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Myths in Emergency Medicine

Myths in Emergency Medicine

Pan-Scans a Weak, Unethical Strategy

Spiegel, Rory MD

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doi: 10.1097/01.EEM.0000511096.75151.e9

    The total-body CT, typically referred to as the pan-scan, has quickly become a key component in initially evaluating trauma patients, even though the evidence supporting its benefits is lacking. Its rise to prominence came more from riotous indignation than evidentiary support. The recent publication of the REACT-2 trial, however, finally provides something other than spit and vigor to support our claims. (Lancet 2016;388[10045]:673.)

    Sierink, et al., randomized 1,403 patients to selective scanning according to a pre-planned protocol or to a total-body CT at presentation. (Lancet 2016;388[10045]:673.) The authors tried to ensure that only high-acuity trauma patients were enrolled by utilizing a strict inclusion criteria (RR >30 or <10, pulse >120, SBP <100, GCS <14, estimated blood loss of >499 mL, abnormal pupils, or high-risk mechanism). A total of 203 patients were excluded after randomization even with these narrow criteria, and the majority were omitted because they experienced only minor trauma.

    No difference was found in the primary endpoint — in-hospital mortality — of the 1,083 patients included in the final analysis. Mortality was 16 percent in the selective scanning group and in the total-body CT group. No difference was found in 24-hour mortality (6% and 8%, respectively) or 30-day mortality (16% and 17%, respectively). No benefit was found for whole-body CT strategy in the subset of patients defined as polytrauma (ISS >16) or those with traumatic brain injury (GCS <9 and AIS head score >2). These findings remained consistent for 30-day mortality as well.

    The researchers established that patients randomized to selective imaging received far fewer radiographic investigations. Only 46 percent of the patients in the selective imaging group underwent total-body CT imaging. This reduction did not result in any clinically important delays in identifying life-threatening diagnoses (58 vs. 50 minutes).

    Supporters of total-body irradiation may take issue with a number of nuances despite these negative findings. Forty-six percent of patients in the selective imaging group ended up undergoing total-body imaging. The argument is that this crossover would dilute the results, obscuring any benefit total-body CT may produce. On the other hand, 54 percent of the patients in the selective imaging group avoided total-body irradiation. This is not a weakness of the trial design but a reality. No one is arguing that total-body radiographic evaluation should be eliminated, but the decision should be based on clinical judgment rather than reflexive impulse induced by the fear of missing clinically occult injuries. This is a pragmatic representation of reality and only strengthens the findings of REACT-2.

    The second and far more important point of contention is that patients randomized to the total-body CT group were sicker, as represented by patients determined to have polytrauma (61% vs. 67%) at presentation. This initial imbalance may obscure the benefits produced by a total-body CT strategy. This position seems reasonable at face value, but it is a mirage. This imbalance is not the random error of sampling but the expected inflation of injury severity scores due to the total-body imaging strategy imposed on these patients.

    Inflated Score

    The more radiographic studies a patient receives, the more injuries with which he will be burdened. These excessive diagnoses have little clinical meaning, but they are exceptionally facile at augmenting the injury severity score (ISS). (Ann Emerg Med 2016;67[1]:71.) This score is solely defined anatomically, and patients who undergo total-body imaging are far more likely to have clinically insignificant injuries detected by unnecessary scans. (JAMA 1971;215[2]:277.)

    Given the exponential nature of the ISS, findings can artificially inflate the resulting score. This shifts a healthier cohort into a more severe ISS, creating the illusion of a more severely injured cohort. This phenomenon is clearly demonstrated in REACT-2. A larger portion of patients randomized to the total-body CT group were considered polytrauma (67% vs. 61). This inflation was more prominent in patients with intermediate scores (ISS of 16-49; Lancet 2016;388[10045]:673) because severely injured patients are likely to have enough serious injuries that incidental findings found on CT will have little influence on the already-high ISS. (Ann Emerg Med 2016;67[1]:71.) A total of 362 patients in the total-body arm and 331 in the selective imaging arm were considered polytrauma, yet the number of patients who died in each group was essentially identical (81 and 82 patients), suggesting that the excess patients observed in the total-body CT group were not sicker but were subjected to the artificial inflation of clinically insignificant radiographic diagnoses.

    This is not the first trial to demonstrate that selective imaging is safe and feasible in trauma patients. Hoffman, et al., published the NEXUS criteria as far back as 2000, demonstrating that select trauma patients could forego radiographic evaluation of the cervical spine if they met specific clinical criteria. (N Engl J Med 2000;343[2]:94.) Other decision aids since then have demonstrated similar findings for the head, chest, and abdomen. (N Engl J Med 2003;349[26]:2510; JAMA 2005;294[12]:1511; JAMA Surg 2013;148[10]:940; PLoS Med 2015;12[10]:e1001883; J Trauma Acute Care Surg 2015;78[6]:1095.) The REACT-2 cohort is essentially a validation of this strategy; patients underwent imaging of the cervical spine only if they could not be cleared clinically by NEXUS. (Lancet 2016;388[10045]:673.)

    The methodological design of REACT-2 failed to address the effect total-body imaging strategies have on the ED as a whole. We have all seen sick medical patients who truly require CT imaging delayed because clinically stable trauma patients require their mandatory pan-scan. These effects are difficult to quantify, but an inability to measure something's presence does not eliminate its existence.

    Total-body imaging is more convenient for clinicians; less time has to be spent assessing and reassessing because most injuries are likely to be identified on CT. Patient satisfaction is also generally higher because clinicians who perform more tests are often perceived to be more thorough. The clinician is spared the often long and contentious discourse on the harms of excessive imaging and overdiagnosis. A missed injury cannot be blamed on failing to obtain inadequate radiographic investigations.

    The ISS inflation caused by the total-body imaging strategy also creates the illusion of better outcomes when trauma centers are compared with the national standard. Exposing patients to dangerous amounts of radiation for what amounts to our convenience is unjustifiable, however. The prior evidence supporting the use of the trauma pan-scan was at best exploratory and supported only by blustery claims of hearsay and what-ifs. The publication of REACT-2 makes it difficult to imagine the current practice of total-body irradiation as an ethically sustainable strategy.

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