What is the risk of toxicity in a 72.72 Kg patient who received 3cc's of 1% lidocaine (lidocaine) with epinephrine (adrenaline) and 33 cc's of 2% lidocaine (lidocaine) without epinephrine (adrenaline) over 3 hours for local anesthesia?

From the Guidelines

The risk of toxicity in this 72.72 kg patient who received 3 cc of 1% lidocaine with epinephrine and 33 cc of 2% lidocaine without epinephrine over 3 hours is minimal and well within safe limits. The total lidocaine dose administered was 690 mg (30 mg from the 1% solution and 660 mg from the 2% solution), which equals approximately 9.5 mg/kg. This is below the maximum recommended dose of 7 mg/kg for lidocaine without epinephrine and 14 mg/kg for lidocaine with epinephrine, as suggested by 1. Additionally, the administration over 3 hours allows for metabolism of the drug during the procedure, further reducing toxicity risk. Lidocaine toxicity typically manifests as central nervous system effects (dizziness, tinnitus, confusion, seizures) followed by cardiovascular depression at higher levels. The presence of epinephrine in part of the dose helps by causing vasoconstriction, which slows systemic absorption and extends the duration of anesthesia. Some studies, such as 1, have shown that exceeding toxic plasma concentrations have been shown with lidocaine doses of 6.0–9.3 mg.kg-1 lean body weight, but the dose in this case is still considered safe. For future reference, calculating the mg/kg dose and comparing it to maximum recommended doses (7 mg/kg without epinephrine, 14 mg/kg with epinephrine) is the appropriate approach to assess lidocaine toxicity risk. Key points to consider in this scenario include:

• The total dose of lidocaine administered
• The presence of epinephrine in part of the dose
• The administration time of 3 hours, allowing for drug metabolism
• The patient's weight and the calculated mg/kg dose
• The maximum recommended doses for lidocaine with and without epinephrine, as outlined in 1 and 1.

From the FDA Drug Label

The maximum recommended dose of 4% Lidocaine Hydrochloride Injection, USP should be such that the dose of lidocaine HCl is kept below 300 mg and in any case should not exceed 4.5 mg/kg (2 mg/lb) body weight. When used without epinephrine, the amount of lidocaine administered should be such that the dose is kept below 300 mg and in any case should not exceed 4.5 mg/kg (2 mg/lb) of body weight.

To determine the risk of toxicity, we need to calculate the total dose of lidocaine administered.

• 3cc's of 1% lidocaine with epinephrine is equal to 3cc * 10mg/cc = 30mg of lidocaine.
• 33cc's of 2% lidocaine without epinephrine is equal to 33cc * 20mg/cc = 660mg of lidocaine. The total dose of lidocaine administered is 30mg + 660mg = 690mg.

For a 72.72 Kg patient, the maximum recommended dose is 4.5 mg/kg * 72.72 kg = 327.24 mg. Since the total dose administered (690mg) exceeds the maximum recommended dose (327.24mg), there is a high risk of toxicity 2.

From the Research

Local Anesthetic Toxicity Risk

The risk of toxicity in a 72.72 Kg patient who received 3cc's of 1% lidocaine with epinephrine and 33 cc's of 2% lidocaine without epinephrine over 3 hours for local anesthesia can be assessed by considering the total dose of lidocaine administered.

• Total dose of 1% lidocaine with epinephrine: 3cc = 3 * 10mg = 30mg
• Total dose of 2% lidocaine without epinephrine: 33cc = 33 * 20mg = 660mg
• Total dose of lidocaine: 30mg + 660mg = 690mg

Maximum Recommended Dose

According to the study 3, the maximum recommended dose of lidocaine is not evidence-based, but a commonly cited maximum dose is 200mg for infiltration anesthesia. However, this dose can be adjusted based on patient-related factors such as age, organ dysfunctions, and pregnancy.

• Maximum recommended dose per kilogram of body weight: not explicitly stated, but a study 4 suggests calculating the maximum recommended dose based on milligrams of drug per kilogram of body weight.

Toxicity Risk Assessment

Considering the total dose of lidocaine administered (690mg) and the patient's weight (72.72 Kg), the dose per kilogram of body weight is approximately 9.5 mg/kg.

• This dose is higher than the commonly cited maximum dose of 200mg, but the patient's weight and other factors may influence the risk of toxicity.
• Studies 5 and 6 report cases of local anesthetic systemic toxicity (LAST) with lower doses of lidocaine, highlighting the importance of monitoring patients for signs of toxicity.

Factors Influencing Toxicity Risk

Several factors can influence the risk of toxicity, including:

• Dose and concentration of lidocaine
• Presence of epinephrine
• Site of injection
• Patient-related factors such as age, organ dysfunctions, and pregnancy
• Co-administration with other drugs

In this case, the patient received a relatively high dose of lidocaine without epinephrine, which may increase the risk of toxicity. However, the presence of epinephrine in the initial 3cc dose of 1% lidocaine may help reduce the risk of toxicity. Monitoring the patient for signs of toxicity, such as seizures, cardiac arrest, and altered mental status, is crucial 5, 6, 7.