Abdominal aortic aneurysm (ruptured and intact)

A ruptured abdominal aortic aneurysm is among the most lethal emergencies in medicine, and the Fellowship candidate must recognise it at the bedside, resuscitate with permissive hypotension (not a full blood pressure), and route the patient to the theatre or the catheter-laboratory without a CT scan. The intact aneurysm, by contrast, is silent, found on screening, and managed electively at the 5.5-cm threshold. The two share a pathology but not an urgency.[1][2]

Definition and classification

An abdominal aortic aneurysm is a permanent, localised dilation of the abdominal aorta to 3 cm or more (or 1.5 times the normal diameter), most commonly infrarenal. It is classified by its clinical state: an intact aneurysm is asymptomatic and found on screening or incidentally; a symptomatic (expanding or tender) aneurysm is a pre-rupture warning that needs urgent repair; and a ruptured aneurysm is the lethal emergency. The rupture is usually into the retroperitoneum (contained by the tissue pressure — a tamponade) and less commonly into the peritoneum (free, and fatal within minutes). [1]

Pathophysiology — Laplace's law and permissive hypotension

The wall tension of a vessel is proportional to the pressure and the radius (Laplace's law), so the larger the aneurysm, the higher the wall stress, the faster it grows, and the greater the risk of rupture — an exponential spiral. The wall thins and the structural elastin and collagen degrade with age, smoking and inflammation. When the aneurysm ruptures into the retroperitoneum, the extravasated blood is contained by the tissue pressure, forming a tamponade that limits the ongoing bleeding — this is the physiology behind permissive hypotension. A full resuscitation to a normal blood pressure raises the transmural pressure and disrupts the tamponade, causing a catastrophic re-bleed; a lower blood pressure (a systolic of 80 to 100) is enough for consciousness and urine output and preserves the tamponade.[1]

Epidemiology and risk factors

AAA is predominantly a disease of the older male smoker. The prevalence is 4 to 8 per cent in men over 65 (the population that screening programmes target), and roughly 1 to 2 per cent in women of the same age.[1] Smoking is the single strongest modifiable risk factor — it triples the risk of aneurysm formation and quadruples the risk of rupture — and smoking cessation slows the growth. The other risk factors are age (prevalence rises steeply after 65), male sex (a four-to-six-fold excess), hypertension, atherosclerosis, and a family history of an AAA in a first-degree relative (which roughly doubles the prevalence and warrants earlier screening, often from age 55 in men with an affected relative). The connective-tissue disorders (Marfan syndrome, vascular-type Ehlers-Danlos, Loeys-Dietz) and the vasculitides (Takayasu, giant-cell arteritis) produce aneurysms at a younger age but are uncommon. Women rupture at smaller diameters and present later, which is why the elective-repair threshold is lower for them.

Rupture risk by aneurysm diameter

The rupture risk is the single statistic that sets the elective-repair threshold, and it rises exponentially — not linearly — with diameter. The widely cited population estimates are: under 4 cm, less than 1 per cent per year; 4 to 5.5 cm, between 1 and 11 per cent per year; over 5.5 cm, over 30 per cent per year; and over 6 cm, the high-risk zone where rupture becomes a near-term probability rather than a distant possibility.[1] The growth rate itself accelerates with size (a 3-cm aneurysm grows roughly 0.1 to 0.2 cm a year; a 5-cm aneurysm grows faster), reinforcing the exponential spiral that Laplace's law predicts. Because the risk is non-linear, the surveillance interval shortens as the aneurysm enlarges — a 3 to 4 cm aneurysm is rescanned every two to three years, a 4 to 4.5 cm aneurysm yearly, and a 4.5 to 5.5 cm aneurysm every six months until it crosses the operative threshold.

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Population screening

A one-time ultrasound of the abdominal aorta in men aged 65 to 74 reduces aneurysm-related mortality and is cost-effective, on the strength of the four randomised screening trials (MASS, Chichester, Viborg, Western Australia).[7] MASS, the largest, showed a sustained mortality benefit out to 10 years and remains the evidence cornerstone. Screening is not routinely recommended for women (the prevalence is low and the benefit marginal), for men under 65 (the prevalence is too low), or as a repeated lifelong test (a normal scan at 65 makes a later rupture very unlikely). The incidental finding of an AAA on an ultrasound, CT, or MRI performed for another reason — the back-pain scan, the renal-colic CT, the prostate workup — is a common route to diagnosis and must always be followed up with a measured diameter and a surveillance or referral plan.

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The rupture — presentation and the triad

The classic presentation is the triad (present in only about half the patients): sudden, severe abdominal, back or flank pain, hypotension, and a pulsatile abdominal mass. The atypical presentations are dangerous: a syncope or a collapse alone (from the acute blood loss), a groin pain that mimics renal colic (the older patient with "a stone" is always an AAA until proven otherwise), an acute limb ischaemia (a thromboembolism from the sac), and a gastrointestinal bleed (an aorto-enteric fistula — a "herald" bleed that precedes a massive, fatal haemorrhage). The key is a high index of suspicion in the older male smoker with abdominal or back symptoms. [1]

The triad is the headline, but the dangerous presentations are the ones that violate it. Each atypical rupture carries a classic trap that the Fellowship candidate must be able to name aloud. [1]

Differential diagnosis

The abdominal or back pain of a ruptured AAA has a differential, and the danger is treating it as something less lethal. [1]

Investigations and the stability decision

The single most important decision is the stability, because it determines the imaging. The unstable patient with a clinically suspected rupture is diagnosed at the bedside — a pulsatile mass and a bedside ultrasound that confirms the aneurysm's diameter — and goes straight to the theatre or the catheter-laboratory without a CT scan, because the delay is lethal. The stable or the equivocal patient (a possible leak, an unclear cause) gets a rapid CT angiography that confirms the aneurysm, the rupture site, the contrast extravasation, and the suitability for an endovascular repair. Blood is drawn for a group and crossmatch (6 to 10 units), a full blood count, the coagulation, the electrolytes and the lactate, and the massive haemorrhage protocol is activated. An ECG excludes a myocardial infarction as a differential or a precipitant. [1]

Bedside ultrasound in the unstable patient

In the haemodynamically unstable patient with a suspected rupture, point-of-care ultrasound is the only imaging that should happen. The operator images the aorta in the transverse plane from the xiphisternum caudally to the bifurcation, measuring the maximal outer-wall to outer-wall diameter; an aortic diameter of 3 cm or more confirms the aneurysm, and in the right clinical setting (an unstable older patient with abdominal or back pain) that confirmation is sufficient to take the patient to theatre. Critically, the ultrasound confirms the aneurysm but not the rupture — there is no free fluid to see because the blood is contained retroperitoneally, and a normal-looking aorta does not exclude a para-anastomotic or iliac rupture — so a clinical suspicion with a confirmatory aneurysm goes to the operating room regardless. The FAST (focused assessment with sonography in trauma) sweep may show a thin sliver of intraperitoneal fluid in the free intraperitoneal rupture, but its absence is meaningless. [1]

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Immediate management — permissive hypotension and the protocol

Stabilise the airway and the breathing, give oxygen, and apply the permissive-hypotension principle. [1]

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The massive haemorrhage protocol delivers the blood products in packs of red cells, fresh-frozen plasma and platelets in a 1:1:1 ratio, and includes calcium replacement (10 mL of 10 per cent calcium chloride intravenously after every four units of red cells) to counteract the citrate-induced hypocalcaemia of the massive transfusion. The resuscitation fluid is blood, not crystalloid: a 250 mL aliquot of a balanced crystalloid is used to maintain the conscious level between the blood-product packs, and a larger crystalloid volume is avoided because it dilutes the coagulation factors and worsens the bleeding. A vasopressor is avoided in principle, but a noradrenaline infusion at 0.05 to 0.5 micrograms per kilogram per minute is reserved for the profoundly unconscious patient (a systolic under 70) where the permissive-hypotension target cannot be met and the brain is at risk. The patient is kept warm with a forced-air warmer and a fluid warmer, because a core temperature below 35 degrees Celsius produces a coagulopathy that worsens the bleeding, and the coagulation is monitored with a point-of-care viscoelastic test (a ROTEM or a TEG) and corrected with cryoprecipitate and fibrinogen as the products are transfused. The anaesthetist is warned of the risk of an induction hypotension and a rapid blood loss on the cross-clamp. The early notification of the vascular surgeon, the anaesthetist, the theatre and the blood bank is the single most important system step — it is the call that buys the minutes the patient has. [1]

Definitive management — the repair

The ruptured AAA is repaired immediately by an open surgical repair (a laparotomy, a supracoeliac cross-clamp, and a tube or a bifurcation graft) or an endovascular aneurysm repair (EVAR) (a stent-graft delivered from the femoral access, if the anatomy is suitable and the centre is equipped). The IMPROVE trial showed that an endovascular-first strategy for a suspected rupture reduced the 30-day mortality in suitable patients.[2] The choice depends on the haemodynamic stability, the computed-tomographic anatomy (if available), and the centre's capability. The symptomatic non-ruptured aneurysm is repaired urgently within 24 hours. The asymptomatic aneurysm is repaired electively at or above 5.5 cm in men and 5.0 cm in women, and surveilled with a yearly ultrasound below the threshold.[1]

Open versus endovascular repair — the anatomy decides

EVAR is only possible if the anatomy fits, and the eligibility rests on four features of the preoperative CT: a proximal aneurysm neck (a length of normal aorta below the renal arteries for the stent-graft to grip) of at least 10 to 15 mm, a neck diameter under about 28 mm, a neck angulation under 60 degrees, and non-diseased access vessels (common femoral and iliac arteries of adequate calibre to admit the delivery sheath). Only about half of all ruptures meet these criteria on anatomy alone. Open repair has no anatomical constraint but carries the cost of a laparotomy, a supracoeliac cross-clamp (with its renal, mesenteric and spinal-perfusion insult), and a higher physiological burden; it remains the default where EVAR anatomy is unfavourable or the centre is not equipped for an emergency endovascular repair. [1]

The endoleak — the EVAR-specific late problem

An endoleak is persistent blood flow into the aneurysm sac after EVAR, and it is the reason every EVAR patient needs lifelong CT surveillance. The five types matter for the viva: type 1 (an incomplete seal at the proximal or distal attachment — high pressure, needs repair), type 2 (retrograde flow from a lumbar or inferior mesenteric artery — low pressure, the commonest, often observed), type 3 (graft fabric tear or component separation — high pressure, needs repair), type 4 (graft porosity, perioperative, self-limiting), and type 5 (continued sac expansion with no identifiable leak — "endotension"). Types 1 and 3 threaten rupture and need re-intervention; type 2 is usually watched unless the sac grows. [1]

REBOA — the bridge to definitive control

Resuscitative endovascular balloon occlusion of the aorta (REBOA) inflates a balloon in the descending thoracic aorta (zone 1, above the coeliac) or the infrarenal aorta (zone 3) to arrest non-compressible torso haemorrhage. In the ruptured AAA it is deployed as a bridge — to stabilise the blood pressure and reduce ongoing loss while the patient is moved to theatre or the endovascular suite — not as definitive treatment. Its risks are ischaemia distal to the balloon (renal, mesenteric, spinal, limb), and the occlusion time must be kept short and reassessed continuously. In the arresting or peri-arrest patient it can replace an emergency resuscitative thoracotomy with aortic cross-clamping as the initial control manoeuvre. [1]

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Elective repair thresholds and surveillance

The asymptomatic aneurysm is managed by diameter against a surveillance schedule, and the operative threshold balances the annual rupture risk against the operative mortality.[1] In men, elective repair is offered at 5.5 cm; in women, at 5.0 cm (because women rupture at smaller diameters). A rapid growth rate (over 0.5 cm in six months, or over 1 cm a year) is an independent indication to repair even below the diameter threshold, as is a symptomatic aneurysm (tenderness or back pain), which is treated as a pre-rupture and repaired urgently. Below the threshold, surveillance follows the growth: 3 to 4 cm every two to three years; 4 to 4.5 cm yearly; 4.5 to 5.5 cm every six months.

The trials in brief — open, EVAR, and the ruptured-aneurysm question

The elective EVAR evidence rests on three randomised trials (EVAR-1, DREAM, OVER) that each showed a short-term survival advantage for EVAR that narrows with long-term follow-up as late ruptures and re-interventions accrue. The ruptured-aneurysm evidence is the IMPROVE trial and its longer-term follow-up, plus the Sweeting individual-patient-data meta-analysis that pooled the rupture trials.[2][3][4][5][6][8]

Aorto-enteric fistula — the herald bleed

An aorto-enteric fistula is a communication between the aorta (native or, far more commonly, a graft) and the bowel, almost always the third or fourth part of the duodenum. The classic history is a herald (sentinel) bleed — a small, self-limiting episode of upper gastrointestinal bleeding — followed hours to days later by a massive, exsanguinating haemorrhage as the fistula opens fully. The single most important risk factor is a prior AAA repair (open or endovascular): any patient with a known aortic graft who presents with any gastrointestinal bleeding has an aorto-enteric fistula until proven otherwise. Endoscopy may miss it (the fistula is distal, in the duodenum, and easy to overlook); CT angiography is the diagnostic test of choice, and the management is urgent surgery, often with an endovascular bridge to control the bleeding first. A primary aorto-enteric fistula (in a native, ungrafted aneurysm) is rarer but follows the same rule. The trap is to manage the herald bleed as a simple upper GI bleed and discharge the patient, who then returns with the fatal bleed. [1]

[1]

Perioperative and anaesthetic pitfalls

The anaesthetic induction in the ruptured AAA is itself a high-risk moment: the sympathectomy of induction on a hypovolaemic, vasoconstricted patient precipitates a profound drop in blood pressure, and the loss of the compensatory tone can unmask the full extent of the bleed. The vascular and anaesthetic teams therefore prepare for an induction hypotension with blood already running and the surgeon scrubbed and ready to cross-clamp or balloon-occlude the moment the patient is anaesthetised. The supracoeliac cross-clamp controls the bleeding but at the cost of mesenteric, renal and spinal ischaemia; it is released to an infrarenal position as soon as the proximal control is secured. The lethal triad of hypothermia, acidosis and coagulopathy is the on-table enemy, and damage-control resuscitation — warmed blood in a 1:1:1 ratio, calcium, viscoelastic-guided factor replacement, and prompt definitive control — is aimed at breaking the triad before it becomes irreversible. The patient who survives the operation is admitted to the intensive care for the reperfusion, the renal, the respiratory and the abdominal-compartment consequences of the insult. [1]

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Complications and pitfalls

The complication of the untreated rupture is a massive haemorrhage and death; the complications of the repair are the renal failure (from hypoperfusion and the contrast), the colonic ischaemia, the spinal-cord ischaemia, the lower-limb ischaemia, the graft infection, and the late aorto-enteric fistula. The pitfalls are the inverse of the protocol: over-resuscitation disrupting the tamponade; waiting for a CT in the unstable patient; missing the diagnosis by treating the patient as a renal colic or a pancreatitis; not activating the massive haemorrhage protocol; and delaying the surgical or the endovascular activation. [1]

Prognosis and disposition

The overall mortality of a ruptured AAA is 80 to 90 per cent, including the pre-hospital deaths; of those who reach the theatre alive, about half survive. The symptomatic non-ruptured aneurysm has a much better prognosis with an urgent repair, and the elective repair carries a mortality of 2 to 5 per cent. The patient with a rupture is taken directly to the theatre or the catheter-laboratory and then to the intensive care. The long-term endovascular patient is surveilled for an endoleak. [1]

The survival is also determined by the time from the rupture to the cross-clamp or the balloon occlusion — every minute of delay increases the blood loss, the coagulopathy and the multi-organ failure that follows, which is why the pre-hospital notification and the theatre-activation pathway are as important as the operative technique itself. [1]

The elderly male smoker is the classic patient, and the combination of smoking and age accounts for most of the population risk. Women have a lower prevalence but a higher rupture risk at a smaller diameter, so the elective-repair threshold is lower (5.0 cm) and the diagnosis is more often missed because it is less expected. A family history of an AAA in a first-degree relative lowers the screening age and raises the prevalence. The cardiac comorbidity (ischaemic heart disease, heart failure) raises the perioperative risk of both the open and the endovascular repair and may determine the repair strategy — the patient who cannot tolerate a cross-clamp may be better served by an endovascular approach. [1]

Evidence and regional guidelines

The contemporary framework is the 2022 ACC/AHA aortic disease guideline.[1] The endovascular-first strategy evidence is the IMPROVE trial.[2] The repair approach (open vs EVAR) and the screening programme follow the local vascular-society pathway — in ANZ there is no universal screening programme, and the repair choice is governed by the centre's vascular service.

A basket of high-yield pearls

[1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1] [1]

Additional red flags

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Exam pearls

• Triad: sudden abdominal/back pain + hypotension + pulsatile mass — present in only ~50 per cent.
• Unstable → clinical diagnosis → theatre, NOT a CT scanner.
• Permissive hypotension: systolic 80 to 100 — do not disrupt the retroperitoneal tamponade.
• Activate the massive haemorrhage protocol: blood : FFP : platelets 1:1:1, crossmatch 6 to 10 units.
• Always consider AAA in the older patient with apparent renal colic.
• 5.5 cm (men) / 5.0 cm (women) = the elective-repair threshold.
• Mortality ~80 to 90 per cent overall; ~50 per cent of those who reach the theatre. [1]

Exam practice

[1] [1]

Red flags

[1]

References

1. [1]Isselbacher EM, Preventza O, Hamilton Black J, et al. 2022 ACC/AHA guideline for the diagnosis and management of aortic disease: A report of the American Heart Association/American College of Cardiology Joint Committee on Clinical Practice Guidelines J Thorac Cardiovasc Surg, 2023.PMID 37389507
2. [2]IMPROVE Trial Investigators. Endovascular or open repair strategy for ruptured abdominal aortic aneurysm: 30 day outcomes from IMPROVE randomised trial BMJ, 2014.PMID 24418950
3. [3]IMPROVE Trial Investigators. Comparative clinical effectiveness and cost effectiveness of endovascular strategy v open repair for ruptured abdominal aortic aneurysm: three year results of the IMPROVE randomised trial BMJ, 2017.PMID 29138135
4. [4]Greenhalgh RM, Brown LC, Kwong GP, et al. Comparison of endovascular aneurysm repair with open repair in patients with abdominal aortic aneurysm (EVAR trial 1), 30-day operative mortality results: randomised controlled trial Lancet, 2004.PMID 15351191
5. [5]Prinssen M, Verhoeven EL, Buth J, et al. A randomized trial comparing conventional and endovascular repair of abdominal aortic aneurysms N Engl J Med, 2004.PMID 15483279
6. [6]Lederle FA, Freischlag JA, Kyriakides TC, et al. Outcomes following endovascular vs open repair of abdominal aortic aneurysm: a randomized trial JAMA, 2009.PMID 19826022
7. [7]Kim LG, Scott RA, Ashton HA, et al. A sustained mortality benefit from screening for abdominal aortic aneurysm Ann Intern Med, 2007.PMID 17502630
8. [8]Sweeting MJ, Bown MJ, Roy-Choudhury P, et al. Ruptured Aneurysm Trials: The Importance of Longer-term Outcomes and Meta-analysis for 1-year Mortality Eur J Vasc Endovasc Surg, 2015.PMID 25981698