258 Section 6: Hardware
the control of remote devices easily accessible? Does the size and weight of the equipment allow for easy transportation?
7 System expansion and integration. Is the system cap-able of easily interfacing with hard-copy devices, video-tape recorders, and computerized image management systems?
During the 1990s, the video-image colonoscope sup-planted the ﬁberoptic colonoscope as the preferred instrument for colonoscopy. The availability of two distinct technologies for generating color images (color-chip vs. RGB sequential) provides the endoscopist with a choice of basic systems, each with its own advant-ages and disadvantages. Although the basic shape and function of the instrument have remained unchanged, recent advancements (including the development of smaller-diameter insertion tubes, instruments with ad-justable stiffness, improvements in image resolution, and advanced video processor features) have continued the evolution of the colonoscope.
1 Moriyama H. Engineering characteristics and improvement of colonoscope for insertion. Early Colorectal Cancer 2000; 4: 57–62.
2 Moriyama H. Variable stiffness colonoscope: structure and handling.Clin Gastroenterol2001; 16: 167–72.
3 Kawahara I, Ichikawa H. Flexible endoscope technology: the ﬁberoptic endoscope. In: Sivak MV Jr, ed. Gastroenterologic Endoscopy, 2nd edn, Vol. 1. Philadelphia: WB Saunders, 2000; 16–28.
4 Barlow DE. Flexible endoscope technology: the video image endoscope. In: Sivak MV Jr, ed. Gastroenterologic Endoscopy, 2nd edn, Vol. 1. Philadelphia: WB Saunders, 2000; 29–49.
5 Sivak MV Jr, Fleischer DE. Colonoscopy with a video endo-scope. Preliminary experience. Gastrointest Endosc 1984; 30: 1–5.
6 Knyrim K, Seidlitz H, Vakil N et al. Optical performance of electronic imaging systems for the colon. Gastroenterology 1989; 96: 776–82.
7 Schapiro M. Electronic video endoscopy. A comprehensive review of the newest technology and techniques. Pract Gastroenterol1986; 10: 8–18.
8 Anonymous. Video colonoscope systems. Health Devices 1994; 23: 151–205.
Colonoscopy Principles and Practice Edited by Jerome D. Waye, Douglas K. Rex, Christopher B. Williams
Copyright © 2003 Blackwell Publishing Ltd
The Colonoscope Insertion Tube
Douglas A. Howell
The colonoscope insertion tube is the largest contributor to overall endoscope performance. Individual practi-tioners develop a preference for individual instruments and develop skill and techniques for their use. Many choose soft ﬂexible insertion tubes for their ability to maneuver through the sigmoid colon easily. However, advancement beyond the splenic ﬂexure can prove challenging, requiring a variety of maneuvers, including patient positioning and counterpressure. Alternatively, stiffer instruments may be preferred for the opposite reason. Some endoscopists accept a more difﬁcult sig-moid negotiation with stiffer instruments in order to permit easier cecal access once the splenic ﬂexure has been negotiated. Examinations with stiffer instruments understandably may require more patient sedation, but there has not been a higher perforation rate reported with their use.
Pediatric-diameter long-length colonoscopies were intro-duced in the late 1980s and reports of successful use in adults soon followed. In 70 of 72 cases where the sigmoid could not be negotiated using standard colonoscopes, Bat and Williams  reported success with pediatric instruments. Reasons for initial failures included stric-tures, severe diverticular disease, and postoperative adhesions.
Several authors have now concluded that women are more difﬁcult to examine at colonoscopy, especially if they have undergone hysterectomy, and are most likely to beneﬁt from the use of pediatric endoscopes [2,3]. In a randomized trial of 100 women with hysterec-tomies, Marshall and colleagues  reported success-ful entry into the cecum in 96% when using pediatric colonoscopes compared with only 71% where stand-ard colonoscopes were employed. When these failures with standard colonoscopes were then attempted with pediatric instruments, more than half could be success-fully completed. Nevertheless, most endoscopists who use pediatric colonoscopes have observed that keep-ing the instrument straight and advancing beyond the
splenic ﬂexure may be difﬁcult. This should not be unexpected in view of the thin ﬂexible insertion shaft of pediatric instruments.
When the more ﬂexible endoscopes loop and bend during intubation, counterpressure and/or patient re-positioning are the most frequently employed maneuvers to help advance the instrument. While these techniques do not add stiffness to the colonoscope shaft, counter-pressure does result in compression of loops to transfer forward motion of the instrument to the tip . Plac-ing the patient on the back or right side can similarly affect insertion, and positional changes are frequently employed when using pediatric equipment. However, these techniques may be ineffective due to patient body habitus, incorrect placement of pressure, adhesions, and looping under the ribcage in either the splenic or hepatic ﬂexures.
On occasion, the push enteroscope has been employed in an attempt to complete a failed colonoscopy. The largest experience was reported after failure with a standard-diameter colonoscope. In 32 such cases, the enteroscope was advanced to the cecum in 22 (68.7%), raising the authors’ overall success rate to 96.4%. Of note, the authors did not attempt these patients with pediatric equipment and their report predates the avail-ability of variable-stiffness technology .
The enteroscope probably does have a role in colono-scopy on occasion. In a 2002 report, Rex and Goodwine  used the enteroscope with a straightener or the colo-noscope with a straightener to successfully study 2 of 42 consecutive patients with failed prior colonoscopies. In my personal experience, patients with extremely long colons with redundant sigmoids are the group in whom previously failed colonoscopy will be successfully com-pleted with an enteroscope. One report of the routine use of an enteroscope rather than a colonoscope to spe-ciﬁcally examine the terminal ileum had disappointing results, in that the technical failure rate for ileal intuba-tion was 33%, attributed to the length of the scope, its smaller diameter, and its tendency to continuously form loops .
Some authors have described the use of gastroscopes in colonoscopy but, in general, only for special circum-stances and almost always for left colon examinations
260 Section 6: Hardware
. Gastroscopes have short bending segments, short transition zones, and stiff short insertion tubes, mak-ing them poor instruments for colonoscopy. Very slim pediatric gastroscopes are useful for performing retro-ﬂexion endoscopy in the rectum and distal sigmoid to assist in difﬁcult polypectomy but advancement be-yond the splenic ﬂexure has rarely been reported. Perhaps the most frequent use of small-caliber gastroscopes is negotiation through severe diverticular disease, with tortuosity of the colonic lumen, narrowing, and rigidity.
A short bending segment colonoscope in prototype form (Olympus, Japan) has been developed to attempt to take advantage of the tight U-turn capability of gastro-scopes. With a pediatric insertion tube and a bending section similar to a pediatric gastroscope, the prototype can be easily retroﬂexed virtually anywhere in the colon including in the cecum. Whether this instrument can be as successfully passed to the cecum and whether this ability will add to diagnostic yields or polypectomy suc-cess will require further study.
Devices to add stiffness to assist in negotiating beyond the splenic ﬂexure have a long history. These include external overtubes and internal biopsy channel devices.
Overtubes were introduced in 1983 to splint the sig-moid colon. Made of rigid tubular plastic, these devices proved painful, cumbersome, and dangerous. A major disadvantage was the need to withdraw the colonoscope to load the earliest overtubes and then repeat the inser-tion to the splenic ﬂexure. A split overtube was mar-keted to avoid this speciﬁc disadvantage but the original drawbacks remained, resulting in abandonment of the technique. Overtubes for colonoscopy are no longer marketed.
Internal stiffening devices were initially tightly closed biopsy forceps, which did not add sufﬁcient additional stiffness to reliably improve success during colon in-tubation. First appearing in 1972, several stainless steel cable devices where tension could be varied with a twist-wheel were produced and marketed (Fig. 23.1). Although often of beneﬁt in performing a successful pro-cedure, the devices were cumbersome, blocked suction capabilities, and were hard to clean. Despite their limited success in stiffening the colonoscope shaft, they were abandoned because of their potential to cause endoscope damage . The last such device (Sullivan Stiffener, Wilson-Cook Medical, Winston-Salem, NC) is no longer manufactured but still exists in many units .
Some endoscopists prefer a double-channel colono-scope for a stiffer insertion tube, offered by all three major endoscopy manufacturers. The second channel adds approximately 1 mm to the overall diameter but increases the stiffness considerably. The additional
Fig. 23.1 Early cable internal stiffening device.
channel can be used to ensure suction capabilities when the ﬁrst channel is occluded by a device. Several second-channel techniques have been used to assist in poly-pectomy, especially collecting resected polyp specimens while additional polyps are being removed. Never pop-ular, these endoscopes have largely been abandoned with the advent of graduated stiffness insertion tubes and newer innovations that permit increasing stiffness during colonoscopy. Nevertheless, double-channel colo-noscopes are still produced and are currently available.
Since no one stiffness is appropriate in all settings, the development of variable-stiffness adjustment in colono-scopes was greeted as a welcome new innovation in endoscope engineering. Marketed by Olympus America (Melville, NY) as Innoﬂex® (i.e. “innovation in ﬂexibil-ity”), this new colonoscope series permits adjustment of the instrument during the procedure from ﬂexible to stiff using a hand dial (Fig. 23.2). The details of the engineer-ing and manufacture are outlined in Chapter 22 but, in summary, these instruments permit adjustment in the range from the most ﬂexible to the stiffest colonoscopes currently in use (Fig. 23.3). It is important to note that the variable-stiffness cable within the insertion tube con-nects at 16 cm behind the tip. Tightening the internal cable does not change the characteristics of the bending section or the adjacent transition section (present in all modern endoscopes). Insertion shafts have always been produced to be stiffer than the initial forward section of the colonoscope, producing so-called graduated stiff-ness. This is in contrast to the ability to vary the stiffness of the insertion shaft during the procedure by chang-ing the tension on a variable-stiffness cable. Innoﬂex® colonoscopes are produced in both standard diameter
Chapter 23: The Colonoscope Insertion Tube 261
which assists in negotiating sharp turns and contributes to its greater ﬂexibility.
Fig. 23.2 Adjustable hand dial for adding stiffness.
(12.8 mm) and pediatric diameter (11.3 mm). The per-formance of these insertion tubes depends upon both the external diameter as well as length of bending sec-tion and the degree of stiffness dialed into the variable-stiffness portion of the insertion tube. The radius of the bending section is shorter in pediatric instruments,
Technique for use of variable-stiffness instruments
The recommended technique for using the variable-stiffness colonoscope is as follows.
1 The instrument is inserted in its maximally ﬂexible mode (dial set at zero). The sigmoid is negotiated until the splenic ﬂexure is achieved and “hooked” by entering the transverse colon. Counterpressure and/or patient positioning may be needed during this phase.
2 The instrument is then straightened by withdrawal, generally with some clockwise torque until about 55– 65 cm of colonoscope remains within the patient as measured at the anal verge.
3 The dial is then twisted, fully tensioning the dial to a setting of 3. Shaft stiffness is not a linear function so that a setting of 1 or 2 does little to affect the character of the insertion tube.
4 Once fully straightened and stiffened, advancement should be facilitated. Even with the instrument in the maximal-stiffness mode, loops can develop in the shaft during insertion. The standard “straightening by with-drawal” techniques should be performed frequently, after removing the tension on the stiffening apparatus.
5 Following straightening, the above procedures can be repeated.
Variable-stiffness colonoscopes have rapidly gained favor, although the literature addressing effectiveness has reported mixed results (Table 23.1). Earlier reports suggested that the variable-stiffness instrument signiﬁc-antly reduced insertion time and was more comfortable
11 11.5 12 12.5 13 13.5
Fig. 23.3 Variable-stiffness graph of pediatric (PCF160A) and standard (CF-O160A) colonoscopes.
Insertion tube outer diameter (mm)
* Existing Olympus colonoscopes
262 Section 6: Hardware
Table 23.1 Variable-stiffness compared with regular colonoscopes.
Brookeret al.  Sorbiet al.  Rex  Howellet al. 
Shumakeret al. 
Yoshikawaet al. 
100 50 358 600 363
VSS vs. SC VSS vs. SC
VSS vs. VSP vs. SC vs. PC VSS vs. VSP vs. SC vs. PC VSP vs. SC vs. PC
VSS vs. SC
NA Improved Same Improved Same
Less Less Same
Least with PC Same
Time to cecum
Less Same Same Same Same
NA, not available; PC, pediatric colonoscope; SC, standard colonoscope; VSP, variable stiffness pediatric; VSS, variable stiffness standard diameter.
* Need for counterpressure or patient repositioning.
compared with conventional colonoscopes [11,12]. Some later reports have agreed that counterpressure and posi-tioning is less often needed, supporting the concept that variable-stiffness instruments do control loop forma-tion; however, their use did not shorten insertion time or improve success [13,14]. Rex  reported a series of patients where success and speed to the cecum was not improved with variable-stiffness colonoscopes, but judged the effectiveness of the stiffening device to be very useful in 40% of cases when he used the standard-diameter variable-stiffness colonoscope and 54% of pediatric variable stiffness cases.
Howell and colleagues  compared standard and pediatric colonoscopes with variable-stiffness standard-diameter and pediatric-diameter colonoscopes in 600 patients. Consecutive patients were examined with either instrument as equipment became available. The results again demonstrated that women were more difﬁcult to examine and had more discomfort than men during colonoscopy but fared better with pediatric equipment. The use of variable-stiffness colonoscopes resulted in less loop formation as assessed by decreased need for counter-pressure. Patients who had undergone prior colonoscopy with a standard adult colonoscope rated the pediatric and variable-stiffness equipment most favorably (Fig. 23.4). In addition, the pediatric variable-stiffness colonoscope was given the best rating by the author, as measured by the subjective score used.
Shumaker and colleagues , using a similar study protocol, did not ﬁnd any signiﬁcant advantages to using
variable-stiffness colonoscopy compared with stand-ard instruments. Nevertheless, they reported that the variable-stiffness colonoscopes performed well and con-cluded that further study might identify subgroups in whom the variable-stiffness instruments would be of beneﬁt. Most recently, Yoshikawa and colleagues  studied patients undergoing sedationless colonoscopy and reported a signiﬁcant reduction in pain scores when using variable-stiffness pediatric colonoscopes. In this setting cecal intubation times by the less experienced colonoscopists were shorter than with conventional instruments.
Recently, the newly released magnetic endoscope imaging (MEI) device (see Chapter 24) has been used with variable-stiffness colonoscopes. The examinations performed with MEI demonstrated surprisingly effect-ive control of sigmoid loop reformation after straighten-ing and applying stiffness when the tip was at the splenic ﬂexure. Despite the control of looping in the sigmoid colon, some examinations may remain challenging due to splenic ﬂexure looping or transverse colon redund-ancy. Combining variable-stiffness technology with MEI is likely to be a major step toward more effective, more comfortable colonoscopy.
Choice of instruments
Now that many variations of insertion tubes are avail-able, how does an endoscopist select an instrument which is most likely to be successful for cecal intubation
Worse 60% Same
C vs PC (p<0.001),C vs VSC (p=0.001), C vs PVSC (p<0.001)
C PC VSC PVSC
Fig. 23.4 Patient comparison to their prior colonoscopy.
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