Local Anaesthesia has two main types, amides and esters. This article discusses dosing, side effects, calculations with examples.
Summary of Local Anaesthesia
The following table summarises local anaesthesia’s agent, class, dosing and duration of action that can be used for injection by doctors and dentists1. For example, in TAP blocks.
|Class||Duration (mins)||Dose (mg/kg)||Max Dose (mg)|
|Lidocaine + Adrenaline||Amide||120-360||7||300|
|Bupivicaine||Amide||120 – 240||2.5||175|
|Bupivicaine + Adrenaline||Amide||180 – 420||2.5-4||225-400|
|Prilocaine||Amide||30 – 90||8||500-600|
Types and classification of local anaesthetics based on agent, doses and duration of action.
Types of Local Anaesthesia
Mnemonic: If the ‘i’ is before the C, the local anaesthetic is an amide.
There are two types of local anaesthetics/anaesthesia. They are classified as:
- Esters: a type of para-aminobenzoic acid (PABA)–based anaesthesia
- Amide: a type of non-para-aminobenzoic acid (PABA)–based anaesthesia
Both ester and amide local anaesthetics can be administered in different formulations (ointments, patches, and injections).
Examples of these two types of local anaesthetics include:
- Esters: Benzocaine
- Amides: Bupivacaine
Local Anaesthesia Calculations
There are 3 required values in local anaesthesia calculations: maximum dose, maximum volume and concentration. In conjunction with patient weight, any local anaesthetic calculation can be performed
Maximum Recommended Dose of Local Anaesthetic
The maximum recommended dose of local anaesthetic depends on the type of local anaesthetic used. This is provided by the manufacturer and is outlined in the summary table above.
Maximum Recommended Volume of Local Anaesthetic
The maximum recommended volume of local anaesthesia can be calculated based on the maximum dose of local anaesthetic, patient weight and concentration. ThePlasticsFella recommends the following formula:
Calculating Concentration of Local Anaesthetic
LA concentration is usually expressed as a percentage (%), whilst maximum safe dose is expressed as mg/kg. Therefore, you need to convert % to mg/kg.
To convert % to mg/kg = Multiply the % by 10
For example, 1% lignocaine is 10mg/ml. This is detailed in the table below.
Calculating Concentration of Epinephrine
Epinephrine concentrations are expressed as ratios. To calculate mg/ml from a ratio you need to:
First, convert the ratio as a %: 1 in 100 is 1% and 1 in 1000 in 0.1%. Second, multiply the % x 10 to get mg/ml. For example, 1:1000 epinephrine is 1mg/ml.
Calculating Body Weight
The Devine formulation is the most commonly accepted calculation (most applicable for people at least 60 inches, or 5 feet, tall):
- IBW for men (kg) = 50 + 2.3 * (Height (in)-60)
- IBW for women (kg) = 45.5 + 2.3 * (Height (in)-60
Examples of Local Anaesthesia
- 1. Mustoe TA, Buck DW II, Lalonde DH. The Safe Management of Anesthesia, Sedation, and Pain in Plastic Surgery. Plastic and Reconstructive Surgery. October 2010:165e-176e. doi:10.1097/prs.0b013e3181ebe5e9
- 2. Williams D, Walker J. A nomogram for calculating the maximum dose of local anaesthetic. Anaesthesia. 2014;69(8):847-853. https://www.ncbi.nlm.nih.gov/pubmed/24820093.