 to 3. The dose consumed in the post-magnesium group was considerably smaller than the control group.

The Conclusion

The results of the present study showed that continuous epidural magnesium infusion started before induction of anesthesia and extended into the postoperative period provided preemptive and preventive analgesia. It also decreased postoperative pain and daily analgesic consumption during the first three postoperative days after abdominal hysterectomy without increasing the occurrence of side effects.

Reference

Pre-Incisional Epidural Magnesium Provides Pre-Emptive and Preventive Analgesia in Patients Undergoing Abdominal Hysterectomy