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On-line version ISSN 1806-907X
Rev. Bras. Anestesiol. vol.58 no.5 Campinas Sept./Oct. 2008
Anesthesia for endovascular surgery of the abdominal aorta*
Anestesia para intervención quirúrgica endovascular en la aorta abdominal
Michelle Nacur Lorentz, TSA, M.D.I; Carlos Leonardo Alves Boni, M.D.II; Raquel Reis Soares, TSA, M.D.I
do Biocor Instituto
IIAnestesiologista do Hospital Life Center e do Biocor Instituto
OBJECTIVES: Endovascular surgery for aneurism of the aorta is less invasive
than the conventional procedure besides other advantages such as the absence
of abdominal incision, absence of ligature of the aorta, and reduced postoperative
recovery time. Since it is a relatively new procedure and to presenting a series
of changes that should be known by the anesthesiologist, the objective of this
report was to review the most relevant aspects of endovascular surgery, allowing
more adequate perioperative anesthetic management.
CONTENTS: A brief description of the technique of endovascular aneurism repair, possible vantages and disadvantages of its use, as well as potential complications are discussed.
CONCLUSIONS: Knowledge of the changes secondary to the endovascular procedure allows a more adequate anesthetic conduct and improves the postoperative results in those patients.
Key Words: DISEASE, Vascular: aneurism; SURGERY, Vascular.
Y OBJETIVOS: El procedimiento endovascular para la corrección del
aneurisma de aorta es menos invasivo que el convencional, además de presentar
otras ventajas como la ausencia de incisión abdominal, ausencia de pinzamiento
de la aorta y un menor tiempo de recuperación postoperatoria. Por tratarse
de un procedimiento quirúrgico relativamente nuevo y por presentar una
serie de alteraciones que deben ser conocidas por el anestesiólogo, se
realizó este trabajo con el objetivo de revisar los aspectos más
relevantes del procedimiento endovascular y posibilitar el manejo anestésico
más adecuado en el perioperatorio.
CONTENIDO: Sencilla presentación de la técnica quirúrgica para la cura de aneurismas vía endovascular, las posibles ventajas y desventajas del procedimiento, como también las complicaciones potenciales. Además de eso, se abordaron los cuidados perioperatorios que el procedimiento exige y las técnicas anestésicas que pueden ser utilizadas.
CONCLUSIONES: El conocimiento de las alteraciones provenientes del procedimiento endovascular posibilita una conducta anestésica más adecuada y la mejora de los resultados perioperatorios en esos pacientes.
Aneurisms are defined as localized and permanent arterial dilations with a more than 50% increase in its normal diameter. Abdominal aorta aneurisms (AAA) represent 65% of all aneurisms of the aorta, and 90% of them are below the renal arteries. They are more common in males than in females, in a proportion of 4:1 1-3, and in patients older than 65 years, affecting up to 8% of elderly men 2. Smoking in itself is the greatest risk factor for AAA and 90% of the patients with this disorder smoke or have smoked. Atherosclerosis is considered the cause of aneurisms, and studies have demonstrated the direct correlation between aneurisms and other cardiovascular disorders, such as carotid and coronary vascular disease; other less common causes include genetic inheritance, including the defect in fibrin I (Marphan's syndrome), and a rare condition consisting in changes in type III pro-collagen (type IV Ehlers-Danlos syndrome) 3.
The natural history of this disease is the progressive increase of the aneurysm, culminating with its rupture and death. In the United States, more than 8,000 deaths a year are due to ruptures abdominal aneurisms 4. Although AAA is the most common disease of the aorta, aneurisms of the thoracic aorta are also frequent, as well as chronic dissections, transections, and other situations that represent a risk of death; and not all of those lesions can be repaired by the endovascular route, although Dellis et al. have described the endovascular repair of ruptured aneurysm in the descending thoracic aorta 5. However, several studies suggest that endovascular resection in selected patients has high short- and medium-term success rates 6-8.
The technique of endovascular surgery was first used by Dotter in 1969; however, only in 1990 it was successfully done by Parodi et al. 9 Since then it has become an alternative to the conventional surgery, which still is the gold standard. The endovascular procedure was developed as a less traumatic treatment for aneurisms. It is an alternative, especially for the elderly, high-risk patients, and those with associated diseases that influence with the risk of the conventional procedure.
The endovascular stent-graft is placed within the aneurism, as shown in figure 1, under fluoroscopic control and, therefore, requires a multidisciplinary team, composed of and interventional radiologist, vascular surgeon, and anesthesiologist 10. Its main advantages (Chart I) include: a less invasive technique without the need of an abdominal incision, absence of aortic clamping, faster recovery, and reduced length of hospitalization. On the other hand, it is associated with serious perioperative complications that include rupture of the aneurism and dislocation of the stent-graft, requiring a change in procedure.
On the short-term, endovascular surgery seems to have benefits regarding reduced blood loss, morbidity, and hospital stay. However, there are controversies about the medium- and long term benefits of this procedure. In the medical literature, several studies question the durability of the stents, as well as the late mortality; other studies have demonstrated similar immediate mortality besides a higher incidence of reoperations 10-16. Another problem is related with cost issues because, on the one hand it decreases the length of hospitalization but on the other hand the stent is very expensive, which results in a higher cost than the open procedure 19.
Some criteria should be observed to make it feasible the implantation of endovascular stent-grafts. The femoral arteries should be at least 8-mm wide because the closed stent has a diameter of 7.5 millimeters, and other parameters have been evaluated, such as the amount of atheromatous plaques in the aneurism and in its distal end. The distal end of the aneurism has to be free of disease to guarantee good perfusion of the limbs, minimizing the migration of plaques 17,18. If those criteria are fulfilled, the endovascular approach is done through the femoral artery, which is dissected in one side and punctured on the other. The repair of infra-renal aortic aneurisms is usually done through a femoral arteriotomy and, if the femoral artery is very tortuous, the iliac artery can be used. After the administration of heparin (1.5 to 2 mg.kg-1) and confirmation of the activated clotting time (ACT), the intraluminal stent is introduced in the aorta. The procedure is guided by fluoroscopy and transesophageal echocardiogram (TE-ECHO). The distal migration of the stent during placement of the device is possible, causing inadequate exclusion of the aneurism (endoleak). Several techniques have been suggested to prevent this migration, which causes a reduction in cardiac output; they include: occlusion of the aorta by an angioplasty balloon, adenosine-induced asystole, electrically-induced ventricular fibrillation, and induction of hypotension 20,21. Induced hypotension seems to be the safer and less invasive, in which nitroglycerin (NTG) or sodium nitroprusside (NTP) is used. In endovascular surgery for repair of the descending thoracic aorta, temporary asystole is promoted during stent placement, and ventricular fibrillation or cardiac arrest induced with high doses of adenosine can also be used. Besides promoting asystole, adenosine is a powerful coronary and encephalic vasodilator, and studies have suggested that it has a neuroprotective effect after acute ischemia 22. However, further specific studies are necessary to prove this effect.
Due to the proximity of the aorta and esophagus, transesophageal echocardiogram (TE-ECHO) is an excellent resource for the diagnosis and aid in the treatment of disorders of the aorta. It orients positioning of the stent, localization of the site of aneurismal rupture, and the outlet of arteries from the aorta, preventing inadvertent obstruction of its branches.
One should use methods to keep the patient warm due to the risk of hypothermia, especially in prolonged procedures 23, and to maintain hemodynamic stability. At the end of the procedure, non-steroidal anti-inflammatories (NSAIDs) or corticosteroids, in those cases NSAIDs are contraindicated, can be administered to reduce the inflammatory reaction of the vascular endothelium caused by the stent, and protamine is also administered slowly, controlled by the ACT. A vascular surgeon or an interventionist radiologist usually perform the surgery, but one should be aware of the possibility of immediate reversal of the surgery to an opened procedure and, therefore, an intensive care unit bed, an operating room, and blood products should be available, and a vascular surgeon should be present.
Pre-Anesthetic Evaluation and Management
Pre-anesthetic evaluation and management of patients scheduled for non-cardiac surgeries should take into consideration both the patient and the type of the surgery. Endovascular surgery of the aorta, as well as peripheral vascular procedures, should be classified as a high-risk procedure.
The decision to institute more advanced cardiac semiology should be based on the clinical history and predisposing factors of each patient. Figure 2 and Table I show a preoperative evaluation schedule 55.
Patients who underwent myocardial revascularization up to 5 years before the current procedure, recent coronary angiography or ischemia tests without recurrent signs or symptoms, or those who present minor stratification signs of cardiovascular risk with moderate tolerance to exercises, are entitled to undergo this surgical procedure. If patients have major predictive cardiovascular signs with increased perioperative cardiovascular risk they should be referred immediately for cardiac angiography before the surgery. All other patients should be referred for non-invasive tests.
Patients with pre-existing chronic obstructive pulmonary disease, older than 60 years, American Society of Anesthesiologists (ASA) classification greater than II, and congestive heart failure are at high risk for the development of postoperative pulmonary complications 56. Serum albumin 3.6 g.dL-1 is related with increased perioperative morbidity and mortality risk 56.
Spirometry should be an auxiliary test, both diagnostically and to optimize the treatment of patients with chronic obstructive pulmonary disease. However, there are no data suggesting a minimal spirometric threshold for extra-thoracic surgeries in which risks are considered unacceptable 55.
Preoperative optimization should be focused on the treatment of concomitant pulmonary diseases. Smoking cessation a few days before the surgery is riskier than its continuous use 56. This could be due to the increased production of mucus and cough which are commonly seen in people who have stopped smoking recently. A study with 200 patients who underwent myocardial revascularization demonstrated greater frequency of pulmonary complications (57%) in patients who stopped smoking between one and eight weeks before surgery 57. The group of patients who did not stop smoking had a 33% frequency of pulmonary complications, while the group of patients who stopped smoking more than eight weeks before surgery had a 12% risk of complications 57.
Several randomized clinical studies have proposed the perioperative use of beta-blockers to decrease the morbidity and mortality after non-cardiac surgeries 31-33 while others have not corroborated their results 34. Mangano et al. found a 10% mortality rate two years after non-cardiac surgeries in 200 patients with risks for coronary heart disease, while patients who were not pre-treated with beta-blockers showed a 21% mortality rate 35. Statins seem to have a perioperative cardioprotective effect, but further studies are necessary before their use is routinely recommended 36,37. However, one should always remember that those patients need myocardial protection 38-45.
Basic monitoring consists of electrocardiogram (EKG), pulse oximetry (SPO2), capnography, and temperature, which are mandatory, a urinary indwelling catheter is desirable, an intra-arterial catheter is essential both for continuous monitoring of the blood pressure (IABP) and to draw blood for laboratory tests. Central venous pressure (CVP) is rarely necessary, unless the patient have any associated disease to justify its use. It should be considered for early detection of pre-load changes and administration of drugs. Pulmonary wedge pressure is also recommended in selected cases. Transesophageal echocardiogram is used in selected cases for better determination of the anatomy of the vessels and to guide positioning of the stent. A large bore venous access is important for eventual blood transfusions and the fast administration of fluids. Both venous and arterial accesses should preferentially be obtained on the right upper limb leaving the left extremity for the surgeon to access the left axillary artery whenever necessary, since this is the best option to gain access to the aorta due to the shorter distance.
Endovascular aneurism repair can be done using different anesthetic techniques, such as general anesthesia, regional block, and local anesthesia associated with sedation 24-26. The influence of the anesthetic technique in the procedure has yet to be determined; however, there are times in which one technique is more beneficial than the others. General anesthesia is the technique of choice for retroperitoneal approaches, respiratory failure, coagulopathies, the use TE-ECHO, long-term surgeries, or refusal of the patient regarding regional blocks 27.
Several spinal block techniques have been successfully used in endovascular surgeries, and this seems to be the technique of choice of most centers for abdominal aneurism. Prevention of the surgical response to stress, associated with tracheal intubation, reduction of the inflammatory response, absence of mechanical ventilation in patients with severe pulmonary and cardiac diseases, besides the possibility of postoperative analgesia, are among its main advantages. The use of epidural and subarachnoid blocks with and without catheter placement, besides epidural block combined with subarachnoid block have been reported 11,54. The use of continuous epidural or subarachnoid blockade seems to be the technique of choice in most centers. When deciding to use spinal blocks one should be aware of the time interval necessary between the blockade and heparinization to reduce the changes of epidural hematomas, whose incidence is increased when the blockade is done within less than two hours from heparinization.
Hernetta et al. described the use of local anesthesia associated with sedation in 47 patients 25 of which only one patient needed conversion to general anesthesia and all patients had significant comorbidities. Cardiopulmonary complications in the first 30 postoperative days were not observed in this study. However, one should remember the possibility of inadequate analgesia, perioperative pain, besides the stress that this type of anesthesia can cause to the patient.
Regardless of the anesthetic technique chosen, this decision should be based on the duration of the procedure and experience of the surgical team 28, it should be previously discussed with the surgeon, and one should be prepared for the possibility of immediate reversal for the opened procedure.
INTRAOPERATIVE HEMODYNAMIC CONTROL
Hemodynamic changes that occur during the conventional procedure are substituted by other in endovascular surgery. This procedure is not associated with laparotomy, clamping of the aorta or loss of large amounts of blood. Hernetta et al. demonstrated a mean blood loss of 632 mL in this procedure, and only three out of 47 patients needed blood transfusion. The mean fluid requirement was 2,491 mL 25. The results of a multicenter study that compared the blood loss between opened and endovascular surgeries 29 demonstrated a blood loss 60% lower in the endovascular (650 mL) than in the opened (1,600 mL) surgery, resulting in a reduced need of blood transfusion in endovascular procedures (12% versus 40%). On the other hand, the anesthesiologist should chose the most adequate technique, remember that the patient is anticoagulated, maintain good intra- and postoperative hydration to reduce the incidence of renal damage caused by the contrast used during the procedure, provide adequate conditions for stent placement, and be prepared for surgical conversion. Anticoagulation should be monitored periodically to maintain the ACT around 250 seconds, which means the need of additional doses of heparin in prolonged procedures. At the end of the surgery, protamine is used to reverse the effects of heparin. Some authors prefer to wait for the normalization of ACT without protamine to avoid the harmful consequences of its use. Periods of hypotension which can be obtained by several techniques to maintain IABP around 60 mmHg are necessary during placement of the stent. Several studies indicated the use of nitroglycerin or sodium nitroprusside; as an alternative, the dose of volatile anesthetics can be increased or additional doses of the local anesthetic can be administered through the catheter if the patient is under continuous blockade.
Several studies reported the use of intravenous esmolol and adenosine to promote bradycardia and ventricular asystole during stent placement. The objective of this technique is to prevent the distal migration of the stent resulting from the propulsive flow during systole in thoracic aorta repairs. However, this technique was used when endovascular surgery was first implanted, when the time of stent expansion was much greater. With the advance of the technique and with the new models of stent (Figure 3), the time of stent expansion and the incidence of stent migration were reduced, decreasing the need of asystole and hypotension and, therefore, their consequences. Adenosine is commonly used in the treatment of supraventricular tachycardia because a bolus injection causes a reduction in heart rate, and even complete AV block, it is a short-acting agent, with return of hemodynamic stability in 10 seconds. The dose used in endovascular surgeries varies from 24 to 90 mg and can result in myocardial ischemia, atrial fibrillation requiring cardioversion, transient cardiac blocks, and prolonged periods of asystole requiring the use of a pacemaker.
Despite being considered a minimally invasive procedure, several complications are associated with the endovascular repair of aneurisms 46-49; among them is the rupture of the aneurism, which can be a disastrous event and demands immediate intervention. Risk factors for this complication include: site of stent placement and its size. Hypotension can result from the migration or improper positioning of the stent leading to vascular occlusion or incomplete exclusion of the aneurism (endoleak), distal arterial embolization with atherosclerotic plaques or thrombi, ischemia of the limbs, or rupture of the aorta. A good venous access must be available for fast volemic replacement and continuous IABP monitoring. The differential diagnosis of hypotension includes sympathetic blockade, in cases of subarachnoid or epidural blocks, allergy to the contrast medium, and use of vasodilators.
The intra- and postoperative risk of myocardial infarction 50 as well as strokes cannot be ignored. Strokes are predominantly ischemic or embolic, and aortic atherosclerotic is an independent risk factor for this severe complication 51,52,. It is extremely important to maintain sinus rhythm, since atrial fibrillation is one of the causes of perioperative strokes.
Spinal cord ischemia may occur and the role of spinal cord fluid drainage to protect spinal cord perfusion in opened thoracic surgeries, although widely used, is controversial. Some authors use this technique in the endovascular surgery, besides avoiding hypothermia and induced hypotension.
Post-stent implantation syndrome may develop, being characterized by fever, increased C reactive protein levels, and leukocytosis in the absence of infection. It lasts from two to 10 days and responds to the administration of non-steroidal anti-inflammatories. It is assumed that the development of a significant inflammatory response secondary to endothelial activation by manipulation of the stent occurs. Occasionally, severe hypovolemia secondary to excessive capillary permeability, decreased venous return, respiratory failure due to excessive capillary permeability, and disseminated intravascular coagulation may develop.
Patients undergoing surgeries of the aorta have a high incidence of vascular disease in other sites, such as coronary and brain circulation, hypertension, and respiratory, metabolic and kidney disorders. Endovascular surgery for repair of the aorta is a relatively new alternative to the conventional treatment. Its main advantage consists of being a less invasive procedure than conventional vascular reconstructions; besides, the duration of aortic occlusion is negligible, hemodynamic and metabolic stresses seem to be reduced, and early ambulation and discharge from the hospital are also associated with this procedure. Although it has potential advantages, further comparative studies are necessary, as well as the late follow-up of those patients53.
It is up to anesthesiologists to understand their importance for the success of this procedure, since it depends on the knowledge of the technique and its complications so they can provide adequate anesthesia in its different phases.
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Correspondence to: Submitted em 12
de julho de 2007 *
Received from Biocor Instituto, Belo Horizonte, MG
Dra. Michelle Nacur Lorentz
Rua Marquês de Maricá, 181/1.502 - Santo Antônio
30350-070 Belo Horizonte, MG
Accepted para publicação em 19 de junho de 2008
Submitted em 12
de julho de 2007
* Received from Biocor Instituto, Belo Horizonte, MG