What is Lidocaine Toxicity?
Lidocaine is a type of local anesthetic, a drug that temporarily stops feeling, movement, and automatic body functions when it’s applied or injected near nerves. It’s the most common local anesthetic used in nearly every medical field. Lidocaine can also be used to control irregular heart rhythms. Some doctors use lidocaine to enhance the effects of general anesthesia during surgery, as it can lower the amount of inhaled anesthetics required by up to 40%, and help with pain relief after surgery. Lidocaine falls under the amide group of local anesthetics, which are usually well-accepted by the body with allergy occurring only rarely. The body breaks down these types of anesthetics in the liver.
Lidocaine can be used in multiple ways including injection, inhalation, or as a cream or gel to numb the skin. It’s generally safe until it reaches high levels in the blood. Because you can apply it in different ways, doctors need to carefully keep track of the total dosage given to avoid potential harmful effects. The total dose of other local anesthetics the patient might have been given also needs to be taken into account due to cumulative effects. Lidocaine’s harmful effects are determined not only by the total dose, generally 4.5 mg/kg of body weight, but also by its absorption rate. Absorption can be slowed, and therefore safer, by reducing blood flow to the injection site with vasoconstrictors like epinephrine—allowing the toxic dose to be increased to 7 mg/kg.
Sometimes Lidocaine can cause injury to muscles and nerves at the injection site. There have been cases where spinal anesthetics using a high concentration of lidocaine led to temporary nerve symptoms. This has prompted either reducing the strength of the dose or switching to a different drug. Besides nerve damage, harmful effects involving the brain or heart muscle can cause sudden significant changes in a patient’s vital signs. Overdose at the application site can cause alarming reactions like total numbness of the spinal cord or the drug unintentionally entering the layer between the spinal cord and its protective sheath, which could then cause severe decreases in blood pressure or heart rate, or even cardiac and respiratory arrest.
What Causes Lidocaine Toxicity?
Toxic effects on local nerves and muscles may occur due to applying high amounts of drugs for a long period of time, or because of the preservatives present in local anesthetic solutions.
An anesthetic, like lidocaine, works to numb a specific part of your body. However, lidocaine can cause problems if it enters the bloodstream in large doses. This can happen because of the rate at which the drug is absorbed into your body, which is quicker in some areas than others. It’s fastest in the windpipe, then the area between the ribs, lower back area, uterus during childbirth, anesthetic for labor, area near the shoulder and nerves in the arm, and finally the skin.
Injecting large amounts of the anesthetic into a big muscle—for instance, when it’s used to block pain in the lower back or sciatic nerve (the major nerve running down the back of each leg)—can result in toxic levels of lidocaine in the body. However, spinal anesthetics, used in some surgical procedures, are safe as they have a very low volume and won’t cause lidocaine toxicity.
An accidental injection into an artery might lead to toxic symptoms in the area that artery supplies, even at doses that are not usually toxic. This mainly happens when an injection is given in the neck, leading to symptoms affecting the brain and nerves often during or just after the injection, without causing any heart-related complications.
Risk Factors and Frequency for Lidocaine Toxicity
Lidocaine toxicity, which can affect anyone regardless of gender, tends to be more common in people at the very young or old age and in pregnant women. Severe cases of this issue, which might include seizures or cardiac arrest, occur in about 1 out of every 10,000 people who get epidural and up to 1 in 2,000 people who have the peripheral nerve blocks, though this can vary depending on the specific type of block used. Those who are under sedation are at a higher risk.
- Lidocaine toxicity affects all genders equally.
- People at extreme ages and pregnant women are more likely to experience lidocaine toxicity.
- Severe lidocaine toxicity happens in approximately 1 in 10,000 cases of epidurals and up to 1 in 2,000 cases of peripheral nerve blocks.
- The risk increases for patients under sedation.
Signs and Symptoms of Lidocaine Toxicity
Overdosing on local anesthetics first affects the central nervous system (CNS). This can be recognized by early symptoms such as numbness around the mouth, a pins-and-needles feeling in the tongue, and dizziness. People may also report unusual ear noises and blurred vision. Other signs might be excitatory symptoms, going from restlessness or nervousness up to muscle twitches and seizures. In severe cases, large overdoses can cause loss of consciousness or even coma. Decreased blood pressure and slowed heart rate are also side-effects that can occur particularly with nerve blocks near the CNS.
Severe damage to the cardiovascular system typically requires a higher concentration of lactic acid in the blood. Accidental injection of local anesthetics into the bloodstream can have serious consequences including low blood pressure, atrioventricular heart block, idioventricular rhythms, and potentially fatal arrhythmias such as fast or chaotic heartbeats. These symptoms usually appear during general anesthesia and can indicate anesthetic toxicity.
Testing for Lidocaine Toxicity
Diagnosing medical conditions often depends on assessing various factors. For example, if a doctor is trying to understand the effects of a lidocaine injection, they’ll look at when the injection was given, the dosage, and where it was injected. This is particularly important because even small doses accidentally injected into an artery leading to the brain can cause symptoms that affect your central nervous system (which includes your brain and spinal cord).
If a patient experiences pain, which might indicate a condition called Transient Neurologic Symptoms (TNS), the doctor will consider the concentration of the lidocaine and where it was injected. Imaging techniques, such as a computed tomography (CT) scan or magnetic resonance imaging (MRI), won’t confirm TNS. However, these scans can help exclude other causes. For instance, something might be pressing on the structures within your spinal canal, causing severe pain after what’s called a neuraxial blockade (a form of pain blocking treatment). This would be a serious issue needing immediate medical attention, possibly even surgery.
Sometimes, the doctor might want to check lidocaine levels in your blood. However, getting these results can take quite a bit of time which means they may not significantly impact immediate decisions about your treatment.
Treatment Options for Lidocaine Toxicity
If you experience a systemic allergic reaction to local anesthesia — meaning the drug spreads throughout your body and causes an unwanted reaction — doctors can manage it by helping your body be less sensitive to seizures. They can achieve this by using certain medications such as benzodiazepines, barbiturates, or propofol. They may also give you a lot of oxygen to reduce the amount of blood that goes to your brain.
Another way to treat the reaction to local anesthesia is by lowering the amount of the anesthetic drug in the blood. This is done by introducing lipid emulsions (fats) into your body. Because the anesthetics are highly attracted to fat, they bind to the lipid emulsions, which results in the lower anesthetic levels in the blood.
Below is what the American Society of Regional Anesthesia and Pain Medicine suggests if you experience an adverse reaction to local anesthesia:
“Ask for Help Right Away”: Even small signs of issues may progress to severe problems affecting the heart and lungs. It is critical to act quickly, like bringing emergency carts and getting the lipid emulsion ready.
“Initial Focus”: Managing the airway by providing a lot of oxygen, and addressing any potential seizures. Benzodiazepines can be useful for dealing with seizures. However, propofol is not recommended if there are signs of heart instability.
“Alert the Closest Facility with Cardiopulmonary Bypass Capability”: This is a procedure that can temporarily take over the function of the heart and lungs.
“Manage Heart Rhythm Problems”: They may need to adjust the drugs used in both Basic and Advanced Cardiac Life Support, which is the emergency medical response to someone whose heart or breathing has stopped. Certain medications like calcium channel blockers, vasopressin, beta-blockers, and local anesthetics should be avoided. The amount of individual epinephrine doses should be less than 1 mcg/kg.
Lipid Emulsion Therapy: Fat emulsions can be introduced intravenously, over a couple of minutes, followed by a continuous infusion. If blood pressure remains low, they can double the infusion rate. The infusion should continue for at least 10 minutes after your circulation stabilizes.
In some cases, you might need a procedure known as cardiopulmonary bypass. Studies have shown that even after prolonged resuscitation — the act of reviving someone from unconsciousness or apparent death — the outcomes can be successful, thanks to recent advances in medical science. Remember, these guidelines are for medical professionals to follow and this information is for you to understand what your treatment may look like.
What else can Lidocaine Toxicity be?
If someone experiences symptoms after getting a large dose of lidocaine, the timing of when these symptoms started can likely point to the cause. Nonetheless, if the person also has conditions like a seizure disorder or is experiencing panic attacks that can cause over-breathing (hyperventilation), these could cause confusion in identifying the cause of the symptoms.
When a patient complains of symptoms like pain radiating from the spine after an injection of lidocaine, the first step is to rule out other potential causes. One of these could be a collection of blood outside of the blood vessels (a hematoma) which may be pressing against parts in the spinal canal. This condition often needs quick surgery to relieve the pressure. In rare cases, these symptoms could be due to an infection in the space around the spine and spinal cord (epidural abscess), but that is not likely if the symptoms occur just after a procedure that involves inserting a needle into the spine’s central canal. However, it’s important to note that most such abscesses happen spontaneously and could possibly occur at the same time as the injection.
What to expect with Lidocaine Toxicity
The outlook for lidocaine toxicity, or basically the harmful side effects of a drug called lidocaine, heavily relies on where these side effects show up in the body. Toxicity in the central nervous system (CNS), which includes the brain and spinal cord, can either resolve itself or be quite treatable with medications known as benzodiazepines. The outlook for this is good and usually doesn’t result in any long-term effects or the need for further brain or nerve tests.
On the other hand, if the toxicity affects the heart, it may require prolonged resuscitation. This is the process of trying to restart the heart or make it work effectively again. Despite this, most patients have a good outlook once the heart starts working again on its own.
Possible Complications When Diagnosed with Lidocaine Toxicity
The complications related to Lidocaine toxicity can include the following:
- Seizures
- Coma
- Low blood pressure (Hypotension)
- Irregular heart rhythm (Atrioventricular heart block)
- Unusual heart rhythms (Idioventricular rhythms)
- Rapid heart rate (Ventricular tachycardia) and chaotic heartbeats (fibrillation)
- Heart failure leading to unconsciousness (Cardiovascular collapse)
- Potential death
Preventing Lidocaine Toxicity
Doctors should use a technique called ultrasound guidance when performing peripheral nerve blocks (a procedure to control pain) if they deem it necessary. This approach can help lower the risk of accidentally injecting the medicine into the patient’s bloodstream, which can prevent potential problems.
