anesthetic
Meaning of anesthetic: Names ending in -caine mark the local anesthetics, a family descended from cocaine, the first substance found to numb living tissue.
Definition of anesthetic
An anesthetic is a drug given to block sensation, most often to prevent pain during a procedure. Local anesthetics act where they are placed, shutting the sodium channels that nerves use to carry signals, so the message never leaves the area. General anesthetics act on the brain instead, producing unconsciousness, loss of memory and stillness throughout the body.
How do the groups differ?
| Group | Examples | How it is given |
|---|---|---|
| Local | Lidocaine, bupivacaine, benzocaine | Injected into tissue, or applied as a gel, spray or skin patch |
| Regional | The same drugs, placed differently | Injected around a nerve bundle or into the space around the spinal cord |
| Inhaled general | Sevoflurane, desflurane, nitrous oxide | Breathed in through a mask or airway tube |
| Intravenous general | Propofol, ketamine, etomidate | Injected into a vein, usually to start anesthesia |
Why do local anesthetics sometimes fail?
They must cross the nerve membrane in an uncharged form before they can work from the inside, and that requires the surrounding tissue to be near its normal acidity. Infected, inflamed tissue is acidic, so more of the drug stays charged outside the nerve and the block is weaker; a dental abscess is the classic example. Other explanations include injecting too far from the target, or a nerve that runs an unusual course. Epinephrine is often added to a local anesthetic because it narrows nearby vessels, keeping the drug in place longer and reducing bleeding at the site.
What limits their use?
Local anesthetics are safe within a ceiling based on body weight, and above it they escape into the circulation and reach the brain and heart, producing tingling around the mouth, a metallic taste, ringing in the ears, then seizures and rhythm disturbance. That ceiling is the reason a large field is covered by a nerve block targeting one nerve rather than by infiltrating a wide area. The drugs divide chemically into esters and amides, which matters because true allergy is uncommon and, when it occurs, is far more often to the ester group or to a preservative than to the amide itself. General anesthetics have separate limits, chiefly their effects on breathing and blood pressure.
Used in a sentence
A local anesthetic was injected before the skin biopsy was performed.
Good to know
A local anesthetic numbs a limited area while a person remains fully awake, which distinguishes it clearly from a general anesthetic, which additionally produces a complete loss of awareness.
Word origin
Where “anesthetic” comes from
Formed from Greek an-, meaning without, and aisthesis, meaning sensation or perception, together describing an agent that removes the ability to feel.