How Well Do You Know Your Injectable Anesthetics?

A significant part of my job as a nurse practitioner in the emergency department is performing procedures. At any given time during my shift, you’re likely to find me gathering supplies for an I&D, placing a few sutures to close a laceration, reducing a dislocation, or removing a pesky foreign body from the bottom of a patient’s foot. Needless to say, I use a lot of injectable anesthetics. 

Lidocaine is the go-to when it comes to local anesthesia for minor in-office and emergency department procedures, but how much do you really know about this medication? When should you consider using other anesthetic agents? And, how much lidocaine is too much? Here’s a quick refresher of your options when it comes to procedural pain control and their considerations. 

Types of Injectable Anesthetics

Lidocaine (Xylocaine) 1 or 2%

Onset of Action: Less than 2 minutes

Duration: 1.5 to 2 hours

Maximum Dose: 4mg/kg, max dose 280mg

Prilocaine (Citanest) 1%

Onset of Action: Less than 2 minutes

Duration: Greater than 1 hour

Maximum Dose: 7mg/kg, max dose 500mg

Bupivacaine (Marcaine) 0.25%

Onset of Action: 5 minutes

Duration: 2 to 4 hours

Maximum Dose: 2.5 mg/kg, max dose 175mg

Lidocaine (Xylocaine) with Epinephrine 1 or 2%

Onset of Action: Less than 2 minutes

Duration: 2 to 6 hours

Maximum Dose: 7mg/kg, max dose 500mg

Helpful Injection Techniques

Naturally, pain is a common concern among patients on the receiving end of injectable anesthetics. There are a few steps nurse practitioners can use to reduce pain at the injection site. First, inject the appropriate volume of medication. In most cases, 1 to 2 mL of local anesthetic are sufficient. Excess volume of anesthetic may increase pain without providing additional benefit.

Second, inject slowly. Subcutaneous tissue expands during the injection process and studies show that slow injection rates decrease pain associated with the process. Selecting a fine needle also helps. You may even use a diabetic syringe with a 30 gauge needle to inject a small amount of anesthetic before introducing a larger 27 or 25 gauge needle.

Finally, select your injection site appropriately. For laceration repair, inject through exposed wound edges directly into the subcutaneous tissue. Studies show this results in less painful anesthetic injection. Know your anatomy and where possible, block nerves to avoid the need for a large amount of anesthetic.

Complications

Allergic Reaction

Few individuals experience allergy to injectable anesthetics. In most cases, allergic reaction is related to preservatives in the medication. Single dose vials contain fewer preservatives and should be used in patients with a history of allergic reaction to injectable anesthetic. 

Local Anesthetic Toxicity

In rare cases, local anesthetic agents can have serious adverse effects. Most commonly, these include CNS and cardiac effects. Symptoms appear about one to five minutes after injection. CNS symptoms may include metallic taste, lightheadedness, dizziness, visual or auditory disturbances, disorientation, muscle twitching, convulsions and respiratory depression and arrest. Cardiac symptoms may include chest pain, shortness of breath, palpitations, diaphoresis, hypotension and syncope. Treatment of complications is mainly supportive. If appropriate supportive therapy is initiated, patients recover well without long-term sequelae. 

Considerations for Kids

As with many medications, children and infants metabolize injectable anesthetics differently than adults. Local anesthetics cannot be metabolized as quickly in the liver in young patients prolonging half-life. Given these considerations, in infants and toddlers, the maximum dose of local anesthetic in mg/kg should be adjusted to one-half that of older children and adults.

Although as nurse practitioners we use local anesthetics often, these medications much be used with care.  

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