SMALL BOWEL INJURY

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CHAPTER 48 SMALL BOWEL INJURY

Injuries to the intestines have been described since antiquity. The statement “a slight blow will cause rupture of the intestines without injury to the skin” is attributed to Aristotle, and Hippocrates was the first to describe intestinal injury from penetrating trauma. In 1275, De Salicet was the first to report lateral suture repair of an intestinal wound. In 1686, Bonet described blunt intestinal injury in a hunter who was thrown violently against a tree by a stag. Autopsy showed rupture of the terminal ileum and cecum. In 1761, Morgagni reported several instances of blunt trauma to the small intestine caused by direct blows to the abdomen. He emphasized the slow and insidious nature of abdominal signs, an observation clinically pertinent to this day. The first long term survivor after repair of a traumatic totally divided small intestine was reported in 1889 by Croft. In the early 20th century, the experience of Bedroitz during the Russo-Japanese War confirmed the advantage of early operative intervention for abdominal injuries. She positioned her operating theatre close to the frontlines and, by being able to treat casualties within 4 hours, showed improved outcomes. In the late 20th century, awareness of the benefits of early repair, coupled with the technologic advances in diagnosis, led to significant improvements in outcome. However, they also led to controversy and loss of consensus regarding both diagnostic and therapeutic approaches to patients at risk. As a result, there continue to be missteps in both diagnosis and management that require surgical vigilance.

INCIDENCE

Injuries to the small intestine must be differentiated by their means of wounding. Because the small intestine occupies the largest portion of the peritoneal cavity, injuries to the small intestine are over-represented after penetrating trauma. Most series cite an incidence of involvement of the small bowel or its mesentery in 80% or greater after gunshot wounds and 25%–30% after stab wounds. In blunt trauma, although the small bowel is acknowledged as the third most common organ injured, after the liver and spleen, the incidence has recently been shown to be much less than previously thought (Table 1). The 1% incidence after blunt trauma increases to 3% in patients with blunt abdominal trauma, with the incidence of free perforation after blunt abdominal trauma still less than 1%. These figures may be misleading. Nance et al., using data from the Pennsylvania Trauma System database, showed a strong statistical correlation between the number of solid organs injured and the likelihood of associated hollow viscus injury.¹ The overall incidence was 9.6%, but climbed appreciably as the number of solid organs increased, reaching 34% with three or more solid organ injuries. Isolated injury to the pancreas was associated with a 33% incidence of hollow viscus injury. Only hollow viscus injuries with an Abbreviated Injury Score (AIS) of 3 or greater were included, but the database also included injuries to the gall bladder and urinary bladder.

Table 1 Prevalence of Blunt Small Bowel Injury

MECHANISM OF INJURY

There are few anatomic areas, other than the hollow viscera, where the mechanism of injury plays as important a role in determining the ease or difficulty of diagnosis or where the treatment is so well defined or confused. The small bowel may be injured by penetrating forces, including gunshot or shotgun wounds, stabbings, or impalements. Although there are recent reports attesting to the validity of nonoperative management of gunshot wounds, most surgeons hold to the belief that operation is mandated for gunshot wounds of the abdomen or where the abdomen is in jeopardy, that is, lower thoracic entry or buttock wounds. Because the likelihood of surgically significant injury exceeds 80% for gunshot wounds of the abdomen, celiotomy is indicated. Further, even when penetration of the peritoneal cavity can be excluded, blast effect leading to perforation has been described from proximity wounds, especially if the offending firearm is of high velocity (>2000 ft/sec).² The injurious nature of shotgun wounds is directly related to the shot size and distance between the victim and the muzzle of the shotgun, with large shot size and close-range wounds being the most damaging. Stab wounds are considerably less lethal, but because most are managed selectively, the risk of missed injury is increased compared with those where protocol demands operation.

The small bowel may be injured by nonpenetrating forces. High-speed modes of transport and the omnipresent use of safety restraints have enhanced the risk of blunt small bowel injury. Whereas traffic casualties died at the scene or sustained rapidly fatal central nervous system injuries in the past, road safety efforts have reduced traffic fatalities and created different patterns of injury, one of which is the seat-belt syndrome, which includes small bowel injuries. In fact, in the multi-institutional report of Fakhry et al., a seat-belt mark was associated with an increased risk of perforated small bowel injury.³ In many cases, the mark represented incorrect usage of the safety belt, that is, too loose, too high, or poor geometry related to body size, as in children restrained by adult belts.

The pathogenesis of small bowel rupture from blunt forces is still speculative, but has variously been ascribed to crushing, shearing, or bursting forces. A violent force directly applied to the abdomen can crush the intestines between the external force and the spine. This mechanism is commonly accompanied by injuries to other organs. Shearing injuries occur from sudden deceleration with typical injuries occurring at points of relative fixation such as the ligament of Treitz and terminal ileum or at sites of adhesive bands. Some investigators have minimized this as an injury mechanism, citing the relatively even distribution of small bowel injuries in some series. The small bowel may burst if force is applied to a distended segment where ends may be temporarily closed. This explains how the small bowel may rupture after relatively minimal force, and has actually been demonstrated in the canine model. In summary, gaping small bowel disruptions with mesenteric mutilation and extensive small bowel contusion suggests a crush injury mechanism (Figure 1). Small bowel injuries with isolated clearly defined points of rupture probably represent burst injuries and shredding injuries, especially if near the ligament of Treitz, cecum, or other points of fixation, and are probably caused by shearing forces (Figures 2 and 3).

Figure 1 Small bowel injury from crushing force. Note extensive areas of nonviability.

Figure 2 Small bowel segment showing burst injury.

Figure 3 Small bowel demonstrating linear perforation, suggesting shear injury mechanism.

DIAGNOSIS

The diagnostic approach to penetrating wounds of the abdomen is slowly evolving based on newer technologies and minimally invasive surgical techniques. In 1960, Shaftan created controversy by suggesting that surgical judgment rather than mandatory celiotomy was the preferred approach to patients with penetrating trauma.⁴ His initial efforts slowly gained support in the management of stab wounds. Stab wounds follow the rule of thirds: one-third do not penetrate the peritoneal cavity, one-third penetrate the peritoneal cavity but do not create injury, and one-third cause injury requiring operative repair. Recognizing that a mandatory policy of celiotomy resulted in negative or nontherapeutic celiotomy in two-thirds of patients, selective management is now a common practice. In 2001, Scalea et al.⁵ reported a prospective series of hemodynamically stable patients with penetrating trauma studied by triple-contrast computed tomography (CT). There were 75 consecutive patients and 60% sustained gunshot or shotgun wounds. Nonoperative management was successful in 96% of patients with a negative CT scan. Despite this impressive series, most surgeons employ celiotomy for the treatment of gunshot wounds and accept a 15% negative or nontherapeutic celiotomy rate. In some institutions, both operative and selective management coexist, with surgical judgment prevailing in instances where the suspicion of intraperitoneal penetration or injury is low, that is, flank wounds and wounds confined to the liver.

Indications for operation follow generally accepted algorithms (Figures 4 and 5). When criteria are met, most surgeons proceed with operative treatment. The emergence of experienced minimally invasive surgeons is beginning to modify indications for celiotomy after penetrating trauma, especially in wounds that potentially injure the hemidiaphragm or where abdominal penetration is in doubt. These enhanced skills have supported the evolution of laparoscopy from a primary diagnostic modality to both a diagnostic and therapeutic tool.⁶ Wounds to the diaphragm can be seen and repaired; wounds to other organ systems can be detected, characterized as to injury severity and, in many instances, repaired or controlled with hemostatics. Small bowel wounds remain problematic. Injuries obvious to the laparoscopic surgeon are probably detectable by other simple or less invasive techniques, that is, physical examination, CT, and diagnostic peritoneal lavage (DPL). Occult injuries may be initially missed regardless of the diagnostic approach, but exclusion of peritoneal penetration is useful whether by local wound exploration or direct visualization via a laparoscope.