AIM: To study the significance of cap-fitted colonoscopy in improving cecal intubation time and polyp detection rate.

METHODS: This study was a prospective randomized controlled trial conducted from March 2008 to February 2009 in a tertiary referral hospital at Sydney. The primary end point was cecal intubation time and the secondary endpoint was polyp detection rate. Consecutive cases of total colonoscopy over a 1-year period were recruited. Randomization into either standard colonoscopy (SC) or cap-assisted colonoscopy (CAC) was performed after consent was obtained. For cases randomized to CAC, one of the three sizes of cap was used: D-201-15004 (with a diameter of 15.3 mm), D-201-14304 (14.6 mm) and D-201-12704 (13.0 mm). All of these caps were produced by Olympus Medical Systems, Japan. Independent predictors for faster cecal time and better polyp detection rate were also determined from this study.

RESULTS: There were 200 cases in each group. There was no significant difference in terms of demographic characteristics between the two groups. CAC, when compared to the SC group, had no significant difference in terms of cecal intubation rate (96.0% vs 97.0%, P = 0.40) and time (9.94 ± 7.05 min vs 10.34 ± 6.82 min, P = 0.21), or polyp detection rate (32.8% vs 31.3%, P = 0.75). On the subgroup analysis, there was no significant difference in terms of cecal intubation time by trainees (88.1% vs 84.8%, P = 0.40), ileal intubation rate (82.5% vs 79.0%, P = 0.38) or total colonoscopy time (23.24 ± 13.95 min vs 22.56 ± 9.94 min, P = 0.88). On multivariate analysis, the independent determinants of faster cecal time were consultant-performed procedures (P < 0.001), male patients (P < 0.001), non-usage of hyoscine (P < 0.001) and better bowel preparation (P = 0.01). The determinants of better polyp detection rate were older age (P < 0.001), no history of previous abdominal surgery (P = 0.04), patients not having esophagogastroduodenoscopy in the same setting (P = 0.003), trainee-performed procedures (P = 0.01), usage of hyoscine (P = 0.01) and procedures performed for polyp follow-up (P = 0.01). The limitations of the study were that it was a single-center experience, no blinding was possible, and there were a large number of endoscopists.

CONCLUSION: CAC did not significantly different from SC in term of cecal intubation time and polyp detection rate.

Colonoscopic examination has been used in clinical practice for approximately 40 years. Despite the fact that colonoscopy is widely available and is performed by many experienced colonoscopists, there are concerns about the quality of colonoscopy as measured by several technical endpoints such as rate of failed cecal intubation and polyp miss rate. A large population-based study[1] has revealed that 13.1% of colonoscopies failed to reach the cecum. In addition, one large review of back-to-back colonoscopies has shown polyp miss rates of 24%[2] for adenoma. Numerous innovations, as described by Rex[3], have been studied to improve these two key issues, with some showing promise.

One potentially promising technique is cap-assisted colonoscopy (CAC). A transparent cap (or hood) is a simple plastic device that can be attached to the tip of a colonoscope before performing the colonoscopy. Several randomized trials from Japan[4-8] have reported mixed results regarding improved cecal intubation times and polyp detection rates. A recent large study from Hong Kong[9] has shown improved time to cecum intubation but a reduced polyp detection rate. To date, as far as we are aware, there is no large randomized study that has used the cap in a western population, in whom the colorectal cancer (CRC) incidence is known to be higher than Asian population[10]. We conducted a randomized controlled trial to investigate the usefulness of CAC in a western population at Royal Prince Alfred Hospital, Sydney.

This was a prospective randomized controlled trial conducted in a tertiary referral hospital from March 2008 to February 2009. All patients who were referred to our endoscopy service for colonoscopy were invited to participate in the study. All were aged 18 years or older. Exclusion criteria included prior colonic resection, pregnancy, severe comorbidity and acute surgical conditions such as severe colitis, toxic megacolon, ischemic colitis, tertiary referral for endomucosal resection, acute gastrointestinal bleeding, or inability to provide consent, such as dementia. This prospective study was approved by Sydney South West Area Health Service Ethics Review Committee. The trial was registered with ClinicalTrial.gov with the registration identification number NCT00930462.

The preparation for the procedure included a clear fluid diet the day before the procedure, routine bowel preparation with either a sodium picosulfate-based (Picoprep, Pharmatel Fresenius Kabi Pty Ltd., Hornby, Australia), or sodium-phosphate-based (Fleet, Ferring Pharmaceuticals, Gordon, Australia) preparation, and a fasting period of 8 h. Colonoscopy was performed in either the hospital endoscopy unit or a private outpatient endoscopy center associated with our hospital. Procedures were performed by a team of five consultant gastroenterologists and 10 trainees. All procedures were performed under conscious or deep sedation with a combination of intravenous midazolam (Pfizer, Bentley, Australia), fentanyl (Mayne Pharma Ltd, Mulgrave, Australia), and propofol (Fresofol 1%; Pharmatel Fresenius Kabi Pty Ltd.) administered by the assistant or attending anesthetist. As an antispasmodic, hyoscine butylbromide was administered as appropriate. Colonoscopes used were CF-Q160AL, CF-Q180AL, PCF-160AL and PCF-180AL (Olympus Optical Co., Tokyo, Japan).

Three sizes of cap were used: D-201-15004 (with a diameter of 15.3 mm, used for CF-Q180AL), D-201-14304 (14.6 mm, used for CF-Q160AL) and D-201-12704 (13.0 mm, used for both PCF-160AL and PCF-180AL). All of these caps were produced by Olympus Medical Systems (Tokyo, Japan). The cap was placed so that 4 mm was beyond the tip of the colonoscope (Figure 1). Even though the rim of the cap was visible on the monitor, the visual field was not limited as the endoscopist was able to see through the transparent cap.

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Figure 1 A cap attached to the tip of the colonoscope, with approximately 4 mm of the cap beyond the tip.

Once informed consent was obtained, patients were randomized according to a computer-generated randomization protocol to standard colonoscopy without the cap (SC) or CAC. Patients were blinded to the allocation. The colonoscopes were assigned in no specific order and were used according to availability after cleaning. Data were collected during and after the colonoscopic examinations on procedure times, polyps, complications and other parameters.

The procedure was defined as successful if the colonoscope reached the cecum, confirmed by either visualization of the appendicular orifice or the ileocecal valve. Trainee success was only recorded if the cecum was reached without help from a consultant. Terminal ileal intubation was attempted in all cases. The quality of bowel preparation was graded either as good (no or small volume of clear liquid, easily removed), satisfactory (moderate to large volume of liquid stool, removable with suction), or poor (presence of semi-solid stool that could not be cleared or washed away).

Polyps were removed in standard fashion and sent for pathology. The size of the polyps was determined by the endoscopist performing the polypectomy. Advanced lesions were defined as lesions > 10 mm, with high grade dysplasia, or villous in nature. If a diminutive polyp was encountered on insertion and the endoscopist wished to remove this during the insertion phase of the procedure, the time taken for this was subtracted from the insertion time but included in the total procedure time.

Despite the fact that polypectomy prevents 76%-90% of CRC when compared to the expected incidence[11], data from interval CRCs (CRCs diagnosed between the time of a negative screening colonoscopy to that of next recommended colonoscopy) raise important questions about how effective colonoscopy is as a screening practice[12]. Possible reasons for these interval cancers include failed colonoscopy and missed lesions. A large population-based study[1] has revealed that 13.1% of colonoscopy failed to reach the cecum. Rex et al[2] have published data on adenoma miss rates based on a large back-to-back colonoscopy series, and estimated that the rate was 17%-48%. Important advances in colonoscopy have been suggested to improve the outcome of colonoscopy. These include improving colonoscopy techniques (optimizing withdrawal time[13-15], chromoendoscopy and bowel preparation quality[16,17]) and technologies (wide-angle colonoscopy in 2003[18], narrow band imaging in 2004[19], and fluorescence confocal endomicroscopy[20].

Caps have been used previously in endoscopic procedures, for instance, in mucosal resection and double balloon enteroscopy. Their use in colonoscopy has been studied in the past with regards to cecal intubation and polyp detection. Our study did not show any benefit of CAC for our primary endpoint of time to cecal intubation Even though all six previous randomized trials of CAC have been faster with the cap, only four were significantly faster. In our study, CAC had a shorter cecal intubation time although this was not statistically significant. One possible explanation is that studies with cecal intubation times below 10 min are inclined to have no significance between the two study arms, with the exception of the study of Lee et al[9]. This illustrates a point whereby the benefit of the cap is small in those procedures where cecal intubation times are already short. The short cecal intubation time and high cecal success rate in our study probably left little room for improvement with the cap. The overall cecal intubation rate was 96.8%, this high success rate was probably due to the fact that our center is a tertiary teaching hospital.

Factors that predicted faster colonoscopy in our multivariate analysis (Table 3) were as expected and well-described in the literature[21-23], except for the use of hyoscine. We reserved hyoscine for difficult insertions, which suggests that we selected patients with difficult colonoscopy, hence the prolonged cecal intubation time in that group.

We also showed no significant improvement of the polyp detection rate in the CAC group. This was almost certainly due to a small sample size because this study was powered to look at cecal intubation time rather than polyp detection rate. Furthermore, our study cohort had a mean age of 52 years (vs 62.0-66.4 in Asian studies[5-8]), older only than the patients in the study of Lee et al[9]. Our low polyp detection rate at 31.8%, despite the fact that the study was carried out on a western population, was likely a consequence of this younger patient population. The youngest population studied to date was in Hong Kong[9], which demonstrated significantly lower polyp detection in the CAC group. Our study does not support the use of a cap for polyp detection, however, the question of any benefit with the cap has not been sufficiently answered. Further studies, particularly in a western population, are required. With the known polyp miss rates at about 24%[2], it is likely that large numbers will need to be recruited in prospective randomized studies to show any benefit of this intervention.

In conclusion, there was no statistically significant difference between CAC and SC with regards to cecal intubation success, time and polyp detection rate.