Regional Anesthesia
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Regional Anesthesia - definition
!!!! no loss of consciousness
No pain=analgesia
No motor response=muscles relaxation
No reflexes
1/ surgery-orthopedics, obstetrics, vascular
surgery, urology
2/ acute pain - postoperative analgesia, acute
pancreatitis, intermittent claudication, trauma
3/ chronic pain
History
• cocaine, an extract of the coca leaf
(=Erythroxylon coca bush) , was the first
effective local anesthetic
• had been known for centuries in Peru, where
folk surgeons performing trepanations of the
skull chewed coca leaves and allowed their
saliva to fall onto the surfaces of the wound
(both the operator and his patient shared the
effects of the same drug)
• in 1884, Koller reported the first use of a local
anesthetic - cocaine for ophthalmologic surgery.
Local anesthetics
• inhibit reversibly impulse conduction along the nerve fibres by
blocking sodium channels.
• block the generation and propagation of impulses in spinal cord,
spinal nerve roots, and peripheral nerves
• with progressive increases in concentrations of local anesthetics, the
transmission of:
1/ autonomic
2/ somatic sensory and
3/ somatic motor
impulses is interrupted, producing:
1/ autonomic nervous system blockade
2/ sensory anesthesia and
3/ skeletal muscle paralysis
in the area innervated by the affected nerve.
Neural cell wall with sodium
channel
Strategies to find nerves include:
• looking for the landmarks
• seeking a paresthesia (recall the old
saying, "No paresthesia, no anesthesia")
or
• using an "electric nerve stimulator."
Electric nerve stimulator
This is a device that gives a short pulse of
electrical current and is attached to a needle.
Electrical impulses reaching a nerve are
transmitted along the nerve fibres.
If the nerve contains
• motor fibres, the electrical current will induce
contraction at the effector muscle.
• sensory fibres they cause parasthesia in the
distribution of the nerve.
Local anesthetics
• aminoesters and the aminoamides
• lidocaine (Xylocaine) intermediate acting (water
soluble jell and a 4% solution, as a 5% solution
with dextrose for spinal administration, and for
injection as 1% and 2% solutions)
• bupivacaine (Marcaine) long acting local
anesthetic (as 0.5% solution)
• mepivacaine
• ropivacaine
Aminoamide local anesthetics are primarily cleared
from the bloodstream by metabolism in the liver.
Local anesthetic toxicity
intravascular injection or systemic
absorption → systemic effects
• allergic reactions – very rare
• neurotoxicity
• cardiotoxicity
The cardiovascular system (CVS) is generally more resistant to
local anesthetic toxicity than is the CNS
Neurotoxicity
NEUROTOXICITY OF LIGNOCAINE-SYMPTOMS:
• Lightheadness
• Tongue Numbness, metallic taste in the mouth
• Visual disturbances
• Generalised twitching
• Convulsions
• Profound Coma
• Respiratory Arrest
• CVS Depression
The important thing about this list is to notice that cardiovascular depression
occurs only at very high blood concentrations. Thus, if the other symptoms
occur, ask the patient to hyperventilate, provide oxygen and prepare to
secure the airway and treat a seizure.
Mechanisms :
→ initially inhibition of inhibitory pathways→convulsions
→ later inhibition both inhibitory and facilitatory pathways→generalized state of
CNS depression
Neurotoxicity
• general relationship between anesthetic potency
and CNS toxicity
Convulsions have been reported at venous blood
levels of approximately:
• 2 to 4 ng/ml of bupivacaine, dose limits is 2
mg/Kg plain and 3 mg/Kg with epinephrine (150
mg)
• 10 ng/ml of lidocaine, dose limits 5 mg/Kg of
plain solution or 7 mg/Kg if the solution contains
epinephrine (200mg, 500mg with epinephrine)
Cardiovascular System Toxicity
• Lidocaine – agent used for treating
ventricular arrhythmias
Mechanisms :
• unidirectional block and a reentrant type of
cardiac arrhythmia
• decreased myocardial contractility
• vasodilation
CHARACTERISTICS OF LOCAL
ANESTHETIC TOXICITY
• (I) CNS toxicity:
a) Excitation Phase: tinnitus, confusion, restlesness, perioral
numbness or tingling, metallic taste, lightheadness, sense of dread
and impending doom.
b) Convulsive Phase: grand-mal clonic-tonic seizure
c) Depression Phase: CNS depression with drowsiness and
unconsciousness.
d) Repiratory depression and apnea.
• (II) CVS Toxicity:
a) Excitation Phase: - hypertension, tachycardia (with convulsions)
b) Depression Phase:
Negative inotropic effect with decreased blood pressure, cardiac
output and stroke volume.
Peripheral vasodilation with further hypotension.
c) Cardiovascular Collapse
LOCAL ANESTHETIC - FACTORS
INFLUENCING SYSTEMIC
ACTIVITY→Toxicity
• choice of drug
• dosage - relation between dosage and
maximum plasma concentration is linear
• addition of Epinephrine
• site of injection - absorption from any site
depends on the blood supply to that site. The
highest concentrations occurred after intercostal
block and the lowest after subcutaneous
abdominal infiltration.
Sites are generally ranked:
intercostal>epidural>brachial plexus>spinal
Addition of epinephrine to local
anesthetic
→vasoconstriction
• commercially available solutions of local anesthetic
containing epinephrine are prepared at a low pH to
prevent degradation of the epinephrine
• concentration of 1:200,000
• purposes:
1) prolongs the action of the local anesthetic
2) blunts systemic uptake and thereby limits systemic
toxicity
3) decreases bleeding at the site of injection
4) serves as a marker of intravascular injection
5) improves the quality of spinal blockade, probably on the
basis of spinal alpha receptors
1/Topical Anesthesia
• local anesthetics may be applied topically-on the
eye, skin, tympanic membrane, oral mucosa,
tracheobronchial tree, and rectum.
• to be effective topically, high concentrations of
local anesthetics are required
• onset of anesthesia usually occurs in 5–10
minutes when applied to mucous membranes
and in 30–60 minutes when applied to the skin
• systemic absorption is greater from mucous
membranes-risk of toxicity if large volumes of
local anesthetic are used
1/ Topical Anesthesia
EMLA® cream provides an alternative for topical
anesthesia
• is a eutectic mixture of lidocaine and prilocaine
containing approximately an 80% concentration of active
base
• has been particularly useful for providing topical
anesthesia for venipuncture in infants and children
• onset of anesthesia after application requires at least 1
hour
• absorption is relatively low
• maximum depth of anesthesia that can be achieved is
approximately 5 mm
2/ Infiltration Techniques
Local anesthetic is given:
• Subcutaneously, intracutaneously,
intramuscularly
• Intravenously =Bier’s block
Intravenous Block =Bier’s block
• Needle is inserted into a distal vein in the extremity.
• Wide rubber band is tightly wrapped starting distally and
working proximally to remove blood from the superficial
veins of limb.
• Pneumatic cuff is inflated to prevent venous outflow from
the extremity.
• 50 to 60 ml of lidocaine 0.5% is injected through the
distal IV.
• The cuff may remain inflated for up to two hours
(ischemic pain limits the time)
• At the end cuff is re-inflated over several minutes
3/ Central Blockades
• The target of the local anesthetic molecules in
central blokade are the neural pathways
traversing the spinal column.
• Spinal cord is protected by the cushion of CSF
that is enclosed with the dura sac.
3/ Central Blockades
• Local anethetics injected within dura sac
(into CSF) penetrate the nerve fibres rapidly
and provide the rapid spinal anesthesia.
• Local anesthetics injected outside the dura
mater produce the slower onset of epidural
blockade.
• Approaches: paramedian and lateral
• Subarachnoid space contains CSF
• Epidural space surrounds the dura sac and
contains fat, air and veins
Needle Tip Designs
Features of note are:
1. The presence of a cutting tip on the Quincke type needle.
2. The dimensions of the terminal hole.
- A large hole contributes to a rapid flashback.
- A long hole increases the possibility of injecting part of the intended sub-arachnoid dose
into the epidural space.
3. The original pencil point needle (HART) is illustrated.
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Spinal block
• The local anesthetic is injected into the cerebral spinal
fluid (CSF).
• As the nerves are unprotected here, a very small amount
of anesthetic will cause the rapid onset of the block.
• The local anestetic may be hyperbaric, hypobaric or
isobaric relative to CSF.
• By having a different baricity from CSF the anesthetic
solution spread and the extent of the block may be
controlled by positioning the patient.
Spinal block
• In 3% of the population the cord ends at
L1 or above.
• In 94% of the population the cord ends at
L1 or L2.
• In 3% of the poulation the cord ends at
L3.
Spinal block -paramedian approach
• The needle passes through :
1/ skin
2/ superspinous ligaments
3/ interspinous ligaments
4/ ligamentum flavum
5/ dura sac
Lateral position for performance
of spinal anesthesia
• Lateral positionknee down up toward
the chest and head
flexed down toward
the knee
Sitting approach for spinal
anesthesia
• Sitting position-feet
supported on the
stool and the
shoulders hunched
forward to increase
flection of the spine.
Spinal block
Extent of spinal block depends on:
• Baricity of solution (density)
• Position of patient (except isobaric
solutions)
• Dose and volume of the drug
• Level of injection
• Speed of injection
Spinal block
LEVEL OF SPINAL ANESTHESIA REQUIRED FOR COMMON
SURGICAL PROCEDURES
T4–5 (nipple)
T6–8 (xiphoid)
pelvic surgery
upper abdominal surgery
gynecologic pelvic surgery,ureter, renal and
T10 (umbilicus) transurethral resection, obstetric vaginal
delivery, and hip surgery
L1 (inguinal ligament) transurethral resection, if no bladder
distension; thigh surgery; lower limb amputations
L2–3 (knee and below) foot surgery
S2–5 (perineal) perineal surgery, hemorrhoidectomy
Spinal block-complications
• Hypotension
• Bradycardia-thoracic sympathetic segments (T1-5) are
blocked Sympathetic blockade above the level of the cardiac
accelerator fibres (T1 - T4) will cause a bradycardia
• Total spinal block
• Neurological complications-damage of the nerves,
hematomas, infections.
• Post dural puncture headache (PDPHA) is related to
low CSF pressure due to leak of the fluid from the
puncture hole in the dura sac with the spinal needle. A
very powerful diagnostic feature of the headache is its
positional nature. It is worse when the patient is sitting or
standing and better when the patient is lying flat. PDPHA
is treated with recumbency, hydration, caffeine, or more
aggressively with an epidural blood patch of the leaking
dural hole.
Cardiovascular changes with
epidural anesthesia
Spinal block-complications
• Hypotension
• Bradycardia-thoracic sympathetic segments (T1-5) are
blocked Sympathetic blockade above the level of the cardiac
accelerator fibres (T1 - T4) will cause a bradycardia
• Total spinal block
• Neurological complications-damage of the nerves,
hematomas, infections.
• Post dural puncture headache (PDPHA) is related to
low CSF pressure due to leak of the fluid from the
puncture hole in the dura sac with the spinal needle. A
very powerful diagnostic feature of the headache is its
positional nature. It is worse when the patient is sitting or
standing and better when the patient is lying flat. PDPHA
is treated with recumbency, hydration, caffeine, or more
aggressively with an epidural blood patch of the leaking
dural hole.
Epidural block
• A needle for the epidural space takes a
similar path to a spinal needle, but is
stopped before the dura.
• If the needle is advanced too far, the
dura will be punctured and CSF will pour
out when the syringe is removed.
Epidural block
• Single shot technique
• Loss of resistance
technique-ligamentum
flavum gives the strong
resistance to
compression of the
syringe barrel. As the
epidural needle passes
through the ligamentum
flavum a sudden loss of
resistance occurs
• Hanging drop technique
Epidural block
Catheter Techniquecontinuous technique
Epidural block
• Epidural anesthesia requires about ten times the dose of local
anesthetic to achieve a block as compared to a spinal. This raises
the potential for systemic toxicity.
• The blocks set up more slowly than spinal blocks, but is good for
controlling blood pressure with fluid resuscitation.
• Postoperative continuous epidural analgesia.
• Epidurals are a frequent method of labor analgesia for pregnant
women because they produce good analgesia
• Testing dose
• Abdominal and thoracic block
Epidural block-complications
• inadvertent dural puncture and total spinal
blockade
• total epidural blockade
• epidural venous injection
• local anesthetic toxicity
• gaps
• neurological complications -damage of the
nerves, hematomas, infections, direct trauma to
the spinal cord.
• backache
1/ Sympathetic block
2/ Sensory block ( cold sensation, pain,
touch)
3/ Motor block
Assessing the quality of a block
Methods of measurement of motor blockade
The Bromage Scoring Method
• 0: No motor block: full flexion of knee and
foot.
• 1: Inability to raise extended le. Just able
to move knee.
• 2: Inability to flex knee. Able to move foot
only.
• 3: Inability to flex ankle joint. Unable to
move foot or knee.
Assessing the quality of a block
Methods of assessing the sensory level of the block
• The sensory level may be determined by
mapping out the distribution of loss of
appreciation of pain to pinprick, cold
sensation with ice and paraesthesiae to
soft touch
Assessing the quality of a block
The assessment of sympathetic blockade
(cardiovascular effects)
• sympathetic blockade below the level of
the cardiac accelerator fibres (T1 - T4)
causes venodilatation→hypotension
• sympathetic blockade above the level of
the cardiac accelerator fibres (T1 - T4) will
cause a bradycardia and hypotention
4/ Blockades of the Peripheral Nerves
• Brachial plexus blockade
→interscalene approach=Winnie’s approach
→axillary approach
• Lumbar plexus blockade (femoral, obturator
and lateral femoral nerves)
→psoas compartment block
→femoral nerve block=3 in 1=inguinal block of the
lumbar plexus
• Sacral plexus blockade (sciatic nerve)
→proximal sciatic nerve block=transgluteal=
acording to Labat
Brachial plexus blockadeinterscalene approach=Winnie’s
Complications:
• Phrenic nerve paralysis
• Horner’s Syndrome
• Reccurent laryngeal nerve paralysis
• Vessel puncture
Brachial plexus blockade- axillary
approach
• Gaps
• Low risk method
Commonly used needles in
nerve blocks
Contraindications
absolute contraindications:
• patient’s refuse
• infection at the injection site
• coagulopathy whether therapeutic or part of the patient's
pathology
• increased ICP - absolute contraindications when epidural
or spinal is considered.
relative contraindications:
• sepsis, hypovolemia,
• neurologic disease, psychologic instability,
• antiplatelet drugs,
• prolonged surgery,
• certain cardiac diseases (idiopathic hypertrophic
subaortic stenosis, aortic stenosis), and
• uncooperative patient or surgeon.
Benefits of local anasthesia
• Diminish a predominant part of the
physiologic response to surgical
procedures=stress response
• Prophylaxis of thromboembolic
complications
• Postoperative analgesia
• Vasodilatation in artheriosclerosis
• Cooperative patient