Contraindications of Local Anesthesia – Cases where LA Should not be given

Local Anesthesia is indicated in several treatment procedures in Dentistry, but it has got many contraindications too, with several conditions and situations where the Local Anesthesia is not indicated. It depends on the case, the medical condition and even the dental condition where it has to be decided whether the Local anesthesia has to be administered. Below are the different categories of contraindications of LA:

a)Absolute contraindications
b)Relative contraindications

Although there are a lot of medical advancements, there are conditions where a small mistake can cause fatal and so every precaution is needed to be taken while administering a small dose of local anesthesia, or in many cases, the usage of the solution has to be avoided. It could not always be the present health condition, but the medical problem of the past, which all has to be taken into consideration before deciding whether to administer LA to the patient or not.

Absolute contraindications

The absolute contraindications are the ones which have no circumstances for undertaking a course of action. The various absolute contraindications of usage of LA include:

• History of Allergy to Local Anesthetic Agents – If the patient was allergic to the LA solution in the past, the usage should be avoided again as this could again produce the same allergic reactions, or worse than that.
• Local anesthetic agents belonging to the same chemical group should not be used. However, local anesthetic agents in the different chemical group can be used. In case, a patient gives history of allergy to an amide local anesthetic agent, an ester local anesthetic agent can be used.
• Documented Allergy to Other Constituents of the solution – The LA solution has got several components and the patient can be allergic to one of them.
• History of allergy to any of the constituents of the local anesthetic solution. Bisulfites, in the form of Sodium-bisulfite and sodium-metabisulfite are used as anti-oxidents or as preservatives to the vasoconstrictor in the local anesthetic solutions. Other general preservatives present in the local anesthetic solution include Thymol, Methylparaben, and Chlorbutol. The solution containing the constituent should be avoided. If possible, any alternate LA solution should be used.

Relative Contraindications

The relative contraindications are the one where the patient is at a higher risk of getting complications and these can be prevented by taking up the various considerations. Following are the relative contraindications for the usage of LA:

• Fear and apprehension: Where the patient is uncooperative or refuses for the usage of local anesthesia, do not administer it forcefully.
• Presence of acute inflammation or Suppurative infection at the site of insertion of the needle: There are increased chances of spreading of the infection with the passage of the needle from the abscessed area to the deeper tissues.
• Infants or small children: These patients lack reasoning and understanding.
• Mentally retarded patients: These patients are unable to cooperate.
• Restricted mouth opening: In conditions such as Trismus, Partial or complete Ankylosis of the Temporomandibular joint, the patient cannot open his mouth sufficiently and here, the usage of local anesthesia is not suggested.
• Patients with Medical disease: Such as the following
  a) Cardiovascular disease – In patients with a cardiovascular disease, all the local anesthetic solutions containing high concentrations of vasoconstrictor, such as epinephrine, as in gingival retraction cords, should be avoided. Local anesthetic agents containing higher dilution of epinephrine, such as 1:100 000 or 1:200 000, or 3% mepivacaine or 4% prilocaine can be used (for nerve blocks) as vasoconstrictors makes the condition worse in cardiovascular diseases.
  b) Hepatic dysfunction – The local anesthetic agents end up in the liver where they undergo biotransformation, and in them, the agents belonging to the amide group would be undergoing the biotransformation. When the liver function is not proper, it is better not to use these LA agents.
  c) Renal dysfunction – The LA agents with amides and esters have to be avoided or judiciously used when the patient is suffering from renal dysfunction.
  d) Clinical hyperthyroidism – The condition and precautions to be taken are the same as with the patients with Cardiovascular disease.
• Major surgical procedures – The LA usage has to be replaced by general anesthesia in major surgeries.
• Presence of certain anomalies or developmental defects: These situations make regional analgesia difficult or impossible.
• Presence of congenital Methemoglobinemia: It can be idiopathic or congenital – When used in large doses, the LA agents like Articaine and Prilocaine can produce Methemoglobinemia (Bellamy Ethan al, 1992). These two drugs should be avoided in patients with congenital methemoglobinemia, and other clinical syndromes with reduced oxygen carrying capacity of blood; because, there is increased risk of producing clinically significant methemoglobinemia. If very much necessary, these can be used but in minimum doses. The maximum recommended dose of Prilocaine is 8 mg/kg body weight. In these cases, the LA agents in groups with both amides or esters can be used. Benzocaine in a topical anesthetic agent, when used in very large doses can also induce methemoglobinemia (Guertler and Pearce, 1994; and Rodriguez et al, 1994).
• Presence of Atypical Plasma Cholinesterase: Cholinesterase, is an enzyme, present in plasma, and is required for biotransformation of all esters by causing hydrolysis. This condition is a relative contraindication to the use of ester type of local anesthetic agents. These agents undergo biotransformation (hydrolysis) in the blood by the enzyme plasma cholinesterase, which is produced in the liver. These agents may be used, if necessary, however, the dose is minimized. In such situations,it is preferable to use an amide type of local anesthetic agent. Amides do not present any risk of high blood levels, because these agents undergo biotransformation in the liver.

Do check out the Indications of Local Anesthesia, Composition of Local Anesthesia, and more info about the Anesthetic solutions.

Note: This information was taken and modified from Manual of Local Anesthesia in Dentistry by AP Chitre