The LSUHSC New Orleans Emergency Medicine Interest Group Presents The Student Procedure Manual

Emergency Department Anesthesia

(Infiltration and Neuro Blocks)

by Chris Gaffga

Contraindications

1. Previous reaction to local anesthetic. Ask questions
   about this to determine whether the reaction was a true allergic reaction, a vasovagal response (bradycardia and syncope without anaphylaxis or hives), or a problem with neuritis after a nerve block (neurogenic pain that usually spontaneously resolves).
   
2. Liver disease, heart disease- R/O amide-based anesthetics (i.e. do not use Lidocaine, Mepivacaine, Prilocaine, Bupicacine, Etidocaine)
   
3. Previous use of MAO inhibitors- R/O use of epinephrine
   
4. Most anesthetics will reduce healing in wounds. Use carefully with slow healing wounds like leg ulcers

Use of Epinephrine
Epinephrine will:

• Increase anesthetic delivery to the area where you inject
  
• Slow diffusion through tissues. This results from its pH and vasoconstrictive ability, and prevents diffusion away from injection site.
  
• Increase the maximum dose of anesthetic you can safely use
  
• Increase the pain on injection (Epi. is acidic)
  
• Cut off circulation if injected into areas with end artery blood flow (penis, digit, tip of the nose, earlobe)
  
• Reduces tensile strength of tissues during initial
  healing, but this is not usually a major consideration

*Epinephrine will often come premixed in a Lidocaine or other cartridge. Know what you are giving the patient, especially if you are working near an extremity.

*Local vasoconstriction can result from accidental intravascular injection. As you inject, watch for blanching. Effect can be reversed by administering 0.5 - 5.0 mg phentolamine. Other effects of intravascular administration of lidocaine include ringing in the ears and a strange taste in the patient's mouth.

Choice of Anesthetic

These are some commonly used anesthetics for wound repair. For dosage information on other drugs, consult a pharmacology manual.

Commonly Used Anesthetics

Agent	Lidocaine	Prilocaine	Bupivacaine
Conc. (for infiltration)	0.5 - 1.0%	0.5 - 1.0%	0.25%
Adult dose	300mg (500mg w/ epi.)	500mg (600mg w/ epi.)	175mg (225 w/ epi.)
Pediatric dose	4.5mg/kg (7mg/kg w/ epi.)	7mg/kg (9mg/kg w/ epi.)	not for peds. use
Duration	1-2 hours	15-45 mins	4-8 hours

Recommendations

• Bupivacaine Use this if it is important to block pain for LONG period of time (ie. abscess drainage).
  
• Lidocaine with epinephrine Use this for a wound that is still bleeding.
  
• Sodium bicarbonate Adding a solution of sodium bicarbonate raises the pH, and makes injection less painful for the patient. The higher pH also means better diffusion through tissue, and faster onset of anesthesia. (see Wound Repair section for tips on using sodium bicarbonate)
  
• Sodium bicarbonate must be added at the bedside in a ratio of 1 cc:10cc NAHCO3:xylocaine, the medication breaks down if stored in this fashion.
  
• Warming the vials - warm anesthetic is less painful. Keep vials in your pants pocket to keep them warm.
  
• You will see a progression after injecting local anesthetic. Pain fibers are the first to be anesthetized by an anesthetic because they lack a thick myelin coat. Moderately myelinized pressure and light touch are second to be anesthetized. Motor fibers require high doses to cease conduction.

Complications of Local Anesthetic

*Be prepared to monitor and treat the following.

• Blanching of nearby skin - Indicates local toxicity.
  • Stop injection and evaluate extent of vasoconstriction
    
  • Vasoconstriction (due to epinephrine) can continue to the point of ischemia and necrosis
    
  • Treat with 0.5 - 5.0 mg phentolarnine.
• Urticaria (hives), edema, anaphylaxis - Allergic reactions
  • Stop injection and monitor patient.
  • Question again about history of allergies.
    
  • If patient shows signs of a severe reaction, act to maintain airway.
• Syncope without edema or other signs of anaphylaxis
  • Vasovagal response.
    
  • Usually result of increased parasympathetic tone at
    the sight of a needle, blood or due to pain
    
  • Monitor heart rate and blood pressure.
• Arterial Puncture- darkening around wound or blood at injection site - hitting artery (hematoma formation)
  • Use a high gauge needle to minimize bleeding
    
  • Apply direct pressure
• Systemic Toxicity
  • Systemic toxicity is the result of anesthetic getting into the systemic circulation and causing CNS deficits (convulsions, central respiratory depression) and causing cardiovascular depression (bradycardia and hypotension).
    
  • Presents an acute crisis possibly requiring ventilation and anti-convulsive therapy.
    
  • Uncommon (0.1-0.4% of local procedures)
    
  • The result of intravascular injections
    
  • Actually more common with overuse of topical anesthetics absorbed through the skin.
    
  • Some drugs are safer (absorbed into blood slowly, eliminated quickly)

Safer-> Etidocaine >Bupivacaine >Lidocaine ->Less safe

*Watch for the following signs/symptoms as you give the injection. If you see any of the following, ask the patient to breathe rapidly to blow off CO2:

*Prepare for further treatment of respiratory depression that may follow (See below).

General Guidelines for Treatment of Systemic Toxicity

• Respiratory Depression
  • Ask the patient (if still conscious) to breathe rapidly to blow off CO2
    
  • This will prevent respiratory acidosis and raise the seizure threshold.
    
  • Patients who show acute respiratory depression may have to be intubated and an IV should be started for administration of meds.
    
  • The priority for these patients is a rapid rate of ventilation.
• Seizures
  • May interfere with ventilation, increase hypoxia, and induce lactic acidosis.
    
  • After maintaining the airway, treatments include low dose lorezapam (0.5-2.0 mg) or an appropriate dose of thiopental.
    
  • Continued seizures may require paralytic agent to avoid lactic acidosis.
• Cardiovascular Complications
  • Hypotension and bradycardia are treated with fluids, leg elevation, and alpha and beta agonists if needed.

Topical Anesthetics

• Topical jelly of lidocaine (2%) is most commonly used
  • Indicated for inflamed mucous membranes, pharyngitis, and dental pain
    
  • Duration 30-60 minutes (ok for most procedures)
    
  • Dosing interval of 3 hours (wait 3 hours to readminister)
    
  • Use limited amount (200-300 mg dosage) because transdermal absorption can cause toxicity.
    
  • Must instruct patient to follow dosing, ad lib use can be toxic
    
  • Base children dosages on weight in kg (see table above for injectable lidocaine: remember jelly is 2%)
    
  • Do not give oral topicals to infants, they cannot expectorate and toxicity builds up easily
    
  • Recommend no food for one hour post dosing because of risk of aspiration
• Benzocaine (Cetacaine, Americaine, Huricaine, Anbesol)
  • Shorter duration of anesthetic
    
  • Is not absorbed across mucosal very low systemic toxicity
    
  • Breaks in skin can allow more to pass through
    
  • Used to prep laryngoscopes, endotracheal tubes, catheters
    
  • Can be used topically to numb mucous membrane prior to nerve block
• TAC - (Solution of 0.5%, 1:2000 adrenaline, 11.8% cocaine)
  • Saturate gauze and apply to the laceration for 10 minutes
• LET - (Solution of 4% lidocaine, 0. 1 % epinephrine, and 0.5% tetracaine)
  • Saturate gauze and apply to the laceration for 10 minutes

General Procedure for Wound Infiltration

1. Use 10 mL syringe, 27 gauge needle
   
2. To access the subcutaneous tissue place the needle in the wound edge if possible.
   • Less painful than piercing the skin and no increased risk of contamination
     
   • If wound is grossly contaminated, do not do this. Irrigation may be performed first.
3. Once in the skin aspirate the syringe
   • Ensure that you are not in vascular bed.
     
   • If in a vascular area, check in this manner several times during the injection
4. Placement of the drug
   • Should be subderrnal to reduce pain
     
   • You can place needle deep and inject as you withdraw needle
5. Numbing over a large field
   • Don't withdraw needle entirely
     
   • Redirect needle and re-inject in another area
     
   • Minimizes number of punctures (less septic and painful)

See Basic Suturing for more information on wound infiltration

General Procedure for Nerve Block

1. Use 25 or 27 gauge, short beveled needle with 10 mL
   syringe for digital or distal blocks.
   
2. Use 23 or 25 gauge, short beveled needle with 30 mL
   Syringe for proximal blocks.

Note differences vs. infiltration procedure.

• Dosage is given as a range specific to the type of block, usually lower than the dose for infiltration. Use the minimum within the stated range, unless you are not sure that you injected near the nerve, in which case use a higher dose.
  
• Onset is 2-15 minutes. You have to wait 30 minutes before you decide that the block did not work.
  
• Choice of anesthetic - In a block you are often dealing with more extensive injury; you may select a longer acting anesthetic (ie. Bupivacaine).
  
• You have to locate a nerve - remember there is overlap between peripheral nerves, and variability between individuals.

Procedure

1. Swab skin with alcohol wipe
   
2. Locate and identify landmarks, including nearby arteries
   
3. Insert the needle parallel to the nerve fibers
   
4. Nerves can be located exactly by eliciting paresthesia (a radiating "jolt" when the nerve is touched)
   
5. After getting paresthesia, pull the needle out I mm and inject anesthetic.
   
6. If you don't pull far enough out you can inject into the nerve sheath; the extra volume injected inside the sheath of a small nerve can compress the nerve and cut off its blood supply. Injection into the sheath will be a VERY sharp, radiating pain.
   
7. Nerve block depends on getting very close to small nerves. If you are not sure that you got the "jolt" of paresthesia use a larger amount of anesthetic because it has to diffuse through tissue. Do not exceed the maximum in the dose range.
   
8. Wait 30 minutes before deciding the block was not successful

Complications

• All of the complications of an infiltration procedure apply here.
  
• In addition, excessive trauma to a nerve may cause neuritis - local neural inflammation.
  
• The patient will have subsequent pain with possible motor and sensory disruption.
  
• Most often neuritis resolves spontaneously.