Efficacy of chrome processed aortic allograft for cervical oesophagoplasty in dogs.
Structural and functional peculiarity of cervical oesophagus necessitates some form of grafting procedures for reconstruction of larger defects (1). Advantages of using synthetic materials, homologous viable functional substitutes or heterologous tissues as graft materials are many. But difficulty in harvesting of suitable and sizeable tissues, availability, trauma and stress on healing, problems of tissue rejection and associated functional disturbances along with long-term complications are the major disadvantages. The present study was undertaken to evaluate the acceptability and functional efficacy of chrome processed aortic allograft following cervical oesophagoplasty in dogs.
MATERIALS & METHODS
The experiment was conducted on twelve apparently healthy adult dogs of either sex weighing 9-13 Kg, randomly divided into two groups (A and B). Under general anesthesia using triflupromazine hydrochloride (Siquil (Vety) 20 mg/ml, Sarabhai Chemical, Baroda)--thiopentone sodium (Intraval sodium Injection IP, Rhone-Poulene (India) Ltd., Bombay) combination, the animals were secured in dorsal recumbency. The cervical oesophagus was exteriorized through an incision made over the skin at the ventral neck region (2), and a segment of oesophageal wall measuring 3-4 cm in length and 1/3rd of its circumference was surgically removed to create the defect. Thoracic aorta, processed with chromium sulfate was used as graft material (3). The graft material was washed in four changes of sterile normal saline solution and trimmed to oval size, sufficient enough to cover the oesophageal defect. The graft was fixed over the wounds edges using 5/0 braided silk thread by through and through continuous locking sutures. The cervical muscles and skin were sutured using 1/0 braided silk and monofilament nylon respectively.
Following aseptic precautions, pharyngostomy was performed on the left side of the neck (4) in 6 dogs (group B). A siliconised catheter (Nelaton Catheter--Sterimed Surgical and General Industries, New Delhi) made up of modified poly vinyl chloride was introduced into the oesophagus through the pharyngostome and anchored to the skin.
Daily dressing of the wound was done using Povidone Iodine (Povidone Iodine IP 5%, Betadine lotion, WinMedicare (Ltd), New Delhi) solution and Gentamycin (40 mg/ml, Blueshield (Pvt) Ltd., Bombay) at 8 mg/Kg body weight was administered IM daily for 7 consecutive days. In animals of group A, dextrose saline solution was administered IV first seven days. Liquid food containing glucose powder, rice porridge, milk and an egg was given in the second week; bread soaked in milk and boiled atta in the third week and a regular diet thereafter. In animals of group B, liquid food of same combination was fed through pharyngostomy tube from the next da y after surgery for 15 days postoperatively. From 15th day onwards, same pattern of feeding as in group A was followed.
Two animals from each group was sacrificed on 15th, 30th and 60th day and cervical oesophagus was exposed to study its grossly, for adhesions and leakage or fistula. The whole oesophagus from pharynx to cardia was harvested, cleaned in normal saline and incised along its dorsal wall.
Biochemical studies of oesophagus from normal and experimental animals were conducted. The tensile strength, breaking strength, extensibility and energy absorption were studied using "disruption from without method (5). Dumbbell shaped specimens of 65 mm length were punched out from the samples. The thickness and width at the center of the dumbbell shaped specimen was measured using screw gauge. The mechanical properties were measured using Universal Testing System (ZWICK 1484). The dilatation capacity (%) at the site of oesophagoplasty was assessed by filling it with water under pressure for maximum dilatation. The outer diameter (OD) was measured horizontally across the grafted site and the adjacent normal oesophagus to derive the total dilatation capacity.
Healing at the oesophagoplasty site was evaluated based on (a) color and appearance of the grafted site (b) degree of epithelialization (c) degree of absorption of suture material and (d) complications on healing if any. The healing tissues collected from the junction of oesophagus and graft were subjected to histomorphological examination after fixing, processing and staining with Ehrlich's haematoxylin and eosin, Verhoeff's and Van Gieson's methods (6).
RESULTS AND DISCUSSION
Clinically all the animals were normal. In two animals, mild swelling below the operated site was observed while swallowing (group A). All the dogs started feeding liquid diet by 7th and 15th day in group A and B respectively and maintained normal appetite and feeding habits throughout the period of observation. The skin wound healed without complication and the sutures were removed by 7-10 days in all the animals.
Vascular and weak fibrinous adhesions were observed between the grafted site and periooesophageal cervical muscles in one dog each in group A and B sacrificed on 15th day postoperatively and one dog sacrificed on 30th day in group B. Such reactions were absent by the 60th day. Amarpal et al (7) reported the occurrence of adhesion between graft and neighbouring muscles as early as 7th postoperative day following cervical oesophagoplasty using gastric seromuscular autogenous grafts in dogs. They observed progressive reduction in adhesion by 60th day. The close contact of oesophageal structures at the cervical region with inflammation caused by the surgical trauma must have initiated the adhesion, but the restricted oesophageal movement due to the parenteral feeding and the animal tissue reaction shown by the graft material during the early phase of healing process probably reduced the intensity of local reaction resulting in formation of weak adhesions between the grafted site and periooesophageal tissues in the present study. However, as healing progressed the adhesions appear to have resolved spontaneously indicating that adhesion in the early phase does not have long standing implications.
Mean values of biomechanical properties of normal oesophagus and the site of oesophagoplasty are given in table I.
Tensile strength of the specimen collected from the site showed a marginal increase on 30th day followed by a marginal decrease on 60th day postoperatively, attaining 22.52 % strength to that of normal oesophagus. While the breaking strength showed a marginal decrease on 30th day, it showed increase on 60th day attaining 22.90 % of the strength that of normal oesophagus. Extensibility and energy absorption showed a steady increase during the period of observation and on the 60 th day, they were 70.05 and 20 % of that of normal oesophagus. Amarpal et al. (8) observed a gradual increase in these parameters up to 60th day postoperatively following cervical oesophagoplasty using sternothyroideus pedicle graft and gastric seromuscular autogenous graft in dogs. Total dilation capacity (%) was 84.27 on 15th day postoperatively and following a marginal decrease on 30th day, it reached to a level of 82.22 % of that of normal oesophagus on 60th day. Todhunter et al (9) observed a reduction in lumen diameter of oesophagus on 15th and 30th day postoperatively and an increase between 30th and 40th days during healing process following cervical oesophageal resection and anastamosis in equines. The reduction in total dilatation capacity noticed on 30th day postoperatively in the present study may be attributed to ciccatrical contraction during the healing process at the site.
Even though the grafted site had not attained sufficient tensile and breaking strengths as normal oesophagus on 60th day postoperatively, the extensibility and dilatability were almost 75-80 %. An extensibility of 98.64 and 96.23 % was reported at the grafted site by 60th day following cervical oesophagoplasty using viable substitutes like split sternothyroideus pedicle graft (8) and gastric seromuscular autogenous graft (7) in dogs. It can be inferred that the graft materials used in this study acquired sufficient functional capacity almost equal to that of normal oesophagus in dogs.
Healing at the grafted site was complete in all the animals by the 15th day postoperatively. Regeneration of mucosa from the sides was grossly visible by 15th day and it covered the whole graft surface by 30th day. The mucosa became thicker with oesophageal folds by the 60th day postoperatively. Mild corded thickening of the mucosa bordering the graft and presence of diphtheritic deposit on external aspect of the grafted site were observed in one animal each in group A and B. The suture material and the technique employed in the present study had facilitated early healing without complication usually encountered in cervical oesophageal surgery in dogs (10). On 60th difference from adjoining tissue.
Histological appearance of the oesophagus at the surgical site did not differ between the groups. Mild inflammatory reaction characterized by infiltration of mononuclear cells, and a few macrophages and inflammatory edema were observed at the level of grafting on 15th day. Mucosal continuity was almost complete at the site. Scattered fibroplasia, neovascularization and disintegration of elastic fibres were the important features in the lamina propria, at this stage.
By 30th day, inflammatory reaction was minimum at the site of graft and macrophages and polymorphs were very few. There was proliferation of the lining mucosa and moderate fibroplasia adjacent to the graft. Lamina propria was devoid of oesophageal glands.
The specimen collected on 60th day revealed the presence of a few polymorphs and macrophages at the site of healing. The squamous cell epithelial lining was slightly hyperplasic and the process of epithelialization was complete. The lamina propria was devoid of oesophageal glands and muscular layer showed proper orientation of collagen and elastic fibers. These observations are similar to the changes reported by Amarpal et al. (7,8). Presence of foreign material in the form of pharyngostomy tube had not adversely influenced the healing process. Todhunter et al. (9) observed a faster healing of wound on oesophageal mucosa in equines following intubations whereas Borgstrom and Lundy (11) observed an interference in normal oesophageal healing on intubations. However in the experimental dogs of the present study the healing at the grafted site was found to be similar to that first intention.
The observations suggest that chrome processed aortic tissue function as an excellent substrate for cellular attachment and cellular in growth. It stimulates fibroneogenesis and epithelialisation and makes it an ideal biomaterial for reconstructive surgery of oesophagus in dogs.
The biological qualities of the graft material used in the present study open up a new avenue for utilization of valuable materials, which are otherwise wasted. The present study was restricted to reconstruction of oesophagus in dogs, but the graft material can be considered for reconstruction of other tubular organs as well in animals. It may provide biomaterials more economical, easily available and effective substitutes for costly synthetic materials.
The authors are thankful to the Dean, College of Veterinary and Animal Sciences, Mannuthy for according sanction to publish this paper.
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(8.) Amarpal, Singh B., Amreshkumar, Prakash P., Mechanical, histological and histochemical evaluation of split sternothyroideus pedicle graft for cervical oesophagoplasty in dogs, Indian J. Vet. Surg., 13 (1), 13-15, 1992.
(9.) Todhunter R.J., Stick J.A., Slocombe R.F., Comparison of three feeding techniques after oesophageal mucosal resection and anastamosis in horses, Cornell Vet., 76, 16-29, 1986.
(10.) Fingeroth J.M., Surgical techniques for oesophageal diseases, cited by Slatter D., in Text Book of Small Animal Surgery, W.B. Saunders Company, London, Vol. I 2nd Ed., 549-559.
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T.P. Balagopalan and K.N. Muraleedharan Nayar
Department of Surgery
College of Veterinary and Animal Sciences
Mannuthy 680 651
Table 1: Biochemical characteristics of normal oesophagus and healing site of oesophagoplasty with chrome processed aortic allograft in dogs. Parameters with Normal oesophagus Healing oesophageal defect units (n=6) (interval in days) n=2 15 Tensile strength 12.03 [+ or -] 2.73 2.74 (22.78%) (N/[mm.sup.2]) Breaking strength 128.19 [+ or -] 13.16 14.38 (11.22%) (N) Extensibility (%) 31.42 [+ or -] 2.58 10.63 (33.83%) Energy absorption 1.35 [+ or -] 0.22 0.04 (2.96%) (Nm) Total dilatation 100.00 84.27 capacity Parameters with Healing oesophageal defect units (interval in days) n=2 30 60 Tensile strength 2.82 (23.44%) 2.71 (22.52%) (N/[mm.sup.2]) Breaking strength 14.20 (11.08%) 29.35 (22.90%) (N) Extensibility (%) 11.17 (35.55%) 23.58 (75.05%) Energy absorption 0.05 (3.70%) 0.27 (20.00%) (Nm) Total dilatation 78.18 82.22 capacity
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|Author:||Balagopalan, T.P.; Muraleedharan Nayar, K.N.|
|Publication:||Trends in Biomaterials and Artificial Organs|
|Article Type:||Clinical report|
|Date:||Jul 1, 2001|
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