Aortic dissection is a disease of the wall of the aorta in which the aortic blood bursts into the muscular layer of the great artery, thus forming a blood filled channel along the planes of the muscularis layer. This false lumen can re-rupture back into the true lumen, through a second distal intimal tear, creating a biluminal or double barrelled aorta. Due to weakened walls, there is threat of rupture into the surrounding tissue with fatal consequences. (Boon, R, Colledge, Walker, & Hunter, 2010)
The pathophysiology behind the condition is often a spontaneous or iatrogenic tear in the intima. However, in about five to ten percent of patients, these tears are absent. An intimal tear can occur anywhere along the aorta, although a vast majority of tears are found within ten centimeters of the aortic valve. The dissection may extend towards the heart, affecting the coronary arteries, or it may rupture in the pericardial sac or pleural cavity. Double barreled aorta protects against such fatal consequences. (Boon et al., 2010)
Aortic dissection has been found to occur mainly in two age groups of patients: hypertensive men aged forty to sixty and in patients with connective tissue disease, such as Marfan’s syndrome. Rarely, aortic dissection has also been reported to occur in pregnancy. Other risk factors that predispose towards the development of aortic dissection are, aortic atherosclerosis, aortic aneurysm, aortic coarctation, fibromuscular dysplasia, previous aortic surgery, trauma and iatrogenic. (Boon et al., 2010)
Acute aortic dissection in pregnancy usually occurs during labor and delivery or in the early peurperum. Patients with already underlying predisposing factors are at a higher risk of developing pregnancy related aortic dissection. Most of these patients have a dilated aortic root of greater than 4 centimeters, although dilatation of lesser than 4 centimeters can predispose to aortic dissection in patients with underlying risk factors. Hormonal changes in the aortic wall have also been hypothesized as a cause in pregnancy. (Boon et al., 2010)
Aortic dissection is of classically two types, type A, which involves the ascending aorta, and type B, which spares the ascending aorta. Type A dissections are more common and comprise of two thirds of all cases. Type A dissections may also extend into the descending aorta. This classification is called the Stanford Classification System. (Boon et al., 2010) Type A aortic dissections are commonly referred to as, ‘the silent killer.’ This is because most patients have underlying hypertension which is asymptomatic initially and gradually worsens the prognosis of aortic dissection if left untreated. Patients present with tearing chest pain only later in the illness. (Duranki)
Patients present with typical chest pain which is located on the anterior aspect of the chest, when it involves the ascending aorta and intrascapsular when it involves the descending aorta. Pain is also felt along the dissection tract. The pain is abrupt in onset and often severe and tearing in character. Patients are hypertensive in about seventy five percent of the cases, unless if there is rupture in which case hypotension is the predominant feature. The brachial, carotid and femoral pulses are often asymmetrical. Signs of aortic regurgitation may also be present. In cases of severe dissection causing occlusion of the vessel, complications, such as, myocardial infarction, spinal paraplegia, mesenteric infaction, renal falure and acute limb ischemia can occur. (Boon et al., 2010)
On routine investigations, chest X ray may show a broad upper mediastinum and distortion of the aortic knucle along with left sided plueral effusion. Other investigations, such as the ECG may show left ventricular hypertrophy corresponding to hypertension. It can also show acute ST segment or q wave changes in cases that are complicated with a myocardial infarction. A Doppler echocardiography may show aortic regurgitation, a dilated aortic root and, occasionally the flap of the dissection. Transoesophageal echocardiography is particularly helpful and provides more information than a transthoracic echocardiograph. This is because a transthoracic echo can only image the first 4 centimeters of the ascending aorta. CT and MRI are also highly specific diagnostic tools for aortic dissection. (Boon et al., 2010)
No laboratory investigation is diagnostic for aortic dissection and current protocols do not recommend the use of a D-dimer test as the sole modality for diagnosis. However, a negative D-dimer test may be helpful in lowering the probability of aortic dissection as a diagnosis. (Boon et al., 2010)
Aortography is an invasive test and may be used if non-invasive tests are inconclusive. It can accurately identify entry point, intimal tear and the false and true lumen. Sensitivity of the test ranges from 70-80%. This test can, however, not recognize intramural hemorrhage. Coronary angiography can be used along with aortography in high risk patients who need to be evaluated and prepared for surgery. (Erbel, Alfonso, Boileau & Dirsch, 2001)
The Stanford Classification System is helpful for evaluating treatment options in patients with aortic dissection. In a pregnant woman with an acute type A dissection, the treatment is usually surgical. The cut off point for performing surgery with the fetus in utero is 28 weeks, after which an elective Caesarean section should precede a few days before the surgery for aortic dissection. If the fetus is at or beyond 32 weeks of gestation, the Caesarean section and aortic repair performed at the same operation is the treatment of choice. Between 28 and 32 weeks of gestation there is a dilemma, with the delivery strategy determined by the fetal condition. The fetal and maternal mortalities for cardiovascular surgery during pregnancy are 20 — 30% and 2 — 6%, respectively. (Erbel et al., 2010)
The management of type B aortic dissection is mainly medical through strict control of hypertension with the use of anti-hypertensive drugs. A combination of sodium nitroprusside and a ss-adrenergic receptor — blocking drug should be administered intravenously. This combination can also be used as an additional treatment for type A aortic dissection. However, the use of nitroprusside in pregnancy has the disadvantage of causing fetal cyanide poisning. The use of beta blockers can cause fetal growth retardation, bradycardia, hypoglycemia, hyperbilirubinemia and apnea in the newborn at birth. (Yee & A.RN, 2007)
Leakage or rupture, severe compromise of an arterial trunk, continued or recurrent pain, extension of the dissection while the patient is receiving adequate medical treatment, or uncontrollable hypertension are indications for surgical treatment in type B. (Erbel et al., 2010)
Drugs, such as morphine, are also given for pain. Although, there are no controlled data for the safety of morphine in pregnancy, there have not yet been any documented fetal abnormalities with morphine use. This drug can be used if benefits outweigh the harms. Morphine has been useful in alleviating the pain in aortic dissection which in turn has a positive effect on blood pressure and tachycardia. (Multum, 2012)
If the patient is hypotensive due to underlying complications of cardiac tamponade, aortic rupture or myocardial infarction, volume replacement should be given and an emergency surgery should be performed. Patients with type A dissection are also candidates for an emergent surgical repair. Patients who do not respond to medical therapy or patients at risk for developing complications are candidates for an elective surgery. (Erbel et al., 2010)
The mortality rate of untreated aortic dissection increases by 1-3% each hour. Complications of untreated dissection include extension into one or both internal iliac arteries. This may cause hypo-perfusion of the uterus, leading to intrauterine fetal death. Prognosis for patients who undergo treatment is 80% for five years and 50% for ten years. (Erbel et al., 2010)
Nursing intervention should begin soon after diagnosis. The patient should be immediately transferred to the I.C.U for continuous monitoring and limiting patient activity. The patient should be reassured and counseled about her condition. Assisted ventilation should be started for patients with decreased oxygen saturation. Assessing for tachycardia or other irregular rhythms through continuous cardiac monitoring is crucial for evaluating complications. Blood pressure should be maintained with a desired systolic between 100 to 120 mm Hg. Two large I.V bore cannulas should be inserted for I.V drug administration and maintaining hydration. Current protocols recommend checking vitals every 15 minutes. Mental status should be assessed frequently for neurologic and peripheral vascular changes. Urine output also needs to be measured frequently. (Yee & A.RN, 2007)
Nurses should also monitor the fetus for intrauterine growth retardation especially in mothers using beta blockers for hypertension. Apnea of the newborn at birth is also a risk that should be kept in mind. The newborn should be assessed for congenital abnormalities that it may have inherited from the mother. Babies born prematurely should be managed accordingly and the baby’s condition and progress should be properly explained to the parents. (Yee & A.RN, 2007)
Nurses are also involved in preparing a patient for surgery. This includes catheterization, draping, inserting I.V cannulas and intubation. During the surgery, a nurse monitors ventilator parameters and periodically interprets the patient’s vital signs. Nurses need to act quicker for patients arriving immediately to the OR. She should reassure and calm patient anxiety while making a quick assessment simultaneously. All observations should be documented and a plan of care needs to be sorted out. A perioperative nurse is also responsible for communicating patient status and a systematic plan of care to all members of the health team. (Yee & A.RN, 2007)
Nurses also play an important role during the postoperative period. Duties include administering drugs, monitoring and maintain target blood pressure and heart rate, and providing patient counseling. The target goal for systolic blood pressure is between 100 and 120 mmHg and the goal for the Mean Arterial Pressure is 65 mmHg. This is to prevent graft occlusion and to reduce the pressure load on the repaired aorta. The target for heart rate is 55-60 bpm. Vital signs and peripheral pulses should be recorded every hour. (Yee & A.RN, 2007)
During the first 2 to 3 days postoperatively, the head end of the bed should be lower than 45 degrees and the legs should be elevated 20-30 degrees to reduce pressure on incision sites. Any increase in abdominal girth should be reported. Other post-operative complications, such as hemorrhage, MI, arrhythmias, heart failure, cardiac tamponade, thromboembolism, renal insufficiency, hospital acquired infections, CNS ischemia, should also be looked for. (Yee & A.RN, 2007)
Fluid output should be measured hourly for the development of hypovolemia. The patient’s activity should be increased gradually. The patient should be encouraged to use a spirometer and to splint when coughing. (Yee & A.RN, 2007)
Nurses should schedule follow-ups for these patients. Patients who have had surgery should have follow-up visits at 1, 3, 6 and 12 months and annually thereafter. They should also have regular imaging to diagnose recurrence or complications. Dietary instructions should be given and patients should be encouraged to exercise to maintain an ideal body weight. Patients should also be counseled regarding risks during future pregnancies and family planning options should be offered. Family members of patients with aortic dissection should also be advised screening for aortic aneurysms. (Yee & A.RN, 2007)
REFERENCES:
Duranki. (n.d.). Type an aortic dissection – the silent killer. Retrieved from http://duranki.hubpages.com/hub/Beware-High-Blood-Pressure-It-will-Kill-You — You-Wont-See-It-Coming
Erbel, R., Alfonso, F., Boileau, C., & Dirsch, O. (2001). Diagnosis and management of aortic dissection*.European Heart Journal, 22(18), 1642-1681. Retrieved from http://www.escardio.org/guidelines-surveys/esc-guidelines/GuidelinesDocuments/guidelines-aortic-dissection-FT.pdf
Multum, C. (2012, Feburary 12). Morphine injection. Retrieved from http://www.drugs.com/pro/morphine-injection.html
Nicholas A. Boon, Nicki R. Colledge, Brian R. Walker, John A.A. Hunter.(2010). Davidson’s Principles and Practice of Medicine . India, Elsevier.
Yee., & A.RN, C. (2007). Aortic dissection: The tear that kills. Nursing, 37, 1-6. Retrieved from http://journals.lww.com/nursing/Fulltext/2007/03001/Aortic_dissection__The_tear_that_kills.1.aspx
