Lidocaine is used during a code because it can help stop dangerous heart rhythms that don’t respond to electrical shocks alone. Specifically, it targets ventricular fibrillation (VF) and pulseless ventricular tachycardia (pVT), the two “shockable” rhythms encountered during cardiac arrest. When defibrillation and CPR aren’t enough to restore a normal heartbeat, lidocaine works by blocking the abnormal electrical signals that keep the heart quivering or racing instead of pumping blood.
How Lidocaine Works on the Heart
Your heart beats because of a precisely timed wave of electrical activity. That wave depends on sodium ions rushing into heart muscle cells through tiny channels, triggering each contraction. During VF or pVT, those channels fire chaotically, and the heart loses its coordinated rhythm.
Lidocaine binds directly to voltage-gated sodium channels in a one-to-one fashion, physically blocking sodium ions from flowing through the channel pore. This suppresses the erratic electrical impulses that sustain fibrillation. Importantly, lidocaine shows what’s called “use dependence,” meaning it preferentially blocks channels that are firing too fast or too often. Cells behaving normally are relatively unaffected, while the overactive cells driving the dangerous rhythm get dampened. In animal studies, therapeutic blood levels of lidocaine raised the fibrillation threshold, essentially making the heart harder to push back into fibrillation, and reversed the drop in that threshold caused by acute ischemia (reduced blood flow to the heart muscle).
When It’s Given During a Code
Lidocaine isn’t a first-line treatment. The standard sequence in a code starts with CPR and defibrillation for shockable rhythms. If the heart keeps returning to VF or pVT after one or more shocks, the team reaches for an antiarrhythmic drug. The two main options are amiodarone and lidocaine. Both are considered acceptable by current American Heart Association guidelines for shock-refractory VF or pVT.
The initial dose is 1.0 to 1.5 mg/kg given intravenously or through an intraosseous line. If the dangerous rhythm persists, a second dose of 0.5 to 0.75 mg/kg can follow. The goal is to chemically stabilize the heart’s electrical environment so the next defibrillation attempt has a better chance of restoring a normal rhythm. Lidocaine doesn’t replace the shock; it works alongside it.
Lidocaine vs. Amiodarone
For years, amiodarone was considered the preferred antiarrhythmic during cardiac arrest, and lidocaine fell out of favor in guidelines. That changed after a large clinical trial published in the New England Journal of Medicine compared both drugs head to head in out-of-hospital cardiac arrest. The results were striking for how similar they were: 24.4% of patients given amiodarone survived to hospital discharge, compared with 23.7% of those given lidocaine. The difference was not statistically meaningful.
This near-identical survival rate is a major reason lidocaine was restored as an equal alternative in the 2018 AHA guideline update. In practice, the choice between the two often comes down to availability, clinician familiarity, and patient-specific factors. Some hospitals stock one more readily than the other, and some patients may tolerate one drug’s side-effect profile better.
What Happens After the Heart Restarts
If lidocaine helped achieve return of spontaneous circulation (ROSC), meaning the heart starts beating effectively again, the team may continue it as a maintenance infusion. The reasoning is straightforward: the same unstable electrical conditions that caused the arrest can trigger it again in the minutes and hours that follow. Keeping a steady level of lidocaine circulating helps suppress those re-entry circuits and reduces the chance of the heart slipping back into a lethal rhythm while the underlying cause is addressed.
Risks of Lidocaine in a Code
Lidocaine has a relatively narrow margin between a therapeutic dose and a toxic one, which is why doses are carefully weight-based. Neurological symptoms of toxicity appear first: tingling, confusion, dizziness, and in more severe cases, seizures or loss of consciousness. On the cardiac side, too much lidocaine can paradoxically cause the very problems it’s meant to fix, including dangerous slowing of the heart rate, widening of the electrical signal pattern on a monitor, and suppression of the heart’s natural pacemaker cells.
Patients who already have significant heart block or who are on other sodium channel-blocking medications face higher risk. In the context of a code, where the patient is already in cardiac arrest, the risk-benefit calculation tilts heavily toward giving the drug. The heart is already in a non-survivable rhythm, so the potential benefit of restoring organized electrical activity outweighs the toxicity concerns that would matter more in a stable patient.
Why Lidocaine and Not Other Numbing Agents
People often associate lidocaine with the dentist’s office or minor skin procedures, and it can seem strange that the same drug shows up in a cardiac arrest. The connection is the sodium channel. Local anesthetics like lidocaine work by blocking sodium channels in nerve cells to stop pain signals. That same mechanism, applied to heart muscle cells, suppresses the abnormal electrical firing behind VF and pVT. Not all local anesthetics share this cardiac utility at safe doses, which is why lidocaine specifically earned a role in emergency cardiac care decades ago and remains there today.