Regional Anesthesia for Vascular Surgery

Abstract

Vascular surgical patients are a diverse group of patients who tend to be elderly, with multiple comorbidities, while vascular procedures may involve significant blood loss and ischemia of tissues beyond the arterial obstruction. Regional anesthesia techniques may offer benefits to patients undergoing vascular surgery because of their cardiorespiratory comorbidities. However, this group of patients is commonly receiving multiple medications, including anticoagulants, so regional techniques are not without risks. This review will discuss this topic based around 3 fundamental revascularization procedures, carotid, abdominal aortic aneurysm repair, and infrainguinal surgery, discussing the clinical applications of regional techniques relevant to each key area.

Keywords

postoperative complications perioperative mortality noncardiac surgery outcome analgesia

Introduction

Vascular surgery involves arterial reconstruction on patients with diseased arteries. Such patients rarely have disease confined to the presenting part but instead have widespread atheromatous disease affecting cerebral (cerebrovascular accidents), cardiac (ischemic heart disease, cardiac failure), splanchnic (renal impairment) and peripheral (distal ischemia) circulations. Clinical trials comparing regional anesthetic techniques (central neuraxial blockade and peripheral nerve blocks) with parenteral opioids have shown that regional techniques provide better analgesia, reduce the “stress response” to surgery, improve pulmonary function, reduce myocardial ischemia, reduce blood loss, and reduce the risk of venous thromboembolic disease. Putting together this “difficult” group of patients with regional anesthetic techniques could be an ideal union; however, it is not as straightforward as this. This article will explore the use of regional anesthesia in vascular surgery concentrating on different regional techniques and present the available evidence of their effectiveness in reducing perioperative morbidity and mortality.

Regional anesthetic techniques have risks as well as benefits. One important risk is hematoma formation in the vicinity of nerves or the spinal cord. Vascular patients are commonly treated with anticoagulant or antiplatelet agents, including aspirin, dipyridamole, clopidogrel, coumadin, or low-molecular-weight heparin. Many newer agents are becoming available, including glycoprotein IIb/IIIa receptor antagonist (abciximab, eptifibatide, and tirofibran), direct Xa inhibitors (xabans), and glycosaminoglycans (fondparinux). Intraoperative heparinization is frequently employed using unfractionated heparin to reduce the risk of intraarterial thrombus formation during arterial cross-clamping. It is therefore important to assess the risk of hematoma formation against the benefits of regional anesthesia in patients receiving these drugs with the aid of recent guidelines.¹ It is also useful to be able to measure patients’ coagulation status using point-of-care testing, such as thrombelastography or platelet function analysis, to aid the decision as to whether or not to perform regional anesthetic techniques, although guidelines are poorly defined in this area.

There are 3 fundamental revascularization procedures: carotid surgery (endarterectomy or bypass) in which an internal carotid artery stenosis is removed or bypassed; aortic aneurysm repair in which an aneurysm of the aorta is bypassed or removed; and infrainguinal bypass surgery in which a stenosis of a lower limb artery is bypassed or removed. All 3 of these operations can also be performed radiologically using stents. In addition to these, vascular surgeons also perform amputations at various levels: specialist venous surgery, thoracic inlet procedures, revascularization of abdominal viscera, and, more rarely, surgery for arteriovenous malformations.

The team-based approach involving surgery, anesthesia, and perioperative care is an evolving concept that may result in significant outcome improvements. In the United Kingdom, vascular surgery is about to be designated as the 10th surgical specialty coinciding with published evidence that the presence of a specialist vascular anesthesiologist—defined in this case as someone who provides vascular anesthesia for one or more whole days per week—is associated with lower mortality in vascular patients than with a more “general” anesthesiologist.² This suggests that anesthetic management of patients with considerable comorbidity can be affected by anesthetic expertise and techniques. To add to this, vascular surgery is being “centralized” into larger more specialized units since the outcome following major vascular surgery has been shown to be better in larger volume units for both carotid³ and aortic⁴ surgery. This general concept should be considered as a background concept while reviewing the available literature.

Regional Anesthesia for Carotid Endarterectomy

Carotid endarterectomy (CEA) was first reported from St Mary’s Hospital, London, in 1954,⁵ although DeBakey may have performed the first operation in the United States the previous year. The description from the original Lancet article is revealing:

In 1954 Pickering, Professor of Medicine at St Mary’s Hospital, London, had a 66-year-old female suffering intermittent attacks of right hemiplegia and left monocular blindness. A carotid arteriogram showed a significant stenosis of the left internal carotid artery. He suggested to the Professor of Surgery, Charles Robb, that the lesion might be corrected by surgery. Felix Eastcott, his Assistant Director, performed the operation with oversight by Robb. Before prepping and draping, the patient was covered with a rubber sheet and ice bags until the body temperature reached 28°C, in an attempt to protect the brain during the period of cross-clamping.

Thus, these pioneers of vascular surgery clearly understood the principal problem of carotid surgery—namely, protection of the brain during carotid cross-clamping. Advancements in carotid surgery over the last 50 years have mainly been concerned with improving knowledge and maintaining cerebral perfusion during this period. Despite this, the overall incidence of mortality/major stroke during CEA remains high—approaching 5% in the recently published GALA (General Anesthesia versus Local Anesthesia) trial.⁶ Considering that the annual mortality of symptomatic patients with a carotid stenosis greater than 70% is approximately 3% to 5% means that a patient needs to survive approximately 18 months or so following carotid surgery in order for it to be beneficial statistically.⁷ Added to the fact that the operation does not “cure” the patient of the risk of stroke may help explain why there is so much dogma associated with this operation in terms of surgical (and anesthetic) techniques.

Two large trials performed in the 1990s in North America and Europe^8,9 demonstrated the benefits of surgery for symptomatic patients with a carotid stenosis greater than 75%, although the benefits of surgery for asymptomatic patients who present coincidentally when being investigated for other reasons are not as clear-cut,¹⁰ and in the United Kingdom, CEA is not commonly performed for asymptomatic patients.

The timing of carotid surgery in relation to the presenting neurological event is also evolving. There are now clear benefits to performing surgery within 2 weeks of the “presenting event,” be it transient ischemic attack or cerebrovascular accident,¹¹ and this is now being extended further so that surgery within 7 or fewer days may soon be commonplace.¹² There may be implications for the management of vascular surgical patients within a hospital with the emergence of such “urgent” carotid surgery.

Regional Versus General Anesthesia

Carotid surgery patients, like most vascular surgical patients, present significant challenges to anesthesiologists, with considerable comorbidity including ischemic heart disease, hypertension, diabetes, and polypharmacy.¹³ There has been considerable debate over the years as to whether regional anesthesia or general anesthesia (GA) conveys advantages for carotid surgery. Historically, proponents of GA have cited “neurological protection” afforded by thiopentone and volatile anesthetic agents,¹⁴ absolute perioperative control of the airway (allowing control of arterial carbon dioxide concentration and its effects on the cerebral vasculature),¹⁵ and, finally, the individual preferences of surgeon, anesthesiologist, and patient.

Proponents of regional anesthesia cite the ease and immediacy of assessment of neurological status during carotid cross-clamping as compared with the alternatives under GA: transcranial Doppler, somatosensory evoked potentials, processed electroencephalogram, and near-infrared spectroscopy.¹⁶ Additional benefits to regional approaches include immediate postoperative neurological assessment, greater cardiovascular stability, better postoperative analgesia, and shorter hospital stay. A Cochrane Database meta-analysis of all the randomized and nonrandomized trials comparing general with regional anesthesia for CEA found that in the 812 randomized patients from 9 trials, regional anesthesia was associated only with a lower incidence of wound hematoma requiring surgical reexploration. However, in the 24 181 patients from nonrandomized studies there were significant reductions in the risk of death, stroke, myocardial infarction (MI), and pulmonary complications from the use of regional anesthesia.¹⁷

The GALA trial, a randomized comparison of general versus local anesthesia (LA) was devised to try to determine whether regional anesthesia for CEA offered survival benefits.⁶ GALA is the largest-ever published comparison of 2 anesthetic techniques. Over 8 years, 3526 patients were recruited and randomized to receive general or regional anesthesia for CEA. A primary outcome (MI, stroke, or death within 30 days of surgery) occurred in 84 (4.8%) patients assigned to GA and 80 (4.5%) of those assigned to LA. Three events per 1000 treated were prevented with LA (95% confidence interval = −11 to 17; risk ratio = 0.94 [95% confidence interval = 0.70 to 1.27]). Despite the size of the trial and the enormity of the undertaking, the GALA trial results have not silenced the debate as to which anesthetic technique gives the best results.¹⁸ GALA trial critics (mostly proponents of regional anesthesia) cite the wide variability in trial methodology, which allowed any general anesthetic technique to be compared with any regional anesthesia technique, together with the changing clinical practice over 8 years and the wide variability in practice between participating countries. On the other hand, proponents of GA have used the GALA results to validate their practice. No details are presented either in the original paper⁶ or on the GALA trial Web site¹⁹ of the techniques of regional anesthesia or GA used. Probably as important as the choice of anesthetic technique used is the concept of the vascular “team” in which clinical staff who are used to working with each other have protocol-driven methods and techniques in order to achieve optimal clinical results. It is certainly true that regional and GA techniques are not interchangeable for CEA. To adopt regional anesthesia requires a commitment and effort to change from surgeons, anesthesiologists, and nurses, and frequently other changes such as the cerebral monitoring modality.

Since the GALA trial results were published, several other articles have been published showing further subtle differences between GA and LA for CEA. The GALA collaborators subsequently published a trial showing that patients receiving GA had higher jugular venous concentrations of a marker of cerebral ischemia (neuronal specific enolase) compared with those patients receiving LA.²⁰ Additionally, carotid shunting (the process by which flow is restored to the ipsilateral cerebral cortex following carotid cross-clamping by using an intraarterial bypass shunt) has come under further scrutiny. The GALA trial⁶ showed significant differences between the 2 groups in terms of the shunt rate (14% LA vs 49% GA), but shunting was used purely at the discretion of the clinicians (at least in the GA group) rather than because of detected neurological deficit. In the GALA patients who were followed up, there was an apparent divergence of the survival curves of the LA and GA patients at 1 year, with more of the GA group dying, although this did not achieve statistical significance.¹⁹ Follow-up of the GALA trial patients was not continued beyond 1 year, so it is unknown if this is a significant observation.

Additionally, insertion of a shunt has been recently shown to be an independent predictor of postoperative carotid stenosis development²¹ and subclinical neurocognitive dysfunction.²² Of course, it may well be that patients who require shunting perioperatively because of a change in the cerebral monitoring modality (as opposed to those who are shunted at the whim of the surgeon) have poorer cerebral collateral circulation, which could itself account for subtle postoperative differences.

The overall goal of CEA of cerebral protection means that the period of carotid cross-clamping is critical to successful outcome. Under GA, some anesthesiologists use augmentation of the blood pressure to maintain cerebral perfusion.²³ However, this is not without risk, involving a greater risk of myocardial ischemia.²⁴ In awake patients who present with neurological dysfunction following carotid cross-clamping, 2 further treatment options are available potentially to avoid the necessity for carotid shunting. First, careful augmentation of the blood pressure to normal, or up to 20% above normal, may reverse the developing neurological ischemia²⁵ (while this is also possible under GA, the difference is that under regional anesthesia, immediate feedback is possible—namely, the prompt reversal of the neurological deficit). Second, the administration of higher concentrations of oxygen has been shown clinically to reverse the developing neurological deficit²⁶ and also increases ipsilateral cerebral oxygenation measured by cerebral oximetry during carotid cross-clamping.²⁷ Using these additional management strategies, the percentage of patients requiring carotid shunting should be 10% or less in patients undergoing awake CEA.

Regional Anesthetic Techniques for Carotid Surgery

The neck is supplied by the anterior primary rami of C1, 2, 3, and 4, which form the deep cervical plexus on the scalenius medius muscle. The deep plexus then gives cutaneous branches (“the superficial plexus”), including the great auricular, lesser occipital, supraclavicular, and transverse cervical nerves that supply the neck. There are no cutaneous contributions from the first cervical nerve root (C1).

It is possible to achieve analgesia of the neck sufficient for CEA to be performed by intermittent infiltration of local anesthetic. However, in most of the published vascular literature, surgeons and anesthesiologists prefer a regional block of some description. In some parts of the world, particularly French-speaking, patients commonly undergo awake carotid surgery under cervical epidural anesthesia.^28,29 However, there are considerable side effects associated with cervical epidural anesthesia. Hypotension and bradycardia occur relatively frequently as it is a bilateral technique. A retrospective comparison between cervical epidural and cervical plexus block for carotid surgery showed no difference in effectiveness of the blocks but more serious complications in the epidural group.²⁹ The commonest anesthetic technique for awake carotid surgery is therefore cervical plexus block (see Figures 1, 2, and 3).

The classic deep cervical plexus block was described by Winnie as a single-injection approach.³⁰ Others have described a multiple-needle technique in which local anesthetic injected down one needle emerges from the others thus “proving” that the tips of the needles are in a continuous fascial space.³¹ Superficial cervical plexus block is simpler, although historically there has been controversy about whether superficial cervical plexus block is deep or superficial to the investing layer of deep cervical fascia. This led to a distinction in nomenclature between these 2 techniques—with “superficial” blocks given subcutaneously and “intermediate” cervical blocks deep to the investing layer of deep cervical fascia. CEA may be performed under any of these 3 methods of blocking the cervical plexus.^31-33 The use of ultrasound³⁴ or a nerve stimulator³⁵ for performing these blocks is well described. However, as yet there are no individual studies showing improved efficacy or safety by using ultrasound or nerve stimulators to perform any of these cervical block techniques.

No matter how apparently effective the cervical block is, it is not uncommon for the patient to experience pain during dissection of the carotid sheath. Additional infiltration or topical application of local anesthetic to the carotid sheath may be required to prevent breakthrough pain from sympathetic nerve fibers that are not reliably blocked by the cervical plexus techniques.³⁶

Sedation

Sedation is commonly used during awake carotid surgery to allay anxiety and improve tolerance in patients who may be uncomfortable during long periods of lying still or experience either referred pain or pain during carotid sheath dissection. Agents used include benzodiazepines, propofol,³⁷ remifentanil,³⁸ and alpha 2 agonists such as clonidine and dexmeditomidine.³⁹ It is important to maintain verbal contact with the patient throughout particularly when assessing neurological status. Importantly, sedation is no substitute for inadequate analgesia, which requires local anesthetic supplementation by the surgeon.

Complications of Regional Anesthetic Techniques

There are multiple studies comparing different local anesthetic agents including bupivacaine, levobupivacaine, ropivacaine, and mepivacaine⁴⁰ used in cervical plexus blocks. None have shown significant differences in outcome or safety except that, in general terms, the greater the dose of local anesthetic the more effective the block. Ropivacaine has been suggested as the local anesthetic agent of choice due to its minimal vasodilatory effect in a total dose of greater than 150 mg.⁴¹ However, it is important to note that high plasma concentrations of local anesthetic agents may follow combined deep and superficial blocks,⁴² perhaps due to the vascularity of the neck. Care obviously needs to be taken not to exceed the recommended maximum doses of local anesthetic drugs. Adjuncts to local anesthetic agents including clonidine⁴³ and fentanyl⁴⁴ have been successfully used to prolong and intensify the block.

Cervical plexus block may be associated with a number of complications including blockade of adjacent nerves (phrenic, recurrent laryngeal, facial, hypoglossal, or vagus nerves), intravascular injection (including vertebral artery and external jugular vein) causing seizures and even intrathecal injection resulting in loss of consciousness. Overall, fewer complications in the literature have been reported from the use of superficial rather than deep block,⁴⁵ although it is important to note that complications can still occur with superficial block.⁴⁶

It is clear that carotid surgery may be performed under general or regional anesthesia. However, there are subtle differences between general and regional techniques in terms of perioperative hemodynamic profile, and there are additional treatment options available for the awake patient. Overall, the vascular “team” is probably the most important part of ensuring the safety of patients undergoing CEA. The risks and benefits of anesthetic techniques should be carefully considered for each individual patient undergoing CEA.

Regional Anesthesia for Abdominal Aortic Aneurysm Repair (Including Abdominal Visceral, Aorto-Iliac, and Aorto-Femoral Revascularization)

Abdominal aortic aneurysm (AAA) repair involves the replacement or bypass of an aneurysmal section of abdominal aorta. AAAs can be repaired by open, laparoscopic, or endovascular surgical techniques. We will discuss the use of regional anesthesia for these procedures, but it is beyond the scope of this review to discuss the relative merits of each surgical approach.^47-49

The early enthusiasm for endovascular aneurysm repair (EVAR) has been tempered slightly by the mid- and longer-term outcomes of patients from the early EVAR trials. However, it is still the preferred treatment for many patients presenting with AAA. Suffice it to say, that for the foreseeable future, both open and endovascular approaches will be used for patients requiring aortic aneurysm repair. Even if EVAR grafts become far safer and ongoing problems, such as endoleak,⁵⁰ are eradicated, there will still be patients unsuitable for EVAR for anatomical or other reasons and who therefore require open surgery.

AAA surgery continues to be a major cause of morbidity and mortality because of the very nature of the surgery and the commonly-associated comorbidity. AAA may cause 15 000 deaths annually in the United States and is the 10th largest killer.⁵¹

Regional Anesthesia for EVAR

EVAR may be successfully performed under local anesthetic infiltration alone, central neuraxial block (spinal, epidural, or combined spinal-epidural block), or under GA. There is some evidence that locoregional techniques offer advantages over GA for EVAR, but the available evidence is largely retrospective.

An early retrospective analysis of 91 patients undergoing EVAR identified less vasopressor support, less fluid requirements, less frequent requirement for postoperative intensive care unit (ICU), and shorter hospital stay in those patients who received local compared with epidural or GA.⁵² However, the study was small, retrospective, and early in the learning curve for this technique.

More recently, analysis of nonrandomized data from 5557 patients in the EUROSTAR registry (nonrandomized) also showed significant differences among local anesthesia group (LA-G 6%), regional anesthesia group (RA-G 25%), and general anesthesia group patients (GA-G 69%).⁵³ The duration of the operation was reduced in the LA-G compared with the RA-G and GA-G (P < .0001). Admission to the ICU was significantly less for LA-G patients (2%) than RA-G (8.3%, P = .0004) and GA-G (16.2%, P < .0001) patients, but RA-G still had a distinct advantage (P < .0001) over GA-G. Hospital stay was significantly shorter in LA-G (P < .0001) versus GA-G, but RA-G still had an advantage (P < .0001) versus GA-G. In EUROSTAR, systemic complications were significantly lower both for LA-G (6.6%, P = .0015) and RA-G (9.5%, P = .0007) than for GA-G (13.0%).

Verhoeven et al⁵⁴ reported a prospective, but not randomized, continuous cohort of 239 patients who underwent EVAR under LA unless patients required additional retroperitoneal approach to the aorta or iliac arteries, required other abdominal procedures (eg, umbilical hernia repair), or refused LA, in which case they received regional anesthesia or GA. Relative exclusion criteria were anxiety, groin reexplorations, and body mass index > 30 kg/m² (obese patients).⁵⁴ LA was associated with a lower incidence of complications, shorter operating time, faster mobilization, and less frequent requirement for ICU care compared with the GA group.

The largest published study concerning anesthetic choice for patients undergoing EVAR comes from the American College of Surgeons National Surgical Quality Improvement Program.⁵⁵ Data from 6009 patients who underwent elective EVAR under GA, spinal anesthesia, epidural anesthesia, or LA were analyzed. GA was associated with an increase in pulmonary morbidity versus spinal anesthesia. In addition, GA was associated with a 10% increase in length of stay over spinal anesthesia and a 20% increase over LA. However, there were no significant differences in mortality between patients receiving different anesthetic techniques.

In conclusion, although there are no large randomized studies comparing GA and locoregional techniques for EVAR, there is considerable level 2 evidence that locoregional techniques are associated with reduced respiratory complications, reduced length of stay admission to ICU, and decreased blood loss. However, it must be remembered that not every patient is suitable for locoregional anesthesia (due to patient or surgical factors), and GA therefore remains an important technique for EVAR.

Regional Anesthesia for Open AAA Repair

In contrast to EVAR, regional anesthetic techniques are usually used as an adjunct to GA for open AAA repair. The aim is to provide good postoperative analgesia and its associated physiological and psychological benefits. There are isolated case reports where AAA repair has been performed under regional anesthesia alone but this is probably uncommon practice.^56,57 Suitable regional techniques include central neuraxial blockade (epidural, spinal, or combined spinal-epidural), transverse abdominal plane and rectus sheath blocks, and continuous wound infiltration.

Thoracic Epidural Analgesia

Two large multicenter trials in the 2000s looked at thoracic epidural analgesia and anesthesia in vascular patients undergoing aortic surgery. The Veterans Affairs (VA) study looked at the effect of epidural anesthesia and analgesia on perioperative outcome (death and major complications) in 1021 patients undergoing major aortic, biliary, gastric, and colorectal surgery. Patients were assigned randomly to receive either GA plus postoperative analgesia with parenteral opioids (group 1) or epidural plus light GA plus postoperative epidural morphine (group 2). Overall, the 30-day follow-up data showed no significant differences in outcome between the 2 treatment groups. However, post hoc subgroup analysis by type of operation showed that for abdominal aortic surgery patients (n = 374), the 30-day postoperative overall occurrence rate of primary endpoints was significantly lower (P < .01) in group 2 patients (40/184, 22%) than in group 1 patients (70/190, 37%). This difference stemmed from the increased incidence in group 1 patients of new MI, respiratory failure, and stroke.⁵⁸ For these aortic surgery patients (n = 374), there were 4 significant predictors of primary outcome: age, congestive heart failure, chronic obstructive pulmonary disease, and duration of surgery. Even after adjusting for the impact of these predictors by comparing logistic regression models, the group 2 patients for vascular surgery still had a significantly lower occurrence rate of primary endpoints.

In the VA study, epidural local anesthetic was only used intraoperatively, with postoperative analgesia in the epidural group being provided by epidural morphine. It is unclear whether the beneficial effects of regional anesthesia on cardiac morbidity are limited to thoracic epidural techniques with local anesthetics⁵⁹ or, as in the case of the VA study,⁵⁸ whether this can be achieved with epidural opioids too.

The MASTER (Multicentre Australian Study of Epidural Anesthesia and Analgesia in Major Surgery) trial of 915 high-risk patients undergoing major abdominal surgery did not show a survival benefit for patients receiving epidural analgesia even in the subgroup of AAA patients.⁶⁰ A total of 255 patients (57.1%) in the epidural group and 268 (60.7%) in the control group had at least 1 morbidity endpoint or died (P = .29). Mortality at 30 days was low in both groups (epidural 23 [5.1%], control 19 [4.3%], P = .67). Only 1 of 8 categories of morbid endpoints in individual systems (respiratory failure) occurred less frequently in patients managed with epidural techniques (23% vs 30%, P = .02). Postoperative epidural analgesia was associated with lower pain scores during the first 3 postoperative days. Post hoc subgroup analysis found no difference in outcome between epidural and control groups, neither in the subgroups with increased risk of respiratory or cardiac complications or undergoing aortic surgery nor in a subgroup with failed epidural block (all P > .05). No differences were found in length of stay in intensive care or in the hospital. However, TEA has shown to reduce pulmonary complications in patients undergoing AAA repair. These include decreased time to extubation,^59,61 less postoperative atelectasis, pneumonia, and hypoxemia,^62-64 and have been summarized in a meta-analysis.⁶⁵ In combination with early enteral nutrition, TEA also leads to an earlier return of gastrointestinal function,⁶⁶ probably because of the effects of TEA on the “stress response” to surgery.⁶⁷

In summary, compared with systemic opioids, TEA for open AAA repair offers superior pain relief, reduced cardiac and pulmonary complications, and earlier mobility. However, there is inconclusive evidence of decreased mortality in patients undergoing AAA repair, and there are significant associated risks and complications. These include epidural hematomas, nerve damage including permanent paraplegia and death,⁶⁸ accidental dural puncture, local anesthetic toxicity, and temporary neurological symptoms. The risk–benefit analysis for placement of a thoracic epidural catheter therefore needs to be addressed for each patient.

Other Regional Techniques for AAA

If TEA is contraindicated or if a patient refuses TEA, other regional anesthetic techniques may offer opioid-sparing techniques in conjunction with patient controlled analgesia.

Transversus abdominis plane block

There is little if any available data on transversus abdominis plane (TAP) blocks in aortic or indeed any vascular surgery. However the benefits of TAP block for postoperative analgesia following other abdominal surgery have been demonstrated⁶⁹ and therefore may warrant extension of this technique for patients undergoing open AAA repair. TAP blocks are relatively straightforward to perform with a low risk profile. They reduce the need for postoperative opioid use, increase the time to first request for further analgesia, provide more effective pain relief, and reduce opioid-associated side effects.⁷⁰ Bilateral TAP blocks with indwelling catheters compared favorably with TEA following upper abdominal surgery with no significant difference in pain score on coughing at 8, 24, and 72 hours between the 2 groups, although there was greater opioid usage in the TAP block group⁷¹ (see Figure 4).

Despite concerns about the quantities of local anesthetic used, plasma concentrations of local anesthetic following TAP block are broadly consistent with plasma levels found after injection at other comparable sites.⁷² For aortic surgery, bilateral TAP blocks with catheter placement are perhaps the best option if an epidural cannot be placed.

There is a paucity of data concerning TAP blocks in vascular surgery, but their use in other abdominal surgery may warrant exploring the extension of this technique to patients undergoing open AAA repair.

Rectus sheath block

An alternative regional anesthetic technique to TAP blocks is bilateral rectus sheath blocks with catheter placement for continuous infusion⁷³ or bolus injection of local anesthetic.⁷⁴ However, there are no published data on the use of rectus sheath blocks in vascular surgery. Concerns have been raised about local anesthetic toxicity because of high volume of local anesthetic required to maintain adequate analgesia,⁷⁵ so care needs to be taken when using this technique.

While TEA remains the gold standard for analgesia for open AAA repair, the advent of catheter techniques and novel nerve blocks together with the need to mobilize patients rapidly following vascular surgery may alter this practice in the future.

Regional Anesthesia for Infrainguinal Arterial Reconstruction

Infrainguinal bypass surgery is performed to restore blood flow to the lower limbs. The aims are to relieve ischemic pain, improve limb function, and prevent critical limb ischemia, which may otherwise progress to limb loss. The prevalence of symptomatic peripheral vascular disease (PVD) increases with age from around 3% in patients aged 40 years to 6% in patients aged 60 years.⁷⁶ The ageing population, in combination with a rapid increase in the prevalence of obesity and diabetes mellitus and improvements in the treatment of concomitant coronary artery disease—resulting in longer life expectancy—is likely to increase the number of patients presenting for peripheral revascularization in the future. In addition, recent data have been published showing improved long-term overall and limb survival with primary surgical bypass compared with angioplasty.⁷⁷

Peripheral vascular disease is a marker of disseminated atherosclerosis. Patients diagnosed with PVD, including those who are asymptomatic, are at increased risk of death, MI, and stroke. Their relative risk is 2 to 3 times that of age and sex matched groups without PVD. Surgery and anesthesia are not without risk in this patient group. A recent analysis found the 30-day mortality to be 2.7% following infrainguinal bypass surgery, and 18.7% of patients developed major morbidity.⁷⁸

General or regional anesthesia (spinal, epidural, or peripheral nerve blockade) or a combination of both may be offered for patients undergoing surgery for PVD. There is a considerable anesthetic literature comparing outcomes for patients undergoing PVD surgery under regional anesthesia or GA; however, as yet there is no ideal anesthetic for infrainguinal bypass surgery.

Central Neuraxial Anesthesia

Spinal anesthesia provides excellent analgesia but its duration is limited, and surgery can be unpredictable in its complexity and duration. A lumbar epidural catheter alone or in combination with a spinal allows the duration of anesthesia to be extended and may also provide postoperative analgesia. The majority of surgery takes place in the L1-4 dermatomes, and a block height of T10 is adequate in most cases. A higher block and the resulting sympathetic blockade can cause problematic bradycardia and hypotension in this elderly population.⁷⁹ Treatment with vasoconstrictors and cautious fluid replacement will help prevent congestive cardiac failure from excess fluids when the sympathetic blockade recedes postoperatively.

A handful of randomized controlled trials have addressed the issue of whether anesthetic technique affects outcome in infrainguinal revascularization.

Cook et al⁸⁰ randomized 101 patients undergoing lower limb vascular surgery to have their surgery performed under spinal anesthesia or GA. There were hemodynamic differences between the 2 groups: the spinal anesthesia group having a significantly higher incidence of hypotension and the GA group more hypertension. Spinal anesthesia overall provided greater hemodynamic stability than GA, which has been confirmed elsewhere.⁸¹ However, the only significant outcome difference was a significantly higher incidence of postoperative chest infection in the GA group (35% vs 16%, P = .023). There was no difference between the 2 groups in terms of cardiac morbidity and mortality, and neither technique appeared superior in terms of graft patency rates at 3 months.

The Perioperative Ischemia Randomized Anesthesia Trial Study Group (PIRAT) randomized 100 patients undergoing elective lower limb revascularization to either GA and postoperative opioid analgesia or epidural anesthesia and postoperative analgesia for 24 hours.⁸² The study demonstrated no significant differences in cardiac-related morbidity, pulmonary complications, or mortality. However, the GA group had a significantly higher rate of regrafting or thrombectomy before discharge (22% vs 4%, P < .01). In a large subset of these patients (95/100) clotting factors were measured before and after surgery (24 and 72 hours) and the results published as a separate article.⁸³ Fibrinogen levels were similar in both GA and epidural anesthesia groups, but there was a significant difference in plasminogen activator inhibitor (PAI; an inhibitor of fibrinolysis) levels at 24 hours (P = .05). In the GA group, PAI levels rose significantly at 24 hours from preoperative levels (P < .001) and then returned to baseline, implying that epidural anesthesia promotes fibrinolysis. This rise was not seen in the epidural anesthesia group, and the authors hypothesized that the early rise in circulating PAI levels in GA patients may contribute to thrombosis in the first 48 hours after surgery. Twenty-two out of the 95 patients suffered an arterial thrombosis, 17 of whom had had GA and 5 epidural anesthesia. GA was shown to be predictive of arterial thrombosis. The effects of epidurals on coagulation and graft occlusion were also noted by Tuman et al,⁸⁴ who performed thrombelastography on patients undergoing lower limb revascularization. Patients were randomized to GA alone group or GA with epidural analgesia group.⁸⁴ Graft failure rates were significantly higher in the GA group (8/40 [20%] vs 1/40 [3%], P = .007) and similar to those seen in the PIRAT study. Thromboelastographic markers of fibrinogen-platelet activity (α angle and MA) increased on the first postoperative day in patients receiving GA. Conversely, use of GA + epidural was associated with significant decline in postoperative α and MA values. The authors concluded that the use of epidural anesthesia may attenuate postoperative hypercoagulabilty because of inhibition of platelet aggregation. Both studies contain only small numbers of patients, and neither addresses the issue as to whether it is the choice of anesthesia or postoperative analgesia that makes the difference. Of relevance perhaps to both these studies is the greater lower limb blood flow seen in patients with a functioning local anesthetic epidural.⁸⁵

Bode et al⁸⁶ subsequently randomized 423 patients having elective femoral-distal bypass surgery to receive spinal anesthesia, epidural anesthesia, or GA. Intraoperative hemodynamic monitoring with invasive arterial and pulmonary artery catheters was continued for 48 hours postoperatively in an ICU setting. The incidence of cardiac events and mortality were very low, and no significant differences between the 3 groups were found. However, it is noteworthy that such invasive hemodynamic monitoring and resultant attention to fluid and vasoactive medication, which is not a standard of care for such patients, itself could have affected outcome for all 3 groups. Also, patients who underwent GA following a failed regional block had a significantly higher death rate (9.4% vs 1.6%) than those who had a successful planned GA or regional anesthetic.

The latest study by Dodds et al⁸⁷ randomly allocated 82 patients scheduled for elective revascularization surgery to either epidural anesthesia or GA.⁸⁷ No other aspects of perioperative care were dictated by the study protocol. They found no significant difference in mortality, cardiac events, or postoperative respiratory failure. However, patients randomized to the epidural group had a decreased incidence of early vascular graft failure at 7 days (6/45 [13%] vs 0/37 [0%], P = .02). This difference was no longer significant 30 days after surgery.

The published literature concerning regional anesthesia or GA for lower limb revascularization has been summarized in a Cochrane database, which concluded that neuraxial anesthesia may reduce pneumonia.⁸⁸ However, no conclusions could be drawn with regard to mortality, MI, and rate of lower-limb amputation. However, only 696 patients were included from the 4 randomized controlled trials discussed above.

A retrospective study of 14 788 patients from the National Surgical Quality Improvement Program database who underwent infrainguinal arterial bypass looked at the effects of the type of anesthesia on outcomes of lower extremity infrainguinal bypass.⁸⁹ The most common type of anesthetic given was GA. However, when compared with spinal anesthesia, the risks of graft failure (odds ratio = 1.43), cardiac events (odds ratio = 1.8), and postoperative pneumonia (odds ratio = 2.2) were significantly higher with GA. GA was also associated with increased odds of requiring reoperation (odds ratio = 1.40). There was no significant difference in 30-day mortality between the groups. Although this is a retrospective review, it involves large numbers of patients. It is also more likely to represent true everyday clinical practice than the patients recruited to randomized controlled trials that have very tightly controlled hemodynamics and postoperative care in an intensive care setting. As such, the true benefits of neuraxial anesthesia, including reductions in postoperative pneumonia and cardiac events, may have been revealed.

Peripheral Nerve Blocks

Although infrainguinal bypass surgery is usually performed under general or neuraxial anesthesia, peripheral regional anesthesia is an option that may be considered, particularly when central neuraxial blockade is contraindicated. No randomized controlled trials comparing peripheral nerve blockade, general, or epidural anesthesia have been done to evaluate the impact of peripheral regional anesthesia on perioperative morbidity and mortality and on vascular graft patency. However, Yazigi et al⁹⁰ found that there were fewer intraoperative episodes of myocardial ischemia in patients undergoing infrainguinal bypass surgery under combined femoral and sciatic nerve blockade compared with GA.⁹⁰ Numerous case reports have been published describing successful completion of infrainguinal bypass surgery under peripheral regional block, mainly combined femoral and sciatic nerve blockade.^91-93

Local Anesthetic Infiltration

Infrainguinal bypass surgery has been reportedly carried out successfully under local anesthetic infiltration alone.⁹⁴ In this study, 86 patients underwent a variety of lower limb arterial reconstruction procedures using infiltration with lignocaine and sedation as required. The procedure was well tolerated, and only 4 patients required conversion to GA. Of the 86 patients two died within 28 days, and a further 2 had subendocardial MIs.

Peripheral nerve blockade or local anesthetic infiltration alone may provide an option for patients who would have otherwise been considered too unfit for surgery or conventional anesthesia.^92-94 Further work needs to be carried out to evaluate whether peripheral regional blockade is superior to either general or epidural anesthesia in terms of postoperative morbidity and mortality reduction.

Conclusion

Vascular surgical patients are some of the most challenging that anesthesiologists care for both in terms of their significant associated comorbidities and the complex surgery with its concomitant acute physiological changes, potential for blood loss, and potential hemodynamic instability. Regional anesthesia may offer benefits for such patients.

While there is no level 1 evidence that regional anesthesia reduces mortality for any of the patient groups discussed in this review, there is certainly evidence in terms of better analgesia and faster recovery together with circumstantial evidence of greater hemodynamic stability and lower associated morbidity. The likelihood of future large, multicentric randomized controlled trials comparing regional anesthesia and GA showing differences in outcome is low—perhaps because other variables concerned with postoperative morbidity and mortality are not possible to control. Despite this, regional anesthetic techniques remain a useful part of the armamentarium of the vascular anesthesiologist.

Footnotes

Acknowledgements

The authors would like to acknowledge the assistance of Dr Mark Crowley, Nuffield Dept Anaesthetics, John Radcliffe Hospital for his assistance in recording the ultrasound images of the deep cervical plexus block.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

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