A nerve block is a medical procedure involving the injection of anesthetic or anti-inflammatory medication near a targeted nerve or group of nerves. The primary goal is to temporarily interrupt or dampen nerve signals for pain management or regional anesthesia during surgery. While nerve blocks are generally considered safe, they carry potential side effects ranging from minor and expected to severe and rare. Understanding these potential outcomes helps patients prepare for the procedure and monitor their recovery.
Temporary and Common Side Effects
Following a nerve block, patients commonly experience minor, localized effects as the body reacts to the needle placement and medication. The most frequent complaint is pain, soreness, or a feeling of fullness at the injection site, which typically resolves within a few hours to a couple of days. This localized discomfort is a normal response to the tissue trauma caused by the needle insertion.
Bruising or a small amount of bleeding near the injection site is also common, especially in areas with many small blood vessels. These superficial effects are self-limiting and fade on their own. Temporary localized numbness or muscle weakness may persist slightly longer than the anesthetic’s intended duration, often dissipating completely within a day.
Some individuals may experience a temporary change in heart rate or blood pressure immediately following the injection, sometimes related to anxiety. Other mild, short-lived sensations can include tingling, warmth, or muscle spasms in the affected limb. These minor side effects are not indicative of a serious problem.
Major Risks and Severe Complications
While the majority of nerve blocks proceed without serious incident, a small chance exists for complications requiring immediate medical intervention or prolonged recovery.
Nerve Injury and Hematoma
One of the most significant concerns is nerve injury, which can range from temporary irritation to permanent damage. The needle may inadvertently contact the nerve, causing a brief electric shock sensation. Damage can occur if the needle is not immediately repositioned before the medication is injected. Permanent nerve damage, though extremely rare, can manifest as persistent numbness, tingling, prolonged weakness, or chronic pain. Most nerve injuries are temporary, resolving within days or weeks, with more significant irritation often recovering fully within three months.
Another serious risk is the development of a significant collection of blood, known as a hematoma, which forms if a blood vessel is punctured. A large hematoma can put external pressure on the nerve, potentially leading to pain or nerve dysfunction.
Infection and Systemic Toxicity
Infection is a risk with any injection procedure, ranging from a localized skin infection to a more serious deep-seated infection, especially in spinal or epidural blocks. Strict sterile technique is employed to minimize this risk.
The most alarming complication is Local Anesthetic Systemic Toxicity (LAST), a rare but life-threatening event that occurs when the local anesthetic medication enters the bloodstream in high concentrations.
Initial signs of LAST often involve the central nervous system, beginning with a metallic taste in the mouth, ringing in the ears (tinnitus), numbness around the mouth, or a feeling of lightheadedness. If toxicity progresses, it can lead to more severe neurological symptoms such as confusion, agitation, slurred speech, or seizures. Cardiovascular effects follow and include changes in heart rate, low blood pressure, and in the most severe cases, cardiac arrest.
Furthermore, for blocks performed near the chest, such as intercostal blocks, there is a distinct, though rare, risk of pneumothorax (collapsed lung) caused by the needle puncturing the lung membrane.
How Risk Varies and When to Contact a Doctor
The likelihood of experiencing side effects depends on several factors related to the patient’s health, the medication used, and the specific location of the injection. Patients with underlying health conditions such as pre-existing neuropathy (like from diabetes), active infections, or a history of heart disease may face a higher risk of complications. Those taking blood thinners also have an increased risk of bleeding and hematoma formation.
The site of the nerve block significantly influences the risk profile. Blocks requiring a larger volume of local anesthetic, such as peripheral nerve blocks, inherently carry an elevated risk of LAST compared to smaller injections. The choice and concentration of the local anesthetic also play a role. Procedures performed with ultrasound or fluoroscopic guidance generally lower the risk of complications by allowing the provider to visualize the target nerve and surrounding structures.
Knowing when a side effect crosses the line from minor to serious is essential for patient safety. Specific warning signs require immediate contact with the healthcare provider or emergency services.
These red flags include:
- The onset of a fever or chills after the procedure, which can signal an infection.
- Symptoms of LAST, such as a metallic taste, ringing in the ears, sudden agitation, or seizures.
- Any new, severe headache.
- Unexpected changes in bowel or bladder function.
- Persistent numbness and weakness lasting more than 48 hours that was not part of the expected recovery.