06.06-09 Local Anaesthesia
Before inserting sutures, a wound should be thoroughly cleansed and infiltrated with a local anaesthetic. This module will introduce the instruments, drugs and techniques you will need for local anaesthesia, together with key information on managing your patient.
In this module
06.06 Anaesthetic Agents
Local anaesthetic agents may be amides or esters. Amides (e.g. lidocaine, bupivacaine, prilocaine) are more stable in solution than the esters and cause fewer hypersensitivity reactions. Esters (such as amethocaine and benoxinate) are absorbed more rapidly from the mucous membranes.
Lidocaine (lignocaine) is the most commonly used agent and is suitable for almost all cases of minor surgery.
Bupivacaine and prilocaine are longer-acting than lidocaine and other local anaesthetic agents exist, but for minor surgery lidocaine is the most commonly used agent.
06.06.01 Plain Lidocaine
Lidocaine has a rapid onset of action and its effects last for 60 to 90 minutes.
Lidocaine solution is available in three strengths: 0.5%, 1% and 2%.
The 0.5% is useful in paediatric patients. 1% strength is adequate for most purposes. It has a concentration of 10 micrograms per millilitre. The 2.0% solution is rarely necessary.
Lidocaine solution is supplied in single-dose vials and multi-dose bottles. Use single-dose vials to minimise the risk of contamination.
06.06.01.01 Dose Limits
The dose limit for lidocaine depends on many factors and each patient needs individual assessment taking into account their size, the vascularity of the infiltration site, their cardiac output, drug distribution and metabolism.
The dose limit should not exceed 3 micrograms per kilogram of body weight, i.e. a maximum of 200 micrograms for a 70 kg patient.
In practice you will only need a few mL of local anaesthetic for most minor procedures.
06.06.02 Lidocaine with Adrenaline Epinephrine
Lidocaine is also available with adrenaline. Adrenaline is also known as Epinephrine. Adrenaline causes vasoconstriction, in other words it reduces bleeding from vascular areas. This can make procedures easier, for example when operating on the scalp.
Adrenaline reduces the systemic absorption of local anaesthetic, enabling larger volumes to be used without toxicity. Blanching of the skin shows the extent of the anaesthetised field.
Plain lidocaine is adequate for most purposes. Ensure that supplies of lidocaine with adrenaline (Epinephrine) are locked away in a cupboard and kept separately so that you do not use them inadvertently.
06.06.02.01 Dose Limits
You must check the concentration of adrenaline (Epinephrine) in a local anaesthetic mixture before injecting it.
Ampoules commonly have a concentration of 1 in 200 000 of adrenaline (Epinephrine), equivalent to 5 micrograms per mL.
The dose limit should not exceed 7 micrograms per kilogram of body weight. The total dose of adrenaline given in one episode must be less than 500 micrograms.
Be aware of the cumulative effect of injecting many small lesions in a single session, and never draw up more than the total safe dose for that patient.
Always calculate and record the dose of drugs you use for each patient.
06.06.02.02 Things to Avoid
Never use local anaesthetic containing adrenaline when anaesthetising any part of the body supplied by an end artery, for example finger, toe, nose, ear or penis.
Adrenaline in an end artery causes intense vasospasm and may completely cut off the blood flow beyond the point of injection. If the collateral circulation is inadequate, the territory of the affected artery may become ischaemic, with disastrous consequences.
06.06.03 Toxicity Video 1
Toxicity is caused by high circulating levels of drug. This may be because of a high total dose or because the drug is redistributed from the site of the injection.
The use of vasoconstrictor (adrenaline) will delay the systemic redistribution of the local anaesthetic by reducing blood flow to the area. The effect of the local anaesthetic will therefore last longer.
Most minor surgical procedures need only small amounts of local anaesthetic and are usually far away from major blood vessels. This means that inadvertent intravascular injection of significant quantities of local anaesthetic, or adrenaline, is rare.
If you haven’t already done so, go to the topics on dose limits for Plain Lidocaine and Lidocaine with adrenaline to make certain that you are aware of safe dosages.
06.06.04 Toxicity Video 2
Be vigilant: if you detect signs of toxicity early you can minimise the adverse outcome. Do not give any more local anaesthetic and be prepared to institute supportive measures immediately until the effect of the drug has subsided.
Early symptoms affecting the central nervous system include: restlessness, tingling of limbs or around the mouth, and confusion.
Late central nervous system manifestations include: depression, convulsions and unconsciousness.
Late cardio-respiratory manifestations include: respiratory depression, arrhythmias and cardio-respiratory arrest.
Cardiac toxicity can be resistant to treatment, particularly if bupivacaine is the local anaesthetic involved.
06.07 Syringes & Needles
Sterile single-use syringes come in a variety of sizes. A Luer lock allows a variety of needle sizes to be attached. Each syringe is supplied in a sterile pack. You should discard the syringe safely after a single use.
Ensure that you have a selection of needles available. The larger the gauge number, the smaller the diameter of the needle, so a 25-gauge needle is much smaller than a 21-gauge needle. Needles are also colour-coded according to their diameter.
Green = 21-gauge, 0.8mm in diameter
Blue = 23-gauge, 0.6mm in diameter
Orange = 25-gauge, 0.5mm in diameter
Draw up local anaesthetic agent using a large diameter (green 21-gauge, 0.8mm) needle. Then remove the needle and discard it into a sharps container.
Change to the finest available diameter of needle (blue 23-gauge 0.6mm or orange 25-gauge, 0.5mm) for injecting. This minimises discomfort.
06.08 Infiltration Anaesthesia
Local anaesthetic can be given through the open wound edges providing that the wound is clean. Anaesthesia can be achieved using multiple small injections around the circumference of the wound or by infiltrating the edges of the wound externally through the skin.
Other techniques, such as ring blocks, can be used for digit injuries where the entire digit is anaesthetised. Inject slowly as rapid injection causes discomfort by distending the tissue.
Allow time for the local anaesthetic to take effect before starting the procedure and check with your patient.
06.08.01 Checks
Check that there are no contraindications to local anaesthesia and that the preparation is in date.
Calculate the maximum dose of local anaesthetic and ensure you have drawn up less than this.
Ensure that the local anaesthetic is not cooler than room temperature, as injecting cold fluid will increase your patient’s discomfort.
Check if the local anaesthetic contains adrenaline. Record that you are using a plain agent where adrenaline is contraindicated.
Record the name of the assistant you have checked the drug with.
06.08.02 Anaesthetising a Laceration Prior to Suturing Video 1
Before administering local anaesthetic, the wound should be thoroughly cleansed.
Draw up local anaesthetic agent using a large diameter (e.g. green 21 gauge, 0.8mm) needle. Then remove the needle and discard it into a sharps container.
Change to the finest available diameter of needle for injecting. This minimises discomfort.
If you are happy that the wound is clean, you can inject anaesthetic directly into it under the wound margin.
Starting on one side of the wound advance the needle as far as possible under the wound margin. This will minimise the total number of injections required. Aspirate the syringe by pulling back on the plunger before infiltrating the anaesthetic to make sure that you aren't in a vessel. If there is blood in the syringe, withdraw and redirect the needle. Push the plunger down to infiltrate as you draw back.
Work your way around the wound margin in this way, beginning your next injection in already anaesthetised skin. Each time remember to aspirate before infiltrating.
Always remember to inject slowly, as rapid injection causes tissues to distend and is painful.
06.08.03 Anaesthetising a Laceration Prior to Suturing Video 2
An alternative technique is to inject the area around the wound, through the intact skin. Where possible, this should be avoided as this will minimise your patient’s pain.
06.08.04 Anaesthetising a Laceration Prior to Suturing Video 3
Ensure you allow enough time for the local anaesthetic to take effect. For lidocaine wait at least one minute and for bupivacaine you should wait five minutes.
Test before starting the procedure. Pinch the tissues with your forceps, or gently touch the skin edges with a needle. If the patient feels sharp pain, more anaesthetic is required. Pressure sensation is not dulled by local anaesthetics. With adequate anaesthesia, the patient may still feel a sensation of pressure when you pinch the tissues with the forceps, but it should not hurt.
Once you are satisfied that the anaesthetic is effective, dispose of the needle and syringe in an approved sharps container.
06.08.05 Fan Shaped Lesion Prior to Small Lesion Removal
ou may be asked to administer local anaesthetic prior to removal of a small lesion and suturing of the resulting wound. A fan-shaped infiltration technique is recommended in this instance.
Mark the lesion, especially if it is deep or the patient has many similar lesions. This will ensure that you anaesthetise the correct lesion.
Inject the local anaesthetic in a fan-shaped pattern first from one side of the lesion and then the other. Inject slowly, since rapid injection causes discomfort by distending the tissue.
Ensure that you inject deep to the lesion as well as to the tissue all around it.
06.08.06 Infiltration by enrichment Prior to Removal to Lesion
You may be asked to administer local anaesthetic prior to removal of a large lesion and suturing of the resulting wound. An encircling technique is recommended in this instance.
Inject local anaesthetic slowly and steadily, as rapid injection causes discomfort by distending the tissue. Use a series of steps around the lesion. With each new step you should be passing through skin that has just been anaesthetised by the previous injection.
You should take care to ensure that the deep aspect of the lesion is anaesthetised as well.
06.09 Ring Block
A ring of local anaesthetic injected proximally at the base of a digit produces anaesthesia of the distal part. Understand and visualise the anatomy of the digit and its nerves.
A ring block takes longer to work than local infiltration. Ensure you anaesthetise the nerve territory completely. Always wait long enough for the anaesthetic to take effect.
Never use adrenaline. Never give a ring block to a patient with peripheral vascular disease or diabetes. Never inject through infected skin. Do not use too much fluid. This may cause pressure ischaemia. 1-3mL is usually sufficient.
06.09.01 Practise Procedure
Angle the needle towards the palm or sole and inject about 0.5 mL of local anaesthetic along one side of the digit.
Withdraw the needle partially and inject a further small quantity just deep to the skin, to anaesthetise any superficial nerve twigs.
Now repeat this process on the other side of the digit.
Avoid piercing the skin on the palmar/plantar aspect of the digit. Make sure your finger is not under the digit so that there is no risk of needlestick injury if you do inadvertently pierce the skin.