Introduction

Cesarean delivery (CD) is one of the most common surgical procedures performed around the world. On average about 21.1% women gave birth by CD globally, ranging from 5% in sub-Saharan African region to 42.8% in Latin America and the Caribbeans. The rates of CD have been rising in almost all regions since 1990, with about 1.8 million cesarean procedures annually [1]. Even with widespread use of multimodal analgesia in recent decades, severe acute pain after CD has been reported in 28-78% of the patients [2, 3]. CD ranks the ninth for pain severity among 179 different surgical procedures [4]. Severe acute post-cesarean pain is associated with greater opioid usage, delayed functional recovery [5], and increased risk of postpartum depression [6], all of which may negatively impact the ability to care for her baby and breastfeeding success [7]. Also, it is at an increased risk of persistent postsurgical pain for months after CD and may take opioids after hospital discharge [8].

Analgesic management for post-CD analgesia seemingly adopts a one-size-fits-all approach, which may not be suitable to all CD patient. Komatsu et al. conducted a prospective cohort study in patient who underwent vaginal and CD and these patients were followed up daily after discharge until opioid-free and pain-free recovery. The results showed that the upper 20th percentile of patients experienced a significantly greater pain burden than the remainder [9]. These finding suggested that a one-size-fits all approach may not appropriate for all parturient. The gap between available knowledge and inadequate pain therapy may lead to inconsistent analgesic responses among individual patients and some unsatisfactory patients who underwent CD. This narrative review, therefore, aims at reviewing the utility of various tools to predict the severity of acute pain after CD. Since this may help identification of those patients who are at more risk for postoperative pain and personalized approach of analgesic protocol may be needed.

Preoperative pain Screening test and Severity of Acute pain and Opioid Consumption after CD

There were several techniques being used as preoperative testing tools in women undergoing cesarean delivery, including preoperative demographic data and psychometric evaluation, quantitative sensory testing (QST), and local anesthetic infiltration.

Preoperative Demographic data/psychometric Evaluations

In general surgical population, preoperative prognosis factors for poor acute postoperative pain control were studied and found that younger age (OR 1.18), female gender (OR 1.29), higher body mass index (OR 1.02), history of smoking (OR 1.33), depressive symptoms (OR 1.71), anxiety (OR 1.22), sleep difficulties (OR 2.32), and presence of preoperative pain (OR 1.21) or using analgesics (OR 1.54) were significant predictors of poor postoperative pain control [10].

In CD population, the preexisting anxiety (OR 1.93), history of chronic pain (OR 4.12), current tobacco use (OR 2.52), previous CD (OR 1.54), Pfannenstiel incision (OR 3.2), absence of regional anesthesia (OR 3.7) and received intraoperative intravenous ketamine or fentanyl (OR 1.56) were significantly associated with moderate-severe postoperative pain after CD [3, 11, 12].

Preexisting chronic pain has been described in previous studies as the existence of pain as a yes/no answer [13, 14] or by numeric rating scale pain measurement [15, 16], and information regarding the influence of specific chronic pain conditions (e.g., fibromyalgia, migraine, dysmenorrhea). Despite the ongoing debate regarding the precise definition of chronic pain, patients with pre-existing chronic pain conditions often present with symptoms and comorbidities, such as anxiety, depression, poor physical conditioning, and opioid tolerance. Consequently, these patients may experience increased intensity and prolonged duration of postoperative pain.

Also, psychological personalities and pain catastrophizing levels on postoperative analgesia have been investigated. The retrospective cohort study of 2,228 CD patients revealed that patients with anxiety disorders had a higher average pain score (Numeric Rating Scale: 3.9 vs. 3.5, p < 0.001) and required more opioids (morphine equivalents used: 110 vs. 102 mg, p < 0.001) [17]. Ren et al. conducted a prospective cohort study enrolled 778 pregnant women demonstrated that personality traits such as psychoticism and neurocriticism (OR = 1.43, 95% CI = 1.104–1.844), as well as pain catastrophizing (OR = 7.72, 95% CI = 0.657–0.783), were significant factors influencing post-cesarean analgesia [18]. Additionally, psychosocial factors like being unpartnered or unemployed were linked to higher pain scores post-delivery. These results indicate that addressing psychological personality and social support could potentially improve the post-delivery pain experience.

Various preoperative questionnaires have also been investigated as a tool for predicting post-cesarean pain and analgesic consumption. These included the state anxiety inventory (40-itmes), somatosensory amplification scale score (10-items) [19], pain catastrophizing scale (13-itmes), Pittsburgh sleep quality index (19-items), hospital anxiety and depression scale (14-itmes), patient reported outcomes measurement information system anxiety scale and Eysenck personality questionnaire revised short scale (23-items). Nevertheless, these questionnaires are time-consuming and yield only weak to moderate correlations when it comes to predicting postoperative pain. As such, they pose challenges for application in everyday clinical practice. (Table 1)

Table 1 Preoperative screening tools and post-cesarean pain outcomes and analgesic requirement
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The preoperatively applied simple rating questionnaire, which allows patients to rate their anxiety, anticipated pain, analgesic needs, and pain thresholds, have been proposed and it showed to predict the intensity of post-CD pain [23, 24]. Pan et al. found that the three screening questions demonstrated a sensitivity and specificity of 0.68 and 0.67, respectively, for identifying patients in the top 20th percentile for post-CD pain. Another study by Carvalho et al. showed that three slightly different questionnaires were able to predict 45% of the variability of post-CD pain and 21% of the variance in opioid consumption. (Table 2) However, the utility of the questionnaire may require more in other institutions/ setting and focus in low-risk group who receiving the same interventions as those predicted as high-risk.

Table 2 Preoperative three simple rating questions to screen post-CD pain
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Although there is currently no consensus on preoperative demographic, psychometric evaluation or screening tools for post-CD pain, these demographic characteristics and preoperative screening tools may assist clinicians in determining high-risk for severe pain patients and tailoring analgesic regimens to achieve individualized pain management.

Preoperative pain Stimulation Methods

QST defined as quantifiable mechanical (pressure), thermal (warm, heat pain) or electrical stimuli, was used in nearly all the studies.

Pressure Stimulation

Pressure stimulation is usually used to determine pain threshold and pain tolerance. A probe is applied to the pulp of the middle finger, and patients are asked to indicate when they first feel pain (pain threshold) and when they can no longer tolerate the pain (pain tolerance) [27, 28]. In three studies, pressure-induced pain tolerance and threshold were determined using a digital algometer. The results of these studies showed a weak correlation between pressure pain threshold/tolerance and postoperative pain outcomes after CD [2, 27, 28] (Table 3). Another technique using a 180 g Von Frey filament to measure mechanical temporal summation (mTS), a dynamic quantitative sensory testing. The result showed that mTS was significantly correlated with 24-hrs VAS on movement but not correlated with 24 h VAS or VAS at rest [2]. Another study by Ortner et al. using the 180 g Von Frey filament to evaluate scar hyperalgesia around the area of prior CD scars and calculate scar hyperalgesia (SHA) index. The results showed that preoperative SHA index was correlated with postoperative pain severity and wound hyperalgesia at 48 h [29]. Contrary to the results found in Chan et al. study, the mTS was not associated with moderate-severe acute pain after CD [25].

Thermal Stimulation

A hand-held device with a contact probe that can generate a range of temperatures was used. The temperature at which the heat stimulus became painful was determined as the pain threshold, and pain scores in response to the heat stimulus were recorded as suprathreshold stimulus. Three studies were conducted to evaluate the correlation between thermal stimulation and post-CD pain outcomes. The results suggested a weak to moderate correlation [20, 21, 30] (Table 3).

Electrical Stimulation

An electrocutaneous stimulation device was used to generate electrical discharges to determine pain/sensation thresholds. Preoperative electric pain/ sensation thresholds were inversely correlated with postoperative pain scores and analgesic requirement. The literature showed that preoperative electric QST can predict some of post-CD pain. One study reported weak correlation [31] (Table 3). However, another study reported moderate-strong correlation [32]. Some studies evaluating experimental models of pain threshold/tolerance with pressure, electric, and thermal stimuli all demonstrated some correlation with postoperative pain outcomes after CD. However, most of the findings were not consistent, and the correlations were weak to modest in most of the studies. Moreover, these tests required approximately 120 min and additional personnel equipment, and training, making it impractical for routine clinical setting. Therefore, the utility of QSTs is still limited in daily practice. Future research may need to incorporate simpler, clinically more applicable prediction tests in a decision algorithm for analgesia after CD.

Table 3 Preoperative quantitative sensory testing and postoperative pain outcomes and analgesic requirement
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Local Anesthetic Infiltration

Local anesthetic skin infiltration is usually performed as part of standard procedure when placing spinal or epidural anesthesia for women who undergoing CD. Regarding the correlation between pain during local anesthetic infiltration and post-cesarean pain, Orbach-Zinger et al. found that pain scores on local anesthetic infiltration were able to predict severe acute postoperative pain with good correlation (r = 0.529, p < 0.001), sensitivity 91.6% and specificity 93.3% [22]. However, Gupta et al. showed the weak correlation of pain intensity upon local infiltration and postoperative pain (r = 0.195) [26]. Another study by Chan et al. found no association between increased pain score upon local anesthetic injection and acute post-cesarean pain (unadjusted OR = 1.10, 95% CI 0.95–1.27, p = 0.21) [25]. Therefore, further study may need to evaluate the utility of this method for predicting post- CD pain.

Combination of Multiple Modalities

There are 4 studies investigated multiple modalities to predict post-CD pain, using questionnaires as QST, and suprathreshold pain intensity and unpleasantness [2, 20, 27, 28]. For example, a 3-item questionnaire (3-IQ) used in combination with mechanical temporal summation and pressure algometry had area under the ROC curve values of 0.64 and 0.67, respectively, to predict VAS scores on movement greater than or equal to 70 [2]. The results showed that a combination of factors would be more accurate in predicting post-CD than a single modality. However, the combination of factors may not always be beneficial for prediction of postoperative pain after CD. The results showed that combined 3-itme question did not enhance the predictive value of VAS scores (correlation coefficient of all 3-IQ vs. anticipated pain: 0.24 vs. 0.25) [2]. Therefore, further studies may need to determine which factors or how many should be utilized to predict postoperative pain following CD. Additionally, these factors should be easily implementable in clinical practice while ensuring the highest level of accuracy.

Conclusions

Postoperative pain following CD poses a significant challenge that warrants future improvement. Acute postoperative pain serves as a strong independent predictor of adverse outcomes and chronic pain following CD. Recent research suggested the one-size-fits-all approach may not be optimal for the entire post-cesarean population. While consensus statements on predicting post-cesarean pain control are lacking, preoperative demographic data and screening tools may help identify patients at higher risk of developing severe acute pain. By targeting these high-risk patients with tailored individualized interventions, outcomes may be enhanced. Future studies should aim to identify additional variables or screening tools for better prediction of post-cesarean pain and investigate whether personalized analgesic regimens can lead to improved outcomes in these individuals.