CV - Lidocaine

Question 1

Lidocaine
Common indications

Answer 1

• Very commonly, as a first choice local anaesthetic in, for example, urinary catheterisation and minor procedures (e.g. suturing).
• Uncommonly, as an antiarrhythmic drug in ventricular tachycardia (VT) and ventricular fibrillation (VF) refractory to electrical cardioversion (although amiodarone is preferred for the latter indication).

Question 2

Lidocaine

Mechanisms of action

Answer 2

• Lidocaine (formerly known as lignocaine) enters cells in its uncharged form, then accepts a proton to become positively charged.
• From inside the cell, it enters and then blocks voltage-gated sodium channels on the surface membrane.
• This prevents initiation and propagation of action potentials in nerves and muscle, inducing local anaesthesia in the area supplied by blocked nerve fibres.
• In the heart, it reduces the duration of the action potential, slows conduction velocity and increases the refractory period. These effects may terminate VT and improve the chances of successfully treating VF.

Question 3

Lidocaine

Important adverse effects

Answer 3

• The most common side effect is an initial stinging sensation during local administration.
• Systemic adverse effects are, predictably, more likely after systemic administration, whether intentional (as when it is used as an antiarrhythmic) or inadvertent (due to accidental intravascular injection during local administration).
• Its effects on the neurological system include drowsiness, restlessness, tremor and fits. It generally causes relatively little cardiovascular toxicity, but in overdose it may cause hypotension and arrhythmias.

Question 4

Lidocaine

Important Interactions

Answer 4

• As the duration of action of local anaesthetics depends on how long they stay in contact with the neurones, co-administration with a vasoconstrictor (e.g. adrenaline [epinephrine]) produces a desirable interaction that may prolong the local anaesthetic effect.

Question 5

Lidocaine

Px and Administartion

Answer 5

• For urinary catheterisation, lidocaine is most commonly given as Instillagel®. This is a gel provided in pre-filled syringes.
• The dose is 6–11 mL. It should be prescribed in the once-only section, although in practice this is often omitted.
• For minor procedures, you usually use a 1% (10 mg/mL) solution of lidocaine hydrochloride.
• The maximum dose is 200 mg or 3 mg/kg, whichever is lower (7 mg/kg, or up to 500 mg, is permitted when it is combined with adrenaline). This should be calculated using ideal body weight. In practice, you draw up the dose you think you will need (ensuring this does not exceed the maximum), then administer enough to produce adequate anaesthesia.
• It is therefore acceptable to write the prescription and sign for its administration after completing the procedure.