lidocaine injection is safe near a vein? answer to fan question

Wed, 20 Aug 2025 18:08:47 +0000

So, to be concise and to the point, YES it is safe to inject lidocaine into the blood stream.

But, let’s dive deeper into this question as it is one of out most importance. Since I was a medical student it was driven into my head to never inject lidocaine into a vein or artery, I guess it ultimately could cause a severe or even deadly reaction.

So every time I am to inject lidocaine you are supposed to pull back on the plunger and check for any blood, and if you see any you are to redirect that the needle repeat the process and then you are safe to inject the lidocaine. I believe this is why Robin Hood asked the question here, and why it is important to know why this is really more of a modern day medical myth.

But first…what is Lidocaine?

Lidocaine is the most commonly used anesthetic for local infiltration. Local anesthetics reversibly block sodium channels within the nerve fibers, which prevents transmission of pain signals by disrupting depolarization of the nerve. Thus, infiltration of dilute solutions of local anesthetics near the nerve fibers produces relief of pain with less interruption in the sense of touch or temperature and without muscle paralysis in most children and adults.

Lidocaine is usually given as a 1 percent solution (10 mg/mL). If large volumes are needed or a smaller dose is desired, the clinician may use a 0.5 percent solution. Higher concentrations of lidocaine beyond 1 percent do not promote improved onset or duration of analgesia and may increase the risk of toxicity.

The dose of lidocaine should not exceed the following:

•Lidocaine WITHOUT epinephrine – 4 mg/kg (0.4 mL/kg of lidocaine 1 %, maximum total dose: 300 mg [30 mL of lidocaine 1 percent])

•Lidocaine WITH epinephrine – 7 mg/kg (0.7 mL/kg of lidocaine 1 percent, maximum total dose: 500 mg [50 mL of lidocaine 1 percent with epinephrine]).

For an added margin of safety, 80% of the maximum allowable dose should be used in children under eight years of age. In addition, because anesthetics in the amide class are metabolized by the liver and excreted by the kidneys, the total dose of lidocaine should be decreased by approximately 50 percent in elderly patients with severe liver or kidney disease.

The information just discussed is of OUTMOST importance and I recommend you memorize these numbers. 4-30 / 7-50 / 80-8

4 mg/kg lidocaine dose max or 30 mL total

7m/kg lido w/epi dose max, or 50 mL total

80% reduction in children under 8

The onset of anesthesia typically occurs within 2 – 5 minutes, and the duration of anesthesia varies from 30 minutes to two hours for plain lidocaine. Adding epinephrine will extend the duration of anesthesia one more hour, it will also decrease local bleeding and reduce systemic absorption of lidocaine (this is why you can inject more lidocaine when it is mixed with epinephrine).

It also is commonly used as an antiarrhythmic agent to depress ventricular arrhythmias.
In addition to direct nerve toxicity, systemic toxicity affecting the brain and/or cardiac muscle can lead to sudden and dramatic changes in the patient’s vital signs.

Finally, there are the side effects of a relative overdose at the site of injection, which can be quite dramatic. Examples include total spinal anesthesia or subdural injection of the drug that can cause severe hemodynamic compromise such as hypotension or bradycardia up to a cardiac and respiratory arrest.

Inadvertent intra-arterial injections may cause local anesthetic toxicity in the tissue beds supplied by that artery even well under the systemic toxic concentration. This complication is seen mostly with injections into the neck, causing central nervous system (CNS) symptoms often during the injection or shortly after that without progressing to the feared cardiac toxicity.

SO… So the routine aspiration while doing local infiltration of areas of the body away from major vessels is just not necessary. This recommendation does change when in close proximity to a large vessel like the groin or in the neck area.

Having said all this, lets consider hematoma blocks. A common procedure of anesthesia performed in the reduction of broken and displaced bones in the Emergency Department. In this technique a needle is inserted into the tissue and aimed towards the site of most swelling, presumably the site of hematoma (a large blood collection in the tissue). Once blood is aspirated then 8-10 mL are injected for anesthesia at that site. Now…based on what we have been discussing this should seem like a crazy thing to do! How do you know you are in the hematoma and not directly into a vein?

You don’t…

Remember that lidocaine is an antiarrhythmic medication, and when treating cardiac issues this medication is injected directly into the intravenous route. This of course is to be done under close cardiac monitoring.

Furthermore, Lidocaine is currently being use in the IV form in the treatment and management of acute renal colic pain.