Preoperative assessment of vascular patients

Vascular

Preoperative assessment of vascular patientsDavid Yates

lawrence caldicott

AbstractVascular surgical patients have a high incidence of morbidity and mortal-

ity following surgery. Preoperative assessment allows the anaesthetist

to judge the risk of anaesthesia and surgery, to identify any medical

factors that can be improved and to plan perioperative care. The risks

and benefits should be fully discussed with the patient. Many proven

risk factors can be readily identified by history and examination and

simple tests. Only rarely will more invasive testing be indicated. risk

assessment, stratification and perioperative optimization are discussed.

specific conditions that occur frequently and their implications for the

vascular anaesthetist are also described.

Keywords preoperative assessment; vascular surgery

Vascular surgical patients have a high incidence of morbidity and mortality following surgery. This is due to pre-existing condi-tions affecting the cardiovascular, respiratory and renal system, and the advanced age of most patients. An accurate assessment of the dysfunction of these systems should be performed before surgery.

The main purpose of preoperative assessment is to provide a measurement of the risk of morbidity and mortality to enable appropriate patient selection, arrange appropriate pre-, peri-, and postoperative management, and ensure that the patient is fully informed of the risk. There has been an upsurge in the provision of pre-assessment clinics. The presence of a consultant anaes-thetist provides leadership and a source of advice on policies and protocols.

Cardiovascular systemMost of the perioperative mortality associated with vascular sur-gery is due to cardiovascular complications. The body’s oxygen demand increases by up to 40% following major surgery, such as aortic aneurysm repair. This extra oxygen demand lasts for several days postoperatively and is met mainly by an increase

David Yates, FRCA, is Specialist Registrar in Anaesthesia at York.

He qualified at the University of Leeds, and trained as an SHO in

the Yorkshire region. His research interests include perioperative

optimization and the identification of high-risk surgical patients.

Lawrence Caldicott, FRCA, is Consultant Anaesthetist at St James’s

Hospital, Leeds. He qualified at St George’s Hospital, London, and

trained in anaesthesia in Leeds and Sheffield. His interests include

anaesthesia for vascular surgery and local anaesthetic techniques.

aNaEsTHEsIa aND INTENsIVE carE MEDIcINE 8:6 2

in cardiac output. An estimate of the patient’s cardiorespiratory reserve and functional capacity is therefore important, but can be difficult in the vascular patient, because of the high incidence of claudication, previous strokes and amputations. A detailed history should be taken. Poor exercise tolerance, dyspnoea, angina, previous myocardial infarction, palpitations, syncope, peripheral oedema and orthopnoea may indicate cardiac disease, which may warrant further investigation.

Guidelines published by the American Heart Association (AHA) and the American College of Cardiologists (ACC) use the concept of metabolic equivalents (Table 1). Risk stratifica-tion is also based on the nature of the surgery and the presence of independent clinical predictors to help stratify preoperative assessment (Figure 1). A metabolic equivalent of task (MET) is the basal metabolic oxygen consumption at rest (about 3 ml/kg/min) and can be measured. Various activities can be assigned approximate MET values and an estimate of the patient’s exer-cise capacity made. An inability to increase oxygen consumption more than 4 METS identifies a high-risk patient.

Scoring systemsOther scoring systems have been devised to assess cardiac risk (Table 2) most of which use straightforward indices that can be established from a history, examination and simple investiga-tions, such as the ECG.

Investigations for cardiac riskAn assessment of functional capacity can be difficult from the history alone, and in some cases more invasive methods of testing are warranted. Exercise ECG testing, 6-minute walking distance and stair climbing can be used if possible. The dura-tion of walking in standard Bruce-protocol exercise ECG can also be useful, even if no ECG changes are detected.

24-hour ECG: preoperative ST segment analysis of a 24-hour ECG recording gives an indication of the frequency and sever-ity of ischaemic episodes. It can detect ‘silent’ ischaemia, and should be used in conjunction with a patient diary to document episodes of angina and physical activity. If there is no sign of silent ischaemia on a 24-hour ECG, the risk of perioperative cardiac complications is very low.

Metabolic equivalents (METs)

Excellent (>7 METs) Moderate (4–7 METs) Poor (<4 METs)

• Playing squash

• Jogging

10 min mile

• scrubbing floor

• singles tennis

match

• cycling

• Playing golf

(no cart)

• Walking at 4 mph

• Gardening

(mowing, weeding)

• Hoovering

• activities of

daily living

• Walk at 2 mph

• Writing

1 MET = oxygen consumption of a 70 kg, 40-year-old at rest

Table 1

39 © 2007 Elsevier ltd. all rights reserved.

Vascular

Risk assessment algorithm

MI, myocardial infarction;

MET, metabolic equivalent of task

Non-emergency surgery

No recent coronary revascularization or evaluation

Assess metabolic equivalents

Major clinical predictors

Unstable angina, recent MI, decompensated

heart failure, arrhythmia or valvular disease

Delay or cancel non-cardiac

surgery pending

medical management

Further care dictated by findings

and treatment results

Consider less invasive surgery

Consider coronary

angiography

Poor

< 4 METs or high-risk surgical procedure

Moderate or good

> 4 METs or low-risk surgery

Non-invasive testing

High risk

Consider coronary angiography

Low risk

Continue to surgery

Intermediate clinical predictors

Mild angina, previous MI, compensated

heart failure, diabetes, renal impairment

Minor clinical predictors

Age > 70, abnormal ECG, not sinus rhythm, poor

functional capacity, previous stroke, hypertension

Recent coronary intervention and asymptomatic

Continue to surgery

Figure 1

myocardial infarction rate of approximately 5%.

Dobutamine stress echocardiography: standard echocardio-graphy is used to assess myocardial contraction during the administration of dobutamine, which causes tachycardia and stresses the myocardium. The presence of wall motion abnor-malities on echocardiography is indicative of ischaemia. These areas of abnormal movement are detected some time before ST segment changes appear on the ECG or the patient complains of angina. The number of myocardial ‘segments’ involved can be seen and gives a quantitative picture of the extent of the ischaemic load. This investigation has a high sensitivity with a relatively low specificity. Thus a positive test is likely to detect those who will go on to have a cardiac event, but it will also pick up many who will not. Resting echocardiography, with requests for an estimate of the ejection fraction, is often performed but has been shown to have little predictive value for postoperative cardiac events.

Dipyridamole–thallium scanning: dipyridamole is a vasodilator that reduces blood pressure and causes a reflex tachycardia. On injection of dipyridamole and thallium normal coronary arteries dilate and thallium (a potassium analogue) is taken up by the myocardium. Narrowed or blocked coronary arteries show little or no thallium uptake. All the thallium is distributed to viable myocardium 4 hours after the injection. Rescanning at this stage (once the tachycardia has subsided) will therefore show areas of reversible ischaemia and, if there is no thallium uptake, infarc-tion. This test will identify ischaemic myocardium accurately, but has a poor predictive value for identifying patients who will have a perioperative myocardial infarction. It also involves injection of a radioactive substance and adds little to what will already be known from taking a history, examining the patient and perform-ing simpler investigations. There is little evidence to support its use in routine practice.


Cardiopulmonary exercise testing is a relatively cheap, non-invasive way to measure cardiac reserve. It involves respiratory gas analysis during an increasing work-rate exercise test, normally performed on a bicycle ergometer. 12-lead ECG monitoring is also used, so that an exercise ECG is performed at the same time. Oxygen consumption and carbon dioxide excretion are measured on a breath-by-breath basis. When the respiratory exchange ratio (CO2 production/O2 consumption) reaches 1.0, the patient is said to have reached their anaerobic threshold (AT). From this point on, the oxygen delivery to the tissues is insufficient to meet the requirements for aerobic respiration, and lactic acidosis develops. The level of oxygen consumption (ml/kg/min) at the anaerobic threshold has been used to risk-stratify patients for high-risk sur-gery. Recent work suggests that an AT greater than 11 ml/kg/min (correlating approximately with 4 METs) predicts a very low risk for perioperative myocardial events.1 The benefit of this test is that even patients with quite significant peripheral vascular dis-ease can perform the test successfully. The AT is reached long before the patient tires or becomes exhausted (Figure 2). A com-prehensive stress testing of the heart and lungs can be achieved.

Coronary angiography is the gold standard for the assessment of coronary artery disease. It allows the measurement of intra-ventricular pressures, ventricular function and the gradients across valves. Suitability for surgical or radiological intervention can be established.

Specific conditionsCoronary artery disease: atherosclerosis is a systemic disease and only 10% of vascular patients have normal coronary arteries, with more than 50% having severe coronary disease demon-strated on angiography. This correlates with a perioperative


Vascular

Cardiac risk indices

Cardiac condition Goldman index (points) Detsky index (points) Eagle index (present or absent)

Third heart sound 11

History of pulmonary oedema 5

Pulmonary oedema in past week 10

unstable angina within 6 months 10

angina (ccsc III)a 10

angina (ccsc IV)a 20

angina (any) yes

Preop MI within 6 months 10 10 yes

Q wave on EcG yes

MI more than 6 months ago 5 yes

> 5 ventricular ectopic beats per minute 7 5

Important aortic stenosis 3 20

Ventricular arrhythmias yes

EcG not sinus rhythm 7 5

age > 70 years 5 5 yes

Intraperitoneal, aortic or thoracic operation 3 3

Poor medical condition 3 5

Diabetes yes

Emergency surgery 4 10

High-risk score > 25 > 31 ≥ 3

Moderate-risk score 6–24 20–30

acanadian cardiovascular society classification (ccsc) of heart disease. III is marked limitation of activity (i.e. walking 100–200m on the level) and IV represents an inability to do anything without pain

MI, myocardial infarction

Table 2

Previous myocardial infarction: patients who have had a previous myocardial infarction (MI) have a 5–6% chance of reinfarction in the perioperative period. Surgery within 3 months of an MI carried up to a 36% chance of reinfarction. With modern preoperative

Figure 2 cardiopulmonary exercise testing. (a) EcG display with sT

segment analysis; (b) commercial software package for results analysis;

(c) mouthpiece for gas analysis; (d) 12-lead EcG; (e) exercise bike;

(f) expiratory gas analyser.


assessment, monitoring and perioperative care, the risk has almost certainly been reduced, but it is recommended that elective surgery should not be carried out within 6 months of an MI.

Cardiac failure: symptomatic cardiac failure implies a severely dysfunctional myocardium. The condition carries a poor prognosis and scores highly in all the risk assessment scores. Risk increases with the severity of the failure. In severe failure consideration should be given to a ‘non-operative’ approach if possible, or a less invasive surgical or radiological procedure. The patient’s medi-cal condition should be preoptimized, with appropriate use of diuretics, vasodilators, or angiotensin-converting enzyme (ACE) inhibitors. A subset of heart failure patients may benefit from heart-rate reduction with the use of β-blockers. These patients should be admitted to hospital and receive a graded introduc-tion of β-blockade. Overall, haemodynamics can improve with the increase in filling time. Invasive monitoring, inotropes and postoperative critical-care facilities may be needed, and can be arranged under the supervision of a cardiologist.

Aortic stenosis is the most common heart valve lesion in the UK. The most frequent causes are congenital abnormalities and degenerative calcific stenosis. Severe aortic stenosis is defined by a mean pressure gradient of more than 50 mm Hg across a valve or a cross-sectional area of less than 0.8 cm2. Care should be taken in interpreting pressure gradients because a small gradient may


Vascular

be falsely reassuring if the left ventricle is failing and therefore no longer able to generate high pressures. Surgery in patients with aortic stenosis is hazardous because of the vasodilatation and myocardial depression caused by induction of anaesthesia. The resulting drop in blood pressure decreases coronary artery filling, leading to ischaemia, decreases in cardiac output and cardiac arrest. Patients with associated angina or syncope have severe disease, and consideration should be given to surgical correction of the valve if possible.

Hypertension is well recognized as a risk factor for ischaemic heart disease. Whilst hypertensive patients are more prone to blood pressure lability both intra- and postoperatively, studies have failed to show that moderate hypertension is a risk factor for perioperative cardiac morbidity. Uncontrolled hypertension is graded as only a minor risk factor in the ACC and AHA guide-lines. There is little evidence to support cancelling hypertensive patients, who are undergoing elective surgery, on the day of surgery. Patients with a diastolic blood pressure of more than 110 mm Hg, which fails to settle, should be referred for further investigation and treatment. Current guidelines suggest a target blood pressure of 140/90 mm Hg. Patients taking antihyperten-sive medication should continue in the perioperative period, but some anaesthetists would omit ACE inhibitors as they may cause an increased incidence of perioperative hypotension.

Atrial fibrillation: patients in atrial fibrillation should have their heart rate controlled to less than 90 beats per min. These patients are frequently anticoagulated to reduce the risk of thrombo-embolic events. Ideally, patients should remain without anti-coagulation for as little time as the surgical procedure allows.

Modifying cardiac riskCoronary artery intervention: patients identified with severe coronary artery disease should be investigated and treated along standard medical, surgical or radiological guidelines, disregard-ing their subsequent need for vascular surgery. Cardiac surgery should be undertaken only if the disease makes it necessary. The concept of correcting severe coronary artery disease before elective surgery to reduce cardiac events does not reduce short-term mortality. Focus is shifting from preoperative correction of coronary artery disease to pharmacological optimization with β-blockers and possibly statins. It seems that vascular surgery immediately following percutaneous coronary stenting is espe-cially hazardous, with a 5% cardiac death rate, despite adequate antiplatelet treatment. It is recommended that surgery should be delayed at least 6 weeks in these patients.

β-blockers: initial studies have shown great benefits with β-blockers, in terms of reduced cardiac morbidity. The study by Poldermans2 in high-risk patients had to be stopped early because β-blockade proved so beneficial. Subsequent studies have failed to reproduce these results, and a recent meta-analysis concluded that, overall, β-blockade reduced arrhythmias and myocardial ischaemia but had no effect on mortality, myocardial infarction rate or length of hospital stay.3 The best regimen in terms of patient selection, timing and duration of treatment is uncertain and the results of large trials (e.g. POISE study) are awaited. It seems prudent to prescribe β-blockers to patients with a history or


evidence of myocardial ischaemia on testing, but a blanket policy of prescribing to all patients will cause an excess of side effects.

Statins: recent evidence suggests that statins have a poten-tially protective perioperative effect (3-hydroxy-3-methylglutaryl coenzyme A inhibitors). They decrease inflammation and stabi-lize atherosclerotic plaques (pleiotropic effects), and may reduce perioperative cardiovascular complications. Because one of the proposed mechanisms of perioperative myocardial infarction is rupture of a coronary artery plaque, this pleiotropic effect is appeal-ing. However, many of the studies have been small, retrospective and non-randomized,4 and large-scale, prospective, randomized trials are needed. All vascular patients should be prescribed a statin according to present medical guidelines to reduce vascular events.

Preoptimization: the concept of maximizing oxygen delivery using incremental fluid boluses and inotropes has shown encour-aging results. Stroke volume monitoring is optimized with a pulmonary artery catheter or, more frequently, an oesophageal Doppler probe. Work is ongoing to determine the best regimen for optimization. The place of preoptimization in the vascular patient remains unclear. The younger, fitter patient undergo-ing aortic aneurysm surgery may benefit from preoptimization, but in the older patient with significant cardiac disease the use of β-blockade and the avoidance of tachycardia would seem logical. Another issue is resources, in terms of critical-care beds and medical input needed for the preoperative care of patients.

Perioperative medical therapyAntiplatelet/anticoagulant agents: there are few guidelines regarding optimal management of these drugs in the perioperative period. Increasing evidence is emerging that aspirin should be con-tinued throughout the perioperative period. Clopidogrel, an ADP/platelet binding inhibitor, should be stopped for at least 5 days before surgery to prevent excess intraoperative blood loss and at least 7 days if insertion of epidural is being considered. However, definitive evidence in terms of the ‘safe’ period in which to place neuro-axial blocks may never become available. Warfarin should also be stopped 5–7 days before surgery and the patient started on either low molecular weight heparin or unfractionated heparin to provide anticoagulation in the perioperative period. A risk/benefit analysis should be made for each patient. Patients with coronary artery stents in situ should not be left without antiplatelet cover.

Respiratory systemBecause the number of vascular patients who smoke is high, chronic obstructive pulmonary disease is very common. Again, a functional assessment of the severity of the condition is useful. Whilst much of the damage to the alveoli will be permanent, there is usually an element of reversible airway disease, and this should be optimized preoperatively.• If functional ability is seasonal, schedule elective surgery for the best time of year.• Try to get the patient to stop smoking 6–8 weeks before surgery to allow ciliary function to return. Failing that, get the patient to stop on the day of surgery to decrease carboxyhaemo-globin and improve oxygen carriage.• Admit the patient several days in advance to allow time for chest physiotherapy.


Vascular

• Bronchodilators, either nebulized or via metered-dose inhalers, and steroids will help treat any reversible element.• Exclude active infection.• Encourage the patient to lose weight.

Investigations: lung-function tests are used to assess the sever-ity of respiratory disease. Forced expiratory volume in 1 second (FEV1) is a good measure of ventilatory capacity. An FEV1 less than 1 litre indicates extremely poor function and predicts a high risk of postoperative ventilation. Forced vital capacity indicates the severity of diffuse parenchymal disease. A value less than 50% of that expected for height, weight and sex indicates a high likelihood of needing postoperative support. Lung-function tests carried out before and after the administration of bronchodila-tors give an indication of the reversibility of the disease. Arterial-blood gas analysis should be done if respiratory function tests are below 50% of the predicted value. This analysis will occasionally identify patients with chronic hypercarbia who are reliant on their hypoxic drive. Chest radiography rarely adds to the assess-ment after history, examination and respiratory function testing.

Renal systemPreoperative renal impairment and postoperative renal failure increase perioperative mortality. Measures should be taken to preserve existing function and avoid perioperative deterioration. In particular, measures should be taken to avoid:• hypovolaemia• hypotension• nephrotoxic drugs (e.g. non-steroidal anti-inflammatory drugs)• sepsis• hypoxaemia• prolonged periods of oliguria.

Angiographic contrast media are potentially nephrotoxic. Pre-angiographic intravenous hydration, the use of low-osmolar dyes, and minimizing the dose used help reduce the renal insult. Aminophylline and N-acetylcysteine have been used to counter-act the toxicity but strong evidence of their efficacy is lacking. Alternative techniques such as carbon dioxide angiography with digital subtraction imaging are non-nephrotoxic and available.

DiabetesDiabetes mellitus is relatively common in vasculopaths. The anaesthetist should seek the presence of associated conditions


such as ischaemic heart disease, renal impairment and peripheral or autonomic neuropathies. Myocardial ischaemia is frequently silent in these patients. Most hospitals have their own regimen for the management of patients with diet, tablet or insulin-controlled diabetes in the perioperative period. This usually involves either omitting the morning dose of oral hypoglycaemics on the day of surgery or a glucose/potassium/insulin infusion through the perioperative period. Patients with diabetes are more likely to suffer from autonomic neuropathy and may not tolerate the vasodilatation associated with the induction of anaesthesia or the fall in venous return on commencing positive-pressure ven-tilation. Preoperative standing/sitting blood pressure, or feeling for a tachycardia during a Valsalva manoeuvre can assess the autonomic nervous system. ◆

KEy REFEREnCES

1 Older P, smith r, Hall a, French c. cardiopulmonary risk assessment

by pulmonary exercise testing. Crit Care Resusc 2000; 2: 198–208.

2 Poldermans D. The effect of bisoprolol on perioperative mortality

and MI in high-risk patients undergoing vascular surgery. N Engl J

Med 1999; 341: 1789–95.

3 Wiesbauer F, schlager O, Domanovits H, et al. Perioperative beta-

blockade for preventing surgery-related mortality and morbidity:

a systematic review and meta-analysis. Anesth Analg 2007; 104:

27–41.

4 Kapoor as, Kanji H, Buckingham J, et al. strength of evidence for

perioperative use of statins to reduce cardiovascular risk: systematic

review of controlled studies. Br Med J 2006; 333: 1149.

FuRThER READInG

cox cD, Tsikouris JP. Preventing contrast nephropathy: what’s the

best stategy? a review of the literature. J Clin Pharmacol 2004; 44:

327–37.

Eagle Ka, Berger PB, calkins H, et al. acc/aHa guidelines update for

perioperative cardiovascular evaluation for noncardiac surgery –

executive summary. Anesth Anal 2002; 94: 1052–64.

Vincenzi MN, Meislitzer T, Heitzinger B, et al. coronary artery stenting

and non-cardiac surgery – a prospective outcome study.

Br J Anaesth 2006; 96: 686–93.


Preoperative assessment of vascular patients

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