Review for 10.1186/s12876-019-1065-2 (2019)

Reviewer ’s report  
 
Title: Water exchange colonoscopy decreased adenoma miss rates compared with literature data 
and local data with CO2 insufflation: an observational study  
 
Version: 0 Date: 02 Jul 2019  
 
Reviewer: Li-Chun Chang  
Reviewer's report:  
Cheng et al. conduct the study to compare two insertion methods with regards to the adenoma 
miss rate (AMR). The insertion methods are water exchange and CO2 insufflation, respectively. 
Their result explores that water exchange could reduce AMR of the right colon and proximal 
colon significantly. This is an interesting study, and my review comments are as following:  
1. Concerning the study design, the study could be classified as a case -control study. The study 
compares the AMR between water exc hange (case) and CO2 insufflation (control). Study 1 and 
study 2 in the text and tables are suggested to be replaced with water exchange group and CO2 
insufflation group, respectively. This may help for better understanding and reading.  
2. Regarding the pr ocedure time in table 2, the withdraw time was 17.85 minutes and 21.00 
minutes in water exchange and CO2 insufflation group, respectively. Theoretically, withdraw 
time is speculated to be longer in water exchange because the water is sucked when withdrawin g. 
I am curious about the reason why the withdraw time is longer in CO2 insufflation group rather 
than in water exchange.  
3. Following the procedure time issue in comment 2, the total procedure time of 2nd -pass 
colonoscopy in two groups is significantly d ifferent. Both two groups use the same protocol, 
CO2 insufflation, in 2nd -pass colonoscopy, and the total procedure time is supposed to be not 
different significantly.  
4. Finally, the hyperplastic polyp is harmless and not associated with the risk of CRC. In 
contrast, conventional adenoma or sessile serrated adenoma/polyp (SSA/P), especially advanced 
adenoma or large SSA/P, are closely associated with the risk of CRC. Interval cancer may 
develop once such risky lesion is missed. In table 4 and 5, the miss r ate of adenoma plus 
hyperplastic polyp in both right and proximal colon are listed. However, I would like to know the 
miss rate of advanced adenoma, SSA/P, large SSA/P in both groups. I believe the importance of 
the study will be increased markedly through  this demonstration.  
  
Are the methods appropriate and well described?  
If not, please specify what is required in your comments to the authors.  
 
Yes 
 
Does the work include the necessary controls?  
If not, please specify which controls are required in your comments to the authors.  
 
Yes 
 
Are the conclusions drawn  adequately supported by the data shown?  
If not, please explain in your comments to the authors.  
 
Yes 
 
Are you able to assess any statistics in the manuscript or would you recommend an 
additional statistical review?  
If an additional statistical review is r ecommended, please specify what aspects require further 
assessment in your comments to the editors.  
 
I am able to assess the statistics  
 
Quality of written English  
Please indicate the quality of language in the manuscript:  
 
Acceptable  
 
Declaration of competing interests  
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5. Do yo u have any other financial competing interests?  
 
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No competing  interests.  
 
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