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Chapter 3 Local Anesthesia
Anesthesiology Chapter 3 Local Anesthesia Content. Local anesthesia refers to applying local anesthetic to a certain part of the body while the patient is conscious, so that the sensory nerve conduction function of a certain part of the body is temporarily blocked, while the motor nerve conduction is maintained. Intact or blocked to varying degrees at the same time.
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Chapter 3 Local Anesthesia
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Chapter 3 Local Anesthesia
local anesthetic
Local anesthetics (local anesthetics, LA): are a class of drugs that can temporarily and reversibly block the occurrence and transmission of nerve impulses, causing loss of sensation and/or movement in the relevant nerve innervation parts.
QSAR
Lipophilic and hydrophilic (strong)
The carbon chain is increased, the lipophilicity is higher, the anesthetic effect is stronger, the duration is longer, and the toxicity is also increased.
Dissociation constant (onset time)
The larger the pKa, the fewer the base parts and the more ionic parts, the less likely it is for the local anesthetic to penetrate the nerve sheath and membrane, and the longer the onset of effect will be.
Protein binding rate (timeliness)
The higher the binding rate, the longer the action time
The lipid solubility, intensity and duration of action of local anesthetics are also positively related to their protein binding rate
drug concentration
The greater the concentration of local anesthetic, the deeper and more complete the nerve block will be.
Classification
Ester local anesthetics
Procaine, chloroprocaine, tetracaine
Amide local anesthetics
lidocaine, bupivacaine, mepivacaine, ropivacaine
Mechanism of action of local anesthetics
Local anesthetics can block voltage-gated sodium channels on nerve cell membranes to inhibit sodium influx, prevent the generation of action potentials and the conduction of nerve impulses, and produce local anesthesia.
Clinical pharmacology of local anesthetics
Effect on body organs
Central Nervous System
Low concentrations have inhibitory, analgesic, and anticonvulsant effects, while high concentrations can induce convulsions.
Cardiovascular System
Reduce myocardial excitability, slow repolarization, and prolong refractory period
respiratory system
Local anesthetics can relax bronchial smooth muscles, but for patients with airway hypersensitivity (asthma), lidocaine aerosol may induce bronchospasm due to direct stimulation.
The cardiovascular system tolerates local anesthetics better than the central nervous system, and toxic reactions occur earlier in the central nervous system.
Factors affecting the action of local anesthetics
Medication method
Dosage of local anesthetic
Dosage → effective speed, block depth and duration
Capacity → blocking range
concentration → retardation depth
Local anesthetic injection site
Add other medications
Adding epinephrine to extend the block time and prevent local anesthetic poisoning
patient factors
patient's age
patient’s vital organ function
pregnancy
Local anesthetic sensitivity↑
rapid drug resistance
Mixed application of local anesthetics (complementary advantages)
internal environment state
Local anesthetics are less effective in patients with acidosis
Toxicity and allergic reactions to local anesthetics
toxic reactions
central nervous system toxicity
Recognize the warning signs
Cardiovascular system toxicity
poor prognosis
Bupivacaine cardiotoxicity
①The ratio of the dose that produces irreversible cardiovascular collapse to the dose that produces convulsions is low
②Can cause ventricular arrhythmias and fatal ventricular fibrillation
③ Pregnant women are more sensitive to its cardiotoxicity
④Difficulty in resuscitating cardiac arrest caused by
⑤Acidosis and hypoxia can significantly enhance cardiotoxicity
Common causes of systemic toxic reactions include
The dose or concentration of local anesthetic is too high
Injecting medication into blood vessels by mistake
Patient's physical weakness, reduced tolerance, etc.
treat
Stop injecting local anesthetic and give pure oxygen
Pay attention to protect the patient when convulsions or convulsions occur to avoid accidental injury
medical treatement
Preferred benzodiazepines (midazolam), or propofol or thiopental
Taking intermediate and advanced life support steps in cardiopulmonary resuscitation
When using epinephrine, give a small initial dose (1ug/kg); use of vasopressors is not recommended, and avoid using calcium channel blockers and beta-blockers.
Amiodarone is recommended when ventricular arrhythmias occur
allergic reaction
Allergic reactions to ester local anesthetics are more common
Local anesthesia
Local anesthesia
Temporary and completely reversible, basically no tissue damage
Classification
Local anesthesia in a narrow sense includes topical anesthesia, local infiltration anesthesia, regional block anesthesia, intravenous local anesthesia and nerve block anesthesia.
Generalized local anesthesia also includes neuraxial anesthesia (subarachnoid block, epidural block and sacral canal block)
topical anesthesia
The local anesthetic with strong penetration is brought into contact with the local mucosal surface, allowing it to penetrate the mucosa and block the superficial nerve endings under the mucosa to produce a painless state.
Suitable for superficial surgery or endoscopic examination of eyes, nose, throat, trachea, urethra, rectum, etc.
Tetracaine and lidocaine are more commonly used
local infiltration anesthesia
Inject local anesthetic into the tissue in the surgical area in layers along the surgical incision to block the nerve endings in the tissue.
It refers to an anesthesia method that uses local anesthetics to temporarily block nerve conduction in a certain area of the body while the patient is conscious.
Suitable for minor surface surgeries, invasive examinations and treatments
Application features
Injecting drugs layer by layer
There should be a little volume to form a tension infiltration in the tissue.
Concomitant use of epinephrine can prolong the action of local anesthetics
area block
Inject local anesthetic around the periphery and base of the surgical area to temporarily block nerve fiber conduction entering the surgical area.
The advantage is that it avoids puncture of diseased tissue and is used for lumpectomy.
peripheral nerve block anesthesia
concept
Peripheral nerve block (PNB) refers to a method of injecting local anesthetic into the vicinity of the peripheral nerve trunk (plexus) to temporarily block the conduction of nerve impulses, making the area innervated by the nerve painless.
nerve localization method
Allopathic localization
Neuroelectric stimulator
Ultrasound direct vision positioning
blood vessels → black
Bones and ligaments→white
cervical plexus block
Anatomy
The cervical plexus is composed of cervical 1 to 4 spinal nerves (C1 to C4). The superficial plexus is at the midpoint of the posterior edge of the sternocleidomastoid muscle. The deep plexus mainly innervates the deep tissues of the front and side of the neck.
blocking method
deep cervical plexus block
anterior cervical block
Traditional three-point method
The transverse process of C2 cervical vertebra can be touched 1.5cm below the tip of the mastoid process, and every 1.5cm downward are C3 and C4 (C4 is often located at the midpoint of the sternocleidomastoid muscle). Each point from C2 to C4 is punctured.
C4 transverse process one point block method
Only inject 10 to 12 ml of local anesthetic into the C4 transverse process.
complication
Phrenic nerve block (most common complication)
recurrent laryngeal nerve block
Horner’s syndrome
cervical sympathetic nerve block
General spinal and epidural anesthesia
Local anesthetic toxic reactions, damage to the vertebral artery causing bleeding and hematoma
brachial plexus block
Anatomy
The brachial plexus is composed of the anterior branches of cervical 5 to 8 (C5 to C8) and thoracic 1 (T1) spinal nerves. It forms the upper, middle, and lower trunks in the interscalene groove of the anterior middle scalene muscle. Each trunk is divided into anterior and posterior branches at the middle part of the clavicle. The two strands have 6 strands in total, and then form 3 bundles: lateral bundle, medial bundle, and posterior bundle. Each bundle branches into 5 main nerve terminal branches at the coracoid process plane.
5 roots - 3 stems - 6 strands - 3 bundles - 5 terminal branches
blocking method
interscalene brachial plexus block
The interscalene groove is a triangle formed by the anterior and middle scalene muscles and the omohyoid muscle.
Puncture point: draw a horizontal line from the cricoid cartilage back, this line is on the same plane as the transverse process of the sixth cervical vertebra, and the intersection of this line and the interscalene groove
Indications
Shoulder and upper limb surgery
supraclavicular brachial plexus block
Puncture point: the lowest point of the interscalene groove, posterior and superior to the pulse point of the subclavian artery, 1 to 1.5 cm above the midpoint of the clavicle
Indications
Upper limb surgery
axillary brachial plexus block
The axillary artery is the most important positioning landmark during axillary block
Puncture point: First feel the pulse of the axillary artery in the armpit, then go up the artery to feel the highest pulse of the artery at the lower edge of the pectoralis major muscle
Indications
forearm hand
complication
Pneumothorax (supraclavicular path)
Horner’s syndrom, spinal and epidural anesthesia (interscalene route)
Infection, hematoma, local anesthetic toxicity, phrenic and recurrent laryngeal nerve blocks, nerve injury and block failure
transversus abdominis plane block
T7-T12 and L1
femoral nerve block