LOCAL ANESTHETICS AND REGIONAL ANESTHESIA

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LOCAL ANESTHETICS AND REGIONAL ANESTHESIA

• UNIFORMED SERVICES UNIVERSITY OF THE HEALTH
  SCIENCES

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Local Anesthetics- History

• 1860 - cocaine isolated from erythroxylum coca
• Koller - 1884 uses cocaine for topical
  anesthesia
  
• Halsted - 1885 performs peripheral nerve block
  with local
  
• Bier - 1899 first spinal anesthetic

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Local Anesthetics - Definition

• A substance which reversibly inhibits nerve
  conduction when applied directly to tissues at
  non-toxic concentrations
  

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Local anesthetics - Mechanism

• Limit influx of sodium, thereby limiting
  propagation of the action potential.

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Local Anesthetics - Classes
Esters
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Local anesthetics - Classes (Rule of is)

• Esters
• Cocaine
• Chloroprocaine
• Procaine
• Tetracaine

• Amides
• Bupivacaine
• Lidocaine
• Ropivacaine
• Etidocaine
• Mepivacaine

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Local anesthetics - Formulation

• Biologically active substances are frequently
  administered as very dilute solutions which can
  be expressed as parts of active drug per 100
  parts of solution (grams percent)
• Ex. 2 solution
• 
  
  
• _2 grams__ _2000 mg_ __20 mg__
  
  
• 100 ccs 100 ccs 1
  cc

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Local Anesthetics - Allergy

• True allergy is very rare
• Most reactions are from ester class - ester
  hydrolysis (normal metabolism) leads to formation
  of PABA - like compounds
  
• Patient reports of allergy are frequently due
  to previous intravascular injections

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Local Anesthetics - Toxicity

• Tissue toxicity - Rare
• Can occur if administered in high enough
  concentrations (greater than those used
  clinically)
  
• Usually related to preservatives added to solution

• Systemic toxicity - Rare
• Related to blood level of drug secondary to
  absorption from site of injection.
  
• Range from lightheadedness, tinnitus to seizures
  and CNS/cardiovascular collapse

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Local anesthetics - Duration

• Determined by rate of elimination of agent from
  site injected
  
• Factors include lipid solubility, dose given,
  blood flow at site, addition of vasoconstrictors
  (does not reliably prolong all agents)
  
• Some techniques allow multiple injections over
  time to increase duration, e.g. epidural
  catheter
  

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Local anesthetics - vasoconstrictors
Ratios Epinephrine is added to local anesthetics
in extremely dilute concentrations, best
expressed as a ratio of grams of drugtotal ccs
of solution. Expressed numerically, a 11000
preparation of epinephrine would be
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Local anesthetics - vasoconstrictors
Therefore, a 1 200,000 solution of epinephrine
would be

or
5 mcg epi 1 cc solution
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Local anesthetics - vasoconstrictors

• Vasoconstrictors should not be used in the
  following locations
  
• Fingers
• Toes
• Nose
• Ear lobes
• Penis

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REGIONAL ANESTHESIA
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Regional anesthesia - Definition

• Rendering a specific area of the body, e.g. foot,
  arm, lower extremities, insensate to stimulus of
  surgery or other instrumentation

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Regional anesthesia - Uses

• Provide anesthesia for a surgical procedure
• Provide analgesia post-operatively or during
  labor and delivery
  
• Diagnosis or therapy for patients with chronic
  pain syndromes
  

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Regional anesthesia - types

• Topical
• Local/Field
• Intravenous block (Bier block)
• Peripheral (named) nerve, e.g. radial n.
• Plexus - brachial, lumbar
• Central neuraxial - epidural, spinal

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Topical Anesthesia

• Application of local anesthetic to mucous
  membrane - cornea, nasal/oral mucosa
  
• Uses
• awake oral, nasal intubation, superficial
  surgical procedure
  
• Advantages
• technically easy
• minimal equipment
• Disadvantages
• potential for large doses leading to toxicity

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Local/Field Anesthesia

• Application of local subcutaneously to
  anesthetize distal nerve endings
  
• Uses
• Suturing, minor superficial surgery, line
  placement, more extensive surgery with sedation
  
• Advantages
• minimal equipment, technically easy, rapid onset
• Disadvantages
• potential for toxicity if large field

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IV Block - Bier block

• Injection of local anesthetic intravenously for
  anesthesia of an extremity
  
• Uses
• any surgical procedure on an extremity
• Advantages
• technically simple, minimal equipment, rapid
  onset
  
• Disadvantages
• duration limited by tolerance of tourniquet
  pain, toxicity
  

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Peripheral nerve block

• Injecting local anesthetic near the course of a
  named nerve
  
• Uses
• Surgical procedures in the distribution of the
  blocked nerve
  
• Advantages
• relatively small dose of local anesthetic to
  cover large area rapid onset
  
• Disadvantages
• technical complexity, neuropathy

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Plexus Blockade

• Injection of local anesthetic adjacent to a
  plexus, e.g cervical, brachial or lumbar plexus
  
• Uses
• surgical anesthesia or post-operative analgesia
  in the distribution of the plexus
  
• Advantages
• large area of anesthesia with relatively large
  dose of agent
  
• Disadvantages
• technically complex, potential for toxicity and
  neuropathy.
  

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Central neuraxial blockade - Spinal

• Injection of local anesthetic into CSF
• Uses
• profound anesthesia of lower abdomen and
  extremities
  
• Advantages
• technically easy (LP technique), high success
  rate, rapid onset
  
• Disadvantages
• high spinal, hypotension due to sympathetic
  block, post dural puncture headache.
  

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Central Neuraxial Blockade - epidural

• Injection of local anesthetic in to the epidural
  space at any level of the spinal column
  
• Uses
• Anesthesia/analgesia of the thorax, abdomen,
  lower extremities
  
• Advantages
• Controlled onset of blockade, long duration when
  catheter is placed, post-operative analgesia.
  
• Disadvantages
• Technically complex, toxicity, spinal headache

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