Technique of Intubation of the Rectum
Prior to the insertion of the colonoscope in the rectum, it is important to perform a digital examination of the anal canal using a lubricating jelly, in order to induce a relaxation of the internal anal sphincter and rule out any abnormality of the anal canal. At the beginning of the intubation, the position of the patient is in the left lateral decubitus (fig. 1); this enables the endoscopist to visualize the anal verge prior to the digital examination through the anus.
To insert the colonoscope, the endoscopist aligns its tip with the index finger and eases the sliding of the scope in the anal canal, taking care to have the axis of introduction oriented toward the umbilicus of the patient. When the instrument passes the anal canal, the nurse grabs it with the right hand holding the scope at a distance of about 20 cm from the anus, while the operator grabs the handle and moves away to achieve a complete straightening of the shaft of the colonoscope (fig. 2).
Fig. 2: After the insertion through the anal canal, the instrument is grasped by the nurse with his/her right hand, while the operator moves away from the table to achieve a complete straightening of the colonoscope.
The endoscopist verifies in the monitor the correct orientation inside the rectum, aspirates any residual fluids and insufflates the minimum amount of air or gas to distend the rectal walls (fig. 3).
Fig. 3: while the nurse steers the tip of the scope, the endoscopist maneuvers the control knobs to guide the direction, aspirates fluids and insufflate air or gas to distend the rectal walls.
Modulating the insufflation (Fig. 4 A), it is possible to recognize the three semi-lunar transverse folds of rectum (inferior, mid and superior Houston’s valves), usually located at about 7, 9 and 11 cm from the anal orifice (fig. 4 B).
Fig. 4: passed the anal canal with the tip of the scope, modulating the insufflation (A), it is possible to recognize the three Houston’s valves (B – yellow arrows) located at about 7, 9 and 11 cm from the anal orifice .
With the patient in the left lateral decubitus, the colonoscope straightened and the endoscopist positioned perpendicularly to it, it is possible to identify the rectal walls and locate the topography of lesions (fig. 5 A-B).
Fig. 5 A-B: with the patient in left lateral decubitus (A), on the right of the monitor (B) the anterior rectal wall can be seen (AW), on the left the posterior wall (PW), above the right lateral wall (RL), and below the left lateral wall (LL).
If the endoscopist explores the rectum during withdrawal with the patient in supine position, then the topographic landmarks change (fig. 6 A-B).
Fig. 6 A-B: with the patient in supine position on the table (A), on the right of the monitor (B) the left lateral wall of the rectum can be seen (LL), above the anterior one (AW), below the posterior one (PW), and on the left of the monitor the right lateral wall (RL).
The operator can choose to perform the rectal retrovision immediately or at the end of colonoscopy; nonetheless, this maneuver is easier with the patient in left lateral decubitus (Fig. 7 A-B).
Fig. 7: the rectal retrovision (A) is usually easier with the patient in left lateral decubitus. This maneuver facilitates the visualization also of the upper portion of the anal canal (B).
Once the exploration of the rectum is terminated, the endoscopist aspirates all the excess air until the rectal walls collapse and the scope progresses to the recto-sigmoid junction, the passing of which represents one of the most crucial steps in the intubation technique (fig. 8).