Comparison of two end-to-end continuous sutures for intestinal anastomoses in dogs.

The this study to compare two suture techniques for end-to-end anastomosis of the canine intestine (jejunum and colon): handsewn intestinal anastomosis by appositional simple continuous su- ture and inverting Cushing suture. The objectives of this study were to investigate 1.) whether the type of suture influences the specific effort to which the anastomosis site is submitted to, 2.) whether the anastomosis technique influences the diameter of the intestinal lumen and 3.) survival and complication 30 rates in canine clinical cases undergoing end-to-end anastomoses. Results: The equilibrium angle for implanting the sutures in an anastomosis is 35°, aspect completely 32 fulfilled by the simple continuous suture. The efforts to which sutures are submitted to in anastomoses 33 are minimal for the Cushing suture. The difference in size of the anastomoses’ lumen b etween simple 34 continuous suture and the Cushing suture are minimal, without being statistically relevant. The differ- 35 ences between the lumen of the anastomoses performed using PDS and those performed using PGA are 36 not statistically relevant. Conclusions: Use of the Cushing suture should be considered for performing an end-to-end intestinal 42 anastomosis, although more studies are required to determine if there are any clinically significant dif- 43 ferences between the sutures investigated in this study. 44

Background: Single-layer appositional closures are preferred to inverting or everting patterns, as sub-21 mucosal apposition has been shown to promote primary healing of the intestinal wall, whereas inverted 22 or everted closures require second-intention healing and can increase the risk of luminal stenosis or 23 anastomosis site leakage. There are different suture patterns available, but relatively few studies com-24 paring these aspects have been published. 25 The aim of this study was to compare two suture techniques for end-to-end anastomosis of the canine 26 intestine (jejunum and colon): handsewn intestinal anastomosis by appositional simple continuous su-27 ture and inverting Cushing suture. The objectives of this study were to investigate 1.) whether the type 28 of suture influences the specific effort to which the anastomosis site is submitted to, 2.) whether the 29 anastomosis technique influences the diameter of the intestinal lumen and 3.) survival and complication 30 rates in canine clinical cases undergoing end-to-end anastomoses. 31 Results: The equilibrium angle for implanting the sutures in an anastomosis is 35°, aspect completely 32 fulfilled by the simple continuous suture. The efforts to which sutures are submitted to in anastomoses 33 are minimal for the Cushing suture. The difference in size of the anastomoses' lumen between simple 34 continuous suture and the Cushing suture are minimal, without being statistically relevant. The differ-35 ences between the lumen of the anastomoses performed using PDS and those performed using PGA are 36 not statistically relevant. 37 The retrospective analysis of the outcome for 676 dogs (clinical cases) that underwent intestinal resec-38 tion and anastomosis reveals that the dehiscence rate was 1.48%, out of which 1.18% following simple 39 continuous anastomoses, and 0.3% following Cushing anastomoses. Narrowing of the intestinal lumen 40 due to anastomotic healing was not registered. 41 Intestinal resection and anastomosis is commonly performed in veterinary patients for treatment of 48 intestinal foreign bodies, intestinal perforation, devitalized tissue secondary to vascular compromise, 49 intestinal neoplasia, or intussusception and in patients that require revision of prior intestinal surgery [1, 50 2]. The potential major complications of intestinal anastomosis are leakage at the anastomosis site and 51 luminal stenosis [1,3,4,5,6,7,8,9,10]. The anastomosis technique used may influence the diameter of 52 the intestinal lumen, as well as the intraluminal pressure and the ability to withstand the normal peri-53 stalsis, with leakage or stenosis at the anastomosis site being the main postoperative complications. 54 A variety of surgical techniques for intestinal anastomosis has been described and analysed [11, 12, 13, 55 14, 15, 16, 17, 18, 19, 20, 21]. 56 In veterinary medicine, a single-layer appositional handsewn anastomosis is preferred. Single-layer 57 appositional closures are preferred to inverting or everting patterns, as submucosal apposition has been 58 shown to promote primary healing of the intestinal wall, whereas inverted or everted closures require 59 second-intention healing and can increase the risk of luminal stenosis or anastomosis site leakage, re-60 spectively [2, 3, 4, 5, 6, 7, 9, 10, 22, 23, 24, 25]. 61 Outcomes following the use of interrupted and continuous suture patterns have been evaluated, and 62 the incidence of leakage is comparable between these methods [13]. Other studies [3,23,26] show that 63 6 The mathematic relation: = tg2β, ties the efforts' intensities (circumferential and longitudinal) to 109 which the intestine is submitted to. 110 Given these conditions, the value of the angle formed by the placement of the sutures with the circum-111 ferential direction (longitudinal axis of the intestiney) called implantation angle (elevation) -β is 112 35°20'. 113 Thus, the internal pressure can be supported by the sutures only if they form a 35°20' implantation an-114 gle with the circumferential direction. 115 The vectorial scheme ( Fig. 1 , a value depending on ɑ is added. In these conditions, R< R'. The orientation direction is dif-127 ferent for the two results, R' being closer to the Y axis, which is why the section (A') to which it is ap-128 plied, is smaller than section A, A>A'. The effective specific effort calculated for the two situations is: 129

Tef1
, resulting that Tef1<Tef2'. 130 7 The effort to which sutures are placed in an anastomose (N) was determined using the relation: 131 N pD , where "p" is the interior pressure, "D" is the intestinal diameter, "t" is the distance between 132 vectorial forces' results, "n" is the number of suture layers. 133 By comparing the calculation elements of the studied suture, it results that given the same distance 134 between sutures, "t" has different values, the relationship being T1<T2<T3, where T1 -Cushing suture, 135 T2simple continuous suture, T3simple interrupted suture. In these conditions, the efforts to which 136 sutures are submitted to in anastomoses (N) are minimal for the Cushing suture. 137 The data obtained by measuring the anastomoses ends' diameters reveals that the single-layer simple 138 continuous suture reduces the least the jejunum lumen diameter (12.55±4.55%) and colon diameter 139 (9.32±2.27%) (Fig. 2). 140 The inverting Cushing sutures maintains the jejunal lumen in the 78.6 -88.9% range and the lumen of 141 the colon in the 83.5-89.9% range (Fig. 3). The differences between the diameter of the simple continu-142 ous suture anastomoses' lumen and the Cushing ones are minimal ( Fig. 4 and Fig. 5), without being sta-143 tistically relevant (p = 0.630 for the jejunum and p=0.632 for the colon after t-test, and p=0.322 for the 144 jejunum and p=0.404 for the colon after applying the Independent samples Kruskal-Walis Test). 145 The differences between the lumen of the anastomoses performed using PDS and those performed us-146 ing PGA, analysed applying the t-test, are not statistically relevant for anastomoses in simple continuous 147 suture (p=0.966 for jejunum and p=0.686 for colon) and Cushing suture (p=0.698 for the jejunum and 148 p=0.705 for the colon). 149 A retrospective analysis of 676 intestinal resections and end-to-end anastomoses performed in the Fa-150 culty of Veterinary Medicine between 1990 and 2020, reveal that 262 were conducted using simple con-151 tinuous sutures and 414 using Cushing sutures. 152 Specific mortality: number of deaths due to anastomotic complications was 3/14. 153 8 Overall anastomotic dehiscence: total number of anastomotic dehiscence (evidenced by clinical and/or 154 radiological findings) was 10 (3 jejunum and 7 colons; 8 following simple continuous sutures and 2 fol-155 lowing Cushing suture). In our study, the dehiscence rates for canine anastomoses were 1.48%, out of 156 which 1.18% were following simple continuous anastomoses, and 0.3% following Cushing anastomoses. 157 Stricture (narrowing in the bowel lumen due to anastomotic healing -evidenced by clinical and/or radio-158 logical findings) was not registered. 159 Reoperation: surgical re-intervention rate for anastomotic complication was 10/14.

172
Our hypothesis is that this phenomenon also occurs in intestinal anastomoses, which suggests that loops sutured 173 using simple interrupted sutures or those performed using skin staples, will undergo the highest deformity when 174 compared to those performed using continuous sutures.

175
The practical significance of rearranging the sutures towards the equilibrium value of the implantation angle con-

191
Our data show that the inverting Cushing suture withstands higher luminal pressures.

192
According to the elasto-plastic deformations theory, suture implantation at an angle smaller than β = 35ᵒ20', the 193 intestine stretches and shrinks in diameter, and if the suture implantation is performed at an angle greater than 194 the equilibrium value (Cushing suture -β=45ᵒ), under the action of pressure, the intestine will shorten and become 195 wider. This phenomenon has also been suggested to be similar to the physiological response to increased intra-196 luminal pressures [53]. These aspects could explain statistically non-significant differences obtained in our study

216
The clinical assessment shows a long-term survival rate of 97% after single-layer end-to-end anastomoses. We determined the equilibrium angle of suture placement, the effective specific effort to which the 263 anastomosis ends were submitted to and the exerted effort upon the sutures placed in an anastomosis. 264 The canine cadavers originated from patients that either succumbed due to untreatable medical condi-265 tions, or were euthanized due to medical conditions, unrelated to the gastrointestinal tract. The time 266 between death or euthanasia of animals and intestinal anastomosis realization ranged from 4 -48 hours. 267 All intestinal (jejunal and colonic) segments were collected from 26 dogs (13 females, 13 males, all 268 mixed breed), with weights ranging from 12 to 35 kg (22.5 kg ± 4.9 kg) and reported ages ranged from 1 269 -7 years (3.4 years ±1.7 years), the number of anastomoses per session ranging from 1 to 12 (median 270 6.5 anastomoses). 271 Within 1-2 hours of euthanasia or death, the gastrointestinal tract was examined to confirm there were 272 no gross abnormalities present. Animals with intestinal diseases were excluded from the study. 273

13
The jejunum and colon were then harvested. Ingesta was milked towards the transected stumps. Jejunal 274 and colon segments were stored at 4 °C until utilized. Each specimen had a length of 40-60 mm. 275 The jejunal and colonic segments from each cadaver were randomly allocated and equally distributed 276 amongst the 2 groups (

Anastomosis construction 282
We conducted end-to-end anastomoses (jejunal and colonic) on canine cadavers, using two techniques 283 (simple appositional suture, and inverting Cushing suture respectively). We conducted 108 jejunal anas- Descriptive statistics for the cadavers, intestinal segments, number of anastomoses in each group, num-319 ber of sutures placed and time between euthanasia and testing were calculated and reported as mean ± 320 standard deviation (SD). 321 The data was statistically calculated using IBM SPSS Statistic Version 23 and Minitab Release 14.20. 322 For analysing the diameters of jejunal and colonic anastomoses, performed using two suturing tech-323 niques (simple appositional suture, and inverting Cushing suture respectively), we used two-sample T-324 test (parametric test), Kruskal-Walis Test (non-parametric test) and 95% confidence intervals. Values of 325 P < 0.05 were considered significant. 326 We also used the parametric t-test for comparative analysis of the influence the suture material (PGA vs 327 PDS) has over the two techniques used to perform the jejunum and colonic anastomoses (simple apposi-328 tional suture, and inverting Cushing suture respectively). The significance level is p=0.05. 329 For our clinical casuistry, we compared the occurrence frequencies (dehiscence, adherences, second 330 surgeries, mortality, success) in relation to the type of suturing technique used (simple appositional su-331 ture, and inverting Cushing suture respectively) and the intestinal segment (jejunum and colon). We 332 used the independence and homogeneity hi 2 test, linked to the frequencies of presentation of such cas-333 16 es. The categories are comprehensive and mutually exclusive: any subject may belong to one category 334 and one alone. 335   Distribution of circumferential and longitudinal forces (efforts) to which the anastomosed intestine is subjected to. Sub-gure I depicts efforts in case of Cushing Type suture. Sub-gure II depicts efforts in case of simple continuous suture. Legend: X and Y represent cartesian coordinates in which Y represents the longitudinal axis of the intestine; D and D' are the diameters of the intestine; B and B' represent the areas of the intestinal lumen; A and A' are the sections to which R applies; R and R' are the action resultants of the vector forces F1, F1', F2 and F2'; β represents the suture implantation angle and α represents the angle formed by the vector forces F1 and F2.  Ex-vivo, variation of colon lumen size after anastomosis. Variation of colonic lumen size under the in uence of end-to-end anastomoses by single-layer simple continuous suture and single-layer inverting