The Disintegration of Surgical Sutures on Exposure to Pancreatic Juice K. MIZUMA, M.D., P. C. LEE, PH.D., JOHN M. HOWARD, M.D.

The loop-breaking strength of various suture materials was tested over a period of 14 days during which time the sutures were incubated in vitro in saline or canine serum, bile, activated or nonactivated pancreatic juice. Under the conditions of the study, silk and nylon maintained their strength in each environment. Polyglycolic acid maintained its strength in saline, bile or serum, but gradually lost much of its strength when exposed to pancreatic juice. Catgut, both plain and chromic, disintegrated almost completely within 24-48 hours respectively when exposed to enterokinase activated pancreatic juice. Inhibition of trypsin by aprotinin (Trasylol) resulted in preservation of catgut strength but inhibition by soybean inhibitor did not. The latter findings suggest that proteolytic enzymes, other than trypsin, may be responsible for the disintegration. C ATGUT IS A WIDELY USED suture

material in

gastrointestinal surgery. Its relative limitations as a suture material are well recognized; more marked tissue reaction,20 predisposition to infection,' and more rapid loss of strength.7 Pancreatic fistulae constitute major complications after pancreaticoduodenectomy,' 5"10 resulting in external loss of fluid and autodigestion of the skin. Although multiple factors may be involved in the development of postoperative pancreatic fistulae, the nature of the suture materials used during operation may be one factor in the genesis of this complication. The majority of absorbable suture materials consist of proteins, theoretically sensitive to proteolytic enzymes contained in pancreatic juice. The aim of this study has been to evaluate the changes in loop-tensile strength of various suture materials when exposed in vitro to pancreatic juice in which, in respective experiments, the trypsinogen was or was not activated. Reprint requests: John M. Howard, M.D., Department of Surgery, Medical College of Ohio at Toledo, P.O. Box 6190, Toledo, Ohio 43614. Supported by Grant # AM-17789-02 From the National Institute of Arthritis and Metabolic Diseases. Submitted for publication: January 8, 1977.

From the Departments of Surgery and Biochemistry of the Medical College of Ohio, Toledo, Ohio

Materials and Methods

Pancreatic juice was collected from a dog via a glass cannula in the pancreatic duct, inserted through a chronically implanted Thomas cannula in the duodenum, and under the constant stimulation of a secretin and pancreozymin infusion. The pancreatic juice was collected over ice and was stored in a freezer at -20° until used. The activation of trypsinogen to trypsin was achieved by the addition of enterokinase prepared from canine duodenal mucosa by the method of Baratti et al.3 up to the acidification step. The final preparation was neutralized to pH 7.0 and stored in small aliquots at -20°. Amylase was measured by the method of Caraway4 and lipase was measured by the method of Vogel and Zieve.21 Trypsin and trypsinogen were measured according to the method described by Erlanger et al.6 using a-N-Benzoyl-DL-Arginine-p-nitroanilide HCI (BAPNA) as the substrate. The suture materials used in this study were braided silk, braided nylon, plain catgut, chromic catgut, and polyglycolic acid sutures. All sutures were 2-0 in size as manufactured by the Davis and Geck Corporation. Aprotinin, soybean trypsin inhibitor and BAPNA were from Sigma Chemical Company, St. Louis, Missouri. The sterile suture materials were incubated in glass tubes, each filled with 10 ml of the test solution including activated pancreatic juice, nonactivated pancreatic juice, serum, bile, or normal saline respectively. All the biological test solutions were canine in origin. The above tubes were incubated at 370 with the test fluids being replaced every 24 hours. Loop strength of the suture materials was measured on a spring scale tensiometer by gradually increasing the tension. The suture loops were fashioned around two opposing pegs of the test apparatus, tying the two ends of the sutures with a

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FIG. 2. Effect of canine serum on the tensile strength of suture materials. Points represent the mean and bars the standard error of the mean.

four throw square knot. The tests were conducted using wet sutures after rinsing and soaking each in normal saline for two minutes. Tensile strength was determined daily for seven days, then on the tenth and fourteenth days. Each suture material, except silk, was tested six times on each of the above days. Silk was tested ten times on each day. Reproducibility was within the limits of approximately 2%. The experiments were divided into six series. In each series, unless otherwise stipulated, each type of suture material was incubated with the respective solution and tested as above. The series were subdivided into various test solutions as indicated below. Each experiment was performed at least three separate times and in duplicate unless otherwise stated. Results represent the average with standard error included wherever appropriate.

Series 4 In nonactivated pancreatic juice, silk and nylon maintained their strength, whereas polyglycolic acid sutures lost two thirds of their strength by the end of two weeks (Fig. 4). Plain and chromic catgut sutures lost much of their strength within the first week and disintegrated almost completely by the tenth and fourteenth days respectively.

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Series 1-3 As controls, sutures were tested in 1) 0.9 normal saline, 2) canine serum, and 3) canine gallbladder bile respectively. The results are depicted in Figures 1-3. Silk, nylon, polyglycolic acid and plain catgut retained their respective strength throughout the two week period. Chromic catgut also retained most of its strength, although it lost approximately one third of its strength in each of the test solutions during the early period of exposure.

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In enterokinase activated pancreatic juice, in which the trypsinogen had been activated to trypsin, silk and nylon maintained their strength (Fig. 5). Polyglycolic acid sutures maintained their strength during the first week, losing 30% of their strength in the second week. Plain and chromic catgut lost their strength precipitously with the plain catgut disintegrating within 24 hours and the chromic catgut within 48 hours. Nonactivated pancreatic juice was tested for its vari-

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ous enzyme contents after thawing and during a 24 hour period of incubation at 37°. Freezing and thawing were found to result in the loss of approximately 25% of the lipase and amylase content. Incubation at 370 reduced the amylase and lipase activities to 65% after three hours and to 40% after 24 hours. Trypsinogen levels fell to 50% of initial values after freezing and thawing, to 35% after three hours of incubation and to 30% after 24 hours of incubation at 37°.

Activation of pancreatic juice by the addition of enterokinase resulted initially in the appearance of significant quantities of trypsin. This was followed by a rapid disappearance of amylase, lipase, trypsinogen and trypsin (Table 1). Presumably the disappearance of the enzymes resulted from tryptic and other proteolytic digestion. The addition of aprotinin (Trasylol) or soybean trypsin inhibitor reduced the detectable activities of trypsin in the activated pancreatic juice and retarded somewhat the disappearance rate of the other enzymes, especially that of lipase. The failure to halt completely the inactivation of the other enzymes, even after all tryptic activity was inhibited (as in the case of soybean trypsin inhibitor), suggested the presence of other active proteolytic enzymes. In an effort to define the mechanism of digestion of the catgut, the plain and chromic catgut sutures were retested as described, daily over a period of four days, while exposed to a) enterokinase alone, b) activated pancreatic juice plus aprotinin (Trasylol) (1000 U/ml), c) activated pancreatic juice plus soybean trypsin in-

SUTURE DISINTEGRATION

Vol. 186 . No. 6

hibitor, d) activated pancreatic juice plus canine serum (0.1 ml serumlml juice). Results are summarized in Table 2. Enterokinase alone exerted no deleterious effect. Neither serum (presumably containing natural trypsin inhibitors) nor soybean trypsin inhibitor provided protection to suture degeneration. Aprotinin, although it did not inhibit all tryptic activity at the concentration used, provided almost complete protection throughout the four day period. Since both aprotinin (Trasylol) and the soybean inhibitor inhibited trypsin significantly in the activated pancreatic juice, the study suggests that trypsin, per se, may not be the major digestive enzyme responsible for the disintegration of catgut. Discussion

The primary purpose of sutures is to maintain approximation between tissues as the wound heals. It is essential that the sutures maintain their strength for sufficient duration to permit the healing process to mature. The duration of wound healing of various organs has been reported previously. Levenson et al.'7 showed that skin wounds in rats develop only 80% of their normal strength within one year postoperatively. Howes et al.'3 reported that in dogs, gastric wounds reach normal strength at ten to 12 days postoperatively. Fellows et al.8 measured the bursting strength of jejunojejunostomies and found them to increase in strength during the first four days after anastomosis. It is to be expected that many sutures will lose their strength at various rates in the various media of the body. In the current experiment, catgut lost its strength surprisingly fast in nonactivated pancreatic juice, extremely rapidly in activated juice. This result suggested that catgut cannot maintain its strength when exposed to pancreatic exudates, especially in a pancreatojejunostomy where proteolytic enzymes would be activated. At least the intraluminal portion of any suture would be exposed to such proteolysis. Beyond 24-48 hours after operation, catgut could not, by its tensile strength, be expected to unite the pancreatic duct and small intestine.

721

This may be one explanation for leakage of pancreatojejunostomies. Howes"2 reported that in the lumen of the dog's stomach, number one chromic catgut lost its strength within 36 hours after implantation. Jenkins et al.,15 showed hydrochloric acid and pepsin resulted in digestion of plain and chromic catgut within approximately 20 hours of exposure. Recently, Everett7 pointed out that in baboons, 2-0 chromic catgut lost most of its strength within 24 hours of implantation in the ileum. Postlethwait et al.20 reported that in dogs, chromic catgut lost its strength more rapidly in the upper digestive tract than in other organs, including the lower digestive tract. This suggests that proteolytic enzymes which are contained in gastric juice, pancreatic juice and other digestive juices have a major deleterious effect on catgut sutures. Several reports indicate that polyglycolic acid sutures are superior to catgut in tensile strength,9"4 tissue reaction'0"18 and clinical application.2 0"8 In our data, polyglycolic acid sutures maintained their strength better than did catgut, but not as well as silk or nylon. This suture material is produced by polymerization of a single amino acid (glycolic acid) and is absorbed by simple hydrolysis, not proteolysis.2 Activated pancreatic juice exerted only a mildly deleterious effect on these sutures. Of interest is that in nonactivated pancreatic juice, this suture deteriorated faster than in activated pancreatic juice. This phenomenon probably results from the fact that activation of trypsin results in the destruction of other pancreatic enzymes which might be involved in polyglycolic acid suture digestion. As controls, serum itself caused only a slight loss of strength of catgut over the period of this study, observations paralleling those of Howes et al.'3 a half century ago. Bile and normal saline produced little

effect. The fact that catgut sutures still disintegrate rapidly, even when almost all trypsin activities are inhibited, suggests the presence of other proteolytic enzymes in the pancreatic juice that may be responsible for the digestion. The observation that nonactivated pancreatic juice is capable of digesting the catgut material fur-

TABLE 2. Effect of Inhibitors on the Degeneration of Catgut and Chromic Catgut Sutures by Enterokinase Activated Pancreatic Juice

Loop Strength of Suture (grams) Enterokinase Control

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Plus Soybean Inhibitor (I mg/ml)

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(0.1 ml/ml)

Time

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Chromic

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Chromic

Plain

Chromic

Plain

Chromic

I day 2 days 3 days 4 days

2516 ± 172 2724 54 2569 ± 126 2554 88

3065 ± 257 3572 138 3027 ± 135 3330 210

2895 ± 110 2611 128 2403 ± 124 2441 122

2877 ± 198 2121 74 2516 ± 102 2626 80

0 0 0 0

1173 + 107 224 66 0 0

0 0 0 0

1892 ± 141 243± 32 130 ± 32 0

MIZUMA, LEE AND HOWARD

722

ther suggests that these enzymes are at least partially active in the form in which they are secreted. The protection seen by the addition of aprotinin is an interesting finding that might have practical application.

References 1. Alexander, J. W., Kaplan, J. Z. and Altmeier, W. A.: Role of Suture Materials in the Development of Wound Infection. Ann. Surg., 165:192, 1967. 2. Anscombe, A. R., Hira, N. and Hunt, B.: The Use of New Absorbable Suture Material (Polyglycolic Acid) in General Surgery. Br. J. Surg., 57:917, 1970. 3. Baratti, J., Maroux, S., Louvard, D and Desnuelle, P.: On Porcine Enterokinase. Further Purification and Some Molecular Properties. Biochim. Biophys. Acta, 315:147, 1973. 4. Caraway, W. T.: A Stable Starch Substrate for the Determination of Amylase in Serum and Other Body Fluids. Am. J. Clin. Pathol., 32:97, 1959. 5. Cattel, R. B. and Warren, K. W.: Surgery of the Pancreas. Philadelphia, W. B. Saunders, Co., 1953. 6. Erlanger, B. F., Kokowsky, N. and Cohen, W.: The Preparation and Properties of Two New Chromogenic Substrates of Trypsin. Arch. Biochem. Biophys., 95:271, 1961. 7. Everett, W. G.: Suture Materials in General Surgery, Progr. Surg., 8:14, 1970. 8. Fellows, N. M., Burge, J., Hatch, C. S. and Price, P. B.: Suture Strength and Healing Strength of End-to-End Intestinal Anastomoses. Surg. Forum, 2:111, 1951. 9. Herrmann, J. B.: Changes in Tensile Strength and Knot Security of Surgical Sutures In-vivo. Arch. Surg., 106:707, 1973.

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10. Hess, W.: Surgery of Biliary Passage and the Pancreas. Princeton, D. Van Nostrand, Co. 1965. 11. Howard, J. M. and Jordan, G. L.: Surgical Diseases of the Pancreas. Philadelphia, J. B. Lippincott Co., 1960. 12. Howes, E. L.: Factors Determining the Loss of Strength of Catgut When Embedded in Tissue. JAMA, 90:530, 1928. 13. Howes, E. L., Sooy, J. W. and Harvey, S. C.: The Healing of Wounds as Determined by their Tensile Strength. JAMA, 92:42, 1929. 14. Howes, E. L.: Strength Studies of Polyglycolic Acid Versus Catgut Sutures of the Same Size. Surg. Gynecol. Obstet., 137:15, 1973. 15. Jenkins, H. P. and Hrdina, L. S.: Absorption of Surgical Gut (Catgut) II. Pepsin Digestion Tests for Evaluation of Duration of Tensile Strength in the Tissues. Arch. Surg., 44:984, 1942. 16. Letwin, E. R.: Evaluation of Polyglycolic Acid Sutures in Colon Anastomoses. Can. J. Surg., 18:30, 1975. 17. Levenson, S. M., Geever, E. F., Crowley, L. V., et al.: The Healing of Rat Skin Wounds. Ann. Surg., 161:293, 1965. 18. Miln, D. C., O'Conner, J. and Dalling, R.: The Use of Polyglycolic Acid Suture in Gastrointestinal Anastomosis. Scot. Med. J. 17:108, 1972. 19. Postlethwait, R. W., Schauble, J. F., Dillon, M. L. and Morgan, J.: Wound Healing II. An Evaluation of Surgical Suture Material. Surg. Gynecol. Obstet., 108:555, 1959. 20. Postlethwait, R. W., Ulin, A. W., Skarin, R. M. and Kaminska, G.: Breaking Strength Loss of Intraluminal Suture Material in Gastrointestinal Tract. Chir. Gastroenterol., (Eng. Ed.) 8:18, 1974. 21. Vogel, W. C. and Zieve, L.: A Rapid and Sensitive Turbidimetric Method for Serum Lipase Based upon Differences Between Lipases of Normal and Pancreatitis Serum. Clin. Chem., 9:168, 1963.

The disintegration of surgical sutures on exposure to pancreatic juice.

The Disintegration of Surgical Sutures on Exposure to Pancreatic Juice K. MIZUMA, M.D., P. C. LEE, PH.D., JOHN M. HOWARD, M.D. The loop-breaking stre...
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