Local Anesthetics and Nerve Blocks
Catherine Hannan, MDDecember 13, 2007
Local Anesthesia 1860, cocaine (ester) extracted from
leaves Erythroxylon coca bush 1884: Sigmund Freud & Karl Koller:
cocaine as local anesthesia for eye procedure
1904: procaine (ester of PABA)- severe allergic reactions;
1930: tetracaine- more potent; more allergies
1943: first AMIDE: lidocaine
Local Anesthetics Method of action:
Reversibly block conduction of nerve fibers Prevent increase in permeability of nerve cell
membranes to Na ions, decreasing rate of depolarization
Binds INTRACELLULAR receptor on Na channel -> inhibit influx
Does not change resting or threshold potential
Local Anesthetics
Esters- plasma/ liver metabolism (pseudocholinesterase) Cocaine Procaine
(Novocaine) Tetracaine
(Pontocaine) Chloroprocaine Benzocaine
AmIdes- hepatic metabolism (CYP450- many interactions) Lidocaine
(Xylocaine) Bupivicaine
(Marcaine) Mepivacaine Etidocaine Prilocaine
Local Anesthetics Hydrophobic
benzene ring, intermediate chain (ester or amide) and tertiary amine (hydrophilic)
all are weak bases. pKa for most 8.0-
9.0. Nonionized more
likely to cross membrane ->stronger
anesthetic Ionized binds
tighter to Na channel
Factors affecting physiologic action: Lipid solubility: potency directly related
(90% of cell membrane lipid) Increased lipid content, faster absorption, blockade
Affinity for protein binding: duration of action More firmly bound, longer duration of action
% ionization at physiologic pH: ionized, nonionized forms
NONIONIZED forms cross membrane, bind to Na channel Anesthetics w/ high % NI, faster onset of action More closely pKa meets physiologic pH, faster onset Low pH ionized (delay of onset) Higher pH (add bicarb) noninonized, faster onset
Inflammation decreases pH, slowing onset of action vasodilating properties: all (except cocaine)
vasodilate direct relaxation of peripheral arteriolar smooth muscle vasodilator activity faster absorption shorter duration Add epi, vasoconstrict longer duration of action
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 cc’s 100 cc’s 1 cc
Duration/ Max Dosage
Agent Duration Max DosageEsters
Cocaine Med N/A
Procaine Short 7 mg/kg
benzocaine N/A N/A
Tetracaine N/A N/A
chlorprocaine Short (15-30min) 800mg w/o epi, 1000 mg w/ epi
Amides
Lidocaine Med (30-60 min) 4.5 mg/kg w/o Epi, 7 mg/kg w Epi
Mepivicaine Med (45-90 min) 7 mg/kg to max of 400 mg
Bupivicaine Long (120-240 min) 2.5mg/kg with Epi (0.25% sol 1cc/kg)
Etidocaine Long (120-180 min) 6 mg/kg w/o Epi, 8 mg/kg with Epi
Prilocaine Med (30-90 min) 500 mg w/o Epi, 600 mg with Epi
Local Anesthetics Local anesthetics
preferentially block small fibers Higher firing frequency More circumferential
(outer) fibers before internal
motor before sensory, prox to distal
Effectiveness affected by pH
high pH, most molecules uncharged-> higher permeability
low pH, molecules ionized, won’t enter cells
Order of blockade 1. pain 2. cold 3. warmth 4. touch 5. deep pressure 6. motor
Recovery in reverse order
Local Anesthetic Toxicity Central Nervous System
Initial symptoms (6.0mcg/ml) Perioral tingling/ numbness Metallic taste Lightheaded/dizzy Visual/auditory hallucinations (tinnitus, difficulty
focusing) Disorientation/ drowsiness
Higher dose (>10mcg/ml) Muscle twitching Convulsing Unconsciousness/ coma Resp depression/ arrest CV depression/ collapse
Toxicity Cardiovascular
Direct cardiac effects myocardial depression(tetracaine, etidocaine,
bupivacaine), cardiac dysrhythmias (bupivacaine), cardiotoxicity in pregnancy
Peripheral Effects Vasoconstrict @ low doses Vasodilate @ higher doses (hypotension)
Range of effects Chest pain Shortness of breath Palpitations Lightheadedness Diaphoresis Hypotension Syncope
Toxicity Hematological
Methemoglobinemia- mostly w/ prilocaine, also reported w/ lidocaine, benzocaine
O-toluidine (metabolite of prilocaine) oxidizes hemoglobin to methemoglobin.
low levels (1-3%) asx higher levels (10-40%)
Cyanosis Cutaneous discoloration (gray) Tachypnea /Dyspnea Exercise intolerance /Fatigue Dizziness and syncope Weakness
Toxicity Allergies: esters derivatives of para-
aminobenzoic acid (PABA) associated with acute allergic reactions. 30% rate of allergic reactions to procaine,
tetracaine, and chloroprocaine Pt allergic to whole ester class
Additives Epinephrine
Decrease systemic toxicity(decrease uptake 30%)
Prolong local anesthesia (by 50%) Decrease local bleeding Detect whether injection “intravascular”
Local anesthetics - vasoconstrictors
Ratios
Epinephrine in extremely dilute concentrations, ratio of grams of drug:total cc’s of solution.
1:1000 preparation of epinephrine would be:
1 gram epi
1000 cc’s solution
1000 mg epi
1000cc’s solution =1 mg epi
1 cc =
Local anesthetics - vasoconstrictors
Vasoconstrictors should not be used in the following locations
Fingers Toes Nose Ear lobes Penis
Local with EpinephrineA. Krunic, L. Wang, K. Soltani, S. Weitzul, R. Taylor. Digital
anesthesia with epinephrine: An old myth revisited. Journal of the American Academy of Dermatology, Volume 51, Issue 5, Pages 755-759, 2004.
Lit review: 50 cases digital gangrene 21 cases local w/ epi (concentration only known in 4 cases) No strong evidence of epi as cause of necrosis older compounds (cocaine, eukaine, and procaine), non-standardized,
inaccurate methods of mixing epinephrine with lidocaine, inappropriate use of a tourniquet, postoperative hot soaks, infection, or large anesthetic volume were also present.
Sodium Bicarbonate Acidity of additives in local causes burning @ site
1 meq/10 ml lidocaine, 0.1 meq/10 ml bupivicaine Increase pH, nonionized, faster onset
TUMESCENT Commonly used in plastic surgery procedures Fluid (NS or LR) with lidocaine (0.5-1%) and epinephrine
(1:1,000,000) Can go up to 35mg/kg as systemic absorption so low
Local Injection Technique
Aspirate while placing needle to prevent intravascular injection
Warm (body temp) anesthetic causes less discomfort
Pressure due to flow of injection ->pain smaller gauge needle -> less pain
Local Blocks
Barry Zide, M.D., D.M.D.
Mitchel Seruya, M.D.
Local/ Regional Blocks 1 Infraorbital 2 Mental and Mental Plus 3 Supraorbital/
supratrochlear infratrochlear
4 Dorsal Nasal Nerve 5 Zygomaticotemporal 6 Zygomaticofacial 7 Great auricular 8 V3 block
Anatomy
Infraorbital Nerve Block Found on vertical line
from medial limbus down, 4 to 7 mm below orbital rim
Transcutaneous approach from lateral alar rim directed up to infraorbital foramen (downward slant)
Can get into foramen can do intraoral
approach 1-2 cc Nose, cheek, lip, eyelid
Mental Nerve Exits from foramen
below apex of 2nd bicuspid
Find 2nd lower bicuspid- place needle tip in buccal sulcus near base of tooth- inject (can palpate)
0.5-1cc Lower lip to
labiomental fold (not always entire chin)
MENTAL PLUS: end branch of mental & terminal of mylohoid Inject subperiosteal
plane anterior to vestibule in front of incisors
Supraorbital/Suptratrochlear Supraorbital notch palpable just above
medial limbus Supratrochlear found under medial cm. of
eyebrow Infratrochlear –br of nasociliary along medial
orbital wall
Supraorbital/Suptratrochlear/Infratrochlear
Inject lat -> med Pierce skin lat part
of mid 1/3 of eyebrow
Aim at supraorb notch
1-2cc under muscle, 1 cc more medially 1 cc at nasal bones
Block of forehead, middle 50% of upper eyelid, frontoparietal scalp
Dorsal Nasal Block Ant enthmoidal br. of
nasociliary n. enters nose on internal surface of nasal bones.
Dorsal nasal n. @ lower border of nasal bone 6-10 mm off midline. small groove in distal nasal
bones under nasalis m. to supply ala, vestibule, lip
Palpate nasal midline w/ thumb & index- Inject 1-2cc 6-10 mm from
midline Numbs dorsum & tip
Zygomaticotemporal
Terminal br. Of V2 Inferior orbital fissure
Lat orbital rim into hairline
Exits fossa on post surface of lat orbital rim at about canthus
Direct needle >1cm behind upper lat orbital rim to pt 5mm below ZMF suture Advance along post bony
wall to 1cm below lat canthus
Zygomaticofacial 2nd br of zygomatic
n. from foramen on ant surface of zygoma
Lateral to intersection of infraorbital & lat orbital rims Inject this area after
previous block Numbs lateral
lower eyelid, upper lateral cheek
Great Auricular Largest branch of C2/C3 Post border of SCM, then climbs it on fascial
surface 6.5 cm distal to lower ext ear canal Pt flex SCM- mark 3 parallel lines, ant, post, mid,
inject 6.5 cm down from ext ear in center Numbs lower 1/3 of ear, lower postauricular skin
Ring Block- Ear Block
Ant ear: auriculotemporal (V2)
Post ear great auricular (C1/C2) & lesser occipital (C2/C3)
Auditory canal: vagusStart preauricular- then
direct posteriorlyAvoid STA
Ring Block- Scalp Block
Front: Supraorbital & supratrochlear (V1)
Lat: Zygomaticotemporal, Auriculotemporal, Lesser occipital
Post: greater & lesser occipital
Inject circumferentially 2 inches apart around head
Digital Blocks
4 digital nerves 2 dorsal (radial & ulnar) 2 palmar (median & ulnar)
Feet: 2 dorsal (peroneal) 2 plantar (tibial)
Traditional Ring Block: Puncture on either side of
digit- 1cc No EPI
Wrist Blocks
Radial, Median & ulnar arteries at wrist
Wrist Block Ulnar nerve: forearm gives palmar sensory br
(runs ulnar to ulnar artery) Deep ulnar w/ deep palmar arch
supplies innervation to three hypothenar muscles, medial two lumbricals, all interossei, and adductor pollicis, palmar brevis.
Median nerve: through carpal tunnel digital branches supply skin of lat 3½ digits and
lat 2 lumbricals Recurrent branch supplies the 3 thenar muscles
Radial: Radial to radial artery (beneath supinator) 3 in proximal to wrist crease, dives & pierces
fascia External branch: radial side and base of the thumb; joins
anterior branch of the musculocutaneous nerve Internal branch: communicates with posterior branch of
musculocutaneous nerve. back of the hand, it forms an arch with the dorsal
cutaneous branch of ulnar nerve.
Wrist Block: Radial
Above the styloid process (circle), gives digital branches for the dorsal skin of the thumb, index finger, and lateral half of the middle finger. Several of its branches pass
superficially over the anatomic "snuff box".
Inject 5cc in “field block” just above styloid (aim medially), then 5cc aiming laterally
Wrist Block: Median Median nerve just
ulnar to palmaris ten
Insert needle b/w palmaris & FCR
Pierce deep fascia Aspirate, then
inject 2-3 cc
Ulnar Nerve Found b/w ulnar
artery and FCU Insert needle under
FCU close to attachment above styloid process of ulna
Needle advanced 5-10 mm to just past tendon of FCU
Aspirate, inject 3-5cc
Inservice Questions
The mental nerve exits the mental foramen at which of the following sites?
(A) Below the canine halfway down the mandible
(B) Below the first premolar halfway down the mandible
(C) Below the first premolar, directed posteriorly
(D) Below the second premolar halfway down the mandible
(E) Below the lateral incisor
Inservice Questions A 55-year-old woman has numbness of the
earlobe after undergoing biopsy of an internal jugular lymph node. The most likely cause is injury to which of the following structures?
(A) Auricular branch of the vagus nerve(B) Auriculotemporal nerve(C) Great auricular nerve(D) Posterior auricular nerve(E) Ventral ramus of the first cervical root
Inservice Questions
A 42-year-old man is scheduled to undergo surgical excision of a lesion of the lower lip. During anesthetic blockade of the mental nerve prior to the procedure, the nerve foramen can be located beneath the apex of which of the following mandibular teeth?
(A) Central incisor(B) Cuspid(C) First molar(D) Lateral incisor(E) Second bicuspid
Inservice Questions
Which of the following nerves provides primary innervation of the dorsal nasal tip?
(A) Anterior ethmoid (B) Infraorbital (C) Infratrochlear (D) Nasopalatine
Inservice Questions During a rhytidectomy procedure, the risk
for injury to the great auricular nerve is greatest at which of the following locations?
(A) 1 cm anterior to the tragus(B) 2 cm posterior to the lobule(C) 4 cm posterior to the lobule(D) 6 cm inferior to the tragus(E) 10 cm inferior to the tragus
Inservice Questions
Which of the following local anesthetics produces vasoconstriction and increases blood pressure?
(A) Bupivacaine(B) Cocaine(C) Lidocaine(D) Mepivacaine(E) Tetracaine
Inservice Questions
A 32-year-old woman is scheduled to undergo suction-assisted lipectomy using tumescent anesthesia with lidocaine. In this patient, the peak plasma concentration of lidocaine is most dependent on the
(A) total mg/kg dose(B) patient’s renal function and rate of excretion of
the drug(C) rate of systemic absorption of the drug(D) ratio of the total volume of the suction aspirate
to the amount of infused solution
Inservice Questions
During resection of a lesion on the conchal bowl, a patient receives a wheal injection of local anesthetic posterior to the sulcus, below the lobule, and anterior to the tragus. After the procedure begins, the patient feels pain. The most likely cause is inadequate anesthetic field block of which of the following nerves?
(A) Auriculotemporal(B) Chorda tympani(C) Great auricular(D) Lesser occipital(E) Vagus (X)
Inservice QuestionsWhich of the following structures provides sensation to the upper cranial surface of the ear?(A) Anterior branch of the great auricular nerve(B) Arnold’s branch of the vagus nerve(C) Auriculotemporal nerve(D) Lesser occipital nerve(E) Posterior branch of the great auricular nerve
Inservice Questions
A 53-year-old woman is scheduled to undergo localized excision of a benign lesion on the upper arm. She has a history of allergic reaction to a local anesthetic. Which of the following is the most likely causative anesthetic?
(A) Bupivacaine(B) Lidocaine(C) Mepivacaine(D) Tetracaine
Inservice Questions
A 34-year-old woman is scheduled to undergo surgical shaving of a lesion of the right forearm during local anesthesia with a solution containing 1% lidocaine. This corresponds to how many milligrams of lidocaine per milliliter?
(A) 0.1 mg(B) 1 mg(C) 10 mg(D) 100 mg
Inservice Questions
Which of the following local anesthetics has sympathomimetic effects?
(A) Bupivacaine (B) Cocaine (C) Lidocaine (D) Mepivacaine
Inservice Questions
In a 50-year-old woman who has a history of allergic reaction to tetracaine, which of the following anesthetics should NOT be used?
(A) Bupivacaine(B) Etidocaine(C) Lidocaine(D) Mepivacaine(E) Procaine
Inservice Questions
A 50-year-old man who weighs 155.5 lb (70 kg) is scheduled to undergo liposuction of theabdomen, flanks, and chest with administration of epinephrine and lidocaine for tumescent anesthesia. Which of the following amounts of lidocaine is the maximum for this patient?
A ) 7 mgB ) 35 mgC ) 150 mgD ) 490 mgE ) 2450 mg
Inservice Questions Which of the following is an
advantage of using bupivacaine over other local anesthetic agents?
A ) Increased vasoconstrictionB ) Less cardiotoxicityC ) Less motor blockadeD ) Rapid metabolismE ) Rapid onset of action
Inservice Questions
Which of the following local anesthetics is associated with the greatest risk for development of a true allergic reaction?
(A) Bupivacaine(B) Lidocaine(C) Mepivacaine(D) Prilocaine(E) Tetracaine
Inservice Questions A 50-year-old woman who is obese undergoes
carpal tunnel release using a lidocaine Bier block for anesthesia. During the procedure, the patient becomes restless and complains of a metallic taste in her mouth and ringing in her ears. As the tourniquet is rechecked, the patient begins having seizures. Which of the following interventions is the most appropriate next step?
A ) Administer intravenous fluidsB ) Administer intravenous lidocaineC ) Administer intravenous thiopentalD ) Establish an airwayE ) Hyperventilate with oxygen
References Zide B. How to Block and Tackle the Face. Plas
Recon Surg. 101(3), March 1998, 840-851. Huang W, Vidimos A. Topical anesthetics in
dermatology. J Am Acad Dermatol 2000;43:286-98.
Salam G. Regional Anesthesia for Office Procedures: Part I. Head and Neck Surgeries. American Family Physician. Vol. 69/No. 3 February 1, 2004.
Gmyrek R. Local Anesthesia and Regional Nerve Block Anesthesia. eMedicine. Feb 7, 2007.
Wrist Block, Digital Block. www.NYSORA.com Revis D. Local Anesthetics. eMedicine July 2005.