Local anaesthetic doses

Local anaesthetic is in general a safe drug which is fortunate because as dentists we use this every day. More than any technique or surgical skill it is the single most effective tool to improve success rates in our procedures. Can you imagine how hard any simple restorative or surgical work would be without the assistance of local anaesthetic?

As it is used locally as opposed to systemically, the body can tolerate a fair amount of solution before we are concerned about toxicity. For most dental procedures toxicity isn't a concern however for complex and lengthy procedures as well as in children and the elderly it must be a consideration. In procedures such as full clearances or lengthy procedures such as rehabilitations you must use a safe local anaesthetic and keep track of the amount used.

Adrenaline containing local anaesthetics cause localised vasoconstriction which reduces the rate at which local anaesthetic solution is washed into the system. Therefore a lower concentration of solution is needed for the same effect and therefore more solution can be used in an equivalent subject.

Articaine is a popular anaesthetic but it is commonly available in 4% solution. This means that only half the volume of anaesthetic can be used as compared to lidocaine 2% with adrenaline. Lidocaine is a proven anaesthetic that is effective for most applications. In lengthy procedures or where a large field of anaesthetic is required, lidocaine with adrenaline is the anaesthetic of choice.

It will be important to be able to calculate the safe dose of anaesthetic (Table 1)  in extreme cases where the procedure is extensive or the patient is compromised.

Drug	mg/ml	Maximum mg/kg dose	mg per 2.2ml cartridge	Maximum 2.2ml cartridges in a 70kg adult
Lignocaine 2% 1:80k adrenaline	20	7	44	11
Mepivcaine 3%	30	Unspecified	66	3
Articaine 4% 1:100k adrenaline	40	7	88	5
Prilocaine 3% 0.03IU/ml Fellypressin	30	9	66	9

Table 1: Maximum safe dose of dental local anaesthetic in Australia. From oral and dental therapeutic guidelines Australia

Points to remember when calculating:

• 1% of anaesthetic solution will equate to 10mg/ml
• Anaesthetic cartridges in Australia contain 2.2ml solution
• Multiply the maximum dose per kg (mg/kg) by the weight of the patient to calculate the maximum dose allowable for the patient
• Divide this by the concentration of the solution mg/ml to obtain the maximum volume of solution allowed
• Divide this by 2.2 to obtain the maximum cartridges allowable