Abstract
Introduction
The clinical significance of isolated free fluid on abdominal computed tomography (CT) in patients with blunt abdominal trauma is unclear. This audit reviews our unit’s experience with isolated free fluid and attempts to refine our clinical algorithms for the assessment of patients with blunt abdominal trauma.
Materials and methods
All patients who sustained blunt abdominal trauma between December 2012 and December 2017 who were subjected to multidetector CT of the abdomen as part of their initial investigation were included in this study.
Results
During the five-year period under review, a total of 1066 patients underwent abdominal CT following blunt poly trauma. A total of 84 (7.9%) patients died. There were 148 (14%) patients with CT finding of isolated free fluid. Of these, 128 (67%) were selected for non-operative management, which included a period of serial abdominal examinations. In this non-operative group, five patients failed their abdominal observations and underwent laparotomy. Findings in these five cases were negative (1), non-therapeutic (1), splenic injury (1), Pancreatic and splenic injury (1) and bladder injury (1). Thirteen patients (10%) died, none of whom had surgery. The causes of death were exsanguination from a major traumatic lower limb injury (1), multiple organ failure (1), traumatic brain injury (10) and spinal cord injury (1). The remaining 20 patients underwent laparotomy. The indications were failed non-operative management (5), abdominal distension (1) and suspicion of a missed hollow viscus injury (14). In this group there were 11 therapeutic and 6 non-therapeutic surgeries and three negative laparotomies. For the 15 patients selected for operative management, the findings were as follows: hollow viscus injury (3), mesenteric bleeds (2), splenic and pancreatic injury (1), liver and bladder injury (1), splenic and bladder injury (1), non-therapeutic (4), negative (3). The finding of isolated free fluid on CT is 98% sensitive and 96% specific for true isolated free fluid (chi square 331.598; P = 0.000). This finding predicts successful non-operative management with a positive predictive value of 93% and a negative predictive value of 96%.
Discussion
In patients with blunt abdominal trauma, the finding of isolated free fluid on abdominal CT alone is no longer an indication for laparotomy. Other clinical factors must be taken into account when deciding on the need for laparotomy, such as haemodynamic status, clinical abdominal findings and the ability to reliably assess the abdomen. In the absence of a clinical indication for urgent laparotomy, patients with isolated free fluid may be observed.
Keywords: Blunt abdominal trauma, Isolated free fluid, Abdominal computed tomography
Introduction
Blunt abdominal trauma can result in both solid and hollow visceral injuries and the management algorithms for these two classes of injury differ greatly. In general, most solid visceral injuries can be treated conservatively while almost all hollow visceral injuries require surgical intervention. The recognition and diagnosis of hollow visceral injuries remains challenging, however, and blunt hollow visceral injuries remain associated with delays in diagnosis and intervention. These delays translate into increased morbidity and poor outcomes. The difficulty in clinically assessing patients with blunt abdominal trauma means that most algorithms rely heavily on imaging of these patients to identify intra-abdominal injuries. Currently, multidetector CT (MDCT) is the investigation of choice in those who are haemodynamically stable. MDCT defines all the intra-abdominal solid viscera and will identify and define injuries to these structures. MDCT is poor at diagnosing hollow visceral injuries and generally can only infer the presence of a hollow visceral injuries from other radiological findings. These findings include retroperitoneal or intraperitoneal air, which suggests perforation, beading of the mesenteric vessels, which suggests a mesenteric tear, and the presence of free fluid. There are generally two types of free fluid, namely free fluid in association with a solid visceral injury such as a splenic or hepatic laceration and isolated free fluid. The presence of isolated free fluid is suggestive of a mesenteric tear, or of bowel contents. As such, the presence of isolated free fluid came to be regarded as an indication for operative exploration.1,2 However, the improved capability of CT has resulted in ever smaller amounts of isolated free fluid being detected, and the clinical significance of isolated free fluid following blunt abdominal trauma is now unclear. This audit reviews our experience with isolated free fluid and attempts to place the radiological finding in context and to clarify our algorithms for the investigation and management of blunt abdominal trauma.
Clinical setting
The Pietermaritzburg Metropolitan Trauma Service (PMTS) at Grey’s Hospital is based in the city of Pietermaritzburg, South Africa. It provides trauma care to the city of Pietermaritzburg with its population of one million people and tertiary trauma care to the predominantly rural western third of the province. This is a large geographical area serviced by 19 district hospitals and three regional hospitals, with a population of two million people. PMTS is one of the largest academic trauma centre within the western part of the province. Our centre maintains the regional electronic trauma registry, a digital data-base called the Hybrid Electronic Medical Registry (HMER) which captures data on all admissions to the service.
Department of radiology
Grey’s Hospital possesses one MDCT scanner (Siemens, Somatom Sensation model).
Materials and methods
All patients who sustained blunt abdominal trauma between December 2012 and December 2017 and who had MDCT of the abdomen and pelvis as part of the initial investigation were included in this study. Those who had a whole-body CT were also included. CT was performed on admission while patients were still in the emergency department. Basic demographic details included age, sex and the mechanism of injury. The records of all scans were reviewed by the first author and the detailed organ injuries were recorded. Details on the presence or absence of free fluid were noted. The presence of free fluid was noted in the conventionally defined regions and anatomical zones on CT: Morrison’s pouch, pouch of Douglas, pelvis, paracolic gutters, perihepatic and perisplenic spaces. Patients in the specific subgroup with isolated free fluid with no evidence of solid or hollow organ injury were reviewed separately. Medical records for these patients were further reviewed to obtain information regarding the outcome of these patients. All data were extracted on a Microsoft Excel spread sheet for processing and analysis. Data were analysed using SPSS version 23. A cross-table analysis was used to calculate the sensitivity, specificity, positive and negative predictive values for the finding of isolated free fluid on abdominal CT and a chi square statistic was generated. The composition of the relevant variables can be seen in Figure 1.
Figure 1.
Contingency table of computed tomography findings.
Results
During the five-year period under review, a total of 1066 patients underwent abdominal CT following blunt poly trauma. The descriptive statistics are summarised in Table 1. A total of 84 (7.9%) patients died. There were 148 (14%) patients with a CT finding of isolated free fluid.3 Of these, 128 (86%) were managed expectantly.4 Of this group, 5 (4%) ultimately failed their trial of non-operative management and required a laparotomy, and 13 patients (10%) eventually died (Table 2).5 The causes of death were exsanguination from a major traumatic lower limb injury (1), multiple organ failure (1), traumatic brain injury (10) and spinal cord injury (1).
Table 1.
Descriptive statistics of patient sample.
| Variable | Median | 25th–75th percentile |
| Age (years) | 30 | 20–39 |
| Heart rate (beats/minute) | 96 | 80–112 |
| Respiration rate (breaths/minute) | 18 | 16–22 |
| Systolic blood pressure (mmHg) | 121 | 109–135 |
| Diastolic blood pressure (mmHg) | 72 | 61–82 |
| Mean arterial pressure (mmHg) | 88 | 78–99 |
| Female : male (N = 1099) | 260 : 806 | |
| Intensive care admissions, n (%) | 98 (9.2%) |
Table 2.
Patients who failed abdominal observations.
| Admission to surgery (hours) | Clinical finding | Biochemical | Physiological | Laparotomy | |
| 1 | 72 | Increased abdominal tenderness | BE 5.4 to –26.8 | Bladder and pelvic hematoma | |
| 2 | 28 | Increased abdominal tenderness | Splenic and pancreas injury | ||
| 3 | 28 | Peritonitic | BE –2.4 | Non-therapeutic | |
| 4 | 144 | Peritonitic | BE –10 to 11.3 | Tachycardia 118 | Non-therapeutic |
| Lactate 0.3 to 0.83 | |||||
| 5 | 7 | Increased abdominal tenderness | BE –3.7 to –4 | Splenic cystic mass injury | |
| Mesenteric tear |
BE, base excess.
The remaining 15 (14%) patients were selected for laparotomy. In this group, there were 11 therapeutic surgeries, 6 non-therapeutic surgeries and 3 negative laparotomies. There were no mortalities in this cohort. Some 291 patients had a documented intra-abdominal injury on CT, 60 of whom had surgery. Of these surgeries, 57 were therapeutic and three negative laparotomies;6 7 of these patients (11.7%) died (fig 2). There were 918 patients excluded from the study: 57 patients had a positive finding on CT and had surgery (all therapeutic); 629 patients had a negative (normal) CT abdomen; of these, only one had failed conservative management but had a negative laparotomy. The remainder (232) had positive findings on CT abdomen and had successful conservative management.
Figure 2.
Summary of patient outcomes.
The finding of isolated free fluid on CT is 98% sensitive and 96% specific for true isolated free fluid’ (chi square 331.598; P = 0.000). This finding predicts successful non-operative management with a positive predictive value and a negative predictive value of 93% and 96%, respectively.7
Discussion
Blunt hollow visceral injury remains somewhat of an occult injury in the sense that it is an injury that is difficult to diagnose and is often difficult and associated with delays. There are two mechanisms responsible for blunt hollow visceral injuries. A direct force to a loop of bowel may result in a dramatic increase in intraluminal pressure and may precipitate an acute blowout-type injury of either the duodenum or a segment of small bowel. The second mechanism involves an acute acceleration and deceleration force applied to the bowel mesentery. Tearing of the mesentery interrupts the bowel vasculature and results in an ischaemic segment of bowel. Blunt abdominal trauma remains very difficult to assess clinically and imaging has a key role in all management algorithms.
MDCT is the gold standard in the evaluation of stable patients with blunt abdominal trauma and can accurately identify and grade almost all solid visceral injuries. The presence of free intraperitoneal or retroperitoneal air is suggestive of an enteric perforation and is an indication for operative exploration. Other features suggestive of a mesenteric injury include beading the mesenteric vessels and signs of extravasation from the mesenteric injury.8 However, these are often difficult to interpret, even with modern CT, and the reported accuracy of CT in identifying mesenteric injury varies greatly.
The presence of isolated free fluid in the peritoneum attracted much attention in the earlier CT era when it was listed as an indicator for laparotomy. Free fluid in association with a solid visceral injury was assumed to be secondary to bleeding from the visceral injury and was therefore not considered as significant in its own right. Isolated free fluid was considered to represent either bleeding from a mesenteric tear injury and therefore was considered to be a surrogate marker of a potential hollow visceral injuries. In the last decade of the twentieth century, most authors considered that the finding of isolated free fluid on CT following blunt abdominal trauma was an indication for operative exploration. However, since the turn of the millennium there has been a dramatic improvement in CT capability and modern 64-slice multidetector CT scanners are capable of detecting smaller and smaller quantities of fluid. This has led to a reassessment of the significance of isolated free fluid.
With modern CT, the incidence of isolated free fluid has increased, and in our study is in the order of 14%. This reflects increased capacity of modern CT. The clinical significance of isolated free fluid is now unclear. Of the patients with isolated free fluid on CT, just under 90% were managed without surgery. This suggests that the radiological finding of isolated free fluid is not in itself sufficient grounds to undertake a laparotomy. Of the patients who had isolated free fluid and who underwent a laparotomy, this was therapeutic in just over 50%, and in 30% was non-therapeutic.9–11 This implies that although the present of isolated free fluid is cause for heightened concern it can no longer be regarded as an indication for laparotomy in its own right in patients following blunt abdominal trauma. These patients should instead be admitted and observed with serial abdominal examinations for 48 hours in a centre capable of performing laparotomies should they fail conservative management. Figure 3 represents our management algorithm for blunt abdominal trauma.
Figure 3.
Local algorithm for management of blunt abdominal trauma.
Conclusion
In patients with blunt abdominal trauma, the finding of isolated free fluid on abdominal CT alone is no longer an indication for laparotomy. Other clinical factors must be taken into account when deciding on the need for laparotomy, such as haemodynamic status, clinical abdominal findings and the ability to reliably assess the abdomen. In the absence of a clinical indication for urgent laparotomy, patients with isolated free fluid may be observed.
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