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.

Inclusion Criteria:

• undergoing lumpectomy
• ASA I and II
• Age between 18-64

Exclusion Criteria:

• pregnancy
• breastfeeding -history of EKG abnormalities-
• kidney disease including: End Stage Renal Disease and polycystic kidney disease
• unable to understand the informed consent
• use of opioid in the last week
• use of calcium channel blockers
• Drop-out: surgeon or patient request

24 hours

Nausea in the post operative period

We only examined subjects with normal kidney function that were at low risk for magnesium toxicity. It is possible that the current intervention regimen could have led to toxic levels in higher risk patients.