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FOCUSED EMERGENCY ULTRASOUND: EVALUATION OF THE ABDOMINAL AORTA

FOCUSED EMERGENCY ULTRASOUND: EVALUATION OF THE ABDOMINAL AORTA. MARY BETH PHELAN, MD, RDMS DEPARTMENT OF EMERGENCY MEDICINE FOREDTERT MEMORIAL HOSPITAL. Lecture Objectives. Describe clinical role of bedside ultrasound in screening for AAA

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FOCUSED EMERGENCY ULTRASOUND: EVALUATION OF THE ABDOMINAL AORTA

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  1. FOCUSED EMERGENCY ULTRASOUND: EVALUATION OF THE ABDOMINAL AORTA MARY BETH PHELAN, MD, RDMS DEPARTMENT OF EMERGENCY MEDICINE FOREDTERT MEMORIAL HOSPITAL

  2. Lecture Objectives • Describe clinical role of bedside ultrasound in screening for AAA • Describe the technique of acquiring sonographic images of the aorta • Describe the sonographic appearance of the normal aorta • Describe the sonographic appearance of AAA SAEM

  3. Case History

  4. Case History A 62-year-old man comes to the emergency department at 11PM complaining of left flank pain for approximately 2 hours. He has a history of hypertension. His initial vital signs are: HR 98, RR 24, BP 190/105, Temp 98.0. SAEM

  5. Case History The emergency medicine resident equipped with the latest in emergency medicine ultrasound technology and training, IMMEDIATELY performs an abdominal ultrasound on the patient. This exam reveals the following: SAEM

  6. SAEM

  7. Case History The patient is taken to the OR after only 30 minutes in the ED. SAEM

  8. OVERVIEW • Epidemiology • Clinical presentation • Anatomy • US exam • Sonographic anatomy • Scanning techniques • Pitfalls

  9. Epidemiology • AAA present in 2-4% of the population > 50 • Incidence increasing • Male > female • 10,000 deaths/yr • Rupture has a > 80% mortality rate

  10. Epidemiology: Risk Factors • Cardiovascular disease • Family History increases risk 10-20% • Age > 50 • Smoker

  11. Clinical Perspective Settings in which to perform US in the ED • Abdominal/back/flank pain and hypotension • Stable elderly patient with abdominal or back pain SAEM

  12. Clinical Perspective • Rate of expansion variable • 4-4.9 cm AAA has a 3.3% risk of rupture • 5cm AAA has a 14% risk of rupture • > 5cm has a 20-40% risk of rupture

  13. Clinical Perspective • 4cm or less: annual US examinations • Between 4-5 cm: US every 6 months • Greater than 5cm: Elective repair • Mortality rate for elective repair is 5%

  14. Clinical Presentation • Highly variable • Classic triad: • Abdominal/Back pain • Pulsatile mass • Hypotension • Less than 1/3 of patients will have the triad

  15. Clinical Presentation • Diagnosis • A formidable clinical challenge • Notorious for masquerading as renal colic • May be mistaken for: • Diverticullitis • GI bleed • MI • Musculoskeletal back pain SAEM

  16. Clinical Presentation • Stable vital signs • Back or flank pain, left side > right • Testicular or leg pain • Hypertension • Mortality rate same as elective repair

  17. Clinical Presentation • Vast majority are retroperitoneal • 10 -30 % intraperitoneal • GI bleeding most often seen in patients with aortic grafts • Mortality 50%

  18. Does this patient have an abdominal aortic aneurysm?LEDERLE, JAMA 99 • 2 groups • Sensitivity of examination for ruptured AAA • Sensitivity of exam with increasing size of AAA • CONCLUSION:Cannot be relied on to exclude AAA

  19. Misdiagnosis of Ruptured Abdominal Aortic AneurysmsMARSTON W ET AL J OF VASCULAR SURG 1992 • Misdiagnosis= delay >6hr or other diagnosis • Most common physical findings in misdiagnosed group: ABD PAIN, SHOCK, BACK PAIN • Pulsatile mass present more often in correctly diagnosed group

  20. SUSPECTED LEAKING ABDOMINAL AORTIC ANEURYSM:USE OF SONOGRAPHY IN THE EMERGENCY ROOMSHUMAN WP, ET AL, RADIOLOGY 88 • US IN ED FOR SUSPECTED AAA • 1 MIN EXAM • CORRECTLY IDENTIFIED 31/32 AAA • DECISION TO OPERATE BASED ON 3 CRITERIA CORRECT 21/22 • DX EXTRALUMINAL BLOOD BY SONOGRAPHY POOR 4% (1/24) • NO FALSE NEG EXAMS

  21. Diagnosing AAA • Palpation of the abdomen alone • Plain radiographs • Computed tomography • ULTRASOUND

  22. Diagnosis: PE • Absence of mass does not R/O AAA • Obesity • Bleeding into retroperitoneum may create doughy abdomen. • Hypotension minimizes pulsations

  23. Diagnosis: Plain Radiographs • AAA can be seen in 60-75% of cases • Calcification of aortic wall • Paravertebral mass • Cross table lateral most helpful view • Negative study not helpful

  24. Diagnosis: CT Scan • Near 100% accuracy • Better demonstration of extent of aneurysm • Will detect complications of the aneurysm • Retroperitoneal blood • Dissection • Drawbacks • Contrast • Patient has to leave the ED • Delays time to diagnosis

  25. Diagnosis: US • Ultrasound • Best test for detection of AAA in the ED • Sensitivity 97% to 100% • Small percentage can not be imaged due to bowel gas • 6% in one study SAEM

  26. Diagnosis: US • Ultrasound • In some studies as accurate as CT • Measurements within 3 mm of surgical specimens • Angiography may underestimate AAA diameter SAEM

  27. Diagnosis: US Emergency department ultrasound scanning for abdominal aortic aneurysm: accessible, accurate and advantageous Kuhn et al. Ann Emerg Med 2000 “Relative neophytes can perform aortic ultrasound scans accurately. These scans appear useful as a screening measure in high-risk emergency patients; they may also aide in rapidly verifying the diagnosis in patients who require immediate surgical intervention” SAEM

  28. Diagnosis: US ED Ultrasound Improves Time to Diagnosis and Survival in Ruptured AAA Plummer D, et al: Abstract at 1998 SAEM, Chicago, IL. • Average time to diagnosis by bedside US = 5.4 minutes • Average time to diagnosis by CT = 83 minutes • Average time to OR for diagnosis by US = 12 minutes • Average time to OR for diagnosis by CT = 90 minutes SAEM

  29. US EXAM • Transducer is 2.5-3.0MHz curvilinear • Place the transducer in the subxiphoid area, using the left lobe of the liver as an acoustic window • Pressure must be applied to displace bowel gas • The aorta must be examined in both the longitudinal and transverse planes

  30. Marker LongitudinalOrientation

  31. Marker Transverse Orientation • Orientation is similar to that of a CT scan • Position probe is perpendicular to long axis of body or to long axis of object that is being studied Aorta IVC,Liver SAEM

  32. US EXAM • The aorta appears as an anechoic, pulsatile tubular structure to the left of the spine • After the longitudinal scan, the transducer is rotated 90 degrees to the aorta to obtain transverse views. • The key landmark in the transverse view is to locate the spinal column as a hypoechoic area at the bottom of the screen. • The aorta is located above and to the left of the spine

  33. Left sided structure Thick vascular wall Not compressible Pulsatile Right sided structure Thin wall Will collapse “Sniff” Valsalva May pulsate from aortic transmission AORTA IVC

  34. US EXAM • Measure from outside wall to outside wall • An aneurysm is identified as any measurement of 3 cm or greater • Measure at: • Epigastric region • Take off of SMA • 3-4 cm intervals to bifurcation • Measure any aneurysm

  35. US EXAM • Obesity or excessive bowel gas may obscure the aorta • A coronal view of the aorta may be a reasonable alternative • The patient is supine • The transducer is placed in the mid-axillary line (probe indicator toward the patient’s head) • The aorta is visualized adjacent to the vena cava

  36. SONOGRAPHIC APPEARANCE OF THE NORMAL AORTA: LONGITUDINAL

  37. SONOGRAPHIC APEARANCE OF THE NORMAL AORTA: TRANSVERSE Mid portion Bifurcation

  38. SONOGRAPHIC APPEARANCE OF THE NORMAL AORTA(L LATERAL DECUB/CORONAL)

  39. ABDOMINAL AORTIC ANEURYSM • 90% of AAA are infra-renal • 70% involve the renal vessels • Thrombus is common, and usually forms on the antero-lateral walls of the aneurysm • Two forms • Sacular • Fusiform – most common

  40. ABDOMINAL AORTIC ANEURYSM • First sign may be loss of normal taper • AP diameter > 3CM • Focal dilitation even if less than 3 cm • Thrombus • Intimal flap

  41. AORTIC ANEURYSM

  42. Large fusiform AAA SAEM

  43. AAA with clot SAEM

  44. Another AAA with clot SAEM

  45. ULTRASOUND EXAM: PITFALLS • Bowel gas can be a major problem • Apply pressure • Roll the patient on their left side ( use the liver as an acoustic window) • Does not detect complications of AAA • Retroperitoneal rupture • Dissection • CT/MRI/angiography for stable patients is still recommended

  46. Failure to acquire high resolution images due to bowel gas Inaccurate measurements – do not measure what you cannot see! Distinguishing the IVC from the aorta Not identifying extraluminal fluid Failing to distinguish the normal “tortuous” aorta from an abdominal aortic aneurysm. Pitfalls in Technique

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