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Local and regional anesthesia by dr. S. Bradulskis General surgery department , Kaunas

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Title: Local and regional anesthesia by dr. S. Bradulskis General surgery department , Kaunas


1
Local and regional anesthesia by dr. S.
Bradulskis General surgery department , Kaunas
2
Local Anesthetic
  • A local anesthetic is an agent that interrupts
    pain impulses in a specific region of the body
    without a loss of patient consciousness.
    Normally, the process is completely
    reversible--the agent does not produce any
    residual effect on the nerve fiber.

3
Chemistry all local anesthetics are weak bases,
classified as tertiary amines.
 
4
  • Characteristics
  • Poorly water soluble weak basic amins (pKa
    7,5-9)
  • Molecular weight between 220 and 288
  • Lipophilic aromatic ring tertiary hydrophilic
    amin
  • Link Ester (-COO-) or Amid (-NHC-) chain

5
Local Anesthetic Classification
  • Aminoesters
  • Cocaine
  • Procaine
  • Chloroprocaine
  • Tetracaine
  • Aminoamids
  • Lidocaine
  • Prilocaine
  • Mepivacaine
  • Etidocaine
  • Bupivacaine
  • Ropivacaine
  • Levobupivacaine

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Local Anesthetic Metabolism
  • Aminoesters (cocaine, procaine, tetracaine, and
    chloroprocaine )
  • Quick degradation
  • Hydrolysis, plasma and liver cholinesterase
  • Produces para-aminobenzoic acid (PABA, allergy.)
  • Aminoamids (lidocaine, mepivicaine, prilocaine,
    bupivacaine, and etidocaine )
  • Slower degradation
  • Liver microsomal enzymes
  • Excretion (metabolites and lt5 unchanged drug)
    via kidneys
  • Prilocain (very large doses)
  • - Accumulation of metabolites risk of
    methemoglobinemia

8
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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Effect on Action
  • Effect of protein binding - increased binding
    increases duration of action
  • Effect of diffusibility - increased diffusibility
    decreased time of onset (pK)
  • Effect of vasodilator activity - greater
    vasodilator activity decreased potency and
    decreased duration of action

11
Vasoconstrictors
  • Vasoconstrictors decrease the rate of vascular
    absorption which allows more anesthetic to reach
    the nerve membrane and improves the depth of
    anesthesia, it .
  • 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.

12
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

13
  • Two forms exist simultaneously
  • Ionised kation (BH)
  • Non ionised base (B)
  • Relation between the two forms
  • depends on
  • pKa of the local anesthetic drug
  • Tissue (and solution) pH
  • Both forms necessary for the action
  • Neutral base
  • - Penetrates the membrane
  • of the nerve cell
  • Kation Active form
  • - Blocks Na-channels (intracellular)

The lower the difference between pKa and pH (less
basic LA), the more non ionised molecules
(base). More non ionised molecules quicker
onset of action
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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
17
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

18
A 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.

19
B FIBER SIZE AND FUNCTION
  • B fibers (dia 2-5um) Myelinated preganglionic
    autonomic. Innervate vascular smooth muscle.
    Though myelinated, they are more readily blocked
    by LA than C fibers.

20
C FIBER SIZE AND FUNCTION
  • 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.

21
TOXICITIES OF LA
  • 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.

22
Toxicity of LA
  • 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.

23
Toxicity of LA
  • 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.

24
Toxicity of LA
  • 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.

25
Toxicity of LA to CNS
  • 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.

26
Toxicity of LA to Cardiovascular system
  • 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.

27
Systemic toxicity prevention
  • IV access secured before injection of the LA
  • Chose least toxic drug suitable
  • Consider block type and patient specific max.
    dose ranges
  • Start with a typical dose
  • Consider adding a vasoconstrictive adjuvant
    (epinephrine)
  • Careful aspiration during injection
  • Observe clinical reactions
  • Talk to the patient and monitor ECG/blood
    pressure to realize
  • early symptoms of central-nervous and
    cardiovascular toxicity
  • Stop injection immediately when early symptoms
    are realized
  • Consider the time course for development of
    toxic signs
  • (5-10 min. after correct injection.)

28
Systemic toxicity treatment
  • Stop injection immediately
  • Treat
  • Give oxygen, (hyperventilate - mask or airway
    device)
  • Stop cerebral excitation (Benzodiazepines,
    Barbiturates, Propofol (Midazolam 2-5
    mg,Thiopental 50-150 mg,Propofol 50-100 mg)
  • Correct hypotension and arrhythmias
  • (crystalloids, vasopressors, antiarrhythmic drugs
    (Ephedrin 5-10 mg, Epine-phrine 10-100 µg )
  • Cardiopulmonary resuscitation for cardiac arrest
    / VF
  • Avoid / treat aggravating factors Hypoxia and
    acidosis (respiratory and metabolic)

29
Influencing factors patient-related
  • Age
  • Old age (gt 70 yr) elimination prolonged
  • - 10-20 dose reduction for continuous
    applications
  • Newborns (lt 4 months) elimination of amid LA
    prolonged
  • - 15 dose reduction per kg
  • Renal dysfunction
  • Excretion reduced
  • - 10-20 dose reductions relative to degree of
    dysfuncion
  • Hepatic dysfunction
  • Low liver blood flow or poor liver function
  • - Higher blood levels of amid local anesthetics
  • - 10-50 dose reduction for repeated or
    continuous applications

30
Influencing factors patient-related
  • Body size
  • In very small adults, the dose for blocks
    requiring large doses (brachial plexus, IVRA)
    should be reduced.
  • Pregnancy
  • Hormonally increased sensitivity of the CNS to
    LA
  • Reduced requirements
  • Risk for toxicity ?
  • Reduced protein binding of bupivacaine
  • Increased cardiac output, perfusion ? and uptake
    ?
  • Anatomic and physiologic changes - 10 dose
    reduction

31
Influencing factors patient-related
  • Infected tissue
  • Low tissue pH
  • More ionised kations
  • Less uncharged base available for penetration
  • Vasodilation
  • Uptake into circulating blood ?
  • Reduced effect of the injected local anesthetic

32
Influencing factors not patient-related
  • Alkalinization (pH ? with sodium bicarbonate)
  • Uncharged base?, diffusion rate through nerve
    membrane ?
  • - Time to onset ?
  • And Injection is less painful ! (higher pH)
  • But Duration of action ?
  • Recipe
  • 9 ml LA (lidocaine, mepivacaine) 1 ml NaBic 8.4
  • Adjuvant (Epinephrine 1 200000 (5 µg/ml))
  • Vasoconstriction Intravascular uptake ?
  • - Duration of action 30-50?
  • only in combination with short acting LA (Lido-,
    Prilo-, Mepivacaine!)
  • - Toxicity ? (all LA)
  • Recipe
  • 20 ml LA 0.1 mg Epinephrine
  • Contraindication for epinephrine
  • Local anesthesia around
  • end arteries (finger, ear, penis)!

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Types of Local Anesthesia
  • 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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  • Lidocaine
  • 5 ointment, 2 gel, 4 solution, 10 aerosol,
    100 mg suppository
  • Onset 3-5 min
  • Bensocain
  • 14-20 solution, gel,
  • Onset 30 s

37
Types of Local Anesthesia
  • Local Infiltration 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).

38
Intravenous regional anesthesia- Bier anesthesia
  • How does it work?
  • Injection into a previously
  • exsanguinated and occluded limb
  • Retrograde spread of the distally
  • injected local anesthetic agent
  • Very rapid onset
  • For arm/leg procedures lt 1hour
  • Can be performed with
  • Prilocaine, Chloroprocaine,
  • Lidocaine (0.5 solution, 40-60 ml)
  • Possible complications
  • LA intoxication when tourniquet
  • is insufficient or released less
  • than 15 - 20 minutes after injection

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Types of Local Anesthesia
  • Peripherial 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.
  • Major nerve block - (plexus brachialis)
  • Minor nerve block - (n. radialis)

41
Peripheral nerve blocks
  • Choice of agent
  • Most local anesthetics can be used. Choice
    depends on intended duration of the block
  • Dose / concentration
  • Lidocaine, Mepivacaine, Prilocaine (1
    solutions)
  • Bupivacaine (0.5 solution), Ropivacaine (0.75
    solution)
  • (10 ) 20 40 ( 50) ml (depending on nerve or
    plexus type)
  • Onset of action and duration
  • Onset is rapid for Lido/Mepi/Prilocaine and slow
    for Bupi/Ropi. Time to onset and duration with
    considerable variations (depending on distance of
    LA deposit to nerves)
  • Epinephrine prolongs duration of
    Lido/Mepi/Prilocaine,
  • but is less effective with Bupivacaine

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Brachial plexus block
  • Block possible at different sites
  • Interscalene Supraclavicular, Infraclavicular
  • Axillary
  • Chosen site
  • Depends on planned surgical procedure
  • Injected volume 30 50 ml
  • Time to onset lt 10 min (Lido, Mepi, Prilo) up to
    25 min (Bupi, Ropi)

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Spinal and epidural anesthesia Main indications
  • Epidural
  • Indications as for spinal,
  • - Thoracic approach in combination with
  • general anesthesia
  • abdominal and thoracic surgery
  • Obstetric analgesia
  • Treatment of acute and chronic pain
  • Spinal
  • Surgery below the umbilicus
  • lower abdomen
  • lower extremities
  • transurethral and vaginal procedures
  • Cesarean section

52
Spinal and epidural anesthesia Contraindications
  • Sepsis
  • (Severe) Coagulopathies
  • Shock, severe hypovolemia
  • Infection at/near puncture site
  • Refusal
  • Certain neurologic diseases
  • Severe aortic valve stenosis
  • Communication problems
  • Elevated intracranial pressure
  • Anatomical abnormalities

53
Spinal and epidural anesthesia effects
  • Main effects
  • Anesthesia and analgesia
  • Cardiovascular system
  • Hypotension (related to extent of sympathetic
    block, volemia)
  • Bradycardia (blocked sympathetic
    cardioaccelerator fibersYoung males more
    frequent)
  • Both effects more pronounced with spinal than
    with epidural anesth.
  • Respiratory system
  • Reduced active exhalation with high block level
  • - Caution in patients with severe COPD!

54
Spinal and epidural anesthesia effects
  • Gastrointestinal and urogenital
  • Unopposed parasympathetic activity
  • Nausea (associated with high block level)
  • Increased secretions, relaxed sphincters, bowel
    constriction
  • Long lasting block of sacral parasympathetic
    nerves
  • Postoperative urinary retention possible
  • Endocrine-metabolic
  • Less perioperative stress-response
  • Reduction of protein catabolism, hyperglycemia,
    sodium and
  • water retention, fever, tachycardia, increased
    minute ventilation
  • Coagulation
  • Reduced hypercoagulability, reduced
    thromboembolic events

55
  • Spinal Anesthesia. In spinal anesthesia, the
    local anesthetic is injected into the
    subarachnoid space of the spinal cord

56
Spinal anesthesia
  • Only use drugs without preservatives!
  • Commonly used 0.5 Bupivacaine (long action)
  • hyperbaric (with 8 glucose) or plain (isobaric)
    solution
  • No hyperbaric (heavy) lidocaine (transient
    neural symptoms)!
  • Rapid onset (injection close to nerve roots)

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Epidural Anesthesia. This type of anesthesia is
accomplished by injecting a local anesthetic into
the epidural space
  • Lido-, Mepiva-, Prilo-, Bupiva-, Ropivacaine
  • Onset 5-15 min (Lido/Mepi/Prilo) to 20-30 min
    (Bupi/Ropi)
  • Anesthesia
  • high concentration 2 Lido/0.5 (L-)Bupi/0.75
    Ropi
  • Analgesia postoperative without motor deficit
  • 0.125-0.25 (L-)Bupi/0.2 Ropi

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Postoperative Analgesia
  • Local anesthetics for postoperative analgesia
  • Thoracic Epidural analgesia
  • Continuous peripheral nerve blocks (Shoulder,
    Arm, Leg)
  • Continuous wound infiltration (Shoulder,
    Tram-Flap, .)

63
Postoperative epidural analgesia
  • Advantages compared with systemic opioid-based
    analgesia
  • Decreased postoperative pain
  • Better analgesic effect
  • Reduced opioid related side-effects
    (Nausea/Vomiting, Pruritus, Sedation)
  • Also suitable for some outpatients (elastomere
    pumps)
  • Less sedation, less postoperative fatigue
  • Higher Health related quality of life
  • Earlier mobilization
  • Better respiratory function, better exercise
    capacity,better bowel function, earlier oral
    nutrition
  • Earlier ready for discharge (not done, other
    factors.)
  • No difference incidence of postoperative
    surgical complications
  • But
  • Method-specific side effects (similar to regional
    anesthesia

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