Ultrasound for Pneumoperitoneum and C-Collar Clearance
Can we use ultrasound to diagnose pneumoperitoneum?
See this 5minsono video for an amazing overview.
The primary sonographic finding of pneumoperitoneum is the enhanced peritoneal stripe sign. The description is in the name—you'll see a brighter peritoneal stripe on ultrasound. This will often have a reverberation artifact with multiple reflections of the parietal peritoneum. Basically, you will see peritoneal "A-lines".
You want to evaluate for free air in the most anti-dependent area. Many will look at the epigastrium with the patient supine. Other options include looking above the liver with the patient in left lateral decubitus.
It may be more sensitive to use the linear probe (which is not typically used for standard abdominal ultrasound)
US has a diagnostic accuracy of 95% and specificity of 81.8% in one recent study. However, studies are generally lacking.
Can I clear the C-collar based on a negative CT?
Trauma EAST would say yes! See their 2015 guidelines on this matter.
Their recommendation: "In obtunded adult blunt trauma patients, we conditionally recommend cervical collar removal after a negative high-quality C-spine CT scan result alone. This conditional recommendation is based on very low-quality evidence but places a strong emphasis on the high negative predictive value of high-quality CT imaging in excluding the critically important unstable C-spine injury."
They go on to say, the "negative predictive value [of a CT] of finding an unstable injury seems to be or is very close to 100%."
To quote the spicy commentary in the discussion, from the SURGEONS themselves.
"...We cannot continue indiscriminate two-stage sequential screening for C-spine injuries if the injury rate is near 0% for the first test [CT] and the second adjunctive test results in false positives and inconsistent treatment plans [MRI]."
" If collars are to be removed in a high-risk obtunded population, then why even use a C-spine clearance protocol for the low-risk neurologically normal who have negative C-spine CT data? With a high-quality C-spine CT, cervical collar removal can be logically argued for any population, obtunded or not."
Why does this matter?
"Continued use of the cervical collar carries the risk of pressure ulcers, decreased cerebral venous return, increased intracranial pressure, secondary brain injury, and difficulties with airway and central line management."
Ultimately, if you consult your trauma team, please respect your trauma surgeon’s recommendations.
Cheers,
Dillon
Resources Cited
Patel, M. B., Humble, S. S., Cullinane, D. C., Day, M. A., Jawa, R. S., Devin, C. J., Delozier, M. S., Smith, L. M., Smith, M. A., Capella, J. M., Long, A. M., Cheng, J. S., Leath, T. C., Falck-Ytter, Y., Haut, E. R., & Como, J. J. (2015). Cervical spine collar clearance in the obtunded adult blunt trauma patient: a systematic review and practice management guideline from the Eastern Association for the Surgery of Trauma. The journal of trauma and acute care surgery, 78(2), 430–441. [pubmed]
