The epidemiology of chronic postsurgical pain after video-assisted thoracic surgery (VATS-CPSP) in China: a multicentre prospective study

Introduction

According to the ICD-11 (The 11^th revision of the International Classification of Diseases) definition, chronic postsurgical pain (CPSP) is the pain that develops in the operating area after a surgical procedure; this pain cannot be explained by other causes and lasts more than 3 months (1). It is an iatrogenic but a devastating condition that influences the physiological, psychological and social recovery of postoperative patients (2-4) and increases medical expenses (5).

Thoracic surgery, owing to its proximity to intercostal nerves, is associated with a greater incidence of CPSP (ranging from 5% to 65%) than other surgeries (6). Recently, as minimally invasive surgery has become commonly used, video-assisted thoracic surgery (VATS) has become the preferred surgery for early-stage lung cancer (7). In China, it is estimated that more than 20,000 thoracic surgeries are performed each month in all provincial medical centres in recent years and that more than 80% of these surgeries are VATS procedures (8,9).

In 2013, the International Association for the Study of Pain (IASP) published guidelines for epidemiological studies on postoperative pain (10) to avoid heterogeneity in global epidemiological studies on CPSP. There are several reports on the incidences of CPSP after open thoracic surgery and VATS (11-17). However, few of these studies are multicentre prospective cohort studies, which limits the implications of their results. The reported incidence of CPSP after VATS ranges from 5% to 44%, and there have been contradictory results concerning whether VATS has a lower incidence of CPSP than open thoracic surgery does (12,13,15-17). Although multiple demographic and clinical factors have been analysed for their associations with CPSP after VATS, only one risk factor, namely, the intensity of acute postoperative pain after VATS, has been widely reported. Therefore, we aimed to perform a multicentre prospective cohort study on the epidemiology of and risk factors for chronic post-surgical pain after VATS. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2024-2220/rc).

Methods

Study design and participants

This was a multicentre prospective observational study conducted in eight participating centres across China (Peking Union Medical College Hospital, Cancer Institute and Hospital-Chinese Academy of Medical Sciences, Shanghai Chest Hospital, First Affiliated Hospital of Chongqing Medical University, Tianjin Chest Hospital, Xiangya Hospital of Central South University, Cancer Hospital Affiliated to Xinjiang Medical University, The Affiliated Hospital of Inner Mongolia Medical University). This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This study was primarily approved (Ethical Committee No. ZS-3560) by the Ethical Committee of Peking Union Medical College Hospital, Beijing, China (Chairperson Prof. Zhaohui Zhu) on May 10, 2022, and each participating hospital was also informed and agreed the study. This study was registered prospectively at ClinicalTrials.gov (NCT05473728) on July 24, 2022. Written informed consent was obtained from patients before enrolment. The first patient was enrolled on August 1, 2022. All in-patients who were scheduled for unilateral thoracoscopic surgery at the participating centres were recruited between August 1, 2022 and September 30, 2022. Patients with known pain sensory impairment or limited self-expression and those undergoing emergency surgeries were excluded. Perioperative and anaesthetic management was left to the discretion of the local clinical care teams, and no adjustments were made.

Data collection

In accordance with the IASP guidelines (10), data on five risk factor domains (demographic, pain, clinical, surgery-related, and psychological features) and four outcome domains (pain, physical functioning, psychological functioning, and global ratings of outcomes) were collected, with a standardized clinical research form used by each participating centre throughout the patient’s stay in the hospital and follow-up period. Dedicated personnel for conducting this study were recruited from each participating centre and trained before enrolment. An electronic data capture system was used for data collection and was overseen by a data inspector.

Preoperative data were obtained through clinical visits by trained personnel (resident anaesthesiologists or research nurses) one day before surgery, during which patients were first screened for eligibility, and informed consent was obtained. The Hospital Anxiety and Depression Scale (HADS) (18,19) was used for preoperative psychological evaluation, and the BPI-9 (Brief Pain Inventory 9 questions) (20) was used for preoperative pain assessment.

On the operation day, intraoperative data were recorded by the attending anaesthesiologists and collected by trained personnel. The surgery-related data were cross-examined with the records in the hospital information system. During the hospital stay, the patients were visited on postoperative days 1–3 (if applicable) and on the day of discharge. For consistency, pain intensity was evaluated with the NRS (Numeric Rating Scale) during the follow-up period. Clinical data (medications and drainage tubes), psychological functioning, and global ratings of outcomes were also evaluated during the clinical visits.

Phone interviews were conducted at 3 and 6 months after surgery by each participating centre. To confirm whether CPSP developed, the following question was asked: “Do you currently have persisting pain related to your thoracoscopic surgery?”. The BPI and DN-4 (Douleur Neuropathique 4 questions, as Neuropathic pain four questions in English) were applied for CPSP evaluation. Owing to the lack of physical examination, the simplified 7-item version of the DN-4 (cut-off value of 3) was applied (21,22). Psychological and global ratings of outcomes were also assessed with the same measurement tools that had been used previously.

Statistical analyses

A data analysis and statistical plan had been written and filed with the institutional review board before the data were accessed. The primary outcome was the incidence of chronic pain related to thoracoscopic surgery at 6 months after surgery. The CPSP incidence was calculated as the number of patients with 6-month CPSP divided by the number of those who completed the 6-month follow-up. Those who failed to follow up were not included in the primary outcome analysis. Subgroup analyses were conducted with the core risk factor domains. Missing data were not imputed. A confidence interval (CI) for the incidence of CPSP was calculated via the Agresti-Coull method (23). For a raw incidence of zero, the Clopper and Pearson method (24) was applied. Chi-squared tests were applied to categorical variables. The data were analysed via R (version 4.3.1; R Foundation, https://www.r-project.org/), and two-sided P<0.05 was considered statistically significant.

Based on the past experience of our participating centres, we considered enrolling roughly 800–1,000 patients who were undergoing VATS from all the participating centres during a 2-month enrolment period. We used 20% as the estimated prevalence according to previous reports (12,13,15-17) and assumed a within-cluster rate of homogeneity of 0.01. The design effect was 1.99, with an anticipated 100 patients at each centre. With 800 patients included, a less than 8% absolute width of the lower to upper bounds of the 95% CI would be achieved.

Results

A total of 904 patients were recruited during the enrolment period; of these, one patient was excluded because surgery was cancelled, and 9 patients were excluded because of bilateral or ipsilateral surgery during the follow-up period. Among the remaining patients, 882 patients completed the 6-month follow-up and were analysed for their 6-month CPSP (Figure 1). The mean age of this cohort was 56.6±11.1 years, and 61.1% were females. The patient characteristics are summarized in Table 1.

Figure 1 Flowchart of the study cohort. POD, postoperative day.

At the 6-month follow-up, a total of 236 patients complained of surgery-related pain, which resulted in a CPSP incidence of 26.8% (95% CI: 23.9–29.8%) in our Chinese VATS cohort, with 4.7% of the cohort (41 of the 882 patients) reporting moderate to severe pain (NRS >3). At the 3-month follow-up, the CPSP incidence was 38.3% (95% CI: 35.2–41.6%), and 10.7% of the patients (94 of the 882 patients) reported moderate to severe pain (Figure 2). The overall NRS scores at 3 and 6 months after surgery were 1.9±1.4 [median (IQR) 2.0: (1.0, 3.0)] and 1.7±1.1 [median (IQR): 2.0 (1.0, 2.0)], respectively. Complaints of 4 patients resulted in a diagnosis of neuropathic pain at 6 months after surgery according to a DN-4 score ≥4.

Figure 2 Incidence of CPSP after VATS. *, moderate to severe CPSP: chronic pain with an NRS score ≥3. CPSP, chronic post-surgical pain; NRS, Numerical Rating Scale; VATS, video-assisted thoracic surgery.

Subgroup analyses were performed on the basis of preoperative factors (Figure 3). There were no significant differences in the CPSP incidence among the different subgroups according to common demographic factors [age, sex, body mass index (BMI), ethnic group, education, occupation, marital status, etc.]. The patients who were currently smoking or drinking tended to have a lower incidence of CPSP at the 3-month follow-up, but the differences were not statistically significant at the 6-month follow-up. The patients with past CPSP experience after other surgeries were shown to have a twofold higher incidence of CPSP. The preoperative psychological status, especially depression, may have influenced the incidence of CPSP.

Figure 3 Subgroup analyses of preoperative factors for 3-month post-surgical pain (A) and 6-month post-surgical pain (B) after video-assisted thoracic surgery. *, past ipsilateral surgery: patients who have undergone ipsilateral thoracic wall/cavity surgeries; ^†, past CPSP: patients who have undergone other surgeries before and suffered from postoperative pain for 3 months and longer; ^‡, ^§, pre-Op anxiety and depression were measured with the Hospital Anxiety and Depression Scale; ^¶, pre-Op pain: any current pain presented at the preoperative visit. ASA, American Society of Anesthesiologists; BMI, body mass index; CI, confidence interval; CPSP, chronic post-surgical pain; Op, operation.

Subgroup analyses were also performed on the basis of intraoperative factors (Figure 4). With respect to surgical factors, the patients with a deeper drainage tube and those whose surgery started later than 6 pm tended to report a higher incidence of CPSP at the 6-month follow-up. However, no such differences in the CPSP incidence were observed at the 3-month follow-up. No significant differences in the CPSP incidence were observed among patients with different incision sizes, types of surgery or durations of surgery. For anaesthetic factors, no significant differences were observed among the different medication groups. However, intraoperative hypoxemia could be related to the incidence of CPSP, as patients with a small sample size had a relatively high incidence of CPSP.

Figure 4 Subgroup analyses of intraoperative factors for 3-month post-surgical pain (A) and 6-month post-surgical pain (B) after video-assisted thoracic surgery. *, intraoperative hypoxemia is defined as any of the following: 80%< SpO₂ <90%, lasting >5 min; SpO₂ <80%; PaO₂ <60 mmHg. CI, confidence interval; CPSP, chronic post-surgical pain; Max., maximum; NSAIDs, nonsteroidal anti-inflammatory drugs; OMEs, oral morphine equivalents; PaO₂, arterial partial pressure of oxygen; PCIA, patient-controlled intravenous analgesia; SpO₂, peripheral oxygen saturation; TIVA, total intravenous anesthesia.

Among postoperative factors (Figure 5A,5B), acute postoperative pain tended to be associated with CPSP. The patients with moderate to severe acute pain after surgery had a higher incidence of CPSP. No significant differences in the CPSP incidence were observed between the patients with or without drainage tubes on postoperative days 1–3. Postoperative psychological factors still played important roles in the incidence of CPSP, as the patients with depression or anxiety tended to have a greater incidence of CPSP. The patients with higher scores of global surgical recovery tended to report less CPSP.

Figure 5 Subgroup analyses of postoperative factors for 3-month post-surgical pain (A) and 6-month post-surgical pain (B) after video-assisted thoracic surgery. CI, confidence interval; CPSP, chronic post-surgical pain; DT, drainage tube; GSR, Global Surgical Recovery; NRS, Numerical Rating Scale; NSAIDs, nonsteroidal anti-inflammatory drugs; OMEs, oral morphine equivalents; POD, postoperative day; POM, postoperative month.

Discussion

This is the first multicentre prospective epidemiological study on CPSP after VATS. Given the large cohort from different parts of China and the small (1.3%) loss to follow up rate at 6 months after surgery, we found that the incidence of CPSP after VATS was still relatively high (38.3% and 26.8% after 3 and 6 months, respectively). However, the percentage of patients with neuropathic pain was relatively low compared with that associated with thoracotomy and that from previous reports. Perioperative psychological factors and acute postoperative pain appeared to be related to CPSP, which emphasizes the importance of acute pain services and the need to pay attention to patients’ psychological status. Given our broad inclusion criteria and the patients enrolled from different parts of China, our results may be generalized to Chinese patients receiving VATS.

Previously published studies reported that the incidence of CPSP after VATS ranged from 5% to 44%, which was due to heterogeneity in study designs and the CPSP definitions (12,13,15-17). In our study, we chose to define CPSP according to the ICD-11 definition, without restrictions on the severity of pain, and designed our study with reference to the suggested CPSP study framework, as proposed by the IASP. A previous prospective study (15) published in Anesthesiology in 2017 adopted a similar CPSP definition by asking the following question: “Do you currently have pain related to your thoracic surgery?”, and the study findings showed that the 6-month CPSP incidence after VATS was 25%, which is comparable to our results. It is difficult to compare our results with those of previous retrospective studies, as the direction of recall bias is uncertain. Compared with that in other prospective studies, our reported incidence of CPSP was relatively high, partly because we included postsurgical pain of any intensity. The incidence of moderate to severe CPSP after 6 months was comparable to that reported in a previous study (12). As Asian people, especially senior people, tend to be introverted while expressing unpleasant feelings, we should not neglect the high incidence of CPSP after VATS in China.

According to previous reports (13,16,25,26), the incidence rates of chronic neuropathic pain after VATS and open thoracotomy were found to be 5–6% and 10–31%, respectively. However, in our cohort, the incidence of neuropathic pain 6 months after VATS was 0.5% (4 of the 882 patients), which accounted for 1.7% of the patients with CPSP. This finding along with previous reports showed advances in surgical techniques, especially minimally invasive techniques lead to a lower incidence of neuropathic pain. And the difference of neuropathic pain incidence among VATS patients could be partly explained by our use of the DN-4 questionnaire, which is a diagnostic tool with a relatively high specificity for neuropathic pain (21).

We performed subgroup analyses for possible risk factors for CPSP on the basis of 3- and 6-month follow-up data. Among the factors, acute postoperative pain, perioperative psychological status, past CPSP and intraoperative hypoxemia were related to the incidence of CPSP in both the 3- and the 6-month follow-up data. As previous publications have shown (14,15), acute postoperative pain is a widely recognized risk factor for CPSP. With respect to the influence of perioperative psychological factors and past CPSP experience, there has not been a consensus based on the results from different studies (14,15,27,28). The relationship between intraoperative hypoxemia and CPSP may need further exploration given the lack of previous evidence and a limited number of intraoperative hypoxemia cases. Recent evidence showed hypoxia may induce pain hypersensitivity (29), nocturnal intermittent hypoxia (30) and obstructive sleep apnoea (31) play a role in chronic pain, the role of hypoxemia in the incidence of CPSP thus worth exploring.

There are several limitations in this study. First, although we enrolled patients from different parts of China, our participating centres were mostly located in large cities and were top hospitals in their provincial districts. Thus, the study may not represent the whole picture of Chinese patients receiving VATS. Although our cohort included patients from different ethnic groups, Han people represented most of our cohort, with their proportion being potentially higher than that in the general population. Second, the question asked for our primary outcome consisted of two main parts, namely, pain and its relation to surgery. We designed this study as described in a previous prospective study published in 2017 (15). The purpose of this design was to ensure that a positive answer strictly referred to a CPSP diagnosis. The limitation is that the low incidence of CPSP in our study may be related to the underestimation of CPSP, as the patients needed to link such pain to surgery. However, as the overall pain intensity and the incidence of moderate to severe postoperative pain in our cohort were lower than those reported in other previously published studies (12,14,16), the conclusion of a low CPSP incidence in our Chinese VATS-CPSP cohort could stand. Additionally, as our results indicate, the preoperative psychological status plays an important role in CPSP after VATS. Our study did not include the Pain Catastrophizing Scale, as we tried to keep our questionnaires short. The patient perception of pain may be an important factor in CPSP. Finally, we chose phone interviews for postoperative follow-ups and NRS scores for pain severity measurement, which may have limited the measurement accuracy. To minimize the influence, we used the same pain-related questions from the preoperative visits to the postoperative follow-ups.

Conclusions

In conclusion, CPSP is relatively common among Chinese patients undergoing VATS, although neuropathic pain is relatively rare. Acute postsurgical pain and the perioperative psychological status may influence the development of CPSP; thus, the perioperative management of acute postsurgical pain and patients’ psychological status should receive sufficient attention.

Acknowledgments

The authors appreciate the help of E Wang, Fufen Meng, Guiping Xu, Hanyu Duan, Hui Zheng, Jiange Han, Jianjun Xue, Jiao Geng, Jingxiang Wu, Ke Wei, Labaciren, Ruifang Gao, Wansheng Liang, Wei Meng, Xiaojian Jin, Yiri Du, Yonggang Hao, Yuan Chen, Yuwei Qiu, Zhe Chen (in alphabetical order) and other personnel involved in this project at each participating medical centre. We would also like to thank Yanan Shang for her administrative work that facilitated this project.

Footnote

The preliminary results of this trial were presented at the 28^th CSA annual meeting in Changsha, China, on September 22^nd, 2023.

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2024-2220/rc

Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2024-2220/dss

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2024-2220/prf

Funding: This study was supported by the CAMS Innovation Fund for Medical Sciences (No. 2023-I2M-1-004).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2024-2220/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This study was primarily approved (Ethical Committee No. ZS-3560) by the Ethical Committee of Peking Union Medical College Hospital, Beijing, China (Chairperson Prof. Zhaohui Zhu) on May 10, 2022 and each participating hospital was also informed and agreed the study. This study was registered prospectively at ClinicalTrials.gov (NCT05473728) on July 24, 2022. Written informed consent was obtained from patients before enrolment.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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