Mechanism: Local anesthetics infiltrate tissues and diffuse across neural sheaths and membranes. They interfere with depolarization.
Onset of action : If anesthetic is delivered at the interface of the superficial fascia and dermis, blockade is very rapid. Wound cleansing and suturing can begin almost immediately. When blocking larger nerve trunks such as digital nerves, onset of action is much slower (4-10 minutes for lidocaine).
Duration: Lidocaine (Xylocaine) is 30-120 minutes. Lidocaine with epinephrine is 60-240 minutes. Mepivacaine (Carbocaine) is 90-180 minutes.
Addition of epinephrine: Decreases the amount of bleeding in a wound. Most serious side effect is tissue ischemia. DO NOT inject into fingers, toes, tip of the nose, pinna of the ear or penis. In susceptible patients, it can cause palpitations and tremors. Known coronary artery disease and hypertension are relative contraindications to the use of epinephrine. It is advisable to aspirate before injection to avoid direct intravascular bolusing.
Toxicity of local anesthetics: Most common is vasovagal syncope secondary to pain and anxiety. Less common are cardiovascular reactions and excitatory central nervous system effects. Cardiovascular reactions include hypotension and bradycardia and are caused by a myocardial inhibitory effect of the anesthetic. Excitatory central nervous system effects can culminate in seizure activity. The less common reactions are usually caused by inadvertent injection of a solution directly into a blood vessel. Management is supportive (airway control, IV access, and administration of epinephrine, diphenhydramine and steroids as needed).
Alternatives for the allergic patient: No anesthetic, ice over the wound, preservative-free anesthetic, use diphenhydramine (Benadryl) - lasts approximately 30 minutes, a 50 mg (1 mL) vial is diluted in a syringe with 4 mL normal saline to produce a 1% solution. Infiltration is carried out in the usual manner. Diphenhydramine is more painful to inject than lidocaine and the pain is not reduced with buffering.
Topical Anesthetic: Onset 5-15 minutes. Duration 20-30 minutes.
Buffer: Use bicarbonate. 1 mL of bicarbonate to 9 mL 1% Lidocaine; buffering of 2% lidocaine may cause precipitates - shelf life 7 days. Mepivacaine (Carbocaine) 0.5-1 mL bicarbonate per 9 mL mepivicaine - shelf-life unknown after 24 hours. Bupivacaine (Marcaine) - 0.1 mL of bicarbonate per 20 mL bupivacaine - shelf-life unknown after 24 hours.
Needle choices: A 25-gauge, 1-inch needle can be used for most local infiltration procedures, as well as facial and digital blocks. 27- or 30-gauge needles - small gauge reduces the pain of needle injection and slows the rate of anesthetic infusion. Rapid injection and tissue expansion is more painful than slow injection.
Most minor lacerations and wounds can be managed by administering a local anesthetic directly into or around (parallel to) the wound area.
Direct Wound Infiltration: Direct infiltration through the wound is indicated for most minimally contaminated lacerations in anatomically uncomplicated areas. Needlestick pain is less because intact skin is not pierced. Use 25-, 27- or 30- gauge needles with length of _ to 1_ inches. Insert the needle through the open wound into the superficial fascia (subcutaneous fat) parallel and just deep to the dermis. Inject a small bolus of anesthetic solution. Remove the needle and inject another bolus at an adjacent site, but just inside the margin of anesthesia of the previous injection. This ensures greater patient comfort. Repeat this process until all edges and corners of the wound are anesthetized. A simple laceration 3-4 cm in length requires 3 to 5 mL of an anesthetic solution.
Parallel Margin Infiltration: Alternative to direct wound infiltration and has the advantage of requiring fewer needle sticks. It is preferred in wounds that are grossly contaminated so that the needle does not inadvertently carry debris or bacteria into uncontaminated tissues. The same plane for direct wound infiltration is used, but approached through intact skin. Parallel infiltration requires at least a 25-gauge, 1 _ to 2 inch needle. The needle is inserted through the skin at one end of the laceration. The needle is advanced to the hub parallel to the dermis-superficial fascia plane. Aspiration is followed by slow injection of a "track" of anesthetic as the needle is withdrawn down the tissue plane to the insertion site. The needle tip is then reinserted at the distal end of the first track where the skin is beginning to become anesthetized. Reinsertion and injection is repeated on all sides of the wound until complete infiltration has been achieved.
Generally, wounds should be closed within 6-8 hours. Less if contaminated.
Appropriate protective gloves and eyewear should be worn at all times.
Cleansing and irrigation are the foundation of good wound care. It is essential that all contaminants and devitalized tissue are removed before wound closure. If not, the risk of infection and a cosmetically poor scar are greatly increased. Hair removal is not necessary prior to wound repair however removing scalp hair may make repair easier as suture material can become entangled. Do not shave or clip eyebrows. Hair re-growth of the brow is unpredictable in many patients. Eyebrow hair can be readily cleansed, and the brow borders provide excellent landmarks for laceration alignment during wound closure.
Nonabsorbable sutures are most commonly used for percutaneous or skin closure.
Absorbable sutures are placed deep for closure of dead space in large wounds or to reduce closure tension.
Note: Percutaneous = skin; deep = dermal layer
Taping can be used for superficial wounds under little tension. Taping is also appropriate in the elderly or steroid-dependent patient who has thin, fragile skin. Taping can also be used for support after sutures are removed. Tape does not work well on irregular wounds, those that can not be made free of blood or secretions, intertriginous areas, scalp and joint surfaces. Tapes are maintained in place at least as long as sutures would be for the anatomic area in question. Taped wounds should not be washed or moistened because premature tape removal can lead to wound dehiscence. Note: Tapes should never be wrapped around a digit in a circumferential manner because they are not expandable and can act as a constricting band.
Wound Adhesives feature short wound closure time and require no anesthesia. Wounds are at greater risk of breaking open during the first 7 days compared to sutures but after that, there is no difference. Indications for use are linear and curvilinear lacerations under little tension (< 0.5 cm wide) where no deep sutures are required. Lacerations should have sharp wound edges before or after debridement. Lacerations should be 5 cm or less. Adhesives are not effective for lacerations over joints, with excessive bleeding, or with high static tension as evidenced by edge gaping. Caution is used for lacerations near the eye. Hair-bearing areas are not a contraindication for adhesive closure. Patients should be instructed to keep the wound clean and dry for 24 hours. Wound dressings can be applied on areas other than the face. Should a wound dehisce, the patient should be instructed to return so that delayed primary closure can be carried out. No follow-up is necessary for glue removal because it will peel off on its own or come off with natural sloughing of keratinized epidermis.
*Add 2 to 3 days for joint extensor surfaces.