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NIHR Signal An ultrasound scan is not as useful as a CT scan in assessing trauma

Published on 5 March 2019

doi: 10.3310/signal-000744

Ultrasound scans can be a useful tool to help pinpoint internal bleeding or organ damage in the chest or abdomen, but a negative scan cannot rule out damage, especially in children.

Many emergency departments use portable ultrasound scanners to assess for internal damage when someone has been subject to blunt trauma (for example, involved in a car accident or fallen from a height). Ultrasound is free from radiation, non-invasive and can be used at the bedside, making it convenient if CT is not available.

A review of 34 studies with 8,635 people found that 73 in 1,000 patients would have their abdominal injury missed if only ultrasound was used – a figure which rose to 118 in 1,000 if only children were included. Ultrasound may be helpful in guiding initial treatment decisions, but other tests such as CT scans should be used to check the ultrasound results.

  •   Child Health, Diagnostics, Emergency and urgent care, Trauma, Acute and general medicine
An ultrasound scan is not as useful as a CT scan in assessing trauma

Why was this study needed?

Around 20,000 people sustain major trauma each year in England, with 5,400 people dying of their injuries. Quick diagnosis of life-threatening internal bleeding, pneumothorax or damage to organs like the liver or spleen can save lives.

Portable ultrasound can be used alongside other interventions such as resuscitation and doesn't expose the patient to radiation. That makes it safe and convenient to use when assessing trauma. It is available in most, if not all, accident and emergency departments in developed countries.

Ultrasound has been shown to have good specificity for internal injury, i.e. if the scan is positive, then injury is very likely. However previous studies have shown widely varying rates of sensitivity – where if the scan is negative it may miss an injury. This study aimed to update evidence about the diagnostic accuracy of chest and abdominal ultrasound imaging for blunt trauma.

What did this study do?

This Cochrane systematic review included 34 diagnostic cohort studies of 8,635 participants investigating the use of ultrasound to diagnose blunt trauma injury to the chest or abdomen. Ultrasound results were compared to another diagnostic tool such as CT, MRI, thoracoscopy or laparoscopy or other diagnostic reference standard.

The authors assessed the studies for bias and pooled the results to calculate the sensitivity and specificity of ultrasound, both in adult-only, child-only and mixed adult and child populations.

The study found substantial variation across the studies, particularly when looking at different populations (adult or child) and body area (chest or abdomen) which reduces confidence in the results.

What did it find?

  • Estimates for all 34 studies included in the review were 74% sensitivity (95% confidence interval [CI] 0.65 to 0.81). This means 26% of injuries would be missed. Specificity was good at 96% (95% CI 0.95 to 0.98) meaning that 4% of those without an injury would be incorrectly diagnosed as having an injury. However, this masked large differences in sensitivity results between adults and children, and for different body areas.
  • For children only, sensitivity was lower at 63% (95% CI 0.46 to 0.77, 10 studies with 1,384 participants) as was specificity at 91% (95% CI 0.81 to 0.96). For adults or mixed populations, excluding the children only studies, sensitivity was 78% (95% CI 0.69 to 0.84, based on 24 studies with 7,251 participants) and specificity was 0.97% (95% CI 0.96 to 0.99).
  • Ultrasound was more accurate for chest injury, with a sensitivity of 96% (95% CI 0.88 to 0.99) and specificity of 0.99 (95% CI 0.97 to 1.00).
  • Ultrasound was less accurate for abdominal injury, with a sensitivity of 68% (95% CI 0.59 to 0.75) and specificity of 0.95 (95% CI 0.92 to 0.97).
  • In a virtual population of 1,000 based on the 34 studies included, using the observed average prevalence of injury of 28%, ultrasound would miss 73 patients with injuries and falsely suggest injury in another 29. In a population of 1,000 children based on the 10 child studies and using the observed average injury prevalence of 31%, ultrasound would miss 118 children with injuries and falsely suggest injury in another 62.

What does current guidance say on this issue?

NICE issued a guideline on the assessment and management of major trauma in February 2016.

The guideline says doctors should consider immediate X-ray and/or ultrasound for adults with suspected chest trauma and breathing difficulties, and immediate CT scan for adults with chest trauma without breathing difficulties. It adds that doctors should ‘Consider chest X-ray and/or ultrasound for first-line imaging to assess chest trauma in children’ and should not ‘routinely’ use CT scan first to assess chest trauma in children.

What are the implications?

The findings come as a reminder that abdominal injury or bleeding cannot be ruled out by ultrasound findings alone, especially in children. While the NICE guideline suggests ultrasound may be used first-line in children, negative findings should not be taken as definitive and further investigations may be required.

Most accident and emergency departments in the developed world will have easy access to portable ultrasound, and many will have a range of diagnostic imaging options available. The convenience of portable ultrasound needs to be considered against the low sensitivity uncovered in this review.

Citation and Funding

Stengel D, Leisterer J, Ferrada P et al. Point-of-care ultrasonography for diagnosing thoracoabdominal injuries in patients with blunt trauma. Cochrane Database Syst Rev. 2018;12:CD012669.

The study was funded by the National Institute for Health Research through Cochrane Infrastructure funding.

Bibliography

NICE. Major trauma: assessment and initial management. NG39. London: National Institute for Health and Care Excellence; 2016.

Expert commentary

Point‐of‐care sonography (POCS) is of limited value in thoracoabdominal trauma. The studies included in this review tend to show the technique at its diagnostic optimum, yet suggest that the value of POCS is marginal at best in settings where CT and MRI scanning are readily available.

POCS has particular potential in two sub-groups. The first is paediatric trauma, where it may reduce harmful radiation exposure; however, the performance of POCS is demonstrably worse in children than in adults.

The second is in resource-poor settings; unfortunately, the review is silent on this, presumably due to a lack of primary research. POCS also risks delaying time-critical interventions, and should, therefore, be applied with caution, taking careful account of the patient's overall clinical presentation.

Jonathan Benger, Professor of Emergency Care, University of the West of England; Consultant in Emergency Medicine, University Hospitals Bristol NHS Foundation Trust

The commentator declares no conflicting interests

Expert commentary

The application of FAST (Focused Abdominal Sonography for Trauma) to guide decision making for patients presenting with injuries would appear a safe and cost-effective intervention. However, studies have been mixed as to its accuracy, especially in children.

This comprehensive review highlights sensitivity may only be around 70% (i.e. 30% of scans may be incorrectly negative).

This work should prompt review of protocols utilising ultrasound, which the review demonstrated was clearly beneficial ruling in injury if present, to enable the impact of its poor sensitivity to be mitigated, particularly in children.

Dr Damian Roland, Consultant in Paediatric Emergency Medicine, University Hospitals of Leicester

The commentator declares no conflicting interests