Title: Local and regional anesthesia by dr. S. Bradulskis General surgery department , Kaunas
1Local and regional anesthesiaby dr. S.
Bradulskis General surgery department , Kaunas
2Local 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.
3Chemistry 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
5Local Anesthetic Classification
- Aminoesters
- Cocaine
- Procaine
- Chloroprocaine
- Tetracaine
- Aminoamids
- Lidocaine
- Prilocaine
- Mepivacaine
- Etidocaine
- Bupivacaine
- Ropivacaine
- Levobupivacaine
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7Local 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
8Mechanism 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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10Effect 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
11Vasoconstrictors
- 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.
12Effect 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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16Order of sensory function block
- 1. pain
- 2. cold
- 3. warmth
- 4. touch
- 5. deep pressure
- 6. motor
Recovery in reverse order
17Susceptibility 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
18A 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.
19B 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.
21TOXICITIES 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.
22Toxicity 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.
23Toxicity 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.
24Toxicity 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.
25Toxicity 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.
26Toxicity 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.
27Systemic 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.)
28Systemic 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)
29Influencing 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
30Influencing 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
31Influencing 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
32Influencing 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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34Types 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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36- Lidocaine
- 5 ointment, 2 gel, 4 solution, 10 aerosol,
100 mg suppository - Onset 3-5 min
- Bensocain
- 14-20 solution, gel,
- Onset 30 s
37Types 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).
38Intravenous 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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40Types 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)
41Peripheral 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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46Brachial 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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51Spinal 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
52Spinal and epidural anesthesiaContraindications
- 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
53Spinal 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!
54Spinal 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
56Spinal 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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58Epidural 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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62Postoperative Analgesia
- Local anesthetics for postoperative analgesia
- Thoracic Epidural analgesia
- Continuous peripheral nerve blocks (Shoulder,
Arm, Leg) - Continuous wound infiltration (Shoulder,
Tram-Flap, .)
63Postoperative 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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