Page 156 - Libro vascular I

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DUPLEX ASSESSMENT OF ANEURYSMS
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A small aortic aneurysm is generally regarded as an aorta having a diameter of 3–3.5 cm, and many sur- geons will not request serial screening scans unless the aorta reaches this level. However, some vascular units monitor patients with slightly enlarged aortas, especially if the patient is young. As the aorta increase in size, there is a potential for rupture due to increased tension in the arterial wall. The UK Small Aneurysm Trial Participants (1998) demon- strated that the average annual growth rate of aneurysms measuring between 4 and 5.5cm was 0.33 cm a year. However, rates will vary among indi- viduals and are also dependent on the size of the aneurysm. The prevalence of aortic aneurysms is six times greater in men than women (Vardulaki et al 2000). In addition, there seems to be a strong famil- ial link, with siblings of aneurysm patients having a higher risk of developing an aneurysm compared with the general population.
Clinically, there are usually no symptoms associ- ated with the development of an aortic aneurysm and many are discovered incidentally, during routine examinations or on plain abdominal radiographs. Occasionally, patients present with symptoms of renal hydronephrosis. This is caused by compression of a ureter leading from one of the kidneys by the aneurysm sac and most frequently occurs on the left side. The symptoms associated with aneurysm leak- age or rupture include back or abdominal pain and acute shock. Ultrasound is occasionally used to con- firm the diagnosis in the emergency room, although the symptoms are usually so acute that emergency surgery is required. The mortality rate for acute rup- ture of an aortic aneurysm is very high, 65–85% (Kniemeyer et al 2000), and many patients do not reach hospital alive.
The risk of aortic aneurysm rupture increases with size. The UK Small Aneurysm Trial Participants (1998) found that the mean risk of rupture of aneurysms measuring 4–5.5cm was 1% per year. However, larger aneurysms carry a higher rate of rupture, and a recent study demonstrated that the average risk of rupture in male patients with a 6 cm aneurysm was 14% per year (Brown et al 2003).
Clearly, there are benefits in detecting aneurysms at an early stage so that serial follow-up can be carried out and elective repair performed if the aneurysm becomes too large. The UK Small Aneurysm Trial Participants (1998) have shown no
survival benefit for open repair of aneurysms meas- uring less than 5.5cm in diameter compared to ultrasound surveillance. In this study, age, sex or ini- tial aneurysm size did not modify the overall hazard ratio. Therefore, many surgeons will only carry out elective repair if the aneurysm has a diameter of equal to or greater than 5.5 cm, or if there are indi- cations that smaller aneurysms are becoming symp- tomatic and are at risk of rupturing. There is now reliable evidence that aortic screening programs, involving a single ultrasound scan of men aged 65 years or over, is beneficial and cost-effective in reducing aneurysm-related mortality (Ashton et al 2002). Although aortic aneurysms are much more prevalent in men, there is some evidence that women with aneurysms in the 5–5.9 cm range may be up to four times more likely to undergo rupture compared to men with similar sized aneurysms (Brown et al 2003). Further research may prompt a lower threshold for repairing aneurysms in female patients.
Surgical techniques for aortic
aneurysm repair
Open repair
Open repair of aortic aneurysms has been performed for over 20 years and involves a large incision in the abdomen and mobilization of the intestines to expose the aorta. Fortunately, the majority of abdominal aneurysms (approximately 95%) start below the level of the renal arteries (infrarenal aneurysms). This means that surgical clamps, to control the aneurysm, can be positioned below the renal arter- ies, ensuring that the kidneys are perfused during the operation. Aortic aneurysms that extend above the renal arteries (suprarenal aneurysms) carry a higher rate of perioperative and postoperative com- plication, as the aorta has to be clamped above the level of the renal arteries and reimplantation of the renal arteries is necessary. Patients can suffer from renal failure following this procedure. This is why it is important that the surgeon be aware of the level of the proximal neck before surgery is performed. Aortic aneurysms are repaired using straight tube grafts unless the aneurysm extends into the iliac arteries, where a bifurcating graft is used. The graft is sutured into position and the sac closed around