Selective Non-Operative Management After Abdominal Gunshot and Blast Injuries in A Porcine Model

Summary

This work describes the establishment of porcine models of abdominal gunshot and blast injuries, provides the outcomes of selective non-operative management (SNOM) and immediate laparotomy in injured pigs, and emphasizes the need for careful observation and predefined criteria for conversion to surgery.

Abstract

The role of selective non-operative management (SNOM) after gunshot and blast injuries has been increasingly recognized but not explored in animal models. Overall, 24 male pigs were prepared, of which 12 were used to create a gunshot wound model, and the remaining 12 a blast injury model. Animals in each injury model were randomly divided into immediate surgery and SNOM groups using a computer-generated random sequence. Gunshot injury was created by firing a 7 mm, 1.45 g steel ball at the right upper abdomen from 10 cm under 170 bar. Blast injury was created by exposing the right upper abdomen to a high-pressure shock wave from 6 cm under 170–190 bar. In the SNOM group, focused assessment with sonography for trauma (FAST) was performed immediately after modeling and repeated when hemodynamic instability or clinical deterioration was suspected. Conversion to surgery was triggered by persistent heterogeneous echogenicity or hypoechoic fluid on FAST, hemodynamic instability, or progressive clinical deterioration. The primary outcome was the 7-day SNOM outcome. SNOM failure was defined as conversion to surgery or death. After gunshot injury modeling, the 7-day survival rate was 91.67% (11/12). In the immediate surgery group, 2 pigs underwent therapeutic laparotomy, and 4 underwent negative laparotomy. In the SNOM group, 1 pig underwent conversion to surgery, 1 died of hemorrhagic shock on day 1 after modeling, and 4 successfully completed SNOM. After blast injury modeling, the 7-day survival rate was 100% (12/12). In the immediate surgery group, 3 pigs underwent therapeutic laparotomy, and 3 underwent negative laparotomy. In the SNOM group, 2 pigs underwent conversion to surgery, and 4 completed successful SNOM. This work describes the establishment of preliminary injured porcine models, presents representative outcomes of the SNOM and immediate laparotomy strategies, and underscores the need for close monitoring when using the SNOM strategy.

Introduction

During World War I, mandatory laparotomy was considered the standard treatment for penetrating abdominal injuries to reduce mortality¹. In 1974, Nance et al. first reported the advantages of selective non-operative management (SNOM) over routine surgery for abdominal penetrating injuries². Since then, the SNOM strategy has been increasingly recognized, because it may reduce hospital stay and hospitalization costs, and avoid the risk of complications associated with non-therapeutic laparotomy^3,4,5. It has been reported that SNOM can effectively avoid 25–47% of non-therapeutic laparotomies⁶. Nevertheless, its clinical applicability in abdominal gunshot and blast injuries remains less clearly defined^7,8. Some surgeons still prefer exploratory laparotomy as the initial treatment strategy, even in patients who meet the criteria for non-operative management⁹. Among adult patients with abdominal gunshot wounds, 73.00% undergo laparotomy, of which 10% are deemed unnecessary¹⁰. The incidence of complications following negative laparotomy can reach as high as 20.00–40.00%¹¹.

Until now, existing studies on the application of SNOM in patients with abdominal gunshot wounds and blast injuries have focused on clinical scenarios^{8,12,13,14,15}. To the best of our knowledge, very few animal studies regarding SNOM have been available. In animal models, experimental conditions can be controlled and adjusted; by contrast, in clinical scenarios, numerous and complex confounding factors are present. Additionally, in animal models, repeated serial measurements are allowed within a relatively short period, thereby providing essential data for evaluating novel clinical management strategies; however, the multisystem complexity of human combat trauma cannot be fully replicated. Compared with small animal models or clinical observational studies, porcine models permit abdominal focused assessment with sonography for trauma (FAST), laparotomy, and serial blood sampling under controlled experimental conditions. This study aims to establish porcine models of abdominal gunshot and blast injuries and to compare their outcomes after SNOM and immediate surgery.

Protocol

This study was approved by the Animal Ethics Subcommittee of the General Hospital of Northern Theater Command (Ethical Approval Number: 2024–23) and conducted in accordance with the ARRIVE guidelines (Animals in Research: Reporting In Vivo Experiments)¹⁶. All pigs were provided and maintained by the Laboratory Animal Center of the General Hospital of Northern Theater Command.

1. Grouping

1. Use 24 male Landrace pigs aged 4 months, with an average body weight of 27.7 kg and a range of 25–30 kg.
2. House each pig individually in a standard cage for at least 48 h before the experiment.
3. Randomly assign 24 pigs to the gunshot injury model group (n = 12) or the blast injury model group (n = 12) using a computer-generated random sequence.
4. Further, randomly assign the pigs in each injury model group to the immediate surgery group (n = 6) or the selective non-operative management (SNOM) group (n = 6) using the same randomization method (Figure 1).
5. Define the surgical and SNOM outcomes as follows: immediate surgery refers to planned laparotomy performed immediately after injury modeling; therapeutic laparotomy refers to laparotomy requiring active surgical intervention for ongoing hemorrhage or surgically treatable visceral injury; negative laparotomy refers to laparotomy without active bleeding or surgically treatable abdominal injury; conversion to surgery refers to laparotomy performed after initial SNOM; SNOM failure refers to conversion to surgery or death during the 7-day observation period; and successful SNOM refers to completion of the 7-day observation period without conversion to surgery or death.

2. Anesthesia and preparation before modeling

1. Fast each pig for at least 12 h before injury modeling and allow free access to water.
2. Induce general anesthesia through the auricular vein using 1% propofol at a dose of 0.8 mL/kg. Administer an additional 2–4 mL of propofol when required to achieve adequate anesthesia.
3. Maintain anesthesia throughout the experiment by continuous infusion of propofol at a dose of 1.2 mg/kg/h.
4. Confirm adequate anesthesia by the absence of corneal reflex, dilated pupils with diminished light reflex, and natural relaxation of the limbs.
5. Place each pig in the supine position after adequate anesthesia is achieved.
6. Intubate each pig with a 7.5F endotracheal tube under laryngoscopy to maintain airway patency.
7. Maintain spontaneous respiration when vital signs remain stable, and provide positive-pressure ventilation in cases of apnea, labored breathing, or oxygen desaturation.
8. Confirm stable vital signs for 10 min before injury modeling.
9. Do not perform prophylactic fluid loading before injury modeling. During the perioperative period, administer warm normal saline only as maintenance or rescue fluid when clinically required. Persistent hypotension or progressive clinical deterioration is used as an indication for immediate surgical exploration or conversion to surgery, rather than prolonged conservative resuscitation.
10. Do not administer blood products during the experiment. When hemorrhage is identified, achieve hemorrhage control by surgical hemostasis in animals assigned to immediate surgery or converted to surgery, rather than transfusion-based resuscitation.

3. Model establishment

1. Place each anesthetized pig in the right lateral decubitus position.
2. Transfer the pig to the multifunctional animal trauma modeling platform at the institution (Figure 2).
3. Identify the target site in the right upper quadrant, immediately below the right costal margin.
4. Mark the target point approximately 27 cm above the pubic symphysis (range: 25–30 cm) and 2 cm lateral to the midline.
5. Establish the gunshot injury model by vertically firing a small steel ball, 7 mm in diameter and 1.45 g in weight, at the marked abdominal point from a distance of 10 cm using a pressure of 170 bar.
6. Establish the blast injury model by directing a high-pressure shock wave at the marked abdominal point from a distance of 6 cm using a pressure of 170–190 bar.
7. Operate the trauma modeling platform using the remote control system.
8. Keep all researchers in a separate, shielded observation area during the model establishment to prevent high-pressure exposure and acoustic trauma.
   NOTE: Allow the penetration depth to be determined by the standardized pressure and individual tissue resistance. Define model failure as immediate mortality upon impact.

4. Management of the immediate surgery group

1. Transfer each pig in the immediate surgery group to the operating room immediately after injury modeling.
2. Place the pig in the supine position.
3. Prepare the abdominal area with iodophor and drape the surgical field in a sterile manner.
4. Make a horizontal incision approximately 10–15 cm in length near the wound site to enter the abdominal cavity.
5. Use a metal retractor to open the abdominal wall adequately and expose the intra-abdominal organs and structures.
6. Evacuate hemoperitoneum using a suction device when intraperitoneal blood is observed.
7. Estimate the total blood loss by combining the blood volume suctioned with the increase in weight of blood-soaked surgical sponges.
8. Examine the abdominal cavity systematically after evacuating intraperitoneal blood, with particular attention to the liver and other injured organs.
9. Determine the subsequent operative management according to the intraoperative findings.
10. Use electrosurgical coagulation at approximately 40 W to manage persistent hemorrhage in the liver injury.
11. Perform partial liver resection when electrosurgical coagulation fails to control bleeding or liver tissue is severely devitalized.
12. Avoid further surgical intervention when no active bleeding or surgically treatable visceral injury is identified during exploration.
13. Close the abdominal incision in layers using 0-gauge sutures.

5. Management of the SNOM group

1. Perform FAST immediately after model establishment.
2. Measure and record post-modeling vital signs, including body temperature, blood pressure, and oxygen saturation.
3. Continuously monitor vital signs during the first 2 h after injury modeling. Record vital signs every 4 h after the first 2 h of continuous monitoring.
4. Perform the initial FAST scan immediately after injury modeling using a portable color Doppler ultrasound diagnostic system equipped with a convex array probe with a frequency range of 1–7 MHz and a center frequency of 3.2 MHz.
5. Conduct repeat FAST scans when clinical deterioration or hemodynamic instability is suspected.
6. Assign FAST examinations to an experienced sonographer who is blinded to the initial physiological parameters of the animals.
7. Perform FAST examinations according to the standard trauma ultrasound protocol.
8. Allow a senior trauma surgeon to make the final decision regarding conversion from SNOM to surgical intervention according to the predefined sonographic or hemodynamic thresholds.
9. Transfer the pig to the operating room for surgical intervention when FAST reveals persistent heterogeneous echogenicity in the liver parenchyma, progressive expansion of intraperitoneal free fluid, or enlarging hepatic hematoma.
10. Transfer the pig to the operating room for surgical intervention when hemodynamic instability, defined as a systolic blood pressure <90 mmHg, occurs.
11. Continue conservative management when vital signs remain stable, and FAST shows no abnormal findings.

6. Blood sampling

1. Collect approximately 2 mL of blood per draw from the marginal ear vein and the carotid artery before modeling (baseline), 24 h, 3 days, 5 days, and 7 days after modeling.
2. Collect blood samples into appropriate tubes according to the requirements of each laboratory test.
3. Process all blood samples within 30 min after collection.
4. Separate serum by centrifugation at 3,000 rpm for 5 min.
5. Store serum samples at -80 °C until further analysis.
6. Exclude missing samples caused by early mortality or technical failure at their corresponding times.
7. Perform arterial blood gas analysis using a blood gas analyzer. Analyze complete blood counts using a hematology analyzer. Measure prothrombin time (PT) and fibrinogen (FIB) levels using a coagulation analyzer. Analyze C-reactive protein (CRP), total bilirubin (TBIL), indirect bilirubin (IBIL), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) levels using an automated biochemical analyzer.
8. Quantify serum levels of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-10 (IL-10) using specific porcine enzyme-linked immunosorbent assay (ELISA) kits.
9. Assay standards and samples in duplicate. Use the mean optical density values of duplicate wells to generate standard curves and calculate inflammatory factor concentrations.

7. Management after modeling

1. House each pig individually in a separate cage after injury modeling. Administer 0.75 g of cefuroxime sodium by intramuscular injection once daily during the first 5 days after modeling to prevent infection.
2. Provide postoperative analgesia under the supervision of trained personnel. Assess pain-related behaviors, including reduced activity, abnormal posture, and decreased food intake, at least three times daily. Administer rescue analgesia when pain-related behaviors are observed.
3. Disinfect the surgical wound with iodine tincture three times daily. Provide food and water three times daily.
4. Continuously monitor the physical condition and mental status of each pig during the 7-day observation period.
5. On day 7 after modeling, euthanize each surviving pig by intravenous overdose of 1% propofol.
6. Make a midline abdominal incision to fully expose the abdominal cavity. Perform a thorough necropsy to confirm the severity and distribution of abdominal injuries.
7. Assess injury severity using the 2015 revision of the Abbreviated Injury Scale (AIS)¹⁷.
8. Assign two experienced surgeons who are blinded to the experimental group assignments and clinical outcomes to independently perform AIS scoring and resolve any discrepancies through discussion until a consensus is reached.

8. Statistical analysis

1. Present continuous variables as medians with interquartile ranges (IQR).
2. Present categorical variables as frequencies and percentages.
3. Compare continuous variables using the Mann-Whitney U test.
4. Compare categorical variables using Fisher’s exact test.
5. Perform all statistical analyses using statistical software.
6. Use a P value of <0.05 to indicate statistical significance.
7. Exclude animals with early mortality from subsequent serial physiological and biochemical assessments and the final AIS assessment.

Results

In all 24 pigs, the vital signs remained stable within 1–2 h after modeling.

Gunshot injury model

In the immediate surgery group, all 6 pigs had penetrating injuries (Table 1). Surgical exploration revealed that 1 pig (16.67%) had a peritoneal penetration without organ injury, 1 (16.67%) a liver penetration injury, and 4 (66.67%) liver lacerations (Figure 3A). Two pigs (33.33%) underwent therapeutic lap...

Discussion

According to the ballistic path, gunshot injuries can be classified into penetrating and blind tube injuries. Blast injuries are generally classified into four types: 1) damage caused solely by the explosive blast wave; 2) damage caused primarily by debris from the explosive device or the surrounding environment; 3) damage resulting from displacement of the victim or environmental structures; and 4) burns, poisoning, and radioactive contamination¹⁵. The present study simulated penetrating gunshot ...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Adjustable single-channel pipette, 20–200 µL	Thermo Labsystems	4642080
AU5800 Series Clinical Chemistry Analyzers	Beckman Coulter	B23279
Automated Blood Coagulation Analyzer CS-5100	Sysmex	BY990757
BC-6800Plus Auto Hematology Analyzer	Mindray	BC-6800Plus
Cefuroxime Sodium for Injection, 0.75 g/vial	Guangzhou Baiyunshan Tianxin Pharmaceutical Co., Ltd.	NMPA approval No. H10940187
Coated braided silk suture	Covidien Healthcare International Trading (Shanghai) Co., Ltd.	N/A
Continuous dispenser	TOMOS Life Science Group	1008004
Convex array probe	SonoScape Medical Corp	Model 3C-A
Denley Dragon Wellscan MK-3 Microplate Reader	Thermo Labsystems	Wellscan MK-3
Digital-display water-jacketed electric thermostatic incubator	Shanghai Yuejin Medical Instrument Factory	PYX-DHS
Electric thermostatic blast drying oven	Shanghai Jinghong Experimental Equipment Co. Ltd.	DHG-9023A
Endotracheal Tube, Size 7.5 mm	Teleflex	5-10114
GEM Premier 3500 Blood Gas Analyzer	Werfen	26000000
High-speed tabletop centrifuge	Shanghai Anting Scientific Instrument Factory	TGL-168
K2 EDTA vacuum blood collection tube	Jiangsu Yuli Medical Instrument Co., Ltd.	N/A
Multifunctional animal trauma modeling platform	Chongqing Zhishangyun Technology Co., Ltd.	23X-FH
Porcine IL-10 Elisa Kit	Aimeng Youning	LV70245
Porcine IL-6 Elisa Kit	Aimeng Youning	LV70293
Porcine TNF-α Elisa Kit	Aimeng Youning	LV70500
Portable color Doppler ultrasound diagnostic system	SonoScape Medical Corp	Model E3
Preset heparinized arterial blood collection syringe	BD	364390
Propofol 1% (10 mg/mL)	Fresenius Kabi	N/A
RM800 Veterinary Multi-parameter Monitor	RWD Life Science Co., Ltd.	RM800
Safety closed IV catheter	Shandong Ande Healthcare Apparatus Co., Ltd.	N/A
Serum separator tube (SST), clot activator + gel	Jiangsu Yuli Medical Instrument Co., Ltd.	N/A
Sodium Chloride Injection 0.9%, 500 mL	Anhui BBCA Pharmaceutical Co., Ltd.	NMPA approval No. H34021876
SPSS	IBM Corp, Armonk, New York, USA	26
Sterile disposable syringe, 10 mL	Shandong Ande Healthcare Apparatus Co., Ltd.	N/A
Sterile disposable syringe, 5 mL	Shandong Ande Healthcare Apparatus Co., Ltd.	N/A
Sterile surgical forceps (straight and curved)
Sterilization wrapping sheet (non-woven fabric)	MPACK	A082700
Vacuum blood collection tube, sodium citrate	Jiangsu Yuli Medical Instrument Co., Ltd.	N/A
Vortex mixer	Shanghai Qingpu Huxi Instrument Factory	XW-80A
Wellwash 4 MK 2 Microplate Washer	Thermo Labsystems	N/A