Comparison of endostapler performance in challenging tissue applications

Surgery for Obesity and Related Diseases 9 (2013) 417–422

Original article

Comparison of endostapler performance in challenging tissue applications Elizabeth Contini, B.S.*, Jennifer Whiffen, M.S., Dwight Bronson, M.S. Covidien Surgical Solutions, Fundamental Biomedical Research Department, North Haven, Connecticut Received June 7, 2012; accepted October 30, 2012

Abstract

Background: Surgical staplers are frequently used in a variety of applications, demanding exacting instrument performance over a huge range of tissue compositions and disease states. The shape of a staple that is formed by a stapling device is one industry-accepted indicator of device performance; typically a B-shaped staple is considered the gold standard for staple formation. This B shape allows blood flow through the tissue, which is one important factor in the healing events that take place clinically after stapling. With the use of an animal model, this ex vivo study investigated staple formation when thick tissue endoscopic staplers were used on challenging and variable tissue. The setting was a corporate institution in the United States. Methods: Two 60-mm linear endoscopic thick tissue reloads, a varied-height stapler (VHS), and a single-height stapler (SHS) were fired on 7 different regions of porcine stomach. Resultant staple formation was assessed per region of the stomach and evaluated for proper B-shaped staple formation and staple malformation. Results: The VHS reload had significantly better B-shaped formation (P o .001) for all regions of the stomach and reduced occurrence of malformed staples in 5 of the 7 regions compared with the SHS reload, wherein the remaining 2 regions exhibited comparable malform occurrence. Conclusions: This study compared 2 thick tissue reloads and found that the VHS reload had superior outcomes, with respect to staple formation, compared with the SHS reload. (Surg Obes Relat Dis 2013;9:417–422.) r 2013 American Society for Bariatric Surgery. All rights reserved.

Keywords:

Surgical stapling; Stapler; Thick tissue; Staple formation

The technology behind stapling devices has advanced considerably since their advent [1,2], as have the surgical procedures in which these devices are used. Surgical applications of these devices require that they perform in highly variable and challenging tissues. Although the manufacturers provide guidance documents for device use, tissue ranges, and indications [3,4], these guidance documents do not ensure their efficacious use. To our knowledge, there are no published studies that describe the performance of the most recent endoscopic stapling product offerings from the primary stapling manufacturers (Covidien, Mansfield, MA, and Ethicon, Cincinnati, OH) comparing their thick tissue reloads’ performance in highly variable and challenging tissue. All work was solely funded by Covidien Surgical Solutions. * Correspondence: Elizabeth Contini, B.S., Covidien, 60 Middletown Avenue, Mailstop 20, North Haven, CT 06473. E-mail: [email protected]

The objective of this study is to compare the performance of the 2 most prominent endoscopic linear staplers used in thick tissue on the market today: Covidien Endo GIA Reload with Tri-Staple technology AXT (black) with the Endo GIA Ultra Universal stapler (EGIA60AXT; Covidien, Mansfield, MA) and the Ethicon Echelon 4.1-mm (green) reload with the Echelon Flex stapler (ECR60G; Ethicon, Cincinnati, OH). The thick tissue reloads were fired in explanted porcine stomach, which is a common tissue model used to compare stapling devices [5,6]. Materials and methods Fresh frozen porcine stomachs were used in this study because they have tissue variability similar to that seen in human stomachs [7] and have been used in previous studies as tissue analogues for device comparisons [5,6]. The cartridge sizes used for this testing included the available thick tissue reload for each manufacturer:

1550-7289/13/$ – see front matter r 2013 American Society for Bariatric Surgery. All rights reserved. http://dx.doi.org/10.1016/j.soard.2012.10.009

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E. Contini et al. / Surgery for Obesity and Related Diseases 9 (2013) 417–422

Fig. 1. Staple line firing orientation and location with respect to the pylorus.

ECR60G and EGIA60AXT. Each manufacturer’s most recent stapler handle was also used for this study: Ethicon’s Echelon Flex 60 (EC60A) and Covidien’s Endo GIA Universal Ultra (EGIAUSTND). Study protocol Stomachs were stored individually and thawed to room temperature before testing. Sixty-millimeter linear reloads were used to divide the tissue along the greater curvature of the stomach, normal to the greater curve, toward the lesser curve [5]. All firings were made on double wall (anterior and posterior) of the stomach, and the distance from the pylorus was documented (Figs. 1 and 2). Staplers were loaded and fired according to the manufacturers’ instructions for use (IFU) [3,4] in the nonarticulated position. Each device was clamped on the tissue for 15 seconds and fired in a controlled and consistent manner, as would be performed during an actual surgery. After each firing of the EC60A, the cartridge was removed and the stapler was rinsed in a beaker of water and then wiped down with gauze. After the Covidien product was fired, the reload was removed and discarded. The maximum number of firings for each manufacturer’s stapler was followed per the respective IFU (12 firings for the EC60A and 25 firings for the EGIAUSTND). After each firing, the tissue was dissolved from the staple line through the use of a chemical dissolution process; the staples were recovered and then mounted flat on a data sheet by an individual skilled in the art. To ensure an unbiased analysis, each staple firing was identified only by the date, a tissue sample identifier, staple line length, and distance from pylorus.

Fig. 2. Representative photo of firings in explanted porcine stomach.

Study analysis Mounted staples were measured by technicians skilled in the art, using a calibrated optical microscope and associated measurement software. Technicians were also blinded to the staple manufacturer. The level of undercrimp of each staple was determined by the distance from the back span to the closest tip of the staple (Fig. 3), and ‘‘malforms’’ were identified per Covidien’s standard quality control metrics. Any staple that had at least one leg less than parallel to the back span or both legs parallel to the back span was considered a malformed staple (Fig. 4). Statistical methods Statistical analysis was performed using Minitab statistical software (Minitab Inc., version 15.1, State College, PA). Undercrimp evaluation. Data sets were non-normal, due to an inherently large number of zeros. A Mood’s median

Fig. 3. Example of an under crimp measurement (x) on a formed staple.

Comparison of Endostapler Performance / Surgery for Obesity and Related Diseases 9 (2013) 417–422

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Fig. 4. (A) Example of a malformed staple, where one leg is less than parallel to the back span; (B) example of a malformed staple, where both legs are parallel to the back span.

test and a Kruskal-Wallis ranked median test with a ¼ .05 to compare the medians were conducted. H0: The population medians are all equal. H1: The medians are not all equal.

Malformed staples evaluation. The number of malformed staples found at each location was compared with the total number of staples evaluated at each location, per stapler. Statistical analysis was performed using a test of 2 proportions with a Fisher’s exact test with a ¼ .05. Results This study evaluated 47000 staples; there were no incidences of device failures or misfires for either manufacturer. Examples of malformed and undercrimped staples from this study can be seen in Fig. 5, and well-formed staples can be seen in Fig. 6.

Fig. 5. Location B. (A) Example of malformed staples; (B) example of undercrimped staples.

ranked median test with a ¼ .05 produced the same results at each location. Malformed staples For locations B, C, D, E, and F, the test of 2 proportions shows sufficient evidence to reject the null hypothesis and conclude there is a difference in proportions between the 2 groups (Fig. 8), indicating that the EGIA60AXT results in fewer malformations than the ECR60G (P ¼ .000 for Fisher’s exact test). The 95% CI for the difference in proportions does not include zero. For locations A and G (Fig. 8), the test of 2 proportions shows insufficient evidence to reject the null hypothesis that there is no difference in proportions between the 2 groups (P ¼ .408 and 1.000, respectively, for Fisher’s exact test).

Undercrimped staples The results of the Mood’s median test to compare the medians for undercrimp data, comparing Covidien and Ethicon at all locations in the stomach (Fig. 7), indicated that there is sufficient evidence to conclude that the median of undercrimp values for EGIA60AXT is lower than that of undercrimp values for ECR60G (P ¼ .000). A Kruskal-Wallis

Fig. 6. Location F. Example of well-formed staples.

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Fig. 7. Interval plot of median values for each stapler at each location.

In both cases, the 95% CI for the difference in proportions includes zero.

Discussion The capability of a stapler to form an aligned B-shaped staple is accepted as one of the most important indications of a secure anastomosis. This study was conducted to provide some evidence regarding how each manufacturer’s thick tissue reload performed when used in a tissue model that replicates the more challenging and variable tissue that a surgeon may encounter during clinical procedures. Mechanical stapling devices provide a quick and easy method to seal and divide tissue during surgical procedures. Although it is well understood that appropriate surgical technique is essential to ensure satisfactory vascular supply and tissue alignment, the stapling device’s ability to perform reliably and repeatedly, especially in the more challenging and variable tissue, is essential to provide appropriate tissue apposition. Clinically, a causal relationship between staple formation and uncomplicated anastomotic healing has always been assumed, with a properly formed B shape accepted as the ideal staple configuration. Both devices form B-shaped staples from titanium wire to appose and compress the tissue, as well as transect the tissue between 3 rows of staggered formed staples. Properly formed staples correlate to appropriate tissue apposition, hemostasis, and leak resistance. Malformed or underformed staples result in poor tissue apposition and are associated with adverse clinical outcomes, namely bleeding and anastomotic leaks, which represent a significant source of morbidity and mortality and are frequently associated with extended hospital stays and increased healthcare costs [8–11]. Challenging tissue is often found in bariatric procedures, particularly in the central region of the stomach [5], where (in the gastrointestinal tract) it is paramount that staple line failures are avoided to reduce the risk of sepsis. In their

review article on laparoscopic sleeve gastrectomy, Bellanger and Greenway discuss the importance of promoting proper staple formation to minimize the chance of leaks [12]. A study investigating stomach thickness from excised sleeve gastrectomies found that the tissue thickness varies significantly from the esophageal junction to the pylorus [7]. An important design goal for laparoscopic stapling device manufacturers is to improve the performance of the devices for the more challenging and variable tissue encountered during surgery. Improving stapling devices’ reliability and performance will reduce certain clinical adverse events associated with these more challenging clinical applications. Intraoperatively, surgeons have 2 means to evaluate the integrity of the staple line: visually inspect the line for proper formation or perform a leak test. Visual inspection of the staples is often difficult because of location and excessive tissue masking the staples. When leak testing is performed, there is no set standard for the amount of pressure applied to the anastomosis and the tissue may be held in apposition well enough by a poor staple line to prevent acute leakage; however, it will slowly lose integrity, which could cause a postoperative leak. There are several limitations to the present study. The ex vivo tissue model does not allow the assessment of clinical relevant metrics: hemostasis, healing, or trauma, such as serosal tearing and bruising. In addition, no comparative testing, such as leak pressure testing, was performed; this type of testing could provide an important correlation between staple formation and anastomotic integrity. Also, the engineers responsible for mounting and measuring the staples were blinded to staple manufacturer and stomach location, and all testing and analysis were completed in a Covidien laboratory by Covidien personnel and were not verified by a neutral observer.

Fig. 8. Percentage of malformed staples at each location for each stapler.

Comparison of Endostapler Performance / Surgery for Obesity and Related Diseases 9 (2013) 417–422

Conclusion This study found that in more challenging and variable tissue applications, the EGIA60AXT reload had superior performance compared with the ECR60G reload with respect to B-shaped staple formation and the incidence of malformed staples. These stapler performance metrics indicate a stapler’s ability to perform reliably and consistently, especially when used in challenging and variable tissue; they may be associated with reducing anastomotic complications, such as dehiscence or postoperative leaks, as noted in many peer-reviewed publications. Disclosures The authors are employees of Covidien Surgical Solutions which solely funded this work. Note added in proof: Following ‘‘in press’’ publication, the Disclosure information was corrected as shown above. References

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[3] Manufacturer’s instruction for use by Covidien, North Haven, CT, USA. [4] Manufacturer’s instruction for use by Ethicon Endo-Surgery Inc., Cincinnati, OH, USA. [5] Nakayama S, Hasegawa S, Nagayama S, et al. The importance of precompression time for secure stapling with a linear stapler. Surg Endosc 2011;25:2382–6. [6] Baker RS, Foote J, Kemmeter P, Brady R, Vroegop T, Serveld M. The science of stapling and leaks. Obes Surg 2004;14:1290–8. [7] Elariny H, Gonzalez H, Wang B. Tissue thickness of human stomach measured on excised gastric specimens from obese patients. Surg Tech Int 2005;14:119–24. [8] Almahmeed T, Gonzalez R, Nelson LG, Haines K, Gallagher SF, Murr MM. Morbidity of anastomotic leaks in patients undergoing Roux-en-Y gastric bypass. Arch Surg 2007;142:954–7. [9] Buchs NC, Gervaz P, Secic M, Bucher P, Mugnier-Konrad B, Morel P. Incidence, consequences, and risk factors for anastomotic dehiscence after colorectal surgery: a prospective monocentric study. Int J Colorect Dis 2008;23:265–70. [10] Lee S, Carmody B, Wolfe L, et al. Effect of location and speed of diagnosis on anastomotic leak outcomes in 3828 gastric bypass cases. J Gastrointest Surg 2007;11:708–13. [11] Platell C, Barwood N, Dorfmann G, Makin G. The incidence of anastomotic leaks in patients undergoing colorectal surgery. Colorect Dis 2006;9:71–9. [12] Bellanger DE, Greenway FL. Laparoscopic sleeve gastrectomy, 529 cases without a leak: short-term results and technical considerations. Obes Surg 2011;21:146–50.

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Editorial comment

Comment on: Comparison of endostapler performance in challenging tissue applications Despite the significant advances in stapling made over the decades, much remains to be understood about the interaction of surgical staples and tissue. We know that a multitude of factors affect stapler performance: some within the control of the manufacturer, some within control of the clinician, and some controlled by neither. We also know that only careful science and well-designed studies will yield the desired new insights. Although appearing to reveal differences in 2 manufacturers’ stapler performance, the article by Contini et al. instead demonstrates the importance of solid experimental design to study conclusions. The study design fails to control important variables and makes potentially faulty assumptions, resulting in conclusions that may not be valid. A basic tenet of good study design is to minimize or remove all potentially confounding variables except for the one of interest. Only then can results be attributed to a specific factor.

As soon as a second variable is introduced, experimental design becomes more complicated. In the case of the Contini et al. study, staple leg length—a factor presumably key to staple formation—is not controlled; that is, the staple cartridges from the 2 manufacturers had 2 different leg lengths. Staple formation with Covidien Tri-Staple EGIA60 AXT reloads (4to 5-mm staple leg lengths) was compared with that with Ethicon ECR60 G reloads (4.1-mm staple leg lengths). It is clear to the observant reader that, given equivalent tissue thickness, staple formation would not necessarily be the same. Adequate staple form can occur only if the penetrating legs of the staple (1) are able to pass through the material to be held and (2) still have sufficient length to fold in the pockets of the stapler’s anvil to make the desired B-form. Solid experimental design would dictate measurement of staple formation on equivalent tissue thicknesses. Although staple line locations and orientations were provided, there is