Anaesthesia for vascular, endocrine and plastic surgery

General considerations

Peripheral vascular disease is a manifestation of generalised cardiovascular disease, and therefore coronary artery disease is present to some degree in almost all patients presenting for major vascular surgery. Most are elderly and have a high incidence of coexisting medical diseases, in particular:

• ischaemic heart disease

• hypertension

• congestive cardiac failure

• chronic obstructive pulmonary disease

• renal disease

• diabetes mellitus

Most of these are risk factors for perioperative cardiac complications after major surgery (see Chapters 19 and 29 ).

The broad aims of preoperative evaluation before vascular surgery are to:

• assist risk assessment, permit further investigation if appropriate and allow optimisation of coexisting medical conditions;

• evaluate and discuss the risks with the patient and surgical team;

• establish the best surgical options (e.g. non-invasive or endovascular surgery) for an individual; and

• plan the anaesthetic technique, perioperative monitoring and postoperative care, and allow required facilities (e.g. ICU) to be organised.

Vascular surgery is associated with high morbidity and mortality, resulting mostly from cardiac complications (myocardial infarction, arrhythmias and heart failure) (see Chapters 29 and 30 ). It is therefore vital that cardiac function is assessed preoperatively and that the risks of surgery are evaluated and discussed with the patient. Although the outcome of subsequent vascular surgery is improved in those who have previously undergone coronary revascularisation by coronary artery bypass grafting (CABG), this is associated with additional risks. Percutaneous coronary interventions (PCIs) are increasingly used in preference to CABG in suitable patients. The perioperative management of antiplatelet medication in patients who have undergone PCI is discussed in Chapters 19 and 30 . Coronary revascularisation should be performed only if indicated because of severe coronary disease; it is not justified simply to improve outcome from subsequent vascular surgery.

Abdominal aortic aneurysm

Abdominal aortic aneurysms (AAA) occur in 2%–4% of the population aged older than 65 years, predominantly in men. Approximately 90% of AAAs arise below the origin of the renal arteries, and they tend to expand over time. The risk of rupture increases exponentially when the aneurysm exceeds 5.5 cm in diameter, and elective surgery is usually then indicated. The in-hospital mortality from elective AAA repair is decreasing and is now 3%–5%, but overall mortality from a ruptured AAA is up to 90% and is 50% in those who survive until emergency surgery can be performed. Consequently, screening programmes are in place to identify patients with a small asymptomatic aneurysm and to offer intervention when the aneurysm reaches a diameter of 5.5 cm. Aortic aneurysm screening has been shown to be cost effective in men but not women. Open surgery involves replacing the aneurysmal segment with a tube or bifurcated prosthetic graft, depending on the extent of iliac artery involvement. In all cases the aorta must be cross-clamped (see later) and a large abdominal incision is required. Surgery is prolonged and blood loss may be substantial. Patients are usually elderly, with a high prevalence of coexisting disease. These factors contribute to the high morbidity and mortality of open AAA surgery. Endovascular AAA procedures avoid some of these problems (see later).

Endovascular aortic aneurysm repair

Endovascular aortic aneurysm repair (EVAR) is now an established alternative to open surgery. In conventional EVAR an expandable stent graft is inserted under radiological guidance via the femoral or iliac arteries into the aneurysm to exclude it from the circulation ( Fig. 39.1 ). Endovascular repair is generally performed via groin incisions, and the aortic lumen is temporarily occluded from within rather than being cross-clamped. The cardiovascular, metabolic and respiratory consequences are reduced compared with conventional open surgery. Perioperative blood loss, transfusion requirements, postoperative pain, hospital stay and morbidity are lower compared with open surgery. In 2016 two thirds of patients undergoing intervention for AAA in the UK underwent EVAR. In-hospital mortality after EVAR was 0.4% in the UK in 2016, whereas that for open repair was 3%. Long-term follow-up data suggest that beyond 8 years, patients who undergo open repair have better survival. However, it must be remembered that many patients die from coexisting disease in the years after repair, with approximately half of patients in one major study surviving beyond 8 years. Patients who undergo EVAR have a significant incidence of late aneurysm rupture. They require lifelong surveillance and may require interventions to treat stent-graft leaks (endoleaks). Despite advances in stent-graft technology, the morphology of the aneurysm in some patients renders it unsuitable for EVAR (based on the site, shape, degree of angulation and the size of iliac arteries). Repeated radiological procedures (e.g. angioplasty) are required in up to 20% of patients. The procedure usually takes 1–2 h and may be performed by radiologists or surgeons, but the patients have the same coexisting diseases and some of the anaesthetic considerations are similar.

In some cases EVAR may be preferred as a less invasive technique in patients judged unfit for open surgery. Access to the iliac vessels is generally possible through infra-inguinal incisions in the groin. The use of low-profile devices with a relatively small diameter allows many cases to be performed under local anaesthetic infiltration. The presence of an anaesthetist is considered essential for such percutaneous access cases both for cardiovascular monitoring and in case of difficulty with the procedure. EVAR is generally performed in the radiology suite, and vascular centres often have a dedicated hybrid suite. Although these are equipped for both anaesthesia and surgery the suite may be remote from the main operating theatres, and considerations for anaesthesia in remote locations apply.

EVAR may be performed under general, regional or local anaesthesia with or without sedative adjuncts. In all cases, direct arterial pressure monitoring is mandatory because rapid fluctuations in arterial pressure may occur during stent-graft deployment. In awake patients, hyoscine butylbromide 20 mg i.v. may be useful to decrease bowel motility during stent-graft placement. CVP monitoring is not usually necessary unless dictated by the patient's medical condition (e.g. moderate/severe cardiac disease). Short periods of apnoea are needed during insertion of the device; this is easy when ventilation is controlled but requires the patient's co-operation if a regional or local anaesthetic technique is used. The devices are positioned under angiographic control, and large volumes of radiocontrast may be used, predisposing to contrast-induced nephropathy (CIN). It is important to avoid hypotension and hypovolaemia, both of which can contribute to CIN. The importance of maintaining hydration before, during and after the case is well recognised. Oral or intravenous prehydration may be used in patients with pre-existing renal impairment, and renal function should be monitored in the postoperative period. As with open repair, there is limited evidence to support interventions such as sodium bicarbonate, N -acetylcysteine or mannitol. Brisk haemorrhage is unusual during EVAR and although bleeding may be significant it is usually insidious. However, large-diameter cannulae should be inserted and vasoactive drugs readily available.

EVAR is now widely used for the repair of leaking and ruptured AAA. In these cases the procedure is performed under local anaesthesia if possible. If the patient is haemodynamically unstable or cannot cooperate with the procedure under local anaesthesia alone, general anaesthesia may be required. An intra-aortic balloon may be placed to act as an internal aortic cross-clamp and provide cardiovascular stability until the stent graft is deployed.

Endovascular graft placement is challenging if there is no normal aorta between the proximal end of an AAA and the renal arteries (a juxtarenal aneurysm), if the length of normal aorta is short or if the neck of the aneurysm is conical in shape. A number of solutions have been developed to address this. A conical-necked aneurysm may be treated with a graft whose top end is sealed in place with polymer-filled rings. Juxtarenal aneurysms may be treated with fenestrated grafts. These have holes (fenestrations) which overlie the position of the renal arteries. The graft is opposed to the aortic wall with the fenestrations opposite the relevant arteries, and stents are placed through the fenestrations into the renal arteries to complete the repair at the top end of the aneurysm. Such procedures may be performed under regional or general anaesthesia.

Thoracic endovascular aortic repair

Endovascular grafts are used to treat disease of the thoracic as well as the abdominal aorta. Aneurysms of the descending thoracic aorta, acute type B dissection (involving the descending aorta or the arch of the aorta distal to the left subclavian artery), penetrating aortic ulcers, intramural haematomas within the aortic wall and traumatic aortic transection may all be treated with thoracic aortic stents. Such repairs may be carried out under regional or general anaesthesia. Many anaesthetists, surgeons and radiologists prefer general anaesthesia to facilitate the delivery of induced hypotension whilst the top end of the stent is being placed. Patients with severe peripheral vascular disease may also require additional surgery with the placing of temporary grafts (conduits) to facilitate the insertion of the stent.

Thoracic endovascular aortic repair (TEVAR) carries risks of acute kidney injury and stroke. A particular concern is the risk of spinal cord injury and consequent paraplegia. The spinal cord receives its blood supply from a (usually single) anterior spinal artery and paired posterior spinal arteries ( Fig. 39.2 ). These arise superiorly from the left subclavian and vertebral arteries and inferiorly from the hypogastric artery. They are supplied throughout their length by a rich anastomotic network of vessels. Classical teaching was that flow from the artery of Adamkiewicz arising on the left between T8 and L1 was of particular importance. It is now understood that there may be multiple segmental feeding vessels contributing to the blood supply of the spinal cord. Stent coverage of a length of 20 cm or more of the thoracic aorta and stent graft exclusion of blood supply in the T8 to L2 region of the aorta pose a particular risk of spinal cord ischaemia and paraplegia. Spinal cord monitoring may be used during surgery, including direct communication with the awake patient or the use of sensory or motor evoked potentials. Paraplegia may present after surgery as well as arising during the intraoperative period, and rigorous postoperative monitoring is paramount. Key manoeuvres to mitigate and reverse cord ischaemia include blood pressure maintenance and CSF drainage. The latter involves placing a catheter into the subarachnoid space, allowing CSF to be drained to reduce pressure in the space to less than 10 mmHg. Spinal cord perfusion pressure depends on the difference between the arterial pressure in the spinal arteries and the CSF pressure. Reducing the latter therefore increases cord perfusion pressure.

Branched grafts and hybrid procedures

A number of alterative graft designs are available to treat anatomically challenging aneurysms. Stenting of a long segment of the aorta may exclude key vessels including the renal arteries, coeliac axis and superior mesenteric artery. Fenestrations, branched grafts (which incorporate side arms) or additional grafts (parallel or chimney grafts) to feed these vessels may be used to overcome this problem ( Fig. 39.3 ). Branch grafts differ from fenestrated grafts in that the side arms cross the aortic lumen, whereas fenestrations are opposed to the aortic wall. In some cases surgery may be performed to preserve the blood supply to vessels that are to be covered by a stent graft. Such hybrid procedures are of particular importance to allow endovascular repair of the ascending aorta and the aortic arch ( Fig. 39.4 ). The treatment of aneurysmal disease or of type A dissection by stent grafting alone would result in the great vessels supplying the head and neck being covered, with potentially catastrophic results. So-called debranching operations which may involve anastomoses between the carotid and subclavian arteries maintain blood supply to the great vessels supporting stent repair or combined stent and surgical repair to the proximal aorta. Such procedures require general anaesthesia and in some cases cardiopulmonary bypass and circulatory arrest.

Surgery for occlusive peripheral vascular disease

Peripheral reconstructive surgery is performed in patients with severe atherosclerotic arterial disease causing ischaemic rest pain, tissue loss (ulceration or gangrene), severe claudication with disease at specific anatomical sites (aortoiliac, femoropopliteal, popliteal or distal) or after failure of non-surgical procedures. Most patients are heavy smokers, suffer from chronic pulmonary disease, have widespread arterial disease and present initially with intermittent claudication. Consequently, exercise tolerance is limited and severe coronary artery disease may be present despite few symptoms. Surgical revascularisation is performed to salvage the ischaemic limb, but arterial angioplasty is a less invasive alternative and is generally performed as a first-line procedure in suitable patients. Patients presenting for surgical reconstruction are often those in whom angioplasties have failed and who may have more severe vascular disease. In-hospital mortality (3% in the UK in 2016) after lower limb revascularisation is comparable to that after elective AAA repair, and long-term outcome is worse as a consequence of associated cardiovascular disease. Acute limb ischaemia that threatens limb viability requires rapid intervention comprising full anticoagulation; intravascular thrombolysis after arteriography; analgesia; revascularisation via embolectomy; angioplasty or bypass surgery as indicated. The clinical findings of sensory loss and muscle weakness necessitate intervention within 6 h, and therefore preoperative evaluation and correction of risk factors may be limited.

Carotid artery surgery

Despite advances in the medical treatment of patients with stroke, it remains a significant cause of death and disability. Carotid endarterectomy is performed to prevent disabling embolic stroke in patients with atheromatous plaques in the common carotid bifurcation or internal or external carotid arteries ( Fig. 39.5 ). Most patients are elderly, with generalised vascular disease. Cerebral autoregulation may be impaired, and cerebral blood flow is therefore much more dependent upon systemic arterial pressure. The main risk of surgery is the production of a new neurological deficit (which may be fatal or cause permanent disability), although cardiovascular complications account for 50% of the overall morbidity and mortality.

The recommendations for carotid endarterectomy are based on an extensive body of research regarding the best management of stroke and transient ischaemic attack. Carotid endarterectomy is recommended in patients with symptoms of embolic carotid artery disease and a 70%–99% carotid stenosis so long as the risk of periprocedural death or stroke is considered to be less than 6%. It should be considered in symptomatic patients with a stenosis of 50%–69% whose surgical risk is considered to be less than 6%. There is also evidence to support carotid endarterectomy in asymptomatic patients with a 60%–99% carotid stenosis. However, the benefit is less marked than in symptomatic disease, and practice is more variable in this setting. Carotid artery angioplasty and stenting is a less invasive alternative to surgical endarterectomy. It is often considered for patients in whom neck surgery may be challenging – for example, after previous radiotherapy or in the patient at particular risk of perioperative cardiac complications. The risks of major stroke are highest within the first few days after a transient ischaemic attack (TIA) or minor stroke. Consequently, carotid endarterectomy should be performed as soon as is feasible (within 14 days and ideally within 48 h) after a minor stroke or TIA when indicated (embolic stroke, significant carotid stenosis). This limits the time available for preoperative preparation, investigation and risk reduction.

During surgery, the internal, external and common carotid arteries are clamped and the atheromatous plaque removed. During application of the clamps, cerebral perfusion is dependent on collateral circulation via the circle of Willis. Many surgeons insert a temporary shunt to bypass the site of obstruction, minimising the period of potential cerebral ischaemia. Several methods are available to assess cerebral blood flow during clamping before proceeding with the endarterectomy; if flow is adequate, some surgeons prefer not to use a temporary shunt. Monitoring of neurological status in an awake patient is considered by many to be the gold standard, but other methods used in practice include the following:

• Transcranial Doppler ultrasonography of the middle cerebral artery flow velocity

• Measurement of arterial pressure in the occluded distal carotid segment (the stump pressure)

• EEG monitoring

Although most strokes related to surgery are associated with thromboembolism rather than hypo- or hypertension, and the majority of these are caused by technical surgical issues, the anaesthetist has a crucial role in the maintenance of cardiovascular stability before, during and after surgery. Rapid swings in arterial pressure are common because of the direct effects of surgical manipulation, plaque removal and carotid cross-clamping in patients with impaired baroreceptor function as a result of carotid atheroma and cardiovascular disease.

The main aims of anaesthesia for carotid endarterectomy are maintenance of oxygen delivery to the brain, cardiovascular stability, airway protection, provision of neurological protection and rapid recovery. Most intraoperative strokes are apparent on recovery from anaesthesia, and early postoperative neurological assessment is important. Any residual postoperative effects of anaesthesia may confuse the diagnosis of intraoperative embolism or ischaemic change, so a technique that permits rapid return of function is required. These aims may be achieved using general, local or regional anaesthetic techniques, with or without sedative or analgesic adjuncts. In all cases an intra-arterial cannula is mandatory for monitoring of arterial pressure, which should be maintained particularly during carotid clamping, and attention paid to maintaining normothermia.

Local infiltration of the surgical field may be used alone or in combination with superficial and intermediate or deep cervical plexus blockade. Cervical plexus block can be performed using landmark- or ultrasound-guided techniques. Superficial cervical plexus block is performed by infiltration of local anaesthetic along the entire length of the posterior border of the sternomastoid muscle, using 10–15 ml local anaesthetic (e.g. levobupivacaine 0.25%). The intermediate block involves injection of 5 ml local anaesthetic 1–2 cm deep to the midpoint of the sternomastoid. Additional infiltration of local anaesthetic by the surgeon may be required and should be anticipated. Advantages of locoregional techniques include definitive neurological monitoring (therefore allowing selective use of shunts), preservation of cerebral and coronary autoregulation and the maintenance of higher cerebral perfusion pressures during the procedure ( Table 39.1 ). These techniques rely on good cooperation among the patient, the surgeon and the anaesthetist. Many patients find it difficult to lie still and supine for the duration of the procedure, particularly those with heart failure or respiratory disease; this may be compounded by diaphragmatic compromise because phrenic nerve paralysis may accompany deep cervical plexus blockade. Sudden loss of consciousness or seizures may occur if cerebral perfusion is inadequate after clamping, and subsequent airway control may be very difficult because access is limited.

Performing surgery under general anaesthesia avoids these problems. Both propofol and volatile agents (at low doses) preserve cerebral and coronary autoregulation, reduce cerebral oxygen requirements and, in theory, may provide some degree of neuroprotection. General anaesthesia with artificial ventilation allows P a co ₂ to be manipulated, but hypotension may be more common compared with regional anaesthesia. The airway is not accessible during surgery, and tracheal intubation with a well-secured reinforced tracheal tube is advisable. Anaesthesia should be induced cautiously using an i.v. agent and maintained with a balanced inhalational or total intravenous technique using an inspired oxygen concentration of 50% in air or nitrous oxide (100% inspired oxygen produces cerebral vasoconstriction). All anaesthetic agents should be short acting, and remifentanil, alfentanil or low-dose fentanyl (100–200 µg) are useful adjuncts. Hypotension may potentially occur after induction and during the placement of cerebral monitoring, but it should be treated promptly. Vasopressors (e.g. ephedrine 3–6 mg or phenylephrine 25–50 µg increments) are often required and should be prepared before induction of anaesthesia. A high P a o ₂ , normocapnia and normothermia should be maintained. Blood loss and fluid requirements are usually modest. Postoperatively, significant pain is unusual and the combination of wound infiltration with local anaesthetic with a nonsteroidal anti-inflammatory analgesic during surgery is effective.

Data from the GALA trial (general anaesthesia vs. local anaesthesia) and systematic reviews have shown no difference in overall outcome with any specific anaesthetic technique.

Patients should be monitored in a high-dependency environment or PACU for several hours postoperatively. Hypertension is common in the early postoperative period because of impaired circulatory reflexes; pain from the wound or from bladder distension may also contribute. Hypertension is associated with adverse neurological outcomes because it may compromise the graft or cause intracranial haemorrhage. Arterial pressure should be controlled to achieve systolic pressures less than 165 mmHg and diastolic pressures less than 95 mmHg, accounting for the range of individual preoperative values. Intravenous α- or β-blockers or an infusion of a vasodilator (e.g. GTN or hydralazine) may be required as prophylaxis or treatment.

The other main postoperative complication is the development of a haematoma. Initial treatment involves local pressure and reversal of heparin with protamine. However, local oedema and the presence of a large haematoma may cause airway compromise and hypoxaemia requiring urgent surgical exploration. Induction of general anaesthesia in these circumstances is particularly hazardous, and evacuation of the haematoma under local infiltration is usually preferable. Recurrent laryngeal nerve damage is a recognised complication of carotid endarterectomy. In most cases this simply causes a hoarse voice, but in patients who have had a previous contralateral carotid endarterectomy, specific preoperative evaluation of vocal cord function should be performed before surgery.