Anaesthesia for carotid surgery

Abstract

Stroke is a leading cause of morbidity and mortality and may be preceded by a transient ischaemic attack (TIA). 20% will have a carotid stenosis caused by atheromatous plaque which can be removed by carotid endarterectomy, reducing the risk of further stroke.

Risk of stroke is highest in the immediate period following TIA and surgery is recommended within 7 days. The benefits of surgery are highest in those with more than 70% stenosis. Preoperative optimization is limited by the urgency of surgery, but assessment focuses on associated cardiac and respiratory comorbidities including blood pressure control.

Carotid endarterectomy can be performed under general or regional anaesthesia (with superficial or intermediate cervical plexus blocks) and while large trials have shown no significant difference in outcomes, there are advantages and disadvantages to each. Intraoperative blood pressure control and care with the effects of positioning is required. Smooth emergence with early neurological assessment is the aim with general anaesthesia. The main risk of surgery is postoperative stroke but there is no high-quality evidence for intraoperative shunting or cerebral monitoring in reducing this.

Other postoperative complications include cardiac ischaemia, hypertension including cerebral hyperperfusion syndrome and airway compromise due to oedema/haematoma.

Learning objectives

After reading this article, you should be able to:

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explain the challenges of preoperative assessment and optimization in patients for urgent carotid endarterectomy after transient ischaemic attack
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analyse the advantages and disadvantages of general and regional anaesthesia for carotid endarterectomy and the evidence comparing the two techniques
•

identify the postoperative complications after carotid endarterectomy and have strategies for managing them

Introduction

Stroke is the greatest cause of disability in the UK and a leading cause of death with around 38,000 deaths a year. The incidence of a first transient ischaemic attack (TIA) is approximately 50 per 100,000. About 20% of patients with TIA or non-disabling ischaemic stroke have an atheromatous plaque causing stenosis near the bifurcation of the ipsilateral carotid artery. Carotid endarterectomy is a surgical procedure performed to reduce the incidence of embolic or thrombotic strokes by removing this plaque and stenosis. Around 3000–3500 procedures are performed in the UK every year.

The risk of disabling stroke or death is highest in the immediate period following the initial TIA. The current National Stroke Service Model endorsed by the UK National Institute for Health and Care Excellence recommends urgent surgery within 7 days of symptom onset, posing challenges for preoperative assessment, optimization and service delivery. From the National Vascular Registry, the median time to surgery most recently was 14 days and only 52% were operated within 14 days.

Surgery is beneficial in reducing five-year stroke risk and death with a stenosis >50%. This benefit is more marked in those with a higher degree of stenosis (70–99%). Most data for this derive from two randomized trials – European Carotid Surgery Trial (ECST) and North American Symptomatic Carotid Endarterectomy Trial (NASCET) – performed over 25 years ago. ECST-2 is currently ongoing to compare carotid endarterectomy with modern medical therapy in those with carotid stenosis >50% but low–intermediate risk of stroke.

Preoperative assessment

Due to the urgency of surgery, time is often limited but common comorbidities associated with stroke/TIA should be optimized as far as possible. These include cardiac disease such as atrial fibrillation and coronary artery disease, smoking-related respiratory disease, chronic renal disease, hypertension and diabetes mellitus. All patients should have a preoperative 12-lead ECG due to the risk of cardiac ischaemia. Other specific investigations (e.g. echocardiogram or chest X-ray) should be guided by examination findings or other comorbidities. Preoperative blood tests include full blood count, urea and electrolytes, clotting and group and save.

Blood pressure (BP) control is recommended if there is an acute hypertensive emergency, or it is above 180/100 mmHg. In acute stroke, there is loss of cerebral autoregulation so cerebral perfusion pressure is directly proportional to the mean arterial pressure (MAP). Uncontrolled hypertension predisposes to recurrent stroke, haemorrhagic transformation and cerebral oedema. Usual antihypertensive medications should be continued in the perioperative period except angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers (ARBs) due to risk of perioperative hypotension and acute kidney injury (AKI).

Acute antiplatelet therapy consists of 300 mg aspirin for 2 weeks from presentation before switching to clopidogrel or alternative antiplatelet agent for secondary prevention. This should be continued through the perioperative period as stroke risk is usually higher than bleeding risk. High-dose statin therapy is also started acutely and is shown to lower stroke and cardiovascular risk perioperatively.

Preoperative neurological assessment should be documented to aid recognition of postoperative changes in neurological function suggesting a cerebrovascular event. CT angiogram or carotid doppler will show the extent of contralateral disease and predict collateral flow.

Surgery

Surgery is performed with a 5–10 cm incision over the border of anterior sternocleidomastoid and dissection down to the common, internal and external carotid arteries [ Figure 1 ]. Heparin 3000–5000 units is given prior to clamping above the stenosis and the internal carotid is clamped first to prevent distal emboli before the arteriotomy and removal of atheromatous plaque (endarterectomy) [ Figure 2 ]. Clamping causes a transient rise in BP due to the effect on carotid baroreceptors but this is ablated by general anaesthesia.

The main risk of surgery is postoperative stroke – the current rate of stroke and/or death at 30 days post-endarterectomy in the UK is 2.1% A proportion of awake patients will develop a transient neurological dysfunction during clamping. Shunting across the clamped section of artery during general anaesthesia has been shown in a Cochrane meta-analysis to reduce stroke-related death within 30 days of surgery and lower stroke rate within 24 hours of surgery. However, evidence is of low quality and there remains a variation in practice between surgeons about when shunts are used. Shunts are not without risk and can cause plaque or air embolism, carotid dissection or occlusion. The artery is usually reconstructed with a synthetic or autologous vein patch.

Carotid stenting is currently performed in some centres as an alternative to open endarterectomy and is useful if surgical access is an issue, e.g. previous neck radiotherapy or surgery (such as parotid), contralateral recurrent laryngeal nerve damage, high bifurcation, obesity or if severe cardiorespiratory co-morbidities preclude a more major open procedure.

Anaesthetic technique

Carotid endarterectomy can be performed under general anaesthesia (GA) or regional anaesthesia (RA) with the two techniques compared in Table 1 . The main advantage with regional anaesthesia is real-time neurological monitoring but if deep sedation is required for patient comfort this advantage is negated.

Table 1

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