Successful cecal intubation depends from the technical skill of the endoscopist, but also in a relevant measure from the anatomical complexity of the colon.
Intuitively, the availability of technologically advanced endoscopic instruments, coupled with the perfect knowledge of its features, play a key role in the safety and success of the procedure, also in terms of reducing patients’ discomfort.
Every colonoscope has its own technical characteristics to be selected for and the endoscopist must be able to “steer” it accordingly.
Therefore, before starting the procedure, the endoscopist may select the type of colonoscope best fitting to the somatic features of the patient, also keeping into due consideration his or her anamnestic data (Fig. 1).
Fig. 1: the choice of the instrument should be based on the somatic features of the patient as well as his or her personal medical history. Beside the standard colonoscope (on the right), a pediatric slim colonoscope (at the center) should be considered in patients with suspected adhesions (i.e. previous hysterectomy) or known severe diverticular disease. Sometimes also a gastroscope (on the left) may be an appropriate choice, provided that it has an auxiliary washing channel (blue circle).
For example, a long, variable stiffness colonoscope will be selected in case of an obese patient or a patient with a pot-belly abdomen, while a pediatric colonoscope will be selected in patients with previous hysterectomy or history of severe diverticulosis.
The expert endoscopist does not achieve the progression inside the colon by simply pushing the endoscope, be it autonomous or assistant-mediated, but rather resorting to a number of simultaneous or sequential maneuvers: tip deflection, torque-steering retraction air suction to shorten the colon, filling with water the exceedingly angled segments (i.e. a sigmoid colon with diverticula) or varying the stiffens of the distal portion of the colonoscope for those model featuring this option.
The tip of the Colonscope
It is extremely important to be familiar with the technical features of the colonoscope(s) adopted (fig.2), including its optical capacity and related available options (possibility of accessory washing channel, size and position of the suction channel, etc).
Fig. 2: technical features of the distal tips of different colonoscopes, with the handle in vertical position and the shaft in rectilinear position. The red circle indicates were optic lens is located, the white circles the light bundles, the blue circle the site of the suction channel, and the cyan circle the washing channel. In the tips on the left (A - series 180) and in the center (B - series 185), the washing channel is not coaxial with the biopsy/suction channel, unlike the tip on the right (C - series 190). Some colonoscopes have three light bundles (white circles), while some other only two.
The handle of the Colonscope
Also during the insertion phase it may be necessary to use the multiple functions of the colonoscope, through the use of the remote switches located on the scope handle (Fig.3); all the modern colonoscopes offer the functions of freezing the image, activating the narrow band imaging (NBI) , enhancing the endoscopic view, and sometimes zooming the image.
Fig: 3 Il manipolo di un moderno colonscopio presenta, oltre alle manopole di angolazione del puntale, pulsanti che consentono di attivare diverse funzioni (frecce); l’operatore seleziona le funzioni da attribuire a ciascun pulsante secondo le proprie preferenze. La manopola scanalata alla base del manipolo (freccia gialla - fig. 3A) attiva la variazione di rigidità della porzione distale del colonscopio.
The shaft of the Colonoscope
From a general standpoint, in the shaft of a modern colonoscope there are structural segments apt for different functions. A standard colonoscope is essentially composed by two functionally different segments: the bending segment, allowing the rotation of the distal tip of the scope in all directions, and the insertion shaft, of variable length, and fitted out with different flexibility in different models, though nonadjustable during the intubation.
Many expert endoscopists prefer to deal with difficult colonoscopies (e.g. in patients with a previous incomplete colonoscopy) using variable stiffness instruments. Such colonoscopes have a build-in variable stiffness segment of about 25 cm in length, placed between the shaft and the bending segment (fig. 4). The ability to vary endoscope shaft flexibility may help insertion to the caecum.
Fig. 4: In variable stiffness colonoscopes, an inner coil-springed segment of about 25 cm (green segment) is inter-placed between the shaft (grey segment) and the bending segment (blue segment).
At the base of the handle, there is the stiffness control ring with dial setting that ranges from 0 to 3. The endoscopist can adjust the relative flexibility of the scope’s insertion tube by rotating the ring. This stretches the spring which stiffens the segment and facilitates the intubation (fig. 5 e 6).
Fig. 5 A-C. In variable stiffness colonoscopes, when the control ring is set on 0 (red arrow), the coli spring is not stretched (B) and the distal segment of the instrument has normal flexibility (C).
Fig. 5 D-F: when the control ring is set on activated position (C – red arrow), the coil spring is stretched (E) and the distal segment has increased stiffness (F).
Variable-stiffness colonoscopes combine the flexibility of pediatric instruments for negotiation of the sigmoid colon with the ability to stiffen the insertion tube to prevent or control looping after straightening. This technology is frequently used to negotiate a deep transverse, but can be of help also to overcome the splenic flexure after straightening maneuvers (alpha loop or long N loop). Activating maximum stiffness appears to be effective once the sigmoid colon has been negotiated and the colonoscope straightened with the tip in the proximal colon, reducing the number of ancillary maneuvers and shortening the insertion time through the proximal colon. This distinctive feature can be activated whenever the insertion by the endoscopist or nurse assistant does not coincide with advancement of the scope, always after complete retraction of the colonoscope for the whole length of the “ineffective” segment.
The most recent technologic development in the structure of a colonoscope is the so-called “Passive Bending” system (Fig. 6).
Fig. 6: passive bending scopes are characterized by the presence of a passive bending segment (yellow) inter-placed between the distal bending segment (blue) and a variable stiffness segment (green).
Inside the fittingly lengthened distal sheath upholstering the bending segment, this innovative technology adopts a 3-cm segment that flexes passively when exposed to angular pressures of the colonic wall (fig. 7 e 8).
Fig. 7 A-B: passive bending colonoscopes (below in the picture A, while a standard colonscope is shown above) are equipped with a built-in 3 cm-short segment inside the distal sheath upholstering the bending segment, that flexes passively when exposed to an angular pressure by the colonic wall. This results in a longer bending segment (blue arrows) compared to a conventional colonoscope (red arrows).
Fig. 8 A-B: on application of a similar advancement force, a passive bending colonoscope (on the left) achieves a wider curvature compared to a conventional colonoscope (on the right)
In most patients with abnormal colon morphology the pain is caused while negotiating the “hairpin” bends of the colon, i.e. the narrower springs of the sigmoid colon, by gently pushing the full-angled colonoscope. The proximal 10-20 cm from the angulated part of the conventional colonoscope is stiff, with a wide turning radius. Over-angulation, using both controls, tends to wedge the scope into a band, making it unlikely to slide around. This unproductive “walking-stick handle” effect (fig. 9) often occurs to the less expert endoscopist when the bending section of the scope is hopelessly impacted into an acute bend and causes significant pain to the patient. The “passive-bending colonoscope” has a flexible tip with a narrow turning radius, so that the scope can be easily negotiated through the “hairpin” bends of the colon, with minimal discomfort.
Fig. 9: the “walking-stick handle” effect of the colonoscope. If negotiating an acute bend of the sigmoid, the endoscopist exerts a pressure (black arrow) pushing the full-angled colonoscope (blue segment); this would stretch the bend and inevitably cause pain, with little or no advancement of the tip of the scope (white arrow) and excessive tension on the sigmoid wall. This is due to the fact that the smaller the circumference within the tip angulation, the higher is the pressure exerted on the segment of the sigmoid wall where the colonoscope lies against.
When the insertion force is exerted, passive bending scopes favor the flexion of the bending segment adjacent to the tip of the instrument (Fig. 10)
Fig. 10: the passive bending effect of the colonoscope. Compared to a conventional colonoscope, the passive flexibility of the bending segment adjacent to the tip of the scope determines a wider opening of the curvature of the portion of the colonoscope engaged in the sigmoid coli spring. Therefore, the pressure is distributed over a wider arch that eases sliding of the colonoscope and hence its progression (white arrow) consistent with the force of insertion applied (black arrow)