Lidocaine is given during ACLS when a patient in cardiac arrest has ventricular fibrillation (VF) or pulseless ventricular tachycardia (pVT) that persists after defibrillation. It is a second-line antiarrhythmic, used alongside or as an alternative to amiodarone, and enters the algorithm only after at least one shock has failed to restore a normal rhythm. Understanding exactly where it fits, how it’s dosed, and what to watch for makes the difference between using it effectively and missing the window.
Where Lidocaine Fits in the Cardiac Arrest Algorithm
The core indication is shock-refractory VF or pVT. That means the patient has received at least one defibrillation attempt, CPR has continued, and the rhythm check still shows a shockable rhythm. At that point, the AHA algorithm calls for either amiodarone or lidocaine via IV or IO access. The two drugs carry the same class of recommendation (Class IIb), meaning they are reasonable options but not strongly mandated by evidence.
Lidocaine may be especially useful when the arrest was witnessed, because shorter time to drug administration has been associated with better outcomes. It is not given for non-shockable rhythms like asystole or pulseless electrical activity (PEA). Those rhythms follow a different branch of the algorithm focused on epinephrine and identifying reversible causes.
Timing Within the Algorithm
In a standard ACLS cardiac arrest sequence, the first drug given is epinephrine (for non-shockable rhythms) or a vasopressor timed around the second shock cycle. For shockable rhythms, the antiarrhythmic slot opens after the second or third shock. Practically, this means lidocaine typically enters the picture a few minutes into the resuscitation, once it’s clear that defibrillation alone isn’t converting the rhythm.
If the first dose of lidocaine doesn’t help and VF/pVT continues, a second dose can be given 5 to 10 minutes later. This cycle repeats alongside ongoing CPR and additional shocks. The maximum cumulative dose during a single resuscitation is 3 mg/kg.
Dosing for Cardiac Arrest
The first IV or IO dose is 1 to 1.5 mg/kg. If the shockable rhythm persists, a second dose of 0.5 to 0.75 mg/kg can follow at 5- to 10-minute intervals, up to the 3 mg/kg ceiling. For a 70 kg adult, that first dose is roughly 70 to 105 mg, with repeat doses of 35 to 52 mg.
If IV or IO access isn’t available, lidocaine is one of the few ACLS drugs that can be given through an endotracheal tube. The endotracheal dose is 2 to 2.5 times the standard IV dose. Diluting the drug in sterile water rather than normal saline may improve absorption through the airway lining.
After Return of Spontaneous Circulation
Lidocaine also has a role after the heart starts beating again. Once a pulse returns (known as ROSC), the rhythm can destabilize and slip back into VF or pVT. AHA guidelines note that prophylactic lidocaine may be considered in specific circumstances where treating a recurrence would be difficult, such as during EMS transport to a hospital. This is a lower-confidence recommendation (Class IIb, Level of Evidence C), so it’s reserved for situations where the risk of recurrent arrest is high and resources to manage it are limited.
When used prophylactically after ROSC, a maintenance infusion follows the initial bolus. The typical approach is a continuous drip to keep blood levels in a therapeutic range and prevent the rhythm from breaking through again.
Lidocaine vs. Amiodarone
For years, amiodarone was the preferred antiarrhythmic in ACLS, and lidocaine was listed as a backup. The 2018 AHA focused update placed them on equal footing, largely because of the results of a major randomized trial published in the New England Journal of Medicine. That trial enrolled over 3,000 patients with out-of-hospital cardiac arrest and found that 24.4% of patients given amiodarone survived to hospital discharge, compared with 23.7% for lidocaine and 21.0% for placebo. The difference between amiodarone and lidocaine was just 0.7 percentage points and was not statistically significant.
In practical terms, this means choosing between the two often comes down to availability, familiarity, and patient-specific factors. Neither drug has a clear survival advantage over the other in cardiac arrest.
How Lidocaine Works on the Heart
Lidocaine stabilizes the electrical activity of heart cells by blocking sodium channels, which are the gates that allow the rapid electrical impulse to fire across cardiac tissue. Specifically, it binds to sodium channels that are already in an inactive state, which is why it preferentially targets cells that are firing too rapidly or abnormally. Healthy heart cells cycling at a normal rate are less affected. This selective action is what makes it useful for suppressing the chaotic electrical activity of VF and pVT without completely shutting down normal conduction.
Contraindications
Lidocaine should not be given to a patient with a known severe allergic reaction to the drug, though true anaphylaxis to lidocaine is rare. It is also contraindicated when the arrhythmia itself may have been caused by local anesthetic toxicity, since adding more of the same class of drug would worsen the problem. Patients with certain blood disorders that affect hemoglobin may be at risk for a condition where the blood can’t carry oxygen effectively, so lidocaine is used cautiously or avoided in those cases.
Signs of Lidocaine Toxicity
During a cardiac arrest, toxicity monitoring is less of an immediate concern because the patient is already in extremis. But once ROSC is achieved and a maintenance infusion is running, toxicity becomes a real risk. Lidocaine primarily causes neurological symptoms when levels climb too high. Early warning signs include numbness or tingling around the mouth, a metallic taste, ringing in the ears, dizziness, muscle twitching, and agitation. If levels continue to rise, seizures can follow, which occurs in up to 68% of toxicity cases.
Cardiovascular effects are less common with lidocaine compared to more potent local anesthetics, but severe toxicity can still cause dangerous drops in blood pressure, abnormal heart rhythms, and in extreme cases, cardiovascular collapse. The risk increases in patients with liver disease, heart failure, or advanced age, all of which slow the body’s ability to clear the drug. Keeping the cumulative dose within guidelines and watching for early neurological symptoms are the most practical safeguards.