- Email: [email protected]
The canine laboratory in the training of the oncology fellow
GYNECOLOGIC
ONCOLOGY
23, 26-34 (1986)
The Canine Laboratory in the Training of the Oncology Fellow WAYNE
A. CHRISTOPHERSON, M.D.,’ HERBERT J. BUCHSBAUM, M.D.,* RICHARD VOET, M.D., AND SAMUEL LIFSHITZ, M.D.
Division of Gynecologic Oncology, Department of Obstetrics and Gynecology, and Department Pathology, Southwestern Medical School, University of Texas Health Science Center, Dallas, Texas 75235
of
Received March 1, 1984 This report deals with one fellow’s experience in the dog lab established to aid in the surgical training of the gynecologic oncology fellow. The first experiment was designed to train the fellow in bowel resection and end-to-end anastomosis, comparing suture and staple techniques. A second study evaluated the physical and biological properties of polyglactin 910 (Vicryl) mesh to determine its applicability in reconstructing the pelvic flOOI’
fOllOWhg
pelvic
eXenteK3tiOl’I.
D 1986 Academic
Press, Inc.
INTRODUCTION The surgical skills of the gynecologic oncologist affect more than the delivery of care to patients with genital malignancies. During his fellowship training program, and certainly later in practice, he may be the teacher of surgery in departments of obstetrics and gynecology, and may be called upon by colleagues or residents to assist in difficult surgery, particularly when pathology distorts or displaces the gastrointestinal and urinary tracts, e.g., endometriosis, pelvic inflammatory disease, or retroperitoneal tumors. The Division of Gynecologic Oncology of the American Board of Obstetrics and Gynecology has listed the surgical skills expected of the trainee, including procedures on the female genitalia and the gastrointestinal and urinary tracts [ 11. The mechanism of achieving these objectives, by observation, as cosurgeon, by performing a given number of procedures under supervision, or by performing a number independently, is left to the program director, as is the number of procedures required to gain the skills to perform them independently. Surgical skills combine two functions: the intellectual exercise of decision making, and more mechanical processes or dexterity. The teaching of the surgical decision-making skills may be unique in medicine. Educational techniques appropriate for the interpretation of X rays, electrocardiograms, and histopathologic slides cannot be applied to surgery. One cannot simulate, project, or view a ’ Supported in part by the American Cancer Society, Clinical Fellowship 5738. ’ To whom reprint requests should be addressed: Department of Obstetrics and Gynecology, University of Pittsburgh, Magee-Womens Hospital, Pittsburgh, Pa. 15213. 26 0090-8258/86$1.50 Copyright All tights
0 1986 by Academic Press, Inc. of reproduction in any form reserved.
ONCOLOGY
FELLOW
TRAINING
27
sequence of conditions encountered in performing an operative procedure. Spencer [2] believes that about 75% of the important events in an operative procedure are related to decision making, and 25% to dexterity. Therefore, the technical aspects, e.g., knot tying, handling and manipulation of surgical instruments, should be mastered before a trainee enters the operating room, so that full attention can be devoted to the critical decision-making aspects of surgery. The radical surgical procedures performed on a gynecologic oncology service, radical hysterectomy and radical vulvectomy, are extensions of gynecologic surgery a resident is exposed to during training. The large number of such procedures available on most oncology services allows a rational and sequential order of training to be established: observation, participation, and lastly, performance as primary surgeon. During the 2 years of clinical fellowship at our institution, the fellow performs approximately 50 radical hysterectomies and 25 radical vulvectomies, both with regional lymphadenectomy. Unlike radical surgery, the fellow may never have been exposed to gastrointestinal and urinary tract surgery in the course of residency training, and is unlikely to have performed a bowel anastomosis or be familiar with the varied gastrointestinal staplers. Furthermore, since the number of such intestinal and genitourinary procedures performed on any gynecologic oncology service is limited, the learning process must be accelerated. A dog lab was established to aid in the training of the oncology fellow. This report deals with one fellow’s experience in the lab. The fellow designed the protocols, performed the dog surgery, and evaluated the results, all with faculty supervision. The first of the studies was designed to train the fellow in the performance of an end-to-end bowel anastomosis by both suture and staple techniques. The second protocol was of a more academic nature, but with obvious clinical application. Seven dogs were operated upon, giving experience in the surgical technique, but only four were available for long-term evaluation of results. MATERIALS AND METHODS Seven conditioned mongrel dogs weighing between 15 and 20 kg were used in the studies. The first two dogs were used in acute experiments; the next five were used in chronic experiments. The dogs were kept NPO the night prior to surgery, and the last four dogs were given 400,000 units of penicillin G and 0.5 gm of dihydrostreptomycin the morning of surgery. This antibiotic dosage was repeated daily for 5 days. All operations were performed under general anesthesia, utilizing sterile technique. After induction of general anesthesia, the abdomen was entered through a ventral midline incision. The rectosigmoid and distal colon were then isolated, and two end-to-end colorectal anastomoses (one suture, one staple) were constructed in each dog. The suture anastomoses were two layered; the mucosa was closed with running 4-O Vicryl, and the serosa was approximated with interrupted 3-O silk Lembert sutures. The staple anastomoses were done utilizing the Auto Suture EEA (U.S. Surgical Corp.) with 25-mm cartridges. To construct the staple anastomoses, the staple device was introduced into the lumen of the colon through a separate enterotomy incision. After completion of the
28
CHRISTOPHERSONET AL.
anastomosis the enterotomy incision was closed utilizing a TA 55 stapler (U.S. Surgical Corp.). In two dogs the suture anastomoses were distal to the staple anastomoses, and in two dogs the staple anastomoseswere distal. At the conclusion of this portion of the procedure the abdomen was thoroughly irrigated with saline. In order to assess the polyglactin 910 mesh, a defect in the abdominal wall was created by resecting an 8 x g-cm section of the ventral abdominal wall, including peritoneum, rectus, transversalus, internal oblique, and external oblique muscles, and the fascia. The polyglactic 910 mesh was then used to replace the resected abdominal wall. The omentum had previously been draped over the ventral surface of the abdominal contents. The skin was then closed utilizing interrupted sutures of 3-O nylon. Vicryl mesh is a tricot knit derived from Vicryl suture yarn and has the same chemical composition as the suture, i.e., lo/90 mole percentage poly (L( -)lactideco-glycolide). The mesh is 7.5 mil thick, weighs 1.5 oz/yd*, and has a Mullen burst strength of at least 60 psi. It will retain at least 25% of its original strength after 21 days in viuo. Postoperatively the dogs were given liquids for 3 days and then fed softened dog food for 1 week. After this they resumed their normal preoperative feeding regimen. One dog died on the fifth postoperative day; four dogs were sacrificed by intravenous barbiturate injection 28 to 30 days postoperatively. The anastomotic sites, as well as the anterior abdominal wall which had been replaced with Vicryl mesh, were evaluated. Macroscopic and microscopic appearance of the anastomotic site. The abdomen was opened and the adhesions at each anastomotic site were noted. The segment of bowel containing the anastomoses was evaluated for evidence of anastomotic leakage or obstruction. This segment was then removed and opened longitudinally. Representative samples of the anastomotic sites were fixed in Formalin, and later embedded in paraffin, sectioned, stained with hematoxylin and eosin, and examined microscopically. Anastomotic strength. The strength of each anastomosis was determined by measuring the breaking strength of the suture or staple line. Strips of bowel 1 x 5 cm, with the anastomosis to be tested transversely bisecting the strip, were obtained using a template. The breaking strength was then determined using a constant speed motor-driven tensiometer previously described by one of us [ 11. Constriction of the anastomotic site. A muscular tube, such as the large bowel, is capable of constriction as well as distension and does not have a “diameter” but rather a range of diameters. Any assessment of anastomotic stricture is dependent on determining the caliber of the normal bowel as well as the caliber of the anastomotic site, both of which are variable. This makes assessment of a bowel stricture dependent on static measurements of dynamic parameters. Realizing these limitations, the caliber of the normal bowel and the anastomotic sites were determined in the following manner: Immediately after a dog was sacrificed, the segment of colon containing the anastomotic sites was removed and opened longitudinally along the mesenteric attachment. The opened bowel
ONCOLOGY FELLOW TRAINING
29
was then placed on a flat surface with the mucosa down and no tension on the bowel wall. The “outside,” or serosal, a circumference of the anastomosis, was then determined by measuring the length of the anastomotic scar as it traversed the serosal surface of the bowel. The “outside” radius was then determined (Y = C/27r). The “inside” radius, or radius of the bowel lumen, was then determined by subtracting the thickness of the bowel wall at the anastomotic site from the “outside” radius. The area of the bowel lumen at the anastomotic site was then calculated (area = T?). Similar determinations were made adjacent to the anastomotic sites to determine the luminal area of the normal bowel. Operating time. The time required to construct each type of anastomosis was determined. For each suture anastomosis the time required to perform the twolayer closure was recorded, For each staple anastomosis the time required to make an enterotomy (for introduction of the end-to-end stapler), construct the end-to-end anastomosis, and to close the enterotomy was recorded. Retrieval of section of anterior abdominal wall replaced by vicryl mesh. After each dog was sacrificed, the section of abdominal wall with Vicryl mesh was retrieved and the skin removed from the specimen. Portions of this were fixed in Formalin, later embedded in parafin, sectioned, and stained with hematoxylin and eosin for microscopic evaluation. Strips of the mesh-replaced abdominal wall measuring 0.5 x 4.0 cm were obtained, and the breaking strength of these strips was determined. Similar size strips were also obtained from the posterior rectus sheath on the last two dogs. These strips were utilized to determine the breaking strength of the normal posterior rectus sheath. Statistical methods. Statistical comparisons were done using the Mann-Whitney test and two-sample t test. RESULTS
No anastomotic leakage nor obstruction was noted. All anastomotic sites had thin, filmy adhesions to adjacent structures. No quantitative measurement was attempted; the adhesions appeared similar at staple and suture anastomoses. Macroscopic examination of the serosal surface of colon revealed the presence of the silk sutures used to construct the suture anastomoses. The site of each staple anastomosis was demarcated by a ring of gray scar tissue encircling the bowel. The bowel wall was thicker to palpation at all anastomotic sites; however, this finding was more marked in the suture anastomoses. None of the anastomotic sites appeared constricted when the unopened bowel was examined. The mucosal surfaces of the suture and staple anastomoses were similar in macroscopic appearance. Staples were being extruded into the lumen of the bowel in two of the dogs. Sections from the suture anastomoses (Fig. 1) showed residual suture material with surrounding chromic inflammatory infiltrate and numerous foreign body giant cells. The submucosal tissue and muscle were well approximated with dense fibrous tissue. The overlying mucosal epithelium was slightly thinned in areas immediately overlying the anastomoses but showed complete replacement with functioning mutinous cells.
30
CHRISTOPHERSON
ET AL.
FIG. 1. Suture anastomosis. A photomicrograph of a suture anastomosis reveals intact overlying epithelium with only slight thinning (arrow). The underlying tissue contains residual suture material with surrounding inflammation (curbed arrows).
The sections from staple anastomoses (Fig. 2) revealed well-healed submucosal and muscular tissue. The areas where the staples had been removed revealed little surrounding inflammation. Occasional foci of entrapped surface epithelium, deposited in the staple tract, were found in the submucosal tissue. The mucosa was thinned, focally ulcerated, and revealed more chronic inflammation and less mutinous epithelium. The mucosa overlying staple anastomoses was less well developed than that overlying suture anastomoses. There was no significant difference in the breaking strength between the staple and suture anastomoses (Table l), while both were significantly weaker (P = < 0.001) than normal bowel. There was a significant difference in the mean luminal area between the suture and staple anastomoses (see Table 2). Suture anastomoses required a mean of 44 min to complete, compared to 28 min for the staple anastomoses (P < 0.01). Histologic examination of the mesh-replaced anterior abdominal wall revealed a similar response in all of the dogs. The ventral abdominal wall was retrieved on the dog that died on the fifth postoperative day. They specimen revealed a foreign body giant cell reaction surrounding the mesh (Fig. 3). In specimens obtained at 28 and 30 days a fibroblast reaction with scattered chronic inflammatory cells was noted. The foreign body giant cells were involving individual fibers as well as surrounding groups of fibers. Examination under polarized light revealed
ONCOLOGY
FELLOW
31
TRAINING
FIG. 2. Staple anastomosis. A photomicrograph of a staple anastomosis reveals thinner epithelial bridging (arrow) than found in Fig. 1. The underlying tissue shows little inflammation. An area of entrapped mutinous glands deposited in a staple tract is identified by curved arrow.
polyglactin 910 fibers scattered throughout the fibrous stroma in clusters (Fig. 4). The pattern was that of a foreign body reaction with mild to moderate chronic inflammation. There was no significant acute inflammation or necrosis identified in the specimens examined. The breaking strength of the 0.5 x 4.0-cm strips of mesh-replaced anterior abdominal wall varied between 2062.5 and 2400 g, with a mean of 2258 g. This TABLE ANASTOMOTIC
1
BREAKING
STRENGTH
Mean
Stapled anastomosis Sutured anastomosis Normal bowel
(d
841 760 1570
SEM 49 64 94
Note. For each sample, n = 16; i.e., 4 samples were taken from each of 4 dogs. The breaking strengths of suture and staple anastomoses were similar. The normal bowel was significantly stronger than either type of anastomosis (P < 0.001).
32
CHRISTOPHERSONET AL. TABLE 2 LUMINAL AREA OF THE COLON
Mean (cm’)
SEM
% Normal bowel area
Normal bowel
2.885
0.160
100
Staple anastomoses
1.870
0.131
65
Suture anastomoses
1.035
0.146
36
P value
Note. For each condition, n = 4. The luminal area was determined in a plane perpendicular to the long axis of the bowel and containing either an anastomotic site or normal bowel adjacent to an anastomotic site.
compares to the breaking strength of the normal posterior rectus sheath in the dog of approximately 720 g. (Breaking strength is the force required to disrupt the wound, as compared to tensile strength which is the force divided by square area of tissue.)
FIG. 3. Photomicrograph of a section from the abdominal wall of dog 5 days after replacement with mesh. There is a mild fibrous reaction; groups of mesh fibers are seen surrounded by foreign body giant cells.
ONCOLOGY
FELLOW
TRAINING
33
34
CHRISTOPHERSONET AL.
DISCUSSION The studies reported here allowed the fellow in gynecologic oncology to gain experience in bowel surgery and evaluate the results of suture and staple anastornoses. As noted earlier, radical hysterectomy and radical vulvectomy are both extensions of surgery the fellow performed during his residency training. It is unlikely that during a residency in obstetrics and gynecology an individual will have performed a bowel anastomosis, either with sutures or staples. These types of experiments in the dog laboratory allow the fellow to gain familiarity with instruments and techniques he may not have been exposed to during residency training. By gaining familiarity with surgical instruments and techniques in the dog laboratory, the individual can then devote full attention to the decisionmaking aspects of the operative procedure. In addition, the second protocol allowed us to evaluate a new mesh before its use in the human. This study was the basis of a clinical study on the use of Vicryl mesh in reconstructing the pelvic diaphragm in patients undergoing pelvic exenteration [4]. We believe that the canine laboratory experience can serve to train the gynecologic oncology fellow in surgical techniques. There are reports describing the use of such facilities in the training of residents in obstetrics and gynecology [5] and urology [6]. We agree with these authors, who concluded that the costs and efforts in establishing and maintaining a surgical dog lab were justified by the benefits received by the trainee. The dog lab experience serves to train the gynecologic oncology fellow in surgical techniques, as well as provides a vehicle for academic studies evaluating new techniques and materials. ACKNOWLEDGMENTS We thank United States Surgical Corporation for providing the EEA and TA-55 Auto Suture instruments, and Ethicon, Inc., for providing the Vicryl mesh.
REFERENCES 1. Guide to learning in gynecologic oncology, 2nd ed. Division of Gynecologic Oncology, The American Board of Obstetrics and Gynecology, Inc. (1980). 2. Spencer, F. C. Observations on the teaching of operative technique, Bull. Amer. Coil. Surg. 68, 3-6 (1983). 3. Buchsbaum, H. J. Healing of experimental fractures during pregnancy, Obsret. Gynecol. 35, 613615 (1970). 4. Buchsbaum, H. J., Christopherson, W., Lifshitz, S., and Bernstein, S. G. Vicryl mesh in pelvic floor reconstruction following exenteration, Arch. Surg., in press. 5. Woods, J. R., Jr., Ansbacher, R., Castro, R. J. et al. Animal surgery: An adjunct to training in obstetrics and gynecology, Obstet. Gynecol. 56, 373-376 (1980). 6. Watson, R. A., Deshon, G. E., and Agee, R. E. Surgical experience with large animals. Important adjunct to residency training in urology, Urology 20, 154-156 (1982).
ONCOLOGY
23, 26-34 (1986)
The Canine Laboratory in the Training of the Oncology Fellow WAYNE
A. CHRISTOPHERSON, M.D.,’ HERBERT J. BUCHSBAUM, M.D.,* RICHARD VOET, M.D., AND SAMUEL LIFSHITZ, M.D.
Division of Gynecologic Oncology, Department of Obstetrics and Gynecology, and Department Pathology, Southwestern Medical School, University of Texas Health Science Center, Dallas, Texas 75235
of
Received March 1, 1984 This report deals with one fellow’s experience in the dog lab established to aid in the surgical training of the gynecologic oncology fellow. The first experiment was designed to train the fellow in bowel resection and end-to-end anastomosis, comparing suture and staple techniques. A second study evaluated the physical and biological properties of polyglactin 910 (Vicryl) mesh to determine its applicability in reconstructing the pelvic flOOI’
fOllOWhg
pelvic
eXenteK3tiOl’I.
D 1986 Academic
Press, Inc.
INTRODUCTION The surgical skills of the gynecologic oncologist affect more than the delivery of care to patients with genital malignancies. During his fellowship training program, and certainly later in practice, he may be the teacher of surgery in departments of obstetrics and gynecology, and may be called upon by colleagues or residents to assist in difficult surgery, particularly when pathology distorts or displaces the gastrointestinal and urinary tracts, e.g., endometriosis, pelvic inflammatory disease, or retroperitoneal tumors. The Division of Gynecologic Oncology of the American Board of Obstetrics and Gynecology has listed the surgical skills expected of the trainee, including procedures on the female genitalia and the gastrointestinal and urinary tracts [ 11. The mechanism of achieving these objectives, by observation, as cosurgeon, by performing a given number of procedures under supervision, or by performing a number independently, is left to the program director, as is the number of procedures required to gain the skills to perform them independently. Surgical skills combine two functions: the intellectual exercise of decision making, and more mechanical processes or dexterity. The teaching of the surgical decision-making skills may be unique in medicine. Educational techniques appropriate for the interpretation of X rays, electrocardiograms, and histopathologic slides cannot be applied to surgery. One cannot simulate, project, or view a ’ Supported in part by the American Cancer Society, Clinical Fellowship 5738. ’ To whom reprint requests should be addressed: Department of Obstetrics and Gynecology, University of Pittsburgh, Magee-Womens Hospital, Pittsburgh, Pa. 15213. 26 0090-8258/86$1.50 Copyright All tights
0 1986 by Academic Press, Inc. of reproduction in any form reserved.
ONCOLOGY
FELLOW
TRAINING
27
sequence of conditions encountered in performing an operative procedure. Spencer [2] believes that about 75% of the important events in an operative procedure are related to decision making, and 25% to dexterity. Therefore, the technical aspects, e.g., knot tying, handling and manipulation of surgical instruments, should be mastered before a trainee enters the operating room, so that full attention can be devoted to the critical decision-making aspects of surgery. The radical surgical procedures performed on a gynecologic oncology service, radical hysterectomy and radical vulvectomy, are extensions of gynecologic surgery a resident is exposed to during training. The large number of such procedures available on most oncology services allows a rational and sequential order of training to be established: observation, participation, and lastly, performance as primary surgeon. During the 2 years of clinical fellowship at our institution, the fellow performs approximately 50 radical hysterectomies and 25 radical vulvectomies, both with regional lymphadenectomy. Unlike radical surgery, the fellow may never have been exposed to gastrointestinal and urinary tract surgery in the course of residency training, and is unlikely to have performed a bowel anastomosis or be familiar with the varied gastrointestinal staplers. Furthermore, since the number of such intestinal and genitourinary procedures performed on any gynecologic oncology service is limited, the learning process must be accelerated. A dog lab was established to aid in the training of the oncology fellow. This report deals with one fellow’s experience in the lab. The fellow designed the protocols, performed the dog surgery, and evaluated the results, all with faculty supervision. The first of the studies was designed to train the fellow in the performance of an end-to-end bowel anastomosis by both suture and staple techniques. The second protocol was of a more academic nature, but with obvious clinical application. Seven dogs were operated upon, giving experience in the surgical technique, but only four were available for long-term evaluation of results. MATERIALS AND METHODS Seven conditioned mongrel dogs weighing between 15 and 20 kg were used in the studies. The first two dogs were used in acute experiments; the next five were used in chronic experiments. The dogs were kept NPO the night prior to surgery, and the last four dogs were given 400,000 units of penicillin G and 0.5 gm of dihydrostreptomycin the morning of surgery. This antibiotic dosage was repeated daily for 5 days. All operations were performed under general anesthesia, utilizing sterile technique. After induction of general anesthesia, the abdomen was entered through a ventral midline incision. The rectosigmoid and distal colon were then isolated, and two end-to-end colorectal anastomoses (one suture, one staple) were constructed in each dog. The suture anastomoses were two layered; the mucosa was closed with running 4-O Vicryl, and the serosa was approximated with interrupted 3-O silk Lembert sutures. The staple anastomoses were done utilizing the Auto Suture EEA (U.S. Surgical Corp.) with 25-mm cartridges. To construct the staple anastomoses, the staple device was introduced into the lumen of the colon through a separate enterotomy incision. After completion of the
28
CHRISTOPHERSONET AL.
anastomosis the enterotomy incision was closed utilizing a TA 55 stapler (U.S. Surgical Corp.). In two dogs the suture anastomoses were distal to the staple anastomoses, and in two dogs the staple anastomoseswere distal. At the conclusion of this portion of the procedure the abdomen was thoroughly irrigated with saline. In order to assess the polyglactin 910 mesh, a defect in the abdominal wall was created by resecting an 8 x g-cm section of the ventral abdominal wall, including peritoneum, rectus, transversalus, internal oblique, and external oblique muscles, and the fascia. The polyglactic 910 mesh was then used to replace the resected abdominal wall. The omentum had previously been draped over the ventral surface of the abdominal contents. The skin was then closed utilizing interrupted sutures of 3-O nylon. Vicryl mesh is a tricot knit derived from Vicryl suture yarn and has the same chemical composition as the suture, i.e., lo/90 mole percentage poly (L( -)lactideco-glycolide). The mesh is 7.5 mil thick, weighs 1.5 oz/yd*, and has a Mullen burst strength of at least 60 psi. It will retain at least 25% of its original strength after 21 days in viuo. Postoperatively the dogs were given liquids for 3 days and then fed softened dog food for 1 week. After this they resumed their normal preoperative feeding regimen. One dog died on the fifth postoperative day; four dogs were sacrificed by intravenous barbiturate injection 28 to 30 days postoperatively. The anastomotic sites, as well as the anterior abdominal wall which had been replaced with Vicryl mesh, were evaluated. Macroscopic and microscopic appearance of the anastomotic site. The abdomen was opened and the adhesions at each anastomotic site were noted. The segment of bowel containing the anastomoses was evaluated for evidence of anastomotic leakage or obstruction. This segment was then removed and opened longitudinally. Representative samples of the anastomotic sites were fixed in Formalin, and later embedded in paraffin, sectioned, stained with hematoxylin and eosin, and examined microscopically. Anastomotic strength. The strength of each anastomosis was determined by measuring the breaking strength of the suture or staple line. Strips of bowel 1 x 5 cm, with the anastomosis to be tested transversely bisecting the strip, were obtained using a template. The breaking strength was then determined using a constant speed motor-driven tensiometer previously described by one of us [ 11. Constriction of the anastomotic site. A muscular tube, such as the large bowel, is capable of constriction as well as distension and does not have a “diameter” but rather a range of diameters. Any assessment of anastomotic stricture is dependent on determining the caliber of the normal bowel as well as the caliber of the anastomotic site, both of which are variable. This makes assessment of a bowel stricture dependent on static measurements of dynamic parameters. Realizing these limitations, the caliber of the normal bowel and the anastomotic sites were determined in the following manner: Immediately after a dog was sacrificed, the segment of colon containing the anastomotic sites was removed and opened longitudinally along the mesenteric attachment. The opened bowel
ONCOLOGY FELLOW TRAINING
29
was then placed on a flat surface with the mucosa down and no tension on the bowel wall. The “outside,” or serosal, a circumference of the anastomosis, was then determined by measuring the length of the anastomotic scar as it traversed the serosal surface of the bowel. The “outside” radius was then determined (Y = C/27r). The “inside” radius, or radius of the bowel lumen, was then determined by subtracting the thickness of the bowel wall at the anastomotic site from the “outside” radius. The area of the bowel lumen at the anastomotic site was then calculated (area = T?). Similar determinations were made adjacent to the anastomotic sites to determine the luminal area of the normal bowel. Operating time. The time required to construct each type of anastomosis was determined. For each suture anastomosis the time required to perform the twolayer closure was recorded, For each staple anastomosis the time required to make an enterotomy (for introduction of the end-to-end stapler), construct the end-to-end anastomosis, and to close the enterotomy was recorded. Retrieval of section of anterior abdominal wall replaced by vicryl mesh. After each dog was sacrificed, the section of abdominal wall with Vicryl mesh was retrieved and the skin removed from the specimen. Portions of this were fixed in Formalin, later embedded in parafin, sectioned, and stained with hematoxylin and eosin for microscopic evaluation. Strips of the mesh-replaced abdominal wall measuring 0.5 x 4.0 cm were obtained, and the breaking strength of these strips was determined. Similar size strips were also obtained from the posterior rectus sheath on the last two dogs. These strips were utilized to determine the breaking strength of the normal posterior rectus sheath. Statistical methods. Statistical comparisons were done using the Mann-Whitney test and two-sample t test. RESULTS
No anastomotic leakage nor obstruction was noted. All anastomotic sites had thin, filmy adhesions to adjacent structures. No quantitative measurement was attempted; the adhesions appeared similar at staple and suture anastomoses. Macroscopic examination of the serosal surface of colon revealed the presence of the silk sutures used to construct the suture anastomoses. The site of each staple anastomosis was demarcated by a ring of gray scar tissue encircling the bowel. The bowel wall was thicker to palpation at all anastomotic sites; however, this finding was more marked in the suture anastomoses. None of the anastomotic sites appeared constricted when the unopened bowel was examined. The mucosal surfaces of the suture and staple anastomoses were similar in macroscopic appearance. Staples were being extruded into the lumen of the bowel in two of the dogs. Sections from the suture anastomoses (Fig. 1) showed residual suture material with surrounding chromic inflammatory infiltrate and numerous foreign body giant cells. The submucosal tissue and muscle were well approximated with dense fibrous tissue. The overlying mucosal epithelium was slightly thinned in areas immediately overlying the anastomoses but showed complete replacement with functioning mutinous cells.
30
CHRISTOPHERSON
ET AL.
FIG. 1. Suture anastomosis. A photomicrograph of a suture anastomosis reveals intact overlying epithelium with only slight thinning (arrow). The underlying tissue contains residual suture material with surrounding inflammation (curbed arrows).
The sections from staple anastomoses (Fig. 2) revealed well-healed submucosal and muscular tissue. The areas where the staples had been removed revealed little surrounding inflammation. Occasional foci of entrapped surface epithelium, deposited in the staple tract, were found in the submucosal tissue. The mucosa was thinned, focally ulcerated, and revealed more chronic inflammation and less mutinous epithelium. The mucosa overlying staple anastomoses was less well developed than that overlying suture anastomoses. There was no significant difference in the breaking strength between the staple and suture anastomoses (Table l), while both were significantly weaker (P = < 0.001) than normal bowel. There was a significant difference in the mean luminal area between the suture and staple anastomoses (see Table 2). Suture anastomoses required a mean of 44 min to complete, compared to 28 min for the staple anastomoses (P < 0.01). Histologic examination of the mesh-replaced anterior abdominal wall revealed a similar response in all of the dogs. The ventral abdominal wall was retrieved on the dog that died on the fifth postoperative day. They specimen revealed a foreign body giant cell reaction surrounding the mesh (Fig. 3). In specimens obtained at 28 and 30 days a fibroblast reaction with scattered chronic inflammatory cells was noted. The foreign body giant cells were involving individual fibers as well as surrounding groups of fibers. Examination under polarized light revealed
ONCOLOGY
FELLOW
31
TRAINING
FIG. 2. Staple anastomosis. A photomicrograph of a staple anastomosis reveals thinner epithelial bridging (arrow) than found in Fig. 1. The underlying tissue shows little inflammation. An area of entrapped mutinous glands deposited in a staple tract is identified by curved arrow.
polyglactin 910 fibers scattered throughout the fibrous stroma in clusters (Fig. 4). The pattern was that of a foreign body reaction with mild to moderate chronic inflammation. There was no significant acute inflammation or necrosis identified in the specimens examined. The breaking strength of the 0.5 x 4.0-cm strips of mesh-replaced anterior abdominal wall varied between 2062.5 and 2400 g, with a mean of 2258 g. This TABLE ANASTOMOTIC
1
BREAKING
STRENGTH
Mean
Stapled anastomosis Sutured anastomosis Normal bowel
(d
841 760 1570
SEM 49 64 94
Note. For each sample, n = 16; i.e., 4 samples were taken from each of 4 dogs. The breaking strengths of suture and staple anastomoses were similar. The normal bowel was significantly stronger than either type of anastomosis (P < 0.001).
32
CHRISTOPHERSONET AL. TABLE 2 LUMINAL AREA OF THE COLON
Mean (cm’)
SEM
% Normal bowel area
Normal bowel
2.885
0.160
100
Staple anastomoses
1.870
0.131
65
Suture anastomoses
1.035
0.146
36
P value
Note. For each condition, n = 4. The luminal area was determined in a plane perpendicular to the long axis of the bowel and containing either an anastomotic site or normal bowel adjacent to an anastomotic site.
compares to the breaking strength of the normal posterior rectus sheath in the dog of approximately 720 g. (Breaking strength is the force required to disrupt the wound, as compared to tensile strength which is the force divided by square area of tissue.)
FIG. 3. Photomicrograph of a section from the abdominal wall of dog 5 days after replacement with mesh. There is a mild fibrous reaction; groups of mesh fibers are seen surrounded by foreign body giant cells.
ONCOLOGY
FELLOW
TRAINING
33
34
CHRISTOPHERSONET AL.
DISCUSSION The studies reported here allowed the fellow in gynecologic oncology to gain experience in bowel surgery and evaluate the results of suture and staple anastornoses. As noted earlier, radical hysterectomy and radical vulvectomy are both extensions of surgery the fellow performed during his residency training. It is unlikely that during a residency in obstetrics and gynecology an individual will have performed a bowel anastomosis, either with sutures or staples. These types of experiments in the dog laboratory allow the fellow to gain familiarity with instruments and techniques he may not have been exposed to during residency training. By gaining familiarity with surgical instruments and techniques in the dog laboratory, the individual can then devote full attention to the decisionmaking aspects of the operative procedure. In addition, the second protocol allowed us to evaluate a new mesh before its use in the human. This study was the basis of a clinical study on the use of Vicryl mesh in reconstructing the pelvic diaphragm in patients undergoing pelvic exenteration [4]. We believe that the canine laboratory experience can serve to train the gynecologic oncology fellow in surgical techniques. There are reports describing the use of such facilities in the training of residents in obstetrics and gynecology [5] and urology [6]. We agree with these authors, who concluded that the costs and efforts in establishing and maintaining a surgical dog lab were justified by the benefits received by the trainee. The dog lab experience serves to train the gynecologic oncology fellow in surgical techniques, as well as provides a vehicle for academic studies evaluating new techniques and materials. ACKNOWLEDGMENTS We thank United States Surgical Corporation for providing the EEA and TA-55 Auto Suture instruments, and Ethicon, Inc., for providing the Vicryl mesh.
REFERENCES 1. Guide to learning in gynecologic oncology, 2nd ed. Division of Gynecologic Oncology, The American Board of Obstetrics and Gynecology, Inc. (1980). 2. Spencer, F. C. Observations on the teaching of operative technique, Bull. Amer. Coil. Surg. 68, 3-6 (1983). 3. Buchsbaum, H. J. Healing of experimental fractures during pregnancy, Obsret. Gynecol. 35, 613615 (1970). 4. Buchsbaum, H. J., Christopherson, W., Lifshitz, S., and Bernstein, S. G. Vicryl mesh in pelvic floor reconstruction following exenteration, Arch. Surg., in press. 5. Woods, J. R., Jr., Ansbacher, R., Castro, R. J. et al. Animal surgery: An adjunct to training in obstetrics and gynecology, Obstet. Gynecol. 56, 373-376 (1980). 6. Watson, R. A., Deshon, G. E., and Agee, R. E. Surgical experience with large animals. Important adjunct to residency training in urology, Urology 20, 154-156 (1982).