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Abdominal CT: Necessity, Nephropathy, and Allergy Myths

Abdominal CT: Necessity, Nephropathy, and Allergy Myths. Joe Lex, MD, FACEP, FAAEM Temple University School of Medicine Philadelphia, PA Joseph.Lex@TUHS.Temple.edu. Disclosure. Nothing to declare. Cape Town, SA. www.GiantSteps-EM.Com. July 19 – 22 nd San Diego, California

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Abdominal CT: Necessity, Nephropathy, and Allergy Myths

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  1. Abdominal CT: Necessity, Nephropathy, and Allergy Myths Joe Lex, MD, FACEP, FAAEM Temple University School of Medicine Philadelphia, PA Joseph.Lex@TUHS.Temple.edu

  2. Disclosure Nothing to declare

  3. Cape Town, SA

  4. www.GiantSteps-EM.Com July 19 – 22nd San Diego, California Four Speakers Only: Amal Mattu Ghazala Sharieff Joe Lex Greg Henry Not a speaker

  5. Mediterranean Emergency Medicine Congress V 14-17 September 2009 Valencia, Spain

  6. III Inter-American Conference on Emergency Medicine – Buenos Aires May 2010

  7. Objectives • Assess the necessity of oral and intravenous contrast material • Discuss strategies to avoid adverse outcomes from intravenous contrast

  8. Question #1 How does oral contrast affect the accuracy of an abdominal CT scan?

  9. Oral Contrast

  10. History of Contrast • “Step and Scan” replaced by helical technology • Single-beam replaced by multiple beam • Rapid scans eliminate artifact from movement, respirations, peristalsis

  11. Importance of Contrast • Many studies show no contrast required in most situations • Confounding variables: • Scanner: dynamic vs. helical vs. multi-detector • Contrast: oral vs. IV vs. rectal • Interpreter reliability

  12. Oral Contrast = Longer Stay • High volume urban ED: 107,000 visits / year • N = 183 patients • Excluded trauma, pediatrics, pregnant Huynh LN, et al. Emerg Radiol. 2004 Jul; 10(6):310-3.

  13. Oral Contrast = Longer Stay Huynh LN, et al. Emerg Radiol. 2004 Jul; 10(6):310-3.

  14. Oral Contrast: Accuracy • 118 patients scanned before and after oral contrast • Blinded interpretation by different radiologists Lee SY, et al. Emerg Radiol. 2006 May; 12(4):150-7.

  15. Oral Contrast: Accuracy • 11 had normal non-contrast but abnormal contrast • 6 had abnormal non-contrast but normal contrast scans • 4 had both scans abnormal, but disagreement over abnormality Lee SY, et al. Emerg Radiol. 2006 May; 12(4):150-7.

  16. Oral Contrast: Accuracy • Post-hoc analysis: one true discordant result • Unblinded review: disagreement due to inter-observer variability • Other studies: discrepancy rates up to 38% Lee SY, et al. Emerg Radiol. 2006 May; 12(4):150-7.

  17. Oral Contrast: Appendicitis • Meta-analysis: 23 studies of CT for appendicitis • CT without contrast similar to or better than CT with contrast Anderson BA, et al. Am J Surg. 2005 Sep; 190(3):474-8.

  18. Oral Contrast: Appendicitis Anderson BA, et al. Am J Surg. 2005 Sep; 190(3):474-8.

  19. Oral Contrast: Conclusion • Many radiologists very comfortable interpreting studies without oral contrast • Although oral contrast takes 90 minutes to opacify bowel, it adds 3 hours to ED stay

  20. Oral Contrast: Conclusion • Oral contrast adds little to accuracy • Local radiologist may not be comfortable interpreting studies without oral contrast

  21. Intravenous Contrast

  22. Question #2 How does intravenous contrast affect the accuracy of an abdominal CT scan?

  23. IV Contrast: Risks • Associated risks • Allergic and anaphylactoid reactions • Contrast induced nephropathy • New scanners adequate to diagnose common problems without IV contrast: appendicitis, diverticulitis, pancreatitis

  24. IV Contrast: Accuracy • 164 unenhanced CT of patients with abdominal pain • Diagnosis made in 71 (43%) • Non-diagnostic given IV contrast • All reviewed by 2 radiologists • No significant difference with IV contrast Basak S, et al. Clin Imaging. 2002 Nov-Dec; 26(6):405-7.

  25. IV Contrast: Necessity • Suspected appendicitis: unenhanced CT  laparoscopy • Appendicitis diagnosed… …by CT in 83/103 (80.6%) …at laparoscopy in 87/103 (84.5%) • CT sensitivity 95.4%, specificity 100% in't Hof KH, et al. Br J Surg. 2004 Dec; 91(12):1641-5.

  26. IV Contrast: Necessity • Unenhanced CT in 109 patients • Final diagnosis by surgery or F/U • 66 TN, 37 TP, 4 FN, 2 FP • Sensitivity: 90%, Specificity: 97% • PPV and NPV: 95% • Accuracy: 94% • Alternate diagnosis on CT: 22% Lane MJ, et al. AJR Am J Roentgenol. 1997 Feb; 168(2):405-9.

  27. Conclusions: IV contrast • CT technology has evolved rapidly • IV contrast adds little to accuracy • Local radiologists may not be comfortable interpreting studies without IV contrast

  28. Radiology Coat of Arms

  29. Allergic Reactions

  30. Adverse Reaction Occurrence • 112,000 patients • Total reactions: 5.65 % Shehadi WH. Am J Roentgenol Radium Ther Nucl Med. 1975 May;124(1):145-52

  31. Question #3 What is the connection between iodine and seafood or shellfish allergy and intravenous contrast material?

  32. “Iodine Allergy” • Physiologic impossibility • Iodine essential to life • Found in thyroid hormones, amino acids • Shellfish allergy to muscle protein tropomyosin Huang SW. Allergy Asthma Proc. 2005 Nov-Dec;26(6):468-9.

  33. Seafood Allergy • Anaphylactoid, not IgE mediated • No response to skin testing • Recurrence: <25% repeat • Increased risk: foods, asthma, hay-fever, hives, drug allergies • No additional risk for seafood Schlifke A, et al. Can J Emerg Med. 2003; 5(3):166-168.

  34. Question #4 If a patient says “I’m allergic to contrast dye,” can’t I just give some diphenhydramine and steroids before they’re injected?

  35. Preventing Adverse Reactions • ACR recommendation if history of moderate or severe reaction 50 mg prednisone 13, 7 & 1 hour prior 50 mg diphenhydramine 1 hour prior 32 mg methylprednisolone 12 & 2 hours prior How does that help us?? http://www.acr.org/s_acr/bin.asp?TrackID=&SID=1&DID=24981&CID=2131&VID=2&DOC=File.PDF

  36. Does Pretreatment Work? • Meta-analysis: six studies • Four used antihistamines • Pooled RR: 0.4 (95% CI 0.18–0.9) • Insufficient data for pooled statistic for corticosteroids • Suggested reduction for methylprednisolone Delaney A, et al. BMC Med Imaging. 2006 Apr 27;6:2.

  37. Does Pretreatment Work? • Steroid pretreatment reduced… …respiratory symptoms from 1.4% to 0.4% …respiratory and hemodynamic symptoms from 0.9% to 0.2% • NNT to prevent one severe reaction: 100 – 150 Tramer MR, et al. BMJ. 2006 Sep 30; 333(7570):675.

  38. Conclusions Pretreatment… …in unselected patients not useful …recommended in patients with prior anaphylaxis …may not prevent severe or life threatening reactions Life threatening reactions rare

  39. Question #5 What about the patient with a history of asthma? Does that increase the risk of an allergic reaction?

  40. Asthmatics and IV contrast • Risk of serious reaction increased 5-fold in patients with asthma, multiple allergies • Rate of serious reactions still sufficiently low (0.1%) that pre-medication not advised Morcos SK. Br J Radiol. 2005 Aug; 78(932):686-93.

  41. Question #6 Should we do a serum creatinine on everyone before they get an intravenous contrast load?

  42. Contrast Induced Nephropathy • Definition of CIN • Absolute  in Cr of 0.5mg/dL • Relative  of 25% in 48 hours • Biggest risk: preexisting  Cr •  exponentially with Cr • Baseline Cr <1.5 mg/dL: 2% • Baseline Cr >2.5 mg/dL: 20% Moore RD, et al. Radiology. 1992 Mar; 182(3):649-55.

  43. Age > 70 years CHF Cirrhosis Diabetes Multiple myeloma Anemia Sepsis Hypotension Hypertension Nephrotoxic drug: NSAID, ACE inhibitor, furosemide When to Check Creatinine

  44. Question #7 Can I prevent contrast-induced nephropathy by giving the patient NAC or bicarb or something else?

  45. What DOESN’T Work Diuresis: mannitol, furosemide • “Flush” contrast through kidneys • Intuitively make since • Actually increase CIN rate Solomon R, et al. N Engl J Med 1994 Nov 24; 331(21):1416-30

  46. What DOESN’T Work Common vasodilators: dopamine, fenoldopam • Increase renal flow • Intuitively make since • Actually increase CIN rate Stone GW et al. Rev Cardiovasc Med. 2001;2 Suppl 1:S31-6.

  47. What DOESN’T Work Other vasodilators: atrial natriuretic peptide, calcium channel blockers, ACE- inhibitors, endothelin receptor antagonists • Intuitively make since • Actually increase CIN rate

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