PERIFERAL NERVE BLOCKS

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PERIFERAL NERVE BLOCKS

• DR. Abdollahi

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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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Indications

• Post operative analgesia
• Diagnosis
• Treatment of chronic pain syndrome
• Acute pain management
• Adjunct of anesthesia

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Preoperative Evaluation

• Reassured (supplemental sedation)
• Examine site of block (infection)
• Preoperative evaluation (same GA)
• Coagulation test
• Preexisting neuropathy
• Premedication (decrease apprehension and decrease
  analgesia during needle insertion)

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Block Room

• The block room must have appropriate monitor,
  equipment, and drug available should adverse
  effect to LA occur.
• Increase turnover of operating room.
• Increase efficiency of block.

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Local Anesthetic

• The choice depend on

1. Desired onset
2. Duration degree of conduction block

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lidocaine and mepivacaine 1-1.5 produce
surgical anesthesia in 10-20 min. that last 2-3
hours.Ropivacaine 0.5 and bupivacaine 0.375 to
0.5 have slower onset and produce less motor
blockaded but the effect last time is 6-8 hours.
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Epinephrine

• 1/200000 (5µg/ml)
• Increase duration of block
• Marker of intravenous injection
• Reduce peak plasma level of LA (vasoconstriction)

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Considerations for choice of LA for intravenous
regional anesthesia are different from those for
PNB.
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Chemistry
All local anesthetics are weak bases, classified
as tertiary amines. 
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• Esters
• These include cocaine, procaine, tetracaine, and
  chloroprocaine.
• They are hydrolyzed in plasma by
  pseudo-cholinesterase. One of the by-products of
  metabolism is paraaminobenzoic acid, the common
  cause of allergic reactions seen with these
  agents.

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• Amides
• These include lidocaine, mepivicaine, prilocaine,
  bupivacaine, and etidocaine.
• They are metabolized in the liver to inactive
  agents. True allergic reactions are rare
  (especially with lidocaine) .

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Mechanism of Action

• Local anesthetics work to block nerve conduction
  by reducing the influx of sodium ions into the
  nerve cytoplasm.
• Sodium ions cannot flow into the neuron, thus the
  potassium ions cannot flow out, thereby
  inhibiting the depolarization of the nerve. 
• If this process can be inhibited for just a few
  Nodes of Ranvier along the way, then nerve
  impulses generated downstream from the blocked
  nodes cannot propagate to the ganglion.

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Factors affecting local anesthetic action

• Effect of pH
• charged (cationic) form binds to receptor site
  uncharged form penetrates membrane ,efficacy of
  drug can be changed by altering extracellular or
  intracellular pH

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Effect of lipophilicity ANESTHETIC POTENCY

• Lipid solubility appears to be the primary
  determinant of intrinsic anesthetic potency.
  Chemical compounds which are highly lipophilic
  tend to penetrate the nerve membrane more easily,
  such that less molecules are required for
  conduction blockade resulting in enhanced
  potency.
• More lipophilic agents are more potent as local
  anesthetics

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• Effect of protein binding - increased binding
  increases duration of action
• Effect of diffusibility - increased diffusibility
  decreased time of onset
• Effect of vasodilator activity - greater
  vasodilator activity decreased potency and
  decreased duration of action

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Susceptibility to Block by Local Anesthetics of
Types of Nerve Fibers

• In general, small nerve fibers are more
  susceptible than large fibers however,

• the type of fiber
• degree of myelination
• fiber length and
• frequency- dependence are also important in
  determining susceptibility

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Order of sensory function block

• 1. pain
• 2. cold
• 3. warmth
• 4. touch
• 5. deep pressure
• 6. motor

Recovery in reverse order
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TOXICITIES OF LOCAL ANESTHETICS

• Essentially all systemic toxic reactions
  associated with local anesthetics are the result
  of over-dosage leading to high blood levels of
  the agent given. Therefore, to avoid a systemic
  toxic reaction to a local anesthetic, the
  smallest amount of the most dilute solution that
  effectively blocks pain should be administered.

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• Hypersensitivity. Some patients are
  hypersensitive (allergic) to some local
  anesthetics. Although such allergies are very
  rare, a careful patient history should be taken
  in an attempt to identify the presence of an
  allergy. There are two basic types of local
  anesthetics (the amide type and the ester type).
  A patient who is allergic to one type may or may
  not be allergic to the other type.

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• Central Nervous System Toxicities

Local anesthetics, if absorbed systematically in
excessive amounts, can cause central nervous
system (CNS) excitement or, if absorbed in even
higher amounts, can cause CNS depression.
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CNS Toxicity Cont

• Excitement Tremors, shivering, and convulsions
  characterize the CNS excitement.
• Depression The CNS depression is characterized
  by respiratory depression and, if enough drug is
  absorbed, respiratory arrest.

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• Cardiovascular Toxicities. Local anesthetics if
  absorbed systematically in excessive amounts can
  cause depression of the cardiovascular system.
• Peripheral vascular action arteriolar dilation
  (except cocaine which is vasoconstrictive
• Hypotension and a certain type of abnormal
  heartbeat (atrioventricular block) characterize
  such depression. These may ultimately result in
  both cardiac and respiratory arrest.

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• Signs of toxicity occur on a continuum. From
  early to late stages of toxicity, these signs
  are circum-oral and tongue numbness,
  lightheadedness, tinnitus, visual disturbances,
  muscular twitching, convulsions, unconsciousness,
  coma, respiratory arrest, then cardiovascular
  collapse.

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Types of Local Anesthesia

• Local Infiltration (Local Anesthesia) Local
  infiltration occurs when the nerve endings in the
  skin and subcutaneous tissues are blocked by
  direct contact with a local anesthetic, which is
  injected into the tissue. Local infiltration is
  used primarily for surgical procedures involving
  a small area of tissue (for example, suturing a
  cut).

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• Topical Block A topical block is accomplished by
  applying the anesthetic agent to mucous membrane
  surfaces and in that way blocking the nerve
  terminals in the mucosa. This technique is often
  used during examination procedures involving the
  respiratory tract. The anesthetic agent is
  rapidly absorbed into the bloodstream. For
  topical application (that is, to the skin), the
  local anesthetic is always used without
  epinephrine. The topical block easily
  anesthetizes the surface of the cornea (of the
  eye) and the oral mucosa.

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• Surface Anesthesia This type of anesthesia is
  accomplished by the application of a local
  anesthetic to skin or mucous membranes. Surface
  anesthesia is used to relieve itching, burning,
  and surface pain (for example, as seen in minor
  sunburns).

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• Nerve Block. In this type of anesthesia, a local
  anesthetic is injected around a nerve that leads
  to the operative site. Usually more concentrated
  forms of local anesthetic solutions are used for
  this type of anesthesia.

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• Peridural Anesthesia. This type of anesthesia is
  accomplished by injecting a local anesthetic into
  the peridural space.
• The peridural space is one of the coverings of
  the spinal cord.

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• Spinal Anesthesia. In spinal anesthesia, the
  local anesthetic is injected into the
  subarachnoid space of the spinal cord .

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Vasoconstrictors

• Vasoconstrictors decrease the rate of vascular
  absorption which allows more anesthetic to reach
  the nerve membrane and improves the depth of
  anesthesia.
• There is variable response between LA and the
  location of injection as to whether
  vasoconstrictors increase duration of action.
  1200,000 epinephrine appears to be the best
  vasoconstrictor.

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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 small
  dose of agent
• Disadvantages
• - technically complex, potential for toxicity
  and neuropathy.

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Cervical Plexus Block

• C1-C4 is formed CP.
• The block include the area from the inferior
  border of mandible to level of clavicle (T2).
• Clinical use carotid endarterectomy, lymph node
  dissection , plastic repair.
• Bilateral block for tracheostomy and
  thyroidectomy.

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• The cervical plexus is derived from the Cl, C2,
  C3, and C4 spinal nerves and supplies branches to
  the prevertebral muscles, strap muscles of the
  neck, and phrenic nerve.
• The deep cervical plexus supplies the musculature
  of the neck segmentally and the cutaneous
  sensation of the skinbetween the trigeminally
  innervated face and the T2dermatome of the trunk.
  Blockade of the superficial cervical plexus
  results in anesthesia of only the cutaneous
  nerves.

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• Bilateral blocks can be used for
• tracheostomy and thyroidectomy.

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Technique Superficial Cervical Plexus

• The superficial cervical plexus is blocked at the
  midpoint of the posterior border of the
  sternocleidomastoid muscle.
• A skin wheal is made at this point, and a
  22-gauge, 4-cm needle is advanced, injecting 5 mL
  of solution along the
• posterior border and medial surface of the
  sternocleidomastoid muscle. It is possible to
  block the accessory nerve with this injection,
  resulting in temporary
• ipsilateral trapezius muscle paralysis.

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Superficial Cervical Plexus Blockade (Technique)
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Technique Deep Cervical Plexus

• A line is drawn connecting the tip of the mastoid
  process and the Chassaignac tubercle (i.e.,
  transverse process of C6) a second line is drawn
  1 cm posterior to this first line. The C2
  transverse process lies 1 to 2 cm caudad to the
  mastoid process, where it can usually be
  palpated. The C3 and C4 transverse processes lie
  at 1.5-cm intervals along the second line. After
  skin wheals are raised over the transverse
  processes of C2, C3, and C4, three 22-gauge, 5-cm
  needles are advanced perpendicular to the skin
  entry site with a slight caudad angulation. The
  transverse process is contacted at a depth of 1.S
  to 3 cm. If a paresthesia is obtained, 3 to 4 mL
  of solution is injected after careful aspiration
  for blood and cerebrospinal fluid. If no
  paresthesia is elicited initially, the needle is
  walked along the transverse process in the
  anteroposterior plane until a paresthesia is
  obtained.

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Deep Cervical Plexus
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• This block can also be performed with a single
  injection of 10 to 12 mL at the C4 transverse
  process

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Side Effects and Complications

• Intravenous injection
• Phrenic nerve block (bilateral is
  contraindicated)
• Sup lary. Nerve block
• Spread of LA to spinal or epidural space
• Horner syndrome (petosis- endophtalmia-
  anhydrose -myosis )

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Brachial plexuses anatomy
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Innervations

• These cords divided into terminal branches that
  supply all motor and sensory innervations of the
  upper extremity with the exception of the skin
  over the shoulders which is supply by the
  cervical plexus and medial aspect of the arm that
  innervated by intercostobrachial branch of
  second intercostal nerve.

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Brachial plexus block

• Four anatomic location for brachial plexus

1. Interscalene block
2. Superaclavicular block
3. Inferaclavicular block
4. Axillarry block

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Interscalene block
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Interscalene block

• 25-40 cc from LA in to interscalen groove
  adjacent to the transverse process of C6 and
  lateral to external jugular.
• Ideal for shoulder surgery with 40 cc of LA that
  anesthetized cervical plexus and brachial plexus
  .

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Complications

• Pneumothorax (rare).
• Phrenic nerve block and diaphragmatic paralysis
  is nearly 100.
• Recurrent laryngeal nerve block (bilateral cause
  airway obstruction).
• Epidural block and subarchnoid
• Intervertebral artery injection (convulsion)

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Supraclavicular block
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Supraclavicular block

• 25 -40 cc LA posterior border and mid portion of
  clavicle.
• Clinical use operation on the elbow, forearm,
  hand.

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Complications

• Pnemuthorax is most common serious (1) can
  manifest by cough and chest pain and dyspnea .
• Phrenic nerve block (50)
• COPD patients not ideal candidate for
  supraclavicular block.

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Advantage

• Rapid onset
• Ability to perform block with arm in any
  position.

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Infraclavicular block

• This block is excellent anesthesia and analgesia
  for hand, forearm and elbow.

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Technique
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Complications

• Vascular puncture
• Patient discomfort (traverse needle from
  pectorals muscle)

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Axillary block
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Method

• Transarterial
• Axillary sheet
• 30-40ml for LA is needed.
• Clinical use anesthesia for hand and forearm and
  elbow.

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Advantage and complications

• Relative safe (remote from lung and neuraxis.
• Systemic local anesthetic toxicity.
• Nerve injury
• Interaneural injection
• Hematoma

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Supplemental block

• Additional 5 cc LA injected in to
  coracobrachilis muscle to block of
  musculocutaneous nerve block.
• Additional 5 cc LA infiltrated in to
  subcoutaneous tissue around of axillary artery to
  block intercostobrachial , medial brachial
  cutaneous and medial antebrachial cutaneous
  nerve.

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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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Distal nerve blocks of the upper extremity
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Wrist block

• Anesthesia for hand surgery without tournique.
• Supplement a brachial plexus block.
• Contain nerves median, ulnar and radial .

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Median nerve

• The median nerve provides most of the sensory
  innervations to the palm of the hand.
• 3-5 cc LA between the palmaris longus and flexor
  carpi radialis tendon.

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Ulnar nerve block

• Sensation of dorsal and palmar sides of the ulnar
  aspect of the hand
• LA injected medial to the ulnar artery between
  the flexor carpi ulnaris and ulna.

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Radial nerve block

• Sensation on the dorsal aspect of hand.
• The superficial radial nerve can block by
  infiltration of LA within snuffbox.

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Musculocutaneous nerve block

• Sensory innervations of radial side of forearm.
• This block perform by axillary block

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Axillary block
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Intercostals nerve block

• Intercostal nerve block provide motor and sensory
  anesthesia of the chest wall without sympatic
  block.
• Postoperative analgesia after thoracic surgery
  and Breast or rib fracture.

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Performance of the block

• Position
• 5-7 cm from midline
• 6-11th ribs can palpate easily.

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Complications

• Pneumothorax
• Intravascular injection
• Systemic toxicity
• If multiple level if necessary epidural
  anesthesia is alternative

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Intravenous regional neural anesthesia

• Another name IV block or bier block
• Anesthesia for arm and leg
• Surgical duration less than 2 hours.
• Not recommended for postoperative pain relief.

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Contraindications

• Contraindications to tourniquettion application
  (sickle cell anemia, infection, ischemic vascular
  disease)
• Pain with bon fracture
• Traumatic laceration

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Performance of the block

• Inflated pressure 250-275 mmHg or about 100 mmHg
  above SBP.
• Plain (without EP) LA (40-50 cc) for upper
  extremity for 70 Kg.
• Intercostobrachial block for proximal tourniquet
  .

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Selection of LA

• Lidocaine 0.5
• Prilocaine
• Racemic Bupivacaine is contraindicated
• Ropivacaine and levobuvacaine
• Preservative free soulutions (thromophelebits)

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Characteristics of the block

• Rapid onset
• Duration of surgery depend On tourniquet time no
  LA characteristic.
• Applicable to all patients including pediatric.

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Risks

• Systemic toxicity
• During deflation(2-5 min after)
• Keep inflation for 20 min even if surgical time
  is less
• After 40 min from inflation can deflate in a
  single maneuver.
• Between 20 40 min defelate and reinflated quickly
  

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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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prilocaine

• Rapid metabolism (low toxicity)
• Methemoglobinemia is unlikely with less than 600
  mg .

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Blocks of the lower extremity

• Sciatic nerve
• Post femoral cutaneous nerve
• Lat.femoral cutaneous nerve
• Obterator
• Femoral

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Lumbar plexuses
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Cutaneous distribution of lumbosacral nerve
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Femoral nerve block L2-L4

• Anesthesia to anterior aspect of thigh and knee
  and medial aspect of leg
• For muscle biopsy and combined block for example
  scitic nerve block
• For post operative analgesia
• Contraindication for neuraxial block

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Femoral nerve
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Obturator nerve block

• Variable cutaneous inervation of the thigh

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Scitic nerve block L4-5 S1-3
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Mechanism of Action

• 1) slow rate of depolarization
• 2) reduce height of action potential
• 3) reduce rate of rise of action potential
• 4) slow axonal conduction
• 5) ultimately prevent propagation of action
  potential
• 6) do not alter resting membrane potential
• 7) increase threshold potential

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FIBER SIZE AND FUNCTION

• a (dia 12-20um cond vel 70-120m/s) largest,
  afferent to and efferent from muscles and joints.
  Actions motor function, proprioception, reflex
  activity.
• ß (dia 5-12um 30-70m/s) large as A-alpha,
  afferent to and efferent from muscles and joints.
  Actions motor proprioception, touch, pressure,
  touch and pressure.
• ? (dia 3-6um 15-30m/s) muscle spindle tone.
• d (dia 2-5um 12-30m/s) thinnest, pain and
  temperature. Signal tissue damage.

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• B fibers (dia 2-5um) Myelinated preganglionic
  autonomic. Innervate vascular smooth muscle.
  Though myelinated, they are more readily blocked
  by LA than C fibers.

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• C fibers (dia 0.4-1.2 um) Nonmyelinated, very
  small nerves. Smallest nerve fibers, slow
  transmission. Transmit dull pain and temperature,
  post-ganglionic autonomic.
• Both A-d and C fibers transmit pain and are
  blocked by the same concentration of LA.