Overview
Review of Local Anesthetics
- 1.
The two most commonly used local anesthetics are lidocaine (Xylocaine) and bupivacaine (Marcaine, Sensorcaine) ( Table 1.1 ).
- a.
Recent studies have suggested that bupivacaine may be toxic to chondrocytes.
- b.
Ropivacaine (Naropin) has been found to be significantly less toxic to chondrocytes.
- c.
Whenever possible, ropivacaine should be used instead of bupivacaine when administering an intraarticular injection. Unfortunately, ropivacaine is not routinely available in hospital emergency departments.
Table 1.1
Local Anesthetics
Maximum Dosage Concentration
Maximum Dosage Amount
Time Until Effective
Analgesic Action Time
Suggested Use
Comments
Lidocaine
5 mg/kg without epinephrine
7 mg/kg with epinephrine
1% concentration without epinephrine
30-kg child: 15 mL
70-kg adult: 35 mL
2–5 min
45 min to 2 h
Short-acting analgesia for a 10–20-min procedure
Can cause vasodilation if not used with epinephrine
Bupivacaine
1.5 mg/kg without epinephrine
3 mg/kg with epinephrine
0.5% concentration without epinephrine
30-kg child: 9 mL
70-kg adult: 21 mL
10–30 min
3–6 h
Procedure >20 min
Avoid use in intraarticular injection if possible
Ropivacaine
3 mg/kg without epinephrine
Not used with epinephrine
0.75% concentration
30-kg child: 12 mL
70-kg adult: 28 mL
7–20 min
2–5 h
Procedure >20 min
safer for use in pediatric population than bupivacaine
Less chondrotoxic than bupivacaine; strong intrinsic vasoconstrictive properties
- a.
- 2.
Epinephrine is a vasoconstrictor and is often added to the local anesthetic.
- a.
Epinephrine improves the onset of action, decreases drug uptake, and prolongs action.
- b.
An epinephrine concentration of 1:200,000 is typically used.
- c.
Because it is a vasoconstrictor, epinephrine should be used with caution in the distal extremities. The following well-known mnemonic is often used to recall the areas where epinephrine should not be used: nose, hose (penis), digits, and toes.
- a.
Types of Local Orthopedic Analgesia
- 1.
In general, three different techniques are used to achieve local analgesia:
- a.
Intraarticular injection
- b.
Hematoma block
- (1)
A hematoma block involves injection of an anesthetic directly into the fracture hematoma.
- (1)
- c.
Nerve block
- (1)
A nerve block involves injection targeted at a specific nerve or a group of nerves crossing a joint.
- (2)
For example, a “wrist block” involves nerve blocks of the radial, median, and ulnar nerves.
- (1)
- a.
- 2.
Regional analgesia may also be established via a Bier block.
- a.
A Bier block is accomplished via an intravenous injection of a local anesthetic into an extremity with a double raised tourniquet to prevent systemic administration of the anesthetic.
- b.
Although it can be useful, a Bier block has the potential for catastrophic complications if the tourniquet fails; thus, this procedure should only be performed by anesthesiologists familiar with this technique.
- a.
Indications for Use
- 1.
An intraarticular injection of an anesthetic is most commonly used for reduction of ankle fractures.
- 2.
A hematoma block is commonly used for reduction of a variety of fractures and is most often used for a distal radius fracture. Hematoma blocks are performed when selective nerve blocks would not offer adequate analgesia.
- 3.
A nerve block is commonly used for reduction of hand fractures and treatment of soft tissue injuries of the hand.
Precautions
- 1.
An unintended intravascular injection of a local anesthetic has the potential to be life-threatening.
- 2.
When injecting an anesthetic, repeated aspiration should be performed to ensure that the needle tip is not intravascular. Use of this technique does not completely exclude the possibility of an intravascular injection.
- 3.
The signs and symptoms of intoxication due to local anesthetics are described in Table 1.2 .
Table 1.2Related posts:
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