Recommendations for research
The guideline committee has made the following recommendations for research.
What are the most effective and cost-effective frequencies for monitoring people with unruptured abdominal aortic aneurysms (AAA) of different diameters, and what is the optimal AAA threshold size (inner-to-inner maximum anterior-posterior diameter on ultrasound) for repair?
More frequent monitoring increases the chances of identifying aneurysms that have grown large enough to be considered for repair. However, monitoring requires resources and the absolute risk of AAA rupture is relatively low, so there are opportunity costs to consider. It is important to establish how often aneurysms should be monitored to keep the risk of rupture as low as possible while making the best use of NHS resources.
The optimal threshold for repair of an AAA is not clear. There is good evidence that in most cases people do not need repair for aneurysms measuring smaller than 5.5 cm (inner-to-inner maximum anterior-posterior aortic diameter) on ultrasound. However, for some people a threshold above 5.5 cm may be more appropriate.
2 Effectiveness of endovascular aneurysm repair and open surgical repair of complex unruptured and ruptured abdominal aortic aneurysms
What is the effectiveness and cost effectiveness of complex endovascular aneurysm repair (EVAR) versus open surgical repair in people for whom open surgical repair is suitable for:
elective repair of an unruptured AAA or
emergency repair of a ruptured AAA?
EVAR is a widely performed non-invasive alternative to open surgical repair. However, it is more expensive. Although standard EVAR has been shown to produce no long-term benefit over open surgical repair in people with an unruptured infrarenal abdominal aortic aneurysm, it is less clear whether this is the same in people with who would need complex EVAR to repair their AAA. The committee's view was that, because current practice is subject to strong prior beliefs about the relative benefits and harms of EVAR and open surgical repair for complex AAA, randomisation is critical to provide an unbiased estimate of comparative effectiveness.
What are the benefits and harms of macrolides (such as azithromycin) for reducing AAA growth rates and the risk of rupture?
Small AAAs are currently managed by monitoring, until the aneurysm reaches a diameter at which surgical repair is considered. There are currently no non-surgical interventions available to prevent AAAs from growing, and subsequently rupturing. A randomised controlled trial would be useful to determine whether macrolides reduce the rate of AAA growth and the risk of rupture.
What are the benefits and harms of metformin for reducing AAA growth rates and the risk of rupture?
Observational study data suggest an association between diabetes and slower AAA growth, and it has been proposed that this may be due to the use of metformin. A randomised controlled trial is needed to determine whether metformin reduces the rate of AAA growth and the risk of rupture.
5 Tranexamic acid for preventing and treating excessive blood loss during EVAR or open surgical repair
Does tranexamic acid reduce blood loss and so improve survival in people who are having repair (EVAR or open surgical repair) of a ruptured AAA?
Tranexamic acid is used to reduce blood loss in major trauma, postpartum bleeding and surgery. By slowing down blood loss from a ruptured AAA, the use of tranexamic acid may improve survival from ruptured AAA. A randomised controlled trial is needed to determine whether tranexamic acid improves survival in people having EVAR or open surgical repair of a ruptured AAA.
6 Prehabilitation (including preoperative exercise programmes) for improving the outcome of aneurysm repair
What is the clinical effectiveness and cost effectiveness of prehabilitation, including preoperative exercise programmes, for improving outcomes of people who are having repair of an AAA?
What are the benefits of postoperative use of direct oral anticoagulants (DOACs) for improving outcomes after repair of AAA?
Does permissive hypotension improve survival of patients undergoing repair of ruptured AAA?