|Year : 2020 | Volume
| Issue : 3 | Page : 189-192
Evaluation of magnesium sulfate as an adjuvant to bupivacaine for postoperative analgesia in ultrasound-guided transversus abdominis plane block in patients scheduled for lower segment caesarean section under subarachnoid block – A prospective, randomized, double-blind study
Mayuresh Umalkar1, Nandini Londhe2
1 Jupiter Hospital, Pune, Maharashtra, India
2 Ruby Hall Clinic, Pune, Maharashtra, India
|Date of Submission||26-Jul-2020|
|Date of Decision||10-Sep-2020|
|Date of Acceptance||30-Oct-2020|
|Date of Web Publication||28-Dec-2020|
Dr. Mayuresh Umalkar
A1 502 Swarganga Society Vallabhanagar, Pimpri, Pune - 411 018 Maharashtra
Source of Support: None, Conflict of Interest: None
Background and Aims: Various adjuvants such as magnesium sulfate (MgSO4), dexamethasone, and clonidine have been used in transversus abdominis plane (TAP) block to prolong the duration analgesia. MgSO4 is N-methyl D-aspartate receptor antagonist (NMDA) and presence of NMDA receptors in skin and muscle can prolong the duration of postoperative analgesia. We aimed to evaluate the effects of MgSO4 as an adjuvant to bupivacaine in ultrasound-guided (USG) TAP block for prolongation of duration of postoperative analgesia. Materials and Methods: Sixty pregnant patients of the American Society of Anesthesiologists physical Status I and II between age group of 18–35 years, scheduled for elective cesarean section under subarachnoid block were allocated randomly into two groups:- Group BM (bupivacaine + MgSO4) and Group B (bupivacaine + Normal saline). All patients received USG bilateral TAP block after caesarean section using either 25 ml of 0.25% bupivacaine and 0.3 ml (75 mg) of 25% injection MgSO4 or 25 ml of 0.25% Bupivacaine and 0.3 ml of normal saline on each side. All patients were evaluated for dynamic pain at 0, 30 min, 1, 2, 4, 6, 12, and 24 h, for postoperative analgesia and adverse effects. The normally and nonnormally distributed data were analyzed using unpaired t-test and Mann–Whitney U-test, respectively. P < 0.05 was considered statistically significant. Results: Duration of analgesia in Group BM (12.3 h. ±0.83666 h) and Group B (12.0333 h. ±1.24522 h) were comparable (P = 0.3348). The average pain scores at different time points did not differ significantly between the two groups (P > 0.05). Conclusion: MgSO4 as an adjuvant to bupivacaine in USG TAP block does not prolong duration of postoperative analgesia.
Keywords: Adjuvants, analgesia, postoperative, regional anesthesia
|How to cite this article:|
Umalkar M, Londhe N. Evaluation of magnesium sulfate as an adjuvant to bupivacaine for postoperative analgesia in ultrasound-guided transversus abdominis plane block in patients scheduled for lower segment caesarean section under subarachnoid block – A prospective, randomized, double-blind study. Indian J Pain 2020;34:189-92
|How to cite this URL:|
Umalkar M, Londhe N. Evaluation of magnesium sulfate as an adjuvant to bupivacaine for postoperative analgesia in ultrasound-guided transversus abdominis plane block in patients scheduled for lower segment caesarean section under subarachnoid block – A prospective, randomized, double-blind study. Indian J Pain [serial online] 2020 [cited 2021 Jan 18];34:189-92. Available from: https://www.indianjpain.org/text.asp?2020/34/3/189/305136
| Introduction|| |
Caesarean section is a major surgical procedure, following which substantial postoperative discomfort and pain can be anticipated. The provision of effective postoperative analgesia is of key importance to facilitate early ambulation, infant care (including breastfeeding, maternal-infant bonding) and prevention of postoperative morbidity. Poorly controlled pain in the early postoperative period may contribute to the generation of chronic pain. Transversus abdominis plane (TAP) block is an effective analgesic technique that has proved its efficacy in postoperative pain management for lower segment caesarean section (LSCS). Postoperative analgesia provided by TAP block depends on the duration of action and dose of local anesthetics (LA) used. Various adjuvants have been added to LA in the TAP block to increase the duration of postoperative analgesia while minimizing the systemic adverse effects. The effect of magnesium sulfate (MgSO4) as an adjuvant to LA in ultrasound-guided (USG) TAP block is controversial. It may or may not increase the duration of analgesia or decrease complications such as postoperative nausea and vomiting (PONV)., Till date, very few studies have been conducted using MgSO4 as an adjuvant to LA in TAP block in patients undergoing LSCS. The present study was conducted to evaluate the efficacy of MgSO4 as an adjuvant to bupivacaine using USG guided TAP block in patients scheduled for elective LSCS under subarachnoid block (SAB).
| Materials and Methods|| |
After approval from the institutional ethical committee, letter no. PS-35-040 dated July 16, 2016, the study was conducted at a tertiary care center over a period of one year from May 2016 to April 2017. This prospective, double-blind, randomized, controlled study included 60 American Society of Anesthesiologists (ASA) physical status II patients, aged 18–35 years with term pregnancy who had undergone elective LSCS under SAB. Patients with local pathology at the site of injection, ASA physical Status III or above, body mass index (BMI) >35 kg/m2, bleeding disorders, and those who did not cooperate or refused to participate in the study were excluded. Patients who were substance abusers and allergic to study medication were also excluded from the study. After a thorough preanesthetic check-up, patients satisfying the inclusion criteria were selected. Written informed consent was taken from each of the 60 enrolled patients for participation in the study. Demographic data like age, weight, height, and BMI were recorded. Patients were explained about the study protocol and the procedure. They were also trained to assess pain using the visual analog scale (VAS). Patients were randomly allocated to one of the two groups:-BM or B with 30 patients in each using a computer-generated random number table. Anesthesiologist performing TAP block was unaware of group allocation. Postoperatively, all observations were made by an independent observer who was unaware of group allocation. In the operation room, standard ASA monitors were attached and intravenous ringer lactate was started. SAB was performed in the sitting position using 25 G Quincke's needle at L3-4 interspace with 12 mg of 0.5% hyperbaric bupivacaine and 10 mcg injection fentanyl. The patients were then placed in the supine position with 15° left lateral tilt and supplemental oxygen was administered through a face mask at 4 l/min. After confirmation of adequate level (T4), surgery was started. After completion of the surgery, bilateral USG guided TAP block (posterior TAP) was performed in supine position under all aseptic precautions. A linear ultrasound probe (6–13 MHz of Mindray USG Machine) was used for carrying out the block. Ultrasound probe was placed transverse to the abdomen in the midaxillary line between the costal margin and the iliac crest [Figure 1]a. The subcutaneous fat, external oblique muscle, internal oblique muscle, transversus abdominis muscle, peritoneum and intraperitoneal structures were identified [Figure 1]b. A 22 G 100 mm short bevel (stimuplex) needle was inserted from anterior to posterior using in-plane technique. The needle passage through the skin and subcutaneous tissue then through the external and internal oblique muscles observed on ultrasound imaging. The needle tip is directed into the plane between the internal oblique and transversus abdominis muscle [Figure 1]c. Initially, 2 ml of study drug was used to separate fascial layers to confirm needle tip location and to open the plane between the two muscles. This was followed by injection of the full dose of LA. When the needle tip was positioned correctly, the hypoechoic injectate was seen on ultrasound to spread out the plane between the two muscles. The study drug solution was injected on each side in 5 ml increments according to respective groups after aspiration to avoid intravascular placement. An echo-lucent lens-shaped space (Kayak sign) between the two muscles was taken as a successful injection [Figure 1]d. The patients in Group BM (n = 30) received injection bupivacaine 0.25% 25 ml + injection MgSO4 0.3 ml (75 mg) on each side whereas the patients in Group B (n = 30) received injection bupivacaine 0.25% 25 ml + 0.3 ml 0.9% saline on each side. All patients received intravenous injection diclofenac 75 mg 12 hourly and intravenous injection Tramadol 50 mg as rescue analgesia as per the institutional multimodal analgesia protocol. Postoperatively, the pain was assessed using VAS score (0–10), with 0 being no pain at all and 10 being the worst pain imaginable. Vitals such as heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), SpO2, and respiratory rate (RR) were also monitored in the postoperative period. Hypotension was defined as a 20% decrease in SBP from the baseline. Bradycardia was defined as HR <60 beats/min and tachycardia were defined as HR >100 beats/min. Respiratory depression was defined as RR <8 breaths/min. Rescue analgesia was given when VAS score >4. The total duration of analgesia was defined as the time from commencement of block to the time when first rescue analgesia was given. Parameters were monitored in post anesthesia care unit and subsequently in the obstetric ward at 30 min, 1, 2, 4, 6, 12, and 24 h. The side effects due to MgSO4 and bupivacaine like, PONV, local anesthesia systemic toxicity, during the first 24 h after the block were also noted.
|Figure 1: Probe position and sonoanatomy of transversus abdominis plane block. (a) Position of ultrasound probe and needle. (b) Abdominal wall layers on ultrasound. (c) Needle placement in transversus abdominis plane. (d) Kayak Sign|
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The sample size was calculated based on a previous study by Rana et al. with VAS score at 6 h between two intervention groups as reference. Considering 80.0% statistical power (Type II error = 0.20) and 5% type I error probability (α = 0.05), the required sample size was 28 in each group. Owing to potential drop outs, 30 patients were included in each group. Raw data was entered into a Microsoft Excel Spreadsheet and analyzed using standard statistical software SPSS® statistical package version 24.0 (SPSS Inc., Chicago, IL, USA). The data on categorical variables were presented as n (%) of cases. The data on continuous variables were presented as mean ± standard deviation and nonnormally distributed continuous variables median (min-max) was used across two intervention groups. The statistical significance of the difference of categorical variables across two intervention grous was tested using Chi-Square test or Fisher's exact probability test. The statistical significance of the inter-group difference of the mean of normally distributed continuous variables was tested using independent sample t-test (unpaired Student's t-test). The statistical significance of the inter-group difference of average (median) of nonnormally distributed continuous variables was tested using the Mann–Whitney U-test. P < 0.05 was considered to be statistically significant.
| Results|| |
We recruited 30 participants in each group and none were excluded from our study. Both the groups were comparable in terms of demographic profiles (age, weight, height, BMI, and duration of analgesia/first rescue analgesia) [Table 1]. No statistically significant difference was observed between the two groups in HR, SBP, and DBP, SPO2 and RR [Figure 2]a, [Figure 2]b, [Figure 2]c, [Figure 2]d. Median VAS score was comparable in Group BM and Group B and the difference was not statistically significant [Table 2]. There was no statistically significant difference of duration of analgesia (time to first rescue analgesia) in Group BM (12.3 h. ± 0.83666 h) and Group B (12.0333 h. ±1.24522 h) (P = 0.3348) [Table 1]. Injection diclofenac was first rescue analgesia given to all patients. Total 8 patients (4 in each group) required tramadol as second rescue analgesia. The incidence of PONV in the group BM was 10% and 13.3% in Group B. There was no local anesthesia systemic toxicity in both the groups.
|Figure 2: Intergroup comparison of hemodynamic parameters in two study groups. (a) Inter-group comparison of heart rate. (b) Inter-group comparison of systolic blood pressure and diastolic blood pressure. (c) Inter-group comparison of oxygen saturation. (d) Inter-group comparison of respiratory rate|
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|Table 2: Posttransversus abdominis plane block visual analog scale score|
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| Discussion|| |
We used TAP block with and without MgSO4 as a part of multimodal systemic analgesia regimen to provide postoperative analgesia in all our patients who underwent LSCS. We did not find any significant difference between Group BM and Group B with respect to VAS score, the requirement of rescue analgesics and the mean duration of analgesia. The duration of postoperative analgesia provided by TAP block depends on the dose of LA used. Various adjuvants such as MgSO4, dexamethasone, and clonidine have been used in TAP block to prolong the duration analgesia., MgSO4 blocks the N-methyl D-aspartate receptor, thus it acts by antagonism of calcium influx into nerve fiber, and interfere with the release of neurotransmitter substances at synaptic junctions. We performed the USG-guided TAP block (posterior TAP) in all our patients without any complications. Ultrasound guidance helps to deposit the LA in the correct neurovascular plane, reduce block failure, and minimize complications. TAP block provides analgesia for skin, muscles of the anterior abdominal wall and parietal peritoneum. TAP block reported to block the anterior and lateral branches of spinal nerves from T6 to L1 via different approaches while posterior TAP blocks the anterior and lateral branches of spinal nerves from T10 to T12. As it does not block the visceral component of pain, multimodal systemic analgesics are required to provide better analgesia. Conflicting results have been reported in the literature with different doses of MgSO4 in the TAP block. Rana et al. reported a statistically significant prolonged duration of analgesia with 300 mg MgSO4 as an adjuvant to 0.25% bupivacaine in the TAP block. Munshi et al. also observed that 300 mg MgSO4 increased the duration of postoperative analgesia in patients undergoing LSCS. However, Imani et al. observed that the addition of 500 mg MgSO4 to ropivacaine in TAP block does not affect the post-hysterectomy pain. These differences could be due to a variation in the study population, anesthesiologists experience, use of different LA and different doses of MgSO4. In our study, we used lower dose of MgSO4 (150 mg) compared to other studies. This may be the reason we did not find any significant increase in the mean duration of postoperative analgesia. We observed similar VAS scores in both the groups in the first 2 h. It was probably due to the analgesic effect of SAB. Rana et al. used 20 ml LA in the TAP block and also observed no difference in mean VAS scores in first two hours. However, a lower VAS score was noted subsequently in patients who received MgSO4 as an adjuvant in TAP block till 12 h. In our study, more volume of LA (25.3 ml) was used for the TAP block. This could be the reason for the delayed requirement of rescue analgesics in both the groups in our study.
Our study has a few limitations. We did not measure the serum Mg2+ level and serum bupivcaine level. Increased duration of analgesia could be due to the addition of intrathecal fentanyl during SAB. PONV could be attributed to the use of intrathecal fentanyl or rescue analgesic tramadol in both groups. Moreover, the effect of different doses of MgSO4 on the prolongation of postoperative analgesia was not studied.
| Conclusion|| |
MgSO4 (150 mg) as an adjuvant to bupivacaine in USG TAP block in patients undergoing elective LSCS does not prolong the duration of postoperative analgesia. Higher dosages of MgSO4 may prolong postoperative analgesia and variable dosages of MgSO4 can be considered in future studies.
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Conflicts of interest
There are no conflicts of interest.
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