Local anaesthesia

Question 1

Adrenaline

Common indications

Answer 1

1. Cardiac arrest- commonly part of advanced life support algorithm
2. Anaphylaxis- adrenaline is a vital part of immediate management
3. Adrenaline may be injected directly into tissues to induce local vasoconstriction- For example during endoscopy to control muscosal bleeding. Combined with local anaesthetics it increases the times there active for

Question 2

Adrenaline

MOA

Answer 2

• Adrenaline is a potent agonist of the a1, a2, b1 and b2 adrenoreceptors and correspondingly has a multitude of sympathetic effects
• These include: Vasoconstriction of vessels supplying the skin, mucosa and abdominal viscera (a1-mediated)
• Increases HR, force of contraction and myocardial excitability (b1)
• Vasodilation of vessels supplying the heart and muscles (B2)
• These explain its use in cardiac arrest, where redistribution of blood flow in favour of the heart is desirable
• Additional effects of adrenaline (B2): Bronchodilation and suppression of inflammatory meditor release from mast cells
• Together vascular effects underpin use in anaphylaxis (release of inflammatory mediators from mast cells, generalised vasodilation, hypotension and often bronchoconstriction)

Question 3

Adrenaline

Adverse effects

Answer 3

• Adrenaline is dangerous but risks are balanced with severity of conditions
• In cardiac arrest- restoration of output is often followed by adrenaline induced HTN
• 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, MI and arrhythmias, particulalry in patients with existing heart disease

Question 4

Adrenaline

Warnings

Answer 4

• 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 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

Question 5

Adrenaline

Interactions

Answer 5

• In patients receiving treatment with a BB, adrenaline may induce widespread vasoconstriction, because its a1-mediated vasoconstricting effect is not opposed by b2-mediated vasodilation

Question 6

Adrenaline

Prescription

Answer 6

• Cardiac arrest associated with a shockable rhythm (ventricular fibrillation or pulseless ventricular tachycardia), adrenaline 1mg IV is given just after the 3rd shock every 5 minutes thereafter
• In Anaphylaxis- dose is 500mcg IM after 5 minutes if necessary
• When administered with a local anaesthetic to induce local vasoconstriction a ready-mixed andrenaline-anaesthetic preparation should be used
• Usually this contains adrenaline at a concentration of 5mcg/L