The handout describes some brief practical points on emergency CT, particularly for emergency physicians. They include imaging utilisation trends, radiation dose, contrast reaction, contrast-induced nephropathy, use of oral contrast medium and some caveats on emergency CT (esp. abdomen)

1. Rathachai Kaewlai, MD
Ramathibodi Hospital, Mahidol University, Bangkok
Annual Conference of Thai Emergency Physicians (ACTEP)
Greenery Resort Khao Yai, Nakhon Ratchasima | 28 Nov 2014
Practical Points in
Emergency CT for EP

2. Emergency Physician Tasks
• Perform a thorough history and physical
• Formulate a reasonable DDx
• Order imaging tests based on suspected
diagnosis
• Correctly perform the imaging test
• Correctly interpret the imaging test
• Correctly apply the test result to patient care
David T. Schwartz, MD. NYU

3. Outline
• Imaging utilization in ED
• Radiation dose from emergency CT
• IV contrast issues
• PO contrast issue
• What CT can diagnose and what it cannot

4. US
3%
MRI
0%
US
4%
CT Imaging Share Increases
Significantly in a Decade
U.S. Medicare Data
CT
18%
XR
78%
NM
1%
2002
CT
30%
XR
65%
MRI
1%
NM
0%
2012
Levin DC, et al. J Am Coll Radiol 2014;11:1044-1047.

5. CT per 1,000 ED visits Also Increases
from 6% to 15%
U.S. Medicare Data
Levin DC, et al. J Am Coll Radiol 2014;11:1044-1047.
Bundling of
upper/lowe
r abdomen
codes
2012: 150 CTs per
1000 ED visits

6. % of Visits with CT Performed
USA (15%) vs. Canada (8%)
Berdahl CT, et al. Ann Emerg Med 2013;62:486-494.
2012 2014

7. Fear of Lawsuits Does Not Drives
Unnecessary ED High-cost Imaging
Waxman DA, et al. N Eng J Med 2014;371:1518-1525.

8. Minimal Variations Found Amount
Emergency Physicians on Imaging
Utilization
Wong HJ, et al. Radiology 2013;268:779-789.

9. Advanced age
Arrived by ambulance
Higher acuity area
More secondary
diagnoses
More
High-cost imaging when
ED most busy
More
Low-cost imaging when
ED least busy
More ED Imaging Utilization in Certain
Patients’ and Visit Characteristics
Wong HJ, et al. Radiology 2013;268:779-789.

10. Lesson #1
• CT continues to be the main imaging
workhorse in ED, following x-ray
• CT utilization increases even in the midst of
cost-cutting reform and in States where
malpractice has been reformed
• What drives CT use in ED is likely multifactorial
and physicians’ characteristics might not be a
culprit

11. There is no safe dose of radiation.
- Edward P Radford, MD
Scholar of the Risks from Radiation

12. Mechanism of X-ray Injury
Medscape © Nat Rev Cancer 2009

13. Tissue Sensitivity
Most sensitive
Bone marrow (red), colon, lung, stomach,
breast
Gonads
Bladder, esophagus, liver, thyroid
Bone surface, brain, salivary glands, skin
Least sensitive
Ref: ICRP 2007
Tissue Sensitivity
 ~ rate of cell proliferation
 Inversely ~ to age
 Inversely ~ to degree of cell
differentiation
 Higher dose = more damage
 Young = more damage

14. Diagnostic x-ray Risk
Procedures Effective Dose
(mSv)
Risks
CXR (PA), extremity XR <0.1 Negligible
Abdomen XR, LS spine XR 0.1-1 Extremely low “death from flying
7200 km”
Brain CT, single-phase
abdomen CT, single-phase
chest CT
1-10 Very low “death from driving 3200
km)
Multiphase CT 10-100 Low
Interventions, repeated CT >100 Moderate

15. Avoid Unnecessary CT

16. In an age in which we can download
movies and music from the cloud, it is
inexcusable to subject patients to
avoidable cost and radiation exposure
when the technology exists to ensure
that images are readily accessible.
Zane RD. JWatch Emergency Medicine
Avoid Unnecessary CT:
Import Outside Studies into PACS
Moore HB, et al. J Trauma 2013;74:813-817.

17. Lesson #2
• CT radiation dose is a real concern especially
in children and young adults who have longer
life expectancy
• High-radiation risk procedures: multiphase CT
and repeated CT
• Beside technical changes on Radiology side, EP
can help by selecting an appropriate imaging
for clinical question and avoid duplicated
exams whenever possible

18. High osmolarity (1500+)
IV Contrast
Ionic
Low osmolarity (300-900)
Non-ionic
OLD, IONIC, HYPEROSMOLAR AGENTS
NEW, NON-IONIC, LOW OSMOLAR AGENTS

19. Benefits of IV contrast
Visualization of structures and pathologies, focal pathology in solid organs and necessary for CT angio

20. http://aic-server4.aic.cuhk.edu.hk/web8/Hi%20res/anaphylaxis.jpg
Disadvantages of IV Contrast
Anaphylactoid reaction (mostly mild: skin rash)

21. No True Iodine Allergy
Iodine is a part of our body and important source of metabolism (thyroid hormone).
Seafood allergy is because of muscular proteins

22. OLD, IONIC, HYPEROSMOLAR AGENTS
NEW, NON-IONIC, LOW OSMOLAR AGENTS
5-15% 0.2-0.7%
Fatality ~ 2.1 per 1 million (US FDA)
Rate of Contrast Reaction
Lasser EC, et al. Radiology 1997;203:605-610.

23. Lesson #3
• Newer, non-ionic, low-osmolar contrast is
much safer than older ones
• Most reactions are mild, cutaneous
• There is no true iodine allergy
• What we should ask patients: prior history of
reaction to IV contrast (most substantial),
atopy and asthma

24. Definition of CIN | No control group on studies of CIN
No risk threshold of renal function test | Problem with sCr vs. eGFR
Contrast-induced Nephropathy
Controversies

25. Acute Kidney Injury: AKIN Definition
• Any one of these within 48 hours
of contrast
– Absolute increase of sCr >0.3 mg/dL
– % increase of sCr >50% (1.5 fold above
baseline)
– Urine output decrease to <0.5 mL/kg/h
for at least 6 hrs

26. • Serum creatinine limited by
– Influence of gender, muscle mass, nutritional status, age
– Can be “normal” until GFR decreases by 50%
• Estimated GFR with Cockcroft-Gault or
Modification of Diet in Renal Disease (MDRD)

27. Cardiac cath data (arterial injection)
IV (venous) injection
Acute Kidney Injury
from IV Contrast
Data from cardiac cath overestimates risk of intravenous contrast
Newhouse JH, et al. AJR Am J Roentgenol 2008;191:376-382.

28. Studies with a control group of patients NOT receiving IV contrast
>50% of 30,000 patients showed change in sCr
>40% showed change of at least 0.4 mg/dL
https://c2.staticflickr.com/6/5049/5241695367_aa1610e8e1_z.jpg
Acute Kidney Injury
from IV Contrast
Newhouse JH, et al. AJR Am J Roentgenol 2008;191:376-382.

29. Risk Threshold
• No universal agreement on threshold
• No agreement on how long from baseline to
use sCr before IV contrast
• Ramathibodi protocol

30. Lesson #4
• Controversies on IV contrast and renal toxicity
persist. Now it is best to follow local
standardized protocol
• Best method to reduce risk of CIN is adequate
hydration prior and after exposure

31. Jakebouma.com
V.S.
BARIUM
Thicker
Lower risk of aspiration
Not used if suspect perforation
WATER SOLUBLE
Higher aspiration risk
Better choice if suspect perforation
Oral Contrast Controversy

32. Oral Contrast: Benefits
better delineation of bowel, movement to rectum suggests incomplete obstruction or ileus

33. Oral Contrast
• New with MDCT, less need for PO contrast
• Dramatic decrease in ED time intervals in
patients receiving NCCT in evaluation of flank
pain (312 min for renal stone NCCT vs. 599
min for abd CT with PO contrast
Hunyh LN, et al. Emerg Radiol 2004;10:310-313.

34. Even without oral contrast, cancer of the colon and terminal ileum can be appreciated

35. Lesson #5
• Avoiding oral contrast can help speed up the
process of getting a CT
• This can be helpful in certain group of
patients: trauma, acute abdomen (not
suspected of perforation or fistula)

36. Select the Right Imaging Exam
• Selecting correct imaging modality can
affect patient outcome, prevent delay and
influence type and onset of Rx
• Acute abdominal imaging options: X-ray,
ultrasound, CT

37. Perforated appendicitis
When CT is Helpful

38. Acute cecal diverticulitis
When CT is Helpful

39. C.difficile colitis
When CT is Helpful

40. Adhesive small bowel obstruction
When CT is Helpful

41. Closed loop small bowel obstruction
Closed loop small bowel obstruction
When CT is Helpful

42. Mesenteric arterial occlusion with bowel ischemia
When CT is Helpful

43. Perforated acute cholecystitis
When CT is Helpful

44. Obstructing right UVJ stone
When CT is Helpful

45. Lesson #6: Disorders that can be
missed by CT -- Abdomen
• Low-grade SBO
• Colonic volvulus
• Mesenteric ischemia
(early)
• Ischemic bowel
obstruction
• Ovarian torsion
• Mild pancreatitis
• Traumatic bowel
perforation
• Diaphragmatic tear
• Mild appendicitis
(occasionally)

46. Lesson #6: Disorders that can be
missed by CT -- Others
• Small SAH
• DAI
• Early cerebral contusion
• Early ischemic stroke
• Small lesions (tumors,
aneurysms)
• Posterior fossa
• Subsegmental PE
• PE in poorly performed
study
• Coronary cause (in non-coronary
CTA)

47. Conclusion
• CT is the main imaging workhorse in ED, following x-ray. What
drives CT use in ED is likely multifactorial
• CT radiation dose concern in people with longer life
expectancy
• Newer, non-ionic, low-osmolar contrast is much safer than
older ones
• Controversies on IV contrast and renal toxicity persist. Now it
is best to follow local standardized protocol
• Oral contrast can be avoided in certain scenarios
• Know things that can be diagnosed or missed on CT