Carotid endarterectomy
Carotid endarterectomy (CEA) is a preventative procedure that aims to reduce the likelihood of a major disabling stroke or death in patients who have experienced a minor stroke or a transient ischaemic attack (TIA) and who also have a significant stenosis of the ipsilateral internal carotid artery. The risk of a major stroke is highest in the period immediately following a minor stroke or TIA. Therefore, to produce the maximum reduction in risk, CEA should be performed within 2 weeks of a minor stroke or TIA.
1 Discuss the preoperative assessments and medical management prior to carotid endarterectomy
2 Appreciate the risks and benefits of regional vs general anaesthesia for carotid endarterectomy
3 Manage an acute airway compromise due to post-operative haematoma formation.
2A03; 2A10; 2G01
A 57-year-old male accountant with a 30 pack year smoking history is scheduled for a left-sided CEA. Seven days previously, whilst in a business meeting, he experienced an episode of weakness affecting his right arm, accompanied by expressive dysphasia. His symptoms resolved completely within 20 min. Previously, he was taking no medications, but, following this event, he has been started on clopidogrel and simvastatin.
The patient is likely to have undergone a CT scan of the head to exclude a cerebral haemorrhage or space-occupying lesion. He will also have had bilateral carotid duplex ultrasonography performed. Clear benefits are gained by carrying out CEA in patients with symptomatic internal carotid artery stenosis of ≥70%. Some male patients (but not females) with lesser degrees of stenosis (50–69%) may benefit from CEA, but the number of patients needed to treat to prevent a stroke is higher in this group. Importantly, a duplex scan should be repeated in the hours prior to surgery to ensure that the carotid artery has not occluded completely, as there is no benefit from proceeding with surgery in this situation.
A standard preoperative assessment should be made, with particular reference to the following points.
◆ It is essential to establish which symptoms occurred at the time of the TIA, the patient’s current neurological status, and the presence of any residual deficits. The occurrence of further TIAs following the index event is also important, as patients with crescendo TIAs are at increased risk of a perioperative stroke
◆ Patients with cerebrovascular disease often have other forms of cardiovascular disease and factors which increase the risk of perioperative complications—ischaemic heart disease, hypertension, chronic kidney disease, and diabetes mellitus are common, as is a history of cigarette smoking
◆ Smokers have a higher incidence of respiratory disease, and, if surgery is planned under regional anaesthesia, the ability to lie flat and still without coughing or desaturation is important. Cognitive function and the ability to obey commands are also important if regional anaesthesia is planned.
◆ All patients should be on antiplatelet therapy. Guidelines regarding the optimal choice of drugs for secondary prevention change frequently, with either clopidogrel as a single agent or aspirin plus dipyridamole currently recommended
◆ In addition to antiplatelet drugs, statin therapy not only reduces the risk of further stroke, but also lowers the incidence of perioperative cardiac events
◆ Poorly controlled hypertension is a risk factor for perioperative stroke. Ideally, the BP should be well controlled when the patient presents for CEA, although this is often not the case. In general, antiplatelet, statin, and antihypertensive drugs should be continued throughout the perioperative period.
◆ BP should be recorded in both arms prior to surgery, as co-existing subclavian artery stenosis (producing unequal brachial BPs) is not uncommon. In this situation, the higher reading should be used for BP measurement
◆ The results of FBC, U&E, glucose, and a 12-lead ECG should be available. A specimen should be sent to the transfusion laboratory for ‘group and save’
◆ It is also important to know the result of the carotid duplex scan. Important features to note include the degree of stenosis in both the carotid artery that is to be operated on and also the contralateral carotid. A high-grade stenosis in the contralateral carotid artery increases the likelihood of an inadequate flow in the circle of Willis during the time that the carotid artery is clamped and may increase the likelihood of requiring a temporary shunt.
CEA can be performed under either general or local anaesthesia. There is no clear-cut evidence that demonstrates the superiority of one technique over the other, although the GALA trial suggested that local anaesthesia may be better for patients in whom the contralateral carotid is occluded. Local anaesthesia is also associated with a reduced use of temporary shunts during the procedure and a reduced incidence of post-operative wound haemorrhage.
Ideally, the patient should be pain-free, well oxygenated, and haemodynamically stable throughout the perioperative period, no matter whether local or general anaesthesia is chosen as the anaesthetic technique. Unfortunately, the BP can be labile during CEA, no matter which anaesthetic technique is chosen, and the anaesthetist must be prepared to manipulate the BP upwards or downwards at any point. A range of drugs, including esmolol, labetalol, ephedrine, and phenylephrine, should be immediately available. It has been suggested that the BP should be maintained within ± 20% of the baseline BP throughout the procedure. However, there are occasions during the period of cross-clamping where a BP in excess of this may be useful in maximizing flow in the circle of Willis and maintaining an acceptable cerebral perfusion. An arterial pressure monitoring line should be inserted prior to the start of anaesthesia.
Superficial, intermediate, deep, or combined cervical plexus blocks, placed with or without the aid of ultrasound, have been described for CEA. Meta-analyses of a number of trials that compared the analgesic efficacy of these different types of cervical plexus blocks concluded that deep blocks do not improve the quality of analgesia, compared with superficial blocks. However, the risk of serious complications (intravascular or intrathecal injection) is significantly higher with deep blocks. Local anaesthetic techniques are often combined with IV sedation—TCIs of propofol and remifentanil (in low doses) are ideal for this purpose, as they are readily titratable and short-acting.
◆ Allows the assessment of neurological status throughout the case (this is the main advantage over general anaesthesia)
◆ Avoids the need for airway management
◆ Reduces the need for temporary shunt placement, hence reduces the incidence of shunt-associated complications (distal emboli and arterial dissection)
◆ Preserves cerebral autoregulation and blood flow to the contralateral hemisphere.
◆ Inadequate analgesia requiring supplemental local anaesthetic by the surgeon (this is almost inevitable during the dissection of the carotid sheath, as this is innervated by the glossopharyngeal nerve, not the cervical plexus)
◆ Oversedation (if sedative drugs are used)
◆ Requirement to lie flat and still
◆ Risks of intraoperative conversion to general anaesthesia (<2% of cases)
◆ Complications associated with the block (intravascular or intrathecal injection; phrenic nerve block).
CEA can also be performed under general anaesthesia. Due to the site of surgery and a difficult access to the airway, a technique that involves tracheal intubation and mechanical ventilation is most commonly used. Short-acting anaesthetic drugs that wear off quickly after surgery and allow a rapid assessment of neurology should be used. Propofol, remifentanil, and desflurane are ideal agents.
◆ Immobile patient for the duration of the operation
◆ Control of airway and ventilation (PaCO2).
◆ No direct neurological assessment possible (with reliance on indirect monitors)
◆ Increased use of shunts
◆ Increased incidence of intraoperative hypotension.
Surgery performed under local anaesthesia allows regular direct clinical assessment of the conscious level, upper limb motor strength, vision, speech, and some higher cognitive functions (e.g. simple arithmetic). This is considered to be the ‘gold standard’ method for assessing the adequacy of cerebral perfusion and is one of the major justifications for performing CEA using local anaesthetic techniques. Obviously, this is not possible during general anaesthesia where a number of alternative indirect methods have been described to assess cerebral perfusion. These include cerebral oximetry using near-infrared spectroscopy; measurement of the cerebral blood flow in the ipsilateral middle cerebral artery using transcranial Doppler; somatosensory evoked potentials; and measurement of carotid artery stump pressures. All of these methods have significant limitations, and the decision to insert a temporary shunt, or not, is often based on somewhat arbitrary cut-off values, depending on which monitoring technique is used. Some anaesthetists and surgeons advocate the routine insertion of an elective shunt if surgery is performed under general anaesthesia.
Communication between the surgeon and anaesthetist is crucial in this situation. The anaesthetist should declare that there is likely to be an inadequate cerebral perfusion, and the surgeon should prepare to insert a temporary shunt. Meanwhile, attempts should be made to improve the cerebral perfusion by increasing the mean arterial BP to a level above the normal baseline. IV fluids, plus bolus doses of ephedrine or phenylephrine, may be required to achieve this. Any sedative agents should be discontinued. If there is no improvement in the neurological status and the patient remains unresponsive after the BP has been raised, the surgeon should proceed with the insertion of a temporary shunt which bypasses the area of the carotid artery that has been clamped. This usually results in a rapid improvement in the conscious level and neurological function. In this situation, it is appropriate to continue surgery under local anaesthesia. However, if there is airway compromise or an inadequacy of ventilation, then conversion to general anaesthesia may be required.
1 Excessive heparin effect: IV heparin (in a dose 70 IU/kg) is usually administered prior to cross-clamping the carotid artery. Occasionally, an excessive heparin effect persists towards the end of surgery that makes haemostasis difficult to achieve. This can be confirmed by measuring APTT in the operating theatre, using a near-patient monitor, and protamine can then be administered, if required
2 Excessive antiplatelet effect: treatment with antiplatelet therapy, particularly when two antiplatelet drugs are used, can also lead to problems with haemostasis. Ideally, the effect of antiplatelet agents should be assessed using a near-patient platelet function analyser. If a profound antiplatelet effect is present, then platelet transfusion should be considered.
The patient has developed a haematoma which is compressing the upper airway; this is an emergency situation that requires immediate action. Call for senior help, and administer high-flow oxygen. If the patient is in extremis, then insufficient time exists to return to the operating theatre. Medical staff on the ward must be prepared to remove the skin sutures (or staples) and evacuate the haematoma. Depending on the exact location of the bleeding point and how the neck has been closed, it may also be necessary to remove deeper sutures that have been used to close the cervical fascia and platysma muscle. This is an emergency, lifesaving act, following which the patient will need to return to theatre for formal exploration and haemostasis.
Summary
CEA is an effective treatment option for some patients with significant carotid artery atherosclerosis who have suffered a TIA or minor stroke. The aim of the procedure is to reduce the risk of a further stroke causing death or disability. For CEA to be of maximum value, the risks around the time of surgery need to minimized as far as possible. The combined risk of death or stroke in the perioperative period should be <3%. In order to achieve this, carotid surgery should only be performed by experienced teams of professionals who are aware of the many potential problems that the patient may experience around the time of surgery.