A nerve block is an injection used to numb a specific area of the body during medical procedures, treatments or surgeries. Local anesthetics like lidocaine or bupivacaine are injected near nerves to temporarily interrupt pain signals being sent to the brain. This creates numbness that can last from several hours to several days depending on the type of anesthetic used.
While nerve blocks can cause temporary loss of muscle control and sensation, they do not cause full paralysis. The effects are localized to a specific region of the body. With proper application, nerve blocks allow patients to remain awake and responsive while avoiding pain. They can be extremely helpful for procedures like surgery, wound treatment or fracture reductions.
What is a Nerve Block?
A nerve block is a form of regional anesthesia. It works by injecting an anesthetic next to a nerve or group of nerves to temporarily interrupt pain signal transmission. This results in numbness and loss of sensation in the area the nerve supplies.
There are many types of nerve blocks named after the area of the body being numbed:
- Brachial plexus block – shoulder, arm
- Axillary nerve block – shoulder, arm
- Femoral nerve block – anterior thigh
- Sciatic nerve block – posterior thigh, leg, foot
- Dental nerve block – teeth, gums, lower jaw
The anesthetic medication travels through the nerve sheath and blocks sodium channels essential for propagating the nerve impulse. This stops pain signals from being carried to the brain.
Nerve blocks involve injection of 5-30 mL of anesthetic, depending on location. Their effects start within 5-30 minutes and can last from 2-12 hours depending on type of anesthetic.
Does a Nerve Block Paralyze You?
While nerve blocks can cause some temporary weakness or paralysis, they do not lead to complete loss of motor function in an entire region. Their effects are limited to a specific nerve’s distribution.
When properly performed, a nerve block only affects sensory function – pain and touch perception. It does not fully paralyze an extremity or body area.
However, motor function can be partially affected:
- Reduced muscle control in the numb region
- Weakness of muscles supplied by the numbed nerve
- Partial paralysis of a limb if a major nerve is blocked
For example, a femoral nerve block in the leg may cause some quadriceps muscle weakness making it difficult to walk. But you still retain the ability to move your leg.
Complete paralysis only occurs with spinal or epidural anesthesia (like an epidural during childbirth). This affects both sensory and motor nerves in lower body regions. Nerve blocks alone will not lead to full paralysis.
Why Do Nerve Blocks Cause Weakness?
Nerve blocks partially affect motor function because many nerves carry both sensory and motor fibers:
- Sensory nerves transmit pain, temperature, touch to the brain
- Motor nerves stimulate muscles to contract
When a local anesthetic is injected around a mixed nerve, it can potentially block both types of fibers to some degree.
However, anesthesia is more likely to interfere with small pain-signaling sensory fibers first. Larger motor neurons are more difficult to block fully, so some motor signaling remains intact.
But as anesthesia diffuses, motor fibers can become partially blocked. This leads to some temporary weakness as muscle activation is impaired.
Differences from General Anesthesia
Paralysis occurs under general anesthesia because medications are delivered via IV or breathing tube to induce a controlled coma-like state. This creates both:
- Loss of consciousness
- Widespread muscle paralysis
Paralysis facilitates surgery by preventing movement and reflexes. But it requires support of breathing with a ventilator.
In contrast, nerve blocks only cause localized numbness and minor weakness around the injection site. Systemic absorption is low so they do not lead to unconsciousness or respiratory impairment.
Advantages of Nerve Blocks
Nerve blocks offer many benefits compared to general anesthesia:
- Patients remain awake and responsive
- Minimal effects on breathing or heart function
- Avoid risks of general anesthesia
- Use less medication than general anesthesia
- Post-op pain relief into recovery period
- Quick onset and offset of effects
They allow for surgeries and procedures to be done with IV sedation plus local nerve blocks. Patients can even remain awake with just numbing injections.
Regional anesthesia techniques like nerve blocks lead to fewer complications and faster recovery compared to general anesthesia. They have become increasingly popular for many types of surgery.
Risks and Side Effects
While extremely safe overall, nerve blocks do carry rare risks including:
- Bleeding, bruising or infection at injection site
- Local anesthetic toxicity if absorbed into bloodstream
- Nerve trauma or damage from needle
- Numbness lasting longer than expected
- Weakness lasting longer than expected
Serious complications like permanent nerve injury are very rare. When they do occur, it is usually related to the needle itself rather than the anesthetic.
Side effects are generally minimal. Temporary numbness and minor muscle weakness around injection site are expected.
Factors Affecting Paralysis Risk
Certain factors can increase the risk of more motor impairment with a nerve block:
- Blocking major nerve like femoral or sciatic
- Injecting near nerve origin vs small branches
- Using large anesthetic dose
- Injecting anesthetic too close to nerve
- Patient has underlying nerve damage
- Patient is very elderly or debilitated
Proper injection technique is vital to avoid extensive spread around motor nerves. Ultrasound guidance helps visualize local anesthetic location and spread.
Effects by Block Type
The degree of motor block can vary depending on the type of nerve block performed:
Brachial Plexus Block
- Numb shoulder, arm, hand
- May cause temporary wrist/hand weakness
- Rarely affects legs or lower body
Femoral Nerve Block
- Numb anterior thigh
- Partial paralysis of quadriceps muscles
- Weakness may make walking difficult
- Does not affect upper body or contralateral leg
Sciatic Nerve Block
- Numb posterior thigh, leg, foot
- Partial paralysis below knee possible
- Foot weakness or difficulty moving ankle/toes
- Does not affect arms or upper body
Monitoring for Excess Paralysis
To ensure a safe nerve block, physicians carefully monitor patients for any signs of excessive motor blockade including:
- Inability to move extremity
- Difficulty speaking or swallowing
- Muscle weakness far from injection site
- Shortness of breath
- Dizziness or fainting
- Confusion, agitation
This may indicate anesthetic being absorbed into circulation. Additional medication can be given to reverse it if needed.
Local vs Spinal/Epidural Anesthesia
Local anesthetics for nerve blocks should not be confused with spinal or epidural anesthesia, which cause more extensive paralysis:
| Nerve Block | Spinal or Epidural Anesthesia |
|---|---|
| Small local anesthetic dose | Large anesthetic dose |
| Limited distribution near injection site | Widespread anesthesia below injection level |
| Partial sensory loss in region | Complete sensory loss below level |
| Mild motor weakness | Extensive paralysis below level |
| Conscious sedation or awake | General anesthesia |
| No effect on respiration | Loss of core strength/breathing |
Epidural or spinal injections near the low back/spine carry higher paralysis risk as they block all nerves below injection point.
Summary
In summary, nerve blocks do not normally cause full paralysis:
- They only cause temporary numbness near injection site
- Some minor muscle weakness can occur
- Paralysis risk is very low with proper injection technique
- Only spinal or epidural anesthesia leads to extensive paralysis
- Nerve blocks allow patients to remain awake and responsive
When performed correctly by an experienced provider, nerve blocks provide safe and effective localized anesthesia during procedures and surgery. They spare patients the risks of general anesthesia while optimizing post-op pain control.
Conclusion
Nerve blocks are an extremely useful anesthesia technique that provide temporary numbness without causing complete paralysis. By precisely injecting local anesthetic next to nerves, they allow patients to avoid pain during procedures while remaining conscious.
While some minor muscle weakness can occur, nerve blocks do not paralyze an entire limb or body region when properly performed. Only extensive spinal or epidural anesthesia can lead to more widespread paralysis. Overall, nerve blocks provide targeted anesthesia that maximizes patient safety and comfort during surgery.