What is the purpose of the Boston bowel preparation scale in colonoscopy and how is bowel preparation typically achieved?

Boston Bowel Preparation Scale in Colonoscopy

The Boston Bowel Preparation Scale (BBPS) is the most validated and reliable scoring system for assessing bowel cleanliness during colonoscopy, with scores ≥6 (with each segment ≥2) indicating adequate preparation for accurate polyp detection and appropriate surveillance interval recommendations. 1

Purpose and Significance of the BBPS

• The BBPS was specifically developed to standardize the assessment of bowel preparation quality during colonoscopy withdrawal, after all cleansing maneuvers have been completed 1
• It directly correlates with clinically meaningful outcomes including polyp detection rates, procedure times, and recommendations for repeat procedures 1
• The scale provides objective criteria to determine if a bowel preparation is adequate for detecting polyps >5mm, which is crucial for cancer prevention 2

How the BBPS Works

• The BBPS divides the colon into three segments (right, transverse, and left) with each segment scored from 0-3 1
  • Score 0: Unprepared colon segment with solid stool that cannot be cleared
  • Score 1: Portion of mucosa not seen due to residual stool
  • Score 2: Minor residual staining, small fragments of stool, visible mucosa
  • Score 3: Entire mucosa visible with no residual staining or fragments
• The three segment scores are summed for a total score ranging from 0-9, with 9 being perfectly clean 1
• A score <5 is considered inadequate preparation, requiring repeat colonoscopy 1
• More recent guidelines define adequate preparation as a total score ≥6 with each segment score ≥2 1

Clinical Implications of BBPS Scores

• Patients with BBPS scores ≥5 have significantly higher polyp detection rates (40%) compared to those with scores <5 (24%) 1
• Segments with BBPS scores of 2 or 3 have statistically similar miss rates for adenomas >5mm, both significantly lower than segments with scores of 1 2
• Higher BBPS scores correlate with shorter insertion and withdrawal times during colonoscopy 1
• Repeat colonoscopy is recommended only 2% of the time for patients with BBPS scores ≥5, compared to 73% for those with scores <5 1

Achieving Adequate Bowel Preparation

• Split-dose bowel preparation is the standard and preferred method for achieving adequate cleansing 1, 3
  • First dose: Evening before colonoscopy (typically between 5:00-9:00 PM)
  • Second dose: Morning of colonoscopy (at least 5 hours before but no more than 9 hours prior)
  • Each dose followed by clear liquids (5 glasses after first dose, 3 glasses after second) 3
• Day-before regimen is an alternative when split-dosing is not appropriate 3
  • First dose: Afternoon/early evening before colonoscopy (4:00-6:00 PM)
  • Second dose: Late evening, approximately 6 hours later (10:00 PM-12:00 AM)
  • Each dose followed by clear liquids 3

Advantages of the BBPS Over Other Scales

• The BBPS is applied after washing and suctioning, making it more clinically relevant than scales that assess preparation before cleaning (like the Ottawa scale) 1
• It has demonstrated excellent interobserver reliability (intraclass correlation coefficient of 0.91) and substantial intraobserver reliability (weighted κ of 0.78) 4
• The BBPS can be easily implemented in clinical practice after brief training, with a 15-minute instructional video available online 1
• It is the most rigorously validated bowel preparation scale, recommended by the US Multi-Society Task Force on Colorectal Cancer 1

Common Pitfalls and Risk Factors for Inadequate Preparation

• Older age, male sex, and higher BMI are occasionally associated with inadequate preparation 1
• Inpatient status is significantly associated with poorer preparation quality 5
• Morning colonoscopies tend to have lower preparation scores compared to afternoon procedures 5
• Educational interventions, such as providing patients with informational booklets, can significantly improve preparation quality (number needed to treat = 4) 6

Endoscopy units should aim for adequate bowel preparation (BBPS ≥6 with each segment ≥2) in ≥90% of screening and surveillance colonoscopies, with an aspirational target of ≥95% 1.