1. History of colorectal surgery 
2. Suspected or known digestive tract obstruction, stricture, or perforation 
3. Serious status of illness, such as severe renal failure whose creatinine clearance<30 ml/min, New York Heart Association grade III or grade IV congestive heart failure, or hemodynamic instability, etc. 
4. Incapable of completing bowel preparation，such as dysphagia, allergy to purgatives, or impaired mental status, etc. 
5. Pregnancy or breastfeeding 
6. Incomplete colonoscopy due to causes except poor bowel preparation 
7. Unable to give informed consent 
8. Have participated in the study before.       
    

NCT03225469_exc_T1
Procedure
colorectal surgery
NCT03225469_exc_T2
Observation
History
NCT03225469_exc_T3
Condition
digestive tract obstruction
NCT03225469_exc_T4
Condition
digestive tract stricture
NCT03225469_exc_T5
Condition
digestive tract perforation
NCT03225469_exc_T9
Condition
renal failure
NCT03225469_exc_T10
Measurement
creatinine clearance
NCT03225469_exc_T11
Value
<30 ml/min
NCT03225469_exc_T12
Qualifier
severe
NCT03225469_exc_T13
Measurement
New York Heart Association
NCT03225469_exc_T14
Value
grade III or grade IV
NCT03225469_exc_T15
Condition
congestive heart failure
NCT03225469_exc_T16
Condition
hemodynamic instability
NCT03225469_exc_T19
Scope
severe renal failure whose creatinine clearance<30 ml/min, New York Heart Association grade III or grade IV congestive heart failure, or hemodynamic instability
NCT03225469_exc_T20
Condition
Serious status of illness
NCT03225469_exc_T22
Condition
Incapable of completing bowel preparation
NCT03225469_exc_T23
Condition
dysphagia
NCT03225469_exc_T24
Condition
allergy
NCT03225469_exc_T25
Drug
purgatives
NCT03225469_exc_T26
Condition
impaired mental status
NCT03225469_exc_T27
Scope
dysphagia, allergy to purgatives, or impaired mental status
NCT03225469_exc_T29
Condition
Pregnancy
NCT03225469_exc_T30
Observation
breastfeeding
NCT03225469_exc_T32
Procedure
colonoscopy
NCT03225469_exc_T33
Condition
poor bowel preparation
NCT03225469_exc_T34
Negation
except
NCT03225469_exc_T35
Qualifier
Incomplete
NCT03225469_exc_T40
Observation
informed consent