What is the appropriate local anesthetic regimen, including concentration, epinephrine use, dosing limits, and alternatives for lidocaine allergy, for suturing a lip laceration sustained from a fall?

Local Anesthesia for Lip Laceration Repair

For suturing a lip laceration from a fall, use topical LET (lidocaine-epinephrine-tetracaine) solution applied for 20-30 minutes first, followed by buffered 1% lidocaine with 1:100,000 epinephrine infiltration if needed, with maximum doses of 7 mg/kg lidocaine with epinephrine in adults (4.5 mg/kg in children), and diphenhydramine 1% or bacteriostatic saline as alternatives for true lidocaine allergy. 1

Topical Anesthesia as First-Line

Start with topical anesthetic application to minimize pain and potentially avoid needle injection entirely:

• Apply LET solution (lidocaine, epinephrine, tetracaine) directly to the open wound for 20-30 minutes until wound edges appear blanched. 1
• Use 3 mL for patients >17 kg or 0.175 mL/kg for patients <17 kg (based on maximum 5 mg/kg lidocaine dose). 1
• Place a cotton ball soaked with LET into the wound and cover with occlusive dressing. 1
• LET provides complete anesthesia for approximately 95% of sutures placed in facial and lip lacerations. 2
• Contraindications include allergy to amide anesthetics and gross wound contamination. 1

Clinical advantage: In adult studies, only 13 of 30 patients (43%) required additional injectable anesthetic after LET application, compared to 100% in placebo groups. 3

Injectable Lidocaine with Epinephrine

If topical anesthesia is insufficient or for urgent situations, proceed with infiltrative lidocaine:

Concentration and Epinephrine Use

• Use 1% lidocaine with 1:100,000 or 1:200,000 epinephrine for lip lacerations. 4
• Epinephrine concentrations between 1:50,000 and 1:200,000 provide equivalent vasoconstriction and anesthetic prolongation. 4, 5
• Adding epinephrine is safe for all facial areas including lips, with no cases of tissue necrosis reported in systematic reviews. 4
• Epinephrine extends anesthesia duration to 90-200 minutes (versus 60-90 minutes without). 6, 4

Maximum Safe Doses

Adults:

• 7 mg/kg (maximum 500 mg) with epinephrine 1, 6
• 4.5 mg/kg (maximum 300 mg) without epinephrine 1, 6
• For a 70 kg adult: up to 490 mg (49 mL of 1% solution) with epinephrine 6

Children:

• 3.0-4.5 mg/kg with epinephrine 1, 6
• 1.5-2.0 mg/kg without epinephrine 1
• Reduce doses by 30% in infants <6 months old 1, 6
• For children <10 years: rarely need more than 0.5 cartridge (40 mg) for single-tooth procedures 7

Pain Reduction Techniques During Injection

Minimize injection pain using these evidence-based methods:

• Buffer lidocaine with sodium bicarbonate (1:9 or 1:10 ratio) to reduce injection pain 1, 4
• Warm the lidocaine solution to body temperature before injection 1
• Use the smallest gauge needle possible 1
• Inject slowly with frequent aspiration 1, 6
• Buffered lidocaine remains stable for up to 30 days when pre-made 1

Alternatives for Lidocaine Allergy

True lidocaine allergy is rare (only 1% of adverse reactions), but when present: 1

1. First choice: Switch to ester-type local anesthetic (e.g., procaine, tetracaine) since cross-reaction between amides and esters is rare 1

2. Second choice: 1% diphenhydramine injection

   • Onset of action: 5 minutes (versus 1 minute for lidocaine) 1
   • Limited efficacy but useful for small excisions and biopsies 1

3. Third choice: Bacteriostatic saline (0.9% benzyl alcohol in normal saline)

   • May be less painful than diphenhydramine when mixed with epinephrine 1
   • Useful for small procedures 1

Critical Safety Monitoring

Implement these safety measures to prevent local anesthetic systemic toxicity (LAST):

• Always aspirate before injection to avoid intravascular administration 1, 6, 7
• Monitor vital signs every 5 minutes when using high doses or injecting into vascular tissues 1, 6
• Wait at least 4 hours between lidocaine infiltration and any other local anesthetic intervention to prevent cumulative toxicity 6
• Have 20% lipid emulsion immediately available when using high doses 1, 6

Early toxicity signs to monitor: 6

• Circumoral numbness and facial tingling
• Slurred speech
• Metallic taste and tinnitus
• Light-headedness
• Toxic plasma levels begin at 6 μg/mL; serious toxicity (seizures, hypotension) at 9-10 μg/mL 6

Special Populations Requiring Dose Reduction

Calculate doses carefully and reduce in these patients: 6

• Hepatic dysfunction
• Cardiac failure
• Hypoalbuminemia
• Low body weight or reduced muscle mass
• Patients taking beta-blockers or amiodarone
• Use ideal body weight (not actual weight) in obese patients to avoid overdosing 6

Common Pitfalls to Avoid

• Failing to wait 20-30 minutes for topical anesthetic to take full effect 1
• Using actual body weight instead of ideal body weight in obese patients 6
• Not accounting for cumulative doses from multiple injection sites 6
• Injecting too rapidly, which increases pain and systemic absorption 1
• Forgetting to aspirate before injection 1, 6
• Applying excessive topical doses to mucosal surfaces where systemic uptake is rapid 1