- Email: [email protected]
The measurement of forces exerted during colonoscopy
NEW METHODS & MATERIALS The measurement of forces exerted during colonoscopy Mark N. Appleyard, MRCP, Charles A. Mosse, PhD, Timothy N. Mills, PhD, G. Duncan Bell, MD, Fortunato D. Castillo, C. Paul Swain, MD Background: The widely varying forces used at colonoscopy have not been measured. An electronic device was designed to measure the forces exerted by the clinician on the endoscope during colonoscopy. Methods: The device featured a handle designed in the shape of a hinged split cylinder that could be locked around the endoscope but readily moved up and down the insertion tube as the colonoscopy proceeded. This cylinder contained strain-gauges arranged so that the forces transmitted could be accurately measured. The device recorded the torque forces in addition to the push and pull forces exerted during diagnostic colonoscopy. Results: In a series of 21 colonoscopies in 20 patients: peak pushing force = 4.4 kg, pulling force = –1.8 kg, anticlockwise torque = 1.0 Newton meters, clockwise torque = 0.8 Newton meters. Percentage time force greater than 1 kg = 5%. Peak anal insertion force = 1.8 kg. Conclusions: These measurements represent the first accurate measurements of the forces exerted during colonoscopy. Reducing the force during colonoscopy is likely to diminish pain and reduce the risk of perforation. A knowledge of these forces may also help with the design of new instruments and models for teaching or research.
Colonoscopy hurts. If colonoscopy hurt less it might be possible to perform this examination with less or no sedation and analgesia, which would be safer. Some experienced endoscopists currently perform colonoscopy with little or no sedation or analgesia1; however, this practice is not universally held.2 The discomfort felt at colonoscopy relates to the force imparted to the colon by the colonoscope stretching the colonic attachments, by gaseous distension, and by the patient’s perception and threshold of pain. The size of these colonoscopic forces, Received October 14, 1999. For revision December 23, 1999. Accepted March 17, 2000. From the Department of Medical Physics, University College London, Royal London Hospital, London, UK, and Department of Gastroenterology, Sunderland Royal Hospital, Sunderland, United Kingdom. Supported in part by a grant from the Trustees of the Royal London Hospital. Reprint requests: C. P. Swain, MD, Academic Department of Gastroenterology, Royal London Hospital, Whitechapel, London E1 1BB, UK. Copyright © 2000 by the American Society for Gastrointestinal Endoscopy 0016-5107/2000/$12.00 + 0 37/69/107218 doi:10.1067/mge.2000.107218 VOLUME 52, NO. 2, 2000
A
B Figure 1. Hand-grip for the force-measuring device: A, open; B, secured onto a colonoscope.
which indirectly relate to the degree of pain, vary widely and are influenced by operator-dependent variables such as experience and technique as well as patient variables such as colonic anatomy.3 The feared complication of perforation occurs at a rate of 0.045% for diagnostic colonoscopy based on combined data from more recent prospective trials.4 It occurs most commonly in the sigmoid colon5 and probably relates to excessive force as a result of either pushing through unreduced sigmoid loops or “slide by” techniques of colonoscopic advancement.6 The measurement of forces at flexible endoscopy has not been reported. The aim of this study was to measure the forces exerted on the colonoscope during diagnostic colonoscopy. A knowledge of the forces applied might help with the design of new colonoscopic methods and with the development of models to teach colonoscopy. Methods that reduce the force exerted during colonoscopy are likely to diminish pain and reduce the risk of perforation. METHODS Force measuring device A device was designed and built to measure forces at endoscopy. The principle of the device is that the endoscopist does not hold the insertion tube of the endoscope directly but instead uses a tubular hand grip that is closed around the insertion tube of the endoscope (Fig. 1A). The GASTROINTESTINAL ENDOSCOPY
237
M Appleyard, C Mosse, T Mills, et al.
The measurement of forces exerted during colonoscopy
Figure 2. Force measurements from a colonoscopy in a 66-year-old man with bleeding per rectum. The solid line represents push/pull forces and the dotted line torque forces. The recording is marked with the colonoscopic insertion lengths, colonoscopists assessment of tip location and performance of various maneuvers. hand grip contains strain gauges that measure the forces transmitted from an external sleeve, that is held by the endoscopist, to an internal sleeve, which holds the insertion tube of the endoscope (Fig. 1B). Strain gauges in the handle were arranged so that they were sensitive to push/pull forces and clockwise/anti-clockwise torque forces. The device was optically isolated and tested by the medical equipment department of our hospital.7
removed if therapeutic procedures were undertaken such as polyp removal. The device was calibrated using known weights. No significant cross-talk was identified between the channels measuring push/pull forces and torque forces. The colonoscopes used were the CFT240L and CFT230L (Olympus Optical Co., Ltd., Tokyo, Japan) which were 12 and 12.9 mm in diameter, respectively. KY jelly (Johnson & Johnson Ltd., London, UK) was used routinely as lubrication.
Use during colonoscopy
Patients
During colonoscopy, the hand grip can be readily unlocked and moved along the insertion tube or removed altogether which is achieved using the catch mechanism that can be seen in Figure 1B. The catch is mounted onto the upper sleeve and can be rotated using the small aluminium lever that can be seen just below the base of the endoscopist’s thumb on the right hand side of Figure 1B. The advantage of this toggle action is that the bore of the hand grip does not have to match the diameter of the endoscope exactly and that the operator does not need to use great force to squeeze the grip tightly closed. The colonoscopist described the frequent moving of the device as only mildly inconvenient, and the larger diameter device as sitting comfortably in the palm of the hand. The calibrated output is displayed on the monitor in real time as a chart recorder style trace with torque measured in Newton meters and push/pull in kilograms force. Kilograms force were used as a measure of push/pull forces because we felt endoscopists would be more familiar with this unit rather than the Newton. The recordings were marked to indicate the position of the colonoscope and the maneuver being performed. During 3 colonoscopies the position of the device was accurately confirmed using electromagnetic imaging apparatus described elsewhere8. The device was
Recordings were made of 21 diagnostic colonoscopies in 20 patients performed by two experienced consultant endoscopists, the 3 colonoscopies using the electromagnetic imaging device being performed by the second colonoscopist. The male/female gender ratio was 12:8, age range 30 to 78, and indications were as follows: colitis surveillance 3; bleeding per rectum 4; anemia 2; polyp surveillance 4; altered bowel habit 4; abdominal pain 2; and positive family history of colorectal cancer in 1. The measurement of push/pull or torque was activated once the device was in position and zeroed with the colonoscope held in a neutral position by the endoscopist. As a result subsequent measurements would take into account the weight of the instrument and any other forces acting on the grip device but not initiated by the endoscopist’s hand for colonoscopic movement.
238
GASTROINTESTINAL ENDOSCOPY
RESULTS Force measurements during colonoscopy are summarized in Table 1. Measurements were made for 179.5 minutes during 21 colonoscopies from anal insertion to the time that the cecum was reached. Peak pushing forces greater than 3 kg (6.6 lb) VOLUME 52, NO. 2, 2000
The measurement of forces exerted during colonoscopy
M Appleyard, C Mosse, T Mills, et al.
Table 1. Summary of force measurements made during 21 colonoscopies Patient (age) 1 (69 yr) 2 (41 yr) 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
(71 (32 (45 (35 (78 (49 (40 (70 (53 (64 (43 (73 (33 (66 (55 (63 (56
yr) yr) yr) yr) yr) yr) yr) yr) yr) yr) yr) yr) yr) yr) yr) yr) yr)
20 (46 yr)
Indication for endoscopy Ulcerative colitis Polyp follow-up (sigmoid colectomy) Abdo pain (L hemicolectomy) PR bleed Chronic diarrhea Altered bowel habit Polyp surveillance Irritable bowel PR bleed Abdo pain Laxative user Chronic diarrhoea Polyp surveillance Anemia Anemia Ulcerative colitis PR bleed Polyp surveillance PR bleed Family history of colon cancer Ulcerative colitis
Duration of record(s)
Peak push (kg)
Peak pull (kg)
Peak clockwise torque (Nm)
240 150 & 300 120 200 600 720 400 700 720 950 320 640 470 630 600 400 660 820 730
4.4 0.7 & 1.7 1.7 1.3 2.2 3.4 2.1 2.5 2.2 2.9 1.2 1.45 0.9 1.3 0.55 1.0 1.3 2.2 1.9
1.2 0.4 & 1.2 0.2 0.2 1.5 1.5 .5 1.5 1.8 1.7 1.0 0.8 0.6 1.1 0.5 0.7 1.0 0.8 1.2
0.6 0.3 & 0.6 0.1 0.2 0.6 0.5 0.3 0.2 0.4 0.5 0.5 0.6 0.3 0.7 0.6 0.8 0.6 0.65 0.8
0.4 0.2 & 0.5 0.2 0.1 0.8 0.5 0.2 0.3 0.2 0.5 1.0 0.5 0.4 0.5 0.55 0.75 0.5 0.65 0.6
0.8 0.7 & NA 0.5 0.9 2.2 0.5 1.1 0.8 1.8 1.0 0.25 0.13 0.3 0.2 0.25 0.2 0.4 0.25 0.6
370
1.4
0.5
1.1
0.9
0.5
occurred in two patients for a total of 6 seconds, greater than 2 kg (4.4 lb) for 58 seconds (0.5% of the recorded time) and greater than 1 kg (2.2 lb) for 29.1 minutes (16% of the recorded time). Peak pushing forces were typically seen on anal insertion, in the sigmoid colon and at the flexures. Peak forces in men (median 1.45 kg, IQR 1.2 to 2.2) did not differ significantly from those in women (1.8 kg, 1.3 to 2.35). Peak forces also did not significantly differ with age below 60 years (1.4 kg, 1.2 to 2.2) and above 60 years (2.1 kg, 1.45 to 2.9). If the first patient with ulcerative colitis, in whom the device was used, is excluded there is a significant positive correlation between the peak push forces and length of procedure (r = 0.55: 95% CI [0.14, 0.8], p < 0.005, Pearson correlation coefficient}). This patient, with the highest peak push force of 4.4 kg, had an isolated, tightly angulated, fibrotic segment of sigmoid colon during an otherwise straight forward procedure and may not be representative generally of forces used in colonoscopy. Torque forces were largest in the sigmoid colon, associated with colonoscope shortening and generally occurred toward the end of the colonoscopies. One colonoscopist used clockwise torque almost constantly during colonoscopies. The peak forces exerted correlated well with empiric observations of the patient’s expression of discomfort. As expected, rapid colonoscope advancement was not associated with large forces in the presence of a straight colonoscope configuration. A typical tracing is seen in Figure 2. VOLUME 52, NO. 2, 2000
Peak anti-(Nm) Push at anal clockwise torque (Nm) insert (kg)
DISCUSSION These are the first measurements of forces exerted on the insertion tube of an endoscope during colonoscopy. The forces measured are an accurate representation of the forces exerted by the hand on the colonoscope during colonoscopy, the size of forces being confirmed by bench test calibration. The transmission of the measured forces to specific areas of the gut wall will vary considerably because of the complex geometry of the floppy curved colon with variable mesenteric attachments and the stiffer, variably looped colonoscope. It is likely that a higher proportion of the hand force exerted on the colonoscope may be transmitted to a small area in the recto-sigmoid colon while much less force is transmitted to the bowel wall on the right side of the colon. The range of push forces exerted was wide as expected. The recordings showed that extremely high levels of peak force were occasionally exerted, but only for short periods of time. For example: the maximum push force in patient 1 of 4.4 kg (9.7 lb) lasted for only 1.5 seconds. Forces greater than 2 kg were not observed to advance the colonoscope tip in this series. Peak push forces were seen in the sigmoid colon just before shortening and at the flexures as would be expected. Forces required to perforate the human cadaveric colon with a colonoscope sized piece of wood have been measured, the average force being 12 lb (range 6 to 20 lb.) or 5.44 kg (range 2.72 to 9.07) in a series of 13 perforations, forces not much above the peak of ones seen in this study.9 GASTROINTESTINAL ENDOSCOPY
239
M Appleyard, C Mosse, T Mills, et al.
High values, of longer duration, were also recorded for torque forces which reached a maximum of 1.75 Nm of clockwise torque in one patient with a 1.3 m length of colonoscope inserted while passing the hepatic flexure. Increasing torque may assist in colonoscopy not only because it alters the angle of approach of the tip of the instrument to the lumen, but also because its association with shortening can reduce formed loops.10 As the endoscope is inserted further the torque force required to angle the tip or reduce loops at the distal end of the endoscope will increase because the insertion tube is not rigid. The instruments we used contain counterclockwise springs along the insertion tube and using torque may also stiffen the endoscope to aid insertion. These observations probably explain some of the rather large torque forces measured toward the end of some of the examinations. Although the small sample size does not allow generalizations about the forces required in different colonoscopic situations some interesting observations can be made. One colonoscopist used more clockwise torque throughout his colonoscopies, perhaps as a method of stiffening a flexible endoscope. The forces required to perform a colonoscopy on one patient with irritable bowel syndrome were in the middle of the force range, but the procedure took slightly longer (700 seconds) and was poorly tolerated despite standard sedation and analgesia suggesting that perhaps increased visceral pain perception is a factor in patient tolerance as has been proposed in these patients.11 Interestingly of the three examinations in patients with colitis, the time taken to reach the cecum was generally short (240, 600, and 370 seconds), one contained the highest peak push at 4.4 kg, although only 27 seconds (11% of the time) of the examination contained push forces greater than 1 kg. In another patient with colitis, the peak push forces were the lowest of all the examinations with a peak of only 0.36 kg (0.8 lb). In the third patient the push values were again low with only 18 seconds (5% of the time) of push force greater than 0.5 kg. This might suggest that the slight increase in perforation rate reported in these patients12 could be due to a combination of a weakened, inflamed bowel wall and perhaps the resulting occasional tight corner or stricture requiring higher forces. Experience would suggest, however, that colonoscopy in the majority of patients with quiescent pancolitis is easier to perform, a point supported by these data. These measurements give some insight into the forces imparted to the colon during diagnostic colo-
240
GASTROINTESTINAL ENDOSCOPY
The measurement of forces exerted during colonoscopy
noscopy. The force-measuring device could be used to validate colon models used for training purposes. Perhaps more importantly the device will be used as an objective measure in the testing of new colonoscopic devices. At present, the ease of colonoscopy is either measured by subjective patient variables, such as pain, or operator variables, such as time to complete colonoscopy, which are unreliable given variable patient sedation and differences between operators. In summary, this force-measuring device allows accurate, objective and reliable measurements of forces imparted to the colonoscope and indirectly to the colon wall and may provide a valuable method for testing new colonoscopic devices and comparing colonoscopic techniques. ACKNOWLEGMENTS We thank Tito Castillo for assistance in writing a software program for data acquisition and the endoscopy staff at the Royal London Hospital and Royal Sunderland Hospital for assistance during these studies. REFERENCES 1. Cataldo PA. Colonoscopy without sedation. Dis Colon Rectum 1996;39:257-61. 2. Saunders BP, Fukumoto M, Halligan S, Masaki T, Love S, Williams CB. Patient-administered nitrous oxide/oxygen inhalation provides effective sedation and analgesia for colonoscopy. Gastrointest Endosc 1994;40:418-21. 3. Hull T, Church JM. Colonoscopy—How difficult, how painful? Surg Endosc 1994;8:784-7. 4. Waye JD, Kahn O, Auerbach ME. Complications of colonoscopy and flexible sigmoidoscopy. Gastrointest Endosc Clin N Am 1996;6:343-77. 5. Orsoni P, Berdah S, Verrier C, Caamano A, Sastre B, Boutboul R, et al. Colonic perforation due to colonoscopy: a retrospective study of 48 cases. Endoscopy 1997;29:160-4. 6. Geenen JE, Schmitt MG Jr, Wu WC, Hogan WJ. Major complications of coloscopy: bleeding and perforation. Am J Dig Dis 1975;20:231-5. 7. Mosse CA, Mills TN, Bell GD, Swain CP. Device for measuring the forces exerted on the shaft of an endoscope during colonoscopy. Med Biol Eng Comput 1998;36:186-90. 8. Bladen JS, Anderson AP, Bell GD, Rameh B, Evans B, Heatley DJ. Non-radiological technique for three-dimensional imaging of endoscopes. Lancet 1993;341:719-22. 9. Wu TK. Occult injuries during colonoscopy. Measurement of forces required to injure the colon and report of cases. Gastrointest Endosc 1978;24:236-8. 10. Coller JA. Technique of flexible fiberoptic sigmoidoscopy. Surg Clin North Am 1980;60:465-79. 11. Whitehead WE, Holtkotter B, Enck P, Hoelzl R, Holmes KD, Anthony J, et al. Tolerance for rectosigmoid distention in irritable bowel syndrome. Gastroenterology 1990;98(Pt1):1187-92. 12. Keeffe ER, Schrock TR. Complications of gastrointestinal endoscopy. In: Sleisenger MH, Fordtran JS, editors. Gastrointestinal disease: pathophysiology, diagnosis, management. Philadelphia: WB Saunders; 1993. p. 301-8.
VOLUME 52, NO. 2, 2000
Colonoscopy hurts. If colonoscopy hurt less it might be possible to perform this examination with less or no sedation and analgesia, which would be safer. Some experienced endoscopists currently perform colonoscopy with little or no sedation or analgesia1; however, this practice is not universally held.2 The discomfort felt at colonoscopy relates to the force imparted to the colon by the colonoscope stretching the colonic attachments, by gaseous distension, and by the patient’s perception and threshold of pain. The size of these colonoscopic forces, Received October 14, 1999. For revision December 23, 1999. Accepted March 17, 2000. From the Department of Medical Physics, University College London, Royal London Hospital, London, UK, and Department of Gastroenterology, Sunderland Royal Hospital, Sunderland, United Kingdom. Supported in part by a grant from the Trustees of the Royal London Hospital. Reprint requests: C. P. Swain, MD, Academic Department of Gastroenterology, Royal London Hospital, Whitechapel, London E1 1BB, UK. Copyright © 2000 by the American Society for Gastrointestinal Endoscopy 0016-5107/2000/$12.00 + 0 37/69/107218 doi:10.1067/mge.2000.107218 VOLUME 52, NO. 2, 2000
A
B Figure 1. Hand-grip for the force-measuring device: A, open; B, secured onto a colonoscope.
which indirectly relate to the degree of pain, vary widely and are influenced by operator-dependent variables such as experience and technique as well as patient variables such as colonic anatomy.3 The feared complication of perforation occurs at a rate of 0.045% for diagnostic colonoscopy based on combined data from more recent prospective trials.4 It occurs most commonly in the sigmoid colon5 and probably relates to excessive force as a result of either pushing through unreduced sigmoid loops or “slide by” techniques of colonoscopic advancement.6 The measurement of forces at flexible endoscopy has not been reported. The aim of this study was to measure the forces exerted on the colonoscope during diagnostic colonoscopy. A knowledge of the forces applied might help with the design of new colonoscopic methods and with the development of models to teach colonoscopy. Methods that reduce the force exerted during colonoscopy are likely to diminish pain and reduce the risk of perforation. METHODS Force measuring device A device was designed and built to measure forces at endoscopy. The principle of the device is that the endoscopist does not hold the insertion tube of the endoscope directly but instead uses a tubular hand grip that is closed around the insertion tube of the endoscope (Fig. 1A). The GASTROINTESTINAL ENDOSCOPY
237
M Appleyard, C Mosse, T Mills, et al.
The measurement of forces exerted during colonoscopy
Figure 2. Force measurements from a colonoscopy in a 66-year-old man with bleeding per rectum. The solid line represents push/pull forces and the dotted line torque forces. The recording is marked with the colonoscopic insertion lengths, colonoscopists assessment of tip location and performance of various maneuvers. hand grip contains strain gauges that measure the forces transmitted from an external sleeve, that is held by the endoscopist, to an internal sleeve, which holds the insertion tube of the endoscope (Fig. 1B). Strain gauges in the handle were arranged so that they were sensitive to push/pull forces and clockwise/anti-clockwise torque forces. The device was optically isolated and tested by the medical equipment department of our hospital.7
removed if therapeutic procedures were undertaken such as polyp removal. The device was calibrated using known weights. No significant cross-talk was identified between the channels measuring push/pull forces and torque forces. The colonoscopes used were the CFT240L and CFT230L (Olympus Optical Co., Ltd., Tokyo, Japan) which were 12 and 12.9 mm in diameter, respectively. KY jelly (Johnson & Johnson Ltd., London, UK) was used routinely as lubrication.
Use during colonoscopy
Patients
During colonoscopy, the hand grip can be readily unlocked and moved along the insertion tube or removed altogether which is achieved using the catch mechanism that can be seen in Figure 1B. The catch is mounted onto the upper sleeve and can be rotated using the small aluminium lever that can be seen just below the base of the endoscopist’s thumb on the right hand side of Figure 1B. The advantage of this toggle action is that the bore of the hand grip does not have to match the diameter of the endoscope exactly and that the operator does not need to use great force to squeeze the grip tightly closed. The colonoscopist described the frequent moving of the device as only mildly inconvenient, and the larger diameter device as sitting comfortably in the palm of the hand. The calibrated output is displayed on the monitor in real time as a chart recorder style trace with torque measured in Newton meters and push/pull in kilograms force. Kilograms force were used as a measure of push/pull forces because we felt endoscopists would be more familiar with this unit rather than the Newton. The recordings were marked to indicate the position of the colonoscope and the maneuver being performed. During 3 colonoscopies the position of the device was accurately confirmed using electromagnetic imaging apparatus described elsewhere8. The device was
Recordings were made of 21 diagnostic colonoscopies in 20 patients performed by two experienced consultant endoscopists, the 3 colonoscopies using the electromagnetic imaging device being performed by the second colonoscopist. The male/female gender ratio was 12:8, age range 30 to 78, and indications were as follows: colitis surveillance 3; bleeding per rectum 4; anemia 2; polyp surveillance 4; altered bowel habit 4; abdominal pain 2; and positive family history of colorectal cancer in 1. The measurement of push/pull or torque was activated once the device was in position and zeroed with the colonoscope held in a neutral position by the endoscopist. As a result subsequent measurements would take into account the weight of the instrument and any other forces acting on the grip device but not initiated by the endoscopist’s hand for colonoscopic movement.
238
GASTROINTESTINAL ENDOSCOPY
RESULTS Force measurements during colonoscopy are summarized in Table 1. Measurements were made for 179.5 minutes during 21 colonoscopies from anal insertion to the time that the cecum was reached. Peak pushing forces greater than 3 kg (6.6 lb) VOLUME 52, NO. 2, 2000
The measurement of forces exerted during colonoscopy
M Appleyard, C Mosse, T Mills, et al.
Table 1. Summary of force measurements made during 21 colonoscopies Patient (age) 1 (69 yr) 2 (41 yr) 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
(71 (32 (45 (35 (78 (49 (40 (70 (53 (64 (43 (73 (33 (66 (55 (63 (56
yr) yr) yr) yr) yr) yr) yr) yr) yr) yr) yr) yr) yr) yr) yr) yr) yr)
20 (46 yr)
Indication for endoscopy Ulcerative colitis Polyp follow-up (sigmoid colectomy) Abdo pain (L hemicolectomy) PR bleed Chronic diarrhea Altered bowel habit Polyp surveillance Irritable bowel PR bleed Abdo pain Laxative user Chronic diarrhoea Polyp surveillance Anemia Anemia Ulcerative colitis PR bleed Polyp surveillance PR bleed Family history of colon cancer Ulcerative colitis
Duration of record(s)
Peak push (kg)
Peak pull (kg)
Peak clockwise torque (Nm)
240 150 & 300 120 200 600 720 400 700 720 950 320 640 470 630 600 400 660 820 730
4.4 0.7 & 1.7 1.7 1.3 2.2 3.4 2.1 2.5 2.2 2.9 1.2 1.45 0.9 1.3 0.55 1.0 1.3 2.2 1.9
1.2 0.4 & 1.2 0.2 0.2 1.5 1.5 .5 1.5 1.8 1.7 1.0 0.8 0.6 1.1 0.5 0.7 1.0 0.8 1.2
0.6 0.3 & 0.6 0.1 0.2 0.6 0.5 0.3 0.2 0.4 0.5 0.5 0.6 0.3 0.7 0.6 0.8 0.6 0.65 0.8
0.4 0.2 & 0.5 0.2 0.1 0.8 0.5 0.2 0.3 0.2 0.5 1.0 0.5 0.4 0.5 0.55 0.75 0.5 0.65 0.6
0.8 0.7 & NA 0.5 0.9 2.2 0.5 1.1 0.8 1.8 1.0 0.25 0.13 0.3 0.2 0.25 0.2 0.4 0.25 0.6
370
1.4
0.5
1.1
0.9
0.5
occurred in two patients for a total of 6 seconds, greater than 2 kg (4.4 lb) for 58 seconds (0.5% of the recorded time) and greater than 1 kg (2.2 lb) for 29.1 minutes (16% of the recorded time). Peak pushing forces were typically seen on anal insertion, in the sigmoid colon and at the flexures. Peak forces in men (median 1.45 kg, IQR 1.2 to 2.2) did not differ significantly from those in women (1.8 kg, 1.3 to 2.35). Peak forces also did not significantly differ with age below 60 years (1.4 kg, 1.2 to 2.2) and above 60 years (2.1 kg, 1.45 to 2.9). If the first patient with ulcerative colitis, in whom the device was used, is excluded there is a significant positive correlation between the peak push forces and length of procedure (r = 0.55: 95% CI [0.14, 0.8], p < 0.005, Pearson correlation coefficient}). This patient, with the highest peak push force of 4.4 kg, had an isolated, tightly angulated, fibrotic segment of sigmoid colon during an otherwise straight forward procedure and may not be representative generally of forces used in colonoscopy. Torque forces were largest in the sigmoid colon, associated with colonoscope shortening and generally occurred toward the end of the colonoscopies. One colonoscopist used clockwise torque almost constantly during colonoscopies. The peak forces exerted correlated well with empiric observations of the patient’s expression of discomfort. As expected, rapid colonoscope advancement was not associated with large forces in the presence of a straight colonoscope configuration. A typical tracing is seen in Figure 2. VOLUME 52, NO. 2, 2000
Peak anti-(Nm) Push at anal clockwise torque (Nm) insert (kg)
DISCUSSION These are the first measurements of forces exerted on the insertion tube of an endoscope during colonoscopy. The forces measured are an accurate representation of the forces exerted by the hand on the colonoscope during colonoscopy, the size of forces being confirmed by bench test calibration. The transmission of the measured forces to specific areas of the gut wall will vary considerably because of the complex geometry of the floppy curved colon with variable mesenteric attachments and the stiffer, variably looped colonoscope. It is likely that a higher proportion of the hand force exerted on the colonoscope may be transmitted to a small area in the recto-sigmoid colon while much less force is transmitted to the bowel wall on the right side of the colon. The range of push forces exerted was wide as expected. The recordings showed that extremely high levels of peak force were occasionally exerted, but only for short periods of time. For example: the maximum push force in patient 1 of 4.4 kg (9.7 lb) lasted for only 1.5 seconds. Forces greater than 2 kg were not observed to advance the colonoscope tip in this series. Peak push forces were seen in the sigmoid colon just before shortening and at the flexures as would be expected. Forces required to perforate the human cadaveric colon with a colonoscope sized piece of wood have been measured, the average force being 12 lb (range 6 to 20 lb.) or 5.44 kg (range 2.72 to 9.07) in a series of 13 perforations, forces not much above the peak of ones seen in this study.9 GASTROINTESTINAL ENDOSCOPY
239
M Appleyard, C Mosse, T Mills, et al.
High values, of longer duration, were also recorded for torque forces which reached a maximum of 1.75 Nm of clockwise torque in one patient with a 1.3 m length of colonoscope inserted while passing the hepatic flexure. Increasing torque may assist in colonoscopy not only because it alters the angle of approach of the tip of the instrument to the lumen, but also because its association with shortening can reduce formed loops.10 As the endoscope is inserted further the torque force required to angle the tip or reduce loops at the distal end of the endoscope will increase because the insertion tube is not rigid. The instruments we used contain counterclockwise springs along the insertion tube and using torque may also stiffen the endoscope to aid insertion. These observations probably explain some of the rather large torque forces measured toward the end of some of the examinations. Although the small sample size does not allow generalizations about the forces required in different colonoscopic situations some interesting observations can be made. One colonoscopist used more clockwise torque throughout his colonoscopies, perhaps as a method of stiffening a flexible endoscope. The forces required to perform a colonoscopy on one patient with irritable bowel syndrome were in the middle of the force range, but the procedure took slightly longer (700 seconds) and was poorly tolerated despite standard sedation and analgesia suggesting that perhaps increased visceral pain perception is a factor in patient tolerance as has been proposed in these patients.11 Interestingly of the three examinations in patients with colitis, the time taken to reach the cecum was generally short (240, 600, and 370 seconds), one contained the highest peak push at 4.4 kg, although only 27 seconds (11% of the time) of the examination contained push forces greater than 1 kg. In another patient with colitis, the peak push forces were the lowest of all the examinations with a peak of only 0.36 kg (0.8 lb). In the third patient the push values were again low with only 18 seconds (5% of the time) of push force greater than 0.5 kg. This might suggest that the slight increase in perforation rate reported in these patients12 could be due to a combination of a weakened, inflamed bowel wall and perhaps the resulting occasional tight corner or stricture requiring higher forces. Experience would suggest, however, that colonoscopy in the majority of patients with quiescent pancolitis is easier to perform, a point supported by these data. These measurements give some insight into the forces imparted to the colon during diagnostic colo-
240
GASTROINTESTINAL ENDOSCOPY
The measurement of forces exerted during colonoscopy
noscopy. The force-measuring device could be used to validate colon models used for training purposes. Perhaps more importantly the device will be used as an objective measure in the testing of new colonoscopic devices. At present, the ease of colonoscopy is either measured by subjective patient variables, such as pain, or operator variables, such as time to complete colonoscopy, which are unreliable given variable patient sedation and differences between operators. In summary, this force-measuring device allows accurate, objective and reliable measurements of forces imparted to the colonoscope and indirectly to the colon wall and may provide a valuable method for testing new colonoscopic devices and comparing colonoscopic techniques. ACKNOWLEGMENTS We thank Tito Castillo for assistance in writing a software program for data acquisition and the endoscopy staff at the Royal London Hospital and Royal Sunderland Hospital for assistance during these studies. REFERENCES 1. Cataldo PA. Colonoscopy without sedation. Dis Colon Rectum 1996;39:257-61. 2. Saunders BP, Fukumoto M, Halligan S, Masaki T, Love S, Williams CB. Patient-administered nitrous oxide/oxygen inhalation provides effective sedation and analgesia for colonoscopy. Gastrointest Endosc 1994;40:418-21. 3. Hull T, Church JM. Colonoscopy—How difficult, how painful? Surg Endosc 1994;8:784-7. 4. Waye JD, Kahn O, Auerbach ME. Complications of colonoscopy and flexible sigmoidoscopy. Gastrointest Endosc Clin N Am 1996;6:343-77. 5. Orsoni P, Berdah S, Verrier C, Caamano A, Sastre B, Boutboul R, et al. Colonic perforation due to colonoscopy: a retrospective study of 48 cases. Endoscopy 1997;29:160-4. 6. Geenen JE, Schmitt MG Jr, Wu WC, Hogan WJ. Major complications of coloscopy: bleeding and perforation. Am J Dig Dis 1975;20:231-5. 7. Mosse CA, Mills TN, Bell GD, Swain CP. Device for measuring the forces exerted on the shaft of an endoscope during colonoscopy. Med Biol Eng Comput 1998;36:186-90. 8. Bladen JS, Anderson AP, Bell GD, Rameh B, Evans B, Heatley DJ. Non-radiological technique for three-dimensional imaging of endoscopes. Lancet 1993;341:719-22. 9. Wu TK. Occult injuries during colonoscopy. Measurement of forces required to injure the colon and report of cases. Gastrointest Endosc 1978;24:236-8. 10. Coller JA. Technique of flexible fiberoptic sigmoidoscopy. Surg Clin North Am 1980;60:465-79. 11. Whitehead WE, Holtkotter B, Enck P, Hoelzl R, Holmes KD, Anthony J, et al. Tolerance for rectosigmoid distention in irritable bowel syndrome. Gastroenterology 1990;98(Pt1):1187-92. 12. Keeffe ER, Schrock TR. Complications of gastrointestinal endoscopy. In: Sleisenger MH, Fordtran JS, editors. Gastrointestinal disease: pathophysiology, diagnosis, management. Philadelphia: WB Saunders; 1993. p. 301-8.
VOLUME 52, NO. 2, 2000