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. 2023 Aug 17;18(8):e0290329. doi: 10.1371/journal.pone.0290329

Carbon dioxide insufflation reduces the relapse of ulcerative colitis after colonoscopy: A randomized controlled trial

Yuriko Otake-Kasamoto 1, Shinichiro Shinzaki 1,2, Satoshi Hiyama 1, Taku Tashiro 1, Takahiro Amano 1, Mizuki Tani 1, Takeo Yoshihara 1, Takahiro Inoue 1, Shoichiro Kawai 1, Shunsuke Yoshii 1, Yoshiki Tsujii 1, Yoshito Hayashi 1, Hideki Iijima 1, Tetsuo Takehara 1,*
Editor: Antonio Brillantino3
PMCID: PMC10434883  PMID: 37590283

Abstract

Background and aim

Colonoscopy is necessary for diagnosing and surveilling patients with ulcerative colitis, though it may cause disease flares. Colonoscopy with carbon dioxide (CO2) insufflation decreases abdominal discomfort; however, its effect on exacerbation incidence in ulcerative colitis remains unclear. Therefore, this study aimed to evaluate the colonoscopy effects using CO2 insufflation in patients with ulcerative colitis.

Methods

Overall, 96 remissive patients with ulcerative colitis (partial Mayo score ≤ 2) who underwent total colonoscopy between March 2015 and December 2019 at Osaka University Hospital were enrolled and blindly randomized to the CO2 (n = 45) and air (n = 51) insufflation group (UMIN-CTR, number: UMIN000018801). The post-procedural abdominal discomfort and the clinical relapse (partial Mayo score ≥ 3) rate within 8 weeks were evaluated.

Results

Baseline backgrounds did not differ between the groups. The mean abdominal fullness and pain scores were significantly lower in the CO2 group than in the Air group immediately (p = 0.0003, p = 0.0003) and 30 min (p < 0.0001, p < 0.0001) after colonoscopy. While the overall clinical relapse rate remained unchanged between the groups, the clinical relapse rate at 8 weeks after colonoscopy was significantly lower in the CO2 group than in the Air group in patients not in complete remission (Mayo endoscopic subscore ≥ 1, p = 0.049; or partial Mayo score ≥ 1, p = 0.022).

Conclusions

CO2 insufflation can reduce abdominal discomfort in remissive patients with ulcerative colitis and decrease clinical relapse at 8 weeks after colonoscopy for those not in complete remission.

Introduction

Ulcerative colitis (UC) is an inflammatory bowel disease (IBD) that causes chronic inflammation of the large intestine. The prevalence of UC worldwide has increased over the last decade [1], especially in the East [2]. Endoscopy is performed to diagnose UC and monitor mucosal inflammation activity and treatment effects [3]. Additionally, because the long disease duration of UC is a risk for colitis-associated colorectal cancer [4, 5], regular surveillance with colonoscopy is necessary to detect precancerous dysplasia [6, 7]. Although colonoscopy is a very useful and indispensable tool for evaluating disease activity and surveilling cancer in patients with UC [3, 4], patients frequently experience disease flares after colonoscopy, sometimes leading to additional UC medications [8]. Colonoscopy in patients with active UC also carries a risk of intestinal perforation [9].

Previous randomized controlled trials (RCTs) reported that using carbon dioxide (CO2) insufflation for colonoscopy is safe and associated with less post-procedural pain than air insufflation [10, 11]. Similarly, a prospective RCT showed that employing CO2 insufflation rather than air insufflation caused less post-procedural abdominal pain and bloating at least 3 h after colonoscopy in patients with IBD [12]. Regarding the quality of endoscopy, CO2 insufflation has been reported to increase the adenoma detection rate, a clinical indicator of colonoscopic performance [13]. However, CO2 insufflation has not been widely used, and air insufflation remains the major method of insufflation for colonoscopy globally, except for some developed countries [12, 14], which is because CO2 insufflation requires a CO2 insufflator and supply of CO2 gas, and is thus more expensive [15]. Furthermore, whether CO2 insufflation reduces post-procedural pain and clinical relapse after colonoscopy in patients with UC remains unclear [15]. Therefore, this study aimed to compare the advantages of colonoscopy with CO2 insufflation or air insufflation in patients with UC in remission regarding subjective symptoms after endoscopy and post-procedural clinical relapse.

Methods

Study design

This study was designed as a single-center, prospective, single-blinded, randomized controlled trial. The study was approved by the Institutional Research Ethics Board at Osaka University Hospital (No. 14372) and conducted in accordance with the Declaration of Helsinki. Written informed consent was obtained from all patients prior to their inclusion in the study. Moreover, this study was registered in the clinical registry (UMIN-CTR, number: UMIN000018801) (http://www.umin.ac.jp/ctr/). This study was designed and analyzed in compliance with the CONSORT (Consolidated Standards of Reporting Trials) guidelines (S1 Checklist).

Protocol

Patients with UC in remission (partial Mayo score [PMS] ≤ 2) who were diagnosed according to the established diagnostic criteria [16] and underwent total colonoscopy using CF-H260AZI or CF-HQ290ZI video colonoscope system manufactured by OLYMPUS (Tokyo, Japan) between March 2015 and December 2019 at Osaka University Hospital were enrolled in our study. Exclusion criteria included a history of colectomy, clinically active UC (PMS ≥ 3), undergoing total parenteral nutrition, a history of chronic obstructive pulmonary disease, sedated colonoscopy, under 15 years of age, in poor general condition, or judged by the doctors to be in a condition unsuitable for the study. The reason for excluding patients who underwent sedated colonoscopy was that it would be difficult to accurately evaluate changes in subjective symptoms immediately and 30 minutes after the colonoscopy in these patients. Furthermore, it was considered that the reduction of pain during the examination might affect the subsequent relapse rate. After scoring PMS and providing informed consent, patients were blindly randomized to the CO2 insufflation (CO2) or air insufflation (Air) groups. Because the button for CO2 insufflation differs from that for air insufflation, the doctors knew the group the patients were in; however, the patients were unaware of the insufflation method used. After the standard bowel preparation using polyethylene glycol, the endoscopists performed the same procedures for all patients regardless of their assigned group. Stratified randomization was used to allocate the patients in a 1:1 ratio to the Air and CO2　groups; and its adjustment factors included sex, age, and disease extent. Satoshi Hiyama was responsible for creating the randomization protocol. The data collection, management, and patient randomization were performed using a secure Research Electronic Data Capture (REDCap) database [17]. All the endoscopists who conducted the colonoscopies had more than 5 years of experience in performing a colonoscopy. Subjective symptoms immediately after colonoscopy and 30 min after colonoscopy were assessed by inquiry forms provided to each patient. Moreover, the PMS was calculated at 1 week and 8 weeks after colonoscopy. The window periods of the visit were + 1 week for Week 1 and +/- 2 weeks for Week 8. The authors had access to information that could identify individual participants during or after data collection in their usual medical care.

Endpoints

We set the primary endpoint as the clinical relapse rate, defined as PMS ≥ 3, at 1 week after colonoscopy. Meanwhile, secondary endpoints were set as follows: clinical relapse rate at 8 weeks after colonoscopy, change in treatment after colonoscopy, changes in vital signs (blood pressure and oxygen saturation [SpO2]) after colonoscopy, subjective symptoms (abdominal fullness and pain) immediately after colonoscopy and at 30 min after colonoscopy, which were scored from 0 to 5 using the visual analog scale, and cecum intubation rate/intubation time/total procedure time. Adverse events were defined as those events deemed by the physician to be harmful regardless of whether or not they were causally related to the protocol treatment, and the following were treated as serious adverse events: events resulting in death, life-threatening occurrence, and events that can result in permanent or marked disability or dysfunction.

Sample size calculation

As a previous report indicated that 16% of patients with UC who underwent colonoscopy experienced symptom exacerbations and required additional UC treatment [8], we assumed an exacerbation rate of 16% in patients who received air insufflation and 5% in those who received CO2 insufflation. Based on an α error of 0.05 and a power of 0.8, the number of cases required to detect a significant effect was estimated to be 119 in each group (total of 238). The number of patients with UC attending our hospital was approximately 250, and therefore we judged that an adequate case accumulation could be expected in 2 years. However, accumulating the appropriate number of cases became difficult; owing to the increasing number of cases undergoing sedated endoscopic procedures, the steering committee discontinued the accumulation of cases after 4 years, twice the originally planned period for case accumulation. The total number of cases was 107 when patient recruitment ended.

Statistical analysis

An intention-to-treat analysis was used to compare the outcomes between the two groups. Additionally, descriptive statistics were used to quantify the results. Continuous variables were presented by the randomized groups, by using the mean with standard deviation for normal distributed data and median with interquartile range (IQR) for non-normal distributed data. Differences among categorical values were analyzed using Pearson’s χ2 test or Fisher’s exact test, while differences between groups were analyzed using Mann–Whitney U test for non-parametric data. We used available-case analysis to deal with missing data. Measurements were analyzed with JMP software version 14.0.0 (SAS Institute, Cary, NC, USA). Differences were considered statistically significant when p < 0.05.

Results

Patients

Informed consent was obtained from 107 patients with UC, all of whom were randomized to either the CO2 or Air group (Fig 1). The first patient was included in the study on September 3, 2015, and the last patient was randomized on September 20, 2019. Of the 107 patients, 6 underwent sedated endoscopy; 4 patients were in clinical remission when the informed consent was obtained, though their PMSs were ≥ 3 at the time of the colonoscopy; 1 patient was unable to give accurate subjective symptoms owing to dementia. After excluding these 11 patients who did not fulfill the inclusion criteria, data for a total of 96 patients (CO2 group; n = 45 and Air group; n = 51) were analyzed (Fig 1). All patients were performed the colonoscopy in the group they were originally assigned by randomization. The baseline characteristics, including sex, age, disease period, disease extent, clinical activity (PMS), endoscopic score (Mayo endoscopic subscore [MES]), and treatment, did not differ between the two groups (Table 1), and no adverse events occurred during the study period.

Fig 1. Flow diagram of the study.

Fig 1

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Overall, 107 patients with UC were recruited, all of whom were randomized into the CO2 group or Air group. After excluding 11 patients, a total of 96 patients (CO2 group; n = 45, Air group; n = 51) were analyzed.

Table 1. Characteristics of the participants in the study.

　 CO2 group (n = 45) Air group (n = 51)
Age, median (IQR) 53 (33.5) 46 (26)
Sex, male/female, n (%) 27 (60)/18 (40) 33 (65)/18 (35)
Disease period, median (IQR) (year) 12 (13.5) 11 (14)
Location of disease (Pancolitis/Left-sided/Proctitis), n 25/13/7 26/13/12
Type of clinical course (Relapse-remitting/chronic continuous/acute fulminating/first attack), n 33/11/0/1 38/11/0/2
Clinical activity (PMS 0/1/2) 27/8/10 30/13/8
Endoscopic activity (MES 0/1/2/3) 24/15/5/1 29/14/8/0
Medications
    Mesalamine, n (%) 40 (89) 43 (84)
    Systemic steroids, n (%) 1 (2.2) 1 (2.0)
    Immunomodulators, n (%) 8 (18) 10 (20)
    Anti-TNF-α (infliximab, adalimumab), n (%) 4 (8.9) 5 (9.8)
    Tac/TOF/VED, n (%) 0 (0) 0 (0)
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IQR; interquartile range, MES; Mayo endoscopic subscore, PMS; partial Mayo score, Tac; tacrolimus, TOF; tofacitinib, VED; vedolizumab

Colonoscopy procedure

Because information regarding the colonoscopy procedure and subjective symptoms after the colonoscopy was missing in 5 patients, analyses of the colonoscopy procedure were only performed on the remaining 91 patients (CO2 group; n = 43, Air group; n = 48). The cecum intubation rate was comparable between the CO2 and Air groups (100% [43/43] vs. 97.9% [47/48]; p = 0.34). The CO2 and Air groups did not differ significantly regarding the cecal intubation time (median [IQR]; 7 [8] min vs. 6 [6] min, respectively; p = 0.11), total procedure time (22 [16] min vs. 24 [13] min, respectively; p = 0.66), or in years of experience of the endoscopists performing the colonoscopies (7 [6] years vs. 7 [5] years, respectively; p = 0.62) (Table 2).

Table 2. Procedural characteristics.

　 CO2 group (n = 43) Air group (n = 48) p
Cecal intubation rate (%) 43 (100) 47 (97.9) 0.34 †
Intubation time, median (IQR) (min)　 7 (8) 6 (6) 0.11 ‡
Total time, median (IQR) (min) 22 (16) 24 (13) 0.66 ‡
Years of experience of the operators, median (IQR) (year) 7 (6) 7 (5) 0.62 ‡
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†; Pearson χ2 test

‡; Mann–Whitney U test, IQR; interquartile range

Clinical relapse rate

The overall clinical relapse rates of this study participant (n = 96) were 8.3% (8/96) at week 1 and 7.3% (7/96) at week 8 (Fig 2A). Subsequently, we investigated the difference in the clinical relapse rate between the CO2 and Air groups. Although the patients in the CO2 group tended to have a lower relapse rate, the difference between the two groups was not significant at week 1 (4.4% vs. 11.8%; p = 0.28) or week 8 (2.2% vs. 11.8%; p = 0.12) (Fig 2B).

Fig 2. Clinical relapse rate after colonoscopy.

Fig 2

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(A) shows the overall clinical relapse rates of the study participants. (B) (left) indicates the clinical relapse rate at 1 week after colonoscopy. (right) The clinical relapse rate at 8 weeks after colonoscopy. Data were analyzed using Fisher’s exact test.

Furthermore, to evaluate whether the severity of the mucosal inflammation identified by colonoscopy affected the post-procedural relapse rate, we divided patients according to the MES, which quantified mucosal disease activity from endoscopic findings. Among patients with MES 0, the clinical relapse rate did not differ between the two groups. Meanwhile, among patients with MES ≥ 1, the clinical relapse rate was significantly lower in the CO2 group than in the Air group at week 8 (0% vs. 22.7%; p = 0.049) (Fig 3A). In addition, to examine whether the clinical activity before colonoscopy affected the post-procedural relapse rate, we also divided patients according to the PMS. Among patients with PMS 0, the clinical relapse rate did not differ significantly between the two groups; however, among patients with PMS 1 or 2, the clinical relapse rate was significantly lower in the CO2 group than in the Air group at week 8 (0% vs. 28.6%; p = 0.022) (Fig 3B). Consequently, colonoscopy with air might be more harmful in patients who are not in complete remission at the time of the procedure.

Fig 3. Clinical relapse rate after colonoscopy adjusted by Mayo endoscopic subscore (MES) or partial Mayo score (PMS).

Fig 3

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(A) indicates the clinical relapse rate at 1 and 8 weeks after colonoscopy based on the MES. Patients were divided into two groups, MES 0 and MES 1–3, and analyzed separately. n.s., not significant. Data were analyzed using Fisher’s exact test. (B) shows the clinical relapse rate at 1 and 8 weeks after colonoscopy bad on PMS. Patients were divided into two groups, PMS = 0 or PMS = 1–2, and analyzed separately. n.s., not significant. Data were analyzed using Fisher’s exact test.

Subjective symptoms

Regarding subjective symptoms, we investigated the difference in post-procedural abdominal fullness and pain between the CO2 and Air groups. The scores of abdominal fullness were significantly lower in the CO2 group than in the Air group immediately after colonoscopy (1 vs. 2; p = 0.0003) and at 30 min after colonoscopy (0 vs. 2; p < 0.0001) (Fig 4A). Similarly, the abdominal pain scores were significantly lower in the CO2 group than in the Air group immediately after colonoscopy (0 vs. 1; p = 0.0003) and at 30 min after colonoscopy (0 vs. 1; p < 0.0001) (Fig 4B). These results strongly suggest that, compared with air insufflation, CO2 insufflation is associated with reduced abdominal discomfort after colonoscopy.

Fig 4. Subjective symptoms after colonoscopy.

Fig 4

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(A) shows the abdominal fullness scores immediately after (left) and at 30 min after (right) colonoscopy. Data were analyzed using the Mann–Whitney U test. The graphs show median with IQR. (B) indicates the abdominal pain score immediately after (left) and 30 min after (right) colonoscopy. Data were analyzed using the Mann–Whitney U test. The graphs show median with IQR.

Changes in vital signs

Systolic blood pressure (SBP), diastolic blood pressure (DBP), and peripheral SpO2 were measured in all study participants at the baseline and end of the colonoscopy procedure. No severe changes in SBP, DBP, or SpO2 were detected in either of the two groups, whereas the CO2 group showed a significantly smaller change in the SpO2 during the colonoscopy procedure than the Air group (0 vs. -1, p = 0.0011) (Table 3). These results indicate that neither CO2 nor air insufflation induces severe changes in vital signs during colonoscopy.

Table 3. Changes in vital signs after colonoscopy.

　 CO2 group (n = 43) Air group (n = 48) P
Pre-CS Post-CS Change Pre-CS Post-CS Change
Systolic blood pressure, median (IQR) (mmHg) 126 (26) 118 (23) -4 (18) 123 (25.75) 116.5 (27.25) -4.5 (15) 0.33 †
Diastolic blood pressure, median (IQR) (mmHg) 74 (19) 74 (22) 0 (12) 72 (17) 75.5 (20) +4 (14) 0.15 †
SpO2, median (IQR) (%) 98 (2) 98 (1) 0 (1) 98 (2) 97.5 (2.75) -1 (2) 0.0011 †
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†; Mann–Whitney U test, IQR; interquartile range, CS; colonoscopy

Changes in treatment due to clinical aggravation after colonoscopy

During the observation period, 4.4% of patients in the CO2 group (2/45) and 7.8% of patients in the Air group (4/51) required more intensive treatment for UC after colonoscopy, and there were no significant differences between the two groups. The treatment changes included dose-escalation or types of 5-aminosalicylic acid (ASA) (CO2 group, n = 2; Air group, n = 1), additional topical therapy of 5-ASA (Air group, n = 1), and additional topical therapy with prednisolone (Air group, n = 1) or hydrocortisone (Air group, n = 1).

Discussion

This study evaluated discomfort following the colonoscopy procedure and the long-term disease relapse rate for approximately 8 weeks after colonoscopy in a single-blinded RCT. Subjective symptoms after colonoscopy were significantly different between the CO2 and Air groups, consistent with findings from previous studies; however, the overall relapse rate did not differ between the CO2 and Air groups for approximately 8 weeks after colonoscopy. Nevertheless, for patients not in complete remission (MES ≥ 1 or PMS ≥ 1), the clinical relapse was significantly lower in the CO2 group at 8 weeks after colonoscopy.

Previous studies reported that colonoscopy performed with CO2 insufflation was safe and reduced post-procedural pain [10, 18], which might be primarily due to the more rapid absorption and elimination of CO2 from the colon, compared to colonoscopy performed using air insufflation [19]. An RCT on patients with IBD also reported that using CO2 insufflation reduced subjective symptoms, including abdominal pain and bloating, at 1 and 3 h after colonoscopy [12]. However, the incidence of longer-term symptomatic worsening in patients with UC after colonoscopy with CO2 insufflation has not yet been investigated. Our results suggest that air insufflation has more harmful effects in patients with subclinical intestinal inflammation, though it takes a comparatively long time until the effect manifests as a clinical relapse. Considering these findings, it may be more economical and preferable for patients and the environment to perform colonoscopy with air insufflation in patients with PMS 0 and CO2 insufflation in patients with PMS ≥ 1.

The reason for the different relapse rates between groups at week 8 but not at week 1 is unclear; nevertheless, changes in the intestinal microbiota of the patients may provide a partial explanation. A recent RCT that examined changes in gut microbiota in fecal samples collected after colonoscopy with CO2 or air insufflation reported that the relative abundance of some Bacteroides members, which were all obligate anaerobes, was significantly higher in the CO2 insufflation group than in the air insufflation group [20]. Furthermore, previous studies reported that a decrease in normal anaerobic bacteria, including Bacteroides, Eubacterium, and Lactobacillus species, is associated with the pathogenesis of mucosal inflammation in patients with IBD [21, 22]. These results suggested that air insufflation may reduce some important anaerobic bacteria that cannot live in the presence of oxygen in the colon and exacerbate the activity of UC through host-pathogen immunological interactions. This process probably takes at least a few weeks, which may explain why the clinical relapse rate in the Air group increased 8 weeks after colonoscopy.

In this study, one patient had an MES = 3 with PMS = 0 at the beginning of the study. The PMS is known to well correlate with the full Mayo score, including the MES, and is widely used because it is noninvasive [23]. However, there are a certain number of cases in which the PMS deviates from the MES. In this study, we found that patients with a high MES were more likely to be aggravated by air insufflation. Accordingly, even if a patient’s PMS is low and the colonoscopy was started using air insufflation, switching to CO2 insufflation when high disease activity is identified during colonoscopy should be considered. Actually, among the other patients with MES ≤ 2, the relapse rate tended to increase in patients with higher MES (S1 Fig).

Furthermore, although blood pressure changes did not differ between the two groups, changes in the SpO2 during the colonoscopy procedure were significantly smaller in the CO2 group than in the Air group. A previous study reported that the increase in the abdominal circumference at 15 min was significantly smaller after a colonoscopy performed with CO2 insufflation than after a colonoscopy conducted with air insufflation and that CO2 insufflation reduced the abdominal distention after colonoscopy [24]. The lower change rate in SpO2 in the CO2 group observed in our study may be due to the slight decrease in abdominal pressure, leading to lower pressure in the lung.

This study has some limitations. First, this was a single-center study and not double-blinded. In addition, the number of participants was relatively small because of the increase in the number of cases undergoing sedated endoscopic procedures, making it difficult to recruit the required number of patients despite nearly doubling the recruitment period. If there had been a larger number of participants, there might have been a significant difference in the primary endpoint. Second, the exact amount of air or CO2 delivered into or suctioned from the colon during colonoscopy could not be measured in this study. Third, we did not specify the type of endoscopes and endoscopists in the study. This was a result of randomizing the study to reduce the impact of these factors on its results; however, the physicians were not blinded, which could have impacted its results. Fourth, the participants of this study only included patients with UC in clinical remission. Finally, we could not eliminate the selection bias and information bias such as the white coat effect, although we tried to reduce this effect by giving the patients inquiry sheets after the colonoscopy and having the office staff collect them, instead of having this inquiry be directly done by the endoscopists. More studies are needed in the future that will include patients with active UC and a double-blind RCT in patients undergoing sedated procedures.

Conclusions

In conclusion, CO2 insufflation could reduce abdominal discomfort after colonoscopy in patients with UC in clinical remission, and may be associated with a decrease in clinical relapse at 8 weeks after colonoscopy in patients not in complete remission (PMS ≥ 1 or MES ≥ 1).

Supporting information

S1 Checklist. CONSORT 2010 checklist of information to include when reporting a randomised trial*.

(DOC)

Click here for additional data file. (221KB, doc)
S1 Text. Protocol of the study.

(DOCX)

Click here for additional data file. (35.9KB, docx)
S1 Fig. Bar graphs showing the clinical relapse rate that was analyzed separately by the Mayo endoscopic subscore.

(TIF)

Click here for additional data file. (939.6KB, tif)

Acknowledgments

We would like to thank Editage (www.editage.com) for English language editing.

Ethical considerations

The study was approved by the Institutional Research Ethics Board at Osaka University Hospital (No. 14372). The study was explained orally and in an attached patient information sheet, and consent was obtained in writing. The consent was obtained after stating in the explanation document that participation in the study is voluntary, that no disadvantages will be incurred if the patient does not agree to participate, and that the patient has the right to withdraw the consent obtained for the study at any time without any disadvantages. For minor patients, consent was obtained from the patients themselves and their parents or guardians. This clinical research was conducted in compliance with the Ethical Guidelines for Clinical Research (Ministry of Health, Labor, and Welfare) and the Declaration of Helsinki (World Medical Association). Adverse events were defined as events deemed by the physician to be harmful regardless of whether or not they are causally related to the protocol treatment and the following were treated as serious adverse events.

  1. Those resulting in death

  2. Life-threatening

  3. Those that result in permanent or marked disability or dysfunction.

In the case of a serious adverse event, the head of the facility and the principal investigator were notified immediately. When handling data related to the study, due consideration will be given to protect the confidentiality of the subjects.

Data Availability

All relevant data are within the manuscript and its Supporting Information files.

Funding Statement

The authors received no specific funding for this work.

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Decision Letter 0

Antonio Brillantino

30 May 2023

PONE-D-23-12603Carbon dioxide insufflation reduces the relapse of ulcerative colitis after colonoscopy: a randomized controlled trialPLOS ONE

Dear Dr. Takehara,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

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Antonio Brillantino

Academic Editor

PLOS ONE

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Additional Editor Comments:

It is an interesting study that needs to be carefully reviewed according to reviewers' comments.

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Reviewers' comments:

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Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

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Reviewer #1: Partly

Reviewer #2: Partly

Reviewer #3: Yes

**********

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: No

Reviewer #2: Yes

Reviewer #3: Yes

**********

3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

Reviewer #2: Yes

Reviewer #3: Yes

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

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Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: This is an interesting study comparing the advantages of colonoscopy with CO2 insufflation or air insufflation in patients with UC in remission regarding subjective symptoms after endoscopy and post-procedural clinical relapse,

Some points to consider:

1. Primary endpoint defined as PMS >=1 after colonoscopy, was there a window before or after this week for logistical reasons? i.e 7 days (+/-1) .

2. In line 151, state the number of cases at the point when the trial steering made the decision to stop recruitment?

3. In the statistical analysis section include as a first sentence or two, that descriptive analysis will be presented by randomised groups (i.e mean (SDs) for normally distributed variables and median(IQR) for non-normal data..

4. Define your populations of analyses for primary outcomes (i.e as randomisation regardless of what treatment was received -ITT, However looks like the analysis population is excludes those patients those lost to follow-up?

5. Mention how missing data will be handled in the stats section?

6. The authors state randomisation accounted for sex, age and disease extent (this is vague and should be more explicit - i.e stratification or minimisation?. Also state the allocation ratio and who was responsible for creating the randomisation schedule?

7. Safety outcomes were considered, i.e adverse events so include this in stats section, after the secondary outcomes.

8. Also mention that that CONSORT guidelines were implemented to report the RCT in the stats section.

9. With the outcome subjective response - did the authors consider a “white coat effect” bias, how was this handled?

10. In results section, state the recruitment period (i.e start date to date last patient was randomised)

11. Table 1 - this is an RCT and not recommended to test between groups, any differences observed will be due to chance. Recommend to remove p-values.

12. Table 2 and Table 3 - the Mann Whitney was performed, then mean (SD) should not be presented and instead median (IQR), otherwise this is misleading in terms what exactly is being compared.

Reviewer #2: This article examines the impact of endoscopy on symptoms and relapses after endoscopy for patients with ulcerative colitis (UC) in remission between those undergoing endoscopy under standard Air and the CO2.

1. This reviewer understood no difference in intubation time between the CO2 and the standard Air groups in this study. However, was no aspiration performed during the endoscopy procedure in this study? This reviewer is sure that there are cases where suction is applied during endoscopy to remove cleaning fluid and residual stools. Therefore, it would be difficult to accurately measure the amount of Air and CO2 delivered to individual patients and assess the impact, even if the procedure time is the same. This is the most disadvantageous point in this study

2. Sedated endoscopy reduces patient stress. Hence, this reviewer recommends excluding data from patients who underwent endoscopy under sedation.

3. Four patients in each group are receiving anti-TNF antibody therapies. Is this treatment a regular regimen? Also, was there any difference in the tendency to relapse after endoscopy in patients receiving these advanced therapies compared to patients in the 5-ASA treatment alone group?

Reviewer #3: Although CO2 insufflation is increasingly used during colonoscopy, this study is original and interesting. It is regrettable that the number of patients studied is too small. As a result, the primary objective of the study is negative, whereas with the appropriate number of patients it might have been positive. This point needs to be addressed more widely in the discussion.

Why only patients who underwent colonoscopy without sedation were included?

One patient had an MES = 3, which is surprising given that the patients were in clinical remission. This point needs to be addressed in the discussion.

Interestingly, only patients with active lesions at endoscopy showed clinical recurrence. Even if the number of patients in each group is small, it would be interesting to know the percentage of clinical recurrence at one and eight weeks according to the MES observed (0, 1, or 2) during colonoscopy.

The conclusion should be more cautious and use the conditional form.

**********

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Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

**********

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PLoS One. 2023 Aug 17;18(8):e0290329. doi: 10.1371/journal.pone.0290329.r002

Author response to Decision Letter 0

28 Jun 2023

Editor:

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Reply: We really appreciate the editor’s comments. According to the reviewer’s suggestions, we have carefully revised the manuscript. We think we responded to all the concerns raised by the reviewers.

Journal requirements:

When submitting your revision, we need you to address these additional requirements.

1. Please ensure that your manuscript meets PLOS ONE's style requirements, including those for file naming. The PLOS ONE style templates can be found at https://journals.plos.org/plosone/s/file?id=wjVg/PLOSOne_formatting_sample_main_body.pdf and https://journals.plos.org/plosone/s/file?id=ba62/PLOSOne_formatting_sample_title_authors_affiliations.pdf

Reply: We have modified the manuscript and file names to meet PLOS ONE's style requirements.

Additional Editor Comments:

It is an interesting study that needs to be carefully reviewed according to reviewers' comments.

Reply: Thank you for the editor’s comments. “Point-by-point responses” to the reviewers’ comments have been provided below. We have carefully reviewed the reviewers’ comments and revised the manuscript accordingly.

Reviewer #1:

This is an interesting study comparing the advantages of colonoscopy with CO2 insufflation or air insufflation in patients with UC in remission regarding subjective symptoms after endoscopy and post-procedural clinical relapse,

Some points to consider:

Reply: Thank you for your review and thoughtful comments regarding our manuscript. Our responses to your comments are as follows:

1. Primary endpoint defined as PMS >=1 after colonoscopy, was there a window before or after this week for logistical reasons? i.e 7 days (+/-1) .

Reply: We appreciate the reviewer’s comments. The window periods of the visit were +1 week for Week 1 and +/- 2 weeks for Week 8. We have added the appropriate description in the Protocol section (page 9, lines 129–130), as follows:

“The window periods of the visit were + 1 week for Week 1 and +/- 2 weeks for Week 8.”

2. In line 151, state the number of cases at the point when the trial steering made the decision to stop recruitment?

Reply: Thank you for pointing this out. The total number of cases was 107 when patient recruitment ended. We have added an appropriate statement in the Sample size calculation section (page 10, lines 157–158), as follows:

“The total number of cases was 107 when patient recruitment ended.”

3. In the statistical analysis section include as a first sentence or two, that descriptive analysis will be presented by randomised groups (i.e mean (SDs) for normally distributed variables and median(IQR) for non-normal data..

Reply: Thank you for the reviewer’s comments. As per the reviewer’s suggestion, we have added a statement that clarifies that we conducted descriptive analysis on two randomized groups and we used “mean with standard error” for parametric data and “median with interquartile range” for non-parametric data presenting continuous variables in the Statistical analysis section (pages 10-11, lines 162-165), as follows:

“Additionally, descriptive statistics were used to quantify the results. Continuous variables were presented by the randomized groups, by using the mean with standard error for normal distributed data and median with interquartile range (IQR) for non-normal distributed data.”

4. Define your populations of analyses for primary outcomes (i.e as randomisation regardless of what treatment was received -ITT, However looks like the analysis population is excludes those patients those lost to follow-up?

Reply: Thank you very much for your significant indication. Six patients (Air = 3, CO2 = 3) whose inquiry sheets, which gathered their subjective symptoms could not be collected were excluded as “lost to follow-up” from analysis for primary and secondary outcomes in the previous unrevised manuscript. Of those 6 patients, one patient was not able to accurately fill out any of the inquiry sheets due to dementia, which prevented us from collecting the essential data for this study including PMS. Therefore, this patient was determined to meet the exclusion criteria (“judged by the doctors to be in a condition unsuitable for the study”) and excluded from the population of the analysis. We have mentioned this in the Patients section, (page 12, lines 178-179), as follows:

“1 patient was unable to give accurate subjective symptoms owing to dementia.”

For the remaining 5 patients, only the inquiry sheets on subjective symptoms immediately after and 30 minutes after colonoscopy were missing. The relapse rate at Week 1 and Week 8 could be evaluated based on their answers on the inquiry sheets; therefore, we have judged that these 5 patients should not be excluded.

In the revised version, we have added the 5 patients to the analysis for the relapse rate, and only excluded them from the analysis regarding colonoscopy procedure and discomfort after colonoscopy. We have mentioned this in the Colonoscopy procedure section, (page 14, lines 196–198), as follow:

"Because information regarding the colonoscopy procedure and subjective symptoms after the colonoscopy was missing in 5 patients, analyses of the colonoscopy procedure were only performed on the remaining 91 patients (CO2 group; n = 43, Air group; n = 48).”

Accordingly, we have modified the flowchart in Fig 1 and amended the results of the analyses in the manuscript in Table 1 and the Patients, Clinical relapse rate, and Changes in treatment due to clinical aggravation after colonoscopy sections.

5. Mention how missing data will be handled in the stats section?

Reply: Thank you for pointing this out. Patients who met the exclusion criteria were first excluded. Then, we used available-case analysis to deal with the missing data. We have added a statement regarding handling the missing data in the Statistical analysis section (page 11, lines 167–168), as follows:

“We used available-case analysis to deal with missing data.”

6. The authors state randomisation accounted for sex, age and disease extent (this is vague and should be more explicit - i.e stratification or minimisation?. Also state the allocation ratio and who was responsible for creating the randomisation schedule?

Reply: Thank you for the reviewer’s thoughtful comments. The randomization in this study was performed using stratified randomization, and the allocation ratio was 1:1 between the Air and CO2 groups. Satoshi Hiyama was responsible for creating the randomization protocol. We have added this information to the manuscript in the Protocol section (page 8, lines 120–123), as follows:

“Stratified randomization was used to allocate the patients in a 1:1 ratio to the Air and CO2　groups; and its adjustment factors included sex, age, and disease extent. Satoshi Hiyama was responsible for creating the randomization protocol.”

7. Safety outcomes were considered, i.e adverse events so include this in stats section, after the secondary outcomes.

Reply: We appreciate the reviewer’s comments. We defined adverse events as those events deemed by the physician to be harmful regardless of whether or not they were causally related to the protocol treatment, and the following were treated as serious adverse events: events resulting in death, life-threatening occurrence, and events that can result in permanent or marked disability or dysfunction. As per the reviewer’s suggestion, we have added an appropriate statement in the Endpoints section (page 9-10, lines 140–144), as follows:

“Adverse events were defined as those events deemed by the physician to be harmful regardless of whether or not they were causally related to the protocol treatment, and the following were treated as serious adverse events: events resulting in death, life-threatening occurrence, and events that can result in permanent or marked disability or dysfunction.”

8. Also mention that that CONSORT guidelines were implemented to report the RCT in the stats section.

Reply: Thank you for the reviewer’s comments. As the reviewer suggested, we had added a sentence mentioning that this study was designed and analyzed in compliance with the CONSORT guidelines in the Study design section (page 7, lines 98–100), as follows:

“This study was designed and analyzed in compliance with the CONSORT (Consolidated Standards of Reporting Trials) guidelines.”

9. With the outcome subjective response - did the authors consider a “white coat effect” bias, how was this handled?

Reply: We appreciate the reviewer’s concern. We have tried to eliminate the white coat bias effect to the best of our ability by giving the patients inquiry sheets, which asked about their subjective symptoms, to fill out after the colonoscopy, and having the office staff collect them, rather than having the colonoscopists directly make this inquiry themselves. However, we think that this bias was not completely eliminated. We have mentioned this point in the Discussion section (page 23, lines 346-349), as follows:

“Finally, we could not eliminate the selection bias and information bias such as the white coat effect, although we tried to reduce this effect by giving the patients inquiry sheets after the colonoscopy and having the office staff collect them, instead of having this inquiry be directly done by the endoscopists.”

10. In results section, state the recruitment period (i.e start date to date last patient was randomised)

Reply: Thank you for pointing this out. The first patient was included in the study on September 3, 2015, and the last patient was randomized on September 20, 2019. As per the reviewer’s suggestion, we have added a relevant statement in the Patients section (page 12, lines 174–175), as follows:

“The first patient was included in the study on September 3, 2015, and the last patient was randomized on September 20, 2019.”

11. Table 1 - this is an RCT and not recommended to test between groups, any differences observed will be due to chance. Recommend to remove p-values.

Reply: Thank you for the important suggestion. As per the reviewer’s suggestion, we removed p-values from Table 1.

12. Table 2 and Table 3 - the Mann Whitney was performed, then mean (SD) should not be presented and instead median (IQR), otherwise this is misleading in terms what exactly is being compared.

Reply: Thank you very much for your comments. As the reviewer mentioned, “mean with SD” was changed to “median with IQR” on Mann–Whitney U test for non-parametric data in Table 2, Table 3, and the error bars on graphs in Figure 4 were changed to show median with IQR accordingly.

Reviewer #2:

This article examines the impact of endoscopy on symptoms and relapses after endoscopy for patients with ulcerative colitis (UC) in remission between those undergoing endoscopy under standard Air and the CO2.

Reply: Thank you very much for your review and valuable comments regarding our manuscript. Our responses to your comments are as follows:

1. This reviewer understood no difference in intubation time between the CO2 and the standard Air groups in this study. However, was no aspiration performed during the endoscopy procedure in this study? This reviewer is sure that there are cases where suction is applied during endoscopy to remove cleaning fluid and residual stools. Therefore, it would be difficult to accurately measure the amount of Air and CO2 delivered to individual patients and assess the impact, even if the procedure time is the same. This is the most disadvantageous point in this study

Reply: Thank you for the significant concerns raised by the reviewers. As the reviewer pointed out, fluids, residual stools, and gases were suctioned during endoscopy, and the exact amount of delivered gas could not be accurately detected by only using the procedure time as a reference. Although it is difficult to accurately measure the volume of both the fluids and gases aspirated, we agree with the reviewer that it is an important limitation of this study and we have added this limitation in the Discussion section (page 23, lines 340-342), as follows:

“Second, the exact amount of air or CO2 delivered into or suctioned from the colon during colonoscopy could not be measured in this study.”

2. Sedated endoscopy reduces patient stress. Hence, this reviewer recommends excluding data from patients who underwent endoscopy under sedation.

Reply: We completely agree with your suggestion. Patients who received sedated colonoscopy met the exclusion criteria and were excluded from the study. Therefore, their data were not included in the present analysis as shown in Figure 1, and we have mentioned this in the Protocol section of the manuscript (page 8, lines 111-114), as follows:

“The reason for excluding patients who underwent sedated colonoscopy was that it would be difficult to accurately evaluate changes in subjective symptoms immediately and 30 minutes after the colonoscopy in these patients. Furthermore, it was considered that the reduction of pain during the examination might affect the subsequent relapse rate.”

3. Four patients in each group are receiving anti-TNF antibody therapies. Is this treatment a regular regimen? Also, was there any difference in the tendency to relapse after endoscopy in patients receiving these advanced therapies compared to patients in the 5-ASA treatment alone group?

Reply: We appreciate the reviewer’s comments. All patients on anti-TNF antibody therapies were receiving regular anti-TNF antibody drugs as a maintenance phase. As shown below, anti-TNF antibody therapies did not affect the clinical relapse rate at Week 1 (p = 0.56) or Week 8 (p = 0.13).

The relapse rate at Week 8 may have had a tendency to be slightly higher in patients on anti-TNF therapies, and this may be because those patients generally have high disease activity and are at high risk of relapse.

The clinical relapse rate at 1 week and 8 weeks after colonoscopy with or without anti-TNF antibodies treatment. n.s., not significant. Data were analyzed using Fisher’s exact test.

Reviewer #3:

Although CO2 insufflation is increasingly used during colonoscopy, this study is original and interesting.

Reply: Thank you very much for your review and fruitful comments regarding our manuscript. Our responses to your comments are as follows:

It is regrettable that the number of patients studied is too small. As a result, the primary objective of the study is negative, whereas with the appropriate number of patients it might have been positive. This point needs to be addressed more widely in the discussion.

Reply: We appreciate the reviewer’s comments. As per the reviewer’s suggestion, we have mentioned the possibility that we might have had a positive result for the primary endpoint if the number of participants was large enough in the Discussion section (page 23, lines 339-340), as follows:

“If there had been a larger number of participants, there might have been a significant difference in the primary endpoint.”

Why only patients who underwent colonoscopy without sedation were included?

Reply: The reviewer’s question is very important. We expected that that it would be difficult to accurately assess changes in subjective symptoms immediately and 30 minutes after the colonoscopy in patients who underwent sedated colonoscopy. Moreover, we were concerned that the reduction of pain during the examination might affect the subsequent relapse rate. Therefore, patients who underwent sedated colonoscopy were excluded from the present study. We have added this information in the Protocol section of the manuscript (page 8, lines 111-114), as follows:

“The reason for excluding patients who underwent sedated colonoscopy was that it would be difficult to accurately evaluate changes in subjective symptoms immediately and 30 min after the colonoscopy in these patients. Furthermore, it was considered that the reduction of pain during the examination might affect the subsequent relapse rate.”

One patient had an MES = 3, which is surprising given that the patients were in clinical remission. This point needs to be addressed in the discussion.

Reply: We appreciate the reviewer’s valuable comments. As the reviewer point out, there are a certain number of cases in which endoscopic findings and clinical symptoms diverge in practice, and we should pay attention to those patients that have high endoscopic activity without any clinical symptoms. We have added this point in the Discussion section (pages 21-22, lines 318-325), as follows:

‘” In this study, one patient had an MES = 3 with PMS = 0 at the beginning of the study. The PMS is known to well correlate with the full Mayo score, including the MES, and is widely used because it is noninvasive[23]. However, there are a certain number of cases in which the PMS deviates from the MES. In this study, we found that patients with a high MES were more likely to be aggravated by air insufflation. Accordingly, even if a patient’s PMS is low and the colonoscopy was started using air insufflation, switching to CO2 insufflation when high disease activity is identified during colonoscopy should be considered.”

Interestingly, only patients with active lesions at endoscopy showed clinical recurrence. Even if the number of patients in each group is small, it would be interesting to know the percentage of clinical recurrence at one and eight weeks according to the MES observed (0, 1, or 2) during colonoscopy.

Reply: Thank you for the reviewer’s valuable comments. As per the reviewer’s suggestion, we have analyzed the proportion of the relapses separately for MES 0, 1, and 2, and found that patients with MES 2 had a higher proportion of relapse both at Week1 and Week 8 than those with MES 0 or MES 1. We have added the graphs below as S3 Fig., and mentioned the relevant information in the Discussion section (page 22, lines 325-326), as follows:

“Actually, among the other patients with MES ≤ 2, the relapse rate tended to increase in patients with higher MES (S3 Fig).”

S3 Fig. The clinical relapse rate analyzed separately by Mayo endoscopic subscore.

The conclusion should be more cautious and use the conditional form.

Reply: We appreciate the reviewer’s valuable comments. We have modified the language used in the conclusions section as per your suggestion. Additionally, we have added the detailed condition "PMS ≥ 1 or MES ≥ 1" after the phrase "not in complete remission" in the conclusions section (pages 23-24, lines 354-357), as follows:

“In conclusion, CO2 insufflation could reduce abdominal discomfort after colonoscopy in patients with UC in clinical remission, and may be associated with a decrease in clinical relapse at 8 weeks after colonoscopy in patients not in complete remission (PMS ≥ 1 or MES ≥ 1).”

Thank you for reviewing our resubmission. We look forward to hearing from you and would be happy to make further changes, if required.

Attachment

Submitted filename: Response to reviewers.docx

Click here for additional data file. (68.3KB, docx)

Decision Letter 1

Antonio Brillantino

4 Aug 2023

Carbon dioxide insufflation reduces the relapse of ulcerative colitis after colonoscopy: a randomized controlled trial

PONE-D-23-12603R1

Dear Dr. Takehara,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org.

Kind regards,

Antonio Brillantino

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

According with reviewers suggestions, the article, in its current form, may be accepted for publication

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #3: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #3: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #3: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #3: Yes

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

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Reviewer #1: Yes

Reviewer #3: Yes

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Reviewer #3: No

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Acceptance letter

Antonio Brillantino

9 Aug 2023

PONE-D-23-12603R1

Carbon dioxide insufflation reduces the relapse of ulcerative colitis after colonoscopy: a randomized controlled trial

Dear Dr. Takehara:

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Kind regards,

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on behalf of

Dr Antonio Brillantino

Academic Editor

PLOS ONE

Associated Data

    This section collects any data citations, data availability statements, or supplementary materials included in this article.

    Supplementary Materials

    S1 Checklist. CONSORT 2010 checklist of information to include when reporting a randomised trial*.

    (DOC)

    Click here for additional data file. (221KB, doc)
    S1 Text. Protocol of the study.

    (DOCX)

    Click here for additional data file. (35.9KB, docx)
    S1 Fig. Bar graphs showing the clinical relapse rate that was analyzed separately by the Mayo endoscopic subscore.

    (TIF)

    Click here for additional data file. (939.6KB, tif)
    Attachment

    Submitted filename: Response to reviewers.docx

    Click here for additional data file. (68.3KB, docx)

    Data Availability Statement

    All relevant data are within the manuscript and its Supporting Information files.

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