How Do You Infiltrate Local Anesthesia?

Local anesthesia infiltration is a superficial method of inducing numbness for dental procedures, minor skin surgeries and similar procedures.

Local infiltration anesthesia is the technique of producing loss-of-sensation restricted to a superficial, localized area in the body. A low concentration of anesthetic agent is infiltrated into the tissues in the area that requires anesthesia.

Local anesthetic agents are a class of drugs used to induce local anesthesia. Cocaine, which is extracted from coca beans, was the first anesthetic compound to be discovered. Cocaine is the only naturally occurring local anesthetic, all other anesthetic compounds are synthetically derived products.

Anesthetic agents are of two classes:

• Amino amides
• Amino esters

Amino amides are stable in solution and are metabolized by the liver and excreted in the urine. Amino esters are unstable in solution and are metabolized by an enzyme in blood plasma. Amino esters are much more likely than amino amides to cause allergic hypersensitivity reactions.

Local anesthetic agents temporarily block the sodium channels at the nerve endings and prevent the flow of sodium ions into nerve cells. Without the inflow of sodium ions, the nerve cells cannot conduct an impulse. The communication from the nerve endings in the specific area to the brain is blocked leading to loss of sensation.

Local anesthesia is used for tissue infiltration and nerve block anesthesia. Infiltration anesthesia is mostly used for minor surgical and dental procedures. Nerve blocks, in addition, are used for diagnostic procedures and pain management as well.

The uses of local infiltration anesthesia include:

• Subcutaneous (fat tissue under the skin) infiltration for
  • IV placement
  • Superficial/shave biopsy
  • Suturing
• Submucosal (mucous tissue) infiltration for
  • Dental procedures
  • Laceration repairs
• Wound infiltration for postoperative pain control at the incision site
• Intraarticular (in the joints) injections for
  • Postoperative pain control
  • Arthritic joint pain control
• Infiltrative nerve blocks such as
  • Ankle block
  • Scalp block
  • Digit block

The local anesthetic for infiltration is prepared by diluting the anesthetic agent with saline solution. The choice of anesthetic agent and concentration depends on the required procedure because different anesthetic agents vary in toxicity and absorption. 

Epinephrine added to the solution can prolong the anesthetic effects, for example. But epinephrine may be detrimental in some wound repair surgeries on the limbs as it can constrict blood vessels thus slowing oxygenation and healing to the damaged tissue.

Other factors that influence the choice of anesthetic agents include:

• Onset of action: The time required for anesthesia to take effect
• Potency: Strength of the anesthetic effect
• Duration of action: The period that anesthetic effects last

Before administration of injections in the skin, the doctor makes the area sterile with an antiseptic solution. A common technique for local anesthesia infiltration is to inject the anesthetic solution in a circular pattern around the operative area.

The doctor keeps the number of needle insertions minimal by inserting the needle in a plane beneath the skin. After aspirating the syringe to make sure the needle is not inside a blood vessel, the doctor slowly injects the anesthetic solution while withdrawing the needle. Fast-acting anesthetic agents take effect in about five minutes, while longer lasting drugs may take up to 20 minutes.

Apart from the sting from the needle prick, there might be some slight pain and tingling. Doctors usually warm the anesthetic solution to 25-40 degrees centigrade before administration, which can minimize the pain. The doctor may also add sodium bicarbonate to decrease the acidity of the solution, which can reduce the pain further.

A list of common local anesthetic agents used for tissue infiltration and their duration of effects is as follows:

Amino amides

• Lidocaine (Xylocaine): Rapid onset and lasts two hours
• Mepivacaine (Carbocaine, Polocaine): Rapid onset and lasts three hours
• Bupivacaine (Marcaine, Sensorcaine): Slow onset and lasts four hours
• Ropivacaine (Naropin): Medium onset and lasts three hours
• Prilocaine (Citanest): Medium onset and lasts 90 minutes

Amino esters

• Procaine (Novocain): Slow onset and lasts 45 minutes
• Chloroprocaine (Nesacaine): Rapid onset and lasts 30 minutes

Adding epinephrine to the anesthetic solution doubles the duration of anesthetic effects.

Local infiltration anesthesia is mostly a safe and effective way to produce local loss of sensation. Adverse effects mainly result from high anesthetic concentration in blood plasma (local anesthesia systemic toxicity), which may be caused by:

• Accidental injection into a blood vessel
• Excessive anesthetic dose
• Excessive rate of administration
• Delayed drug clearance from the tissues
• Fast clearance from the infiltrated tissues which may lead to systemic absorption of the anesthetic agent

Most of the above risks can be eliminated with careful administration of the injection.

The possible risks and side effects of local anesthesia include:

• Central nervous system (CNS): High concentration of anesthetic in the plasma first causes CNS stimulation (including seizures), followed by CNS depression (including respiratory arrest). Amide anesthetics may not produce a stimulatory effect on CNS, but adding epinephrine may add to the stimulatory effect.
• Cardiovascular system: High plasma levels of anesthetics depress the heart and may cause:
  • Slow heart rate (bradycardia)
  • Irregular heartbeat (arrhythmia)
  • Low blood pressure (hypotension)
  • Cardiovascular collapse
  • Cardiac arrest

Addition of epinephrine may have the opposite effect and can lead to:

• High blood pressure (hypertension)
• High heart rate (tachycardia)
• Chest pain (angina)
• Hypersensitivity reactions: Hypersensitivity to amino amide anesthetics is rare and may be caused by preservatives in the anesthetic solution. Amino ester anesthetics, when metabolized in the plasma, release an allergen known as para-aminobenzoic acid, which may cause hypersensitivity. Allergic reactions may also result from local anesthesia systemic toxicity.

Effects on other systems:

• Burning sensation at the injection site
• Skin discoloration
• Swelling
• Nerve inflammation in the infiltration area (neuritis)
• Tissue death (necrosis) and sloughing
• Decrease in oxygen supply to tissue (methemoglobinemia), with prilocaine