The Focused Assessment with Sonography for Trauma (FAST) is an important tool for blunt trauma assessment in the Adult Emergency Department (ED). It is widely used to assist the ED provider with medical disposition in a rapid, accurate and cost-effective manner during trauma assessment. Despite its limitations, the FAST has become the standard of care in adult trauma with up to 96% use among adult trauma centers.1,2 The use of FAST in pediatrics is proportionally lower than in adults. There has been interest in enhancing the utilization of FAST in pediatric blunt trauma. It is important, however, to understand that there are many unique factors that differentiate the use of FAST between the adult and pediatric population.
Why is this relevant?
Increasing acceptance of point-of-care ultrasound in the management of pediatric patients has generated an interest in utilizing the FAST exam for efficient and effective pediatric trauma assessment. Pediatric trauma continues to be the leading cause of death and hospitalization in pediatric patients after infancy.3 Pediatric patients can be a challenge to evaluate during trauma for many reasons including the developmental stage of the patient, lack of verbal skills, and lack of accurate prehospital care information. It is worthwhile to note that significant blunt abdominal trauma, although rare, carries a high risk of morbidity and mortality. While CT is the standard of care for the evaluation of suspected intra-abdominal injury related to blunt abdominal trauma, it involves emitting a high dose of radiation which has been shown to increase the lifetime risk of radiation-induced malignancy. Therefore, the introduction of the FAST scan among pediatric patients was seen to have the potential to assist the provider in evaluating this challenging population and prevent some unnecessary irradiation during trauma assessment.
Adult vs. Pediatric FAST
The successful use of FAST in adult populations has led to its wide acceptance. In adults FAST has almost eliminated the need for deep peritoneal lavage (DPL). The principles of the FAST exam are generally based on the presumption that fluid will accumulate in dependent regions of the peritoneal cavity. It used to detect fluid in the abdomen, the thorax, and around the heart. In adults, the sensitivity of the FAST exam is between 73% and 88% and the specificity is between 96% to 98%.4-6 The FAST is simple to perform while being non-invasive, reproducible, and involves no ionizing radiation. Furthermore in adult trauma, it has been shown to decrease time to operative care, decrease the number of CT scans performed, decrease hospital lengths of stay, generate lower hospital charges, and decrease patient complications. The test characteristics of FAST are dependent on factors that include operator experience, time since injury, and volume of intraperitoneal fluid.
Yet, only 15% of pediatric trauma centers in the United States have adopted FAST as an assessment tool.2 One reason for the low adoption of FAST in the evaluation of children is the rare occurrence of unstable children with intra-abdominal injury. Because of the slow adoption of FAST in pediatrics, much of evidence for the use of FAST is generated from studies in adults with limited understanding in patients, especially those under the age of 2 years old. The test characteristics of FAST plus some unique factors in the pediatric population, (such as the low incidence of intra-abdominal injury and the fact most children with intra-abdominal injuries are clinically stable,) have made the results from the existing FAST exam studies in children less successful than hoped. A meta-analysis using the most methodologically rigorous studies in pediatrics yielded a FAST exam sensitivity of 66% (95% CI 56%-75%); specificity, 95% (95% CI 93%-97%); positive likelihood ratio, 14.5 (95% CI 9.5-22.1); and negative likelihood ratio, 0.36 (95% CI 0.27-0.47.7 Some research, however, has suggested combining the FAST exam with a thorough physical examination & sound clinical assessment can produce effective results up to 97% of the time for select patient needing surgical intervention.8
The way forward
It should be remembered that the vast majority of pediatric solid intra-abdominal organ injuries are managed non-operatively with observation. Thus one important strategy for using FAST in pediatric trauma evaluation may be the use of serial FAST exams to guide clinical decision-making. Evidence from the adult emergency medicine has shown that repeat FAST examinations at 4 hours post-injury increased the sensitivity for detecting clinically significant hemoperitoneum from 31% at time 0 to 72% at 4 hours. The specificity was 99% at both 0 and 4 hours.9 Serial FAST exams may yet prove useful in pediatrics.
In an effort to increase the utility of the FAST as a screening tool in pediatrics, other factors combined with the FAST have been studied. One study showed that elevated liver transaminases has shown to increase the sensitivity of the FAST,(88%) and NPV, (96%).10 The use of contrast enhanced ultrasound has preliminarily shown that it may be more accurate than regular ultrasound in detecting solid organ injury in pediatric patients.11
Recent research done in a modern pediatric trauma center has noted that although the accuracy of FAST is significantly lower than values reported for adults, the absence of peritoneal fluid may strongly suggest the absence of intra-abdominal injury. FAST was able to predict the need for an exploratory laparotomy in 89% of the injured children in that study. The researchers were specific in looking at children under two years of age and felt that FAST examination combined with good clinical judgment may reduce the need for further imaging and therefore reduce the radiation exposure of children under the age of 2 years.12
FAST has long been accepted a part of the assessment of trauma for the adult population. The literature is more complicated for pediatric patients. To muddy the waters, many of the previous pediatric studies apply different definitions of gold standards and outcomes. As providers of emergency care in pediatrics we always want to employ any valid tool available to us to support the children we see. Further study of the FAST exam is needed. For now, FAST may allow prioritization of CT use in areas where CT use is limited. Limited studies show that the combination of a negative FAST and a careful examination with close observation has favorable prognosis in the stable pediatric blunt trauma. Future studies may show that combining an initial FAST with other factors such as repeat FAST exams, liver enzymes, or contrast may enhance the utilization of FAST as a screening tool. Nevertheless, the current state of evidence necessitates new collaborative studies to define the role of FAST in pediatric trauma. Maybe with fine tuning, the FAST exam will be found to be useful as an adjunct in the assessment of the pediatric trauma patient and ultimately reduce the use of radiation in their evaluation.