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.

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.¹

Aortic aneurysm can occur anywhere along the length of the vessel but they are usually in the first part or just before the bifurcation. Those in the first part of the thoracic aorta are often the result of diseases of connective tissue like Marfan's syndrome and late syphilis must not be forgotten. Ehlers-Danlos type IV is also a risk and even without such diseases there are reports of familial clusters. Aneurysm of the abdominal aorta is usually degenerative in origin (see Aortic aneurysm for hypotheses) and hypertension is a risk factor at all levels and regardless of the aetiology.

• About 6,000 men a year die from ruptured aortic aneurysm in England and Wales accounting for about 2% of deaths in men. Women are much less frequently affected.²
• The incidence of abdominal aortic aneurysm (AAA) increases markedly with age after 55 for men and 70 for women.³ Older patients frequently have multiple pathology. For thoracic aortic aneurysm (TAA), the mean patient age is 60-70 years.⁴
• The incidence of abdominal aneurysm (not rupture) is 2-5% of individuals over the age of 60.⁵ The incidence is higher in patients with hypertension and/or peripheral vascular disease, patients with a positive family history, and in smokers.⁶
• Whereas mortality and morbidity associated with coronary artery and cerebro-vascular disease have been declining rapidly, the incidence and mortality associated with AAA have increased. One large recent Swedish study found that the overall incidence of ruptured AAA has increased from 5.6 per 100,000 person-years between 1971 to 1986 to 10.6 per 100,000 person-years between 2000 and 2004. The biggest increase was in men aged 60-79. A similar increase was not seen in women in the same age group.⁷

Risk factors

The presence of an aneurysm is a risk for rupture. The larger the lesion the more likely it is to bleed. Smoking and hypertension are additional risks.

History

A dissecting or ruptured aneurysm usually presents with pain. In a 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 be rapidly fatal. The patient will probably never reach hospital alive and the diagnosis is made post mortem.

Ruptured AAA presents with a classical triad of pain in the flank or back, hypotension and a pulsatile abdominal mass but only about half have the full triad. The patient will complain of the pain and may feel cold, sweaty and faint on standing. The following symptoms are listed with approximate frequency of presentation:

• Abdominal pain 60%
• Back pain 70%
• Syncope 30%
• Vomiting 20%

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 centimeters 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. The following findings are listed with approximate frequency:

• Palpable mass 90%
• Tenderness 80%
• Systolic blood pressure below 80mm Hg 40%

Presentation can be atypical such as intestinal obstruction from haematoma or an apparent irreducible inguinal hernia

• Whenever a man over 55 or a woman over 70 presents with circulatory collapse a ruptured aneurysm should be considered.
• 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. A high white cell count occurs in 80% and should not detract from the possibility of a ruptured aneurysm. An infected, toxic patient will be peripherally warm with a bounding pulse but here there is circulatory collapse and a cold periphery. Renal colic, gastrointestinal haemorrhage and diverticular disease all need consideration.

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

Laboratory studies

• Full blood count Remember that 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 10,000/μl or more.
• Group and cross match whilst arranging surgery.
• Baseline biochemistry of urea and electrolytes should be performed.

Radiology

• Chest Xray For a TAA the chest x-ray may well show an enlarged base of aorta.
• Plain abdominal x-ray For AAA this will show the lesion in about 75% as it is often calcified.
• Portable ultrasound This examination may be helpful but there is not time for detailed assessment. If there is strong suspicion of a ruptured aneurysm then immediate surgery may be the investigation of choice.
• Other investigations CT scan, MRI and angiography are occasionally useful in stable patients, but most patients require life-saving emergency surgery before these investigations can be carried out.

ECG

This is important in patients presenting with chest pain.

Get intravenous access as soon as possible and preferably before hospital.
Groups and cross match and get to theatre.
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. The leaking or ruptured piece of aorta is replaced by a prosthetic graft. Techniques previously used in elective surgery for pre-ruptured aneurysms such as stent graft therapy are now being used in patients with ruptured aneurysms, with encouraging results.⁸

This is dramatic surgery, often in the old and frail. Complications include acute renal failure, multi-organ failure and respiratory failure including pneumonia.

No more than 1 in 3 patients with a ruptured aortic aneurysm will reach hospital alive and 20% of those who do fail to reach theatre. Delay in diagnosis is a major risk factor. Elective repair of AAA has a mortality of around 5% compared with 60% for emergency repair.⁹ The following factors are associated with a mortality rate in excess of 80%.

• Age over 80
• Presentation in shock with free intra-peritoneal rupture
• Failure of BP to rise despite attempts at resuscitation
• Haematocrit below 25% on admission
• Pre-operative cardiac arrest

AAA represents serious arterial pathology and considering the shared coronary artery risks it is unsurprising that the early and late mortality from CHD is very high. A paper examining cases operated on between 1972 and 1983 showed that the mortality rate of those who reached operation was 43% with a mortality of 30% even in those who survived the day of surgery.¹⁰ Risk factors included age over 76, haematocrit below 30%, abnormalities on ECG, extension above the renal arteries and low blood pressure. Prognosis is generally poor but swift and skillful operation represents the only chance for survival. A very high mortality is more dependent upon failure to operate than operative mortality, and a decision whether or not to operate should be made on the clinical assessment of individual patients, not on a calculation of pre-operative risk factors.¹¹ A third of patients do not have a known aneurysm at the time of rupture and delay is a major contributor to mortality.¹²

Because of the association with CHD, the state of the coronary arteries should be evaluated in all surviving patients.

Because the prognosis for a burst aortic aneurysm is so poor, even in patients who survive long enough to have surgery, the issue of screening and pre-rupture elective treatment is paramount. The Gloucester aneurysm project involved ultrasound screening of all men over 65, as women do not seem to be sufficiently at risk, with action depending upon the size of any aneurysm.² The conclusions they came to are as follows:

• <26mm diameter can be ignored
• 26 to 39mm - screen annually
• 40mm and above refer to surgeon who may screen every 6 months if <55mm
• If diameter 56mm and above or increasing in size by 10mm a year or more, surgery probably required

Although women seem rather less likely than men to have an aneurysm, if they do, all other parameters being equal, they have 3 times the risk of rupture.
A recent Cochrane review concluded that there is a significant reduction in mortality from AAA in men aged 65-79 who undergo ultrasound screening. Evidence to support similar screening in women is less convincing. The review commented that further work is needed on the cost-effectiveness of a population-based screening programme.¹³