The Variable-Stiffness Colonoscope: “Too Stiff or not Too Stiff, that is the Question” - A New Twist to the Plot

The initial goal of any colonoscopist is to pass the instrument quickly and painlessly to the caecum, whilst straightening it to facilitate an accurate and comprehensive examination during withdrawal. Although many insertions are relatively straightforward, a significant proportion prove difficult and a small percentage are close to impossible without patience, expertise and the right instrumentation. Difficulty occurs both when the bowel is fixed or angulated due to postsurgical or diverticular adhesions and when it is unusually long and mobile, resulting in atypical loops which are difficult to manage or straighten. For many years expert endoscopists have recognized the benefit of changing the endoscope to suit the type of colon encountered. In patients with a relatively fixed sigmoid colon, it is easier to achieve intubation using a floppy paediatric colonoscope which adapts without undue force to fixed bends, whilst long or mobile colons are better examined using a stiffer conventional instrument which resists recurrent looping. Prior to the examination, it is impossible to predict which instrument will be best suited to which colon. Until now, in such cases, the colonoscopist has been faced with the prospect of having either to “soldier on regardless” or to withdraw the colonoscope and exchange it for another. It has been necessary occasionally to try two or even three instruments in one patient, incurring significant costs in terms of colonoscope disinfection and patient turnaround times.

To prevent recurrent looping, through-the-scope stiffening wires and a variety of overtube splinting devices have been developed. However, these have not been widely accepted because of their awkwardness, uncertain efficacy and the perceived (and occasionally real) risk of trauma to instrument and patient. It is therefore extremely logical to employ a colonoscope in which the shaft can be adapted according to the type of colon encountered: the so called “variable-stiffness” colonoscope (although we favoured the description “variable flexibility”, as it is less threatening to the patient). The idea for this instrument is not a new one and indeed the first prototype (Olympus Optical Co., Tokyo, Japan) was developed at the request of one of us (CBW) as long ago as 1973, as “the ideal colonoscope” (Figure [1])! The design of this original instrument was essentially similar to that of today's variable-stiffness colonoscopes, but it was cumbersome to use. It could be adjusted from stiff to stiffer still, and so proved less than ideal at that time.

Figure 1The first prototype variable-stiffness colonoscope, circa 1973

The modern version of the variable-stiffness colonoscope comes with adult- and paediatric-size insertion tubes and has four grades of stiffness ranging from paediatric (floppy) to standard adult (stiff) mode. The variable-stiffness portion of the shaft extends to 25 - 30 cm from the tip and is controlled by a rotatable dial situated just below the instrument head. Twisting the dial mechanically tightens or relaxes an internal stiffening coil attached within the insertion tube of the colonoscope (Figure [2]), thus imparting more or less rigidity to the shaft (Figure [3]). In all other ways the variable-stiffness instruments handle and function like a standard endoscope.

Figure 2The mechanism of action of the variable-stiffness colonoscope, showing the internal cable in a coil sheath which stiffens when tensioned. a Relaxed. b Stiffened

Figure 3Bench-top demonstration of the variable-stiffness scope. a Floppy mode (coils easily). b Stiff mode (unwinds automatically)

In this issue of Endoscopy, two studies, from Japan and America, describe initial experiences with variable-stiffness colonoscopes. Odori et al. compared colonoscopy performance by moderately experienced endoscopists (700 previous cases) using standard Olympus colonoscopes and two prototype variable-stiffness instruments [1]. Consecutive colonoscopies were assessed and patients were not sedated. In those patients examined with variable-stiffness instruments the examination was begun with the instrument in the floppy mode, but maximal stiffening was used immediately if difficulty occurred, and before using standard ancillary manoeuvres such as position change and abdominal hand compression. The stiffening function was used in approximately 70 % of cases, most commonly with the tip in the descending colon or transverse colon. Stiffening was considered effective 79 - 96 % of the time and led to quicker insertion times and fewer ancillary manoeuvres when compared with the conventional instruments. Pain scores were similar for all instruments.

In the second study, Douglas Rex, recognized as a world expert in all things colonoscopic, also compared adult and paediatric variable-stiffness instruments with conventional adult and paediatric colonoscopes [2]. Rex assessed the instruments in a nonrandomized way and in a selected group of consecutive patients who were all examined with sedation. Those patients with known severe diverticular disease or inflammatory bowel disease, and those who requested no sedation were all excluded from the study. The stiffening function was used if recurrent looping occurred with the colonoscope tip beyond the sigmoid/descending junction and only after fully straightening the instrument. The stiffening device was found to be very or somewhat useful 90 % of the time when activated, but this did not translate into quicker insertion times when compared with the conventional instruments. Given the mean insertion times of just 4 minutes in all groups and the impressive caecal intubation rate of 99.2 %, it is perhaps not surprising that there were no easily demonstrable differences between the instruments in this study. Perhaps a better study for an endoscopist of the experience and skill of Dr Rex would be to compare performance using the different instruments in patients known (or likely) to be technically difficult to examine - precisely the patients excluded from his study!

We have compared the variable-stiffness colonoscope with a standard instrument in a group consisting mainly of patients in whom previously examinations had failed or in whom examination was known to be technically difficult, and did find significant benefits in terms of faster insertion and reduced patient discomfort [3]. When used, the stiffening function proved effective in enabling tip advancement on approximately 70 % of occasions and appeared to be most effective for rapid negotiation from splenic flexure into and across the transverse colon, preventing recurrent sigmoid colon looping. Total colonoscopy was eventually achieved in all patients without stenosing lesions, but a small-diameter (10 mm) paediatric instrument was still necessary in four patients with a narrowed, angulated and fixed sigmoid colon. A small-diameter, paediatric instrument, preferably with a variable-stiffness capability, will therefore still have a place in any busy colonoscopy unit as a second-line instrument in certain difficult cases.

Since this early report we have gained experience of the variable-stiffness scope in over 1000 examinations, and have found it to be durable and the instrument of choice in all difficult cases. Our nurses, knowing how much quicker examination with the variable-stiffness scope will be in cases previously found to be “difficult”, choose the instrument for any subsequent exam without prompting - because they know they will get home on time!

We always commence the examination with the scope in floppy mode and only apply maximum stiffness (the intermediate grades appear to us to be of no benefit) once the colonoscope has been pulled back and the sigmoid straightened. We usually only find it necessary or helpful to apply stiffening for brief periods, typically for no more than 5 % of insertion time. The action of stiffening the instrument alone does not always enable deeper intubation. Attention to good insertion technique, preventing recurrent looping with frequent straightening manoeuvres and the appropriate use of position change and/or abdominal hand compression remain important to ensure success. We have found that stiffening the instrument to prevent colonic looping during ileal intubation often facilitates deep intubation of the ileum and that a single instrument, the paediatric variable-stiffness colonoscope, makes an excellent push enteroscope for small-bowel examination - from either top (stiffening prevents gastric looping) or bottom ends! The stiffened instrument also appears to help the examination during colonoscopy withdrawal, steadying the colonoscope tip, preventing sudden slippage, and allowing a more controlled mucosal inspection.

In our opinion the variable-stiffness colonoscope represents a significant step forward in colonoscope design, providing the endoscopist with a new modality to counteract looping and facilitate rapid insertion. In the future, colonoscopes with magnetic endoscope imaging [4] and a variable-stiffness capability will be available (Figure [4]), making use of the stiffening function intuitive and inherently safer. Imaging will make it clear when to use the stiffening device and should encourage manufacturers to incorporate a greater degree and range of shaft stiffness into new instruments. With developments such as the variable-stiffness capability the ultimate goal of safe, pain-free (and hence sedationless) colonoscopy is not far away. If we can get close to this ideal then colonoscopy will not only be the procedure of choice for diagnosis and surveillance but will also irresistibly become the optimal screening test in the asymptomatic population.

Figure 4A prototype variable-stiffness magnetic-imaging scope. Generator coils are built into the casing and electronics pass out from the scope along the second umbilical

References

• 1 Odori T, Goto H, Arisawa T, et al. Clinical results and development of variable-stiffness video colonoscopes.  Endoscopy. 2001;  33 65-69
• 2 Rex D K. Effect of variable-stiffness colonoscopes on cecal intubation times for routine colonoscopy by an experienced examiner in sedated patients.  Endoscopy. 2001;  33 60-64
• 3 Brooker J C, Saunders B P, Shah S G, Williams C B. A new variable stiffness colonoscope makes colonoscopy easier: a randomised controlled trial.  Gut. 2000;  46 801-805
• 4 Shah S G, Saunders B P, Brooker J C, Williams C B. Magnetic imaging of colonoscopy: an audit of looping, accuracy and ancillary maneuvres.  Gastrointest Endosc. 2000;  52 1-8