Feb 6, 2023, 10:12 AM by Beth VanderWielen, MD; Unyime Ituk, MBBS, FCARCSI; Ruth Landau, MD; Pervez Sultan, MBChB, FRCA, MD; and Ashraf Habib, MBBCh, MSc, MHSc, FRCA

 

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^{Cite as: VanderWielen B, Ituk U, Landau R, Sultan P, Habib A. Post-cesarean delivery analgesia and the role of peripheral nerve blocks: a review. ASRA Pain Medicine News 2022;47. https://doi.org/10.52211/asra020123.009}  

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Introduction

Optimizing post-cesarean delivery (CD) analgesia is essential to the quality of postpartum recovery.^1,2 Severe acute pain is associated with increased risk of chronic pain and postpartum depression.³ Furthermore, adequate analgesia is associated with improved maternal-neonatal bonding and higher breastfeeding success.⁴ The Society for Obstetric Anesthesia and Perinatology (SOAP)⁵ and the PROSPECT guidelines⁶ recommend a multimodal approach to post-cesarean analgesia. This includes the administration of long-acting neuraxial opioids such as morphine, scheduled non-steroidal anti-inflammatory drugs (NSAIDs) and acetaminophen, and rescue oral opioids for breakthrough pain. SOAP guidelines also recommend consideration of local anesthetic (LA) techniques, including regional nerve blocks, in situations when long acting neuraxial morphine is not used. This article will review the current data on methods to optimize post CD pain. Data at this time suggest peripheral nerve blocks provide analgesic benefit in cases where intrathecal morphine cannot be utilized or as a rescue technique for refractory pain.     

Neuraxial Morphine

Neuraxial morphine is associated with lower pain scores, longer time to first rescue analgesia, reduced postpartum opioid consumption and less sedation following CD, compared to parenteral opioids, though the risk of pruritus and nausea may be higher.⁷ An analgesic ceiling effect and dose related side-effects with the use of neuraxial morphine have previously been described.^8,9 Higher doses of intrathecal morphine (ITM) (>100-250 mcg) are associated with a prolonged time until first analgesia request (by 4.5 hours) with a higher risk of opioid related side-effects such as pruritus and postoperative nausea and vomiting (PONV) when compared with lower doses (50-100 mcg). Therefore a balance between analgesia and side-effects must be considered for each patient when deciding individual neuraxial morphine dosing strategies.⁹ For epidural administration, a 1-3 mg dose is recommended by SOAP.^5,6,10

Multimodal Analgesia

In addition to neuraxial morphine, NSAIDs and acetaminophen should be administered on a scheduled basis,¹¹ starting preoperatively or intraoperatively,¹² and should be given concurrently.¹³ Furthermore, acetaminophen should be administered in a scheduled rather than as needed manner, with preference for sole agents rather than acetaminophen-opioid combination preparations, as these provide comparable analgesia with significant opioid sparing effects.^14,15 This regimen avoids the risk of exceeding the maximum recommended dose of acetaminophen and restricts the use of oral opioids to only in the event of breakthrough pain. 

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Data at this time suggest peripheral nerve blocks provide analgesic benefit in cases where intrathecal morphine cannot be utilized or as a rescue technique for refractory pain.

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In addition to its antiemetic effects, intravenous dexamethasone might provide a useful analgesic effect after CD¹⁶ and can be considered as a component of the multimodal analgesic regimen.

Transversus Abdominis Plane Block (TAPB)

Indication

The transversus abdominis plane block (TAPB) has been the most investigated regional anesthesia technique in this patient population. Several meta-analyses have concluded that TAPB provides postoperative opioid-sparing and improved analgesia in patients who do not receive ITM. This is not surprising given that TAPB is less effective for treating visceral pain, compared to ITM which treats visceral and somatic components. When ITM is used, additional analgesic benefit from TAPB has not been demonstrated.^17-19 TAPB should therefore mostly be considered when long-acting neuraxial opioids are not used, as occurs with CD performed under general anesthesia or if long-acting neuraxial opioids are contraindicated or not available. TAPB may be useful as a rescue technique, such as in cases of severe breakthrough postpartum pain or in women requiring escalating doses of opioids.²⁰ 

Local Anesthetic and Dosing

Doses of ≤50 mg bupivacaine equivalents (20 ml 0.25% bupivacaine on each side, for example) are recommended on each side to balance analgesia efficacy with risk of local anesthetic systemic toxicity (LAST).²¹ The role of liposomal bupivacaine, which provides longer duration of analgesia, shows some promise in the CD setting. A recent study reported that TAPB with liposomal bupivacaine was associated with 52% reduction in postoperative opioid consumption compared with TAPB with immediate-release bupivacaine, when used in the context of multimodal analgesia involving neuraxial morphine with scheduled NSAIDs and acetaminophen.²² However, further studies are needed to corroborate these findings prior to recommending its routine use.

Approach

Significantly longer time to request supplemental analgesia by about 6.5 hours and a decrease in opioid consumption by 30% were reported in patients receiving a TAPB with the posterior compared to lateral approach following CD performed under an opioid-free spinal anesthetic.²³ This may be explained by broader dermatomal coverage provided by a more posterior technique (Table 1).²⁴ 

 

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Table 1: Approaches to the transversus abdominis plane block (TAPB).

TAPB Type	Local Anesthetic Target	Dermatomal Coverage
Lateral	Between the IO and TA muscles	T10-12*
Posterior	Injection after the TA tapers, within the IO/EO aponeurosis and anterior to QL muscle	T9-T12*

*The lateral approach reliably covers T10-T11, with less predictable coverage to T12, while the posterior approach reliably covers T10-T12, with frequent coverage of T9 and occasional coverage to L1.²⁴

TAPB, transversus abdominis plane block; TA, transversus abdominis; IO, internal oblique; EO, external oblique; QL, quadratus lumborum

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Quadratus Lumborum Block (QLB)

Indication

The quadratus lumborum block (QLB) has gained popularity due to the promise of paravertebral spread and thereby visceral coverage. However, when compared to or in combination with ITM, the QLB does not provide additional analgesic benefit.^19,25-28  In the absence of ITM, studies have reported that both the posterior and anterior QLB approach provides superior analgesia in comparison to either a posterior or lateral TAPB approach.^29-31 Conversely, a recent network meta-analysis concluded no difference in analgesia when TAPB was compared to QLB.¹⁹ Since all QLB approaches (lateral, posterior, and anterior/transmuscular) and TAPB approaches (posterior and lateral) were combined and several indirect comparisons were included, more studies directly comparing the different approaches of QLB vs TAPB are needed to assess if there is a superior technique and approach based on location of local anesthetic deposition. 

Approach

There are three common approaches to the QLB including the lateral, posterior, and anterior (Table 2).³² There is limited data on a fourth type which refers to intramuscular injection of local anesthetic into the QLB muscle itself.³³ Lower opioid consumption for CD pain with the anterior versus posterior approach was reported in one study,³⁴ while another concluded that combined anterior and posterior blocks provide superior analgesia than either block alone (Table 3). ³⁵ The optimal approach for CD pain remains to be determined.

 

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Table 2: Approaches to the quadratus lumborum block (QLB).

QLB Type	Local Anesthetic Target	Dermatomal Coverage32
Lateral	Between the IO and TA muscles	T12-L1
Posterior	Lumbar interfascial triangle which is posterior to the QL an deep to the erector spinae muscle	T4-L1
Anterior	Anterior to the QL muscle at the level of L4 vertebrae (between psoas major muscle and QL muscle)	T4-L1

QLB; quadratus lumborum block; TA, transversus abdominis; QL, quadratus lumborum.

 

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Table 3: Summary of the randomized controlled trials for QLB approaches for CD pain.

*P <0.001

ITM, intrathecal morphine; PQLB, posterior quadratus lumborum block; AQLB, anterior quadratus lumborum block; iQLB, intramuscular quadratus lumborum block; EA, epidural analgesia; VAS, visual analog score

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Erector Spinae Plane Block (ESPB)

Data regarding the ESPB are encouraging but limited. The block is typically performed at T9 using an in-plane approach under ultrasound guidance. A recent meta-analysis concluded that ESPB may be associated with reduced postoperative opioid consumption compared to control, but the quality of evidence was very low.³⁶ Similar to QLB, the analgesia provided with ESPB may be superior to that provided by TAPB in the absence of neuraxial morphine, but data are limited.^37,38

Ilioinguinal-Iliohypogastric Nerve Block (II-IH)

A recent network meta-analysis concluded that the use of the II-IH nerve block was associated with a significant reduction of 24-hr opioid consumption and a decrease in PONV compared to either systemic analgesia alone or a placebo block.³⁹ The authors also reported a reduction in pain scores and a longer time to first request for rescue analgesics. However, the quality of evidence was low due to significant heterogeneity among the included trials. Furthermore, only two of the included trials administered ITM to the study participants. 

Ilioinguinal-TAP Block (i-TAP)

The ilioinguinal-TAP (i-TAP) block is a combination of an II-IH nerve block with a TAP block to address sparing of the L1 dermatome in a significant proportion of TAPBs.⁴⁰ In a randomized controlled trial comparing the i-TAP block plus ITM to ITM alone as part of a multimodal analgesia strategy in women who underwent CD, opioid consumption and pain scores were lower in the i-TAP plus ITM group.⁴¹ Further studies are needed to confirm these findings.

Wound Infiltration

Local anesthetic wound infiltration or infusion through a wound catheter have also been shown to provide opioid sparing effects following CD in women who do not receive ITM.^18,42 In the presence of ITM, these techniques do not provide analgesic benefit in the first 24 hours. A recent study, however, reported an almost 50% reduction in median opioid consumption with wound infusion from 24-48hr in women who received a multimodal regimen incorporating ITM, but the study was not powered for this endpoint and the results were not statistically significant.⁴³ Placement of the wound catheter below the fascia is associated with 40% less opioid consumption compared to placement above the fascia.⁴⁴ A recent network meta-analysis reported comparable analgesia with the use of local anesthetic infiltration/infusion to that provided with TAPB in the absence of ITM.¹⁸ 

Special Circumstances 

It has previously been determined that up to 15% of patients experience severe acute post-cesarean pain in the first 24 to 48 hours, despite multimodal analgesia including neuraxial long-acting opioids (usually preservative free morphine).^3,45 For these specific patients and under special circumstances, enhanced approaches to tailor the intraoperative anesthesia and postoperative analgesia are beneficial.⁴⁶

Enhanced dosing of ITM (up to 300 mcg) has been shown to be effective in patients predicted to experience severe pain after CD,⁴⁷ and such dosing requires adherence to SOAP Monitoring Recommendations for respiratory depression,⁴⁸ with hourly monitoring in the first 12 hours. 

Additional strategies to consider may include neuraxial clonidine, either epidurally (50-100 mcg) or intrathecally (30-60 mcg or 0.5mcg/kg), with benefits including increased duration of surgical block and time to first analgesia rescue, anti-hyperalgesia, and reduced opioid consumption in patients with opioid use disorder.^49-52 However, clonidine is associated with increased risk of sedation and it should be noted that there is a Food and Drug Administration (FDA) black box warning against the use of clonidine due to the risk of maternal hypotension. Similarly, dexmedetomidine, given intravenously or intrathecally as off-label use, appears to be an effective analgesic adjuvant,^53-55 but may cause maternal bradycardia and sedation, warrants further study, and is not currently FDA-approved for intrathecal use.

Conclusion

ITM as part of a stepwise multimodal analgesia strategy remains the gold standard for post-CD analgesia. In clinical scenarios where ITM is not utilized, regional nerve block techniques (TABP and QLB are the most-well studied) can be a beneficial opioid-sparing analgesic strategy. In the absence of ITM, QLB shows the most promise but due the multiple different possible approaches, further investigation on the optimal technique and LA dose is required before further conclusions can be made. Much remains to be learned about ESPB, II-IH, and i-TAP blocks, and future study is needed to determine how these blocks or combinations of blocks perform against the QLB when ITM cannot be given. Additionally, more data on optimal LA dose, combination of blocks, and the role of liposomal bupivacaine are needed. Enthusiasm for peripheral nerve blocks must be balanced with the current evidence that demonstrates the unequivocal superiority of ITM, therefore the authors recommend prioritizing ITM whenever able in concert with scheduled non-opioid oral analgesics.

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Beth VanderWielen, MD, is a staff anesthesiologist and clinical adjunct assistant professor in the department of Anesthesia at the University of Wisconsin School of Medicine and Public Health, Gundersen Health System in Madison, WI.

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Unyime Ituk, MBBS, FCARCSI, is the obstetrical anesthesia division chief and clinical associate professor in the department of Anesthesia at the University of Iowa Carver College of Medicine in Iowa City, IA.

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Ruth Landau, MD, is the immediate past president of SOAP, a Virginia Apgar professor of anesthesiology, and director of obstetric anesthesia at Columbia University Irving Medical Center in New York, NY.

Disclosure: Dr. Landau serves on the Research Advisory Board of Pacira Pharmaceuticals and serves on the Executive Editorial Board of Regional Anesthesia and Pain Medicine.

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Pervez Sultan, MBChB, FRCA, MD (Res), is an associate professor of anesthesiology at Stanford University School of Medicine in Stanford, CA.

Disclosure: Dr. Sultan is an Arline and Pete Harman Endowed Faculty Scholar of the Stanford Maternal and Child Health Research Institute.

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Ashraf Habib, MBBCh, MSc, MHSc, FRCA, is women’s anesthesia division chief and professor of anesthesiology and obstetrics and gynecology at Duke University Medical Center in Durham, NC.

Disclosure: Dr. Habib has received research support from Haisco USA and Pacira Pharmaceuticals. He is also a consultant for Vertex Pharmaceuticals and has served on the Advisory Board for Heron Therapeutics and MDoloris.

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References

1. Ciechanowicz S, Setty T, Robson E, et al. Development and evaluation of an obstetric quality-of-recovery score (ObsQoR-11) after elective Caesarean delivery. Br J Anaesth 2019;122(1):69-78. https://doi.org/10.1016/j.bja.2018.06.011.
2. Sultan P, Jensen SE, Taylor J, et al. Proposed domains for assessing postpartum recovery: a concept elicitation study. BJOG 2022;129(1):9-20. https://doi.org/10.1111/1471-0528.16937.
3. Eisenach JC, Pan PH, Smiley R, et al. Severity of acute pain after childbirth, but not type of delivery, predicts persistent pain and postpartum depression. Pain 2008;140(1):87-94. https://doi.org/10.1016/j.pain.2008.07.011.
4. Karlström A, Engström-Olofsson R, Norbergh KG, et al. Postoperative pain after cesarean birth affects breastfeeding and infant care. J Obstet Gynecol Neonatal Nurs 2007;36(5):430-40. https://doi.org/10.1111/j.1552-6909.2007.00160.x
5. Bollag L, Lim G, Sultan P, et al. Society for Obstetric Anesthesia and Perinatology: consensus statement and recommendations for enhanced recovery after cesarean. Anesth Analg 2021;132(5):1362-77. https://doi.org/10.1213/ANE.0000000000005257.
6. Roofthooft E, Joshi GP, Rawal N, et al; PROSPECT Working Group of the European Society of Regional Anaesthesia and Pain Therapy and supported by the Obstetric Anaesthetists’ Association. PROSPECT guideline for elective caesarean section: updated systematic review and procedure-specific postoperative pain management recommendations. Anaesthesia 2021;76(5):665-80. https://doi.org/10.1111/anae.15339.
7. Bonnet MP, Mignon A, Mazoit JX, et al. Analgesic efficacy and adverse effects of epidural morphine compared to parenteral opioids after elective caesarean section: a systematic review. Eur J Pain 2010;14(9):894.e1-9. https://doi.org/10.1016/j.ejpain.2010.03.003.
8. Sultan P, Gutierrez MC, Carvalho B. Neuraxial morphine and respiratory depression: finding the right balance. Drugs 2011;71(14):1807-19. https://doi.org/10.2165/11596250-000000000-00000.
9. Sultan P, Halpern SH, Pushpanathan E, et al. The effect of intrathecal morphine dose on outcomes after elective cesarean delivery: a meta-analysis. Anesth Analg 2016;123(1):154-64. https://doi.org/10.1213/ANE.0000000000001255.
10. Neall G, Bampoe S, Sultan P. Analgesia for caesarean section. BJA Educ 2022;22(5):197-203. https://doi.org/10.1016/j.bjae.2021.12.008.
11. Yefet E, Taha H, Salim R, et al. Fixed time interval compared with on-demand oral analgesia protocols for post-caesarean pain: a randomised controlled trial. BJOG 2017;124(7):1063-70. https://doi.org/10.1111/1471-0528.14546.
12. Herbert KA, Yurashevich M, Fuller M, et al. Impact of a multimodal analgesic protocol modification on opioid consumption after cesarean delivery: a retrospective cohort study. J Matern Fetal Neonatal Med 2022;35(24):4743-9. https://doi.org/10.1080/14767058.2020.1863364.
13. Forkin KT, Mitchell RD, Chiao SS, et al. Impact of timing of multimodal analgesia in enhanced recovery after cesarean delivery protocols on postoperative opioids: a single center before-and-after study. J Clin Anesth 2022 Sep;80:110847. https://doi.org/10.1016/j.jclinane.2022.110847.
14. Smith AM, Young P, Blosser CC, et al. Multimodal stepwise approach to reducing in-hospital opioid use after cesarean delivery: a quality improvement initiative. Obstet Gynecol 2019;133(4):700-6. https://doi.org/10.1097/AOG.0000000000003156.
15. Valentine AR, Carvalho B, Lazo TA, et al. Scheduled acetaminophen with as-needed opioids compared to as-needed acetaminophen plus opioids for post-cesarean pain management. Int J Obstet Anesth 2015;24(3):210-6. https://doi.org/10.1016/j.ijoa.2015.03.006.
16. Singh NP, Makkar JK, Yadav N, et al. The analgesic efficacy of intravenous dexamethasone for post-caesarean pain: a systematic review with meta-analysis and trial sequential analysis. Eur J Anaesthesiol 2022;39(6):498-510. https://doi.org/10.1097/EJA.0000000000001626.
17. Mishriky BM, George RB, Habib AS. Transversus abdominis plane block for analgesia after Cesarean delivery: a systematic review and meta-analysis. Can J Anaesth 2012;59(8):766-78. https://doi.org/10.1007/s12630-012-9729-1.
18. Sultan P, Patel SD, Jadin S, et al. Transversus abdominis plane block compared with wound infiltration for postoperative analgesia following cesarean delivery: a systematic review and network meta-analysis. Can J Anaesth 2020;67(12):1710-27. https://doi.org/10.1007/s12630-020-01818-x.
19. El-Boghdadly K, Desai N, Halpern S, et al. Quadratus lumborum block vs. transversus abdominis plane block for caesarean delivery: a systematic review and network meta-analysis. Anaesthesia 2021;76(3):393-403. https://doi.org/10.1111/anae.15160.
20. Sultan P, Sultan E, Carvalho B. Regional anaesthesia for labour, operative vaginal delivery and caesarean delivery: a narrative review. Anaesthesia 2021;76 Suppl 1:136-47. https://doi.org/10.1111/anae.15233.
21. Ng SC, Habib AS, Sodha S, et al. High-dose versus low-dose local anaesthetic for transversus abdominis plane block post-Caesarean delivery analgesia: a meta-analysis. Br J Anaesth 2018;120(2):252-63. https://doi.org/10.1016/j.bja.2017.11.084.
22. Nedeljkovic SS, Kett A, Vallejo MC, et al. Transversus abdominis plane block with liposomal bupivacaine for pain after cesarean delivery in a multicenter, randomized, double-blind, controlled trial. Anesth Analg 2020;131(6):1830-9. https://doi.org/10.1213/ANE.0000000000005075.
23. Faiz SHR, Alebouyeh MR, Derakhshan P, et al. Comparison of ultrasound-guided posterior transversus abdominis plane block and lateral transversus abdominis plane block for postoperative pain management in patients undergoing cesarean section: a randomized double-blind clinical trial study. J Pain Res 2017;11:5-9. https://doi.org/10.2147/JPR.S146970.
24. Furuya T, Kato J, Yamamoto Y, et al. Comparison of dermatomal sensory block following ultrasound-guided transversus abdominis plane block by the lateral and posterior approaches: a randomized controlled trial. J Anaesthesiol Clin Pharmacol 2018;34(2):205-10. https://doi.org/10.4103/joacp.JOACP_295_15.
25. Hussain N, Brull R, Weaver T, et al. Postoperative analgesic effectiveness of quadratus lumborum block for cesarean delivery under spinal anesthesia. Anesthesiology 2021;134(1):72-97. https://doi.org/10.1097/ALN.0000000000003611.
26. Singh N, Makkar J, Borle A, et al. The analgesic efficacy of quadratus lumborum block in caesarean delivery: a meta-analysis and trial sequential analysis. J Anesth 2020;34(6):814-24. https://doi.org/10.1007/s00540-020-02822-7.
27. Tan H, Taylor C, Weikel D, et al. Quadratus lumborum block for postoperative analgesia after cesarean delivery: A systematic review with meta-analysis and trial-sequential analysis. J Clin Anesth 2020;67:110003. https://doi.org/10.1016/j.jclinane.2020.110003. 
28. Xu M, Tang Y, Wang J, et al. Quadratus lumborum block for postoperative analgesia after cesarean delivery: a systematic review and meta-analysis. Int J Obstet Anesth 2020;42:87-98. https://doi.org/10.1016/j.ijoa.2020.02.005. 
29. Blanco R, Ansari T, Riad W, et al. Quadratus lumborum block versus transversus abdominis plane block for postoperative pain after cesarean delivery: a randomized controlled trial. Reg Anesth Pain Med 2016;41(6):757-62. https://doi.org/10.1097/AAP.0000000000000495.
30. Verma K, Malawat A, Jethava D, et al. Comparison of transversus abdominis plane block and quadratus lumborum block for post-caesarean section analgesia: a randomised clinical trial. Indian J Anaesth 2019;63(10):820-6. https://doi.org/10.4103/ija.IJA_61_19. 
31. Jadon A, Amir M, Sinha N, et al. Quadratus lumborum or transversus abdominis plane block for postoperative analgesia after cesarean: a double-blinded randomized trial. Braz J Anesthesiol 2022;72(4):472-8. https://doi.org/10.1016/j.bjane.2021.06.014. 
32. Elsharkawy H, Bendtsen T. Ultrasound-guided transversus abdominis plane and quadratus lumborum nerve blocks. NYSORA. https://www.nysora.com/topics/regional-anesthesia-for-specific-surgical-procedures/abdomen/ultrasound-guided-transversus-abdominis-plane-quadratus-lumborum-blocks/#toc_PATIENT-POSITIONING-AND-EQUIPMENT-SELECTION. Accessed August 2022.
33. Yoshida K, Tanaka S, Watanabe K, et al. The effectiveness of the intramuscular quadratus lumborum block in postoperative analgesia after cesarean section with vertical incision: a randomized, double-blinded placebo-controlled study. J Anesth 2020;34(6):849-56. https://doi.org/10.1007/s00540-020-02829-0. 
34. Koksal E, Aygun H, Genç C, et al. Comparison of the analgesic effects of two quadratus lumborum blocks (QLBs), QLB type II vs QLB type III, in caesarean delivery: a randomised study. Int J Clin Pract 2021;75(10):e14513. https://doi.org/10.1111/ijcp.14513. 
35. Kang W, Lu D, Yang X, et al. Postoperative analgesic effects of various quadratus lumborum block approaches following cesarean section: a randomized controlled trial. J Pain Res 2019;12:2305-12. https://doi.org/10.2147/JPR.S202772.
36. Ribeiro Junior IDV, Carvalho VH, Brito LGO. Erector spinae plane block for analgesia after cesarean delivery: a systematic review with meta-analysis. Braz J Anesthesiol. Published Online First: 18 Oct 2021. doi: 10.1016/j.bjane.2021.09.015. 
37. Boules ML, Goda AS, Abdelhady MA, et al. Comparison of Analgesic Effect Between Erector Spinae Plane Block and Transversus Abdominis Plane Block After Elective Cesarean Section: A Prospective Randomized Single-Blind Controlled Study. J Pain Res. 2020 May 19;13:1073-1080. doi: 10.2147/JPR.S253343.
38. Malawat A, Verma K, Jethava D, et al. Erector spinae plane block and transversus abdominis plane block for postoperative analgesia in cesarean section: A prospective randomized comparative study. J Anaesthesiol Clin Pharmacol. 2020 Apr-Jun;36(2):201-206. doi: 10.4103/joacp.JOACP_116_19. [published Online First 15 June 2020].  
39. Singh NP, Makkar JK, Bhatia N, et al. The analgesic effectiveness of ilioinguinal-iliohypogastric block for caesarean delivery: A meta-analysis and trial sequential analysis. Eur J Anaesthesiol. 2021 Aug 1;38(Suppl 2):S87-S96. doi: 10.1097/EJA.0000000000001379. 
40. Lee TH, Barrington MJ, Tran TM, et al. Comparison of extent of sensory block following posterior and subcostal approaches to ultrasound-guided transversus abdominis plane block. Anaesth Intensive Care. 2010 May;38(3):452-60. doi: 10.1177/0310057X1003800307.
41. Staker JJ, Liu D, Church R, et al. A triple-blind, placebo-controlled randomised trial of the ilioinguinal-transversus abdominis plane (I-TAP) nerve block for elective caesarean section. Anaesthesia. 2018 May;73(5):594-602. doi: 10.1111/anae.14222. [published Online First 29 Jan 2018].
42. Adesope O, Ituk U, Habib AS. Local anaesthetic wound infiltration for postcaesarean section analgesia: A systematic review and meta-analysis. Eur J Anaesthesiol. 2016 Oct;33(10):731-42. doi: 10.1097/EJA.0000000000000462.
43. Barney EZ, Pedro CD, Gamez BH, et al. Ropivacaine and Ketorolac Wound Infusion for Post-Cesarean Delivery Analgesia: A Randomized Controlled Trial. Obstet Gynecol. 2020 Feb;135(2):427-435. doi: 10.1097/AOG.0000000000003601.40.
44. Rackelboom T, Strat SL, Silvera S, et al. Improving continuous wound infusion effectiveness for postoperative analgesia after cesarean delivery: a randomized controlled trial. Obstet Gynecol. 2010 Oct;116(4):893-900. doi: 10.1097/AOG.0b013e3181f38ac6.
45. Orbach-Zinger S, Aviram A, Fireman S, et al. Severe pain during local infiltration for spinal anaesthesia predicts post-caesarean pain. Eur J Pain. 2015 Oct;19(9):1382-8. doi: 10.1002/ejp.737. [published Online First: 29 May 2015]. 
46. Landau R, Richebé P. Tailoring postoperative pain management with a procedure-specific approach: how to best apply this concept to caesarean deliveries. Anaesthesia. 2021 May;76(5):587-589. doi: 10.1111/anae.15251. [published Online First: 14 Oct 2020]. 
47. Booth JL, Harris LC, Eisenach JC, et al. A Randomized Controlled Trial Comparing Two Multimodal Analgesic Techniques in Patients Predicted to Have Severe Pain After Cesarean Delivery. Anesth Analg. 2016 Apr;122(4):1114-9. doi: 10.1213/ANE.0000000000000695.
48. Bauchat JR, Weiniger CF, Sultan P, et al. Society for Obstetric Anesthesia and Perinatology Consensus Statement: Monitoring Recommendations for Prevention and Detection of Respiratory Depression Associated With Administration of Neuraxial Morphine for Cesarean Delivery Analgesia. Anesth Analg. Aug 2019;129(2):458-474. doi:10.1213/ANE.0000000000004195.
49. Cook MI, Kushelev M, Coffman JH, et al. Analgesic Outcomes in Opioid Use Disorder Patients Receiving Spinal Anesthesia with or without Intrathecal Clonidine for Cesarean Delivery: A Retrospective Investigation. J Pain Res. 2022 Apr 21;15:1191-1201. doi: 10.2147/JPR.S358045.
50. Hoyt MR, Shah U, Cooley J, et al. Use of epidural clonidine for the management of analgesia in the opioid addicted parturient on buprenorphine maintenance therapy: an observational study. Int J Obstet Anesth. 2018 May;34:67-72. doi: 10.1016/j.ijoa.2018.01.001. [published Online First: 31 Jan 2018].
51. Allen TK, Mishriky BM, Klinger RY, et al. The impact of neuraxial clonidine on postoperative analgesia and perioperative adverse effects in women having elective Caesarean section-a systematic review and meta-analysis. Br J Anaesth. 2018 Feb;120(2):228-240. doi: 10.1016/j.bja.2017.11.085. [published Online First: 5 Jan 2018]. 
52. Crespo S, Dangelser G, Haller G. Intrathecal clonidine as an adjuvant for neuraxial anaesthesia during caesarean delivery: a systematic review and meta-analysis of randomised trials. Int J Obstet Anesth. 2017 Nov;32:64-76. doi: 10.1016/j.ijoa.2017.06.009. [published Online First: 27 June 2017].
53. Davis PR, Sviggum HP, Delaney DJ, et al. Intravenous Dexmedetomidine as an Adjunct to Neuraxial Anesthesia in Cesarean Delivery: A Retrospective Chart Review. Anesthesiol Res Pract. 2021 Dec 27;2021:9887825. doi: 10.1155/2021/9887825.
54. Li XX, Li YM, Lv XL, et al. The efficacy and safety of intrathecal dexmedetomidine for parturients undergoing cesarean section: a double-blind randomized controlled trial. BMC Anesthesiol. 2020 Aug 3;20(1):190. doi: 10.1186/s12871-020-01109-4.
55. Shen QH, Li HF, Zhou XY, et al. Dexmedetomidine as an adjuvant for single spinal anesthesia in patients undergoing cesarean section: a system review and meta-analysis. J Int Med Res. 2020 May;48(5):300060520913423. doi: 10.1177/0300060520913423.