The Effect of Magnesium Sulfate Infusion on the Quality of Recovery of Ambulatory Patients

A national survey has revealed that 80% of patients experienced pain after surgery and 86%
of these patients had moderate, severe or extreme pain (1).Postoperative pain can extend
recovery room stay after surgery and it is also a common cause of unanticipated admissions
which have important economic implications(2).More importantly, postoperative pain can lead
to a poor quality of recovery in ambulatory patients. The Intraoperative use of medications
that might decrease postoperative pain is therefore highly desirable.

Some medications such as lidocaine and ketamine have been proved to decrease postoperative
pain when given during the Intraoperative period in ambulatory patients(3,4) but it is still
unknown if those medications can in fact lead to a better quality of recovery .

Magnesium sulfate is a non-competitive calcium antagonist at the N-methyl-D- aspartate
(NMDA) receptor(5). NMDA receptors have an important role on pain modulation (6). The use of
Intraoperative magnesium in order to decrease postoperative pain had contradictory results
in different studies. Some studies have shown a potential benefit of magnesium in decreasing
postoperative pain (7,8) while others have not demonstrated any benefit (9,10).

In the ambulatory setting, specifically, Tramer et al. did not find any improvement on
postoperative pain after an Intraoperative dose of magnesium for patients undergoing
ilioinguinal hernia repair(11). Koinig et al., however, demonstrated a significant reduction
in the postoperative analgesic requirements in patients undergoing arthroscopic knee surgery
(12).

Even though, the reduction of postoperative opioid requirement has been used in many studies
in the ambulatory literature, it has been recently questioned by some investigators
(13).Patients might take more opioid medications but they may not necessarily develop opioid
related side effects such as nausea and vomiting. A more global evaluation of the patient
involving several aspects of recovery would be more significant.

The modified quality of recovery 40(MQOR40) is a validated 40 item instrument to assess the
quality of postoperative recovery (14). Myles et al. concluded that the MQOR40 would be a
useful outcome measure to assess the impact on changes in health care delivery (15), but
anesthesia studies underutilize this instrument.

As more complex and painful procedures are being done in the ambulatory setting , the use of
non-opioid strategies to control postoperative pain and to enhance quality of recovery will
have even a greater role in the anesthetic management of patients. Magnesium has not been
established as a potential adjuvant in ambulatory patients with conflicting results of
previous investigators. The main objective of this study is to evaluate if the
Intraoperative use of magnesium have the ability to improve postoperative quality of
recovery in ambulatory patients.