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  1. Lidocaine

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In this lesson, we'll cover the medication lidocaine and all of its effects, including its mechanism of action, clinical indications, precautions, contraindications, and adult dosages.

Lidocaine works by bringing about negative inotropic effects and antiarrhythmic actions in the heart. This serves to weaken the force of muscular contractions and can effectively calm erratic and uncoordinated electro-myocardial activity. In other words, lidocaine decreases automaticity and suppresses ventricular arrhythmias.

Lidocaine Indications

Due to lidocaine’s antiarrhythmic properties, its primary clinical use is for cardiac arrest resulting from ventricular fibrillation (V-Fib) and pulseless ventricular tachycardia.

However, lidocaine is also highly effective in treating the following conditions:

  • Stable monomorphic ventricular tachycardia with preserved ventricular function.
  • Stable polymorphic ventricular tachycardia with a normal baseline and a normal QT interval, alongside preserved lower ventricular function once ischemia is treated and electrolyte balance is fully corrected.
  • Stable polymorphic VT with baseline and QT-interval prolongation when torsades de pointes is suspected.

Lidocaine Precautions and Contraindications

It is important to remember that lidocaine should never be used as a prophylactic treatment in acute myocardial infarction. Furthermore, healthcare professionals are suggested to reduce the maintenance dose in the presence of impaired liver function or lower ventricular dysfunction. You must discontinue the infusion immediately if any clinical signs of toxicity begin to develop.

Pro Tip #1: Lidocaine is strictly contraindicated if there is a known hypersensitivity to lidocaine or any of its derivatives, such as xylocaine or novocaine. Additionally, lidocaine is contraindicated in cases of sinus bradycardia and atrioventricular (AV) blocks, as it can suppress the escape pacemakers responsible for maintaining basic cardiac perfusion.

Adult Dosage of Lidocaine

When administering lidocaine to adult patients, dosages depend heavily on whether the patient presents with a perfusing rhythm or a cardiac arrest rhythm:

  • Cardiac Arrest (V-Fib/Pulseless V-Tach): Provide an initial dose of 1 to 1.5 mg/kg IV or IO. For refractory V-Fib, an additional dose of 0.5 to 0.75 mg/kg may be administered via IV push. This can be repeated in 5 to 10 minutes to a strict maximum of 3 doses, or a total cumulative dose of 3 mg/kg.
  • Perfusing Arrhythmias: For conditions like stable ventricular tachycardia, wide-complex tachycardia of uncertain type, or significant ectopy, the initial doses range from 0.5 to 0.75 mg/kg, and up to 1 to 1.5 mg/kg. This can also be repeated at 0.5 to 0.75 mg/kg every 5 to 10 minutes up to the maximum total limit of 3 mg/kg.
  • Maintenance Infusion: Administer 1 to 4 mg per minute, which is equal to a rate of 30 to 50 mcg/kg per minute. Keep in mind that a microdrip infusion set is absolutely required in order to deliver this dose accurately.

Pro Tip #2: A common but simple calculation for mixing a lidocaine drip is: (IV Bag Amount in ml) × (Dose Ordered in mg/min) × (Drip Set in gtts/ml) ÷ (Drug on Hand in mg). Running this math will give you the exact drops per minute required to safely maintain your patient's infusion.