Ruptured aortic aneurysm

What is a ruptured aortic aneurysm?

When the aorta ruptures spontaneously, rather than as the result of trauma, it is usually in an aortic aneurysm. Rupture of an aortic aneurysm should not be confused with aortic dissection. Aortic rupture describes a tear through all three layers of the aorta, whereas an aortic dissection describes when there is a tear in the tunica intima, allowing blood to separate (dissect) the tunica intima from the tunica media.

Progressive aneurysm enlargement can lead to rupture and massive internal bleeding, which is a fatal event unless timely repair can be achieved.¹

The aorta is such a large blood vessel that, if it ruptures, death is very rapid, although the process might be slow enough to permit emergency surgery. However, time is of the essence. The ideal management is to repair the aneurysm before rupture occurs. Often there is no knowledge of the presence of an aneurysm and the first sign is rupture, rapid exsanguination and death.

How common is a ruptured aortic aneurysm? (Epidemiology)?

Ruptured abdominal aortic aneurysms (AAAs) cause 6,000 deaths per year.² Around two-thirds of deaths from AAAs occur in men.³

Risk factors

The presence of an aneurysm is a risk for rupture.⁴⁵ The larger the lesion, the more likely it is to bleed; aneurysms over 6 cm have a 25% annual risk of rupture. Smoking and hypertension are additional risks.

Symptoms of a ruptured aortic aneurysm (presentation)⁶

A dissecting or ruptured aneurysm usually presents with pain and collapse.

Thoracic aortic aneurysm (TAA)

• It will cause chest pain that may be indistinguishable from acute myocardial infarction in terms of nature and distribution.

• Haemoptysis can occur.

• If bleeding occurs into the mediastinum, it can cause cardiac tamponade and rapidly be fatal. The patient will probably never reach hospital alive and the diagnosis is made post-mortem.

Abdominal aortic aneurysm (AAA)

• Ruptured AAA presents with a classical triad of pain in the flank or back, hypotension and a pulsatile abdominal mass; however, only about half have the full triad.

  • A ruptured AAA can present with similar symptoms to renal colic and may be misdiagnosed as such, particularly in older adults.

• The patient will complain of the pain and may feel cold, sweaty and faint on standing.

• Other common symptoms include syncope and vomiting.

Examination

• A patient with a ruptured aneurysm at any level is likely to look pale and unwell and to be cold and sweaty.

• The pulse will be rapid, weak and thready. Hypotension is common.

• With a ruptured AAA there may well be a pulsatile mass in the vicinity of the bifurcation of the aorta. This is a few centimetres above the umbilicus and a little to the left.

• It may be tender and a bruit may be audible. Bleeding causes peritoneal irritation and it may appear as an acute abdomen.

• Occasionally the presentation can be atypical - eg, intestinal obstruction from haematoma or an apparent irreducible inguinal hernia.

Differential diagnosis

• The differential diagnosis for a ruptured TAA is that of chest pain, especially myocardial infarction with cardiogenic shock but also massive pulmonary embolism.

• The differential diagnosis for ruptured AAA involves other causes of abdominal pain, including acute abdomen.

Diagnosing a ruptured aortic aneurysm (investigations)

If an aneurysm is ruptured, investigations need to be swift and pertinent.

Where there is a strong clinical suspicion of an aneurysmal rupture, investigations should not delay transfer to a specialised vascular centre.⁶

Laboratory studies

Blood tests do not make the diagnosis of a rAAA, but may be useful to identify organ dysfunction, coagulopathies, and, potentially, alternative diagnoses. The following may be considered, but, again, should not delay definitive surgical management:

• FBC: NB: if there has not been time for haemodilution then haemoglobin will be normal. Anaemia is present in less than half of patients. Around 80% have a white cell count of 10 x 10⁹/L or more.

• Group and rapid cross-match: in anticipation of the need for massive transfusion intraoperatively.

• Venous blood gases.

• Baseline biochemistry of U&Es.

• If alternative diagnoses are suspected: amylase, troponin.

Radiology⁶

• Ultrasound: Point-of-care ultrasound can confirm the presence and size of an aortic aneurysm, although it cannot exclude rupture alone. It is operator-dependent and requires sufficient training and expertise; however, this is now widely present amongst emergency physicians.

  • The presence of an AAA on ultrasound, along with abdominal or back pain, or hypotension, strongly supports the clinical diagnosis of a ruptured AAA.

  • Conversely, a well-visualised, normal aorta in a haemodynamically stable patient excludes a ruptured AAA.

• CT: A CT with IV contrast is the 'gold standard' investigation in haemodynamically-stable patients. It is also usually performed pre-operatively even in haemodynamically-unstable patients.⁷ As well as diagnosing or excluding a ruptured AAA, it aids surgical planning for endovascular or open repair.

Managing a ruptured aortic aneurysm

This is a surgical emergency.

• Get large-bore intravenous access as soon as possible and preferably before hospital.⁸

• Group and cross-match. Large supplies of blood and blood products, including platelets and fresh-frozen plasma, should be readily available.

• When using fluid resuscitation, aim to keep the systolic blood pressure between 90 and 120mmHg.⁶ Excessive fluid resuscitation may worsen bleeding, both by increasing blood loss as blood pressure rises, and by haemodilution of clotting factors. Some recommend permissive hypotension, ie aiming for systolic blood pressures between 70 and 90mmHg,⁷ although this may be too low in older patients.⁶

Transfer to a specialist centre

• Vascular surgery is increasingly concentrated within fewer, but higher-volume, specialist hospitals.

• Therefore, patients often need to be referred and transferred from the initial presenting hospital to a receiving specialist centre for definitive management.

• Both RCEM⁶ and NICE⁹ have produced guidance on selecting patients who are candidates for emergency transfer:

  • Patients with a ruptured AAA and persistent loss of consciousness, or cardiac arrest, have a negligible chance of surviving surgical repair, and it is often more appropriate to offer palliative end-of-life treatment without transfer.

  • Likewise, patients requiring intubation or inotropes are unlikely to survive transfer, and it may be appropriate not to transfer, following discussion between a senior emergency medicine physician and the vascular specialists.

  • Older patients (>85 years of age) and patients with severe systemic disease may also have poor outcomes even with surgery, and the decision to transfer should be discussed between the most senior emergency doctor available, and the on-call vascular surgeons.

• Patients who are transferred should leave the referring unit by emergency ambulance within 30 minutes of the decision to transfer.⁹

• A specially-trained transfer doctor is usually not required.⁶

Surgical management

• CT imaging is usually performed pre-operatively (if not already done) to guide the choice of endovascular or open repair, although sometimes patients are taken directly to theatre for open repair.⁶⁷

• The aim of surgery in an unstable patient is to secure surgical proximal aortic control without disturbing any tamponade effect provided by extra-aortic structures or haematoma.

• Resuscitation of hypovolaemic shock may require surgery to stem the bleeding rather than satisfactory resuscitation before induction of anaesthesia. Therefore an experienced anaesthetist is essential.

• Induction of general anaesthesia may lead to cardiovascular collapse; therefore, patients are usually prepped and draped whilst awake, with the aim to proceed immediately once endotracheal intubation is performed.⁷

• Emergency endovascular aneurysm repair (EVAR) has been used successfully to treat ruptured AAA, proving that it is feasible in selected patients.⁸ A Cochrane review found insufficient data to evaluate the relative benefits and risks of endovascular treatment for ruptured AAA when compared with open repair.¹⁰ There is still debate as to the relative merits of EVAR versus open repair, but many centres favour EVAR as their primary treatment option.⁷ NICE recommends that either EVAR or open repair can be used, highlighting that EVAR has a better risk-benefit balance for many people, especially men over 70 and women of any age, but that open surgical repair may be favourable in men under the age of 70.¹¹

Complications of a ruptured aortic aneurysm

Complications include:

• Acute kidney injury.

• Multi-organ failure.

• Respiratory problems, including respiratory failure and pneumonia.

Prognosis

Without surgical or endovascular treatment, the short-term mortality rate from a ruptured aortic aneurysm is close to 100%. A large proportion of patients die before reaching hospital, or before reaching the operating theatre.¹² With prompt treatment, mortality rates can be as low as 20%, but there is significant heterogeneity between patient groups.⁶¹³

Factors associated with an increased likelihood of poor outcome include increasing age of the patient, failure of initial resuscitation to increase the blood pressure and pre-operative cardiac arrest.