Preoperative assessment for cardiac surgery

CARDIAC ANAESTHESIA

Preoperative assessment forcardiac surgeryCaroline Evans

Robert Abel

AbstractPreoperative assessment enables anaesthetists to tailor an anaesthetic to

an individual patient. Established classification systems give objectivity

to a patient’s description of his or her effort limitation. Anaesthetists

need a working knowledge of the preoperative investigations. They

also need to understand risk stratification tools for cardiac surgery to

answer questions from patients that relate to the risks of surgery and

anaesthesia. Most preoperative medications should be continued until

surgery. Antiplatelet therapy should be discontinued 7 days before

surgery, if possible. Anaesthetists should explain the likely events in

the anaesthetic room, such as the placement of venous and arterial

cannulae before preoxygenation and induction of anaesthesia as well

as the likely postoperative course on a cardiac intensive care unit. Estab-

lishing a rapport with the patient preoperatively and a benzodiazepine

anxiolytic are useful adjuncts to anaesthesia.

Keywords anaesthetic assessment; cardiac surgery; heart surgery;

preoperative assessment

The preoperative visit

Most patients presenting for cardiac surgery have been thor-

oughly investigated. Careful review of the notes before meeting

the patient enables the subsequent history and examination to be

tailored to the individual patient.

In addition to the usual anaesthetic preoperative questioning,

particular attention should be directed towards cardiovascular

pathology and the extent of any myocardial damage. Anaesthe-

tists need to determine whether there is ongoing ischaemia,

significant arrhythmias or evidence of cardiac failure.

The Canadian Cardiovascular Society classification (Box 1) of

effort angina is a widely used scoring system and correlates well

with angiographic findings. The New York Heart Association

classification of functional capacity (Box 2), in the context of

cardiac surgery, equates to the degree of dyspnoea secondary to

heart failure (although patients commonly have co-morbid

pulmonary pathology contributing to their dyspnoea).

Caroline Evans MB BCh FRCA is a Fellow in Cardiac Anaesthesia at Bristol

Royal Infirmary, UK, and Specialist Registrar on the All Wales rotation.

Conflicts of interest: none declared.

Robert Abel BSc MB BCh FRCA is a Consultant Cardiothoracic Anaesthetist

at the University Hospital of Wales, UK. Conflicts of interest: none

declared.

ANAESTHESIA AND INTENSIVE CARE MEDICINE 10:9 40

Both scoring systems add objectivity to patients’ description

of their symptoms and should alert anaesthetists to potential

ventricular dysfunction and potential difficulties in separating

from cardiopulmonary bypass.

The increasingly elderly cardiac surgery population has

a higher incidence of co-morbidities such as chronic pulmonary

disease, systemic hypertension, diabetes, previous cerebral

vascular accident, renal impairment and peripheral vascular

disease. Any existing neurological defect should be documented

as a baseline for postoperative assessment. Gastro-oesophageal

symptoms should be elucidated to identify patients at risk of

aspiration during induction of anaesthesia and those with

oesophageal pathology that contraindicate transoesophageal

echocardiography (TOE). Height, weight and body mass index

(BMI) should be documented.

Medication

Polypharmacy is common. Blood pressure and heart rate control

is paramount and beta-blockers should be continued. The

continued administration of angiotensin-converting enzyme

inhibitors or angiotensin receptor antagonists up to and including

the day of surgery is controversial. Some centres discontinue

these 24e48 hours before surgery on the grounds that their

continuation can predispose to perioperative hypotension,

particularly on cardiopulmonary bypass. Aspirin and clopidogrel

should normally be discontinued 7 days before elective surgery

to reduce the risk of perioperative bleeding. This is not always

possible in the presence of unstable acute coronary syndrome or

in the emergency patient, or in the presence of coronary artery

stents. In the last case, a discussion between the anaesthetist,

surgeon and cardiologist is required to consider the relative risks

of stent thrombosis with drug withdrawal against excessive

perioperative bleeding with continuation of antiplatelet therapy.

Mortality and risk stratification

Cardiac surgery carries a risk of death and serious complications.

Recent Care Quality Commission (formerly the Healthcare

Commission) data (2007) gave a risk of death for first-time coro-

nary artery bypass surgery (CABG) of 1.7% and 2% for isolated

aortic valve replacement. Individual risk varies widely according

to the procedure(s) being undertaken, the age of the patient and

any associated co-morbidities. A number of risk-scoring systems

have been developed to better estimate an individual’s risk when

undergoing a particular cardiac operation. The Parsonnet score

has largely been superseded in Europe by the European System for

Learning objectives

After reading this article, you should be able to:

C name and detail two classification systems that describe effort

limitation

C describe four investigations to confirm diagnosis of ischaemic

heart disease

C calculate predicted risk of mortality for patients undergoing

cardiac surgery.

5 � 2009 Elsevier Ltd. All rights reserved.

CARDIAC ANAESTHESIA

Cardiac Operative Risk Evaluation (EuroSCORE) (Table 1).

Originally designed as a simple additive score that could be

calculated at the bedside, it underestimates predicted mortality in

high-risk patients. The logisitic EuroSCORE, although lacking the

simplicity of a simple additive score, provides a more accurate

prediction of outcome. An online calculator for the logistic

EuroSCORE can be found at www.euroscore.org. The EuroSCORE

has been validated in the UK, Europe and North America and has

been shown to be predictive of major complications, duration of

intensive care stay and resource utilization.

Investigations

Guidance produced by the National Institute for Health and

Clinical Excellence (see Further Reading) dictates that a full

blood count, renal profile, electrocardiogram and chest radio-

graph are mandatory before cardiac surgery. In practice, most

centres also routinely screen for coagulation, hepatitis serology

and methicillin-resistant Staphylococcus aureus.

Patients will have undergone a range of diagnostic investi-

gations to define the pathology and to determine whether it is

surgically correctable. Anaesthetists should have a working

knowledge of these investigations and attempt to assess the

patient’s functional reserve.

Exercise stress electrocardiography

Suspected ischaemic heart disease (IHD) is most commonly

confirmed by exercise stress electrocardiography (ECG). The

most widely used protocol is the modified Bruce protocol. The

continuously monitored patient exercises (usually on a treadmill)

with progressively higher work rates at 3-minute intervals.

Patients who achieve 85% of their maximum heart rate (220

minus their age for men or 210 minus their age for women) with

The Canadian Cardiovascular Society classification ofeffort angina

Class 1

Ordinary physical activity does not cause angina. Angina occurs

with strenuous or rapid or prolonged exertion either at work or

during recreation.

Class 2

Slight limitation of ordinary activity. Angina occurs with walking or

climbing stairs rapidly, walking up hill, walking or stair climbing

after meals or in the cold or wind, or under emotional stress, or

during the few hours after awakening only. Angina occurs when

walking more than two blocks on the level or climbing more than

one flight of stairs at a normal pace and under normal conditions.

Class 3

Marked limitation of ordinary physical activity. Angina occurs with

walking one to two blocks on the level and climbing one flight of

stairs under normal conditions at a normal pace.

Class 4

Inability to carry on any physical activity without discomfort.

Angina may be present at rest.

Box 1


a normal exercise-induced increase in blood pressure (BP) and

no ST segment depression on ECG have a very low probability of

having IHD. Patients who manifest ST depression at a low work

rate with a fall in BP accompanied by typical angina pain have

a high probability of having IHD.

The test has an appreciable false-negative rate in general as

well as a false-positive rate particularly in women.

The presence of resting STeT wave abnormalities, left bundle

branch block (LBBB), left ventricular hypertrophy, a paced

ventricular rhythm or digoxin therapy makes the test unlikely to

be diagnostic. Patients with these pre-existing conditions and

those who are physically unable to perform the exercise stress

protocol will require an alternative non-invasive test such as

stress echocardiography, radionuclide perfusion imaging or

cardiac magnetic resonance imaging. The choice of investigation

is largely determined by local expertise and local infrastructure.

Cardiac catheterization and angiography

Cardiac catheterization and angiography is an invasive proce-

dure used to confirm the diagnosis of IHD made by exercise

stress ECG testing (or other investigation in those patients

unsuitable for exercise stress ECG testing). Detailed images of

coronary anatomy provide information about coronary artery

lesions requiring bypass surgery and the calibre and quality of

target vessels distal to the stenotic lesions.

Images are obtained by injecting contrast, under radiographic

guidance, into the left and right coronary arteries by way of

a catheter passed in a retrograde fashion from a femoral or radial

artery puncture site to the coronary ostea (Figure 1).

If the cardiac catheter is advanced further into the left

ventricle (LV) through the aortic valve, estimates of LV function

and measurements of pressure gradients across the aortic valve

can be made. This information is now largely provided by less

invasive echocardiography.

New York Heart Association functional classification

Class 1

Patients with cardiac disease but without resulting limitations of

physical activity. Ordinary physical activity does not cause undue

fatigue, palpitations, dyspnoea or angina.

Class 2

Patients with cardiac disease resulting in slight limitation of

physical activity. Comfortable at rest. Ordinary physical activity

results in fatigue, palpitations, dyspnoea or angina.

Class 3

Patients with cardiac disease resulting in marked limitation of

physical activity. Comfortable at rest. Less than ordinary physical

activity results in fatigue, palpitations, dyspnoea or angina.

Class 4

Patients with cardiac disease resulting in an inability to carry out

any physical activity without discomfort. Fatigue, palpitations,

dyspnoea or angina may be present at rest. If any physical activity

is undertaken the symptoms of cardiac insufficiency are increased.

Box 2


http://www.euroscore.org

CARDIAC ANAESTHESIA

The European System for Cardiac Operative Risk Evaluation (EuroSCORE)

Factor Definition Simple score

General factors

Age Per 5 years or part thereof over 60 (simple), continuous (logistic) 1

Gender Female 1

Chronic lung disease Long-term use of bronchodilators or steroids for lung disease 1

Extracardiac arteriopathy One or more of the following: claudication, carotid occulusion or >50% stenosis,

previous or planned surgery on the abdominal aorta, limb arteries or carotids

2

Neurological dysfunction Disease severely affecting ambulation or day-to-day functioning 2

Previous cardiac surgery Involving opening of the pericardium 3

Serum creatinine >200 mmol/l preoperatively 2

Active endocarditis Still on antibiotic treatment for endocarditis at the time of surgery 3

Critical preoperative state Any one or more of the following: ventricular tachycardia or fibrillation or aborted sudden death,

preoperative cardiac massage, preoperative ventilation before arrival in the anaesthetic room,

preoperative inotropic support, intra-aortic balloon pump or preoperative acute renal failure

(anuria or oliguria <10 ml/h)

3

Cardiac factors

Unstable angina Rest angina requiring intravenous nitrates until arrival in the anaesthetic room 2

Left ventricular dysfunction Moderate ejection fraction (30e50%) 1

Poor ejection fraction (<30%) 3

Recent myocardial infarction <90 days 2

Pulmonary hypertension Systolic pulmonary artery pressure >60 mm Hg 2

Operative factors

Emergency surgery Carried out on referral before the beginning of the next working day 2

Other than isolated CABG Cardiac surgery other than or in addition to coronary artery bypass surgery 2

Thoracic aortic surgery For disorder of ascending arch or descending aorta 3

Post-infarction septal rupture 4

Table 1

Echocardiography and stress echocardiography

All patients presenting for cardiac surgery should have undergone

transthoracic echocardiography (TTE). TTE provides information

about both valvular disease and ventricular function. The severity

and mechanism of regurgitant and stenotic pathology can be

assessed. Similarly important information about systolic and dia-

stolic ventricular function, extent of infarct and delineation of

regional wall motion abnormalities (RWMAs) can be obtained.

Patients with IHD can develop new RWMAs as a result of

inadequate perfusion, when the heart is ‘stressed’ compared with

at-rest images.

The most physiological means of ‘stressing’ the heart is to

exercise the patient. Because many patients referred for stress

echocardiography are unable to exercise, a pharmacological

stressor such as dobutamine is commonly used.

The imaging technique can be limited by the fact that patients

with LBBB or a paced ventricular rhythm will have a resting


RWMA, making interpretation of images difficult. Image quality

can also be a problem in obese patients.

Nuclear imaging

Single photon emission computed tomography (SPECT): in

this imaging technique, a gamma camera rotates through 180�

about the patient and detects gamma rays omitted by ‘tracer’

radiopharmaceuticals injected into the patient that are subse-

quently taken up into the myocardium in proportion to the

myocardial blood flow.

The technetium scan has now largely superseded the thallium

scan as the radionuclide perfusion imaging technique for those

patients in whom exercise stress ECG testing is contraindicated

or in whom it is unlikely to be diagnostic.

Technetium has the advantages over thallium that it has

a shorter half-life and therefore exposes the patient to less radi-

ation but at the same time it has higher photon energy resulting


CARDIAC ANAESTHESIA

Images obtained from coronary angiography illustration stenotic lesions in a the left anterior descending artery (LAD), b the circumflex artery, and

c the right coronary artery (RCA).

Figure 1

in less signal attenuation from the point of emission, thus

producing better-quality images.

Furthermore, because the technetium-labelled radiopharma-

ceuticals are irreversibly bound within the myocardial mito-

chondria, images can be obtained several hours after injection

and still represent the pattern of perfusion of the myocardium at

the time of injection. This makes the practicalities of image

acquisition in an outpatient setting easier to manage.

Two injections of technetium-labelled radiopharmaceutical

are required, one at rest and one at stress/exercise, usually on

two separate days. The ‘stress’ images are generally obtained by

the use of adenosine, a potent coronary vasodilator. Adenosine

causes normal coronary arteries to dilate, ‘stealing’ perfusion

(and thereby tracer isotope) from myocardium perfused by

coronary arteries with pathologically fixed stenoses.

Localized areas of signal defect (representing areas of low or

no perfusion) occurring with stress or exercise that are not

apparent on the ‘at-rest’ images indicate either ischaemia or

infarct. Those defects present even in the ‘at-rest’ images repre-

sent infarct. Thus, SPECT can be used to make a diagnosis of IHD

and to differentiate between viable, but perfusion-vulnerable

myocardium that will benefit from revascularization interven-

tions, and myocardium that is infarcted (Figure 2).

ECG-gated SPECT in which image acquisition is synchronized

with multiple time-points or ‘gates’ within the cardiac cycle over

a number of cardiac cycles can allow evaluation of ventricular

wall motion and ejection fraction.

Similarly, by radiolabelling red blood cells the gamma camera

can be used to measure ventricular cavity volumes at multiple

time-points (or gates) in the cardiac cycle. This is sometimes

referred to as a MUGA (MUltiGated Acquisition imaging) scan.

Comparison of the signal at end-diastole with that at end-systole

gives an accurate measure of ejection fraction.

Positron emission tomography (PET): this technique can be

used to produce images of high spatial resolution and very

accurate identification of viable myocardium. A glucose analogue


is radiolabelled with a positron-emitting isotope. Upon encoun-

tering an electron, both the emitted positron and electron are

annihilated, producing a pair of annihilation photons (gamma

rays) that move in opposite directions. These are detected by the

gamma camera, and it is their coincidental detection that sepa-

rates the signal from ‘noise’. Only viable myocardium will take

up the glucose analogue; thus, only viable myocardium (that

would benefit from reperfusion interventions) is represented in

the computer-generated images.

PET scanners are extremely expensive but are likely to

become increasingly common for myocardial viability studies.

Magnetic resonance imaging (MRI): an attractive feature of

MRI images is the absence of radiation exposure for the patient;

however, cardiac imaging is time-consuming, taking up to

1 hour.

A powerful electromagnet causes hydrogen atoms in the body

to become aligned. A radiofrequency emission distorts this

alignment; on cessation of this emission, the hydrogen atoms

return to their original aligned orientation, releasing energy as

they do so. This energy is detected, and the data are gathered to

reconstitute a computer-generated image.

MRI is useful in the assessment of myocardial viability, and

cardiac structure and function. It is generally restricted to diag-

nosis of pericardial and aortic disease, cardiac masses and

congenital heart disease.

During MRI cardiac viability studies, gadolinium contrast agent

is injected into the patient. There is rapid wash-in and wash-out of

gadolinium in the myocardium, except in those parts that are

infarcted in which there is slower wash-in and much slower wash-

out, giving a window of opportunity for capturing images of so-

called ‘delayed enhancement’ infarcted myocardium. The logical

assumption is that myocardium that is not infarcted is viable.

Gated image acquisition, synchronized with the ECG and

breath-holding techniques in conjunction with ultra-fast

sequences of image acquisition, allows imaging of coronary

arteries, but this is far from commonplace.


CARDIAC ANAESTHESIA

Short axis ‘slices’ through the left ventricle. a Normal left ventricular uptake on single photon emission computed tomography (SPECT) yields a

yellow ‘doughnut’ both at rest and when stressed. b The lateral wall of the left ventricle shows defects in the yellow ‘doughnut’ during stress

that are not apparent in resting images. The defects represent ischaemia. c There is a fixed (present both at rest and during stress) inferior

defect of the left ventricle that represents an infarct.

Figure 2

ANAESTHESIA AND INTENSIVE CARE MEDICINE 10:9 409 � 2009 Elsevier Ltd. All rights reserved.

CARDIAC ANAESTHESIA

Computed tomography (CT): this is a rapidly evolving technology.

Newer-generation CT scanners have improved spatial and

temporal resolution, making contrast-enhanced, gated CT coro-

nary angiography a reliable method of identifying coronary

atherosclerosis. Although the more invasive cardiac catheteriza-

tion and angiography remain the gold standard for visualizing

stenoses of the coronary arteries, coronary CT angiography is

becoming more popular and might become the imaging modality of

choice.

Currently, cardiac CT is the imaging technique of choice for

acute aortic or pulmonary vascular disease. It is also useful

before re-sternotomy in patients who have undergone prior

CABG to identify grafts close to the sternum that may be

vulnerable to transection by the surgeon’s saw.

Patient consent and premedication

A report was produced in 2008 by the National Confidential

Enquiry into Patient Outcome and Death (NCEPOD) on mortality

following first-time, isolated CABG (www.ncepod.org.uk/

2008cabg.htm). One of the recommendations of the report was

that a consultant surgeon should obtain consent for surgery, and

that the consent should include a specified, accurate risk of death

as well as potential complications. It is logical to extrapolate that

recommendation to all cardiac surgery.

Nonetheless, anaesthetists should be able to answer questions

relating to the risks of surgery (see Mortality and Risk Stratifi-

cation) and anaesthesia. It is the anaesthetist’s role to describe

the train of events that patients are likely to experience up to

induction of anaesthesia (e.g. placement of intravascular

cannulae while the patient is awake and preoxygenation) as well

as the likely postoperative course on an intensive care unit. This

should include a longer-than-‘normal’ stay and duration of

mechanical ventilation in patients with pre-existing lung disease


or an increased likelihood of renal replacement therapy in

patients with pre-existing renal impairment.

The Association of Anaesthetists of Great Britain and Ireland

(www.aagbi.org/publications/guidelines/docs/consent06.pdf)

recommends that a separate consent form is not required for

anaesthetic procedures that are done to facilitate another

treatment. Anaesthetists should, however, record details of the

elements of any discussions in patients’ records, noting risks,

benefits and alternatives where available.

The same principle applies to consent for the use of intra-

operative TOE. No separate consent form is required, but its

use and possible complications should be explained to the

patient.

Benzodiazepines such as lorazepam or temazepam are

commonly prescribed for anxiolysis and should be accompanied

by supplemental oxygen. A

FURTHER READING

Care Quality Commission. Heart surgery in the United Kingdom. Available

at: http://heartsurgery.cqc.org.uk/ (accessed 20 Feb 2009).

Gothard J, Kelleher A, Haxby E. Cardiovascular and thoracic anaesthesia.

London: Butterworth-Heinemann, 2003.

Mackay JH, Arrowsmith JE, eds. Core topics in cardiac anaesthesia.

London: Greenwich Medical Media, 2004.

National Confidential Enquiry into Patient Outcome and Death. Coronary

artery bypass grafts: the heart of the matter (2008). Available at: www.

ncepod.org.uk/2008cabg.htm (accessed 20 Feb 2009).

National Institute for Health and Clinical Excellence. Preoperative tests:

the use of routine preoperative tests for elective surgery. Available at:

www.nice.org.uk/Guidance/CG3 (accessed 20 Feb 2009).

� 2009 Elsevier Ltd. All rights reserved.

http://www.ncepod.org.uk/2008cabg.htm


http://www.aagbi.org/publications/guidelines/docs/consent06.pdf

http://heartsurgery.cqc.org.uk/



http://www.nice.org.uk/Guidance/CG3

Preoperative assessment for cardiac surgery

Documents

Transcript of Preoperative assessment for cardiac surgery