Simplified dressing change after loose combined cutting seton surgery for high anal fistula: a prospective, single center randomized controlled study

Introduction

High anal fistula (HAF) can be defined as an anal fistula, which has a higher risk and cannot be safely treated using conventional fistula incision (1). In clinical practice, HAF is a refractory disease. Its lesions invade many muscles, and the pipes are packed and disjointed. The main pipe often passes through the deep part of the external sphincter and invades the puborectalis and levator ani muscle. HAFs can hardly heal by themselves and must be treated with surgery (2-4). The loose combined cutting seton (LCCS) method is based on the traditional Chinese medicine thread-hanging technique. After a long period of continuous improvement, it has developed into a new surgical method. Due to its high cure rate and low anal function loss rate, it has gradually become a common surgical method for the treatment of HAF in China. The LCCS method for HAF can reduce the damage to the sphincter while ensuring the function of the anal sphincter as much as possible. The solid thread mainly plays the role of cutting the sphincter. After the sphincter is partially suspended, the solid thread naturally becomes a virtual thread. The thread can drain the fistula and other necrotic tissues along the silk thread, play a good drainage effect, and is not prone to pseudo-healing (5-7).

Due to the deep location of HAF anal fistulas, postoperative wounds are large, the pain patients experience during a dressing change is severe, and patients resist anal contraction, which makes it more difficult to clean the dressing. The dressing of the wound after anal fistula surgery affects the success of the operation to a certain extent. According to wound infection or contamination, wounds can be divided into clean wounds, contaminated wounds, and infected wounds (8,9). The wound of a HAF is an infected wound. Because intestinal fluids and feces pass through the wound, this type of wound is directly exposed to the bacterial infection and sinuses. There is continuous pus, exudate, and necrotic tissue drain from the inside to the outside. Dampness and fluid accumulation in the wound greatly increase the risk of infection. At the same time, the anus is easily squeezed by the large buttocks muscle tissue on both sides, has poor air permeability, and hence many bacteria can multiply. To avoid infection, care should be taken to ensure smooth drainage during and after surgery to avoid new infections caused by fluid accumulation in the dead space of the wound.

The basic principles of postoperative wound management for HFA are: (I) keep the perianal clean, (II) allow drainage to flow, and (III) prevent false healing. The purpose of dressing change is to eliminate the pus and necrotic tissue of the infected fistula, prevent the accumulation of blood and exudate in the intestinal cavity and anal canal leading to tissue damage and the re-formation of the local necrotic cavity, and avoid premature healing of the wound and the formation of false healing (10,11). Traditional HAF dressing changes are based on the principle of aseptic technology. Doctors always work under strictly sterile conditions when washing and debriding the wound, packing drainage gauze and changing the dressing. Such dressing changes are performed daily (to be done 1–2 times a day) and the steps are cumbersome and time-consuming. In the clinic, we found that patients are very fearful when dressings are changed. We found that the secretions adhere to the wound during dressing change. The tearing and pulling of the wound when changing dressings destroy the new granulation tissue. Wiping the wound with a cotton ball can also cause severe pain due to the stimulation of peripheral nerves around the wound. Sphincter spasm pain is often caused when new drainage gauze is filled, which leads to severe pain and psychological fear of changing dressings (12-15). Due to the special anatomical location of HFAs, patients with anal fistulas take a long time to recover after surgery. Improper application of dressing changes will cause a significant waste of medical resources and greatly increase the cost of patient care. In addition, strict aseptic conditions are important for the operation during dressing changes. The demands on the environment, equipment, and personnel are high. Therefore, simplifying the dressing procedure without affecting the cure rate can not only reduce the patient’s pain and save doctors’ time but also shorten hospital stays and reduce in-hospital infection.

During LCCS the sphincter does not need to be completely cut off to retain the normal function of the anus, such that continuous, good and smooth drainage is achieved after the operation, which in turn not only reduces postoperative pain but also avoids poor drainage after the traditional hanging thread has fallen off (16-18). Studies have shown that using tap water to flush wounds does not increase the infection rate compared to normal saline. Flushing can also help patients to freely adjust water pressure and temperature according to their pain conditions and reduce the pain of patients’ wounds during washing (19-21). Therefore, the treatment of HAF patients through the LCCS can fully guarantee drainage and reduce the incidence of false healing. We can greatly simplify the dressing procedure and only perform necessary wound cleaning and external packing dressings to absorb excessive secretions. Therefore, we will undertake a single-center randomized controlled trial to compare the clinical efficacy of simple dressing change with that of traditional debridement and dressing change and assess the incidence of postoperative complications, so as to provide clinicians with more data on which to base clinical decisions.

Study objectives

In this study, we will compare the clinical efficacy of a simplified dressing change method and the traditional debridement dressing method in the treatment of postoperative wounds of HFAs. We hope that the results from this trial will provide the basis for the clinical implementation of the simplified dressing change.

Study design

The study is a prospective, randomized controlled, single-blind, and single-center non-inferiority clinical trial. We present the following article in accordance with the SPIRIT reporting checklist (available at https://dx.doi.org/10.21037/apm-21-2726).

Methods

Protocol writing

The writing of this article is based on the recommendations of the relevant clinical trial protocol and related documents published in the SPIRIT 2013 statement in the “Journal of Evidence-Based Medicine in Traditional Chinese Medicine” (22). All procedures performed in this study involving human participants will be in accordance with the Declaration of Helsinki (as revised in 2013).

Study settings

This study will enroll patients who have been diagnosed with HFAs in the Anorectal Clinic of the China-Japan Friendship Hospital (Beijing, China) and have been planned to be admitted to the hospital for surgical treatment.

Enrollment and eligibility criteria

All patients diagnosed with HFAs can participate in this study. The Western medicine diagnostic criteria are in accordance with the “Guidelines for the Clinical Diagnosis and Treatment of Perianal Abscesses, Anal Fistulas, and Rectovaginal Fistulas” compiled by the American Association of Colorectal Surgeons in 2016 (23). The traditional Chinese diagnostic criteria are in accordance with the 2012 Chinese Society of Chinese Medicine’s “Guidelines for the Diagnosis and Treatment of Common Diseases in the Anorectal Department of Traditional Chinese Medicine” (24).

Inclusion criteria

Participants must meet all of the following criteria to be included in this study: meet the diagnostic criteria for HAF; have received LCCS treatment; have normal anal function; are aged 18–65 years; show good compliance; fully understand the purpose, methods and significance of this study; volunteer to participate in this study; and sign an informed consent form.

Exclusion criteria

Potential subjects who meet any one of the following criteria will be excluded from this study: patients with non-HAF; patients not treated with LCCS; suffering from active inflammatory bowel disease (ulcerative colitis and Crohn’s disease); and pregnant or lactating women.

Intervention procedures

The research process is divided into three stages.

The first stage is the screening period. The main task will be to evaluate cases according to the inclusion and exclusion criteria and to sign the informed consent form before inclusion. Before being selected for the study, the doctor will ask and record the patient’s medical history and perform screening examinations such as digital rectal examination and intrarectal ultrasound.

The second stage is the treatment period, which mainly includes: (I) preoperative preparations: The two groups will undergo the same preoperative preparations, that is anorectal cavity color Doppler ultrasound and other examinations before the operation; the diagnosis will be confirmed; it will also be confirmed that the patient has no contraindications for surgery; the patient will fast for 8 hours prior to surgery, empty the bowels normally, and will be given an enema if necessary. (II) Surgical operation: Both groups of patients will be treated with LCCS. The patient will assume a lateral position, and after intravenous anesthesia, the operation area will be disinfected and draped. Once the anal canal will have become loose, the anal canal will be disinfected and an anorectal exploration will be performed to determine the area and location of the anal fistula, and whether there are branches and dead spaces. During the operation, a radial incision will be made from the inner orifice outward from the dentinal line, about 3 to 4 cm in length, and the incision position will generally be on the same side as the outer orifice to fully drain the infection foci at the inner orifice. The inner orifice will be cut, extending 0.5–1.0 cm upwards, and extending downwards to the outside of the anal margin. Curved hemostatic forceps will be used to probe the upper end of the fistula from this incision until the top of the fistula. Fingers will be used to reach into the intestinal cavity for guidance, and the tip of the forceps will be employed to penetrate the stoma of the intestinal wall. The finger will be withdrawn, four 10-gauge silk threads will be used, with one end tied to the fingertip, and placed into the intestinal cavity. The hemostatic forceps will be opened to clamp the thread, the silk thread will be drawn from the intestinal cavity through the fistula, and the two ends will be gathered and secured with a knot. Routine cleaning will be carried out and the dressing will be changed once a day after the operation. The Vaseline gauze will be drained, and the gauze will be applied and secured. About 7 days after the operation, the hanging silk thread will be loose. At this time, the thread will be kept hanging there without tightening. After the granulation tissue of the fistula will have been filled, the thread will be removed on the 20th day. (III) Postoperative medication: Both groups of patients will receive routine intravenous infusions of broad-spectrum and anti-anaerobic antibiotics for 3 days after surgery. (IV) The dressing on wounds will be changed after surgery: for those who defecate within 24 hours after the operation, the dressing is changed immediately after defecation. For those who have a bowel movement after more than 24 h, the dressing shall be changed 24 h after the operation. After defecation, both groups will use Chinese medicine preparations to fumigate and wash for 10 minutes. The prescription of Chinese medicine preparations for fumigation and washing will be: 15 g of Chinese gallnut, 30 g of dandelion, 15 g of arborvitae, 30 g of Sophora flavescens, 15 g of Glauber’s salt, 15 g of Atractylodes, 15 g of sanyu, 15 g of fangfeng, 30 g of Phellodendron 30, 15 g of red peony, 15 g honeysuckle, 10 g raw licorice, one dose a day each. Usage: These will be wrapped with gauze, put it in a basin, and brewed with 2,000 mL hot water. When the water temperature is about 40 °C, the anus and wound will be washed for 10 minutes, twice a day.

After fumigating and washing in the sitz bath, the dressing will be changed. The dressing change method will be adapted based on the plan that will be made at the time of enrollment. A. Intervention group: The simplified dressing change method will be used. Preparation before operation: The operator will wash his/her hands and will wear a mask and a hat. He/she will inform the patient about the purpose of the dressing change and obtain the patient’s cooperation. A disposable sterile dressing change box (containing 2 curved trays, 1 pad towel, 2 tweezers, gauze, and cotton balls) will be set aside in addition to medical tape. Operation steps: (I) the old dressing will be removed from the wound: The patient will be instructed to assume a lateral position (to fully expose the perianal drainage wound), the disposable dressing pack will be opened, and the items will be set aside. First, the outer dressing will be removed by hand, and then a pair of tweezers will be used to remove the inner dressing and the stuffed cotton ball. If it adheres to the wound surface, care will be taken that it does not peel off too vigorously. It will be soaked with a normal saline cotton ball and removed to avoid injury and bleeding. (II) The wound will be washed: After instructing the patient to sit in the bath, the contralateral buttocks muscle will be moved firmly with one hand to fully expose the wound. The shower will be held with the other hand, or the shower will be applied by a family member using tap water (set temperature is 36–37 °C) within 5 cm from the wound; and the wound and the skin within 5 cm from the wound will be washed under pressure, with the order being from top to bottom, from the inside to the outside, the wound surface will be washed, the solid line will be pulled gently to locate the wound cavity, and the dotted line will be rotated to wash the necrotic tissue attached to the line until the pus on the wound surface has been completely washed out. (III) Change dressing: Sterile cotton balls or sterile gauze will be placed in each wound cavity, whereby the outer layer will not need to be covered with sterile gauze. Patients and family members will pay attention to the dry cotton balls placed in the wound cavity and replace it immediately once it is soaked with secretions and pus. Cotton balls and gauze will be used to fill local wound defects in the perianal area to prevent the wound from healing earlier than the wound cavity, leading to pseudo-healing and forming a new sinus tract. A hanging thread will be able to provide adequate drainage, allow excessive exudate and pus to be fully discharged, provide a relatively moist rather than humid environment for wound healing, and reduce edema of the tissue around the wound (25).

B. Control group: traditional debridement and dressing change will be used. Preparation before operation: the dressing operator washes will wash his/her hands and will wear a mask and a hat. The patient will be informed about the purpose of the dressing change and the patient’s cooperation will be obtained. Preparation before operation: a disposable sterile dressing change box (containing two curved trays, one pad towel, two tweezers, gauze and cotton balls), one bottle of iodophor, several petroleum jelly sticks, one bottle of saline, one pair of curved forceps, one pair of curved scissors, one syringe (50 mL), and medical tape. The operation will be conducted as follows: (I) the previous dressing will be removed from the wound, the patient will be instructed to assume a lateral position (to fully expose the perianal drainage wound), the disposable dressing pack will be opened, and the items will be set aside. First, the outer dressing will be removed by hand, and then a pair of tweezers will be used to remove the inner dressing. If it adheres to the wound surface, care will be taken to not remove it too vigorously. It will be soaked with a cotton ball of saline and removed to avoid injury and bleeding. Tweezers will be used to slowly pull out the old petroleum jelly gauze along the long axis of the wound. (II) Mechanical debridement: Because the infected wound has more secretions and the wound is deep, the patient is asked to forcefully break the contralateral buttocks muscle with one hand to fully expose the wound. A syringe will be used to draw physiological saline, 5 cm away from the wound, and the wound and the surrounding 5 cm area will be flushed under pressure (26), with the order being from top to bottom, from the inside to the outside, gently pulling the solid line to locate the wound cavity and rotating the dotted line to wash the attached necrotic tissue until the pus on the wound surface has been thoroughly rinsed, and a cotton ball will be used to wipe the wound with curved forceps to remove slough, tissue fragments, foreign bodies on the wound, and reduce the growth of bacteria on the wound until the wound is rosy, and there is a trace of blood exudation. (III) Wound disinfection: Sterile gloves will be worn, the tweezers will be held in the left hand to keep the wound aseptic, and the tweezers will be held in the right hand to touch the wound. An iodophor cotton ball will be used to disinfect the skin and wound area within 5 cm of the wound from the outside to the inside three consecutive times. The wound and the surrounding 5 cm skin will be wiped with a cotton ball of isotonic saline. The sterile curved forceps will be held, and the wound will be blotted with gauze. (IV) Packing the drainage strip: When plugging the drainage strip, this will start from the bottom of the wound, and curved forceps will be used to pack up along the long axis of the perianal radial wound until it will have reached the highest point of the fistula. It should not be too tight or too loose. If it is too tight, this will affect the drainage of pus. If it is too loose, it will easily fall off the wound. The end of the oil gauze will be left outside the wound, such that it can be taken out and drained smoothly during the next dressing change. (V) Changing the dressing: Eight to 10 layers of sterile gauze will cover the wound and will be fixed with tape. The direction of the fixation will be perpendicular to the long axis of the body. If there are more secretions and pus, a layer of cotton pad will be covered over the sterile gauze.

Both groups of patients will have their dressing changed twice a day, once in the morning and once in the evening. (Dressings should be changed within half an hour after defecation every day. If there is no bowel movement that day, the first dressing change will be performed at 9–10 am and the second dressing change at 21–22 pm).

The third period is the follow-up period. During the hospitalization period, the patients and their families will be trained in dressing change (Appendix 1: training guide for patient changing dressing). Follow-up plan: The follow-up time is half a year, including six medical visits. Telephone follow-up or face-to-face follow-up will be conducted on the first consultation day, and the 3rd, 7th, 14th, 21st, and 180th day after surgery. The main contents include: patient’s current symptoms, anorectal ultrasound, rectal pressure measurement, and anal function score. The Wexner Incontinence Score will be measured.

Outcome measures and data collection

The main outcomes will be: postoperative wound and fistula complete healing rate, long-term recurrence rate, poor wound healing rate, and complete wound healing time. Secondary outcomes to be evaluated will be: postoperative pain visual analogue score (VAS) score, wound secretion, edema, granulation morphology, wound depth, the duration of each dressing change, and the incidence of adverse events.

Primary outcomes

Main indicator of curative effect: complete cure rate of postoperative wounds and fistulas.

Secondary outcomes

These will include secondary efficacy evaluation indicators and safety evaluation indicators. The secondary efficacy evaluation indicators will include: (I) six months of recurrence, (II) poor wound healing rate, and (III) anorectal ultrasound. Safety evaluation indicators will include: (I) VAS score for postoperative pain, (II) measurement of anal and rectal pressure before and after treatment, (III) assessment of anal function before and after treatment: Wexner anal function assessment, and (IV) adverse events.

Sample size

This study will be a non-inferiority clinical randomized controlled trial. The cure rate will be the main outcome indicator, and N will be the sample size. The ratio of the test group and the control group is 1:1. According to previous literature reports and clinical application summaries, the cure rate will be set to be 95%. The statistical tests will use P2=0.95 for the control group, α=0.025 (one-sided), and the power will be set at 80%. The non-inferiority margin will be d=0.15. Using PASS15 software, the sample size of each group will be 34. Assuming that the loss of follow-up rate of the research subjects is 10%, the sample size of each group will be N=34/0.9=38.

Recruitment

Recruitment for this trial will be carried out through the internet and public release of the subject recruitment information, and recruitment materials will be placed in outpatient clinics. After registration, subjects will be enrolled after having passed through the regular medical treatment process and screening using the admission and discharge criteria.

Method of allocation of interventions

Randomization and blinding

Before enrollment, we will tell patients that during the treatment process, the surgeon will use the LCCS to perform the operation. The postoperative dressing change method will be the traditional method or the simplified method. The dressing change method will be specifically determined by the doctor. To minimize the bias of the trial, after the clinical follow-up has been completed, the data will be sent to a third party for statistical analysis. The third party will not know which data belongs to which group before the results are generated. Finally, the physician and the third party performing the statistical analysis will jointly announce the results relating to each group.

Randomization method: random allocation will be undertaken using cards according to a random number table, which will have the random number of the serial number and the group allocation written on them. The random distribution card will be placed into a special opaque kraft paper bag with a serial number, and it will be sealed, and the envelopes will be opened in sequence after the patients will have been admitted to the hospital according to the admission criteria. Group A is the experimental group, where the simplified dressing change method will be used. Group B will be the control group, where traditional debridement and dressing change will be used.

Statistical analysis

The statistical software package SPSS 20.0 will be used for statistical analysis. All statistical tests will be performed using two-sided tests, and a P value of <0.05 will be considered statistically significant.

The mean, standard deviation or median, and interquartile range of blood pressure, heart rate, body temperature, measured value of anorectal pressure, wound and fistula, and finally healing time will be described. The number of cases and the percentage of classification indicators such as gender, wound pain degree score, anal function evaluation score, and curative effect evaluation results will be described. The Kaplan-Meier method will be used to estimate the healing rate at each time point after surgery, and the log rank test method will be used to compare the healing times between the two groups.

The mean ± standard deviation will be used to describe the resting pressure of the anorectal anal canal, the length of the anal canal high pressure area, and the maximum systolic pressure of the anal canal before treatment and after healing in the experimental group and the control group, respectively. The above indicators before treatment will be used as covariates, and analysis of covariance will be used to compare whether the above indicators are statistically different between the test group and the control group after surgery.

To compare quantitative data between two groups, for example, when comparing the final healing time of wounds and fistulas between the test group and the control group, normality and homogeneity of variance will be considered. If normality and uniform variance are satisfied, a t-test is used, if not, a t’-test is used. A Wilcoxon rank sum test will be used for non-normally distributed data. To compare categorical data between the two groups, such as the results of anal function curative effect evaluation, the χ² test will be used, and for grade data the rank sum test. The paired signed-rank test will be used to compare the changes of incontinence scores before and after treatment in each group, and the one-way ordered χ² test will be used to compare the groups.

Record of adverse events

We will record adverse events during clinical trials. Serious adverse events will be defined as: events that require hospitalization, prolonged hospitalization, disability, ability to work compromised, life-threatening conditions or death, and congenital malformations occur during the trial. Clinical adverse events may occur during the treatment of subjects. Once adverse events (including important adverse events) occur, the time of occurrence, clinical manifestations, treatment process and duration, outcome, and related events will be recorded in detail on the case report form. If there is an abnormal laboratory test, the patient must be followed up until the test result will have returned to normal or to the level before the treatment, or it is determined that it has nothing to do with the treatment. Serious adverse events will be recorded on the serious adverse event form and reported to the ethics committee within 24 hours.

Ethics committee review

This protocol, written informed consent, and materials directly related to the subjects will be submitted to the ethics committee, and the research will be formally carried out after obtaining the written approval of the ethics committee. The investigator will submit a research report to the ethics committee at least annually (if applicable). When the research is suspended and/or completed, the researcher will notify the ethics committee in writing; the researcher will report to the ethics committee all changes in the research (such as the revision of the protocol and/or the number of informed consents). These changes may not be implemented until approved by the committee, unless they will be made to eliminate obvious and direct risks to the subject. In such cases, the ethics committee will be notified.

Informed consent

Procedure for obtaining informed consent

The researcher will provide the subjects or their legal representatives with an easy-to-understand informed consent form approved by the ethics committee and give the subjects or their legal representatives sufficient time to consider this research. Subjects will not be allowed to be allocated to their group before their signed written informed consent has been obtained. During the participant’s participation, all updated informed consent forms and written information will be provided to the participants. The informed consent form will be kept as an important document for clinical trials for future reference.

Confidentiality measures

The results of this research project may be published in medical journals, but we will keep the patient’s information confidential in accordance with the legal requirements, and the patient’s personal information will not be disclosed unless required by relevant laws. When necessary, government and hospital ethics committees will be able to access patients’ data in accordance with regulations.

Ethics and dissemination

This study was approved by the Institution Review Board of China-Japan Friendship Hospital (approval number: 2020-89-K53). The results of this study will be submitted to international scientific peer-reviewed journals or conferences in surgery, anorectal surgery, or anorectal diseases.

Discussion

How to protect the integrity of the sphincter and maintain the normal function of the anus is the biggest difficulty in the surgical treatment of HAFs. Doctors have different treatment approaches for HAFs. Some foreign doctors and scholars advocate surgical procedures that preserve the sphincter, such as rectal flap operation, intersphincteric fistula ligation, anal fistula clogging, loose threading, and fibrin glue occlusion (27-31). The problem is that the fistula between the sphincter muscles may become a new focus of infection. Domestic anorectal doctors advocate that the sphincter be preserved as much as possible, while the fistula should be removed. Therefore, the thread-hanging operation has emerged. As a traditional surgical treatment in China, written records existed of the clinically application of thread-hanging therapy as early as the Yuan Dynasty. After the continuous improvement and development of this technique by doctors during past centuries, there are currently two types of mainstream clinical thread-hanging methods: real thread-hanging and virtual thread-hanging. Through tightening of the thread and using its contraction, the elastic force slowly squeezes the sphincter. The disadvantage is that the patient feels as if a foreign body hangs on the thread, the pain is heavier, and the healing time is longer. The virtual thread draws only the drainage effect of the silk thread and does not cut the sphincter. The patient’s pain is significantly reduced compared with the cutting thread method, and the anus control function is better after the operation. Due to the incomplete treatment of the infection foci, as the follow-up time increases, the postoperative recurrence rate gradually increases, which leads to an increased risk of the patient’s second surgery (32).

The LCCS method adopts the silk thread hanging thread, which combines the advantages of real thread hanging and virtual thread hanging. During the operation, the real thread hanging usually uses the silk thread without elastic effect. Silk thread reduces the suffering of patients. After the operation, the necrotic tissue falls off, the real hanging becomes empty, and the drainage is continued during the recovery process. The long thread tail is stuffed in the incision and drainage under the anal straight ring, which can also prevent false healing. This technique has been used in clinical practice for many years, which has been proven effective and safe. The pain score, cure rate, and recurrence rate of the patients is better than those of traditional thread-hanging surgery (6,7,18). In the clinic, we found that many patients who were discharged early after the operation due to family or work reasons did not have time to return to the hospital frequently for dressing changes. In these cases, the dressing was changed at home. The wounds of these patients also healed well, and no pseudo-healing was found. These observations fully demonstrated good drainage and prevention of false healing of the LCCS method. At the same time, studies have shown that repeated or excessive use of disinfectants can affect normal human cells and adversely affect normal tissue repair (33). Therefore, we put forward the idea of simplifying dressing change and formulated a patient dressing change training plan to reduce the pain of patients, reduce the length of hospital stays, and improve the efficiency of specialist medical treatment. Since we abandon the traditional debridement and disinfection, more attention on the wounds should be paid in nursing care after LCCS to make sure the wounds heal.

The purpose of our single-center randomized controlled trial is to further verify the effectiveness and safety of simplified dressing change after LCCS treatment to support its clinical application.

Acknowledgments

Funding: This study was funded by the Wu Jieping Medical Foundation (Project number: 320.6750.2020-8-34).

Footnote

Reporting Checklist: The authors have completed the SPIRIT reporting checklist. Available at https://dx.doi.org/10.21037/apm-21-2726

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://dx.doi.org/10.21037/apm-21-2726). All authors reported they received support from Wu Jieping Medical Foundation (Project number: 320.6750.2020-8-34). The authors have no other 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. This study was approved by the Institution Review Board of China-Japan Friendship Hospital (approval number: 2020-89-K53). All procedures performed in this study involving human participants will be in accordance with the Declaration of Helsinki (as revised in 2013). This protocol, written informed consent, and materials directly related to the subjects will be submitted to the ethics committee, and the research will be formally carried out after obtaining the written approval of the ethics committee.

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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(English Language Editor: B. Meiser)