Abdominal Ultrasound in Trauma Patients: Can We Do It?

ABSTRACT & COMMENTARY

Source: Shackford SR, et al. Focused abdominal ultrasound and trauma: The steep learning curve and proficiency of nonradiologist clinicians. J Trauma Inj Infect Crit Care 1999;46:553-564.

Shackford and colleagues prospectively evaluated the ability of nonradiologist clinicians to detect hemoperitoneum using focused abdominal sonogram for trauma (FAST). Twelve nonradiologist clinician sonographers (4 surgeons, 8 emergency physicians) performed FAST according to a strictly defined protocol for teaching ultrasound in trauma. The study employed statistical methods to graphically construct a learning curve for the 12 clinicians, plotting both error rate and the number of indeterminate exams as their experience increased.

All sonographers received a minimum of eight hours of didactic training in ultrasound including physics and instrumentation, followed by supervised practice sessions of a minimum of 10 normal examinations of volunteers. In the study, 234 FAST examinations were analyzed—an average of 20 per sonographer. The etiology of trauma was blunt in the majority of cases (all but 2) and the most frequent indication for the performance of the sonogram was a suggestive physical examination. Examinations were categorized as positive, negative, or indeterminate. The gold standard for comparison was diagnostic peritoneal lavage (6 patients), CT scan (211 patients), laparotomy (only 3 patients), or admission to the hospital for serial physical examinations (14 patients).

The adjusted error rate for the entire cohort was 5.9%. The adjustment made to the primary error rate was the subtraction of CTomas, which were injuries of no clinical significance found on CT. After the first 10 examinations, there was a significant reduction in the error rate of the examiners, going from approximately one in five examinations to one in 20 examinations. After 20 examinations, FAST had a sensitivity of 68%, specificity of 98%, positive predictive value of 92%, and negative predictive value of 92%.

The discussion that follows the article is very thoughtful and thought-provoking. The primary message is that previous recommendations for anywhere up to 500 examinations to demonstrate competency is without basis in the literature and is not warranted. Reasonable positive predictive values and negative predictive values can be achieved after relatively few examinations. The learning curve is steep; performance and accuracy are greatly improved over the first 10 to 20 ultrasound examinations.

Comment by Jeffrey W. Runge, MD, FACEP

Shackford and colleagues have convincingly shown that surgeons and emergency physicians can gain proficiency in focused abdominal ultrasound for trauma after a series of 10-20 examinations. The exact number required of physicians to learn will vary according to the prevalence of positive sonograms in the specific emergency department (ED) population, but certainly

any academic hospital has a sufficient prevalence for this purpose. Community physicians may gain the necessary information through didactic courses and practice sessions, and may be proctored until they demonstrate proficiency through the use of photographic imaging and review at a remote location. Previous recommendations by the American Institute for Ultrasound in Medicine for 100 hours of didactic learning plus 300 practical examinations are not supported by data and may be motivated by other concerns.

Focused abdominal ultrasound following trauma should be employed in every community hospital that takes care of injured patients. With the reported high sensitivity and specificity, FAST should evolve into the modality of choice for the diagnosis of hemoperitoneum prior to transfer to a trauma center, as well as for triage within trauma centers. Current recommendations for diagnostic peritoneal lavage may be rendered obsolete as technology advances and the proficiency of clinician sonographers increases.

Only a decade ago, emergency physicians were told by many in the anesthesia community that we could not become proficient at rapid sequence intubation techniques, and that neuromuscular blockade was too dangerous for our hands. It is now the standard of care in the ED. There is a familiar echo in the rooms of many credentials committees as ED ultrasound is discussed. As diagnostic techniques like ultrasound get closer to the point of patient care, the quality of care is enhanced. It is incumbent upon emergency physicians to acquire these skills, understand their limitations, and maintain proficiency for the benefit of those we serve.

Focused abdominal ultrasound in cases of known or suspected trauma, as described by Shackford and colleagues:
a. has replaced CT imaging.
b. can be performed only by radiologists.
c. can be learned by emergency physicians and surgeons in a relatively short period of time with a steep learning curve.
d. is more sensitive than specific.