ANAESTHESIA FOR CAROTID ENDARTERECTOMY
Mike James
Department of Anaesthesia, University of Capetown, South Africa
Carotid artery surgery is essentially a preventative operation as it is performed to decrease the risk of the patient developing a stroke. Carotid disease accounts for around 30% of all strokes, and, since there are 500 000 new strokes each year in the US, this represents a considerable burden of disease. Carotid endarterectomy may, therefore, make a significant impact on this common and incapacitating disease, but the procedure is not, in itself, curative. Given this fact, any centre wishing to perform carotid end of directive these must be able to deliver a perioperative mortality rate of < 3%. In view of this, it is essential that patient selection is appropriate, that preoperative preparation is adequate, the anaesthesia is the best for the patient, and that there is excellent co-operation between anaesthetist and surgeon.
Recent studies have shown that, for high-grade carotid stenosis (> 70%), surgical treatment carries a significantly better prognosis for subsequent stroke development than does medical management. Many of these patients have significant intercurrent cardiac disease, as the majority of them will be either heavy smokers or diabetics. The issue is one of risk management in which the risks of the patient having a stroke need to be balanced against the perioperative mortality of the procedure.
The commonest cause of post-operative morbidity is cardiac disease. Preoperative evaluation rests primarily on good clinical history and examination. Hypertension must always be adequately controlled preoperatively as good control of BP for the surgery significantly reduces the risk of post-operative hypertension and of neurological events. Respiratory function must be properly assessed especially if regional anaesthesia is the management of choice. Diabetes mellitus is common in these patients and good control over the glycaemic state is required in the perioperative period.
Evaluation of myocardial status is controversial. Discovery of risk factors and assessment of effort tolerance are important. The need for special investigations is generally established on the basis of the presence and severity of risk factors and the urgency of the surgery to be undertaken. The large number of algorithms that exist for the identification of patients to undergo advanced cardiological investigation is indicative of the lack of agreement in this area. Advanced testing of all patients presenting with possible cardiac disease is non-productive, expensive and may even increase patient risk, so the selection of patients for testing remains a problem. The purpose of testing must be to identify patients who could be improved, or to identify patients in whom the risk of the operative procedure outweighs the potential benefit of the surgery. The AHA/ACC joint guidelines suggest evaluating the urgency of the procedure; if the procedure is deemed to be a justifiable emergency, surgery should proceed with due attention to the risks. If more time is available, consideration should be given to the current cardiac status of the patient. The patient who has undergone recent coronary revascularisation (within the last 5 years, but more than 3 months previously) and who has no recurrent symptoms can proceed directly to surgery. If no recent coronary evaluation has been conducted, clinical risk predictors should be considered. Similarly, if the patient has had a previous coronary revascularisation and symptoms have recurred, clinical predictors should also be considered (1).
The major clinical predictors indicate an unacceptably high risk of perioperative myocardial events for elective surgery and only life-threatening urgent surgery should be undertaken in patients with these risk factors, and medical optimisation should be conducted where feasible. Interventional cardiology should be undertaken where indicated by valid medical reasons, and not simply because these patients are about to undergo a surgical procedure (2).
The presence of minor clinical predictors is not controversial, as these do not indicate an increased risk although they may indicate a requirement for increased care as they indicate an increased probability of the presence of coronary heart disease.
If a patient has intermediate risk factors, the next step in assessment is to establish the level of activity that the patient can sustain. The general cut off that is accepted for reasonable effort tolerance is between 4-5 METs. Below that, further cardiac evaluation is indicated. Of the many tests advocated, my own preference is for echocardiography, and preferably dobutamine-stress echocardiography as this gives information, not only about the anatomical status of the coronary vessels, but also about the functional status of the ventricles and cardiac valves. Coronary angiography should only be performed in high-risk patients who warrant coronary revascularisation for medical reasons irrespective of the fact that they are about to undergo surgery. There is little evidence to support interventional cardiology prior to non-cardiac surgery unless such an intervention is indicated by the medical condition of the patient. Unless the carotid surgery can safely be postponed for at least three months after the intervention, no benefit can be expected.
It is important to ensure good perioperative medical management of these patients, whatever strategies are adopted and that all factors that may impose any increased myocardial stress are avoided. The maintenance of heart rates below 80 beats a minute appears to be associated with improved outcome in terms of ischaemic events, and the use of beta-blockers in patients with clear risks of myocardial ischaemia is now widely recommended, although optimal time periods and dosages are still to be established (3).
There is an increasing trend in many centres worldwide towards the use of regional anaesthesia for carotid endarterectomy as the awake patient provides the best possible monitoring of cerebral function during carotid cross clamping. Regional anaesthesia may reduce the requirement for shunt placement, but also poses significant problems. No definitive studies have clearly demonstrated any advantage in terms of patient outcome or the incidence of perioperative stroke related to the use of shunts. Some studies suggest that, in experienced hands, regional anaesthesia results in a reduction in the incidence of shunt placement in centres where shunting is performed electively.
General anaesthesia offers advantages of a secure airway and control of arterial carbon dioxide concentration and permits the use of cerebral protection including mild hypothermia. The disadvantages include more difficult haemodynamic control and the problem of monitoring cerebral perfusion.
The literature is still divided regarding the balance of risks, but current, rather poorly-controlled, studies do imply at least potentially better outcomes from regional rather than general anaesthesia (4), with possibly lower costs (5).
Post-operative haemodynamic instability is common, particularly in the first few hours postoperatively. There is some evidence that this instability is less frequent when regional anaesthesia has been used (6). During the post-operative period ECG monitoring, direct intra-arterial monitoring and neurological monitoring should be maintained for at least eight hours postoperatively and it is a practice to admit all these patients to ICU for 24 hours.
Time of Presentation
Sunday 2 May 2004 - 1330-1500
References
1. Chassot PG, Delabays A, Spahn DR: Preoperative evaluation of patients with, or at risk of, coronary artery disease undergoing non-cardiac surgery. Br.J.Anaesth. 2002; 89: 747-59
2. Kertai MD, Klein J, van Urk H, Bax JJ, Poldermans D: Cardiac complications after elective major vascular surgery. Acta Anaesthesiol.Scand. 2003; 47: 643-54
3. Poldermans D, Boersma E, Bax JJ, Thomson IR, van de Ven LL, Blankensteijn JD, Baars HF, Yo TI, Trocino G, Vigna C, Roelandt JR, van Urk H: The effect of bisoprolol on perioperative mortality and myocardial infarction in high-risk patients undergoing vascular surgery. Dutch Echocardiographic Cardiac Risk Evaluation Applying Stress Echocardiography Study Group. N.Engl.J Med 1999; 341: 1789-94
4. Bowyer MW, Zierold D, Loftus JP, Egan JC, Inglis KJ, Halow KD: Carotid endarterectomy: a comparison of regional versus general anesthesia in 500 operations. Ann.Vasc.Surg. 2000; 14: 145-51
5. Illig KA, Shortell CK, Zhang R, Sternbach Y, Rhodes JM, Davies MG, Ouriel K, Tansky W, Johansson M, Green RM: Carotid endarterectomy then and now: outcome and cost-effectiveness of modern practice. Surgery 2003; 134: 705-11
6. Sternbach Y, Illig KA, Zhang R, Shortell CK, Jeffrey M, Davies MG, Lyden SP, Green RM: Hemodynamic benefits of regional anesthesia for carotid endarterectomy. J Vasc.Surg. 2002; 35: 333-9
