Basic Principles of Analgesia

Published on 16/03/2015 by admin

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Last modified 22/04/2025

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Chapter 1 Basic Principles of Analgesia

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 performing an intraarticular injection. Unfortunately, ropivacaine is not routinely available in hospital emergency departments.
2. Epinephrine is a vasoconstrictor and is often added to the local anesthetic.

a. Epinephrine improves 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 not be used 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, toes.

Table 1-1 Local Anesthetics

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Types of Local Orthopaedic Analgesia

1. In general, three different techniques are used to achieve local analgesia:

a. Intra-articular injection
b. Hematoma block

(1) A hematoma block involves injection of anesthetic directly into the fracture hematoma.

c. Nerve block

(1) A nerve block may be of a specific nerve or of a group of nerves crossing a joint.
(2) For example, a “wrist block” involves nerve blocks of the radial, median, and ulnar nerves.

2. Regional analgesia also may be established via a Bier block.

a. A Bier block is accomplished via 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 be performed by anesthesiologists familiar with this technique.

Indications for Use

1. Intraarticular injection of 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. 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 intravascular injection.
3. Signs and symptoms of intoxication due to local anesthetics are described in Table 1-2.
4. Intraneural injection also should be avoided.

a. If a needle is inserted and immediate paresthesias are felt by the patient, it is likely that the needle is intraneural.
b. When it appears that the needle is intraneural, the needle should be withdrawn slightly until the paresthesias are resolved.

Table 1-2 Signs and Symptoms of Intoxication Due to Local Anesthetics

  Central Nervous System Cardiovascular System
Mild Lightheadedness, tingling of lips, tinnitus, tongue paresthesias Palpitations, tachycardia, hypertension, dry mouth
Moderate Speech and visual disturbances, confusion, twitching Arrhythmias, tachycardia, hypotension, cyanosis
Severe Seizures, flaccidity, coma Bradycardia and hypotension, ventricular fibrillation

Pearls

1. Sometimes it is useful to spray ethyl chloride (Cryogesic), a topical anesthetic, on the skin overlying the injection site immediately before inserting the needle.

a. Ethyl chloride should be applied immediately before injection because its effects last a very short time.
b. There is some debate regarding whether ethyl chloride has antimicrobial activity, rendering it acceptable for use on sterilized skin.

2. Palpation of landmarks before beginning the procedure is advisable. Do not hesitate to use a skin pen to mark landmarks or injection sites.
3. Different persons use different techniques for skin preparation.

a. We prefer using chlorhexidine, which is commercially available in 3-mL applicators.
b. Alcohol is an alternative skin preparation solution. However, more than one alcohol wipe should be used because one wipe typically contains insufficient alcohol to prepare the skin.

4. The practice of wearing one sterile glove on the nondominant arm is useful because it allows continued palpation of landmarks after the skin has been prepared. This practice also prevents confusion regarding which hand is sterile.

Basic Technique

The basic technique for all procedures is:

1. Prepare anesthetic
2. Palpate landmarks
3. Prepare skin with antiseptic solution
4. Numb skin with ethyl chloride (if desired)
5. Inject anesthetic
6. Place sterile bandage (if desired)

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Intra-articular Ankle Block Hematoma Block Calcaneal Skeletal Traction Basic Principles of Reduction Maneuvers Forearm, Wrist, and Hand Reduction Lower Extremity Splints and Casts