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.