Objective: The aim of this study is to determine the role of preoperative low dose intravenous MgSO 4 when given adjuvant to ultrasound guided transversus abdominis plane (TAP) block in augmenting postcesarean analgesic effects and reducing opioid requirements during the first 24 hours. Subjects and Methods: In this prospective, randomized double blind study, a total of sixty full term pregnant women were recruited for the study underwent caesarean section. Thirty patients were assigned to MgSO 4 group (A) and another thirty to placebo group (B). Participants in group (A) received 50 mg/kg MgSO 4 in 100 ml isotonic saline intravenous (IV) over 20 minutes prior to induction of general anesthesia by 30 minutes while participants in group (B) received 100 ml isotonic saline (placebo) by the same route and over the same duration as control. Results: Visual Analogue Scale (VAS) was analysed within 24 hours postoperatively. The mean pain score at 6 and 12 hours postoperatively was significantly lower in MgSO 4 group compared to control group (40.4 ± 5.12 vs 53.6 ± 4.92; 26.1 ± 3.01 vs 35.5 ± 3.98 respectively, p = 0.012, 0.005). Comparing both groups regarding the mean time interval of first rescue analgesia (morphine sulphate) requested by the patients, it was longer in MgSO 4 group compared to control group. The total dose of rescue analgesia consumed during 24 hours was analysed and it was significantly higher in control group compared to MgSO 4 group (10.1 ± 0.95 vs 6.2 ± 0.87, p = 0.001). Conclusion: We concluded that preoperative low doses (50 mg/Kg) of MgSO 4 with general anesthesia combined with ultrasound guided TAP block offer longer postoperative pain free periods thus reducing total opioid consumption. In addition to the safety of the drug to the mother and fetus so we recommend IV MgSO 4 as an adjuvant therapy with TAP block.
Pain intensity and duration are elevated after central sensitization initiated by surgical incision and tissue damage. Start of preventive measures before incision and their implementation through the peri- and post-operative period, have a great impact in preventing the central sensitization, thereby ameliorating the acute pain, hyperalgesia and chronic pain [
Preventive analgesia has been defined as an anti-nociceptive treatment that prevents establishment of altered central processing of afferent input from injuries. One of the intravenous adjuvants that have been shown potential in preventive analgesia is magnesium sulphate (MgSO4) that could be administered with multiple routes or methods and one of those is preventive single low dose [
Cesarean section is one of the most commonly performed surgical procedures, it accounts for about 15% of births worldwide and 21.1% of those in the developed world [
The Transversus Abdominis Plane (TAP) Block is a local anesthetic block used to provide analgesia to the anterior and lateral abdominal wall. Rafi et al. [
The aim of this study is to determine the role of preoperative low dose intravenous MgSO4 when given adjuvant to ultrasound guided transversus abdominis plane (TAP) block in augmenting postcesarean analgesic effects and reducing opioid requirements during the first 24 hours.
This is a prospective, randomized, double blind study carried out at Ibn Sina Medical College Hospital, Jeddah, Saudi Arabia from December 2015 till November 2016. Randomization was done with the help of a computer-generated list of numbers. A total of sixty full term pregnant women (completed 37 weeks) were recruited for the study underwent cesarean section. Thirty patients were assigned to MgSO4 group (A) and another thirty to placebo group (B). Group assignment, preparation and administration of drugs were performed by a nurse anesthetist who was neither involved nor interested by any means in the study. Blind grouping was kept to all including the patients themselves, until the completion of study. This study was approved by the Hospital Research Ethics Committee and has been performed in accordance with the ethical standards as in Declaration of Helsinki (1964) and its latter amendments, and a written informed consent was obtained from each participant prior to the study.
The inclusion criteria of these patients include class I-II according to American society of anaesthesiologists (ASA) physical status, singleton full term pregnancy subjected to cesarean section.
Exclusion criteria include; patients with ASA physical status class III-IV, morbid obesity with BMI > 35 kgm−2 at initial hospital visit , neuro-axial anaesthesia, severe pre-eclampsia, diabetes mellitus, cardiovascular disease, renal disease, hypermagnesemia, history of analgesic administration or intake during past 24 hours, urgent cesarean sections, multiple gestations, history of relevant drug allergy, any possibility of anticipated difficult intubation.
Participants in group (A) received 50 mg/kg MgSO4 in 100 ml isotonic saline intravenous (I.V) over 20 minutes prior to induction of general anesthesia by 30 minutes while participants in group (B) received 100 ml isotonic saline (placebo) by the same route and over the same duration as control.
All patients were subjected to a thorough medical history, physical examination, laboratory investigations (fasting blood sugar, kidney, liver function tests, serum electrolytes, coagulation profile, and electrocardiogram) preoperatively. They were also counselled about the anesthetic management and potential complications of both surgery and anesthesia, and the explanations of visual analogue scale (VAS) from 0 - 100. All these data were documented. A thorough airway assessment by Mallampati classification [
General anesthesia was induced with intravenous lignocaine 1.0 mg/kg, propofol 2.0 mg/kg, succinyl choline 1.0 mg/Kg then they were intubated and then atracurium 0.2 mg/kg was given for maintenance of muscle relaxation based on using a peripheral nerve stimulator. Anesthesia was continued by mixture of O2 and N2O along with 2% sevoflurane. After delivery of the fetus and placenta, 1 mg midazolam, 1 µg/kg fentanyl and 10 IU oxytocin (in 500 ml ringer solution) was administrated. Immediately after completion of surgery, each patient received ultrasound guided bilateral TAP blocks in the operating theatre. After that muscle relaxant was antagonized by 40 µg/kg neostigmine and 20 µg/kg atropine, then awake extubation was done and the patients were transferred to the recovery unit.
It started in the recovery unit where patients received 16 mg lornoxicam slowly IV over 5 minutes. After that all patients received acetaminophen 1 gm/6 h IV and 3 mg morphine sulfate IV if breakthrough pain developed.
All patients were assessed for
1) Hemodynamic variables (heart rate, and mean arterial blood pressure) prior to anesthesia, post-intubation, post-extubation, and thirty minutes postoperative.
2) VAS (0 = no pain, 1 - 30 = mild pain, 40 - 60 = moderate pain, 70 - 10 = severe pain) at 2, 6, 12 and 24 hours postoperative.
3) Time elapsed till morphine is requested postoperatively for break through pain.
4) Total dose of rescue analgesia (morphine sulphate) used within the first 24 hours.
5) Time to ambulate the patient postoperatively.
6) APGAR scores at 1st and 5th minutes for neonates.
Using an 18 G Tuohy needle (80 mm Smiths medical Portex®) and the layers of the abdominal wall were identified guided by superficial high-frequency 45 mm linear array ultrasound probe (13 MHz) as described by McDonnell and colleagues [
All TAP blocks were performed by the same anesthetist and the operations by the same obstetrician.
The Data was collected and entered into the personal computer. Statistical analysis was done using Statistical Package for Social Sciences ( SPSS /version 20) software. Arithmetic mean, standard deviation, t-test was used to compare the two groups. The level of significance was 0.05.
Sample size calculation: Sample size was calculated by using Med Calc statistical software. Assuming area under ROC to be 0.80, an alpha of 0.05 and power of study 90.0%. A minimum sample size required was calculated to be 30 patients in each group for this study.
This is a prospective, randomized, double blind study. A total of sixty consented full term pregnant women were classified into two groups, MgSO4 group (N = 30), and placebo group (N = 30) all participants completed the trial. The demographic characteristics of the study participants are illustrated in
Regarding Hemodynamic variables of patients, the mean pre-anesthetic heart rate and MAP showed statistically insignificant difference between both groups (P = 0.098, 0.068 respectively). The mean post-intubation and post-extubation
Variables | TAB + MgSO4 (Group A = 30) | TAB (Group B = 30) | p |
---|---|---|---|
Age (years) Mean ± S.D | 28.2 ± 4.33 | 27.4 ± 3.02 | 0.4211 |
BMI (Kg/m2) Mean ± S.D | 26.2 ± 2.25 | 27.1 ± 1.98 | 0.526 |
Gestational age (weeks) Mean ± S.D | 37.9 ± 0.67 | 38.3 ± 0.48 | 0.458 |
Parity Mean ± S.D | 2.1 ± 0.58 | 2.2 ± 0.78 | 0.401 |
Duration of Surgery (minutes) Mean ± S.D | 43.6 ± 3.2 | 48.2 ± 4.22 | 0.136 |
APGAR Score | |||
1st Minute Mean ± S.D | 8.1 ± 0.89 | 8.3 ± 0.74 | 0.352 |
5 Minutes Mean ± S.D | 9.4 ± 1.03 | 9.7 ± 1.11 | 0.625 |
Duration of Anesthesia (minutes) Mean ± S.D | 54 ± 6.25 | 56 ± 7.01 | 0.558 |
Estimated blood loss (ml) Mean ± S.D | 570 ± 162.3 | 520 ± 207.6 | 0.107 |
Data are presented as mean ± SD; TAB: transverses abdominis plain block; MgSO4: magnesium sulphate; BMI: Body mass index; *Significant.
heart rate was significantly higher in group (B) compared to group (A) (91.2 ± 5.98 vs 85.1 ± 7.32; 100.3 ± 6.22 vs 90.1 ± 6.21 respectively; P = 0.011, 0.005). While, the mean heart rate showed insignificant difference between both groups (P = 0.067) 30 minutes postoperatively. On the other hand the MAP was statistically significant higher with respect to post-intubation, and post-extubation readings in group (B) compared to group (A) (P = 0.035, 0.017 respectively). While the MAP showed statistically insignificant difference between both groups (P = 0.065) 30 minutes postoperatively (
VAS was analysed within 24 hours postoperatively. The mean pain score at 2 hours postoperatively showed statistically insignificant difference between both groups (P = 0.071). While it was statistically significant lower in MgSO4 group compared to control group at 6, 12 hours postoperatively (40.4 ± 5.12 vs 53.6 ± 4.92; 26.1 ± 3.01 vs 35.5 ± 3.98 respectively, p = 0.012, 0.005). Twenty four hours postoperatively, the mean VAS showed statistically insignificant difference between both groups (p = 0.655) (
Comparing both groups regarding the mean time interval of first rescue analgesia (morphine sulphate) requested by the patients , it was longer in MgSO4 group compared to control group (200.2 ± 16.5 vs 120 ± 11.65, p = 0.002). The total dose of rescue analgesia consumed during 24 hours was analysed and it was
Variables | HR bpm | MAP (mmHg) | ||||
---|---|---|---|---|---|---|
TAB + MgSO4 (Group A = 30) | TAB (Group B = 30) | p | TAB + MgSO4 (Group A = 30) | TAB (Group B = 30) | p | |
Pre-anesthetic Mean ± S.D | 82.9 ± 9.65 | 87.1 ± 6.23 | 0.098 | 72.4 ± 6.89 | 78.1 ± 6.45 | 0.068 |
Post Intubation Mean ± S.D | 85.1 ± 7.32 | 91.2 ± 5.98 | 0.011* | 82.1 ± 6.52 | 89.3 ± 7.01 | 0.035* |
Post Extubation Mean ± S.D | 90.1 ± 6.21 | 100.3 ± 6.22 | 0.005* | 83.2 ± 7.23 | 91.4 ± 8.25 | 0.017* |
30 minutes in Recovery Room Mean ± S.D | 84.2 ± 10.2 | 90.1 ± 7.05 | 0.067 | 84.1 ± 5.21 | 90.3 ± 8.21 | 0.065 |
Data are presented as mean ± SD; TAB: transverses abdominis plain block; MgSO4: magnesium sulphate; HR: heart rate, bpm: beat per minute; MAP: mean arterial pressure; mmHg: millimetre mercury; *Significant.
Pain Score VAS (0 - 100) | TAB + MgSO4 (Group A = 30) | TAB (Group B = 30) | p |
---|---|---|---|
2 hours Mean ± S.D | 51.3 ± 9.22 | 58.7 ± 8.22 | 0.071 |
6 hours Mean ± S.D | 40.4 ± 5.12 | 53.6 ± 4.92 | 0.012* |
12 hours Mean ± S.D | 26.1 ± 3.01 | 35.5 ± 3.98 | 0.005* |
24 hours Mean ± S.D | 23.3 ± 2.46 | 24.2 ± 6.02 | 0.655 |
Data are presented as mean ± SD; TAB: transverses abdominis plain block; MgSO4: magnesium sulphate; *Significant.
significantly higher in control group (10.1 ± 0.95) compared to MgSO4 group (6.2 ± 0.87) and the p-value was (0.001). Moreover, the mean time needed for the patients to ambulate independently was significantly longer in control group (6.3 ± 0.97 hr) compared to MgSO4 group (4.2 ± 0.89) and p value was (0.0041) (
Patients undergoing cesarean sections with general anesthesia routinely experience noxious stimuli during laryngoscopy, intubation and abdominal incision prior to fetal delivery, during which they do not receive adequate analgesia due to fetal concerns. Therefore central sensitization occurs, leading to increased probability of acute and chronic post-operative pain [
MgSO4 is an intracellular cation acts as a calcium channels antagonist and as noncompetitive NMDA receptors antagonist [
TAB + MgSO4 (Group A = 30) | TAB (Group B = 30) | p | |
---|---|---|---|
Interval of 1st Analgesic Requirement (minute) Mean ± S.D | 200.2 ± 16.5 | 120 ± 11.65 | 0.0025* |
Total Dose of Rescue Analgesics (Morphine Sulfate) (mg) Mean ± S.D | 6.2 ± 0.87 | 10.1 ± 0.95 | 0.001* |
Time to Ambulate Unassisted (hours) Mean ± S.D | 4.2 ± 0.89 | 6.3 ± 0.97 | 0.0041* |
Data are presented as mean ± SD; TAB: transverses abdominis plain block; MgSO4: magnesium sulphate; *Significant.
analgesic and may have a role in prevention of post-operative pain [
Many studies assessed the perioperative analgesic effect of MgSO4. Mavrommati and colleagues reported that low dose MgSO4 infusion in hernioplasty was an effective adjuvant for perioperative analgesic management [
Recently, Sayed et al. studied the administration of 50 mg/kg IV bolus MgSO4 prior to induction of general anesthesia in elective cesarean candidates, and they concluded that it could curtail the acute postoperative pain and has sparing effects on morphine requirement during first 24 hrs [
In our study we investigated IV low dose MgSO4 (50 mg/kg) combined with TAP block in order to intensify the potency and duration of analgesia, thus reducing the required doses of opioids postoperatively and allows early ambulation and consequently reducing hospital stay and total patient costs. We documented that VAS score at 6 and 12 hours postoperatively was significantly lower in MgSO4 group compared to placebo group, while the VAS score at 24 hours was insignificant between both groups. The total dose of rescue analgesia consumed during 24 hours was significantly lower in MgSO4 group compared to control. Therefore, the analgesic effect of MgSO4 is maximally effective during the first 12 hours, and our results are in agreement with the previously mentioned studies [
Hypotensive effect of MgSO4 explained with its direct vasodilatation effect through the calcium channel blockade and rarely observed up to 60 mg/kg [
Our study had some limitations such as; sample collection for this study requires accurate patient selection based on inclusion and exclusion criteria particularly the body mass index because obesity offers technical challenging difficulty for ultrasound guided TAP block. In addition, smaller sample size hence our findings still need more interpretation for further study. This should be addressed by future prospective studies to verify and clarify the role of MgSO4 as an adjuvant analgesic with local nerve blocks.
We concluded that preoperative low doses (50 mg/Kg) of MgSO4 with general anesthesia combined with Ultrasound guided TAP block offer longer postoperative pain free periods thus reducing total opioid consumption. In addition to the safety of the drug to the mother and fetus so we recommend IV MgSO4 as an adjuvant therapy with TAP block.
This study was not funded.
The authors declare that they have no conflict of interest.
Elrahman, T.N.A. and Youssry, M.A. (2017) The Impact of Single Low Dose IV Magnesium Sulphate Adjuvant to Ultrasound Guided Transverses Abdominis Plain Block for Control of Postcesarean Pain. Open Journal of Obstetrics and Gynecology, 7, 269-280. https://doi.org/10.4236/ojog.2017.73029