Review for 10.1186/s12876-020-01341-9 (2020)

Reviewer ’s report  
 
Title: CO2 or air cholangiography reduces the risk of po st-ERCP cholangitis in patients with 
Bismuth type IV hilar biliary obstruction  
 
Version: 1 Date: 28 Mar 2020  
 
Reviewer's report:  
 
This is a retrosp ective study comparing 3 methods of cholangiogram (contrast, air and CO2) in 
70 patients with Bismuth IV biliary stricture. The study demonstrates that air and CO2 have less 
post-ERCP cholangitis than contrast injection. I have some comments as following.  
 
- Abstract:  
 
1. Authors should emphasize in the methods that the 3 methods of cholangiogram were separated 
chronologically.  
 
2. The conclusion in the abstract is not clear and might mislead. And based on the result there 
was no difference between air and CO2.  
 
- Manuscript:  
 
3. Page 3, line 7. In the background, the evidence and recommendation (e.g. Medicine 
(Baltimore). 2017 Oct ;96(43):e8372. J Gastroenterol Hepatol. 2013 Apr;28(4):593 -607.) show 
that percutaneous is superior to endoscopy for drainage of Bismuth -IV hilar obstruction.  
 
4. Page 3, line 11. The definition of Bismuth -IV described in the manuscript is not correct.  
 
5. Please clarify the cause of obstruction in the methods part. Are all patients diagnosed with 
malignant obstruction? What is the pathology (e.g. cholangiocarcinoma, hepatocellular 
carcinoma)?  
 
6. Please provide the detail of fluoroscopy system used in the s tudy. As the use of air or CO2 
provide less contrast with liver soft tissue than contrast media. What techniques the authors use 
to optimize image quality while using air or CO2. And how the authors prepare CO2 for 
cholangiogram.  
 
7. Page 5, line 5 -9. The definition of clinical success is not available in the cited reference (No. 
1), and the definition described is far different from the recent studies.  
 
8. Page 5, line 17. The unit of hemoglobin is g/dL  
 
9. The statistic part needs rewrite. For example, wha t statistic methods use to describe the 
categorical data, are all the continuous data distributed normally, if not what statistical tests were 
used. The authors should provide sample size calculation.  
   
Are the methods appropriate and well described?  
If not, please specify what is requir ed in your comments to the authors.  
 
No 
 
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 e xplain in your comments to the authors.  
 
No 
 
Are you able to assess any statistics in the manus cript or would you recommend an 
additional statistical review?  
If an additional statistical review is recommended, please speci fy what aspects require further 
assessment in your comments to the editors.  
 
I recommend additional statistical review  
 
Quality of written English  
Please indicate the quality of language in the manuscript:  
 
Not sui table for publication unless extensively edited  
 
Declaration of competing interes ts 
Please complete a declaration of competing interests, considering the following questions:  
 
1. Have you in the past five years received reimbursements, f ees, funding, or salary from an 
organisation that may in any way gain or lose financially from the pu blication of this 
manuscript, either now or in the future?  
2. Do you hold any stocks or shares in an organisation t hat may in any way gain or lose 
financially from the publication of this manuscript, either now or in the future?  
3. Do you hold or are you c urrently applying for any patents  relating to the content of the 
manuscript?  
4. Have you received reimbursements, fees, funding, or salary from an organization that 
holds or has applied for patents relating to the content of the manuscript?  
5. Do you have any other financial competing interests?  
6. Do you have any non -financial competing interests in relation to this paper?  
 
If you can answer no to all of the above, write 'I declare that I have  no competing interests' 
below. If your reply is y es to any, please give details below.  
 
I declare that I have no competing interests.  
 
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on my report to the authors and, if the manuscript is accepted for publicati on, my named report 
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to the editors, which will not be published.  
 
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