This study was conducted to compare the effects of two analgesia methods on pain relief during the 24 hours after CS in an Iraqi population. The study's findings showed that the pain intensity of patients in both PCA and TAP block groups increased during the 4 hours after surgery and then gradually decreased over the next 20 hours. In this study, we demonstrated that patients who received TAP block tolerate less pain after CS than those under PCA. This difference in pain intensity was observed during the first 6 hours after CS and disappeared within 12 and 24 hours after the procedure.
The surgical TAP block is a new and easy technique for postoperative pain management that any obstetrician can learn. This effective method provides long-lasting analgesia and reduces the use of rescue analgesics. As an adjunct to multimodal pain management, the TAP block improves patient satisfaction after CS. Salem et al. indicated that intravenous PCA outperformed the TAP block because of its impact on the visceral response, whereas the TAP block was favored to prevent the systemic effects associated with the opioids used in PCA (
10). The findings of the present study were in contrast to those of Salem et al. In the present study, pain intensity, as calculated by the SF-MPQ, was significantly lower during the first 6 hours after CS in the TAP block group compared to the PCA group. However, when pain intensity was measured using a numeric rating scale, this difference was observed only at 4 and 6 hours post-surgery. The observed difference between the two studies could be attributed to the use of different anesthesia techniques during the operation and the varying methods employed for recording postoperative pain intensity. Although the pain rating scale offers a one-dimensional view of pain, one of the strengths of this study is the use of the SF-MPQ. This tool assesses pain both qualitatively and quantitatively, allowing patients to provide more precise information to anesthesiologists. As a result, anesthesiologists can adjust postoperative analgesia by considering the different descriptions of pain intensity provided by patients (
12,
13). Another study indicated that using a patient-controlled pethidine pump significantly reduced pain compared to a TAP block procedure with 0.25% bupivacaine (
14).
The findings of analgesia in the present study were consistent with some other studies. One study found that using TAP block analgesia after laparotomies led to lower pain levels and reduced opioid requirements compared to a PCA method (
15). Another study indicated that the use of TAP block analgesia after gynecological surgeries under general anesthesia significantly reduced the patients' pain 8 to 12 hours after surgery compared to the control group (
16). In addition to the analgesia technique employed, one of the key reasons for the existence of conflicting evidence in analgesia studies is related to the type of drug and its concentration (
17).
Understanding the type and severity of pain is crucial for selecting the most effective analgesia with minimal side effects, thereby reducing the patient's discomfort. The specific circumstances of the patient determine the choice between various opioid and non-opioid analgesic drugs (
18). In the case of a CS, the mother's successful recovery with minimal pain is closely linked to the health of her baby. Therefore, it is essential to prescribe an effective analgesic that alleviates the postpartum pain while also minimizing side effects for both the mother and the baby (
19).
Nalbuphine is a morphine-like analgesic that acts as an agonist on both μ and κ receptors, providing strong analgesic effects. This makes it a suitable option for alleviating gynecological pain, such as severe contractions during childbirth (
20). The superior analgesic effects of nalbuphine, along with its low side effects and lack of neurotoxicity, have made it a suitable option for post-CS analgesia, which can be used alone or in combination with other analgesic agents, such as bupivacaine (
20,
21). Bupivacaine is a long-acting local anesthetic that has been mainly used in operations under general anesthesia due to its good properties in controlling postoperative complications. The binding of this drug to plasma proteins has increased its half-life to approximately 5.5 hours (
22). Numerous studies have examined various concentrations of this drug, both alone and in combination with other analgesic agents, to assess their effectiveness in reducing postoperative pain, often yielding conflicting results (
23-
25). In the present study, the TAP block and PCA groups were similar in terms of postoperative complications, including heart rate, respiratory rate, nausea, vomiting, and the need for diclofenac suppositories. This suggests that the combination of drugs used in both methods has a comparable effect in controlling post-CS complications.
The findings of our study exhibited that, although the level of the inflammatory marker hs-CRP was within the normal range in both analgesia groups, a significant and positive correlation was observed between hs-CRP levels 24 hours after CS and pain intensity at all measured times in the TAP block group. Postoperative pain is generally caused by inflammation. Bupivacaine can reduce pain intensity through various mechanisms, including epidural block, peripheral nerve block, subarachnoid block, and the blocking of sodium channels in the nerve membrane. Additionally, it increases the threshold of the action potential and decreases its speed, as well as the speed of nerve impulses (
26,
27). The results of an in vivo study on a mouse model have demonstrated that bupivacaine reduces NF-κB expression and increases IκB expression, leading to effective relief of inflammation‑induced pain (
28). A study has shown that in women undergoing CS with spinal anesthesia using 0.5% bupivacaine, the intensity of pain measured 6 hours after surgery showed a significant and positive correlation with hs-CRP levels before operation (
29).
This study had several limitations. Since a randomized clinical trial was not feasible, we conducted a quasi-experimental study. Participants were selected from those available, and no randomization was used. Although informed consent was obtained from all participants before they entered the study, many expressed dissatisfaction with the presence of the study administrator at their bedside, prompting completion of questionnaires with the cooperation of the patients' companions. Although the study administrator trained these companions on how to administer the questions and when to complete the questionnaires, variations in how different subjects were asked could introduce bias. According to the companions, questionnaires were sometimes completed later than scheduled, particularly because many patients were sleepy or restless, especially during the first 6 hours after surgery. Nonetheless, at 12 and 24 hours postoperatively, the majority of participants completed the questionnaires themselves on schedule.
4.1. Conclusions
The findings of this study indicated that TAP block analgesia is more effective than PCA in relieving pain in women who have undergone CS within less than 12 hours after the procedure. However, postoperative outcomes, including nausea, vomiting, diclofenac usage, heart rate, respiratory rate, and hematological and inflammatory factors, did not show significant differences between the two analgesia methods. This study also revealed that the severity of pain, measured by the SF-MPQ, in women who had undergone CS and had received TAP block analgesia was directly correlated with the serum level of the inflammatory marker hs-CRP at all assessed time points.