The successful intubation of the cecum during screening or surveillance colonoscopy is vital to ensure complete mucosal inspection of the colon on withdrawal. Even when performed by an experienced endoscopist, colonoscope insertion can sometimes be challenging. Water-aided colonoscopy can be used to assist the endoscopist in navigating colons with anatomies that may be challenging owing to severe angulation or redundancy. Water-assisted colonoscopy involves the infusion of water without air and subsequent suctioning during insertion (exchange) or withdrawal (immersion or infusion). This review discusses the technique, effectiveness, safety of water-assisted colonoscopy as well as the application in sedationless endscopy.
Key points
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Water-assisted colonoscopy involves the infusion of water without air and subsequent suctioning during insertion (exchange) or withdrawal (immersion or infusion).
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Water-assisted colonoscopy can be used to decrease sedation requirements in patients undergoing colonoscopy.
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Water-assisted colonoscopy can increase completion rate in examinations not using sedation.
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Water-assisted colonoscopy can be used to complete difficult examinations owing to redundancy or severe angulation in the distal colon.
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Water-assisted colonoscopy may yield more proximal adenomas than air insufflation for some operators, perhaps due to longer withdrawal/examination time and bowel preparation salvaging.
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Water exchange may be superior to water immersion with regards to pain experience by patients.
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Water infusion has been shown to not deleteriously alter serum electrolyte levels or vital signs.
Introduction
Colorectal cancer prevention with colonoscopy depends on the successful insertion of the colonoscope to the cecum with subsequent careful mucosal inspection on withdrawal. The recommended target for an endoscopist’s cecal intubation rate is 90% for all examinations and 95% for healthy screening patients. Thus, a significant number of colonoscopies may still be incomplete. In addition, colonoscope insertion, even in those examinations with ultimately successful cecal intubation, can still be associated with many challenges. Previous investigators have observed that predictors such as female gender and thin body habitus may be associated with difficult or incomplete examinations. There have been attempts to produce new scopes that may aid in the completion of colonoscopies. In addition, new techniques such as water-aided colonoscopy have been developed.
The infusion of water during colonoscopy has been used in an attempt to allow easier insertion of the scope. One of the initial studies involved the use of 100 to 200 mL of sterile water to facilitate the passage of the colonoscope through the left colon. The investigators observed that water infusion in the left colon reduced insertion time by nearly one-third as compared with the traditional insertion method. Since that publication, several studies have examined the utility of water infusion as well as water exchange. This review provides insight into the rationale and utility of water-assisted colonoscopy and highlights important clinical studies.
Introduction
Colorectal cancer prevention with colonoscopy depends on the successful insertion of the colonoscope to the cecum with subsequent careful mucosal inspection on withdrawal. The recommended target for an endoscopist’s cecal intubation rate is 90% for all examinations and 95% for healthy screening patients. Thus, a significant number of colonoscopies may still be incomplete. In addition, colonoscope insertion, even in those examinations with ultimately successful cecal intubation, can still be associated with many challenges. Previous investigators have observed that predictors such as female gender and thin body habitus may be associated with difficult or incomplete examinations. There have been attempts to produce new scopes that may aid in the completion of colonoscopies. In addition, new techniques such as water-aided colonoscopy have been developed.
The infusion of water during colonoscopy has been used in an attempt to allow easier insertion of the scope. One of the initial studies involved the use of 100 to 200 mL of sterile water to facilitate the passage of the colonoscope through the left colon. The investigators observed that water infusion in the left colon reduced insertion time by nearly one-third as compared with the traditional insertion method. Since that publication, several studies have examined the utility of water infusion as well as water exchange. This review provides insight into the rationale and utility of water-assisted colonoscopy and highlights important clinical studies.
Difficult colonoscopies
When assessing the efficacy of any modality designed to assist the endoscopist during colonoscope insertion, the clinically important outcomes and benchmarks need to be identified. Thus, it is important to examine how difficulty in colonoscopy insertion can be defined, measured, and characterized. The most important outcome for colonoscopy is completion of the examination as defined by successful cecal intubation. Because this rate is often greater than 95%, other important measures may be considered. Despite the potential for gaming, time to the cecum or insertion time has been used to determine the difficulty of colonoscopy. Other measures may include the ability to retroflex in the cecum, which can often be a manifestation of redundancy or looping of the scope, and the need for maneuvers such as abdominal pressure, stiffening of the colonoscope, and changing the position of the patient. These measures likely reflect the degree to which the colonoscope is looping in the patient. The ability to perform endoscopy without sedation or the amount of sedation medication required may also be considered relevant measures. Finally, the patient’s experience, often reported as pain during or after the examination, is also an important outcome. Except for cecal intubation, these measures are subjective, and thus the results of studies based exclusively on them may be difficult to interpret.
Adequate discussion of difficult insertion requires understanding the underlying mechanisms. Difficult insertion is often related to the anatomic location of the colonoscope tip when the challenge is encountered and can be categorized into challenges that are distal or in the sigmoid and those that are related to redundancy or persistent looping. Sigmoid challenges might be observed in patients with severe angulation, such as thin women or patients with diverticular disease. Issues related to redundancy or excessive looping may be seen in patients with central obesity or severe constipation.
Rationale for use of water-assisted colonoscopy
There are several proposed mechanisms through which water may facilitate the passage of a colonoscope through the colon. When filled with water, the sigmoid colon may be weighted down into the left lower quadrant if the patient is in the left lateral decubitus position. This can straighten the sigmoid and make tight angles less acute. Another mechanism may be related to the shortening of the colon through the use of water as opposed to air, which may elongate the colon. In addition, the use of water may help to lubricate the scope, allowing for easier passage. Other proposed mechanisms include decreased colonic spasm.
Technique of water-assisted colonoscopies: immersion versus exchange
During water immersion, water is infused during insertion and the air pump is turned off. Infused water is then aspirated during scope withdrawal. Water exchange involves the infusion of clean water with suction and removal of the fecal suspension during insertion. Water exchange also involves turning off of the air pump. A hybrid of these methods is often used in practice and in trials. In this technique, water is used as an adjunct to air insufflation during the passage through tight strictures or angles often observed in the sigmoid colon.
With regards to water exchange, one expert has offered helpful maneuvers in a recent editorial. These maneuvers include the infusion of a minimal amount of water that is sufficient to open the lumen or spasm. The investigator suggests that to minimize inadvertent mucosal suction, the endoscopist should decrease the level of suction and point the suction port toward the center of the lumen. In addition, if bowel preparation is not optimal, the endoscopist should infuse clean water and suction the debris simultaneously. In the author’s opinion, cleaning of the bowel is easier in a water-filled colon than in an air-filled lumen because the simultaneous infusion and suctioning of water creates a turbulent environment that suspends the fecal debris, allowing for efficient suctioning of fecal debris. Finally, although maneuvers such as abdominal compression and change of patient position may be required less often in water techniques, these adjunctive techniques should still be considered an integral part of the examination.
Learning the water technique
It has been suggested that the water technique may seem too cumbersome for endoscopists who are accustomed to air insufflation. One report examined the cecal intubation rate for an experienced endoscopist during the learning phase of the water technique. The investigators examined 4 groups or quartiles of 25 water-aided colonoscopies and compared these examinations to 100 historical colonoscopies performed by the same endoscopist in which air insertion was used. The cecal intubation for the water technique increased from 76% in the first quartile to 96% in the fourth quartile. The cecal intubation rate for the final quartile was comparable to the 98% observed in the air cohort. Other trends observed included a faster cecal intubation time, higher adenoma detection rate (ADR), and a lower rate of change in patient position when compared with the air cohort. These data suggest that an experienced endoscopist might require only 100 examinations to become proficient at the water technique. The most common reason for failure to intubate the cecum was misidentification of the cecum. The identification of the usual landmarks was initially more difficult in the water-filled colon. The hepatic flexure was the most common anatomic location that was mistaken for the cecum. The investigators observed that suction marks on the cecum were good indicators of cecal intubation. They speculated that these marks were the result of the attempts by the endoscopist to open the appendix, believing that this was the lumen. Another reliable indicator of cecal intubation was the insertion of 90 cm of colonoscope.
Water-assisted colonoscopy and completion rate
Cecal intubation has been assessed by several trials, which are shown in Table 1 . One meta-analysis observed no difference between water infusion and air insufflation in 6 randomized controlled studies (odds ratio [OR] = 1.0; 95% confidence interval [CI], 0.96–1.03). Another meta-analysis also observed that there was no difference in cecal intubation rate between the standard air and water methods (OR = 0.67; 95% CI, 0.24–1.89). However, the investigators of this meta-analysis highlighted that 4 trials used the assistance of air insufflation in their water method groups; this might also explain the moderate heterogeneity observed in the previous meta-analysis (I 2 = 61%), which examined a similar group of trials. The examinations that used adjunctive air were considered as incomplete in these 4 trials. When the cecal intubation rates were recalculated after reclassifying the examinations with air as complete, the cecal intubation rates were higher for water infusion as compared with air insufflation. Thus, the published data regarding cecal intubation and the use of water infusion seem to be inconsistent. As stated earlier, the completion rates in average patients, with no risk factors that predict difficult colonoscopy, may be close to 100%. Therefore, even large studies or meta-analyses may not detect significant differences.
| Author, Year, Country | Subjects | Design | Comparison | Outcome | Results | Limitations | Conclusions |
|---|---|---|---|---|---|---|---|
| Brocchi et al, 2008, Italy | Colonoscopy patients | RCT (170 patients in each arm) | Standard jelly for lubricating vs corn seed oil vs warm water | CI rate Time to cecum and for examination Pain Difficulty of examination for endoscopist |
| Unblinded single center | Warm water– and oil-assisted examinations may allow for easier cecal intubation and less pain for patient |
| Leung J, et al, 2009, USA | Minimally sedated Veterans Affairs patients | RCT (28 patients in each arm) | WI vs AI | Sedation Pain CI rate Willingness to repeat examination |
| Older male population | WI may be superior to AI in minimally sedated patients |
| Leung F, et al, 2009, USA | Two consecutive groups of unsedated Veterans Affairs patients | Observational (62 AI & 63 WI) | WI vs AI | CI rate Willingness to repeat examination |
| Nonrandomized older men | RCT required to examine WI vs AI |
| Radaelli et al, 2010, Italy | Consecutive outpatients initially having no sedation | RCT (116 WI & 114 AI) | Warm WI vs AI | Patients requesting sedation CI rate |
| Single center physicians not blinded | Borderline significant results suggest more data needed to support the decreased need for sedation in WI examinations |
| Leung F, et al, 2010, USA | Unsedated Veterans Affairs patients | RCT (40 AI & 42 WI) | WI vs AI (some WE occurred in poor preparations) | Pain CI rate Willingness to repeat examination |
| Older male population | Water infusion may increase CI rate and decrease patient pain in unsedated male patients |
| Pohl et al, 2011, Germany | Consecutive outpatients initially having no sedation | RCT (58 patients in each arm) | WI vs AI | Patients requesting sedation |
| Single center physicians not blinded | Suboptimal bowel preparation may limit benefit of using water method |
| Ramirez & Leung, 2011, USA | 368 consecutive screening patients | RCT | WI vs AI | ADR CI rate WT Sedation required Abdominal pressure used |
| Male population | WI may increase yield of proximal adenomas perhaps due to longer insertion time |
| Hsieh et al, 2011, China | Consecutive minimally sedated patients | RCT (AI 89 & 90 WI) | WI in left colon vs AI | CI rate Time for insertion Need for maneuvers during examination such as abdominal pressure Pain |
| Single center | Limited water infusion may lower pain but lengthen insertion time |
| Leung J, et al, 2011, USA | Veterans Affairs patients accepting on demand sedation | RCT (50 patients in each arm) | WI vs AI (some WE occurred in poor preparations) | proportion of patients completing examination with no sedation CI rate Sedation medications Pain |
| Older male population | Benefit of WI in reducing sedation requirement is confirmed in this study |
| Leung F, et al, 2011, USA | Combination of 2 RCTs (see earlier text) from Veterans Affairs health centers | WI (92) and AI (90) | WI vs air | CI rate ADR |
| Older male population | Water had modest increase in yield of small proximal adenomas but with higher WT |
| Vemulapalli & Rex, 2012, USA | Patients referred for incomplete colonoscopy | Observational: 345 patients | WI vs AI | CI rate Equipment required |
| Single endoscopist | Water immersion may aid in completing examinations of patients with previously incomplete colonoscopies using standard equipment |
| Leung F, et al, 2012, USA | Various published studies | Systematic review | WI vs WE vs AI | Pain ADR |
| Differences in study design | WE may be superior to WI and a study examining 3 approaches is needed |
| Jun & Bing, 2013, China | Various published studies | Meta-analysis | WI vs air | CI rate Total examination time Abdominal compression or position change ADR Pain On demand sedation |
| Few studies and differences in study design | WI may be associated with less patient discomfort |
| Lee et al, 2012, USA | 175 Patients having colonoscopy with sedation | RCT | Warm vs cold water-assisted colonoscopy | Sedation medication used Pain score CI rate Time Satisfaction Willingness to repeat examination | No differences between warm and cold water groups | Results may be limited to sedated patients with good to excellent bowel preparations | Temperature may not matter in water-assisted colonoscopies |
| Leung F, et al, 2013, USA | Various published studies | Meta-analysis | WI or WE vs AI | Insertion pain ADR |
| Differences in study design | Pain may be reduced in water technique. ADR may be higher in WE |
| Luo et al, 2013, China | Patients with previous abdominal surgery having colonoscopy without sedation | RCT (55 patients in each arm) | WE vs AI | CI rate |
| Single center unblinded physicians | WE may help in patient with previous surgery having examination with no sedation |
| Lin et al, 2013, China | Various published studies | Meta-analysis | WI vs AI | Pain CI rate Sedation required |
| Differences in study design | Water can reduce sedation requirement and lower pain with higher CI rates |
| Hsieh et al, 2014, China | Patients having minimally sedated colonoscopy | RCT (90 patients in each arm) | WI vs WI vs AI | Painless insertion Pain scores ADR CI rate |
| Single center and single unblinded endoscopist | WE may be better than AI or WI in achieving painless colonoscopy |
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