Introduction
Considering the notable increase in surgical volumes worldwide, there is growing recognition of the burden posed by chronic postsurgical pain (CPSP) [
1,
2]. Currently, CPSP is far more common and excruciating than previously considered [
3,
4]. The incidence of CPSP is highly variable depending on the type of surgery, with a 5–65% incidence rate following thoracic surgery [
5,
6]. Although it has been reported that there is a lower incidence of CPSP after video-assisted thoracoscopic surgery (VATS) than after open thoracotomy [
7], VATS has been widely used as an alternative to open thoracotomy since its introduction into clinical practice [
8]. Therefore, the incidence of CPSP after VATS has great potential. Moreover, any occurrence of CPSP after VATS has a notable effect on patients’ quality of life, with considerable effects on the healthcare system and socioeconomic costs [
5,
9].
Estimates of the prevalence of CPSP following VATS vary widely (7.7–50%), presumably because of differences in definitions and postoperative follow-up periods and the small sample sizes of published studies [
10]. In recent years, several studies have evaluated CPSP after thoracoscopic surgery, although significant controversy still exists surrounding their findings [
10,
11]. Furthermore, the etiology of CPSP after VATS is multifactorial and may involve both patient- and treatment-related factors [
12]. Although multiple retrospective studies have investigated the predictors of CPSP after VATS, there were significant dissimilarities due to confounding of the predictors assessed in these studies, leading to inconclusive results. More notably, some studies on predictors of CPSP after VATS did not report effect estimates for nonsignificant predictors or predictors that were significant in the univariate analysis although nonsignificant in the multivariate analysis [
12]. This may have led to the exaggeration of existing predictors and neglect of potential predictors.
Elucidating the incidence of CPSP after VATS, accurately identifying predictors, and obtaining a precise understanding of the independent role of each predictor may help clinicians better recognize patients at risk of CPSP. It may also facilitate the early implementation of effective interventions, which is crucial in reducing the occurrence of CPSP. Accordingly, this study aimed to evaluate the incidence of CPSP after VATS and identify its potential predictors, which may help improve the prognosis of high-risk patients.
Discussion
To our knowledge, this is the first systematic review of the prevalence and predictors of CPSP after VATS. The primary outcome of this study demonstrated a prevalence of CPSP after VATS of 35.3% and identified three definite CPSP predictors (female sex, age, and APSP) and four likely predictors (insufficient analgesia, operation time, port number, and duration of drainage) with qualitative and quantitative synthesis. Secondary outcomes showed that only by quantitative analysis, postoperative chemotherapy and an educational level less than junior school were CPSP predictors after VATS. However, the results of smoking and drinking histories, which showed a reduced risk of CPSP, should be considered with caution. The effect of other potential predictors on the occurrence of CPSP after VATS requires further investigation. Furthermore, on the basis of the results of this study, pathological stage was not considered a predictor of CPSP. Despite robust results, additional large-scale studies are required as a few included studies only considered certain predictors and the effect evaluation of some predictors has certain heterogeneity.
CPSP refers to chronic pain that develops or increases in intensity after surgery [
6]. Owing to different patient characteristics, surgical types, and follow-up periods, the incidence rate of CPSP varies widely, ranging from 25% to 75% [
3,
35]. One systematic study reported an overall incidence rate of 57% for CPSP after thoracotomy [
36]. The incidence rate of CPSP is significantly lower following VATS than following thoracotomy. However, our meta-analysis revealed that the overall incidence rate of CPSP after VATS was 35.3%, with the incidence rates of CPSP with pain scores ≥ 3 and ≥ 1 being only 10.5% and as high as 41.0%, respectively. According to previous studies, any intensity of CPSP can decrease postoperative quality of life [
3,
37]. Hence, a pain score of ≥ 1 should be considered clinically meaningful. On the basis of our current analysis, to raise clinicians’ vigilance of CPSP, a pain score of 1–2 points should be reviewed to avoid neglecting patients with mild CPSP.
We performed subgroup analyses with different pain scores. Although the pooled results for CPSP incidence showed a decrease in heterogeneity, the group with scores ≥ 1 remained relatively heterogeneous. Going back to the original study, this may be due to differences in the duration of follow-up, type of disease, and underlying patient conditions. However, there are few related homogeneity studies, so we cannot conduct a meta-analysis. Therefore, further large-scale homogeneity studies are needed to confirm our results.
Women have an increased risk of sensitivity and clinical pain [
38]. Similarly, this study demonstrated an increased risk of CPSP in female patients after VATS, even with the addition of select values that were discarded owing to nonsignificance. However, the precise reason that chronic pain is more common in women than in men is not fully understood. Studies have established that women have lower pain thresholds and tolerance and are more likely to experience additional intense pain and less pleasant sensations than men [
39]. This phenomenon may be due to sex differences in the drivers of neuroimmune interactions in the development and maintenance of pain hypersensitivity and chronic pain [
40]. Furthermore, several psychosocial mechanisms are involved in biological mechanisms, including differences in pain management strategies, discrepancies in sociocultural beliefs, and women’s greater early exposure to environmental stress [
40].
Notably, our meta-analysis showed that patients undergoing VATS with smoking and drinking histories had a lower risk of developing CPSP. This may be due to sex-related differences in smoking and drinking histories, and we could not adjust for sex. Most studies did not determine a direct association between drinking history and CPSP [
11,
41]; however, patients with a smoking history had an increased incidence of CPSP [
42]. Substances in tobacco increase the body’s inflammatory response and oxidative stress and can lead to increased pain sensitivity by remodeling neural circuits [
42]. Taken together, our results should be cautiously considered.
Age is a crucial factor in the occurrence of CPSP; the younger the age, the higher the risk of CPSP [
37,
43]. This study showed that the patients’ mean age was lower in the CPSP group than in the non-CPSP group. A further meta-analysis of aOR and uOR revealed that advanced age was a protective factor for CPSP in patients who underwent VATS. This phenomenon may be related to increased pain thresholds due to aging and decreased pain perception, organ dysfunction, and other conditions that can seriously affect chronic pain perception and response [
44]. Moreover, older people are more stoic regarding pain and more reluctant to report pain when it occurs than younger people are [
45]. Conversely, lower educational levels lead to pain catastrophizing [
46]. This socioeconomic characteristic plays a vital role in pain perception. Our study also showed that an educational level below junior high school level is more likely to predispose patients to CPSP. Thus, physicians should pay particular attention to counseling such patients prior to and during treatment.
Our study also discovered that several surgical and therapeutic factors were related to the occurrence of CPSP after VATS. Some studies have suggested that prolonged operation time increases the risk of CPSP [
47]. Although minimally invasive, VATS can increase the incidence of CPSP if the operative time is prolonged. Furthermore, three-port VATS, increased drainage time, and administration of postoperative chemotherapy also contributed to the increased incidence of CPSP. The underlying mechanisms may be related to intercostal nerve injury [
48]. Tissue edema caused by postoperative chemotherapy can also have an effect similar to that noted in double crush syndrome [
49]. Moreover, postoperative chemotherapy leads to central sensitization, contributing to spontaneous pain and hyperalgesia [
50]. Therefore, surgical and perioperative management plans should be optimized, patients who need postoperative chemotherapy should be carefully monitored, and pain management should be instituted as early as possible.
Regarding perioperative pain-related parameters, our study ascertained that APSP was a risk factor for CPSP after VATS, whereas postoperative analgesia was a protective factor. A current study showed that CPSP can transition from APSP [
4]; however, it is not just a simple continuation of acute pain [
51]. It may involve structural remodeling and reorganization of synapses, cells, and circuits, which contribute to the chronicity of pain [
52]. Intraoperative tissue damage plays a decisive role in CPSP development and triggers profound modifications in peripheral and central sensory circuits. Once these structural changes occur, it is too late to effectively intervene; therefore, preventing acute pain from progressing to chronic pain is a top priority. Our study also confirmed that postoperative analgesia can reduce the risk of CPSP after VATS. Consequently, clinicians should be aware of the importance of pain management during the acute phase after VATS. However, currently available drugs and regimens for the effective treatment of acute pain remain limited, and there is an urgent need to develop new interventions to prevent the acute pain progression to CPSP.
This study had some limitations. First, the predictors in the included studies were sorted, resulting in few included studies and difficulty analyzing some predictors, thus limiting the reliability of our results regarding certain predictors. Second, as a result of the evolution of definitions, the definitions of CPSP varied slightly across studies [
4,
34], which is bound to produce a certain degree of heterogeneity. Third, we combined the uOR from the baseline data of the study with the aOR from the multivariate analysis. Although this mitigated the inflated assessments of some predictors, it increased heterogeneity. Fourth, some factors that may have had collinearity (e.g., smoking and drinking histories) could not be adjusted for because we did not have access to the raw data of the included studies. Finally, since most of the existing studies on the risk factors of CPSP after VATS are retrospective, the number of prospective studies included in this study is limited, which will also affect our conclusion. Thus, although our results are robust, the results should be interpreted with caution owing to limited data.