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The SCRAP Rule: Indications for chest CT in blunt trauma

Posted Apr 25 2013 12:00am


At my institution, trauma patients frequently receive the “Pan Scan,” to rule out acute injury. Recently, Payrastre et al published the SCRAP Rule article in CJEM 2012 looking to derive and internally validate a clinical decision rule that would identify blunt trauma patients at very low risk for major thoracic injury with 100% sensitivity, thereby eliminating need for a chest CT. Currently, the decision on whether to perform a chest CT is made mostly by clinical judgment.

Reducing the number of unnecessary CT scans would be in the best interest of patients and physicians for several reasons:
  1. Radiation exposure from a CT scan can cause long-term damage (i.e. malignancy).
  2. Hospitals without 24-hour CT capabilities are forced to transfer trauma patients after hours.
  3. Time spent in the CT scanner can potentially delay transfer to operating room for definitive care.
  4. False positive CT scans can lead to other invasive tests and procedures.
  5. Contrast induced nephropathy and anaphylactoid reactions
  6. Significant financial costs associated with scans

What is the SCRAP Rule?

If all five variables below are normal, you do not need chest CT. If any one variable is positive, you may need a chest CT.
  1. Oxygen Saturation (Abnl is <95% on RA or <98% on any supplemental 02)
  2. Chest Radiograph (Abnl is any acute change that could be due to trauma)
  3. Respiratory Rate (Abnl is RR > 25)
  4. Chest Auscultation
  5. Thoracic Palpation


Study Methodology:
  • Retrospective medical record review
  • Single trauma center in southern Ontario
  • 614 patients (434 in derivation and 180 in internal validation)
Inclusion Criteria:
  • Injury Severity Score (ISS) > 12
  • Underwent chest CT at admission
  • Major thoracic injury documented in trauma database
Exclusion Criteria:
  • Penetrating injuries
  • Signs of paralysis
  • GCS < 9
  • Intubated patients
  • Age < 16 years
  • ISS < 13
Primary Outcome:
  • SCRAP rule's ability to detect the presence of a major thoracic injury noted on a CT scan, at discharge, or at clinic follow up
Results:
  • Derivation Set
    • 274/434 (63.1%) patients had a major thoracic injury
    • When all 5 variables were normal (SCRAP neg): Sens 100%, Spec 46.9%,  Neg LR of 0, PPV 76.3%, & NPV 100%
    • This would lead to 17% absolute reduction in CT scans and a 47% reduction in negative CT scans
    • NO missed major thoracic injuries
  •  Internal Validation Set
    • 104/180 (57.8%) had a major thoracic injury
    • When all 5 variables were normal (SCRAP neg): Sens 100%, Spec 44.7%, Neg LR 0, PPV 71.9%, & NPV 100%
    • This would lead to a 19% absolute reduction in CT scans and a 45% reduction in negative CT scans
    • NO missed major thoracic injuries
Limitations:
  • Retrospective chart review
  • Only derivation and internal validation study (Still needs large multi-center, prospective, external validation)
  • 28 patients with rib, clavicle, or spinous process fractures were documented as having no thoracic tenderness
  • CXR interpreted by staff radiologists (not all institutions have staff radiologists) 
Conclusions:
  • In major blunt trauma patient with a GCS >8, the SCRAP Rule has a 100% sensitivity for major thoracic injury.

Currently, there are no accepted guidelines that aid physicians in determining which patients are at low risk for major thoracic injury in blunt trauma. Published results reveal that approximately half of the thoracic CT scans performed in blunt trauma are negative for major thoracic injury.

“Selective Scanning” as opposed to “Pan Scanning” in blunt trauma patients, is an interesting clinical concept, but the SCRAP Rule still needs a prospective, multicenter external validation before implementation into the clinical setting.

References: Payrastre J et al. The SCRAP Rule: The Derivation and Internal Validation of a Clinical Decision Rule for Computed Tomography of the Chest in Blunt Thoracic Trauma. CJEM 2012; 14(6): 344-53. PMID: 23131481
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