Primer: Local Anaesthetics
DISCLAIMER: The following is for educational purposes only and is not meant as an instructional tool. Any surgical procedures should be undertaken under the supervision and by a medical professional.
PRIMER ON LOCAL ANAESTHETICS
Local anaesthetics block pain by inhibiting certain electrolyte channels at the cellular membrane of neurones, inhibiting nociception and numbing the affected area. As with all medical procedures, local anaesthesia carries a risk of side effects and care must be taken with its use.
COMMON TYPES OF LOCAL ANAESTHETIC
- Likely the most common type of local you will encounter
- Onset: 3-5 minutes
- Duration: 30 minutes to an hour
Bupivocaine & Ropivocaine
- Long acting local
- Onset: 15 minutes
- Duration: 2-8 hours
For the purposes of simple surgeries Lidocaine should be more than sufficient.
THE USE OF VASOCONSTRICTIVE AGENTS WITH LOCAL ANAESTHETIC
Vasoconstrictive = reduces the calibre of blood vessels, reducing blood flow and subsequent bleeding from the surgical wound. In almost all cases this will be adrenaline (AKA epinephrine). Local anaesthetic comes prepared either with adrenaline or without.
Adrenaline is an excellent agent to reduce bleeding and increase the visibility of the surgical field. As long as the agent is injected SC (subcutaneously) there will be no systemic effects (i.e. it will only be an issue if you hit a blood vessel).
WARNING - Adrenaline is NOT to be used on structures with relatively small blood supply. This includes fingers and toes, nose and ears and the penis (among other structures). These have relatively small vascular structures, and the use of adrenaline can cut off blood supply, inducing ischaemia and necrosis if used improperly. Unless you are a medical specialist DO NOT ATTEMPT THIS. Fingers get local anaesthetic ONLY.
LOCAL ANAESTHETIC TOXICITY
Local anaesthetic is meant to be used locally. That is, subcutaneously. When infiltrating the needle into tissue, retract the plunger BEFORE pushing it down - if blood is drawn into your syringe you have hit a blood vessel. If local anaesthetic is injected into the systemic circulation the patient is in for a bad time - certain agents are actually cardiotoxic.
- Blurring of vision
- Anxiety and confusion
- Tingling around the lips and tongue
- Metallic taste in the mouth
- Seizures, coma
- Bradycardia, hypotension, cardiac dysrhythmias
- Respiratory depression
If ANY of these symptoms occurs following surgery call an ambulance - these patients will need full tertiarty work up.