Water-aided methods for colonoscopy include the established water immersion and the recent novel modification of water exchange. Water immersion entails the use of water as an adjunct to air insufflations to facilitate insertion. Water exchange evolved from water immersion to facilitate completion of colonoscopy without discomfort in unsedated patients. Infused water is removed predominantly during insertion rather than withdrawal. A higher adenoma detection rate has been reported with water exchange. Aggregate data of randomized controlled trials suggest that water exchange may be superior to water immersion in attenuating colonoscopy discomfort and optimizing adenoma detection, particularly in the proximal colon.
Key points
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Water immersion and water exchange are characterized by removal of the infused water predominantly during withdrawal and insertion, respectively.
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Randomized controlled trial data suggest that water exchange may be superior to water immersion in minimizing insertion pain and optimizing adenoma detection, particularly in the proximal colon.
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Although simple, the novel techniques of water exchange require practice to master all of the maneuvers.
Introduction
Water-aided methods for colonoscopy have received renewed attention in the literature in recent years. There are 2 major categories, namely water immersion and water exchange. Water immersion was described in the English-language literature in 1984 as an adjunct to air insufflation to aid insertion. The method was characterized by suction removal of the infused water during the withdrawal phase of colonoscopy. Water exchange is a recent modification of water immersion, first reported in 2007. Water exchange is advocated currently as the sole modality to use air exclusion to aid insertion and is characterized by suction removal of the infused water, predominantly during the insertion phase of colonoscopy. The water method studies that did not show an advantage for water compared with air used primarily water immersion rather than water exchange. The current article is intended to clarify these nuances by providing a description of the two major water-aided methods. Reference is made to studies other than randomized controlled trials (RCTs) to provide a historical perspective. A comparison of recent RCTs of water-aided methods and traditional air insufflations is presented to support the possibility that one approach (water exchange) may be superior to the other (water immersion) in minimizing pain and optimizing adenoma detection. The comparative data call for further head-to-head RCTs to assess air insufflations, water immersion, and water exchange.
Introduction
Water-aided methods for colonoscopy have received renewed attention in the literature in recent years. There are 2 major categories, namely water immersion and water exchange. Water immersion was described in the English-language literature in 1984 as an adjunct to air insufflation to aid insertion. The method was characterized by suction removal of the infused water during the withdrawal phase of colonoscopy. Water exchange is a recent modification of water immersion, first reported in 2007. Water exchange is advocated currently as the sole modality to use air exclusion to aid insertion and is characterized by suction removal of the infused water, predominantly during the insertion phase of colonoscopy. The water method studies that did not show an advantage for water compared with air used primarily water immersion rather than water exchange. The current article is intended to clarify these nuances by providing a description of the two major water-aided methods. Reference is made to studies other than randomized controlled trials (RCTs) to provide a historical perspective. A comparison of recent RCTs of water-aided methods and traditional air insufflations is presented to support the possibility that one approach (water exchange) may be superior to the other (water immersion) in minimizing pain and optimizing adenoma detection. The comparative data call for further head-to-head RCTs to assess air insufflations, water immersion, and water exchange.
Historical perspective
Pioneer colonoscopists used air insufflations to distend the colonic lumen in unsedated patients. Despite traditional maneuvers of loop reduction, patient position change, and abdominal compression to minimize pain, these early colonoscopic examinations were associated with unavoidable discomfort. Sedation was introduced to increase patient tolerance and soon became the standard of practice in the United States and elsewhere. Cleaning of the mucosal surface for inspection involved boluses of water injected by a syringe through the biopsy channel. In 1984, water immersion was described as an adjunct to conventional air insufflations to facilitate passage through the sigmoid colon affected by severe diverticulosis. Water immersion was reported to speed up passage through the left colon. Use of warm water to counter spasm was described as simple, inexpensive, and effective. Water immersion is characterized by removal of the infused water predominantly during the withdrawal phase of the colonoscopy.
In 2002, a nursing shortage curtailed the ability to routinely offer conscious sedation for colonoscopy at the author’s institution. After a search of the literature, unsedated colonoscopy was offered to restore local access. When the pros and cons of sedation versus no sedation were presented, about 30% of veterans accepted the scheduled unsedated option, primarily because of lack of escorts. Using the same method as was used in sedated patients, the success rate of cecal intubation was only about 80%, but comparable with the best reports on unsedated colonoscopy of the time.
The limiting factor during insertion was pain brought on by lengthening of the colon caused by the insufflated air needed to expand the lumen for visualization, preventing cecal intubation in ∼20% of the unsedated patients. To complete the failed cases without sedation, the first clinical research question was whether cecal intubation could be accomplished without the use of air insufflations. Of all the modalities for reducing colonoscopy discomfort, water immersion as an adjunct to conventional air insufflations seemed to be the most promising. Subsequent work focused on whether cecal intubation with water infusion in lieu of air insufflations (water exchange) could be accomplished. The results of a series of observational studies and RCTs confirmed the feasibility of water exchange to aid insertion and accomplish cecal intubation.
Methodological details of water-aided methods
Water immersion used as an adjunct to conventional air insufflations does not require the acquisition of new skills or the use of new maneuvers. It entails distention of the colon by water that is removed predominantly during withdrawal, but the method has varied in the literature. The water is infused by syringe or water pump through the biopsy channel. One RCT reported less colonic spasm by the use of warm-to-touch water ; however, a recent RCT showed no difference between warm water (35°–38°C) and cool water (20°–23°C) with regard to sedation requirement, pain or satisfaction scores, or cecal intubation times. Other descriptions permitted insufflation of puffs of air as needed or when water immersion was deemed a failure based on intention to treat. Some studies using water immersion also described complete exclusion of air.
Water exchange was modified from water immersion specifically to develop the least painful method for use in scheduled, unsedated patients in the United States. Water exchange involved complete exclusion of air (no air insufflations and suction of all residual air in the colonic lumen). Infusion of an unrestricted volume of water coupled with removal of residual feces to clear the view is used to identify the lumen during insertion. It requires acquisition of a new set of skills, and practice is necessary to master the maneuvers. Unique to the approach is the following maneuver to distinguish water exchange from water immersion: the infused water is removed predominantly during insertion. A detailed description of the pearls and pitfalls of water exchange is provided in Box 1 .
- 1.
The air and water pump on the colonoscope and the accessory water pump used to deliver water for water exchange are checked to confirm proper function.
- 2.
The air pump is turned off to avoid inadvertent air insufflations, which can elongate the colon.
- 3.
On insertion of the colonoscope through the anus, the location of the lumen is noted. All residual air is removed. Point the suction port at the tip of the colonoscope (located at the 5 o’clock position) into the air pocket. Apply suction to collapse the lumen (the steps are repeated in the rectal sigmoid junction, splenic flexure, hepatic flexure and cecum, and redundant segments to decrease angulations and minimize loop formation).
- 4.
The tip of the colonoscope is directed to abut the slitlike opening ahead or where the folds converge ( Fig. 1 A). Water is infused to confirm that the lumen opens (see Fig. 1 B). The farther the tip is to the target the less effective the infused water will be in opening the lumen ahead.
- 5.
If there is no obvious opening ahead, move the tip of the colonoscope systemically in a 360° fashion while simultaneously infusing and suctioning water to clear the residual fecal debris.
- 6.
Only a sufficient amount of water is infused to confirm that the lumen ahead opens to allow passage of the colonoscope. Water infusion is stopped if the lumen does not open. The tip of the colonoscope is pulled back from the mucosa, redirected, and the process is repeated.
- 7.
Suction of the mucosa is avoided by adjusting the level of wall suction, and by initiating water infusion just before pressing the suction button. The suction port is pointed toward the center of the lumen, away from the mucosa on the right side, which translates into seeing more mucosa on the left side and upper portion of the monitor screen (see Fig. 1 C).
- 8.
Be patient if bowel preparation is suboptimal. Remove the suspended residual feces and infuse clean water for visualization of the lumen. If the colonoscope is equipped with a single working channel, the maneuvers are done in rapid sequence. If the colonoscope is equipped with 1 working and 1 accessory channel, the maneuvers can be done simultaneously. The process seems to take time during insertion. The paradox is that it is easier to clean the mucosa in a collapsed water-filled colon during insertion with water exchange than in a distended air-filled colon during withdrawal with the water jet followed by suction.
- 9.
It is important not to forget to remove the infused water by suction when the insertion is going smoothly. Failure to do so results in a water-distended colon. The distention caused by water increases discomfort for the patient and predisposes to loop formation. If the appearance of the lumen ahead is round rather than slitlike and narrowed, there is likely to be too much water in the colon., which is the signal to perform more suction than infusion.
- 10.
Recognition of the underwater appearance of diverticular openings is critical to avoid mistaking it for a true lumen and inappropriate infusion of excess water into the diverticulum.
- 11.
Cecal intubation is suggested by finding characteristic red suction marks ( Fig. 2 A) after attempts to further advance the colonoscope fails, or intubation of the terminal ileum (see Fig. 2 B), or observing the ileocecal valve facing the tip of the colonoscope (see Fig. 2 C), and confirmed by observing the appendix opening under water ( Fig. 3 ). Remove as much of the infused water in the cecum as possible before insufflating air to initiate the withdrawal phase.
- 12.
Other integral components of the water exchange method include colonoscope-shortening maneuver, abdominal compression, and change of patient position. These maneuvers may be needed less often than when air insufflation is used but they are needed for the same reason (eg, lumen ahead cannot be seen, paradoxic movement occurs) to assist advancement.
RCTs comparing conventional air insufflations with water immersion or water exchange: impact on pain
The data from RCTs comparing traditional air insufflations with water immersion or water exchange from 2008 to 2011 were summarized in a recent systematic qualitative review. In the current article, the data from 3 additional RCTs published in 2012 are added. The mean (standard deviation [SD]) or median (interquartile range [IQR]) pain score in the air insufflations and water-aided method groups are shown in Table 1 . The reductions in mean or median pain scores of the water-aided method groups are presented as percentages of the air insufflation groups (see Table 1 ). The overall reduction of pain scores was qualitatively greater with water exchange compared with water immersion in patients not given full sedation (see Table 1 ).
| (A) Water Immersion: Removal of Infused Water Occurred Predominantly During Withdrawal | ||||||
|---|---|---|---|---|---|---|
| References | Air | Water Immersion | Pain Score Reduction | P | ||
| N | Pain Score | N | Pain Score | |||
| , a , b | 170 | 4.6 (1.8–9.2) c | 170 | 2.9 (1.0–5.8) c | −1.7 d (37%) | .001 e |
| , a , d | 39 | 2.6 (2.2) | 41 | 2.4 (2.2) f | −0.2 (7.7%) | .894 |
| , g , d | 114 | 5.3 (2.7) | 112 | 4.1 (2.7) | −1.2 (23%) | .001 h |
| , g , d | 89 | 3.4 (2.8) | 90 | 2.5 (2.5) | −0.9 (26%) | .021 h |
| , g , d | 51 | 4.4 (2.6) | 51 | 3.0 (2.2) i | −1.4 (32%) | .004 h |
| 51 | 3.3 (2.4) j | −1.1 (25%) | .028 h | |||
| , k , b | 114 | 3.9 (1.4–5.4) c | 116 | 2.8 (1.2–4.4) c | −1.1 d (28%) | .001 e |
| , g | 31 | 5.5 (NR) | 31 | 3.6 (NR) | −1.9 (35%) | <.05 h |
| , k | 58 | 4.2 (2.3) | 58 | 2.8 (1.9) | −1.3 (31%) | .01 l |
| , a | 53 | 1.0 (2.0) | 55 | 1.2 (2.5) m | +0.2 (−2%) | .920 |
| 51 | 1.2 (2.5) n | +0.2 (−2%) | ||||
| 48 | 0.9 (1.9) o | −0.1 (1%) | ||||
| , g | 97 | 0 (0.24) | 85 | 0 (0.22) | 0 (0%) | NS |
| Average | 19% | — | ||||
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