Currently, cesarean section is an important and the only effective method to solve high-risk pregnancies and dystocia; it is crucial to provide perfect analgesia after operation. At present, the clinical analgesic methods after cesarean section are mainly patient-controlled epidural analgesia (PCEA) and PCIA, supplemented by oral or intramuscular injection of analgesics, which have their own analgesic advantages, but each one still has different limitations [17]. Studies have shown that PCEA has a good analgesic effect [12], which can not only increase the enthusiasm for breastfeeding, but also accelerate the recovery of gastrointestinal function [18]; however, there are some related complications such as lower limb weakness, numbness and urinary retention [19]. Hence, there is currently a clear downward trend in the amount of post-cesarean analgesia clinically used by PCEA. At the same time, PCIA also attracted the attention of anesthesiologists. In this study, for humanitarian reasons, we set postoperative analgesia using PCIA alone to a positive control group.

Satisfaction with the analgesic effects of PCIA is generally directly related to the type and concentration of analgesics. Currently, the preferred analgesic in the PCIA after cesarean section is sufentanil [20]. When the concentration of sufentanil is not enough, the analgesic effect is unsatisfactory, but when the concentration of drug is too high, side effects such as nausea, vomiting, skin itching and so on are likely to occur. In addition, the routine drugs such as oxytocin after cesarean section make the incidence of maternal nausea and vomiting higher [21], so the anesthesiologist will always hear complaints about the side effects of the analgesic drug affecting the puerperae during postoperative follow-up. The dose of sufentanil used in this study was set based on rich clinical experience and research data from multiple investigators, and its safety and efficacy have also been validated in clinical practice. However, the gastrointestinal side effects of group A with the highest dose of sufentanil in this study were significantly higher than those of the other two groups [22,23,24,25,26,27], so its clinical application needs to be further improved. Although PCIA has an acceptable analgesic effect on pain at rest, it has poor analgesic effect on wound pain caused by turning over, pressing the uterus and abdominal wall tension during breastfeeding [28].

With the development of the concept of enhanced recovery after surgery (ERAS), MMA has also emerged [29]. As a regional block technique and an important part of MMV, TAPB is simple and safe to operate and has a satisfactory analgesic effect on the abdominal wall and has few side effects. Therefore, in our study we combined PCIA with TAPB to try to explore the most suitable analgesia regimen for puerperae after cesarean section.

As a cornerstone of the study, we first evaluated the safety of three methods. This study applied TAPB and PCIA analgesia alone or in combination to 180 puerperae after cesarean section, and it was observed that the SBP, DBP, HR and SpO2 of the three groups at five time points were within the scope of clinical normality, demonstrating that the methods used in the three groups were all safe. At the same time, it was found that the patient satisfaction of groups A and B was high, which proved that both regimens could be effectively applied to post-cesarean analgesia. In the post-cesarean analgesic group with PCIA alone, we routinely added haloperidol 2.5 mg to PCIA to prevent side effects such as nausea and vomiting caused by sufentanil. So, it was also found that the number of gastrointestinal side effects of the puerperae was still higher than those of the other two groups. The US Food and Drug Administration (FDA) reported that nine patients had a Q-T interval prolonged after intravenous injection of low-dose haloperidol and led to cardiac accident-related events [30]. Therefore, although the postoperative analgesia group with PCIA alone after cesarean section is convenient to operate, it carries a greater risk to women with cardiac insufficiency and more obvious side effects.

By comparing the static and dynamic VAS score of three groups of puerperae at five different time points after surgery, it was found that TAPB by using ropivacaine could significantly reduce maternal pain within 12 h after surgery, but had little effect on the score after 12 h. Consequently, the puerperae in group A pressed the analgesic pump earlier. These results demonstrate that PCIA combined with TAPB can be more effective in preventing pain in the short term after surgery, but cannot completely replace the application of opioids in post-cesarean analgesia. On the other hand, it is worth noting that the VAS score of group C increased significantly after 12 h postoperatively, which was higher than in groups A and B, and remedial measures were needed. In addition, the Ramsay score and BCS score of puerperae in group C after 12 h were lower than those in groups A and B, indicating that the regimen of group C was insufficient for continuous analgesia. One potential explanation for this may be the underdose of sufentanil in PCIA. These findings are in line with the research results of scholars such as P. Fusco [31] and Mishriky [32], so the implementation of TAPB after cesarean section can significantly improve the analgesic effect and reduce the dosage of opioids. However, their study did not address the optimal dose of sufentanil. In this study, through the analysis of various indicators of three groups of puerperae, it was found that PCIA combined with TAPB can reduce the dosage of sufentanil in PCIA, and when the dosage is reduced to 1.5 μg/kg, the analgesic satisfaction is the best.

Nonetheless, the successful and effective implementation of TAPB nowadays in clinical practice still requires ultrasonic testing equipment and professional technical support. Non-visual TAPB procedures have a high risk of puncture and low success rates and may even damage the liver and intestines in the abdominal cavity [9, 33]. With the wide application of visual ultrasound technology in the field of clinical anesthesia, we can clearly distinguish the direction of tissues and the scope of drug diffusion, with high puncture success and few complications [34]. In this study, the implementation of TAPB was performed by the same fully qualified clinical anesthesiologist, who was proficient in TAPB puncture technology, coupled with the application of ultrasound visualization technology, which strongly guaranteed the accuracy and safety of the operation.

The local anesthetic selected for TAPB in our study is ropivacaine hydrochloride injection [35], which is a long-acting amide local anesthetic; it mainly exerts a local anesthetic effect by inhibiting the pain conduction fibers of nerves. The concentration of ropivacaine used was 0.4%, no patients had neurotoxicity-related. Effects and the duration of analgesia was about 6–12 h, so it can be seen that the concentration of ropivacaine designed in this study is safe and effective. Previous studies have performed TAPB in post-cesarean section patients by setting different concentration gradients of ropivacaine. The results showed [36] that when the concentration of ropivacaine was > 0.2%, and the toxic dose was not exceeded; the combination of TAPB and PCIA for postoperative analgesia after cesarean section was safe and effective. The use of 0.375% ropivacaine for TAPB is preferred in clinical work [37], which also supports the setting of ropivacaine concentration in this study. In addition, this study has demonstrated that by combining TAPB, it is feasible to reduce the dose of sufentanil, thereby avoiding the use of droperidol. This is undoubtedly that the best choice for postoperative analgesia for puerperae with cardiac insufficiency.

This study is a single-center study with a small sample size, and there are limitations in terms of regions and races. The grouping on the dose of the drug is still not detailed enough. In the follow-up study, we will use better methods such as the PASS to calculate the sample size, further expand the sample size to include multi-center clinical cases and establish more detailed drug dose groupings, further explore the model of TAPB combined with PCIA for postoperative analgesia and try to explore more analgesic methods combined with MMA to seek the best effect of post-cesarean analgesia.