Adrenaline

Also known as 

Epinephrine

 

Common indications

1. In cardiac arrest, adrenaline is routinely administered as part of the Advanced Life Support (ALS) treatment algorithm.
2. In anaphylaxis, adrenaline is a vital part of immediate management.
3. Adrenaline may be injected directly into tissues to induce local vasoconstriction. For example, it is used during endoscopy to control mucosal bleeding, and it is sometimes mixed with local anaesthetic drugs (e.g. lidocaine) to prolong local anaesthesia.

 

Mechanisms of action

• Adrenaline is a potent agonist of the α1, α2, β1 and β2 adrenoceptors, and correspondingly has a multitude of sympathetic (‘fight or flight’) effects. These include: vasoconstriction of vessels supplying skin, mucosa and abdominal viscera (mainly α1-mediated); increases in heart rate, force of contraction and myocardial excitability (β1); and vasodilatation of vessels supplying the heart and muscles (β2). 
• These explain its use in cardiac arrest, where the redistribution of blood flow in favour of the heart is desirable, at least theoretically, and may improve the chances of restoring an organised rhythm. 
• Additional effects of adrenaline, mediated by β2 receptors, are bronchodilatation and suppression of inflammatory mediator release from mast cells. 
• Together with its vascular effects, these underpin its use in anaphylaxis, where widespread release of inflammatory mediators from mast cells produces generalised vasodilatation, profound hypotension and often bronchoconstriction.

 

Important adverse effects

• Adrenaline is a dangerous drug, but its risks are balanced against the severity of the condition being treated. 
• In cardiac arrest, restoration of output is often followed by adrenaline-induced hypertension. 
• When given to conscious patients in anaphylaxis or in an attempt to produce local vasoconstriction, it often causes anxiety, tremor, headache and palpitations. 
• It may also cause angina, myocardial infarction and arrhythmias, particularly in patients with existing heart disease.

 

Warnings

• There are no contraindications to its use in cardiac arrest and anaphylaxis. 
• When given to induce local vasoconstriction, it should be used with caution in patients with heart disease. 
• Combination adrenaline–anaesthetic preparations should not be used in areas supplied by an end-artery (i.e. with poor collateral supply), such as fingers and toes, where vasoconstriction can cause tissue necrosis.

 

Important interactions

• In patients receiving treatment with a β-blocker, adrenaline may induce widespread vasoconstriction, because its α1-mediated vasoconstricting effect is not opposed by β2-mediated vasodilatation.