Local anaesthetics are infiltrated into a small/local area or surgical site to stop pain. People remain awake and fully aware during the use of local anaesthetic and it is much safer than general anaesthetics that put people to sleep. While there are numerous different types and methods of local anaesthetics, on this page we focus on those that are primarily used at Skintel.
We also describe the techniques we use to reduce the pain from injecting local anaesthetic.
Mechanism of action of local anaesthetic
Local anaesthetics work by temporarily blocking the nerve conduction of sensory impulses from the peripheral skin back to the brain. Nerve signalling uses impulses or action potentials by allowing sodium ions to pass through sodium channels. Local anaesthetics bind to these sodium channels, which blocks the flow of sodium ions and prevents the conduction of nerve impulses.
This results in the treated area feeling numb. Local anaesthetic does not affect your level of consciousness, so you remain awake and fully aware when local anaesthetic is used.
Different types of local anaesthetic
There are numerous different types of local anaesthetics, however, the most commonly used is lignocaine (known as lidocaine in the USA). Bupivacaine is used when a longer duration of effect is desired – although it takes longer to start working. The common trade (brand) names are Xylocaine and Marcaine respectively.
Lignocaine is labelled as an FDA pregnancy category B and is considered to have almost no negative effect on pregnant women or the unborn baby.
| Lignocaine | Bupivicaine | |
| Onset | < 1 min | 2-10 min |
| Duration | 1-6 hrs | 4-8 hrs |
| FDA cat | B | C |
| Max dose | 7 mg/kg | 3 mg/kg |
Local anaesthetics are often mixed with adrenaline (epinephrine in the USA) which acts to constrict the blood vessels (vasoconstriction). This has the benefit of increasing the duration of the effect by slowing the absorption of the medication by the body. This allows us to use lower doses of lignocaine which reduces the risk of toxicity. Adding adrenaline also helps to reduce the amount of bleeding during surgery.
Adrenaline is an FDA pregnancy category C as it can reduce uterine blood flow.
While lignocaine is acidic, commercial preparations often use acidic preservatives resulting in a pH of around 3.3-5.5. This contributes to the pain experienced when injecting into the tissues. Sodium bicarbonate is often added to the mix, raising the pH and minimising the stinging and burning sensation. It also has the beneficial effect of speeding up the onset of action.
Infiltration of local anaesthetic
There are different types of infiltrative techniques when using local anaesthetics. Local infiltration involves injecting the local anaesthetic directly into the surgical site. It can be administered either into the dermis or into the subcutaneous fat which has pros and cons.
| Dermis | Subcutaneous | |
| Onset | Immediate | Delayed |
| Duration | Prolonged | Reduced |
| Pain | More painful | Less painful |
| Bleeding | Less bleeding | More bleeding |
Field blocks
A field block (also called a ring block) involves injecting the local anaesthetic circumferentially around the surgical site. This can be beneficial for large surgical sites as it reduces the amount of solution required. It is also often used for inflamed or infected tissue which can reduce the efficacy of anaesthesia.
Facial nerve blocks
Nerve blocks require anatomical knowledge of the sensory innervation of the relevant area. They can be a useful technique for skin surgery. However, they do take longer to work and don’t reduce bleeding at the surgical site (like local infiltration does).
Common nerve blocks used:
- Supraorbital (above the eye) nerve block.
- Infraorbital (below the eye) nerve block.
- Mental nerve block.
Digital nerve block
A digital nerve block is commonly used when undertaking procedures on nerves or toes. However, it requires administration of anaesthetic to four sites as there are two nerves on each side of the digit. It is best to avoid adrenaline when performing a digital nerve block so that blood flow is not compromised.
Reducing pain
There are various techniques that can be used to reduce the pain from administering local anaesthetic. Unfortunately, more anxious individuals will experience more pain as their nervous system will be more sensitive due to heightened levels of adrenaline.
- Reducing anxiety by providing reassurance and a relaxed environment can go a long way when it comes to reducing the pain from local anaesthetic.
- Music has been described as a mild anxiolytic and can be helpful in reducing the pain.
- Using small diameter needles.
- Injecting slowly.
- Adding a buffer to the anaesthetic such as sodium bicarbonate which increases the pH to a more physiologic level.
- Warming the temperature of the solution.
- Counter-irritation can diffuse pain signals. This involves pinching the skin around the injection site.
We use all of these techniques at Skintel when appropriate to improve your experience.
