Increased staple loading pressures and reduced staple heights in laparoscopic sleeve gastrectomy reduce intraoperative bleeding.

Abstract

Background:

In laparoscopic sleeve gastrectomy (LSG), tissue thickness (TT) and closed staple height (CSH) of the staple cartridge determine the pressure applied to the tissue. Prior studies have suggested 8g/mm² to be ideal to minimize leaks or bleeding.

Methods:

We evaluated the relationship between staple loading pressure (SLP) applied to gastric tissue and bleeding rate prospectively with a novel tissue measuring device and video-recorded operative findings for 116 patients undergoing LSG performed by two surgeons at a single institution. Stapling Protocol 1 (SP1) was used for 64 cases, defined as standard practice, typically using green-blue-blue-blue Ethicon staple cartridges. Stapling Protocol 2 (SP2) was defined as blue-blue-white-white or gold-blue-white-white.

Results:

TT measurements from 39 cases and staple load selection showed that surgeons preferred a median SLP of 15 g/mm². TT measurements at 15 g/mm² had a mean of 1.86 mm at the antrum, 1.71 mm at the body, and 1.15 mm at the fundus, all significantly thinner than TT at 8 g/mm². For each 10 g/mm² increase in minimum pressure and maximum pressure value within each cartridge zone, there was a reduction in bleeding rate by 59.8% and 38.7%, respectively. Compared to SP1, SP2 had a lower intraoperative bleeding rate (90.2% vs 70.7%, p<0.0001), usage of preventive hemostatic techniques (100% vs 10%, p<0.0001), and hemostatic treatments (66% vs 46%, p=0.04). In 30-day postoperative period, there was one bleed in SP1; there were no leaks.

Conclusions:

Our data suggest using shorter CSHs to exert higher SLPs decreases intraoperative bleeding rates in LSG.

Using smaller staples to exert higher staple loading pressures than previously suggested in laparoscopic sleeve gastrectomy can reduce intraoperative bleeding. This leads to decreased use of hemostatic agents and techniques.

Introduction

Surgical weight loss techniques, especially laparoscopic sleeve gastrectomy (LSG), are increasingly popular worldwide to combat the spread and severity of morbid obesity. In LSG, the lateral portion of the stomach is simultaneously sealed and resected using surgical endocutter staplers. Several studies have demonstrated that there is a significant variation in stomach tissue thickness (TT) not only between individuals, but also between locations along the stomach itself^1–3. There has been limited research on TT of the stomach and there is much discordance amongst the available literature, likely due to the high variability of stomach tissue thickness and small study sizes. For example, multiple studies have found the stomach to be thickest at the antrum, thinner at the midbody, and thinnest at the fundus^1,2. However, even this widely accepted pattern of tissue thickness was found to be not universally applicable³. Additionally, one study found the male gender to be associated with thicker stomach tissue compared to female patients at all locations¹, while another study found that male stomach tissue was thicker only at the antrum².

For optimal tissue apposition that prevents bleeding and leakage, the closed staple height (CSH) must be appropriate for the tissue thickness^4,5. A taller CSH may result in a lower staple loading pressure (SLP), resulting in inadequate tissue apposition. Conversely, a shorter CSH may result in an excessive SLP, resulting in ischemia or mechanical tissue damage. In both cases, staple line leakage or bleeding can occur ^4,5. In order to accommodate different TTs, staples with different closed staple heights are available for use during LSG⁶. Most modern surgical staples, including the Echelon Flex GST System (Ethicon, Inc.), are indicated for use with TT measurements performed at 8 g/mm², as recommended by Astafiev in 1967⁷. This is the only study to investigate the goal pressure to achieve hemostasis of the cut edge of two sides of several tissue types in a canine model. However, of the studies that have used 8 g/mm², there is a large difference between the measured TT and the CSH^1–3,8. In practice, many surgeons have developed their own preferences for the sequence of staple cartridges they use along the LSG staple line, allowing for deviations based on TT assessment by surgeon gestalt derived from visual inspection and tactile feedback from laparoscopic instruments. It has been shown that this assessment has an accuracy of 0–38% and that surgeons tend to stick to their preferred staple cartridges even when a different CSH may have been more appropriate³. A recent study also showed that in clinical practice, surgeons preferred shorter CSHs than recommended by Ethicon, meaning they preferred more pressure applied to the gastric tissue than Astafiev had recommended. The Echelon Flex GST system (Ethicon, Inc) used by our surgeons is the system recommended by Ethicon for LSG⁹. Our surgeons typically use green-blue-blue-blue with some deviation depending on intraoperative visual inspection and tactile feedback. This is in accordance with the International Sleeve Gastrectomy Expert Panel Consensus Statement in 2012, which states that surgeons should never use any staple with CSH less than that of a green load (2.0mm) in the antrum or staples with a CSH less than that of a blue load (1.5mm) on any part of sleeve gastrectomy¹⁰.

Although LSG has evolved into a safe and effective surgery, post-operative leak and bleeding from the staple line remain the most serious complications that arise in 1–3% of cases¹¹. In our experience, intraoperative bleeding is much more common and surgeons often use preventive hemostatic techniques with additional hemostatic treatments as necessary. Using freshly excised human gastric tissue, we aimed to first, indirectly measure the compressive pressure the average staple applies to tissue and second, develop and evaluate the clinical outcomes of a data-driven staple cartridge selection algorithm based on that pressure.

Methods

All eligible patients 18 years and older who were undergoing LSG performed by two surgeons at University of Cincinnati Health West Chester Hospital over a six month period were included. Those with previous gastric band history were excluded. A total of 116 patients were enrolled. Patient demographics were reviewed. This quality improvement project was determined to be ‘not human subjects research’ by the institutional review board of the University of Cincinnati (IRB#2017–2793).

LSGs were performed by the two surgeons per standard practice, using 60mm Echelon Flex™ Powered Plus Stapler with GST staple reloads (Ethicon, Inc.). Surgeons marked sites 1 cm lateral to the gastroesophageal junction, 3 cm from incisura angularis, and 6 cm from pylorus perpendicularly to serve as a guide for the staple line. Their standard practice for intraoperative staple cartridge selection, typically green-blue-blue-blue with room for deviations, was used to define Stapling Protocol 1 (SP1).

For the first 39 cases, freshly excised stomach tissues were studied immediately after surgery. All measurements were taken using a portable Tissue Measuring Device (TMD, Figure 1). TT was measured every 10 mm along the staple line at 5 mm perpendicularly away from the staple line, using sequential loads of 100 g, allowing for 15 seconds of equilibration. The exact load necessary to achieve CSH was estimated via linear interpolation. The load values were converted into pressures using TMD surface area of 34.21 mm². TT at relative distances from antrum in relation to total staple line at both 8 g/mm² and the median pressure necessary to achieve CSH were derived via linear interpolation. For the first 64 cases performed under SP1, de-identified video recordings of LSG procedures provided data on intraoperative bleeding by cartridge zone and hemostatic techniques used. In order to be as objective as possible, we used a very strict criterion for intraoperative bleeding, defined as any visible bleeding at the staple line, either before or after any hemostatic techniques are used.

Figure 1.

Standard Bariatrics tissue measuring device (TMD).

Based on the TT findings, the next 52 cases were performed under Stapling Protocol 2 (SP2), which typically consisted of cartridge sequences of blue-blue-white-white for one surgeon and gold-blue-white-white for the other, allowing for intraoperative deviations. All other aspects of LSG remained unchanged. Data on intraoperative bleeding rates by cartridge zone and hemostatic techniques used were derived from de-identified video recordings for 52 cases. Intraoperative bleeding was defined as any visible bleeding along the staple line. In addition, 30-day postoperative bleeding and leak data were collected for all cases in SP1 and SP2.

Statistical analysis

Data collection and storage were performed using Microsoft Excel (Redmond, WA). Continuous variables are expressed as mean ± standard deviation (SD) or with 95% confidence interval reported as (95% CI: lower limit, upper limit). Student’s t-test was used to compare continuous variables. Categorical data were analyzed using Fisher’s exact test and Chi-square test. Mantel-Haenszel Chi-square test was used for ordinal data. Cartridge zones 4–6 were combined due to the small number of samples that required more than 4 cartridges. A p value of less than 0.05 was considered significant.

Results

There were no significant differences in demographic data between SP1 and SP2, as illustrated in Table 1.

Table 1.

Demographic data in SP1^* and SP2^†.

		SP1	SP2	P value
n		57	51	-
Age (years)		41.8 ± 11.4	44.5 ± 11.5	0.2238
Female		49 (86%)	48 (94%)	0.2102
BMI‡ (kg/m2)		49.1 ± 9.6	46.5 ± 7.8	0.1282
Race	Caucasian	43 (75%)	34 (67%)
	African American	12 (21%)	14 (27%)
	Hispanic	2 (4%)	2 (4%)
	Not specified	0 (0%)	1 (2%)

^*SP1, stapling protocol 1.

^†SP2, stapling protocol 2.

^‡BMI, body mass index.

The closed staple height in the tissue was defined as indicated by the manufacturer (White 1 mm, Blue 1.5 mm, Gold 1.8 mm, Green 2.0 mm, and Black 2.3 mm). The distribution of load required to achieve CSH is shown in Figure 2. Median load to achieve CSH was found to be 517 g (IQR 250 – 890 g), corresponding to a median pressure of 15 g/mm² (IQR 7 – 26 g/mm²).

Figure 2.

Distribution of load required to achieve CSH. Exact load values that would lead to CSH were calculated by interpolation. Vertical lines denote loads corresponding to previously reported 8g/mm² (274g) and median pressure of 15 g/mm² (517g).

The tissue thickness was indexed to length to generate relative distance maps from the antrum of the stomach, using the entire staple line length as 1.0. At 8 g/mm², mean TTs were 2.13 mm at the antrum, 1.99 mm at the body, and 1.37 mm at the fundus (Figure 3A). At 15 g/mm², mean TTs were 1.86 mm at the antrum, 1.71 mm at the body, and 1.15 mm at the fundus (Figure 3B). At each location along the staple line, TT at 15 g/mm² was significantly shorter than TT at 8 g/mm² (Table 2).

Figure 3.

TT map along the staple line at constant pressure. Red dots indicate mean values. a) TT map at 8g/mm² and b) TT map at 15g/mm².

Table 2.

TT^* under a pressure of 15g/mm² is significantly thinner than under 8g/mm² at all locations along the staple line.

Relative distance from antrum	0.1	0.2	0.3	0.4	0.5	0.6	0.7	0.8	0.9
Mean TT at 8 g/mm2 (mm)	2.01	2.13	2.13	2.04	1.99	1.77	1.57	1.48	1.37
Mean TT at 15 g/mm2 (mm)	1.76	1.86	1.86	1.77	1.71	1.53	1.33	1.27	1.15
P value	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001	<0.0001

^*TT, tissue thickness.

With SP1, for each 10 g/mm² increase in minimum pressure value within the cartridge zone, defined as the lowest recorded pressure to achieve CSH in each cartridge zone, the odds ratio for bleeding rate was found to be 0.41 (95% CI: 0.21 – 0.81). This meant that there was a 59% reduction in bleeding rate per 10 g/mm² increase in minimum pressure value. Similarly, for each 10 g/mm² increase in maximum pressure value within cartridge zone, the odds ratio for bleeding rate was found to be 0.61 (95% CI: 0.42 – 0.89), corresponding to a 39% reduction in bleeding rate for every 10 g/mm² increase in maximum pressure value.

Video review of SP1 and SP2 procedures demonstrated a significant difference in the intraoperative bleeding rates between groups. (Table 3) There was a significantly lower rate of bleeding using SP2 compared to SP1 (70.7% vs. 90.2%, p<0.0001). There was a significant difference in bleeding rates by cartridge zone, with an overall decreasing trend in bleeding rate with increasing cartridge zone (further from antrum). Cartridge zone 1 (closest to antrum) had the highest bleeding rate (96.5%).

Table 3.

Rate of bleeding in SP1^* and SP2^†, by staple cartridge color and zone.

		Bleeding by staple cartridge
		n	Yes n (%)	No n (%)	P value
Total		494	405 (82.0)	89 (18.0)
Protocol	SP1	272	248 (91.2)	24 (8.8)
	SP2	222	157 (70.7)	65 (29.3)
Cartridge zone	1	113	109 (96.5)	4 (3.5)
	2	113	92 (81.4)	21 (18.6)
	3	113	95 (84.1)	18 (15.9)
	4–6	115	109 (70.3)	46 (29.7)

^*SP1, stapling protocol 1.

^†SP2, stapling protocol 2.

Hemostatic agents and methods used by the two surgeons are shown in Table 4. There was a significantly decreased usage of preventative hemostatic methods (oversewing and Tisseel (Baxter) application) using SP2 compared to SP1 (10% vs. 100%, p<0.0001). There was also a significant reduction in total hemostatic treatments (clips, cautery, and Floseal application) used with SP2 compared to SP1 (46% vs. 66%, p=0.04).

Table 4.

Hemostatic methods used in SP1^* and SP2^†.

Hemostatic methods		SP1 n (%)	SP2 n (%)	P value
n		57	51
Preventive		57 (100)	5 (10)	<0.0001
	Oversew	29 (51)	0 (0)	<0.0001
	Tisseel	28 (49)	5 (10)	<0.0001
Treatment		39 (68)	23 (45)	0.0194
	Clips	19 (33)	8 (16)	0.0453
	Cautery	17 (30)	20 (39)	0.3186
	Floseal	13 (23)	5 (10)	0.0777

^*SP1, stapling protocol 1.

^†SP2, stapling protocol 2.

Total 30-day postoperative complication rates were 1.8% and 0% in SP1 and SP2, respectively. There was one incident of 30-day postoperative complication, which was bleeding in SP1. There were no staple line leaks in either group.

Discussion

In this project, we examined freshly excised human stomach tissue and intraoperative bleeding data from LSGs using staple cartridges of different CSHs. To our knowledge, we are first to examine freshly excised stomach TT at pressures beyond 8 g/mm² and investigate intraoperative bleeding rate utilizing higher stapling pressures with shorter staple heights. We have shown that the median loading pressure on the stomach under stapling conditions is 15 g/mm², significantly greater than the widely accepted pressure of 8 g/mm². Our results also suggest that use of shorter CSHs can significantly reduce intraoperative bleeding.

In LSG, the pressure of 8 g/mm², originally reported by Astafiev⁷, is widely regarded as the ideal loading pressure for adequate tissue apposition without causing tissue injury. Our results show that the staple cartridges typically used actually exert a much higher median pressure of 15 g/mm² on the gastric tissue. Given the fact that Astafiev only studied the clamping pressure to stop cut edge bleeding in canine tissue and did not deploy any staples or look at any stapled tissue, we believe that our loading pressure is more valid for use in LSG. Our higher loading pressure is in agreement with a recent study that showed that surgeons seem to prefer shorter CSH than recommended for exerting a pressure of 8 g/mm², meaning they prefer a higher loading pressure⁸. This new loading pressure of 15 g/mm² should be considered for use in future studies to mimic clinical stapling biases and for development of new stapling devices. Of note, we found the interquartile range of pressures exerted on gastric tissue to be unusually large (19 g/mm²), despite the large sample size. This wide distribution is likely due to variability of the true gastric TT along the staple line, as well as human error introduced by the surgeon’s staple cartridge selection. In LSG, it is difficult to accurately gauge the true thickness of the gastric tissue, since the surgeon must rely on visual inspection and indirect tactile feedback from laparoscopic instruments. The variability in pressure exerted on gastric tissue further illustrates the need to better characterize the TT for optimal staple cartridge selection. It also demonstrates the wide range of clinically acceptable pressure, as there was only 1 clinical bleed and no leaks in our study.

By recording TT under various pressures, we were able to produce a TT map along the length of the gastric staple line. The results provide a better understanding of the true relationship between TT and loading pressure, and therefore the CSH. The updated pressure of 15 g/mm² was shown to compress the gastric tissue significantly more than the 8 g/mm², emphasizing the discrepancy between published data and current clinical practice. Our map shows that TT decreases with increasing distance from the antrum. This is in agreement with the previously reported data^1–3. Of note, the point closest to antrum (relative distance of 0.1) was the only location that was shorter than the TT at the subsequent location. This is likely due to the tissue extrication process, which is discussed below.

Optimal tissue apposition is thought to require enough pressure to seal the two sides, but not enough pressure to cause crush injury^4,5. Therefore, intraoperative bleeding can be caused by both inadequate and excessive pressure exerted on the gastric tissue. We found that for every 10 g/mm² increase in minimum and maximum pressure values within each staple cartridge zone, there was 59.8% and 38.7% reduction in bleeding rate, respectively. This suggests that intraoperative bleeding in SP1 was caused predominantly by inadequate pressure. Of note, Ghosh et al. found that intraoperative bleeding rates in LSG were reported to be anywhere from 0.42% to 4.07%¹². This is significantly lower than our intraoperative bleeding rate of 90.2% with SP1. As Ghosh et al. suggested, this is likely due to underreporting in the literature and precautionary use of preventive hemostatic techniques, as well as a difference in the definition of intraoperative bleeding. In order to be as objective as possible, we used a very strict criterion for intraoperative bleeding, defined as any visible bleeding at the staple line, either before or after any hemostatic techniques are used. While not every recorded incidence of bleeding necessarily resulted in an intervention, the bleeding rate is interpreted in the context of concurrent changes in rate hemostatic agent usage, as discussed below.

Given our preliminary results, the surgeons opted to change their stapling protocol to use staples with shorter heights, increasing the pressure exerted on the gastric tissue. This led to development of SP2. Overall intraoperative bleeding rate decreased with the new protocol, with concurrent decrease in use of hemostatic methods. Methods to prevent staple line bleeding were used less frequently with SP2. It is important to note that these are heavily susceptible to surgeon bias by nature since each surgeon needs to predict the need for preventive techniques intraoperatively. However, the fact that there was a significant decrease in all hemostatic treatments used despite the 90% reduction in preventive technique usage confirms better intrinsic hemostatic control with SP2. While the 30-day postoperative bleeding or leak rates were very low in both groups, it is worth noting that the only case of complication was a bleed in the SP1 group. To our knowledge, there are no other studies that show the effects of hemostatic techniques or CSH on intraoperative bleeding rates or postoperative complication rates. Very high staple loading pressures were recorded when SP1 was used. We did not measure the indirect pressures during SP2. Given that the cartridge selection went from green-blue-blue-blue (SP1) to gold-blue-white-white or blue-blue-white-white (SP2), we can infer that the median pressure likely exceeded 15 g/mm² and likely resulted in an even greater maximum pressure than was observed in SP1 (80 g/mm²). Despite this change in staple loads and associated pressures, there were no leaks in either group. Although staple line over-compression is often suggested as the causal mechanism for ischemia, necrosis, and leak, it has long been known that staple lines themselves have little to no perfusion¹³. More recently, with the advent of indocyanine green (ICG) fluorescence, staple lines without perfusion can be observed without causing leaks¹⁴. Many ICG studies only evaluate blood flow to the staple line, not at the staple line itself. A rat model of sutured colonic anastomoses, under the highest possible tension, has also confirmed that the absence of blood flow between the tight sutures does not generate leak¹⁵. Thus, over-compression by staples leading to ischemia, necrosis and leak does not seem to be a substantiated risk in this study.

There are several limitations to this study. First, the TT measurements were taken adjacent to the staple line, because the excised stomach specimens had already been stapled. Second, the resected stomach tissue was removed from the abdomen per standard practice, by firmly grasping the antrum end with a Kelly clamp and pulling through the laparoscopic incision. This tissue compression and stretching likely led to a thinner mean TT at the antrum end. Given the higher bleeding rate in the corresponding cartridge zone, further studies are needed to better characterize the TT in this region. In order to minimize systematic error due to the extrication process and indirect approximation of TT, a laparoscopic device would be necessary for measuring the true TT along the staple line prior to stapling, as previously proposed by Huang and Gagner³. Given the variability of the gastric TT, such a device may prove to be extremely valuable in preventing intraoperative bleeding in LSG. Previous studies show that the current clinical practice of estimating tissue thickness by tactile-feedback is often done incorrectly³, also indicating the desirability of a more objective method to be used in the operating room. An objective method of assessing tissue thickness would aid in staple cartridge selection, resulting in a lower rate of bleeding and leakage at staple line. Third, in order to obtain the pressure at CSH, we had to linearly interpolate between existing data points, which introduced a margin of error. While the relationship between weights and TT were non-linear as we had expected, there was no suitable alternative model. In addition, there was an assumption that the closed staple height of the cartridge provided by the manufacturer results in the same closed staple height in tissue. Lastly, while the 30-day postoperative data suggests no impact on clinical outcome, postoperative complication rates derived from a larger sample with a longer follow-up period may be warranted in future investigations.

Conclusions

Our experience demonstrates that the use of higher loading pressures and shorter CSHs in LSG is not only biomechanically acceptable, but also yields better tissue apposition. We show that by using staple cartridges with shorter CSHs, we can reduce both intraoperative bleeding and hemostatic techniques used.

Abbreviations:

LSG

laparoscopic sleeve gastrectomy

TT

tissue thickness

CSH

closed staple height

SLP

staple loading pressure

SP

stapling protocol

TMD

tissue measuring device

SD

standard deviation

CI

confidence interval

BMI

body mass index

ICG

indocyanine green