Friday, April 22, 2011

Case Discussion by Dr. Dan Paling

Abdominal Aortic Aneurysm (AAA) is a potentially life-threatening condition that is frequently diagnosed incidentally when working up various abdominal complaints, and is often undiagnosed until the time of rupture. It is important for EM physicians to know that elderly  white males are at the highest risk of having an AAA. High risk patients complaining of abdominal or back pain should receive a bedside ultrasound to screen for the possibility of AAA as the cause of their clinical presentation. 

Managing patients with an AAA in the emergency department is primarily focused on heart rate and blood pressure control as well as appropriate surgical consultation. Once an AAA is diagnosed (normally with u/s), a CT angiogram should be performed to determine the AAA’s location and potential involvement with other vessels including the SMA, IMA, renal and iliac arteries. Patients with asymptomatic AAAs less than 5.5 cm can be watched and followed by a vascular surgeon. The patient should undergo abdominal ultrasonography every 6 to 12 months to assess the extent of further dilation if the aneurysm is less than 5.5 cm, is completely infrarenal, and only involves the aorta. 

A CT angiogram should be performed every 6 to 12 months in patients with SMA, renal and/or iliac artery involvement. 

Symptomatic patients may present with vague or sharp abdominal pain, low back pain, and/or the sensation of an abdominal pulsation. Patients with AAA not complaining of pain may present with syncope, nausea, vomiting, or early satiety. Patients with AAA that complain of abdominal tenderness (usually epigastric) are likely to have an expanding or infected AAA. These patients should receive an immediate surgical consultation as rupture can be spontaneous and imminent. Blood pressure control is the goal in these patients. Intravenous beta blockers are the drug of choice for acutely reducing blood pressure and heart rate. Goals of treatment include a heart rate of 55 to 65 bpm and a systolic blood pressure of 100 to 120mmHg or a MAP of 60 to 65 mmHg. If this SBP range is not achieved with a beta blocker alone and the patient has good mentation, nitroprusside can be added at 0.5mcg/kg/min until the blood pressure is controlled. 

A ruptured AAA can present similarly to a myocardial infarction with syncope, hypotension, epigastric pain, nausea, vomiting, and diaphoresis. As many as 30% of AAAs are misdiagnosed on presentation, therefore ED physicians should have a high level of suspicion in patients with h/o AAA or that fall into the high risk categories (ie., white males of advanced age, patients with MCTD (spell out), or smokers with PVD). Rapid diagnosis, resuscitation and surgical consultation are required for treating these patients.

Answers to Questions
  1. “(e) tobacco smoking” is the correct answer. There are several risk factors, both unmodifiable and modifiable, for developing an AAA. Smoking is the leading modifiable risk factor. It is hypothesized to increase a patient’s risk by 8-fold over a nonsmoker of similar age and comorbidities. (c) stress and (d) insomnia are not risk factors for the development of an AAA.  (a) alcohol abuse and (b) diabetes mellitus are modifiable risk factors for the development of many other disorders including cardiovascular disease, but have not been linked to an increased incidence of AAA.
  1. “(b) AAA that has enlarged from 4.7 to 5.0cm in the past 6 months” is the correct answer. Many AAAs are medically managed while being monitored by a vascular surgeon. Asymptomatic AAAs that are less than 5.5cm in diameter are managed medically until they become (a) symptomatic (regardless of size), (b) rapidly expanding (>0.5 cm in a 6 month period), (c) larger than 5.5 cm in diameter, or (e) ruptured, at which time surgical intervention is necessary.
  1. “(b) aneurysm diameter” is the correct answer. The three main predictors of AAA rupture are size (aneurysm diameter), (c) rapid expansion (>0.5cm in 6 month period), and (e) female gender (18 vs 12% in males with aneurysms > 5.5cm), but the most important predictor for AAA rupture is aneurysm diameter. (d) Family history of AAA rupture and (a) advanced age are risk factors for AAA development, not rupture.
Clinical Pearls
  • AAA rupture is misdiagnosed in nearly 30% of patients upon presentation. Have a high level of clinical suspicion for the high risk groups!
  • Heart rate (<65 bpm) and systolic blood pressure (100 to 120 mmHg) control are the keys to managing symptomatic / acutely expanding AAAs. Intravenous beta blockers are the drug of choice for HR and BP control.
  • Patients should be counseled on smoking cessation and proper follow-up once an AAA is diagnosed.

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