Lidocaine is a frequently used local anesthetic administered to prevent pain during medical and dental procedures. It is available in several formulations designed for specific clinical situations. The drug’s function is to create a temporary loss of sensation in a targeted area, allowing procedures to be performed without discomfort. Lidocaine is administered by injection or as a topical agent applied to the skin or mucous membranes.
How Lidocaine Provides Numbness
Lidocaine achieves its numbing effect by interrupting the communication system between nerves and the brain. Nerve cells transmit sensations like pain by sending electrical impulses. These impulses are generated by the movement of sodium ions across the nerve cell’s membrane through specialized openings called sodium channels. When these channels open, sodium rushes in, creating the electrical signal that travels along the nerve.
The medication works by blocking these sodium channels. When lidocaine is injected near a nerve, it stabilizes the nerve membrane and prevents the ionic fluxes necessary for an impulse to start and travel. This action creates a temporary roadblock for pain signals, preventing them from reaching the brain. This results in a state of numbness, with an onset that is rapid, often occurring within a few minutes of administration.
Understanding the Role of Epinephrine
In many clinical settings, lidocaine is combined with another medication called epinephrine. Epinephrine is a vasoconstrictor, meaning it causes blood vessels to narrow. Its inclusion in a lidocaine solution enhances the anesthetic’s effectiveness by reducing blood flow in the area where it is injected.
The first benefit of adding epinephrine is prolonging the duration of the numbing effect. By constricting local blood vessels, epinephrine slows the rate at which the bloodstream absorbs and carries away the lidocaine from the injection site. This keeps the anesthetic concentrated around the targeted nerves for a longer period, which is useful for longer procedures.
A secondary advantage is the reduction of bleeding at the procedure site. The narrowed blood vessels mean less blood flows through the area, which provides a clearer field of view for the clinician. This effect is helpful in surgeries where minimizing blood loss is important for safety and precision.
When Plain Lidocaine is Used
The decision to use lidocaine without epinephrine, often called plain lidocaine, is based on specific anatomical factors. Certain areas of the body have a blood supply delivered by “end arteries,” meaning they are the sole source of blood for that tissue. Using a vasoconstrictor like epinephrine in these areas could excessively reduce blood flow, posing a risk of ischemia, a condition where tissue does not receive enough oxygen. This can lead to tissue damage, so plain lidocaine is the standard choice for procedures in these regions:
- Fingers
- Toes
- Tip of the nose
- Ears
- Penis
Patient health status is another consideration. Epinephrine can have systemic effects, meaning it can affect the entire body, not just the injection site. It can increase heart rate, elevate blood pressure, and potentially cause palpitations, which can be dangerous for patients with certain health conditions. Clinicians opt for plain lidocaine for individuals with severe cardiovascular disease, uncontrolled hypertension, or certain thyroid disorders to avoid placing stress on the cardiovascular system.
Potential Side Effects and Considerations
Lidocaine can have potential side effects, although serious reactions are uncommon when administered by a healthcare professional. The most frequent side effects are localized to the injection site and are temporary. Patients may experience a lingering feeling of numbness, tingling, or a pins-and-needles sensation as the anesthetic wears off. Minor swelling, redness, or tenderness at the injection spot are also possible but resolve on their own.
More significant side effects are rare but can occur if a large amount of the anesthetic enters the bloodstream. These systemic reactions can affect the central nervous system, leading to symptoms such as dizziness, drowsiness, blurred vision, or muscle twitches. Rarely, an allergic reaction to lidocaine may occur, causing a rash, itching, or difficulty breathing. Patients should always inform their provider of any known allergies or medical conditions before receiving a local anesthetic.