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Stent-graft induced aortic wall injury – Anesthesia pitfalls and pearls for the TEVAR procedure

Published:January 21, 2023DOI:https://doi.org/10.1053/j.jvca.2023.01.017
      The development of thoracic endovascular aortic repair (TEVAR) has allowed a minimally invasive approach for the management of thoracic aortic pathologies. Compared to conventional open surgical repair, TEVAR is less invasive and associated with lower perioperative mortality and morbidity.1 Initially utilized in the treatment of aortic aneurysmal disease, the indications for TEVAR have expanded to include treatment of Stanford Type B aortic dissections, traumatic aortic injuries, penetrating ulcers, intramural hematomas and pseudoaneurysms.2
      Despite advances in endovascular techniques and devices over more than two decades, there remains significant morbidity and mortality associated with the TEVAR procedure. Complications include endoleak, graft migration, retrograde dissection, stroke, spinal cord ischemia, mesenteric ischemia, limb ischemia, renal injury, aortoesophageal and aortobronchial fistulas, and access related complications.3,4 Data on the long-term durability of TEVAR also remains limited. Although TEVAR is associated with reduced early perioperative mortality, it has higher reintervention rates compared to open repair surgery.5,6
      Stent graft-induced new entry tears (SINE) in patients undergoing TEVAR for aortic dissection is a postoperative complication that is increasingly described in the literature.7-12 It is defined as a new tear caused by the stent graft itself, excluding natural disease progression or iatrogenic injury from endovascular manipulation.7 The tear occurs in the dissection membrane at the distal end of the stent graft, leading to continued false lumen pressurization. This complication is associated with high reintervention rates and mortality.7,10-12
      In a recent issue of The Annals of Thoracic Surgery, Doberne and colleagues identified the occurrence of stent-graft induced aortic wall injury (SAWI), a term that encompasses all forms of aortic wall injury after TEVAR, including SINE.13 Doberne et al. defined SAWI as a new saccular aortic wall defect extending outward from the intimal surface of at least 5 mm in depth that had not been present on prior scans and developed at any time after thoracic aortic endograft deployment. The authors presented a retrospective observational study investigating the incidence, risk factors and outcomes of SAWI, reviewing all post-TEVAR computed tomography angiograms over 13 years at an aortic referral centre for radiographic evidence of SAWI. Within the study cohort of 430 patients, 38 patients (9%) had SAWI during a median follow up of 2.3 years. Although the rate of SAWI after TEVAR was low, there was a significant rate of operative reintervention (29%) to repair the aortic wall injury, with 45% of cases requiring open surgical approach, conferring even higher operative risk. Risk factors for SAWI development include TEVAR for acute aortic dissection and the deployment of stents with proximal bare springs or barbs. In patients with both risk factors, the predicted probability of SAWI over time reaches 50% by 4 years. Notably, the occurrence of SAWI may be delayed by several years postoperatively, highlighting the need for vigilant long-term imaging surveillance post-TEVAR.
      Achieving optimal outcomes following TEVAR requires a dedicated multidisciplinary care team with attention to detail throughout the preoperative, intraoperative and postoperative periods, ideally in a specialized aortic referral center. The anesthesiologist plays an important role during this perioperative course.
      Patients with aortic pathologies presenting for TEVAR are typically elderly with significant comorbidities. These include hypertension, coronary artery disease, diabetes mellitus, renal disease, and pulmonary disease.14 Careful preoperative evaluation of these comorbidities will identify patients at high risk of complications, enabling individualized management to reduce operative risks. Although TEVAR is associated with lower perioperative morbidity and mortality compared to open surgical repair, there is potential for hemorrhage and conversion to open repair, hence preoperative evaluation and preparation should be as thorough as for open repair. In addition to functional capacity assessment and screening electrocardiogram, a transthoracic echocardiogram is recommended to be performed as part of the diagnostic workup in the elective setting to exclude significant structural and valvular heart disease. 4 Coronary angiography and revascularization may be required in patients with suspected ischemic heart disease.
      Acute kidney injury (AKI) occurs in 10 to 15% of patients following TEVAR,15,16 and prevention is a priority. The cause is multifactorial, including hypoperfusion, stent graft encroachment of renal arteries, embolic phenomena, and contrast induced nephropathy. Important risk factors include pre-existing renal impairment, intraoperative blood transfusion, and extent of thoracoabdominal aortic disease.16 TEVAR for type B dissection with malperfusion is also associated with higher risks of postoperative renal dysfunction as these patients are treated after organ malperfusion has occurred.17 In a multicenter study by Piffaretti and colleagues, postoperative AKI was associated with a five to six-fold increased risk of hospital mortality and 5 to 10-day increase in hospital length of stay.16 To reduce the risk of postoperative AKI, patients should be adequately hydrated before the TEVAR procedure, nephrotoxic agents discontinued and attention paid to maintaining intravascular volume, cardiac index and mean arterial pressure intraoperatively. In patients at high risk of postoperative AKI, intraoperative contrast angiography may be supplemented with intravenous ultrasound and transesophageal echocardiogram (TEE) to position and deploy the endograft in order to minimize the use of intravenous contrast.18
      It is vital that the anesthesiologist has a clear understanding of the surgical procedure to tailor management to the individual patient. For instance, adjunctive procedures such as debranching procedures and retroperitoneal dissection to create surgical conduits for vascular access would be associated with greater blood loss and longer procedure times. A team huddle prior to the start of surgery to discuss the surgical plan and potential complications allows the entire surgical team to share the same mental model, improving teamwork and communication to facilitate a complex procedure.
      TEVAR is usually performed under general anesthesia (GA), although regional and local anesthesia techniques may be suitable for select patients with straightforward anatomy. GA is generally preferred for complex repairs with longer expected duration, higher risk of bleeding and conversion to open repair, such as procedures involving fenestrated grafts, debranching procedures, and aortic or iliac artery access through a retroperitoneal incision. In addition to ensuring patient immobility, GA allows control of ventilation to facilitate intraoperative angiography and graft positioning, and enables TEE monitoring. Regardless of technique, intraoperative anesthetic goals are to provide hemodynamic stability, maintain end organ perfusion, and maintain patient immobility to facilitate optimal positioning and deployment of the endovascular stent.
      Direct arterial pressure monitoring is usually accomplished via right radial arterial cannulation as the left brachial or subclavian artery may be accessed during repair, particularly for procedures involving the distal aortic arch or proximal thoracic aorta. Large bore intravenous access is mandatory due to the potential for catastrophic bleeding. Where peripheral access is challenging, central venous access provides reliable access and also facilitates use of inotropes and vasopressors. TEE is recommended as an adjunctive intraoperative imaging technique in patients with complex aortic pathologies undergoing TEVAR.4,19 It can be used to assess the aortic pathology, guide stent graft positioning and evaluate for complications such as endoleaks after graft deployment. In the event of hemodynamic instability, it is a valuable tool to guide decision making about volume replacement, inotropic and vasopressor support.
      Spinal cord ischemia (SCI) is one of the most severe complications of TEVAR and may lead to immediate or delayed onset paraparesis and paraplegia. The incidence of SCI after TEVAR is between 3 and 10%, and is associated with higher mortality than in patients without SCI.20,21 The etiology is multifactorial, but includes interruption of spinal cord perfusion due to stent graft coverage of the aortic branches, impeding collateral spinal circulation.22 Strategies to reduce the risk of SCI thus mainly aim to increase spinal cord perfusion pressure by augmenting arterial pressure and decreasing cerebrospinal fluid (CSF) pressure through CSF drainage. However, routine prophylactic CSF drainage is not recommended as it does not significantly reduce the incidence of SCI in patients undergoing TEVAR, and the invasive procedure is not without associated risks.23 CSF drainage complications may be related to drain insertion and removal, presence of an indwelling drain, and rate of CSF drainage, and include spinal hematoma, infectious complications, and intracranial hemorrhage. The American College of Cardiology and American Heart Association practice guidelines recommend prophylactic CSF drainage as a protective strategy in descending aortic endovascular repairs for patients at high risk of developing SCI.24 Extent of stent graft coverage is the major risk factor, with segment coverage more than 20 cm associated with high risk, in addition to prior aortic aneurysm repair and involvement of the left subclavian artery or hypogastric arteries. 25-27 One study reported a 14.3% incidence of SCI in patients undergoing TEVAR after prior abdominal EVAR.26 Neuromonitoring of the spinal cord with somatosensory evoked potentials or motor evoked potentials may also be considered to allow prompt intervention when neurological compromise is detected.24 Rescue interventions include elevating the arterial blood pressure, ensuring adequate hemoglobin concentration, optimizing intravascular volume and cardiac output, and systemic steroid therapy.4,27 Where CSF drainage was not implemented preoperatively, it may still be performed postoperatively if patients develop clinical signs of SCI. 28 This approach may be in preferred in patients with lower risk of SCI, who may on the balance be at higher risk of complications from prophylactic CSF drainage.
      The anesthesiologist must remain engaged and in close communication with the surgical team to optimize hemodynamic management throughout the endovascular procedure. Prior to graft deployment, hemodynamic goals are to ensure adequate perfusion pressure to reduce the risk of myocardial, renal, cerebral, and spinal cord ischemia, while avoiding hypertension in patients at risk of aneurysm rupture or dissection extension. During graft deployment, blood pressure is transiently lowered to reduce the risk of stent migration by administration of short acting pharmacological agents such as propofol, remifentanil, esmolol, nitroglycerin, and volatile anaesthetics. If further blood pressure lowering is required in proximal aortic procedures, rapid ventricular pacing (RVP) is the modality of choice.4,29 Whilst RVP is associated with more precise placement at the designated location than with any pharmacological intervention, this intervention has associated risks.29 A lower blood pressure may also be useful during post deployment ballooning to fully expand the endograft. After graft deployment, a higher blood pressure is targeted to optimize spinal cord perfusion and collateral blood flow to vital organs.28
      Aortography is repeated at the end of the procedure to confirm treatment success and to exclude immediate complications such endoleak and retrograde dissection. This can also be evaluated with TEE if utilized. In uncomplicated and hemodynamically stable cases, patients can be extubated in the operating room to facilitate early neurological assessment. Postoperatively, patients should be managed in a high acuity or critical care unit by providers who are familiar with the procedure and potential complications, so that any complication may be promptly detected and treated for optimal outcomes.
      Advances in endovascular techniques have substantially broadened treatment options for patients with a wide spectrum of acute and chronic thoracic aortic pathologies, and TEVAR has evolved to be the treatment of choice for many of them. Although less invasive than open aortic repair, it is a complex procedure. Understanding the procedure and its immediate and delayed complications is critical for the perioperative management of these patients. Accurate placement of the endovascular grafts requires high quality imaging, stable hemodynamics and a motionless field during deployment. With vigilant monitoring, good teamwork and precise hemodynamic control, the anaesthesiologist is ideally positioned to provide the endovascular team with the optimal intraoperative conditions to facilitate safe and accurate placement of the aortic endograft.

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