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To discuss the perioperative care of patients undergoing aortic aneurysm surgery, we must address the preoperative, intraoperative, and postoperative issues and concerns. In addition, the perioperative discussion of patients for aortic surgery should take into account the location of the pathology (thoracoabdominal vs. abdominal), the proposed surgical method (open vs. endovascular), and the specific comorbidities of each patient. We will briefly discuss the major differences between the perioperative, intraoperative, and postoperative considerations for a patient undergoing an open thoracoabdominal aneurysm repair, an endovascular thoracoabdominal aneurysm repair (TEVAR), an open abdominal aortic aneurysm repair, and an endovascular abdominal aortic aneurysm repair (EVAR). In addition, we will address specific patient comorbidities and their concerns and management, relating them again both to the location of the aneurysm as well as the type of surgery. Lastly, we will discuss the "hybrid" surgical procedure, and the unique perioperative considerations associated with this approach.
To begin our discussion, let's briefly compare the open vs. endovascular approaches and discuss which patients are likely to be candidates for each approach.
- In general, unless the anatomy of the aneurysm makes an endovascular approach unfeasible, the endovascular approach is preferred in patients with significant comorbidities, as it reduces systemic complication rates when compared to an open approach.
- Specifically, cardiopulmonary complications are greatly reduced via the endovascular approach.
- Renal complications are not significantly different between the two.
- Additional advantages to the endovascular repair are decreased blood loss, shorter hospital and ICU stays, and a more rapid return to prior level of functioning.
- The main disadvantages to the endovascular approach are a higher risk of local arterial injuries, mainly femoral artery injuries, and a unique set of postoperative complications and failures that are not present in the open approach. These are mainly due to endograft migration and "endoleak", which leads to further enlargement of the aneurysmal sac, necessitating additional secondary procedures.
- Due to the presence of these unique and often late-presenting failures of the endovascular approach, there is a need for much closer follow up in these patients with recurrent surveillance imaging studies at regular intervals postop, often indefinitely.
- Lastly, the long-term durability of an endovascular repair when compared to an open one is still of much debate. Therefore, due to these issues, an open repair is often preferred in young patients who are healthy enough to tolerate the procedure.
Reducing risk factors
In all patients undergoing repair of an aortic aneurysm regardless of the location, type of surgery, and comorbidities, the main preoperative goal involves the control of risk factors.
- This includes smoking cessation, control of hypertension, lipid profiles and blood glucose levels, and if tolerated, beta-blockade to control heart rate and reduce strain on the aneurysmal sac.
- In addition, all patients regardless of age should be worked up for coronary artery disease with at minimum an EKG, possibly also an echocardiogram and cardiac stress test, and even a coronary angiogram where indicated.
- Patients with significant pulmonary disease should be worked up with pulmonary function tests to determine their risk of postoperative pulmonary complications and, in the case of an open thoracoabdominal approach via left thoracotomy, their ability to tolerate single lung ventilation.
- Patients with significant cardiopulmonary disease should be strongly considered for an endovascular approach whenever possible. When an open approach in such patients is necessary, additional preoperative optimization should be explored.
- In patients with significant coronary artery disease, percutaneous coronary intervention should be considered prior to surgery.
- In those with a history of congestive heart failure, preoperative admission and optimization of fluid status with diuresis guided by a pulmonary artery catheter is advised.
Open Thoracoabdominal Aortic Aneurysm Repair
Preoperatively and in the intraop period prior to aortic cross clamping, the goal is optimal control of heart rate and blood pressure along with conservative fluid management to reduce the strain on the aneurysm sac.
- If the aneurysm involves the ascending aorta and aortic arch, the usual surgical approach is via a median sternotomy.
- If mainly the descending thoracic aorta distal to the left subclavian artery is involved, a left thoracotomy is preferred.
- If there is extension of the aneurysm below the diaphragm, the abdominal aorta will have to be accessed via either a transabdominal or retroperitoneal approach.
Stages of the procedure
For most open thoracoabdominal aortic aneurysm repairs, a lumbar drain will be placed preoperatively, often the day before surgery, to facilitate the intraop and postop regulation of intrathecal pressures and reduce the risk of paraplegia secondary to compromised blood flow to the spinal cord.
- In the case of aneurysms involving the ascending aorta and aortic arch, circulatory arrest is usually employed along with cardiopulmonary bypass.
- With the exception of circulatory arrest procedures, normothermia or mild hypothermia to not lower than 32 degrees Celcius is often the goal intraop to provide protection to the spinal cord and visceral organs while at the same time minimizing the risk of cardiac arrhythmias and significant coagulopathy that might be induced by lower temperatures.
- The potential for a sudden, large amount of blood loss should be anticipated in all open aortic aneurysm repairs, regardless of anatomic location. Large bore and central IV access should be obtained for the infusion of blood products and vasopressor agents. In addition, several units of type-specific blood should be immediately available at all times during the operation. Patients with reservations regarding blood transfusions, such as Jehovah's Witnesses, should be adequately counseled preoperatively and an acceptable strategy determined should the need arise for blood products. Autologous blood donation is strongly encouraged, and an intraop cell saver device is often employed.
- Postoperatively, mean arterial blood pressures are usually kept on the higher side, often with the use of vasopressors, to encourage adequate perfusion to the spinal cord and visceral organs.
- In addition, the spinal drain is left in place and cerebrospinal fluid is drained to likewise encourage increased cord perfusion.
- In terms of postoperative monitoring, patients with known or suspected coronary artery disease should be monitored closely in a telemetry unit. Postoperative myocardial infarction is high in this patient population, and usually presents within 48 hours after surgery.
- Patients with baseline chronic pulmonary disease have the highest likelihood of remaining intubated or requiring reintubation following the procedure and, if necessary, may warrant ICU admission postoperatively for close monitoring.
- Renal failure is another complication following surgery on the aorta that carries a high morbidity.
- Patients with baseline chronic kidney disease are at highest risk, and any procedure in which suprarenal clamping will be employed naturally also carries an increased risk.
Open Abdominal Aortic Aneurysm Repair
With the exception of circulatory arrest and cardiopulmonary bypass, most of the above-mentioned considerations for open thoracoabdominal aortic repair also apply to open abdominal aortic surgery.
- Most abdominal aortic aneurysms are fortunately below the level of the renal arteries, making the risk of renal failure much less likely than when a suprarenal aortic clamp is employed.
- As mentioned above, patients with baseline chronic kidney disease naturally have a much higher risk of postoperative renal failure following open abdominal aortic repair than those with normal renal function.
- Another concern during open abdominal repairs is intestinal ischemia as a result of cross clamping above the abdominal visceral arteries. Even with infrarenal clamping, blood flow to the descending and sigmoid colon via the inferior mesenteric artery is halted.
- In patients with inadequate collateral blood flow to this region via other mesenteric vessels, colonic ischemia is a potential complication with very high morbidity.
Endovascular Thoracoabdominal and Abdominal Aortic Aneurysm Repair
We will discuss the care of patients undergoing endovascular thoracoabdominal and abdominal aortic repairs together, as there is little difference between the two cases in regards to perioperative care.
- The use of lumbar drains in patients undergoing endovascular repairs is not routine, and their use is dependent on the specific case, the anatomy of the aneurysm, and surgeon and institutional preference.
- In terms of the type of anesthesia administered, unlike open repairs where general anesthesia is required, endovascular procedures can often be performed with the patients awake but deeply sedated, a type of anesthesia referred to as "monitored anesthesia care", or simply "MAC".
- Whether an endovascular procedure is done under general anesthesia or MAC depends on the specific case as well as the preference of both the surgeon and the anesthesiologist.
- Proponents of general anesthesia point to the necessity of having the patient completely still while placing and deploying the stent graft, as well as the need for general anesthesia should major blood loss and hemodynamic instability ensue.
- Proponents of MAC argue that for patients who are really sick there is less of a cardiopulmonary insult, and the ability to quickly convert to a general anesthetic is always available.
"Hybrid" Endovascular and Open Aortic Aneurysm Repairs
The goal of the hybrid approach is to minimize blood flow interruption to critical organs by, first, creating selective bypasses to individual vascular structures and, second, avoiding aortic cross clamping by treating the aneurysm with an endovascular stent graft.
Stages of the procedure
- The first stage of the procedure, which is performed open and often called the "debranching" procedure, involves selectively creating surgical bypasses to critical vessels that feed off from the aorta in the area where the aneurysm lies and also in the proposed endovascular stent graft landing zone, which is the "healthy" area of aorta on either side of the aneurysm that will also be covered by the stent graft.
- This is then followed by the endovascular second stage of the procedure, which is simply placing the endovascular stent graft in the devascularized area of the aneurysm and healthy landing zone that was created during the first stage.
- The two stages can either be done in succession on the same day, or on different days as entirely different procedures.
- The advantages of doing both procedures on the same day are that the patient will only have to undergo one general anesthetic, and the small but potential risk of aneurysmal rupture between the first and second stages is mitigated.
- The advantage to doing the two stages on separate days is that the patient will have a chance to recover from the stress of the first operation before being subjected to the stress of another surgical procedure.
- Whether or not the two stages are done on the same day or separate days is a decision that depends on the patient's tolerance of the first stage, surgeon and institutional preference, and operating room scheduling.
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