"improving intensive care in Scotland"

Shock

Inotropes, vasopressors and vasodilators

Inotropes are drugs that increase contractility of the heart, while vasopressors are drugs that lead to vasoconstriction. These drugs are sometimes used in combination to achieve an improvement in contractility and vasoconstriction (increase in SVR).

All of these drugs should be infused centrally through a dedicated port. They should be given centrally because they are irritant drugs and extravasation can cause skin necrosis. They should be given through a dedicated port because these are very potent drugs and should never be given as a bolus (unless patient in cardiac arrest, in which case adrenaline 1 mg should be given as per ALS guidelines).

Adrenaline (epinephrine)

Acts on both ß and α adrenoreceptors. In a low dose infusion the ß effects predominate, leading to an increase in heart rate, contractility and cardiac output. In high doses the α effects predominate, leading to vasoconstriction and an increase in blood pressure.

Disadvantages - excessive tachycardia, dysrhythmias, myocardial ischaemia, hyperglycaemia, lactic acidosis (which is usually transient).

Uses – as a positive inotrope to increase cardiac output and provide vasoconstriction at higher doses. Due to its dual action it is sometimes used in the moribund shocked patient until further investigations/monitoring ascertain the cause of shock.

It has a role in anaphylaxis due to its ability to stabilise mast cells and prevent further histamine release as well as treat hypotension.

Concentration - There are many ways to prepare all inotropes and each unit will have a agreed policy which must be followed carefully due to the high potency of these drugs.

If you want to establish an average (50-100 Kg) adult patient on adrenaline and do not have access to your local policy, then dilute 3mg of adrenaline in 50ml of saline and start an infusion at 5ml/hr. You should notice an effect within a few minutes. Then change rate to achieve target BP or cardiac output.

All inotropes/vasopressors work within 1-2 minutes and their effect wears off within minutes.

Noradrenaline (norepinephrine)

Acts mainly on α1 receptors causing vasoconstriction and increasing SVR. This leads to an increase in the BP (perfusion pressure) which leads to an improvement in organ perfusion (provided the patient is adequately fluid resuscitated). It also acts on ß1receptors causing an increase in contractility and heart rate.

Disadvantages – excessive vasoconstriction seen as blue/ black peripheries, dysrhythmias, myocardial ischaemia.

Uses – it is many intensivists' drug of choice for improvement of BP in septic shock. Used in neuro ICU patients to increase BP to maintain cerebral perfusion pressure.


Dopamine

Stimulates α, ß, and dopamine receptors to varying degrees. It is therefore a non specific inotrope/vasopressor that can be used to increase cardiac output and SVR.

Disadvantages – excessive tachycardia and dysrhythmias

Uses – as a positive inotrope to increase cardiac output and provide vasoconstriction at higher doses. Used in septic shock in some centres.

Note: there is no role for "renal dose" dopamine in modern intensive care medicine.

Dobutamine

Mainly acts on the ß receptors leading to an increase in heart rate and contractility together with vasodilatation mediated via the ß2 receptors. The net effect is an increase in cardiac output.

Disadvantages – hypotension, tachycardia

Uses – low cardiac output states especially cardiogenic shock.


GTN

Is a nitrate vasodilator that is commonly used in cardiogenic shock. In a low dose it acts as a venodilator, thus offloading the heart and reducing preload. In higher doses it acts as an arterial dilator, thus reducing afterload. The net effect is to improve the function of the myocardium and cardiac output by reducing both preload and afterload.

It also causes relaxation of the coronary arteries and is therefore useful in angina.


Further information

Further information on inotropes is available from the following website:

http://www.frca.co.uk/

Key message 1

Inotropes/vasopressors to treat shock, should only be considered after adequate fluid resuscitation.

The administration of inotropes/vasopressors to a patient who is under filled is not only futile, but is potentially harmful.

Rules of thumb

After adequate fluid resuscitation:

For shock of unknown cause use adrenaline.

For septic shock use noradrenaline.

For cardiogenic shock use dobutamine.

 

Word of caution

Inotropes/vasopressors are very potent and potentially lethal drugs.

You should not use these drugs if you are unfamiliar with them.

You should NEVER administer these drugs as a bolus, with the exception of adrenaline in a cardiac arrest situation.

You should infuse them through a central line via a dedicated port.

Make sure you adhere to the local policy for dilution in your unit.

If in doubt ask a senior member fob your team.

Page 6

Backwards Button Forward Button