- Email: [email protected]
Self-propelling endoscopes
Gastrointest Endoscopy Clin N Am 14 (2004) 697 – 708
Self-propelling endoscopes Yang K. Chen, MD University of Colorado Hospital, Division of Gastroenterology and Hepatology, Anschutz Centers for Advanced Medicine, 1635 N. Ursula Street, Box F-735, Aurora, CO 80010, USA
Colon cancer is the third most common type of cancer and the second leading cause of cancer death in the United States [1]. Indirect evidence and modeling analyses suggest that colonoscopy may be the most cost-effective way to screen the average-risk population for colorectal neoplasia [2 –4]. The American Cancer Society and the American College of Gastroenterology recommend endoscopic screening for the average risk population beginning at age 50 years [5,6]; however, the sheer number of potential patients who would qualify for colon cancer screening exceeds available technological resources and trained medical personnel. As waves of baby boomers reach 60 years of age, the aging United States population will further escalate the demand for these services. Currently less than 30% of eligible patients undergo a screening colonoscopy [7– 9]. The low compliance with screening recommendations may be attributable to several factors including lack of patient education, unfavorable patient attitudes toward bowel cleansing and colonoscopy, long waiting times for scheduling a screening procedure, and failure of some primary care physicians to uniformly implement the screening recommendations [9,10]. Rising demand for screening colonoscopy and the projected numbers of eligible patients puts a major strain on the health care system in general and on gastrointestinal endoscopy units in particular. In the United States, the problem is aggravated by a chronic nationwide shortage of qualified nurses [11]. The average age of endoscopy nurses belonging to the Society of Gastrointestinal Nurses and Associates (SGNA) is reported to be 48 years of age (unpublished data, SGNA). Most fellowship programs in gastroenterology cannot afford to increase the number of postgraduate trainees due to limited federal funding. Using nurse practitioners and physician assistants to perform screening endoscopies has been modestly successful for sigmoidoscopies [12,13], but the strategy has not been seriously considered for the more demanding skill of screening colonoscopy. Because human resource is not the only limiting factor, other potential solutions to address the widening gap between supply and demand E-mail address: [email protected] 1052-5157/04/$ – see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.giec.2004.04.007
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must be considered. Shrinking reimbursements for endoscopy and limited budgets for expensive capital equipment are forcing health care providers to scrutinize the profitability and operational efficiency of their endoscopy units. One potential solution is to identify or develop more cost-effective and efficient alternatives for colon cancer screening.
Conventional push colonoscopy Classic colonoscopes are semiflexible tubes that are inserted into the colon by pushing. The procedure requires a skilled endoscopist and is associated with significant discomfort for the patient. Thus, sedation and analgesia is almost always necessary. As the colon is elastic and contains multiple sharp bends, looping may occur during scope advancement, particularly in patients with redundant colons. In turn, this may result in longer procedure times, failure to reach the cecum, higher complication rates, more patient discomfort, or increased sedation requirements. Several factors have an impact on operator efficiency during push colonoscopy. The amount of time required to reach the cecum without compromising patient comfort and safety is operator- as well as patient-dependent and may be variable. And as yet there is no universal benchmark for the minimum amount of time that should be taken to carefully and thoroughly inspect the entire colon and rectum, usually during scope withdrawal. Of course, if pathology is encountered during a screening procedure, more time is needed for tissue sampling or endoscopic therapy. Of these three basic procedural steps, the latter is the most difficult to supplant with an alternative screening modality that is not operator dependent. Other important factors affecting operator efficiency include the time required to achieve conscious sedation and duration of postsedation recovery; both are functions of patient characteristics and of the type and quantity of preprocedure medications given. Because the endoscopist is generally responsible for overseeing sedation and analgesia, operator efficiency is significantly affected by the time needed to achieve (and maintain) the desired level of sedation and analgesia. Total colonoscopy time would be significantly reduced and procedural efficiency enhanced if complete examination of the colon could be performed without sedation.
Competing technologies If we were to design the ideal alternative to conventional push colonoscopy, we would want the procedure to be safer, faster, technically less demanding, more comfortable for the patient, less expensive and resource intensive, and at least as accurate if not better than conventional colonoscopy. Physician time may be reduced by eliminating the need for sedation and analgesia, by limiting physician involvement to the diagnostic and therapeutic components of the procedure, or by computerizing and automating the most essential step of real-time inspection and lesion detection.
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To help overcome some of these hurdles, a number of competing nonendoscopic technologies recently have been introduced into clinical practice, including virtual colonoscopy [14,15] and capsule endoscopy [16 – 19]. Capitalizing on recent advances in microrobotics, biomedical engineers are also developing and testing prototypes of a self-propelling endoscope as one potential way to surmount the technical challenges of performing push colonoscopy. Virtual colonoscopy Virtual colonoscopy (CT colonography) involves taking standard helical CT images of a patient’s gas-filled colon and using them to generate 2-D and 3-D computerized images. The images can be combined into a ‘‘fly-through’’ view of the colonic lumen that is similar to that seen during colonoscopy. The test has high theoretic patient acceptance and is safer to perform than conventional push colonoscopy, although the technique involves some radiation exposure. Because the procedure is painless, no sedation is required; however, rigorous colon cleansing is still an unpleasant but essential requirement [20,21]. Oral contrast tagging of fecal contents promises to eventually do away with the need for rigorous bowel preparation, thereby improving patient compliance [21]. Although initial results of virtual colonoscopy were inferior to push colonoscopy [15], recent reports from major centers in the United States show accuracy to be comparable to conventional colonoscopy for detection of polyps of clinically relevant size with few false positives [22 – 24]. The sensitivity drops significantly for detection of polyps less than 10 mm in size. The technology is expensive, and the sophisticated software used to reconstruct the 3-D images of the colonic lumen remains labor intensive. Whether the test ultimately will result in better patient compliance, require less physician time, and prove to be more cost-effective than conventional colonoscopy for screening, the average risk population remains to be proven. One major limitation of this technology is inability to obtain tissue samples and provide therapy. Some experts have speculated that widespread use of virtual colonoscopy for colon cancer screening paradoxically may lead to an even greater demand for push colonoscopy resulting from true- and false-positive lesions identified at virtual colonoscopy. Others have estimated that the overall likelihood of a therapeutic colonoscopy being required as a result of a potentially significant finding at virtual colonoscopy is approximately 10% at most [20]. One cost analysis assumed all polyps found at virtual colonoscopy justified a referral for colonoscopy and found that even if virtual colonoscopy could evolve into a perfect test, to be cost-effective it would have to offer 15% to 20% better compliance and cost 54% less than conventional colonoscopy [25]. Capsule endoscopy Invention of the transistor made it possible to design electronic radiotelemetry capsules that are small enough to be swallowed and used for examining the gastrointestinal tract [17,26 – 28]. Wireless capsule endoscopy has no external wires,
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fiber-optic bundles, or cables. Using a miniature complimentary metal oxide semiconductor camera and a short focal length lens, images are obtained, as the optical window of the capsule sweeps past the gut wall, without requiring air inflation of the gut lumen [17]. The capsule endoscope is propelled by peristalsis through the gastrointestinal tract. The video images are transmitted using radiotelemetry to an array of aerials attached to the body, which allow image capture. The images are stored on a small portable recorder worn on a belt and later downloaded for analysis. The system allows more than 7 hours of continuous recording and patients are able to continue their daily activities during the test. The capsule endoscope has performed well in trials involving patients with difficult gastrointestinal bleeding and in comparative studies with push enteroscopy [29 – 31]. Only preliminary data have been reported for capsule colonoscopy [32]. There is no clinical data on capsule colonoscopy as a screening test for detecting polyps and cancer. If used for this purpose, capsule endoscopy would be easier and safer to undergo than conventional push colonoscopy, but it is more time consuming. The procedure has the advantage of being painless and thus there is no need for sedation; however, adequate visualization of the entire colon using the capsule is highly dependent on a clean colon. Furthermore, for the first time in endoscopic practice there is a temporal dissociation between the technical and cognitive components of the examination. Subsequent physician review and interpretation of the recorded images may require more time than real-time colon examination during push colonoscopy. Poor physician reimbursements for the cognitive component may further discourage its widespread use. Rapid transit through the colon is undesirable and may adversely affect the capsule’s diagnostic accuracy; there is no opportunity for the reviewer to carefully interrogate a suspicious lesion or inadequately examined area after the fact. It is not known if capsule colonoscopy can approach the sensitivity and specificity of push colonoscopy as a screening test for colon polyps and cancer. Commercially available capsules do not have any steering or interventional capabilities; however, prototypes have been designed that may be able to actuate and navigate the capsule. For now developing biopsy and therapeutic capabilities in a steerable capsule remains a distant goal. Despite the limitations cited, these competing technologies will continue to improve. Eventually one of the less invasive imaging modalities will likely replace push colonoscopy as a more cost-effective means of colon cancer screening. Conventional colonoscopy will be relied upon primarily for therapeutic interventions.
Self-propelling endoscopes Recent advances in microrobotics have made the concept of a ‘‘self-propelling’’ endoscope an attainable goal (Fig. 1). Its successful application in the clinical arena may decrease our dependence on the time and services of an expert endoscopist and ultimately contribute to improved efficiency in endoscopy.
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Fig. 1. Self-propelling robotic endoscope.
Self-propelling endoscopes currently under development move through the colon by simulating inchworm locomotion (Fig. 2) [33 – 36]. The inchworm system consists of a propulsion unit, a miniature robotic arm, and a tail (umbilical cable) [33]. The propulsion unit consists of two suction clamps connected by expansion bellows. The tail connects the endoscope (miniature robot) to an external unit; it contains electrical wiring, pneumatic tubes, an operating channel, a flushing channel, and illumination fibers. The unit outside the body provides pneumatic actuation signals in the appropriate sequence to the miniature robot and feedback information on the robot’s movements to the endoscopist who can either telemanipulate or directly supervise its operation [37]. Because the tail does not have to transfer the pushing force, it can be made thinner and more flexible, causing less stress on the walls of the colon and thus, less pain. Future
Fig. 2. Typical inchworm motion and typical inchworm prototype.
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developments in wireless technology can be expected to eliminate the cumbersome endoscopic tail. The ultimate goal of self- propelling endoscope development is to design a miniature robot capable of performing the same functions as a conventional colonoscope, such as mucosal inspection and tissue sampling. A miniature robotic arm or manipulator can be placed at the front of the endoscopic system to orient and position accessory devices and the camera or video chip [38 – 40]. The manipulator may be driven by shape memory, alloy actuation, hydraulic pistons, or electromagnetic motors. In vivo experiments using one prototype (Endocrawler) were able to propel the endoscope at an average speed of 150 mm/ min in the live pig colon, suggesting that some day self-propelling endoscopes may become a viable alternative to push colonoscopy [34]. Clinical and technical issues Push colonoscopy is a safe test with an excellent record of procedural success [41]. Technical failures, missed lesions, and procedural complications are uncommon. Furthermore, a plethora of sophisticated accessory devices have been developed for tissue sampling, hemostasis, endoscopic resection of pathologic lesions, and other therapeutic interventions. Actual procedure time is a function of operator skill, patient factors, and instrument design. The average endoscopist can perform a complete examination of the colon in 30 minutes or less [41]. Of course one major drawback of the push technique is the discomfort associated with both air insufflation and scope advancement or looping, necessitating the use of conscious sedation and monitoring. To replace push colonoscopy as the screening procedure of choice, a selfpropelling endoscope would have to match its track record of safety, reliability, efficiency, and accuracy. As is true of any evaluation of new or proposed biomedical instruments, several technical and clinical issues must be addressed before a realistic assessment can be made regarding its feasibility for clinical use. With regard to the technical performance characteristics of self-propelling endoscopes, the following questions will need further clarification: Instrument-induced trauma is related to any potential stress on soft tissue. In the case of a self-propelling endoscope, the gut wall is the biologic interface of the instrument and its anatomic support. Is the instrument safe for human use? Will contact between colonic wall and the instrument during self-propulsion cause changes in colonic mucosa that may compromise subsequent interpretation of endoscopic and microscopic findings? Can the robot negotiate acute angles in the colon and navigate through collapsed bowel? What is its locomotion efficiency? Is the performance reliable? Is the instrument durable? Can the robot run on a miniaturized energy source? Can the robotic functions be remotely controlled by using wireless technology? Can the self-propelling scope perform a systematic and thorough inspection of the colonic lining? What is the angle of view of the optical window? Is the image quality equivalent to conventional endoscopes? Can a sophisticated compound
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lens system be mounted on the scope to provide several sets of eyes that can see in multiple directions during scope advancement and withdrawal? If so, this would significantly enhance imaging efficiency. Can the acquired images be transmitted via radiotelemetry for viewing in real time? Will self-propelling scopes have tissue sampling and interventional capabilities? Without these important robotic functions, the self-propelling endoscope will have the same basic limitations as virtual colonoscopy and commercially available capsule endoscopy. Patient and physician acceptance of this new technology may be affected by the answers to the following questions: Is self-propulsion faster than push colonoscopy? Does it require a human operator to advance and direct the endoscope to the cecum? If so, can this be performed by a trained endoscopy assistant? Is the procedure safer than push colonoscopy? Is this a painless procedure? Will inspection of the entire colon using robotic technology require more time than push colonoscopy? How easy is it to learn how to control the robotic functions? What is the relative cost of the technology? Will selfpropulsion technology adversely affect physician reimbursement?
Impact on efficiency Efficiency in colonoscopy may be defined as the number of procedures each endoscopist can perform per unit time. In conventional colonoscopy, major factors affecting procedure time include how quickly and safely the desired level of sedation and analgesia can be achieved and maintained, the scope insertion time (to the cecum), and the time required to perform a systematic inspection of the colonic mucosa for detection of pathology. Obviously, additional time will be required for tissue sampling and endoscopic treatment if a pathologic lesion is encountered. More broadly speaking, efficiency in endoscopy transcends the total procedure time to encompass more global issues affecting operational efficiency. For example, the requirement for conscious sedation and postprocedure observation is arguably the single most important factor affecting the operational efficiency in an endoscopy unit. Likewise, any need for personnel to assist in an endoscopy procedure will contribute to the costs of running the unit. Thus, the overall efficiency of the endoscopist, as well as the endoscopy unit, may be increased or decreased depending on the performance characteristics of self-propelling endoscopes that we have already discussed. Because self-propelling colonoscopy is presently available only as a bioengineering prototype and has never been clinically tested, any discussion regarding its potential impact on endoscopic efficiency will have to be based on theoretic assumptions and postulated scenarios. Sedation and analgesia The main rationale for developing self-propelling endoscopes is the avoidance of the mechanical stress on tissue inherent in push colonoscopy. If the instrument
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design and performance characteristics of self-propelling instruments are such that the entire procedure can be painlessly performed, this would be a major breakthrough in endoscopic practice associated with a substantial positive impact on endoscopic efficiency at more than one level. Cardiopulmonary adverse events are the most frequently observed events during any endoscopic procedure requiring conscious sedation, although these are rarely life threatening [42 –45]. All sedation-related complications would disappear if sedation and analgesia were no longer necessary, thus improving the safety of the procedure. This concern is particularly relevant to screening colonoscopy because it is commonly performed in older patients whose age and co-morbidities may make them more susceptible to sedation-related adverse events. More importantly, eliminating the need for sedation and analgesia would dramatically improve the overall efficiency of an endoscopy unit, making screening colonoscopy even more cost-effective. There are no studies looking at the overall impact of such a change on efficiency in endoscopy, assuming that all endoscopic procedures could be performed without sedation or analgesia, although one could easily surmise that the repercussions are substantial; it would drastically alter the way we design and operate an endoscopy unit. The additional time, monitoring resources, nursing personnel, pharmacy costs, and observation unit space currently being used to accommodate the demands of presedation assessment, sedation, and postprocedure observation would be totally eliminated from the equation. Total procedure time and room turn-around time would be reduced. Other things being equal, this could be the single most important factor affecting efficiency in endoscopy. Instrumentation-induced Injury Although uncommon (0.2%), colon perforation is the most feared serious complication of colonoscopy. The major mechanisms leading to perforation are mechanical pressure transmitted through the scope to the antimesenteric border of the sigmoid and descending colon, and manipulations during torsion or straightening of the instrument [46,47]. Looping of the scope in the colon is a major cause of prolonged procedure time or failure to complete the procedure during push colonoscopy. Thus complications related to instrumentation may be significantly reduced if self-propelling instruments can circumvent the mechanical risks of push colonoscopy without resulting in other types of tissue injury. In addition, prolonged procedure time caused by a redundant or tortuous colon would be minimized. Scope insertion time Current prototypes require a human operator to remotely control the movements of the robot inside the gut lumen using an external unit; however, it is plausible to assume that autopropulsion could be added as a feature in selfpropelling endoscopes. In this scenario, the robot would autopropel to the cecum
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without human assistance, then an expert endoscopist would step in to manipulate the robot in real time and perform the tasks of colon inspection, tissue sampling, or other endoscopic interventions as needed. In this hypothetic calculation, the maximum impact of autopropulsion on endoscopic efficiency would be equal to the average cecal intubation time of the endoscopist. One large scale screening colonoscopy study reported a mean insertion time to the cecum and a total procedure time of 10.5 (8.7) and 30.6 (19.1) minutes, respectively [41]. Using this as a rough benchmark, one could postulate that physician involvement potentially can be reduced by approximately one third of the total procedure time using autopropulsion. This assumes that the time required for scope withdrawal and colon examination using a robotic instrument is roughly equivalent to conventional push colonoscopy, and other efficiency factors are unaffected. Complete robotic control If the self-propelling colonoscope can perform the entire procedure without human assistance including instrument withdrawal and colon inspection, then no physician time is required upfront. Most likely, a trained endoscopy assistant would set up the system, introduce the instrument into the rectum, and supervise the actual procedure. In this hypothetic scenario, however, the physician would have to spend time reviewing the recorded images after the fact. Thus, there will be a temporal dissociation between the technical component of performing the procedure (a component the physician presumably can no longer bill for) and the cognitive component of inspecting the colon and making a diagnosis. This situation is similar to the reimbursement issues gastroenterologists have already encountered in performing capsule endoscopy. If the subsequent physician review of the recorded images takes longer than real-time examination of the colon during push colonoscopy, then any hoped for gains from reducing physician scope time will be effectively nullified. Perhaps there is still an efficiency factor stemming from the physician no longer having to be present for the procedure. They can have better control over their time by reviewing the results of the test at their convenience, a practice that many diagnostic radiologists and pathologists have enjoyed all along. Nevertheless, this minor advantage is offset by a more significant downside—there is no opportunity for the physician to interrogate or re-examine a suspicious or inadequately examined area of the colon after the procedure. This approach is analogous to a radiologist reviewing the films or even the recorded fluoroscopic footage after a barium study, instead of being on hand during fluoroscopy to supervise the radiologic examination. Furthermore, manipulation of the robot and its accessories for tissue sampling and endoscopic interventions can only be achieved in real time. Forgoing such robotic capabilities would relegate this technology to a passive colon cancer screening tool with limited diagnostic and no therapeutic benefits. And, additional costs would be incurred, because a proportion of patients would have to undergo a second procedure to biopsy or treat abnormal findings found by screening colonoscopy, as is now true of virtual colonoscopy.
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Telemanipulation One of the exciting applications of robotic technology is the potential for telemanipulation. Sitting at a control console, the endoscopist could use wireless technology to direct a self-propelling colonoscope remotely and manipulate various endoscopic accessories. Such a capability would expand the horizons of endoscopic efficiency dramatically by making colon cancer screening and endoscopic intervention more easily accessible. A trained endoscopy assistant could assist the patient at a remote colon cancer screening station, while an endoscopist located elsewhere could teleoperate a miniature endoscopic robot, view and interpret the findings, and administer the appropriate endoscopic treatment in real time.
Summary Self-propelling endoscopes offer exciting possibilities for improving access to colon cancer screening, safety of colonoscopy, and efficiency in endoscopy. From an operational perspective, efficiency in endoscopy may be increased or decreased by the introduction of a self-propelling endoscope, depending on the instrument’s technical performance characteristics and capabilities, its safety profile, ease of use, the physician time required to review the endoscopic findings, and requirements for sedation, if any. In addition, patient acceptance of such new technology will be a driving force determining its potential for success in the competition for a niche in the diagnostic armamentarium of colon cancer screening.
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Self-propelling endoscopes Yang K. Chen, MD University of Colorado Hospital, Division of Gastroenterology and Hepatology, Anschutz Centers for Advanced Medicine, 1635 N. Ursula Street, Box F-735, Aurora, CO 80010, USA
Colon cancer is the third most common type of cancer and the second leading cause of cancer death in the United States [1]. Indirect evidence and modeling analyses suggest that colonoscopy may be the most cost-effective way to screen the average-risk population for colorectal neoplasia [2 –4]. The American Cancer Society and the American College of Gastroenterology recommend endoscopic screening for the average risk population beginning at age 50 years [5,6]; however, the sheer number of potential patients who would qualify for colon cancer screening exceeds available technological resources and trained medical personnel. As waves of baby boomers reach 60 years of age, the aging United States population will further escalate the demand for these services. Currently less than 30% of eligible patients undergo a screening colonoscopy [7– 9]. The low compliance with screening recommendations may be attributable to several factors including lack of patient education, unfavorable patient attitudes toward bowel cleansing and colonoscopy, long waiting times for scheduling a screening procedure, and failure of some primary care physicians to uniformly implement the screening recommendations [9,10]. Rising demand for screening colonoscopy and the projected numbers of eligible patients puts a major strain on the health care system in general and on gastrointestinal endoscopy units in particular. In the United States, the problem is aggravated by a chronic nationwide shortage of qualified nurses [11]. The average age of endoscopy nurses belonging to the Society of Gastrointestinal Nurses and Associates (SGNA) is reported to be 48 years of age (unpublished data, SGNA). Most fellowship programs in gastroenterology cannot afford to increase the number of postgraduate trainees due to limited federal funding. Using nurse practitioners and physician assistants to perform screening endoscopies has been modestly successful for sigmoidoscopies [12,13], but the strategy has not been seriously considered for the more demanding skill of screening colonoscopy. Because human resource is not the only limiting factor, other potential solutions to address the widening gap between supply and demand E-mail address: [email protected] 1052-5157/04/$ – see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.giec.2004.04.007
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must be considered. Shrinking reimbursements for endoscopy and limited budgets for expensive capital equipment are forcing health care providers to scrutinize the profitability and operational efficiency of their endoscopy units. One potential solution is to identify or develop more cost-effective and efficient alternatives for colon cancer screening.
Conventional push colonoscopy Classic colonoscopes are semiflexible tubes that are inserted into the colon by pushing. The procedure requires a skilled endoscopist and is associated with significant discomfort for the patient. Thus, sedation and analgesia is almost always necessary. As the colon is elastic and contains multiple sharp bends, looping may occur during scope advancement, particularly in patients with redundant colons. In turn, this may result in longer procedure times, failure to reach the cecum, higher complication rates, more patient discomfort, or increased sedation requirements. Several factors have an impact on operator efficiency during push colonoscopy. The amount of time required to reach the cecum without compromising patient comfort and safety is operator- as well as patient-dependent and may be variable. And as yet there is no universal benchmark for the minimum amount of time that should be taken to carefully and thoroughly inspect the entire colon and rectum, usually during scope withdrawal. Of course, if pathology is encountered during a screening procedure, more time is needed for tissue sampling or endoscopic therapy. Of these three basic procedural steps, the latter is the most difficult to supplant with an alternative screening modality that is not operator dependent. Other important factors affecting operator efficiency include the time required to achieve conscious sedation and duration of postsedation recovery; both are functions of patient characteristics and of the type and quantity of preprocedure medications given. Because the endoscopist is generally responsible for overseeing sedation and analgesia, operator efficiency is significantly affected by the time needed to achieve (and maintain) the desired level of sedation and analgesia. Total colonoscopy time would be significantly reduced and procedural efficiency enhanced if complete examination of the colon could be performed without sedation.
Competing technologies If we were to design the ideal alternative to conventional push colonoscopy, we would want the procedure to be safer, faster, technically less demanding, more comfortable for the patient, less expensive and resource intensive, and at least as accurate if not better than conventional colonoscopy. Physician time may be reduced by eliminating the need for sedation and analgesia, by limiting physician involvement to the diagnostic and therapeutic components of the procedure, or by computerizing and automating the most essential step of real-time inspection and lesion detection.
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To help overcome some of these hurdles, a number of competing nonendoscopic technologies recently have been introduced into clinical practice, including virtual colonoscopy [14,15] and capsule endoscopy [16 – 19]. Capitalizing on recent advances in microrobotics, biomedical engineers are also developing and testing prototypes of a self-propelling endoscope as one potential way to surmount the technical challenges of performing push colonoscopy. Virtual colonoscopy Virtual colonoscopy (CT colonography) involves taking standard helical CT images of a patient’s gas-filled colon and using them to generate 2-D and 3-D computerized images. The images can be combined into a ‘‘fly-through’’ view of the colonic lumen that is similar to that seen during colonoscopy. The test has high theoretic patient acceptance and is safer to perform than conventional push colonoscopy, although the technique involves some radiation exposure. Because the procedure is painless, no sedation is required; however, rigorous colon cleansing is still an unpleasant but essential requirement [20,21]. Oral contrast tagging of fecal contents promises to eventually do away with the need for rigorous bowel preparation, thereby improving patient compliance [21]. Although initial results of virtual colonoscopy were inferior to push colonoscopy [15], recent reports from major centers in the United States show accuracy to be comparable to conventional colonoscopy for detection of polyps of clinically relevant size with few false positives [22 – 24]. The sensitivity drops significantly for detection of polyps less than 10 mm in size. The technology is expensive, and the sophisticated software used to reconstruct the 3-D images of the colonic lumen remains labor intensive. Whether the test ultimately will result in better patient compliance, require less physician time, and prove to be more cost-effective than conventional colonoscopy for screening, the average risk population remains to be proven. One major limitation of this technology is inability to obtain tissue samples and provide therapy. Some experts have speculated that widespread use of virtual colonoscopy for colon cancer screening paradoxically may lead to an even greater demand for push colonoscopy resulting from true- and false-positive lesions identified at virtual colonoscopy. Others have estimated that the overall likelihood of a therapeutic colonoscopy being required as a result of a potentially significant finding at virtual colonoscopy is approximately 10% at most [20]. One cost analysis assumed all polyps found at virtual colonoscopy justified a referral for colonoscopy and found that even if virtual colonoscopy could evolve into a perfect test, to be cost-effective it would have to offer 15% to 20% better compliance and cost 54% less than conventional colonoscopy [25]. Capsule endoscopy Invention of the transistor made it possible to design electronic radiotelemetry capsules that are small enough to be swallowed and used for examining the gastrointestinal tract [17,26 – 28]. Wireless capsule endoscopy has no external wires,
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fiber-optic bundles, or cables. Using a miniature complimentary metal oxide semiconductor camera and a short focal length lens, images are obtained, as the optical window of the capsule sweeps past the gut wall, without requiring air inflation of the gut lumen [17]. The capsule endoscope is propelled by peristalsis through the gastrointestinal tract. The video images are transmitted using radiotelemetry to an array of aerials attached to the body, which allow image capture. The images are stored on a small portable recorder worn on a belt and later downloaded for analysis. The system allows more than 7 hours of continuous recording and patients are able to continue their daily activities during the test. The capsule endoscope has performed well in trials involving patients with difficult gastrointestinal bleeding and in comparative studies with push enteroscopy [29 – 31]. Only preliminary data have been reported for capsule colonoscopy [32]. There is no clinical data on capsule colonoscopy as a screening test for detecting polyps and cancer. If used for this purpose, capsule endoscopy would be easier and safer to undergo than conventional push colonoscopy, but it is more time consuming. The procedure has the advantage of being painless and thus there is no need for sedation; however, adequate visualization of the entire colon using the capsule is highly dependent on a clean colon. Furthermore, for the first time in endoscopic practice there is a temporal dissociation between the technical and cognitive components of the examination. Subsequent physician review and interpretation of the recorded images may require more time than real-time colon examination during push colonoscopy. Poor physician reimbursements for the cognitive component may further discourage its widespread use. Rapid transit through the colon is undesirable and may adversely affect the capsule’s diagnostic accuracy; there is no opportunity for the reviewer to carefully interrogate a suspicious lesion or inadequately examined area after the fact. It is not known if capsule colonoscopy can approach the sensitivity and specificity of push colonoscopy as a screening test for colon polyps and cancer. Commercially available capsules do not have any steering or interventional capabilities; however, prototypes have been designed that may be able to actuate and navigate the capsule. For now developing biopsy and therapeutic capabilities in a steerable capsule remains a distant goal. Despite the limitations cited, these competing technologies will continue to improve. Eventually one of the less invasive imaging modalities will likely replace push colonoscopy as a more cost-effective means of colon cancer screening. Conventional colonoscopy will be relied upon primarily for therapeutic interventions.
Self-propelling endoscopes Recent advances in microrobotics have made the concept of a ‘‘self-propelling’’ endoscope an attainable goal (Fig. 1). Its successful application in the clinical arena may decrease our dependence on the time and services of an expert endoscopist and ultimately contribute to improved efficiency in endoscopy.
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Fig. 1. Self-propelling robotic endoscope.
Self-propelling endoscopes currently under development move through the colon by simulating inchworm locomotion (Fig. 2) [33 – 36]. The inchworm system consists of a propulsion unit, a miniature robotic arm, and a tail (umbilical cable) [33]. The propulsion unit consists of two suction clamps connected by expansion bellows. The tail connects the endoscope (miniature robot) to an external unit; it contains electrical wiring, pneumatic tubes, an operating channel, a flushing channel, and illumination fibers. The unit outside the body provides pneumatic actuation signals in the appropriate sequence to the miniature robot and feedback information on the robot’s movements to the endoscopist who can either telemanipulate or directly supervise its operation [37]. Because the tail does not have to transfer the pushing force, it can be made thinner and more flexible, causing less stress on the walls of the colon and thus, less pain. Future
Fig. 2. Typical inchworm motion and typical inchworm prototype.
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developments in wireless technology can be expected to eliminate the cumbersome endoscopic tail. The ultimate goal of self- propelling endoscope development is to design a miniature robot capable of performing the same functions as a conventional colonoscope, such as mucosal inspection and tissue sampling. A miniature robotic arm or manipulator can be placed at the front of the endoscopic system to orient and position accessory devices and the camera or video chip [38 – 40]. The manipulator may be driven by shape memory, alloy actuation, hydraulic pistons, or electromagnetic motors. In vivo experiments using one prototype (Endocrawler) were able to propel the endoscope at an average speed of 150 mm/ min in the live pig colon, suggesting that some day self-propelling endoscopes may become a viable alternative to push colonoscopy [34]. Clinical and technical issues Push colonoscopy is a safe test with an excellent record of procedural success [41]. Technical failures, missed lesions, and procedural complications are uncommon. Furthermore, a plethora of sophisticated accessory devices have been developed for tissue sampling, hemostasis, endoscopic resection of pathologic lesions, and other therapeutic interventions. Actual procedure time is a function of operator skill, patient factors, and instrument design. The average endoscopist can perform a complete examination of the colon in 30 minutes or less [41]. Of course one major drawback of the push technique is the discomfort associated with both air insufflation and scope advancement or looping, necessitating the use of conscious sedation and monitoring. To replace push colonoscopy as the screening procedure of choice, a selfpropelling endoscope would have to match its track record of safety, reliability, efficiency, and accuracy. As is true of any evaluation of new or proposed biomedical instruments, several technical and clinical issues must be addressed before a realistic assessment can be made regarding its feasibility for clinical use. With regard to the technical performance characteristics of self-propelling endoscopes, the following questions will need further clarification: Instrument-induced trauma is related to any potential stress on soft tissue. In the case of a self-propelling endoscope, the gut wall is the biologic interface of the instrument and its anatomic support. Is the instrument safe for human use? Will contact between colonic wall and the instrument during self-propulsion cause changes in colonic mucosa that may compromise subsequent interpretation of endoscopic and microscopic findings? Can the robot negotiate acute angles in the colon and navigate through collapsed bowel? What is its locomotion efficiency? Is the performance reliable? Is the instrument durable? Can the robot run on a miniaturized energy source? Can the robotic functions be remotely controlled by using wireless technology? Can the self-propelling scope perform a systematic and thorough inspection of the colonic lining? What is the angle of view of the optical window? Is the image quality equivalent to conventional endoscopes? Can a sophisticated compound
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lens system be mounted on the scope to provide several sets of eyes that can see in multiple directions during scope advancement and withdrawal? If so, this would significantly enhance imaging efficiency. Can the acquired images be transmitted via radiotelemetry for viewing in real time? Will self-propelling scopes have tissue sampling and interventional capabilities? Without these important robotic functions, the self-propelling endoscope will have the same basic limitations as virtual colonoscopy and commercially available capsule endoscopy. Patient and physician acceptance of this new technology may be affected by the answers to the following questions: Is self-propulsion faster than push colonoscopy? Does it require a human operator to advance and direct the endoscope to the cecum? If so, can this be performed by a trained endoscopy assistant? Is the procedure safer than push colonoscopy? Is this a painless procedure? Will inspection of the entire colon using robotic technology require more time than push colonoscopy? How easy is it to learn how to control the robotic functions? What is the relative cost of the technology? Will selfpropulsion technology adversely affect physician reimbursement?
Impact on efficiency Efficiency in colonoscopy may be defined as the number of procedures each endoscopist can perform per unit time. In conventional colonoscopy, major factors affecting procedure time include how quickly and safely the desired level of sedation and analgesia can be achieved and maintained, the scope insertion time (to the cecum), and the time required to perform a systematic inspection of the colonic mucosa for detection of pathology. Obviously, additional time will be required for tissue sampling and endoscopic treatment if a pathologic lesion is encountered. More broadly speaking, efficiency in endoscopy transcends the total procedure time to encompass more global issues affecting operational efficiency. For example, the requirement for conscious sedation and postprocedure observation is arguably the single most important factor affecting the operational efficiency in an endoscopy unit. Likewise, any need for personnel to assist in an endoscopy procedure will contribute to the costs of running the unit. Thus, the overall efficiency of the endoscopist, as well as the endoscopy unit, may be increased or decreased depending on the performance characteristics of self-propelling endoscopes that we have already discussed. Because self-propelling colonoscopy is presently available only as a bioengineering prototype and has never been clinically tested, any discussion regarding its potential impact on endoscopic efficiency will have to be based on theoretic assumptions and postulated scenarios. Sedation and analgesia The main rationale for developing self-propelling endoscopes is the avoidance of the mechanical stress on tissue inherent in push colonoscopy. If the instrument
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design and performance characteristics of self-propelling instruments are such that the entire procedure can be painlessly performed, this would be a major breakthrough in endoscopic practice associated with a substantial positive impact on endoscopic efficiency at more than one level. Cardiopulmonary adverse events are the most frequently observed events during any endoscopic procedure requiring conscious sedation, although these are rarely life threatening [42 –45]. All sedation-related complications would disappear if sedation and analgesia were no longer necessary, thus improving the safety of the procedure. This concern is particularly relevant to screening colonoscopy because it is commonly performed in older patients whose age and co-morbidities may make them more susceptible to sedation-related adverse events. More importantly, eliminating the need for sedation and analgesia would dramatically improve the overall efficiency of an endoscopy unit, making screening colonoscopy even more cost-effective. There are no studies looking at the overall impact of such a change on efficiency in endoscopy, assuming that all endoscopic procedures could be performed without sedation or analgesia, although one could easily surmise that the repercussions are substantial; it would drastically alter the way we design and operate an endoscopy unit. The additional time, monitoring resources, nursing personnel, pharmacy costs, and observation unit space currently being used to accommodate the demands of presedation assessment, sedation, and postprocedure observation would be totally eliminated from the equation. Total procedure time and room turn-around time would be reduced. Other things being equal, this could be the single most important factor affecting efficiency in endoscopy. Instrumentation-induced Injury Although uncommon (0.2%), colon perforation is the most feared serious complication of colonoscopy. The major mechanisms leading to perforation are mechanical pressure transmitted through the scope to the antimesenteric border of the sigmoid and descending colon, and manipulations during torsion or straightening of the instrument [46,47]. Looping of the scope in the colon is a major cause of prolonged procedure time or failure to complete the procedure during push colonoscopy. Thus complications related to instrumentation may be significantly reduced if self-propelling instruments can circumvent the mechanical risks of push colonoscopy without resulting in other types of tissue injury. In addition, prolonged procedure time caused by a redundant or tortuous colon would be minimized. Scope insertion time Current prototypes require a human operator to remotely control the movements of the robot inside the gut lumen using an external unit; however, it is plausible to assume that autopropulsion could be added as a feature in selfpropelling endoscopes. In this scenario, the robot would autopropel to the cecum
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without human assistance, then an expert endoscopist would step in to manipulate the robot in real time and perform the tasks of colon inspection, tissue sampling, or other endoscopic interventions as needed. In this hypothetic calculation, the maximum impact of autopropulsion on endoscopic efficiency would be equal to the average cecal intubation time of the endoscopist. One large scale screening colonoscopy study reported a mean insertion time to the cecum and a total procedure time of 10.5 (8.7) and 30.6 (19.1) minutes, respectively [41]. Using this as a rough benchmark, one could postulate that physician involvement potentially can be reduced by approximately one third of the total procedure time using autopropulsion. This assumes that the time required for scope withdrawal and colon examination using a robotic instrument is roughly equivalent to conventional push colonoscopy, and other efficiency factors are unaffected. Complete robotic control If the self-propelling colonoscope can perform the entire procedure without human assistance including instrument withdrawal and colon inspection, then no physician time is required upfront. Most likely, a trained endoscopy assistant would set up the system, introduce the instrument into the rectum, and supervise the actual procedure. In this hypothetic scenario, however, the physician would have to spend time reviewing the recorded images after the fact. Thus, there will be a temporal dissociation between the technical component of performing the procedure (a component the physician presumably can no longer bill for) and the cognitive component of inspecting the colon and making a diagnosis. This situation is similar to the reimbursement issues gastroenterologists have already encountered in performing capsule endoscopy. If the subsequent physician review of the recorded images takes longer than real-time examination of the colon during push colonoscopy, then any hoped for gains from reducing physician scope time will be effectively nullified. Perhaps there is still an efficiency factor stemming from the physician no longer having to be present for the procedure. They can have better control over their time by reviewing the results of the test at their convenience, a practice that many diagnostic radiologists and pathologists have enjoyed all along. Nevertheless, this minor advantage is offset by a more significant downside—there is no opportunity for the physician to interrogate or re-examine a suspicious or inadequately examined area of the colon after the procedure. This approach is analogous to a radiologist reviewing the films or even the recorded fluoroscopic footage after a barium study, instead of being on hand during fluoroscopy to supervise the radiologic examination. Furthermore, manipulation of the robot and its accessories for tissue sampling and endoscopic interventions can only be achieved in real time. Forgoing such robotic capabilities would relegate this technology to a passive colon cancer screening tool with limited diagnostic and no therapeutic benefits. And, additional costs would be incurred, because a proportion of patients would have to undergo a second procedure to biopsy or treat abnormal findings found by screening colonoscopy, as is now true of virtual colonoscopy.
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Telemanipulation One of the exciting applications of robotic technology is the potential for telemanipulation. Sitting at a control console, the endoscopist could use wireless technology to direct a self-propelling colonoscope remotely and manipulate various endoscopic accessories. Such a capability would expand the horizons of endoscopic efficiency dramatically by making colon cancer screening and endoscopic intervention more easily accessible. A trained endoscopy assistant could assist the patient at a remote colon cancer screening station, while an endoscopist located elsewhere could teleoperate a miniature endoscopic robot, view and interpret the findings, and administer the appropriate endoscopic treatment in real time.
Summary Self-propelling endoscopes offer exciting possibilities for improving access to colon cancer screening, safety of colonoscopy, and efficiency in endoscopy. From an operational perspective, efficiency in endoscopy may be increased or decreased by the introduction of a self-propelling endoscope, depending on the instrument’s technical performance characteristics and capabilities, its safety profile, ease of use, the physician time required to review the endoscopic findings, and requirements for sedation, if any. In addition, patient acceptance of such new technology will be a driving force determining its potential for success in the competition for a niche in the diagnostic armamentarium of colon cancer screening.
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