cardiologia veterinaria

1. Anaesthesia for the Feline Patient with Heart Disease
© Vet Education Pty Ltd 2016
Anaesthetic Management of the Patient with Cardiac Disease
The Problems in Patients with Cardiac Disease
1. Heart Disease – Patients with heart disease may have one or more of the following
a. Arrhythmias/dysrrhythmias
b. Valvular insufficiency
c. Abnormal cardiac mass – dilative, restrictive or hypertrophic cardiomyopathy
d. Pericardial effusion
Abnormal heart valve function, cardiac contractility, heart rhythm, and pleural fluid
accumulation may all lead to decreased cardiac output, which will result in stimulation of
the sympathetic nervous system activation and adrenaline release – leading to reduced blood
flow through tissues including the gut, kidney, liver, spleen etc. This places these organs at
high risk of sustaining damage when cardiovascular depressant effects of anaesthesia are
superimposed on heart disease. In addition, increases in preload and afterload in the patient
with heart failure place additional stress on cardiac tissue, and can lead to the development
of pulmonary oedema, pleural fluid accumulation and myocardial hypoxia, compromising
ventilation and predisposing the patient to cardiac arrhythmias.
2. Stress – patients with cardiovascular disease have reduced cardiac reserve – that is to say
that cardiac output is unable to increase significantly should the patient be placed in a
stressful situation, experience pain, hypovolaemia, or other physiological stress. The
consequences of reduced cardiac reserve include reduced tissue perfusion and exacerbation
of clinical signs of heart failure.
3. Fluid load – patients with cardiac disease may not cope well with the boluses of intravenous
fluid required in order to maintain normal blood pressure and tissue perfusion in the
anaesthetised patient, may decompensate and develop symptoms of overt heart failure.
4. Disease resulting from decreased cardiac output – Reduced cardiac output reduce tissue
perfusion in tissues throughout the body and may result in organ dysfunction and/or failure
in these tissues. For example:
a. Renal dysfunction - azotemia is common in many patients with cardiac disease and
is typically pre-renal or renal. Evaluation of renal function using urine analysis
(including urine sediment examination) and serum biochemistry should be performed
prior to anaesthesia, so that appropriate patient support may be administered prior
to anaesthesia
b. Gastrointestinal dysfunction – patients with cardiac disease frequently develop
symptoms of gastrointestinal dysfunction such as anorexia, vomiting, and/or
diarrhoea due to reduced gut perfusion. This can result in patient dehydration and
abnormal serum electrolyte concentrations, and pre-renal azotemia – all of which
should be assessed and correct prior to induction of anaesthesia

2. Anaesthesia for the Feline Patient with Heart Disease
© Vet Education Pty Ltd 2016
Anaesthetic Management of the Patient with Cardiac Disease
Having looked at some of the key problems with the cardiovascular patient, strategies that may
improve anaesthetic safety in these patients include the following…
1. Pre-anaesthetic assessment – all patients with clinical evidence of cardiac disease should
have thorough assessment of tissue perfusion prior to anaesthesia so that disorders related
to poor tissue perfusion may be corrected prior to anaesthesia. Samples taken for assessment
should include
a. Complete blood count
b. Serum biochemistry – to assess hepatic and renal parameters
c. Urine analysis – urine specific gravity, chemical analysis and urine sediment
d. Serum electrolyte concentrations
e. Blood lactate concentration.
2. Assessment of cardiac function – Cardiac function assessment may include some or all of the
following (depending on the cardiac disease present)
a. Thorough cardiac auscultation
b. Electrocardiograph
c. Cardiac ultrasound
d. Thoracic radiography (3-view)
Any patient showing signs of cardiac failure should have their anaesthetic delayed if possible
and appropriate treatment initiated to improve their clinical condition before anaesthesia
3. Normalize electrolyte concentrations – Abnormal electrolyte concentrations can cause
abnormal cell function – including cells in blood vessel walls and in the myocardium, which
can lead to inappropriate vascular tone and altered cardiac function (including the
development of arrhythmias and decreased myocardial cell contractility). Every attempt
should be made to normalize serum electrolyte concentrations prior to anaesthesia.
4. Correct organ perfusion abnormalities and function – azotemia, and intestinal dysfunction
should be managed prior to anaesthesia if possible using the following strategies -
a. Correct dehydration – Dehydration should be corrected over a period of 12-24 hours
depending on the degree and severity of dehydration. The fluid of choice for
rehydration is a poly-ionic isotonic fluid such as lactated Ringer’s solution. If the
patient does not tolerate infusion with an isotonic solution, as evidenced by increased
respiratory rate, frequent posture changes etc., hydration deficits should be corrected
at a slower rate using a glucose-containing fluid such as 0.45% NaCl + 2.5% glucose,
which will lead to less blood volume expansion.
b. Normalise electrolyte concentration – Supplement intravenous fluids with electrolytes
to correct abnormalities as required.
c. Control nausea and vomiting – using anti-emetics such as maropitant citrate or
metoclopramide as indicated to minimise fluid loss.
5. Fluid therapy – Patients undergoing anaesthesia usually require intravenous fluid therapy
support during the anaesthetic period in order to offset some of the undesirable decreases in
blood pressure caused by anaesthetic drugs. This principle still applies in cardiac failure
patients, despite their limited cardiac reserve and relative intolerance to provision of
intravenous fluid loading. If possible, begin lactated Ringers’ solution at 2-3 ml/kg/hr 1-2

3. Anaesthesia for the Feline Patient with Heart Disease
© Vet Education Pty Ltd 2016
hours prior to anaesthesia, and maintain this rate during anaesthesia. Should symptoms of
volume overload begin to be present (increased respiratory sounds, moist lung sounds,
increased respiratory rate or effort harsh lung sounds, or decreasing pulse oximetry readings
etc.) intravenous fluid therapy should temporarily cease, and a bolus of furosemide at 2-4
mg/kg IV should be administered every 3-4 hours until the patient’s symptoms improve.
High sodium fluids such as hypertonic saline, or 0.9% sodium chloride should be generally
avoided unless specifically indicated. Hypotension should be managed by reducing inhalant
anaesthesia as much as practical, and administration of a bolus of lactated Ringer’s solution
at 5-7 ml/kg IV over 10 minutes, followed by detailed patient reassessment.
6. Normalise myocardial contractility – Patients with dilative cardiomyopathy frequently have
poor myocardial contractility. These patients, in addition to management of contractile
function with drugs such as Pimobendan, may require inotropic support in the anaesthetic
period with adrenergic drugs such as dobutamine. Adrenergic drugs should be administered
at the lowest dose that results in clinical evidence of improved cardiac output only, due to
their potential to induce cardiac arrhythmias at higher doses. Dobutamine is preferred over
dopamine in most cardiac failure patients, as dopamine can produce significant increases in
afterload at higher dose rates, which may reduce cardiac output in the patient with impaired
cardiac function.
7. Anaesthetic medications to avoid, or use with extreme caution in the heart disease patient
include the following
a. Drugs that may cause excessive blood vessel dilatation, such as acepromazine, and
propofol should be used with caution, and at the lowest effective dose.
b. Drugs that increase sympathetic tone with caution at the lowest effective dose e.g.
ketamine
c. Avoid routine use of atropine unless treating bradycardia.
d. Avoid hypotensive drugs such as medetomidine or xylazine.
e. Avoid drugs that increase sympathetic tone
f. Avoid pro-arrhythmogenic drugs such as thiopentone
8. Suggested anaesthetic protocols for the patient with heart disease include the following
a. Premedication: Fentanyl 2-4 micrograms/kg given IV, or butorphanol 0.1 mg/kg IV
b. Induction: Alfaxalone IV, OR low-dose propofol
c. Maintenance:
i. Fentanyl CRI +/- midazolam CRI plus isoflurane maintenance OR
ii. Fentanyl CRI + propofol CRI OR
iii. Fentanyl CRI + alfaxalone CRI OR
iv. Fentanyl CRI + ketamine CRI + alfaxalone or propofol CRI
v. Isoflurane may be added to the above protocols at the lowest possible dose
(<1% is preferred)