The Effect of Peritoneal Contamination of the Tensile Strength of Small and Large

Bowel Anastomosis*

 

D. Cottam, MD

A. Chendrasekhar, MD

F. Raymond

E.T. Burt, PhD

D.W. Moorman, MD

G.A. Timberlake, MD

 

Departments of Surgery Education and Trauma

Iowa Methodist Medical Center

Des Moines, IA

 

*This work was supported by the Iowa Health System, Des Moines, Iowa.

 

KEY WORDS: peritoneal contamination, tensile strength, anastomosis

 

ABSTRACT

Background: Peritoneal contamination is thought to be a contraindication to primary anastomoses for bowel laceration. Recent trauma literature has suggested that primary anastomoses may be an option in cases of limited contamination. We have previously shown that 12-hour peritoneal contamination does not seem to affect the tensile strength of primary anastomosis in a clinically relevant model of peritonitis. This study evaluates the effects of 18-hour contamination on primary repair bowel lacerations.

Materials and Methods: 20 Sprague-Dawley rats were divided into two groups: control rats (n = 10), and cecal ligation and puncture rats (CLP; n = 10). After performing a laparotomy with cecal manipulation (control) or CLP, the animals recovered for 18 hours. A second laparotomy was then performed where the cecum was resected and primarily anastomosed in animals with cecal ligation and puncture. Mid-jejunum and mid-colon were divided and primarily repaired. All animals were recovered and received postoperative fluid boluses, daily antibiotics, and free access to food and water. The studied group received an additional dose of antibiotic daily as well as a larger fluid bolus. On postoperative day 4, all animals were euthanized and the anastomotic sites were resected and loaded onto a tensiometer and pulled apart under dynamic tension. Peak load and tissue tension were measured as the anastomoses were disrupted. Peak load and maximum standard load were disrupted and calculated for each anastomosis. Then tissue was sent for hydroxproline content analysis. Study animal values were compared with control values using the student t-test Statistical significance threshold was P < .05.

Results: There was no statistically significant difference between the control and study animals with regard to anastomotic strength of colon or small bowel. There was no statically significant difference between hydroxyproline content of colon between the two groups. Small bowel hydroxyproline levels, however, were significantly greater in the control group than in the study group (54% greater).

Conclusion: Eighteen-hour peritoneal contamination does not seem to adversely affect the tensile strength of large and small bowel anastomosis in a clinically relevant rat model.

 

INTRODUCTION

Anastomotic strength with maintenance of luminal integrity is a fundamental necessity to a successful outcome of bowel repair.¹ Primary repair in a contaminated field was thought to be associated with leakage from bowel anastomosis.¹ For this reason, major surgical textbooks have stated that primary repair has a very limited or no role in the face of peritoneal contamination.^2,3 Previous military experience has suggested that the performance of a primary anastomoses in the face of peritoneal contamination related to trauma was associated with a higher mortality than performance of a colostomy.⁴ Recent experience with civilian injuries has lead to a reevaluation and subsequent endorsement of the primary anastomoses option with regard to trauma patients.^4-7 Detailed basic science information regarding the effect of peritoneal contamination on the tensile strength of anastomoses is lacking. We have previously published data on the effect of 12-hour peritoneal contamination on the tensile strength of primary bowel anastomosis.¹ We found that 12-hour peritoneal contamination did not have any effect on hydroxyproline levels or the tensile strength of primary anastomosis in either the large or small bowel 4 days after surgery. The purpose of this study was to determine the effect of 18-hour peritoneal contamination on hydroxyproline levels and tensile strength of primary anastomosis 4 days after surgery.

 

MATERIALS AND METHODS

This protocol was approved by our Institutional Laboratory Animal Utilization Committee. Animals were cared for in accordance with the current guidelines of the National Institutes of Health (Bethesda, MD). Twenty Sprague-Dawley rats were housed

In individual cages in a 12:12-hour light:dark, temperature-controlled environment and were allowed ad libitum access to standard rat chow and water. Each animal was assigned to one of the two groups. The groups were 18-hour cecal ligation and puncture (CLP; n = 10) or 18-hour control (n = 10). Animals were anesthetized using 5 mg/kg Ketamine IM and 25 mg/kg pentobarbital SQ. Individual weights were recorded (range, 300 to 400 g), then each rat's abdomen was shaved and prepped with a betadine solution. A midline incision was made and the cecum was identified. The study animals (CLP) underwent division of an avascular band between the cecum and the terminal ileum. The mobilized cecum was then ligated using ligature and doubly punctured with an 18-gauge needle. Control animals underwent division of the avascular band without subsequent CLP. All animals had the cecum returned to its anatomic position, and the abdomen was closed. All animals were then allowed to recover for 18 hours before a second laparotomy was performed. At the repeat laparotomy, peritoneal cultures were taken, and the abdominal cavity was irrigated with 30 cc warm normal saline. The CLP group had a partial cecectomy to remove the source of peritoneal contamination. Next, the mid-descending colon and the mid-jejunum were divided and re-anastomosed. Control animals underwent the same operation with the exception of the partial cecectomy.

All animals received immediate postoperative doses of gentamicin (5 mg/kg IM) and ampicillin (75 mg/kg IM) followed by a warm saline subcutaneous fluid bolus. The study animals also received an additional single postoperative dose of metronidazole (15 mg/kg IM).

All animals recovered in the controlled environment, were allowed free access to food and water, and received three additional daily doses of gentamicin and ampicillin.

On postoperative day 4, the animals were sacrificed with an intramuscular and subsequent intracardiac injection of beuthanasia. The abdomens were opened and anastomoses were identified and resected 2 cm proximal and 2 cm distal to the suture line. Specimens were gently flushed with iced normal saline and skeletonized free from adherent tissues. Each piece was then loaded onto a tensiometer (United Calibration Corporation, Des Moines, IA). The machine was zeroed before each measurement, and load strain curves were produced. Maximum load for each specimen was recorded. Immediately after the procedure, anastomotic specimens were cleared of suture material, placed in individual containers, and frozen in liquid nitrogen for hydroxyproline determination. Maximum standard load (g/cm² body surface area) was calculated by dividing each individual peak load by the animal's body surface area, thus allowing a comparison between different sized animals. The average maximum standard load for each group, along with the standard deviation of the mean, was then calculated. Hydroxyproline content was determined via alkaline hydrolysis at the University of Osteopathic Medicine and Health Sciences (Des Moines, IA) as described by Reddy and Enwemeka.⁸ The averaged values with the associated standard deviation of the mean were calculated.

Statistical analysis was performed using the average values for the maximum standard load and hydroxyproline content. Eighteen-hour CLP was compared with 18- hour controls using the unpaired student's t-test. Statistical significance threshold was P < .05.

 

RESULTS

All animals survived to postoperative day 4. No anastomotic leaks were noted, all control animals were culture negative, all the study animals were culture positive with purulent peritonitis, and all anastomotic segments failed at the anastomotic site during the disruption procedure. The maximum standard load and hydroxyproline content are listed in Table 1. There was no significant difference between the maximum anastomotic standard load (P = .699 for small bowel and P = .475 for colon). The hydroxyproline content of the colon showed no significant difference between the two groups (P = .142). However, there was a statistically difference between the two groups hydroxyproline content in the small bowel. The hydroxyproline content was 54% greater in the control group than the study group.

 

DISCUSSION

Wound healing in the face of peritoneal soilage and associated generalized peritonitis is the real issue addressed by this study. Previous surgical thinking based on observational studies have led to the assumption that wound healing is abnormal in the presence of peritonitis.⁴ Recent trauma literature, as well as our basic science experimental data, has shown that primary anastomoses in early peritonitis is a viable option.^4-7

Obviously, many factors go into whether a primary anastomoses is feasible or whether an ostomy of some sort should be performed. These include the presence of shock, gross appearance of the viable bowel, and location and duration of peritoneal soilage. This study was designed to assess the duration of peritoneal soilage with the associated acute inflammatory response present at that time interval and its effect on anastomotic strength and new collagen synthesis (hydroxyproline levels) 4 days postoperatively.

Our 4-day postoperative course was chosen based on work done by Uden and Blomquist that demonstrated that by postoperative day 4 the anastomotic strength in animals similar to our controls had returned to initial values and an increase in hydroxyproline content could be detected.⁹ This time frame also allowed comparison with our own previous studies as well as a study by Ahrendt et al that studied 24-hour peritoneal contamination.¹⁰ Our previous data demonstrated that short-term soilage for 12 hours does not significantly affect anastomotic strength or hydroxyproline content (a standard indicator of new collagen synthesis) in both colonic and small bowel anastomosis 4 days after surgery. Ahrendt et al published their results on long-term peritoneal contamination, which showed a significant decrease in new collagen synthesis after 24 hours of peritoneal soilage in a similar rat model.¹⁰ Our current study, which studied 18 hours, did not show a difference in anastomotic strength; however, the hydroxyproline content was significantly lower in the small bowel anastomoses of the study group compared with the control group. This may be the transition period to the results seen by Ahrendt et al.¹⁰ Another difference between our series of studies and the study published by Ahrendt et al may be related to our protocol's use of antibiotics and irrigation, which was not used by Ahrendt et al. Our protocol more accurately simulates the clinical scenario. Other studies, including those by Irvin and Goligher, failed to show that fecal soiling or peritoneal sepsis caused anastomotic complications and cited the use of broad-spectrum antibiotics as a possible reason.¹¹

 

CONCLUSION

Clearly, the understanding of the effect of peritoneal soilage on primary bowel anastomoses is evolving. It is becoming more accepted in certain patients, such as trauma patients as well as those with diverticulitis, to perform resection and primary anastomoses even in the face of peritoneal soilage. Our current study does show that the hydroxyproline content starts dropping after 18 hours of contamination in small-bowel anastomosis. However, the tensile strength is still not adversely affected. More studies are needed to clearly understand the effects of peritoneal soilage and how they can be altered using other medications and approaches such as growth factors, fibrin glue, steroids, and antineoplastics.

 

REFERENCES

1.            Orlando MD, Chandrasekhar A, Bundz S, et al: The effect of peritoneal

contamination on wound strength of small bowel and colonic anastomoses. Am Surg 65:673, 1999.

2.      Sabiston D: Textbook of Surgery: The Biological Basis of Modern Surgical Practice, ed 15. Philadelphia, WB Saunders Co, 1997, pp 989-990.

3.      Schwartz SI: Principles of Surgery, ed 7. New York, McGraw Hill Co, 1999, p 1280.

4.      Fabian TC, Croce MA: Small and large bowel injuries, in Cameron JL (ed): Current Surgical Therapy, ed 6. St Louis, MO, Mosby, 1998, pp 957-959.

5.      Ryan MS: The effect of surrounding infection upon the healing of colonic wounds. Dis Colon Rectum 13:124-126, 1970.

6.      Gonzalez RP, Merloth GJ, Holevar MR: Colostomy in penetrating colon injury: Is it necessary? J Trauma 41:271-275, 1996.

7.      Ivatury RR, Guadino J, Nallathambi MN, et al: Definitive treatment of colon injuries: A prospective study. Am J Surg 59:43-49, 1993.

8.      Reddy GK, Enwemeka CS: A simplified method for the analysis of hydroxyproline in biological tissues. Clin BioChem 29:225-229, 1996.

9.      Uden P, Blomquist P: Influence of proximal colostomy on the healing of a left colonic anastomosis: An experimental study in the rat. Br J Surg 75:325-329, 1988.

10.  Ahrendt GM, Tantry US, Barbul A: Intraabdominal sepsis impairs colonic reparative collagen synthesis. Am J Surg 171:102-107, 1996.

11.  Irvin TT, Goligher JC: Aetiology of disruption of intestinal anastomoses. Br J Surg 60:461-464, 1973.

 

Table 1. Maximum Standard Load and Hydroxyproline Content

 

	Jejunum Standard Peak Loads (g/g body weight)	Left Colon Standard Peak Loads (g/cm2)	Jejunum Hydroxyproline (µg/mg of tissue)	Colon Hydroxyproline (µg/mg of tissue)
Group A	19115.5 + 5812.5	32782.3 + 10212.2	0.1058 + 0.0550	0.1084 + 0.0447
Group C	20155.5 + 5722	35883.9 + 6603.8	0.0578 + 0.0261	0.0776 + 0.0425
P Value	.6998	.4753	.0292	.1425