Introduction
Abdominal aortic aneurysms (AAAs) are a significant health concern, leading to more than 15,000 hospital admissions and 8,500 deaths annually in England and Wales. Many of these deaths could be prevented because elective repair surgery has a mortality rate of less than seven percent. When AAAs rupture, the overall mortality rate is around 80 percent, but with surgery, the survival rate increases to 50 percent. An aneurysm occurs when the diameter of the abdominal aorta exceeds 3.0 cm. The prevalence of AAAs is increasing, affecting approximately ten percent of men and three percent of women above the age of 65.
What Are Abdominal Aortic Aneurysms?
Abdominal aortic aneurysms (AAAs) are bulges or enlargements in the lower part of the aorta, the main blood vessel that carries blood from the heart to the rest of the body. When the wall of the aorta weakens, it can swell and form an aneurysm, which poses a serious health risk. AAAs often go unnoticed until they rupture, which can be life-threatening. Regular check-ups and monitoring of risk factors like smoking and high blood pressure are essential to detect and manage AAAs in time. Treatment, often through surgery, aims to prevent rupture and its 3 potentially fatal consequences.
What Are the Clinical Features of Abdominal Aortic Aneurysms?
Clinical features of Abdominal Aortic Aneurysms (AAAs) include a pulsating mass or tenderness in the abdomen, especially near the navel. In some cases, individuals might experience constant, gnawing pain in the back or abdomen. As the aneurysm enlarges, it can cause deep, steady pain and discomfort. However, AAAs often remain asymptomatic until they rupture, leading to sudden, severe abdominal or back pain, dizziness, and low blood pressure.
When Is Surgical Necessary for Abdominal Aortic Aneurysms?
Smaller aneurysms, those less than 5 cm in size, are unlikely to rupture and do not require immediate surgery. Regular ultrasound scans are recommended to monitor their growth. Surgery is usually considered when the aneurysm reaches 5.5 cm or larger, following current guidelines. Traditional open surgery is the standard treatment, but for suitable cases, a less invasive option called Endovascular Aneurysm Repair (EVAR) is becoming popular. It is important to assess each case individually to determine the most appropriate treatment approach.
What Is Involved in Preoperative Patient Preparation?
Patients scheduled for abdominal vascular surgery often have several underlying health issues, including:
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Coronary artery disease, often with reduced heart function.
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High blood pressure (hypertension).
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Lung problems are often linked to smoking.
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Kidney problems (renal impairment).
For some patients, these conditions may make major surgery risky. Therefore, a thorough evaluation by the surgeon and anesthesiologist is necessary to identify high-risk patients and optimize their medical care. This assessment should ideally take place one to two months before the surgery. One good way to assess cardiovascular and respiratory fitness is to evaluate a patient's ability to perform physical activities like climbing stairs or walking at a brisk pace. Patients who struggle with these activities often face higher risks.
Other significant cardiac risk factors include recent heart attack, unstable or severe angina, heart failure, certain arrhythmias, severe heart valve disease, and recent coronary artery procedures. The Vascular Society of Great Britain and Ireland offers online calculators to estimate risk scores. In some cases, pharmacological stress tests using dipyridamole thallium scintigraphy and dobutamine stress echocardiography can be useful. While they have a relatively low positive predictive value (meaning they do not always predict complications), they have a high negative predictive value (meaning a negative test result is usually reliable). Patients with positive stress test results should undergo coronary angiography. Heart murmurs should be further investigated with trans-thoracic echocardiography.
Cardiopulmonary exercise testing, which involves cycling while monitoring respiratory gasses and ECG, can also help identify high-risk patients. An anaerobic threshold of less than 11milliliters per kilogram per minute, particularly when combined with ECG evidence of ischemia (inadequate blood flow to the heart), is associated with a higher risk of complications after surgery.
What Is the Procedure for Conducting Anesthesia in Abdominal Aortic Aneurysm Surgery?
Patients should continue their regular medications on the day of surgery. During surgery, the goal of anesthesia is to keep the patient stable, pain-free, and at a normal body temperature. For vascular surgeries, anesthesiologists commonly use a balanced general anesthesia method (combining opioids, oxygen, air, and a small amount of volatile agent) along with a thoracic epidural. The epidural helps reduce the body's stress response, lessening the strain on the heart during surgery. It also provides good pain relief after the operation, allowing for early removal of the breathing tube and decreasing the risk of lung complications.
Various measurements are taken during the surgery, including arterial and central venous pressure, temperature, and urine output. Electrocardiogram (ECG) monitors are used to detect any changes in heart activity. Heparin, an anticoagulant, is given to reduce the risk of blood clots, but excessive bleeding due to Heparin can be reversed with Protamine, although this needs to be carefully managed to prevent complications. Maintaining the patient's body temperature is crucial to prevent complications such as heart issues and infections. Devices to warm the patient are used, but active warming of the legs is avoided during certain parts of the surgery.
Blood loss during surgery can vary significantly. To minimize the need for blood transfusions, intraoperative cell salvage (ICS) is employed. Patients' hemoglobin levels are monitored, and if there's significant bleeding, clotting factors like fresh frozen plasma and platelet transfusions are administered. The aorta is clamped during the surgery, which can lead to high blood pressure. Medications like Glyceryl trinitrate and Sodium nitroprusside are used to control blood pressure, but they need to be carefully managed to avoid reduced blood flow to vital organs. When unclamping the aorta, blood pressure can drop dramatically due to various factors, including changes in resistance and the release of substances from deprived tissues. Adequate fluid and controlled unclamping help minimize the drop in blood pressure. In cases of severe low blood pressure, reclamping might be necessary.
What Is Involved in Postoperative Care After the Surgery?
After abdominal vascular surgery, patients need careful monitoring. Traditionally, this was done in an Intensive Care Unit (Level III facility). However, with advancements in anesthesia and surgery, selected patients can be extubated early and transferred to a High Dependency Unit (Level II facility). Providing nutrition through the digestive system (enteral nutrition) early on is encouraged to maintain the health of the gut lining and prevent bacterial movement from the gut into the bloodstream. Tubes through the nose into the stomach are not typically needed. It's crucial to control blood sugar levels closely. Patients also receive appropriate medications to prevent acid buildup in the stomach and blood clots in the veins.
Conclusion
In summary, timely intervention through elective repair surgery is crucial for Abdominal Aortic Aneurysms (AAAs). Comprehensive preoperative assessment, advanced anesthesia techniques, and careful postoperative care significantly enhance patient outcomes. Early transfer to specialized units allows for effective monitoring and support, promoting a smoother recovery process. Prioritizing these measures ensures optimal patient safety and reduces mortality associated with AAAs.
