The risk of rupture of AAA is related to size and rate of expansion. There have been multiple studies that have found a consistent relationship with risk of rupture and size > 5 cm. Expansion rates vary as well with the highest risk in those expanding at a rate > 0.4 cm/year. The most important factor affecting this rate, based on the Law of Laplace, is blood pressure. The risk of rupture for aneurysms < 4 cm is 2%, 4-5 cm 3-12% and > 5 cm 25-41%. The figure demonstrated rupture risk in person years.

Only 50% of patients with rupture have the classic signs. However any patient with hypotension and abdominal pain with a known history of AAA is taken for surgery. Aneurysms typically rupture into the retroperitoneum and are frequently tamponaded initially. Resuscitation to a euvolemic state should be tempered and take place in the operating room if the patient is conscious and has adequate peripheral perfusion (Fig. 18.1).

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