In the present study, we evaluated the antinociceptive effects of intravenous magnesium sulphate by reducing perioperative analgesics requirements during hysteroscopy in patients under monitored anesthesia care. We demonstrate, in hysteroscopy, that adding intravenous magnesium sulphate to propofol-fentanyl anesthesia results in a reduction in intraoperative fentanyl and postoperative rescue analgesic needs. Patients receiving magnesium displayed lower heart rate and less postoperative pain.
While opioids are the most effective antinociceptive agents, they have undesirable side effects, including respiratory depression, nausea, vomiting, urinary retention, constipation, ileus, and pruritus. Another problem is opioid addiction, a 4.8%-6.5% incidence of persistent opioid use after surgery in older children and adults in the United States [12]. With this mind, opioid-free anesthesia (OFA) was introduced to avoid current crisis. This can be achieved with alpha-2-agonists, ketamine, lidocaine, nonsteroidal anti-inflammatory drugs (NSAIDs) and magnesium, each working on a different target and therefore described as multitarget anesthesia [13]. In hysteroscopy, non-opioid analgesics such as NSAIDs and dexmedetomidine had been evaluated. Although both of these drugs could reduce the pain after hysteroscopy, NSAIDs fail to eliminate the discomfort occurring during the procedure [14] and dexmedetomidine may cause prolonged hypotension and bradycardia [15].
A case report indicated that there is a close connection between hypomagnesaemia and pain. Séamus et al. [16] reported two patients with hypomagnesaemia suffer from severe cancer pain. Their pain was well controlled after treating with intravenous magnesium. During hysteroscopy, distending media is essential to allow for optimal uterine visualization. Nevertheless, excess absorption of large volumes of electrolyte-free, low-viscosity fluid can result in volume overload with hyponatremia and water intoxication [17]. In our study, patients’ postoperative serum magnesium level was consistent with a recent research [8] which significantly decreased. Therefore, patients undergo hysteroscopy may be more susceptible for hypomagnesaemia.
Magnesium has antinociceptive effect in animal and human models of pain [18]. As a matter of fact, noxious stimuli activate the release of glutamate in the dorsal horn, which then activates the NMDA receptors, causing intracellular calcium influx, neuronal excitation, and central sensitization and hyperalgesia [19]. Therefore, NMDA receptor antagonists play an important role in perioperative pain control. Furthermore, compared with acute cutaneous pain sensation, NMDA receptor antagonist provide better pain control for acute visceral pain [20]. Therefore, we choose magnesium sulphate as a component to multimodal general anesthesia in hysteroscopy.
Less opioid consumption and better analgesia were observed when patients’ magnesium deficiency was corrected. These observations support both the opioid-sparing effect and co-analgesic properties of magnesium. Common causes of hypomagnesemia include diarrhea, alcoholism, acute pancreatitis, uncontrolled diabetes mellitus, and medication such as a proton pump inhibitor and diuretics [21]. Our results indicate that if patients have these risk factors with complex pain, assess and correct of magnesium level will be necessary. There is a declining trend for the risk of oxygen desaturation and PONV in the magnesium group, although it did not reach statistically significant. This probably due to short operating time and propofol’s antiemetic effect. Moreover, the recovery of consciousness was not delayed in Group M, while Altan et al. [22] reported that magnesium sulphate caused a delay in recovery for patients undergoing spinal surgery. Magnesium sulphate is known to prolong and potentiate neuromuscular block by non-depolarizing neuromuscular blocking agents [23, 24]. Patients in our study did not receive muscle relaxant and they keep breath spontaneously. Different surgical model may explain the diverse results on the time of recovery of consciousness between the present study and the results of Altan et al.
Jee et al. [25] found that magnesium administration can reduce the release of catecholamine and vasopressin during laparoscopic cholecystectomy. Its antinociceptive effect and direct vasodilatory effect through a calcium channel blockade might explain the lower HR and MBP in Group M. Magnesium can induce relaxation of uterine arteries [26] and the risk of hypotension was not increased in our study. Lower HR and MBP might be helpful to reduce intraoperative bleeding and stress responses, this might be helpful for postoperative recovery. Even though we did not record the specific reasons for adding bolus doses of fentanyl in our study, less fentanyl consumption can reflect fewer times of body movement. These advantages of magnesium sulphate may create good conditions for operation, shorten the duration of procedure and eventually improve the satisfaction of gynecologists.
Some limitations of the present study should be noted. First, it was a single-center study, and the relatively small number of patients limited the ability to detect statistically significant differences in adverse events of fentanyl between two groups. Second, we only applied magnesium to multimodal general anesthesia in hysteroscopy. The combination of magnesium with some other medicine in different targets such as lidocaine, ketamine, and dexmedetomidine may be more effect to reduce opioids consumption, even achieve opioid-free anesthesia.
In conclusion, intravenous infusion of magnesium sulphate significantly reduces opioids requirement and improve gynecologists’ satisfaction during hysteroscopy. In addition, it is beneficial to reduce postoperative pain and maintain stable of serum magnesium concentration after the procedure. Thus, we conclude that magnesium sulphate is a rational strategy for multimodal general anesthesia in hysteroscopy.