How to Prevent Local Anesthetic Overdose

I recently attended a course, hosted by the Fraser Valley Dental Society, on medical emergencies in the dental office. One of the many topics we covered was local anesthetic (LA) emergencies. It was clear from speaking with other attendees and the questions that arose with our speaker, Dr. David Isen, that most were a bit uncertain on how much LA could safely be given to a patient during an office visit.

Articaine Carpule

LAs are formulated with one of a variety of amide anesthetic molecules such as Articaine, Lidocaine, or Mepivicaine, etc. Often the amide anesthetic is accompanied by epinephrine, and a preservative, sodium metabisulfite, which prevents the degradation of the epinephrine.

LA toxicity is rare in the dental office but nonetheless easy to create if we are not consciously aware of the quantity of LA we are administering, especially when performing extensive treatment or when profound anesthesia is difficult to obtain. Very few attendees could come up with the maximum amount, in milligrams, of a particular anesthetic a patient could be given at one appointment though most knew the amount they could safely give in carpules, more on that later.

The signs and symptoms of mild LA overdose include dizziness, disorientation, and drowsiness. In severe cases, the patient can become unconscious. Though extremely rare, there have been reported cases of death from LA overdose, especially in children.

Three items are necessary to calculate how many carpules of a given anesthetic can be administered safely to a patient:

  • The type and concentration (%) of anesthetic in the carpule
  • The volume of LA in the carpule (usually 1.8 ml)
  • The maximum recommended dose (MRD) for that particular LA (The MRD is the maximum total dose, in milligrams, that can be safely given to a 70kg patient at one sitting)

Let’s use my favorite LA, 4% Articaine, as an example (Trade name Astrocaine in the picture). The brand of Articaine LA that I use is a 4% solution with 1:100,000 epinephrine, in a 1.8 ml carpules.

First, we have to convert the LA concentration as a percentage into mg/ml. By definition, a 100% solution contains 1000 mg per ml of solution. Therefore my 4% Articaine solution contains:

  • 4/100 (4%) x 1000 mg/ml = 40 mg/ml

The amount of Articaine in milligrams in a 1.8 ml carpule is:

  • 40 mg/ml x 1.8 ml/carpule = 72 mg/carpule

The MRD for Articaine is 500 mg:

  • 500 mg / 72 mg/carpule = 7 carpules

Thus, the maximum dose of the Articaine 4% anesthetic that I use is 7 carpules. A couple of things need to be noted. First, this is the maximum dose for a 70 kg healthy, ASA I patient. You might need to reduce that for a smaller person, especially children, though the maximum dose should not be exceeded for a larger person (see MRD tables for the anesthetic you use). Secondly, epinephrine which provides vasoconstriction, reduces the uptake and metabolism of the LA and subsequently increases the duration of anesthesia. Anesthetics which do not contain a vasoconstrictor will be taken up more rapidly and have the potential to have increased toxicity. These types of anesthetics usually have a lower MRD, so you need to adjust appropriately. On a final cautionary note, there are idiosyncratic responses to LA. Some people can experience LA toxicity even when given LA in amounts within the MRD guidelines so we should always be visually monitoring our patients during treatment.

As always we at Langley Endodontics are pleased to be to be a part of your referring community, and we value our ongoing relationship.

On May 9, 2016, posted in: News for Doctors by