Page 64 - Ultrasonography in Prehospital and Emergency Medicine - Rein Ketelaars

62
Chapter 2
Challenges
PHUS is subject to specific challenges in the prehospital environment: ambient lighting, confined space, extremes of temperature, precipitation, dressings, splints, and rapid trans- port times.3,6
Diagnostic ultrasound is generally considered harmless. However, it may heat up tissue de- pending on these factors: exposure duration, the acoustic output, and tissue characteristics. For instance, some unique properties of the eye such as high absorption of ultrasound and the absence of cooling blood supply may cause the lens to heat up faster than other tis- sues.149,150 Therefore, this has to be considered in ocular ultrasound or ONSD measurements.
PHUS is used by nonradiologists mainly to answer simple yes/no questions and to guide treatment decisions. Sensitivity for solid organ injuries is low and small quantities of blood early in the post-injury phase may be missed. Traumatic aortic pathology cannot be detected by chest or abdominal US, therefore, PHUS is not a valid replacement for CT angiography in patients subjected to high-energy thoracic trauma.78 False negatives will occur; therefore, negative findings should not indicate a final exclusion of diagnoses.3 Thus, for some indica- tions, the sensible choice might be to use PHUS only as a rule-in tool not to be falsely reas- sured by (false) negative test results.
Another concern of PHUS is the potential delay in treatment. In general, a slight delay might occur when PHUS is performed on-scene. However, delays are non-existent when performed in parallel with other procedures, while in-flight, or during ground ambulance transport. Busch found the median PHUS duration to be 2.5 min (range 1–3).13 For a range of PHUS examinations, Hoyer measured a mean of 1 min 54 s, decreasing to 56 s during the three-year study period.3 In their review, Jørgensen et al. reported a delay of 0–6 minutes. Examination time depends on the protocol and the results: positive findings will reduce the examination time.5
Although a slight delay may occur, this might easily be outweighed by the advantage of im- proved diagnostic and therapeutic accuracy, and the potential time gains by transporting the patient directly to the most appropriate hospital.