Perioperative magnesium infusion and postoperative pain

Unravelling the analgesic effects of perioperative magnesium in general abdominal surgery: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Prior research has established the effectiveness of magnesium in relieving postoperative pain. This article aims to evaluate magnesium sulfate for perioperative analgesia in adults undergoing general abdominal surgery under general anesthesia.

OBJECTIVE

The primary aim was to assess pain scores at 6 and 24 hours postoperatively in patients receiving magnesium sulfate vs. the control group. Secondary outcomes were postoperative opioid consumption, perioperative complications, and time to rescue analgesia.

METHODS

A comprehensive database search identified studies comparing magnesium sulfate with control in adults undergoing general anesthesia for general abdominal surgery. Using random-effects models, data were presented as mean ± Standard Deviation (SD) or Odds Ratios (OR) with corresponding 95% Confidence Intervals (95% CI). A two-sided p-value < 0.05 was considered statistically significant.

RESULTS

In total, 31 studies involving 1762 participants met the inclusion criteria. The magnesium group showed significantly lower postoperative pain scores at both early (within six hours) and late (up to 24 hours) time points compared to the control group. The early mean score was 3.1 ± 1.4 vs. 4.2 ± 2.3, and the late mean score was 2.3 ± 1.1 vs. 2.7 ± 1.5, resulting in an overall Mean Difference (MD) of -0.72; 95% CI -0.99, -0.44; p < 0.00001. The magnesium group was associated with lower rates of postoperative opioid consumption and shivering and had a longer time to first analgesia administration compared to the saline control group.

CONCLUSION

Magnesium sulfate administration was linked to reduced postoperative pain and opioid consumption following general abdominal surgery.

Intravenous Versus Wetting Solution Magnesium Sulphate to Counteract Epinephrine Cardiac Adverse Events in Abdominal Liposuction: A Randomized Controlled Trial

Background

The increased frequency of liposuction has resulted in more complications being reported. Adding epinephrine to the wetting solution could induce some cardiac adverse effects, some of which may be fatal. For instance, magnesium sulfate (MgSO₄) is known for its cardioprotective effects.

Objectives

This study aimed to evaluate the efficacy of intravenous (IV) versus wetting solution containing MgSO₄ in decreasing such cardiac adverse events during abdominal liposuction.

Methods

This randomized controlled study included 129 adult cases undergoing abdominal liposuction under general anesthesia. The participants were divided into 3 groups: Group I (control group) was only subjected to the injection of the wetting fluid (1 mL 1/1000 epinephrine added to every 1000 mL of normal saline), group II was subjected to IV MgSO₄ (40 mg/kg over 1 minute) at the same time of installing the wetting solution, and group III was subjected to MgSO₄ (40 mg/kg) added to the wetting solution.

Results

Intraoperative isoflurane consumption, intraoperative heart rate (HR), mean arterial pressure (MAP), and postoperative pain scores were significantly lower in the MgSO₄ groups (groups II and III) than group I. Cardiac adverse events (sinus tachycardia and premature ventricular contractions (PVCs)) were also significantly less frequent in groups II and III compared to group I.

Conclusions

Adding MgSO₄, either through IV or subcutaneous routes, is associated with lower intraoperative HR, MAP, and postoperative pain scores and a remarkable decrease in epinephrine-induced cardiac adverse events during liposuction.

The effect of intravenous magnesium on postoperative morphine consumption in noncardiac surgery: A systematic review and meta-analysis with trial sequential analysis

BACKGROUND

Several studies suggest that systemic magnesium reduces postoperative opioid consumption and the intensity of pain, but others report conflicting results. The efficacy and safety profile of intravenous magnesium in noncardiac surgery remain uncertain.

OBJECTIVES

The aim of this review was to investigate the effect of intravenous magnesium on the consumption of postoperative morphine in the first 24 h in adults undergoing noncardiac surgery.

DESIGN

Systematic review and meta-analysis with trial sequential analysis.

DATA SOURCES

MEDLINE, EMBASE, CENTRAL from their inception until January 2019.

ELIGIBILITY CRITERIA

All randomised clinical trials comparing intravenous magnesium versus placebo in noncardiac surgery were systematically searched in the databases. Observational studies, case reports, case series and nonsystematic reviews were excluded.

RESULTS

Fifty-one trials (n=3311) were included for quantitative meta-analysis. In comparison with placebo, postoperative morphine consumption at 24-h was significantly reduced in the magnesium group, with a mean difference [95% confidence interval (CI)] of -5.6 mg (-7.54 to -3.66, P < 0.001, I = 92%, level of evidence low). The trial sequential analysis for the effect of magnesium on postoperative morphine consumption was conclusive. Patients who received magnesium had a longer time to the first analgesia request [143 (103 to 183) min, P < 0.001, I = 99%, level of evidence low] and a lower incidence of shivering [0.26 (0.15 to 0.44), P < 0.001, I = 35%, level of evidence very low]. However, no significance differences were demonstrated in postoperative pain scores in the first 24 h (mean difference, 95% CI) -0.30 (-0.69 to 0.09, P = 0.13, I = 91%, level of evidence low), bradycardia (odds ratio, 95% CI) 1.13 (0.43 to 2.98, P = 0.80, I = 35%, level of evidence very low) and postoperative nausea and vomiting (odds ratio, 95% CI) 0.90 (0.67 to 1.22, P = 0.49, I = 25%, level of evidence moderate).

CONCLUSION

The current meta-analysis demonstrates that the use of intravenous magnesium as part of multimodal analgesia may reduce morphine consumption in the first 24 h after surgery and delay the time to the first request for analgesia in patients undergoing noncardiac surgery. However, the included studies were of low-quality with substantial heterogeneity.

TRIAL REGISTRATION

CRD42018086846.

Recommendations from the Italian intersociety consensus on Perioperative Anesthesa Care in Thoracic surgery (PACTS) part 2: intraoperative and postoperative care

Introduction

Anesthetic care in patients undergoing thoracic surgery presents specific challenges that require a multidisciplinary approach to management. There remains a need for standardized, evidence-based, continuously updated guidelines for perioperative care in these patients.

Methods

A multidisciplinary expert group, the Perioperative Anesthesia in Thoracic Surgery (PACTS) group, was established to develop recommendations for anesthesia practice in patients undergoing elective lung resection for lung cancer. The project addressed three key areas: preoperative patient assessment and preparation, intraoperative management (surgical and anesthesiologic care), and postoperative care and discharge. A series of clinical questions was developed, and literature searches were performed to inform discussions around these areas, leading to the development of 69 recommendations. The quality of evidence and strength of recommendations were graded using the United States Preventive Services Task Force criteria.

Results

Recommendations for intraoperative care focus on airway management, and monitoring of vital signs, hemodynamics, blood gases, neuromuscular blockade, and depth of anesthesia. Recommendations for postoperative care focus on the provision of multimodal analgesia, intensive care unit (ICU) care, and specific measures such as chest drainage, mobilization, noninvasive ventilation, and atrial fibrillation prophylaxis.

Conclusions

These recommendations should help clinicians to improve intraoperative and postoperative management, and thereby achieve better postoperative outcomes in thoracic surgery patients. Further refinement of the recommendations can be anticipated as the literature continues to evolve.

The Efficacy of Intravenous Magnesium Sulfate versus Intravenous Paracetamol on Children Posttonsillectomy Pain and Analgesic Requirement: A Randomized Controlled Study

Background:

One of the most common complications of tonsillectomy is pain, which leading to delayed recovery and later hospital discharge.

Aims:

We intended to compare the efficacy of magnesium sulfate versus paracetamol on the posttonsillectomy pain and analgesic requirement.

Settings and Design:

This study design was a prospective randomized controlled double-blinded clinical study.

Patients and Methods:

A total of 60 children with the American Society of Anesthesiologists physical status classes I and II, aged 3–12 years, scheduled for tonsillectomy were randomly divided into two groups each group contains 30 patients: (Group M): received an initial loading dose of magnesium sulfate 30 mg/kg over 15 min started with induction followed by continuous infusion of 10 mg/kg/h for 1 h regardless of the operation time and (Group P): received paracetamol infusion 10 mg/kg started with induction and continued for 1 h. Postoperatively, a blinded postanesthesia care unit (PACU) nurse observed the quality of analgesia using the face, legs, activity, cry, and consolability pain scores, bleeding, and sedation.

Statistical Analysis Used:

Student's t-test and Chi-square test were used for analysis.

Results:

Regarding postoperative pain, there was a statistically significant difference between the two groups at the time of admission in PACU (P = 0.025) as children who experienced pain already had taken rescue analgesic to alleviate pain. There was a statistically significant difference between the two groups regarding the need for analgesics (P = 0.038). There was no statistically significant difference regarding bleeding and sedation scores between the two study groups.

Conclusions:

Magnesium sulfate provided better postoperative analgesia and reduced need for analgesics after tonsillectomy compared to paracetamol, and regarding the incidence of bleeding and the degree of sedation the outcome in both groups was readily comparable.

An Update on Nonopioids: Intravenous or Oral Analgesics for Perioperative Pain Management

Despite an appreciation for many unwanted physiologic effects from inadequate postoperative pain relief, moderate to severe postoperative pain remains commonplace. Although treatment options have evolved in recent years, the use of nonopioid analgesics agents can reduce acute pain-associated morbidity and mortality. This review focuses on the importance of effective postoperative nonopioid analgesic agents, such as acetaminophen, nonsteroidal anti-inflammatory agents, gabapentinoid agents, NMDA antagonists, alpha 2 agonists, and steroids, in opioid sparing and enhancing recovery. A careful literature review focusing on these treatment options, potential benefits, and side effects associated with these strategies is emphasized in this review.

Multimodal Analgesia, Current Concepts, and Acute Pain Considerations

PURPOSE OF REVIEW

Management of acute pain following surgery using a multimodal approach is recommended by the American Society of Anesthesiologists whenever possible. In addition to opioids, drugs with differing mechanisms of actions target pain pathways resulting in additive and/or synergistic effects. Some of these agents include alpha 2 agonists, NMDA receptor antagonists, gabapentinoids, dexamethasone, NSAIDs, acetaminophen, and duloxetine.

RECENT FINDINGS

Alpha 2 agonists have been shown to have opioid-sparing effects, but can cause hypotension and bradycardia and must be taken into consideration when administered. Acetaminophen is commonly used in a multimodal approach, with recent evidence lacking for the use of IV over oral formulations in patients able to take medications by mouth. Studies involving gabapentinoids have been mixed with some showing benefit; however, future large randomized controlled trials are needed. Ketamine is known to have powerful analgesic effects and, when combined with magnesium and other agents, may have a synergistic effect. Dexamethasone reduces postoperative nausea and vomiting and has been demonstrated to be an effective adjunct in multimodal analgesia. The serotonin-norepinephrine reuptake inhibitor, duloxetine, is a novel agent, but studies are limited and further evidence is needed. Overall, a multimodal analgesic approach should be used when treating postoperative pain, as it can potentially reduce side effects and provide the benefit of treating pain through different cellular pathways.

Whether preventive low dose magnesium sulphate infusion has an influence on postoperative pain perception and the level of serum beta-endorphin throughout the total abdominal hysterectomy

OBJECTIVE

Due to the known role of preventive low dose magnesium sulphate on postoperative pain management, in this randomized, double-blinded, placebo-controlled study, we tried to investigate the possible relationship between low dose intra-operative magnesium sulphate infusion, postoperative analgesia and the level of serum beta-endorphin during total abdominal hysterectomy under general anesthesia.

METHODS

Forty women undergoing total abdominal hysterectomy were randomly allocated into 2 groups (20 in each arm). Fifteen minutes before induction of anaesthesia, the case group received a continuous intravenous infusion of magnesium sulphate (15mg/kg/h) and placebo control group received the same volume of isotonic saline. Pain scores were assessed at 0, 6, 12, and 24h after operations using Verbal Numeric Rating Scale. Pethidine consumption was recorded precisely. Serum level of beta-endorphin just 15min before the induction and at the end of the operations was determined by ELISA technique.

RESULTS

At 6 and 12h after the operations, Verbal Numeric Rating Scale in the case group was significantly lower than that of placebo control group (P=.0001). Over 24h after the operations, pethidine consumption was significantly lower in the case group compared with control group (P=.0001). In the case group, serum level of beta-endorphin was significantly decreased at the end of the operations compared with before the induction (P=.04).

CONCLUSION

We illustrated that preventive low dose intra-operative magnesium sulphate infusion reduces postoperative pain, has opioid sparing effect and declines serum beta-endorphin concentration during total abdominal hysterectomy.

Effect of low-dose (single-dose) magnesium sulfate on postoperative analgesia in hysterectomy patients receiving balanced general anesthesia

Background and Aim. Aparallel, randomized, double blinded, placebo-controlled trial study was designed to assess the efficacy of single low dose of intravenous magnesium sulfate on post-total abdominal hysterectomy (TAH) pain relief under balanced general anesthesia. Subject and Methods. Forty women undergoing TAH surgery were assigned to two magnesium sulfate (N = 20) and normal saline (N = 20) groups randomly. The magnesium group received magnesium sulfate 50 mg·kg⁻¹ in 100 mL of normal saline solution i.v as single-dose, just 15 minutes before induction of anesthesia whereas patients in control group received 100 mL of 0.9% sodium chloride solution at the same time. The same balanced general anesthesia was induced for two groups. Pethidine consumption was recorded over 24 hours precisely as postoperative analgesic. Pain score was evaluated with Numeric Rating Scale (NRS) at 0, 6, 12, and 24 hours after the surgeries. Results. Postoperative pain score was lower in magnesium group at 6, 12, and 24 hours after the operations significantly (P < 0.05). Pethidine requirement was significantly lower in magnesium group throughout 24 hours after the surgeries (P = 0.0001). Conclusion. Single dose of magnesium sulfate during balanced general anesthesia could be considered as effective and safe method to reduce postoperative pain and opioid consumption after TAH.

The Effect of Intravenous Magnesium Sulphate Treatment on the Spinal Anaesthesia Produced by Bupivacaine in Pre-eclamptic Patients

OBJECTIVE

In our study, the effect of intravenous magnesium sulphate in normal and pre-eclamptic patients on spinal anaesthesia produced by bupivacaine was investigated.

METHODS

Sixty-four pregnant (32 normal and 32 pre-eclamptic) were accepted in this study. Pregnants were divided into four groups as patients given intravenous magnesium sulphate and as control. Spinal anaesthesia was induced with 12.5 mg 0.5% hyperbaric bupivacaine. Intraoperative and postoperative haemodynamic variables, sensorial block periods, onset times of sensorial and motor block, maximum sensorial block levels, the time to reach maximum block level, Bromage scores, consumptions of intraoperative analgesic and ephedrine, the quality of anaesthesia, the duration of spinal anaesthesia and magnesium levels in blood and cerebrospinal fluid were measured and recorded.

RESULTS

The level of magnesium in blood and cerebrospinal fluid was significantly higher in the group given magnesium in pre-eclamptic patients (p<0.01). Onset of sensory block times were significantly longer in intravenous magnesium group than in groups 1, 2 and 3 (p<0.05). Onset of motor block times were significantly longer and the duration of anaesthesia was shorter in groups given magnesium (p<0.05). Although the quality of anaesthesia was similar, supplemental analgesic consumption was significantly higher in pre-eclamptic pregnants given magnesium sulphate than in pre-eclamptic pregnants who were not given magnesium sulphate (p<0.05).

CONCLUSION

Intravenous magnesium sulphate treatment during the spinal anaesthesia produced by bupivacaine extended the onset of sensory and motor block times, shortened the duration of spinal anaesthesia and therefore led to early analgesic requirement.

Perioperative Systemic Magnesium to Minimize Postoperative Pain

Background:

Systemic magnesium has been used to minimize postoperative pain with conflicting results by clinical studies. It remains unknown whether the administration of perioperative systemic magnesium can minimize postoperative pain. The objective of the current investigation was to evaluate the effect of systemic magnesium on postoperative pain outcomes.

Methods:

A wide search was performed to identify randomized controlled trials that evaluated the effects of systemic magnesium on postoperative pain outcomes in surgical procedures performed under general anesthesia. Meta-analysis was performed using a random-effect model. Publication bias was evaluated by examining the presence of asymmetric funnel plots using Egger regression.

Results:

Twenty randomized clinical trials with 1,257 subjects were included. The weighted mean difference (99% CI) of the combined effects favored magnesium over control for pain at rest (≤4 h, −0.74 [−1.08 to −0.48]; 24 h, −0.36 [−0.63 to −0.09]) and with movement at 24 h, −0.73 (−1.37 to −0.1). Opioid consumption was largely decreased in the systemic magnesium group compared with control, weighted mean difference (99% CI) of −10.52 (−13.50 to −7.54) mg morphine IV equivalents. Publication bias was not present in any of the analysis. Significant heterogeneity was present in some analysis, but it could be partially explained by the sole intraoperative administration of magnesium compared with the intraoperative and postoperative administration. None of the studies reported clinical toxicity related to toxic serum levels of magnesium.

Conclusion:

Systemic administration of perioperative magnesium reduces postoperative pain and opioid consumption. Magnesium administration should be considered as a strategy to mitigate postoperative pain in surgical patients.

To evaluate the efficacy of intrathecal magnesium sulphate for hysterectomy under subarachnoid block with bupivacaine and fentanyl: A prospective randomized double blind clinical trial

BACKGROUND

Intrathecal magnesium has been found to prolong the duration of analgesia in various surgical procedures like lower limb surgeries and as adjuncts to general anesthesia for pain management. The present study was designed to examine whether addition of intrathecal magnesium sulfate would enhance the analgesic efficacy of intrathecal bupivacaine and fentanyl in patients undergoing total abdominal hysterectomy.

METHODS

After taking informed consent, 60 patients were randomised into two groups with 30 patients. Group "S" received 2.5 mL (12.5 mg) of hyperbaric bupivacaine + 0.5 mL (25 mcg) of fentanyl + 0.5 mL of normal saline and Group "M" received 2.5 mL (12.5 mg) of hyperbaric bupivacaine + 0.5 mL (25 mcg) of fentanyl + 0.5 mL (100 mg) of magnesium sulfate. Onset of sensory, motor block and duration of analgesia was noted.

RESULTS

Demographic profile and duration of surgery were comparable (P>0.5). Time of onset of sensory and motor blockade was delayed in Group M compared with Group S, and this was statistically significant. A statistically significant longer duration of analgesia was observed in Group M compared with the control Group S. However, the recovery of motor blockade was found to be statistically insignificant in both the groups. The hemodynamic parameters were comparable in the perioperative period (P>0.05). The incidence of side-effects in both the groups were also comparable (P>0.05).

CONCLUSION

The addition of 100 mg intrathecal magnesium led to prolonged duration of analgesia significantly without increasing the incidence of side-effects. Also, there was a significant delay in the onset of both sensory and motor blockade.

Comparison of postoperative analgesic effect of intrathecal magnesium and fentanyl added to bupivacaine in patients undergoing lower limb orthopedic surgery

OBJECTIVE

To compare the analgesic efficacy and side effects of magnesium and fentanyl as an additive to intrathecal bupivacaine.

METHODS

Ninety adult patients scheduled for femur surgery under spinal anesthesia were randomly allocated to one of the following three groups to receive intrathecally: bupivacaine 15 mg combined with 0.5 mL magnesium 10%; bupivacaine 15 mg combined with 0.5 mL fentanyl; or bupivacaine 15 mg combined with 0.5 mL distilled water (control). The time to first analgesic request, sensory and motor blockade onset time, duration of sensory and motor blockade, analgesic requirement in the first 12 hours after surgery, and the incidences of hypotension, bradycardia, hypoxemia and ephedrine were recorded.

RESULTS

Magnesium caused a significant delay in the onset of both sensory and motor blockade compared with the fentanyl (95% CI 3 to 4; p < 0.001) and control (95% CI 3.5-5; p < 0.001) groups. The duration of spinal analgesia in group F (fentanyl) was significantly greater than in group C (control) (95% CI 365-513; p < 0.001) and group M (magnesium) (95% CI 385-523; p < 0.001). The total amount of methadone consumption over 12 hours was significantly lower in the magnesium and fentanyl groups than in the control group (5 mg vs. 5.666 ± 1.728 mg; p = 0.04).

CONCLUSION

Addition of intrathecal magnesium sulfate to spinal anesthesia induced by bupivacaine significantly prolonged the onset of both sensory and motor blockade compared with fentanyl. Although magnesium failed to prolong the time to first analgesic requirement as seen with fentanyl, it reduced the total consumption of opioids in the first 12 hours postoperatively compared with the control group.

Effects of adjunct intrathecal magnesium sulfate to bupivacaine for spinal anesthesia: a randomized, double-blind trial in patients undergoing lower extremity surgery

PURPOSE

The aim of this study was to evaluate the effect of additional magnesium sulfate (MgSO(4)) 100 mg to intrathecal (IT) isobaric 0.5% bupivacaine 3 ml on spinal anesthesia in patients undergoing lower extremity orthopedic surgery.

METHODS

In a double-blind randomized clinical trial, 79 American Association of Anesthesiologists (ASA) I or II adult patients undergoing lower extremity orthopedic surgery were recruited. The patients were randomly allocated to receive 100 mg MgSO(4) 5% (0.2 ml) plus 15 mg of bupivacaine 0.5% (MgSO(4) group) or 15 mg bupivacaine 0.5% combined with 0.2 ml normal saline (control group) intrathecally. Response to treatment was assessed as onset and duration of sensory block, the highest level of sensory block, time to complete motor block recovery, duration of spinal anesthesia, and postoperative analgesic requirement.

RESULTS

The onset of the sensory block was slower in the MgSO(4) group than in the control group (13.3 vs. 11.6 min, P = 0.04), and the duration of the sensory blockade was significantly longer in the MgSO(4) group than the control group (106.5 vs. 85.5 min, P = 0.001). Total analgesic requirements for 24 h following surgery were lower in the MgSO(4) group than in the control group (96.8 vs. 138.5 mg, P = 0.001). Mean duration of spinal anesthesia was not significantly different between two groups (178.0 vs. 167.4 min, P = 0.23).

CONCLUSION

In patients undergoing lower extremity surgery with spinal anesthesia, the addition of 100 mg IT MgSO(4) to 15 mg bupivacaine without opioid supplement, prolonged the duration of the sensory block, decreased postoperative analgesic consumption, and significantly prolonged the onset of spinal anesthesia.

Lidocaine vs. magnesium: effect on analgesia after a laparoscopic cholecystectomy

BACKGROUND

This double-blinded study aimed at evaluating and comparing the effects of magnesium and lidocaine on pain, analgesic requirements, bowel function, and quality of sleep in patients undergoing a laparoscopic cholecystectomy (LC).

METHODS

Patients were randomized into three groups (n=40 each). Group M received magnesium sulfate 50 mg/kg intravenously (i.v.), followed by 25 mg/kg/h i.v., group L received lidocaine 2 mg/kg i.v., followed by 2 mg/kg/h i.v., and group P received saline i.v. Bolus doses were given over 15 min before induction of anesthesia, followed by an i.v. infusion through the end of surgery. Intraoperative fentanyl consumption and averaged end-tidal sevoflurane concentration were recorded. Abdominal and shoulder pain were evaluated up to 24 h using a visual analog scale (VAS). Morphine consumption was recorded at 2 and 24 h, together with quality of sleep and time of first flatus.

RESULTS

Lidocaine or magnesium reduced anesthetic requirements (P<0.01), pain scores (P<0.05), and morphine consumption (P<0.001) relative to the control group. Lidocaine resulted in lower morphine consumption at 2 h [4.9 + or - 2.3 vs. 6.8 + or - 2.8 (P<0.05)] and lower abdominal VAS scores compared with magnesium (1.8 + or - 0.8 vs. 3.2 + or - 0.9, 2.2 + or - 1 vs. 3.6 + or - 1.6, and 2.1 + or - 1.4 vs. 3.3 + or - 1.9) at 2, 6, and 12 h, respectively (P<0.05). Lidocaine was associated with earlier return of bowel function and magnesium was associated with better sleep quality (P<0.05).

CONCLUSION

I.v. lidocaine and magnesium improved post-operative analgesia and reduced intraoperative and post-operative opioid requirements in patients undergoing LC. The improvement of quality of recovery might facilitate rapid hospital discharge.

Comparison of intrathecal magnesium, fentanyl, or placebo combined with bupivacaine 0.5% for parturients undergoing elective cesarean delivery

BACKGROUND

Intrathecal (i.t.) administration of magnesium has been reported to potentiate opioid antinociception in rats and humans. In this prospective, randomized, double-blind, study, we investigated the sensory, motor, and analgesic block characteristics of i.t. magnesium 50 mg compared with fentanyl 25 microg and saline when added to 0.5% bupivacaine (10 mg).

METHODS

Ninety ASA I or II adult patients undergoing cesarean section were randomly allocated to receive 1.0 ml of 0.9% sodium chloride in group S, 50 mg of magnesium sulfate (1.0 ml) 5% in group M, or 25 microg of fentanyl (1.0 ml) in group F following 10 mg of bupivacaine 0.5% i.t. We recorded the following: onset and duration of sensory and motor block, maximal sensory block height, the time to reach the maximal dermatomal level of sensory block, and the duration of spinal anesthesia.

RESULTS

Magnesium did not shorten the onset time of sensory and motor blockade or prolong the duration of spinal anesthesia. The duration of sensory (P<0.032) and motor (P<0.002) blockade was significantly shorter in M and S groups than in the F group. The time to reach the maximal dermatomal level of sensory block was significantly shorter in the F group than in the S and M groups (P<0.002).

CONCLUSION

In patients undergoing cesarean section with spinal anesthesia, the addition of magnesium sulfate (50 mg) i.t. to 10 mg of spinal bupivacaine (0.5%) did not shorten the onset time of sensory and motor blockade or prolong the duration of spinal anesthesia, as seen with fentanyl.

Effects of magnesium sulphate on intraoperative anaesthetic requirements and postoperative analgesia in gynaecology patients receiving total intravenous anaesthesia

BACKGROUND

This randomized, double-blind, prospective study was undertaken to evaluate the effects of magnesium sulphate on anaesthetic requirements and postoperative analgesia in patients undergoing total i.v. anaesthesia (TIVA).

METHODS

Fifty patients who underwent gynaecological surgery were randomly divided into two groups. Before induction of anaesthesia, the magnesium group (Group M) received magnesium sulphate 50 mg kg(-1) i.v. as a bolus and then 15 mg kg(-1) h(-1) i.v. by continuous infusion. The control group (Group S) received the same amount of isotonic saline. TIVA (propofol+remifentanil) was administered under bispectral index monitoring during anaesthesia induction and maintenance. Rocuronium was administered before orotracheal intubation and during surgery when the train-of-four count was 2 or more. After operation, patient-controlled analgesia with a solution of ketorolac and morphine was used and the consumption of this solution was recorded. Pain scores at rest and upon movement were evaluated 30 min, 4, 24, and 48 h after surgery.

RESULTS

Patients in Group M required less rocuronium than those in Group S [mean (SD) 0.44 (0.09) vs 0.35 (0.07) microg kg(-1) min(-1), P<0.05]. The total amounts of propofol and remifentanil administered were similar in the two groups. Postoperative pain scores, cumulative analgesic consumption, and shivering incidents were significantly lower in Group M (P<0.05). Mean arterial pressure just after intubation and during the immediate postoperative period was also significantly lower in Group M (P<0.05).

CONCLUSIONS

I.v. magnesium sulphate during TIVA reduced rocuronium requirement and improved the quality of postoperative analgesia.

Efficacy of pre- and postoperative oral dextromethorphan for reduction of intra- and 24-hour postoperative morphine consumption for transabdominal hysterectomy

OBJECTIVE

We studied the effect of dextromethorphan (DEX), an N-methyl-D-aspartate receptor antagonist, on analgesic consumption and pain scores after abdominal hysterectomy. We aimed to compare the analgesic effectiveness and incidence of adverse side effects of oral DEX with placebo (P).

DESIGN

This was a double-blinded, randomized, placebo-controlled study.

SETTING AND PATIENTS

One hundred patients were randomized to two groups. Group DEX was given 30-mg tablets of oral DEX with their premedication and three more times in the first 24 hours after surgery. Group P received the placebo following the same schedule. Postoperative analgesic requirements were assessed using a patient-controlled analgesia system. Pain was assessed at rest using a visual analogue scale in the post-anesthetic care unit (PACU), 6 and 24 hours after surgery.

RESULTS

Mean pain scores were significantly lower at the PACU (62.6 vs 75.7) as was the mean sum of all resting pain scores (144.5 vs 173.1). Mean morphine consumption was greatest in the DEX group (35.1 vs 33.0 mg; P < 0.05). The sedation scores, postoperative analgesic requirements, and incidence of side effects were similar between the P and DEX groups as were the mean pain scores.

CONCLUSIONS

During PACU, however, there were two differences between the DEX and placebo groups: 1) a lower pain score at PACU; and 2) a prolonged time to the first use of morphine at PACU in the DEX group as compared with the placebo group. A low-dose DEX had a weaker though still measurable effect in this clinical trial compared with trials using higher doses.

Magnesium as an adjuvant to postoperative analgesia: a systematic review of randomized trials

BACKGROUND

Randomized trials have reached different conclusions as to whether magnesium is a useful adjuvant to postoperative analgesia.

METHODS

We performed a comprehensive search (electronic databases, bibliographies, all languages, to 4.2006) for randomized comparisons of magnesium and placebo in the surgical setting. Information on postoperative pain intensity and analgesic requirements was extracted from the trials and compared qualitatively. Dichotomous data on adverse effects were combined using classic methods of meta-analysis.

RESULTS

Fourteen randomized trials (778 patients, 404 received magnesium) tested magnesium laevulinate, gluconate or sulfate. With magnesium, postoperative pain intensity was significantly decreased in four (29%) trials, was no different from placebo in seven (50%), and was increased in one (7%); two trials (14%) did not report on pain intensity. With magnesium, postoperative analgesic requirements were significantly reduced in eight (57%) trials, were no different from placebo in five (36%), and were increased in one (7%). Magnesium-treated patients had less postoperative shivering (relative risk 0.38, 95% confidence interval 0.17-0.88, number-needed-to-treat 14). Seven trials reported on magnesium serum levels. In all, serum levels were increased in patients who received magnesium; in six, serum levels were decreased in those who received placebo.

CONCLUSIONS

These trials do not provide convincing evidence that perioperative magnesium may have favorable effects on postoperative pain intensity and analgesic requirements. Perioperative magnesium supplementation prevents postoperative hypomagnesemia and decreases the incidence of postoperative shivering. It may be worthwhile to further study the role of magnesium as a supplement to postoperative analgesia, since this relatively harmless molecule is inexpensive, and the biological basis for its potential antinociceptive effect is promising.

The clinical role of NMDA receptor antagonists for the treatment of postoperative pain

Recent advances in the understanding of postoperative pain have demonstrated its association with sensitization of the central nervous system (CNS) which clinically elicits pain hypersensitivity. N-methyl-D-aspartate (NMDA) receptors play a major role in synaptic plasticity and are specifically implicated in CNS facilitation of pain processing. Therefore, NMDA receptor antagonists, and specifically ketamine commonly used in clinical practice, have been implicated in perioperative pain management. At subanesthetic (i.e. low) doses, ketamine exerts a specific NMDA blockade and hence modulates central sensitization induced both by the incision and tissue damage and by perioperative analgesics such as opioids. However, the mechanisms underlying ketamine anti-hyperalgesic effect are not totally understood, and neither is the relationship between central sensitization and the risk of developing residual pain after surgery. This chapter examines the role of low doses of ketamine as an adjuvant drug in current perioperative pain management and questions the anti-hyperalgesic mechanisms involved.

Does magnesium sulfate reduce the short- and long-term requirements for pain relief after caesarean delivery? A double-blind placebo-controlled trial

OBJECTIVE

The purpose of this study was to determine whether magnesium sulfate decreases postoperative pain and analgesic consumption.

STUDY DESIGN

Women who underwent elective cesarean delivery were randomized into groups according to high-dose magnesium sulfate (50 mg/kg load and 2 g/h), low-dose magnesium sulfate (25 mg/kg load and 1 g/h), or placebo. Before the delivery, the dose of patient-controlled opioid that was used and the visual analogs of pain during the first 48 hours after delivery and at 6 weeks were assessed.

RESULTS

Forty-two women were assigned randomly to the high-dose arm; 38 women were assigned to the low-dose magnesium arms, and 40 women were assigned to the control arm. The cumulative opioid use (P = .636); pain scores at 6, 12, 24, and 48 hours at rest (P = .786) and with movement (P = .179); the use of analgesics after hospital discharge (P = .711); and wound pain with movement (P = .429) or pressure (P = .144) after 6 weeks were similar.

CONCLUSION

Magnesium sulfate does not reduce the severity of short-term or long-term (6 weeks) pain after cesarean delivery.

Effects of three different dose regimens of magnesium on propofol requirements, haemodynamic variables and postoperative pain relief in gynaecological surgery

BACKGROUND

In this double-blind, randomized, placebo-controlled study we compared the effects of three different dose regimens of magnesium on intraoperative propofol and atracurium requirements, and postoperative morphine consumption in patients undergoing gynaecological surgery.

METHODS

Eighty women were allocated to four equal groups. The control group received normal saline; magnesium groups received 40 mg kg(-1) of magnesium before induction of anaesthesia, followed by i.v. infusion of normal saline, magnesium 10 mg kg(-1) h(-1) or magnesium 20 mg kg(-1) h(-1) for the next 4 h. Propofol infusion was targeted to keep bispectral index values between 45 and 55. Postoperative analgesia was achieved using PCA with morphine.

RESULTS

Magnesium groups required significantly less propofol [mean (sd) 121.5 (13.3), 102.2 (8.0) and 101.3 (9.7) microg kg(-1) min(-1) respectively] than the control group (140.7 (16.5) microg kg(-1) min(-1)). Atracurium use was significantly higher in the control group than magnesium groups [0.4 (0.06) vs 0.34 (0.06), 0.35 (0.04), 0.34 (0.06) mg kg(-1) h(-1) respectively]. Morphine consumption was significantly higher in control group than magnesium groups on the first postoperative day [0.88 (0.14) vs 0.73 (0.17), 0.59 (0.23), 0.53 (0.21) mg kg(-1) respectively]. The heart rate was lower in magnesium groups and 20 mg kg(-1) h(-1) infusion group demonstrated the lowest values.

CONCLUSION

Magnesium 40 mg kg(-1) bolus followed by 10 mg kg(-1) h(-1) infusion leads to significant reductions in intraoperative propofol, atracurium and postoperative morphine consumption. Increasing magnesium dosage did not offer any advantages, but induced haemodynamic consequences.

Effect of intravenous magnesium sulphate in reducing irritability and restlessness in pure and polysubstance opiate detoxification

The aim of this double-blind, placebo-controlled study was to evaluate the efficacy of intravenous magnesium sulphate (MgSO(4)) on the need for chlormethiazole in pure or polysubstance opiate detoxification. Forty-one inpatients suffering from pure and polysubstance opiate dependence were treated with morphine sulphate pentahydrate in a gradual detoxification program. Morphine reduction took about 11 days. Additionally, 5% MgSO(4) was administered intravenously to the intervention group (Mg group, n=22) over 24 h by perfusor (150-200 mg MgSO(4)/h; plasma level of 2.36+/-0.29 mmol/l), whereas NaCl 0.9% was intravenously administered in the placebo group (n=19). In case of withdrawal symptoms (irritability, restlessness, and insomnia), patients received chlormethiazole p.o. Our hypothesis that the need for chlormethiazole would be decreased by adjunctive administration of Mg was not confirmed in our study population (2180 mg/day in the Mg group vs. 2360 mg/day in the placebo group). There was neither a difference in the quantity of chlormethiazole required nor a difference in the severity of withdrawal symptoms measured with the Wang scale between the two comparison groups. We observed that calcium plasma levels decreased and phosphate plasma levels increased significantly during intravenous therapy with Mg. Despite promising pilot studies, the administration of Mg did not enable a dose reduction of tranquilizing medication (chlormethiazole) in pure and polysubstance opiate detoxification.

Role of Analgesic Adjuncts in Postoperative Pain Management

Postoperative pain remains a major problem. A multi-modal analgesic approach is recommended to optimize pain management and reduce opiate-related adverse effects. Several analgesic adjuncts have been investigated, and many have proved to have a useful analgesic effect. This article reviews the literature regarding use of analgesic adjuncts in the perioperative period.

Effect of intraoperative magnesium infusion on perioperative analgesia in open cholecystectomy

STUDY OBJECTIVE

To study the role of magnesium sulphate (MgSO4) on analgesic requirement, pain, discomfort, and sleep during perioperative period.

DESIGN

prospective, double-blinded, randomized study.

SETTINGS

Operating room and recovery ward at a university teaching hospital.

PATIENTS

50 ASA physical status I and II patients scheduled for elective open cholecystectomy with general anesthesia.

INTERVENTIONS

patients were randomly allocated to receive MgSO4 or saline intravenously (i.v.). Patients in the magnesium group received 50% MgSO4 (50 mg kg(-1)) in 100 mL saline and those in the control group received an equal volume of saline i.v. during the preoperative period followed by 50 mL hr(-1) infusion of either MgSO4 (15 mg kg(-1) hr(-1)) or saline until the end of surgery.

MEASUREMENTS AND MAIN RESULTS

Morphine requirement, pain during rest and on coughing, discomfort, and insomnia were assessed during the postoperative period for 24 hours. Intravenous morphine 40 microg kg(-1) increments were given to all patients in the postoperative period for analgesia. Patients in the magnesium and control groups had similar morphine requirement during the first 24 hours postoperatively (p = 0.07). Patients in the magnesium group experienced less discomfort during the first hour after the operation. They also had better sleep quality during the first postoperative night than did the control group patients (p < 0.05). The frequency of side effects was similar in the two groups.

CONCLUSION

Administration of intraoperative MgSO4 as an adjuvant analgesic in patients undergoing open cholecystectomy resulted in better pain relief and comfort in the first postoperative hour, but it did not significantly decrease the postoperative morphine requirement. Magnesium sulphate resulted in better sleep quality during the postoperative period, without any significant adverse effects. The role of MgSO4 as an adjuvant analgesic in open cholecystectomy needs to be studied further.

A Qualitative Systematic Review of the Role of N-Methyl-d-Aspartate Receptor Antagonists in Preventive Analgesia

We evaluated in a qualitative systematic review the effect of N-methyl-D-aspartate (NMDA) receptor antagonists on reducing postoperative pain and analgesic consumption beyond the clinical duration of action of the target drug (preventive analgesia). Randomized trials examining the use of an NMDA antagonist in the perioperative period were sought by using a MEDLINE (1966-2003) and EMBASE (1985-2003) search. Reference sections of relevant articles were reviewed, and additional articles were obtained if they evaluated postoperative analgesia after the administration of NMDA antagonists. The primary outcome was a reduction in pain, analgesic consumption, or both in a time period beyond five half-lives of the drug under examination. Secondary outcomes included time to first analgesic request and adverse effects. Forty articles met the inclusion criteria (24 ketamine, 12 dextromethorphan, and 4 magnesium). The evidence in favor of preventive analgesia was strongest in the case of dextromethorphan and ketamine, with 67% and 58%, respectively, of studies demonstrating a reduction in pain, analgesic consumption, or both beyond the clinical duration of action of the drug concerned. None of the four studies examining magnesium demonstrated preventive analgesia.

IMPLICATIONS

We evaluated, in a qualitative systematic review, the effect of N-methyl D-aspartate antagonists on reducing postoperative pain and analgesic consumption beyond the clinical duration of action of the target drug (preventive analgesia). Dextromethorphan and ketamine were found to have significant immediate and preventive analgesic benefit in 67% and 58% of studies, respectively.

The therapeutic use of magnesium in anesthesiology, intensive care and emergency medicine: a review

PURPOSE

To review current knowledge concerning the use of magnesium in anesthesiology, intensive care and emergency medicine.

METHODS

References were obtained from Medline(R) (1995 to 2002). All categories of articles (clinical trials, reviews, or meta-analyses) on this topic were selected. The key words used were magnesium, anesthesia, analgesia, emergency medicine, intensive care, surgery, physiology, pharmacology, eclampsia, pheochromocytoma, asthma, and acute myocardial infarction.

PRINCIPLE FINDINGS

Hypomagnesemia is frequent postoperatively and in the intensive care and needs to be detected and corrected to prevent increased morbidity and mortality. Magnesium reduces catecholamine release and thus allows better control of adrenergic response during intubation or pheochromocytoma surgery. It also decreases the frequency of postoperative rhythm disorders in cardiac surgery as well as convulsive seizures in preeclampsia and their recurrence in eclampsia. The use of adjuvant magnesium during perioperative analgesia may be beneficial for its antagonist effects on N-methyl-D-aspartate receptors. The precise role of magnesium in the treatment of asthmatic attacks and myocardial infarction in emergency conditions needs to be determined.

CONCLUSIONS

Magnesium has many known indications in anesthesiology and intensive care, and others have been suggested by recent publications. Because of its interactions with drugs used in anesthesia, anesthesiologists and intensive care specialists need to have a clear understanding of the role of this important cation.

Does ketamine or magnesium affect posttonsillectomy pain in children?

BACKGROUND

Many previous studies have suggested a role for the N-methyl-D-aspartate (NMDA) receptor antagonists ketamine and magnesium in decreasing postoperative pain and analgesic requirements in adults, but none has investigated these medications in children.

METHODS

This randomized, double-blind, placebo-controlled study evaluated the effects of ketamine and magnesium in children undergoing tonsillectomy. Eighty patients, aged 3-12 years, were randomly assigned to four groups. Patients received either ketamine 0.15 mg.kg-1, magnesium sulphate 30 mg.kg-1, ketamine 0.15 mg.kg-1 plus magnesium sulphate 30 mg.kg-1, or placebo intravenously 5 min prior to the start of surgery. Intraoperative analgesia was standardized, and included fentanyl and dexamethasone.

RESULTS

There were no differences among the groups with respect to pain assessment postoperatively. Compared with placebo, the treatment groups did not require less fentanyl in the postanaesthesia recovery room or consume less codeine in the first 24-h postoperatively. There was no evidence of synergism between ketamine and magnesium. There were no differences among the groups in the incidence of nausea, vomiting, sedation, bleeding, or dreaming postoperatively.

CONCLUSION

This study did not demonstrate a decrease in pain or analgesic consumption in children undergoing tonsillectomy when pretreated with a small dose of ketamine and/or magnesium.

Effect of intra-operative magnesium sulphate on pain relief and patient comfort after major lumbar orthopaedic surgery

The effects of intra-operative magnesium sulphate on pain relief after major lumbar surgery were investigated in 24 patients. Patients were randomly allocated to receive either an infusion of 50 mg x kg(-1) magnesium sulphate or an equivalent volume of saline at induction of anaesthesia. Anaesthesia was induced with propofol and remifentanil. Tracheal intubation was facilitated using rocuronium. Maintenance was achieved with remifentanil and sevoflurane in nitrous oxide/ oxygen. Intra-operative monitoring included standard equipment and neuromuscular transmission. During surgery, neuromuscular block recovery was longer in the magnesium group. Postoperative opioid consumption and pain scores were lower in the magnesium group. The first night's sleep and the global satisfaction scores were better in the magnesium group. The results of the study support magnesium sulphate as a useful adjuvant for postoperative analgesia after major lumbar surgery.

A comparative study on the analgesic effect of tramadol, tramadol plus magnesium, and tramadol plus ketamine for postoperative pain management after major abdominal surgery

BACKGROUND

We tested whether, after major abdominal surgery, the addition of magnesium or ketamine to tramadol for intravenous (IV) patient-controlled analgesia (PCA) improved analgesia and lowered pain scores, compared to a PCA containing only tramadol.

METHODS

Sixty-six patients were allocated randomly to receive a PCA with tramadol alone (T), tramadol plus magnesium (TM) or tramadol plus ketamin (TK), in a double-blind randomized study. Postoperative analgesia was started when the verbal rating scale (VRS) score was 2 or more. Following a loading dose of the study solution (which contained 1 mg/kg tramadol), a background infusion of 0.4 mg/kg/h was started. Patients were allowed to use bolus doses of 0.2 mg/kg every 20 min without a time limit. Discomfort, sedation, pain scores, total and bolus PCA tramadol consumption, and side-effects, were recorded for up to 24 h after the start of PCA.

RESULTS

Pain and discomfort scores were lower (P < 0.01) in groups TM and TK at 15, 30, 60 and 120 min than in group T. The addition of magnesium or ketamine significantly reduced the consumption of tramadol at 6, 12 and 24 h (P < 0.01). The incidence of nausea did not differ between the groups.

CONCLUSION

Adding magnesium or ketamine to tramadol improved analgesia and patient comfort and decreased the amount of tramadol required for postoperative pain management after major abdominal surgery.

Glutamate receptors and nociception: implications for the drug treatment of pain

Evidence from the last several decades indicates that the excitatory amino acid glutamate plays a significant role in nociceptive processing. Glutamate and glutamate receptors are located in areas of the brain, spinal cord and periphery that are involved in pain sensation and transmission. Glutamate acts at several types of receptors, including ionotropic (directly coupled to ion channels) and metabotropic (directly coupled to intracellular second messengers). Ionotropic receptors include those selectively activated by N-methyl-D-aspartate, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid and kainate. Metabotropic glutamate receptors are classified into 3 groups based on sequence homology, signal transduction mechanisms and receptor pharmacology. Glutamate also interacts with the opioid system, and intrathecal or systemic coadministration of glutamate receptor antagonists with opioids may enhance analgesia while reducing the development of opioid tolerance and dependence. The actions of glutamate in the brain seem to be more complex. Activation of glutamate receptors in some brain areas seems to be pronociceptive (e.g. thalamus, trigeminal nucleus), although activation of glutamate receptors in other brain areas seems to be antinociceptive (e.g. periaqueductal grey, ventrolateral medulla). Application of glutamate, or agonists selective for one of the several types of glutamate receptor, to the spinal cord or periphery induces nociceptive behaviours. Inhibition of glutamate release, or of glutamate receptors, in the spinal cord or periphery attenuates both acute and chronic pain in animal models. Similar benefits have been seen in studies involving humans (both patients and volunteers); however, results have been inconsistent. More research is needed to clearly define the role of existing treatment options and explore the possibilities for future drug development.

Magnesium sulfate potentiates morphine antinociception at the spinal level

Intrathecal magnesium sulfate coinfusion with morphine increases antinociception in normal rats; however, because magnesium also delays the onset of tolerance, it is not clear whether this additional antinociception is a result of potentiated analgesia or tolerance abatement. We examined the antinociceptive interaction of intrathecal (IT) bolus magnesium sulfate and morphine in morphine naive rats and those with mechanical allodynia after a surgical incision. After intrathecal catheter implantation, rats were given preinjections of magnesium or saline, followed by injections of morphine or saline. In morphine naïve rats, IT bolus magnesium sulfate 281 and 375 microg followed by IT morphine 0.25 or 0.5 nmol enhanced peak antinociception and area under the response versus time curve two-to-three-fold in the tail-flick test as compared with morphine alone. Likewise, in rats with incisional pain, IT bolus magnesium sulfate 188 and 375 microg followed by morphine 0.5 nmol reduced mechanical allodynia, whereas morphine 0.5 nmol alone did not. This study suggests that IT magnesium sulfate potentiates morphine at a spinal site of action.

IMPLICATIONS

Magnesium sulfate potentiates morphine analgesia when coadministered intrathecally in normal rats, and in an animal model of mechanical allodynia after a surgical incision. These results suggest that intrathecal administration of magnesium sulfate may be a useful adjunct to spinal morphine analgesia.

Magnesium sulfate potentiates morphine antinociception at the spinal level

Intrathecal magnesium sulfate coinfusion with morphine increases antinociception in normal rats; however, because magnesium also delays the onset of tolerance, it is not clear whether this additional antinociception is a result of potentiated analgesia or tolerance abatement. We examined the antinociceptive interaction of intrathecal (IT) bolus magnesium sulfate and morphine in morphine naive rats and those with mechanical allodynia after a surgical incision. After intrathecal catheter implantation, rats were given preinjections of magnesium or saline, followed by injections of morphine or saline. In morphine naïve rats, IT bolus magnesium sulfate 281 and 375 microg followed by IT morphine 0.25 or 0.5 nmol enhanced peak antinociception and area under the response versus time curve two-to-three-fold in the tail-flick test as compared with morphine alone. Likewise, in rats with incisional pain, IT bolus magnesium sulfate 188 and 375 microg followed by morphine 0.5 nmol reduced mechanical allodynia, whereas morphine 0.5 nmol alone did not. This study suggests that IT magnesium sulfate potentiates morphine at a spinal site of action.

IMPLICATIONS

Magnesium sulfate potentiates morphine analgesia when coadministered intrathecally in normal rats, and in an animal model of mechanical allodynia after a surgical incision. These results suggest that intrathecal administration of magnesium sulfate may be a useful adjunct to spinal morphine analgesia.

Perioperative dextromethorphan reduces postoperative pain after hysterectomy

We studied the effect of dextromethorphan, an N-methyl-D-aspartate antagonist, on analgesic consumption and pain scoring after abdominal hysterectomy. In this double-blinded study, 50 patients were randomized into two groups. Group DM was given oral dextromethorphan 40 mg with their premedication, then 40 mg three times per day for the next 2 days. Group P received placebo at identical times. Postoperative analgesic requirements were assessed using a patient-controlled analgesia system and subsequent oral analgesic intake using a set protocol. Pain was assessed at rest and on movement using a visual analog scale 4, 24, 48, and 72 h after the operation. Median pain scores at rest were significantly lower at 48 and 72 h and also for the sum of all resting pain scores. Mean morphine consumption was less in Group DM (1.1 vs 1.5 mg/h; P = 0.054). Usage of oral diclofenac, given every 8 h as needed, did not differ between groups, but consumption of codydramol (paracetamol 500 mg and dihydrocodeine 10 mg) was significantly less in Group DM. We conclude that the use of oral dextromethorphan has an analgesia-sparing effect and some beneficial effects on pain scoring at rest after abdominal hysterectomy.

IMPLICATIONS

Patients given dextromethorphan before and after surgery had a significant reduction in some pain scores at rest, but not on movement. There was a trend to lower morphine requirements in the first 24 h. Over the next 48 h, oral analgesic usage was significantly reduced.

Sensory changes and pain after abdominal hysterectomy: a comparison of anesthetic supplementation with fentanyl versus magnesium or ketamine

Drugs interacting with opioid or N-methyl-D-aspartate (NMDA) receptors may have differing effects on post-surgical sensory changes, such as central inhibition or spinal excitation. We compared the effect of supplementing isoflurane/N2O/O2 anesthesia with an opioid agonist (fentanyl [n = 15]) or two drugs inhibiting the NMDA system differently (magnesium, ketamine [n = 15 in each group]) on sensory changes after abdominal hysterectomy. Electric sensation, pain detection, and pain tolerance thresholds were determined (preoperatively and 1, 4, 24 h, and 5 days postoperatively) in arm, thoracic, incision, and leg dermatomes together with pain scores and cumulative morphine consumption. Thresholds relative to the arm were derived to unmask segmental sensory changes hidden by generalized changes. Absolute thresholds were increased 1-24 h, returning to baseline on Day 5, without overall differences among drugs. Fentanyl thresholds were lower 1 h and higher 5 days postoperatively compared with magnesium and ketamine; thresholds were lower at 24 h for magnesium versus ketamine. Relative thresholds increased compared with baseline only with fentanyl (1-4 h); none decreased. Pain scores and morphine consumption were similar. Thus, all adjuvants suppressed spinal sensitization after surgery. Fentanyl showed the most, and magnesium the least, central sensory inhibition up to 5 days postoperatively, with different patterns of inhibition directly postsurgery versus later. Differences in sensory processing were not reflected in clinical measures.

IMPLICATIONS

We studied the effects on postsurgical sensory processing of general anesthesia supplemented by drugs affecting opioid or N-methyl-D-aspartate receptors using sensory thresholds. Generalized central sensory inhibition, differently affected by the drugs, predominated after surgery. All drugs suppressed spinal excitation. Clinical pain measures did not reflect sensory change.