The Effect of Magnesium Gluconate on Postoperative Pain After Cardiac Surgery

What is the use of Remifentanil?

A recent study showed that using a low dose of remifentanil can help to relieve pain after cardiac surgery within 30 minutes (min) after tracheal extubation. Remifentanil is tightly titrated to effect, so it is an excellent model to study the impact of co-analgesics.

Magnesium for Postoperative Pain Relief

Magnesium ions (Mg2+) have been shown to have analgesic and anti-nociceptive properties. They stop calcium from entering the cell, thus blocking the N-methyl-d-aspartic acid (NMDA) receptor from sending pain signals. When Mg2+ is low, the NMDA receptor is more sensitive to pain signals.

Although clinical studies have found that magnesium can help with pain relief after surgery, magnesium gluconate’s ability to reduce the use of pain-relieving drugs after an on-pump cardiac surgery has not been investigated.

The Study on Magnesium Gluconate for Pain Relief after Surgery

39 patients completed the study. They were induced with anesthesia (midazolam followed by etomidate) and a continuous remifentanil infusion until loss of consciousness. Tracheal intubation was done.

The participants were randomly assigned into two groups. 19 of them received magnesium gluconate, while the rest were given equal volume of saline as a placebo for 30 min.

After arrival in the intensive care unit (ICU), continuous administration of propofol was started, and the remifentanil infusion was decreased. Propofol was stopped after 90 min.

The postoperative pain intensity was assessed using the pain intensity scale (PIS). If PIS ≥ 3, remifentanil dose is increased. After tracheal extubation, pain evaluation was performed with a visual analog color scale (VAS). A VAS ≥ 30 in the extubated patient, similar to a PIS ≥ 3 in the intubated patient, would induce a step increase of the remifentanil dose. Pain was regularly assessed up to 12 hours after extubation.

30 min before the scheduled completion of the remifentanil infusion, an intravenous bolus of opioid piritramide was administered, and the remifentanil infusion rate was decreased by 50%. In patients still reporting moderate or severe pain, an increased dose of piritramide was given before the termination of the infusion. Pain relief after discontinuation of remifentanil was managed by additional piritramide and paracetamol according to a four-point verbal rating scale (VRS).

The Results

Magnesium lowered the cumulative remifentanil requirement after surgery. PIS of at least three before extubation was more frequent in the placebo group. VAS scores were also higher in this group at eight and nine hours after extubation despite increased remifentanil demand. In contrast, remifentanil dose reductions based on lower PIS values, VAS scores, and ventilatory frequencies occurred more often in the magnesium group. Time to remove the tracheal tube was not delayed in magnesium-treated patients.

The Conclusion

Magnesium gluconate moderately reduced remifentanil consumption after cardiac surgery without serious side effects. The opioid-sparing effect of magnesium may be greater at higher pain intensities and with increased dosages.

Reference

Magnesium Moderately Decreases Remifentanil Dosage Required for Pain Management after Cardiac Surgery