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CT of Nontraumatic Abdominal Fluid Collections After Initial Fluid Resuscitation of Patients with Major Burns

¹ All authors: Department of Radiology, FND 216, Division of Emergency Radiology, Massachusetts General Hospital, PO Box 9657, 55 Fruit St., Boston, MA 02114.

Received October 31, 2003; accepted after revision November 20, 2003.

 
Address correspondence to V. M. Chapman.

Abstract

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OBJECTIVE. The purpose of this study was to describe the presence and CT distribution of nontraumatic fluid collections and edema in the abdomen and pelvis after initial fluid resuscitation of patients with major ( 25% total body surface area) thermal burns.

CONCLUSION. Awareness of the presence and expected CT distribution of nontraumatic fluid after initial fluid resuscitation in patients with major burns can assist the radiologist in differentiating such collections from those caused by mechanical trauma.

Introduction

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In the United States, approximately 2.4 million burn injuries are reported per year, of which 75,000 require hospitalization. Of those patients who require hospitalization, 20,000 have major burns, defined as burns involving at least 25% of the total body surface. Approximately 12% of major burn patients die as a result of their injuries [1]. With advances in medical care and the advent of aggressive fluid resuscitation in the 1960s and 1970s, irreversible shock has been replaced by wound sepsis as the most common cause of death in patients who have suffered major burns [2].

Fluid resuscitation of the burn patient is primarily accomplished with large volumes of crystalloid fluid, totaling between 10 and 20 L in the first 24 hr for most adults, depending on body mass and percentage of total body surface area burned. Such large fluid volumes are required to maintain intravascular volume and tissue perfusion because these patients experience evaporative losses from their burns as well as intra- to extravascular fluid shifts caused by hypoalbuminemia and other metabolic derangements. Extravascular fluid shifts result in significant soft-tissue edema, including the brain, lungs, airways, and subcutaneous tissues [3, 4].

We report the presence and distribution of nontraumatic fluid in the abdomen and pelvis in eight patients who presented to our hospital 24 hr after initiation of fluid resuscitation after severe thermal injury resulting in major burns.

Materials and Methods

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Patients
Eight patients (four men and four women; age range, 21–44 years; mean age, 33 years) with major thermal burns and mechanical trauma were transferred to our hospital approximately 24 hr after injury. All patients were victims of the same event and were evaluated by MDCT of the abdomen and pelvis as part of an evaluation for mechanical trauma. Examination of the patients' medical records and imaging for the purposes of our study was approved by our hospital's institutional review board.

CT
CT scans were obtained with an MDCT scanner (LightSpeed Plus, General Electric Medical Systems). Patients were given 200–300 mL of a 2.5% dilution of diatrizoate meglumine and diatrizoate sodium solution (Gastrografin, Mallinckrodt) via a nasogastric tube before scanning. In all patients, the entire abdomen and pelvis were scanned from the dome of the diaphragm to the ischial tuberosities using the following parameters: high-speed mode, pitch of 6, 5-mm slice thickness and 5-mm image spacing. Scanning was performed 75 sec after injection of 120 mL of nonionic IV contrast material (iopromide, Ultravist 300, Berlex Laboratories) using an Envision CT injector (Medrad).

Image Analysis
The CT scans were retrospectively reviewed in consensus by two radiologists. Scans were evaluated for the presence of abnormal intraperitoneal fluid, which included any fluid in men and fluid extending beyond the pelvic cul-de-sac in premenopausal women. The presence and distribution (but not the volume) of soft-tissue edema were determined and categorized as subcutaneous, mesenteric, perirenal, anterior pararenal, or posterior pararenal. Scans were also assessed for the presence of intrahepatic periportal edema. All images were reviewed using soft-tissue window settings (window level, 40 H; window width, 400 H) on a PACS (picture archiving and communications system, Agfa).

Results

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All eight patients examined showed evidence of soft-tissue edema or intraperitoneal fluid collections measuring less than 20 H. No CT evidence of traumatic injuries involving the abdomen or pelvis was present. Clinical, laboratory, and radiographic follow-up during the 4 weeks after CT showed no evidence of mechanical trauma involving the abdomen or pelvis.

The distribution of nontraumatic fluid in the abdomen and pelvis is depicted in Table 1. All eight patients showed intrahepatic periportal edema of varying degree, as shown in Figure 1. All eight patients showed patchy subcutaneous edema, which was diffusely distributed and often remote from the site of the patient's burns, as shown in Figure 2. Six patients had edema in the anterior pararenal space, predominantly surrounding the pancreas and porta hepatis, as shown in Figure 3A, 3B. Four patients had edema in the perirenal space. All these patients had a small amount of edema near the lower pole of the kidneys, as shown in Figure 4. Two patients had mesenteric edema, as shown in Figure 5. No patients had edema in the posterior pararenal space. Three patients showed intraperitoneal fluid that was considered abnormal by virtue of its presence (any fluid in men) or volume (fluid extending beyond the pelvic cul-de-sac in premenopausal women).

View larger version (107K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1. —Transverse CT scan obtained with oral and IV contrast media in 40-year-old woman with major burns shows edema surrounding right portal vein and its branches (arrows).

View larger version (113K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2. —Transverse CT scan obtained with oral and IV contrast media in 29-year-old man with major burns shows fluid and edema in subcutaneous tissues of back and flanks (arrows).

View larger version (114K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3A. —Transverse CT scans obtained with oral and IV contrast media in 33-year-old woman with major burns. CT scan shows fluid and edema in anterior pararenal space (arrows), particularly surrounding pancreas.

View larger version (115K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3B. —Transverse CT scans obtained with oral and IV contrast media in 33-year-old woman with major burns. CT scan shows edema involving porta hepatis (arrows).

View larger version (99K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4. —Transverse CT scan obtained with oral and IV contrast media in 31-year-old woman with major burns shows fluid in perirenal space (arrows) adjacent to lower pole of kidneys.

View larger version (97K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5. —Transverse CT scan obtained with oral and IV contrast media in 33-year-old woman with major burns shows fluid and edema in small-bowel mesentery, predominantly at root of mesentery (arrow). Prominent enhancement of bowel mucosa, likely caused by hypoperfusion, is also present.

The significance of peripancreatic edema was evaluated by comparison with amylase and lipase values in the 2 weeks after CT. Two (33%) of the six patients with peripancreatic edema and one (50%) of the two patients without peripancreatic edema developed an elevated level of amylase. Five (83%) of the six patients with peripancreatic edema and one (50%) of the two patients without peripancreatic edema developed an elevated level of lipase. Using chi-square analysis, we saw no statistically significant difference in the incidence of pancreatic enzyme elevation between the two groups.

Discussion

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Over the past 40 years, tremendous advances in medical technology and our understanding of the physiology of patients who have experienced major burns have led to the development of aggressive fluid resuscitation regimens and significantly reduced the mortality caused by shock in the early postburn period. Such resuscitation regimens result in the infusion of as much as 10–20 L of fluid in the first 24 hr after the injury. Soft-tissue edema and related complications of resuscitation in the burn patient have been described, such as airway, pulmonary, and cerebral edema, as well as compartment syndromes in the extremities [3]. Our study shows the presence and distribution of nontraumatic fluid on abdominal or pelvic CT after initial fluid resuscitation of patients with major burns.

The patchy subcutaneous edema observed in all eight patients examined is not surprising because this has been previously described in burn patients and attributed to decreased plasma osmotic pressure after fluid resuscitation [4]. Similarly, the finding of intrahepatic periportal edema in all eight patients is predictable because this phenomenon has been previously reported in trauma patients during IV resuscitation [5]. The proposed mechanism is elevated central venous pressure caused by rapid expansion of intravascular volume, and this mechanism likely applies to the patients examined in this study.

Patients with major burns are at significantly increased risk of developing postburn pancreatitis, with 40% developing laboratory evidence of pancreatitis [6]. Though most patients in the current study developed edema in the anterior pararenal space, particularly surrounding the pancreas and porta hepatis, no statistically significant increase in pancreatic enzyme levels in patients with peripancreatic edema was seen.

According to this study, perirenal fluid collections in patients with major burns are not rare. Delayed imaging and assessing attenuation values may assist in differentiating such collections from urine extravasation or hemorrhage, respectively.

Most patients in this study did not have mesenteric edema or intraperitoneal fluid. Therefore, patients presenting with such a collection after a major burn injury should be carefully evaluated and followed up closely to exclude mechanical trauma, including injury to the bowel, urinary bladder, and gallbladder.

Lack of involvement of the posterior pararenal space is not surprising because this space is rarely involved in processes affecting the retroperitoneal soft tissues. Any fluid collection in the posterior pararenal space after a major burn should be considered the result of mechanical trauma.

In conclusion, fluid resuscitation of patients with majors burns leads to multicompartmental edema and fluid in the abdomen and pelvis, which is well shown on CT. Patients with major burns uniformly develop subcutaneous and periportal edema and frequently develop edema in the anterior pararenal space, particularly surrounding the pancreas and porta hepatis. Peripancreatic collections in such patients are not predictive of subsequent pancreatic enzyme elevation. Intraperitoneal or mesenteric collections in patients with major burns should raise suspicion of mechanical trauma, and collections in the posterior pararenal space are the result of mechanical trauma until proven otherwise. Awareness of the expected CT distribution of fluid and edema should assist in discriminating between traumatic and nontraumatic fluid collections in patients with major thermal burns who have undergone initial fluid resuscitation.

References

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1. Erickson EJ, Merrell SW, Saffle JR, Sullivan JJ. Differences in mortality from thermal injury between pediatric and adult patients. J Pediatr Surg1991; 26:821 –825[Medline]
2. Nguyen TT, Gilpin DA, Meyer NA, Herndon DN. Current treatment of severely burned patients. Ann Surg1996; 223:14 –25[Medline]
3. Ahrns KS, Harkins DR. Initial resuscitation after burn injury: therapies, strategies, and controversies. AACN Clin Issues 1999;10:46 –60[Medline]
4. Kinsky MP, Guha SC, Button BM, Kramer GC. The role of interstitial starling forces in the pathogenesis of burn edema. J Burn Care Rehabil 1998;19:1 –9[Medline]
5. Shanmuganathan K, Mirvis SE, Amoroso M. Periportal low density on CT in patients with blunt trauma: association with elevated venous pressure. AJR 1993;160:279 –283[Abstract/Free Full Text]
6. Ryan CM, Sheridan RL, Schoenfeld DA, Warshaw AL, Tompkins RG. Postburn pancreatitis. Ann Surg1995; 222:163 –170[Medline]

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