Summary
Anesthetic management of vascular surgery is highly demanding, due to physiologic perturbations caused by major vascular procedures, as well as the high burden of existing atherosclerotic disease or disease equivalents that are often poorly controlled in this patient population. The perioperative care of the vascular patient is often complex, requiring a thorough preoperative evaluation, sophisticated intraoperative management, and attentive postoperative care. Of paramount importance to the anesthesiologist is the likelihood of major adverse cardiac events (MACEs), the incidence of which may be mitigated by appropriate risk stratification and a detailed understanding of specific major vascular surgical procedures.
Introduction
Anesthetic management of vascular surgery is highly demanding, due to physiologic perturbations caused by major vascular procedures, as well as the high burden of existing atherosclerotic disease or disease equivalents that are often poorly controlled in this patient population. The perioperative care of the vascular patient is often complex, requiring a thorough preoperative evaluation, sophisticated intraoperative management, and attentive postoperative care. Of paramount importance to the anesthesiologist is the likelihood of major adverse cardiac events (MACEs), the incidence of which may be mitigated by appropriate risk stratification and a detailed understanding of specific major vascular surgical procedures.
Preoperative Assessment and Risk Stratification
Among noncardiac surgical procedures, the risk of MACEs has remained highest in vascular surgery, accounting for 7.7% of cases between 2004 and 2013 [Reference Smilowitz and Gupta1]. Prior myocardial infarction (MI) or stroke are both important independent risk factors for MACE, so appropriate screening, evaluation, and testing of these and other high-risk patients who present for elective vascular surgery may reduce their overall risk.
Preoperative testing for nonemergent vascular surgery varies widely; it is important to note that there are no Class I recommendations for testing supported by the American College of Cardiology (ACC) and American Heart Association (AHA). The following table outlines the recommendations of the ACC/AHA for supplemental tests that may be of use in specific clinical scenarios and patient populations (see Table 15.1). The decision for testing should be made with consensus agreement among the surgeon, anesthesiologist, and cardiologist, if applicable.
Table 15.1 Common preoperative tests and recommendations in noncardiac surgery
| 12-lead ECG |
|
| Transthoracic echocardiography |
|
| Exercise or pharmacologic stress testing |
|
| Coronary angiography |
|
HF, heart failure; MET, metabolic equivalent.
There is more substantial evidence regarding coronary revascularization and management of such patients. Routine coronary revascularization is not recommended, but patients who meet cardiac indications for undergoing percutaneous coronary intervention should delay noncardiac surgery, depending on the intervention (14 days after percutaneous old balloon angioplasty (POBA), 30 days after bare metal stent (BMS), and 365 days after drug-eluting stent (DES)) [Reference Fleisher and Fleischmann2].
Special circumstances and pathologies may warrant additional investigation. The presence of valvular lesions, pulmonary hypertension and/or right ventricular (RV) dysfunction, and indwelling pacemakers or an automatic implantable–cardioverter defibrillator (AICD) should prompt further evaluation and involve expert consultation, if possible, as these factors tend to be independently associated with a greater incidence of MACEs [Reference Chou and Gylys3].
The anesthesiologist should also consider, in addition to the risk of MACEs, the impact of major vascular surgery on postoperative renal function. The balance of oxygen supply and demand is often disrupted during intraoperative fluid shifts and the physiologic demands of anesthesia; maintenance of mean arterial pressure within strict parameters can help to preserve baseline renal perfusion. Renal comorbidities (chronic kidney disease, hypertension, insulin-dependent diabetes, peripheral vascular disease) and intraoperative risk factors (intraabdominal surgery, aortic reconstruction and/or cross-clamping, use of intraoperative bypass) all contribute to the incidence of postoperative acute kidney injury (AKI) [Reference Meersch and Schmidt4]. Measurement of serum creatinine concentration and urine output may be helpful in managing suspected AKI; however, options for pharmacologic management are limited, with some evidence supporting the use of dexmedetomidine infusion in cardiac surgery [Reference Ji and Li5]. Diuretic therapy and previously touted renal protective agents, such as dopamine and fenoldopam, have not been proven to reduce postoperative AKI. Severe injury may progress to acute renal failure, and in these cases, the decision of whether or not to initiate renal replacement therapy (RRT) should be considered within the larger clinical context; there are some data to suggest that there may be a trend towards decreased mortality in intensive care unit (ICU) patients who are started on RRT early versus late [Reference Nadim and Forni6].
Carotid Endarterectomy
Atherosclerotic plaques of the carotid arteries contribute to embolic and ischemic cerebrovascular disease, with significant, high-grade lesions (symptomatic patients with >70% luminal stenosis) clearly benefiting from surgical intervention over medical management [Reference Howell7]. Data for carotid endarterectomy (CEA) are equivocal in those with symptomatic stenosis ranging from 30% to 69%, and suggest that in those with minimally stenotic lesions (<30% luminal narrowing), surgery may be harmful [Reference Ferguson and Eliasziw8].
Minimally invasive techniques have also gained traction in treating carotid artery stenosis. Stenting and angioplasty may be beneficial in patients with comorbidities that prevent safe execution of traditional CEA; the Carotid Revascularization Endarterectomy Versus Stenting (CREST) trial demonstrated no difference in composite primary outcome (4-year perioperative stroke, MI, or death); however, stenting was associated with a higher risk of perioperative stroke versus CEA, which carried a higher risk of MI [Reference Brott and Hobson9].
Anesthetic techniques for CEA should be tailored for individual patients and their comorbidities, but the overall goals are to maintain hemodynamic stability in the perioperative period and to facilitate a prompt postoperative neurologic examination. The General anaesthesia versus local anaesthesia for carotid surgery (GALA) trial is the largest study to compare general anesthesia versus local anesthesia for CEA; a similar composite outcome to the CREST trial was used, which included stroke, MI, and death up to 30 days after surgery. No difference was seen between the two groups for the primary composite outcome [10]. As with the surgical technique for treating carotid artery stenosis, provider expertise and patient characteristics should determine the appropriate anesthetic technique.
Whichever modality of anesthetic is selected, the anesthesiologist has a large armamentarium of monitoring options for patients presenting for intervention. An awake patient undergoing CEA under local and regional anesthesia (via superficial cervical plexus blockade) (see Figure 15.1) provides the surgeon and anesthesiologist with the most reliable method of neurologic assessment, given appropriate patient selection; cortical function and motor and sensory pathways can be easily assessed during critical portions of the surgery. EEG may also be used and is considered the most sensitive modality when general anesthesia is used, effectively detecting regional or global ischemic events intraoperatively [Reference Ferguson and Eliasziw8]. Somatosensory evoked potentials (SSEPs) and transcranial Doppler (TCD) are additional methods that may be used at institutions to assess global or regional cerebral blood flow during critical portions of the revascularization procedure.
Figure 15.1 Ultrasound anatomy highlighting placement of local anesthetic for superficial cervical plexus block. * denotes the superficial cervical plexus. SCM, sternocleidomastoid muscle; CA, carotid artery; C5, C5 vertebral body.
Arterial line placement is mandatory for all cases, as stringent control over hemodynamics will allow for maintenance of adequate cerebral perfusion pressures. Surgeon preference and institutional practices will largely determine the use of selective hypertension during carotid artery cross-clamping, stump pressure measurements, shunt placement to promote collateral flow, or a combination of the three, along with the aforementioned monitoring modalities [Reference Howell7]. The anesthesiologist must judiciously use fluids and vasopressors to ensure adequate cerebral blood flow whether an awake or general anesthetic technique is used. Special attention should be given to the carotid cross-clamping period, and ongoing communication between the surgeon and the anesthesiologist is crucial to the success of the case.
Postoperative care of the patient undergoing CEA is as instrumental in preventing morbidity and mortality as intraoperative management. Immediate assessment of neurologic function is paramount, as embolization of air or plaque (especially if a carotid shunt was placed intraoperatively) is a major contributing factor to postoperative stroke. Maintenance of adequate cerebral perfusion (by avoidance of hypo- or hypertension) mitigates the risk of postoperative cerebral ischemia and hyperperfusion injury. Additional postoperative assessments include close monitoring for neck hematoma, potential airway compromise, and myocardial ischemia.
Abdominal Aortic Aneurysm
Defined as an enlargement of the aorta of >3.0 cm in diameter, abdominal aortic aneurysm (AAA) has known associations with advanced age, male gender, and a history of smoking at any point. The risk of rupture is associated with increasing AAA diameter, advanced age, female gender, and poorly controlled blood pressure [Reference Smaka, Miller, Barash and Cullen11]. The US Preventive Services Task Force has recommended one-time ultrasound screening for AAA in men aged 65–75 years who have ever smoked, but found little benefit in routine screening in all groups [12].
Patients presenting for elective repair of AAA may opt for open aneurysm repair (OAR) versus an endovascular aneurysm repair (EVAR). Selection often occurs based on patient frailty, the complexity of the repair to be performed, and surgeon and institutional experience. Two early European trials (EVAR-1 and DREAM) demonstrated that EVAR conferred a 30-day perioperative mortality benefit over OAR; however, the incidence of reintervention and “catch-up” deaths in the EVAR arm of both trials over years of follow-up data has put this benefit into question, even suggesting that patients undergoing EVAR may experience higher long-term mortality [13, Reference De Bruin and Baas14]. A more recent study from the United States, the OVER trial, showed similar long-term mortality in its endovascular and open aortic repair arms [Reference Lederle and Kyriakides15].
From the perspective of intraoperative management, EVAR has a number of advantages over OAR for the anesthesiologist. Hemodynamic perturbations are minimal, as volume loss and fluid shifts are significantly less when using an endovascular technique [Reference Smaka, Miller, Barash and Cullen11]. Arterial blood pressure monitoring is still mandatory, given patient comorbidities, the potential for conversion to open repair, and frequent sampling for arterial blood gas and activated clotting time (ACT) monitoring. Central venous cannulation can be considered in case large-bore intravenous access is not easily obtainable. The specific anesthetic technique should be determined by the length of the procedure, patient comorbidities, and other special considerations (e.g., presence or absence of a lumbar drain, specialized lower or upper extremity vascular access by surgeon, patient comfort, etc.). Local, regional, and general anesthesia have all been used successfully in the patient undergoing EVAR, although data on outcomes comparing anesthetic techniques are conflicting and lag significantly behind advances in surgical technique and approach [Reference Baril and Kahn16].
While the intraoperative physiologic changes of EVAR may not be as dramatic as a traditional OAR, unique anesthetic challenges remain. Patient positioning and location are often remote; principles of out-of-OR procedures often apply, with the anesthesiologist having limited access to the patient due to the geography of angiography or hybrid OR suites. Heparinization is commonly employed throughout, with use of ACT to guide therapy until procedure end and protamine reversal. Maintenance of normothermia may prove challenging, as patient exposure for angiographic evaluation can be extensive and prolonged, based on the complexity of the graft and length of procedure. Spinal cord ischemia is perhaps the most feared complication related to EVAR, and the anesthesiologist and surgeon must communicate and employ multiple strategies to mitigate the risk of partial or complete occlusion of collateral vessels that supply the anterior spinal artery. Permissive hypertension and/or drainage of the cerebrospinal fluid (CSF) are the two mainstays of increasing spinal cord perfusion in patients at high risk of spinal cord ischemia. Risk increases with longer procedures, complex fenestrated grafts, and reduced preoperative renal function [Reference Spanos and Kolbel17].
Postoperative endoleak from EVAR may occur after endovascular repair and, depending on the pressure gradient created by the leak, may place the patient at continued risk of aneurysmal rupture despite graft deployment. The type of leak will be determined by examination and angiographic evaluation, and may necessitate re-repair (see Figure 15.2).
