-------------------------------------------------------------------------------- TITLE: Local Anesthetics and Analgesia SOURCE: Dept. of Otolaryngology, UTMB, Grand Rounds DATE: March 21, 1990 RESIDENT PHYSICIAN: Wayne Williams, M.D. FACULTY: Charles Stiernberg, M.D. DATABASE ADMINISTRATOR: Melinda McCracken, M.S. -------------------------------------------------------------------------------- "This material was prepared by resident physicians in partial fulfillment of educational requirements established for the Postgraduate Training Program of the UTMB Department of Otolaryngology/Head and Neck Surgery and was not intended for clinical use in its present form. It was prepared for the purpose of stimulating group discussion in a conference setting. No warranties, either express or implied, are made with respect to its accuracy, completeness, or timeliness. The material does not necessarily reflect the current or past opinions of members of the UTMB faculty and should not be used for purposes of diagnosis or treatment without consulting appropriate literature sources and informed professional opinion." I. Local Anesthetics A. Pharmacology B. Chemistry C. Topical Anesthetics D. Injectable Anesthetics E. Adverse Reactions F. Drug Interactions II. Local and Regional Anesthesia A. Patient Preparation B. Field Block and Infiltration C. Scalp and Forehead D. Auricle E. Nose F. Mental Nerve G. Mandibular Nerve H. Maxillary Nerve III. Analgesia and Sedation A. Premedication for Local Anesthesia B. Approach to Premedication C. Intraoperative Sedation Definitions: 1. Local Anesthesia- The use of a nonvolatile substance applied to nerves to produce an area of diminished or no sensation. 2. Local Infiltration- Injection of local anesthetic to throughout an area of skin. 3. Ring Block- Injection of anesthetic subcutaneously around surgical field to produce anesthesia in center. 4. Field Block- Injection of a wall of anesthetic to deep fascia around operative field. 5. Nerve Block- Infiltration of anesthetic along major nerve to produce anesthesia throughout the area supplied by the nerve. I. Local Anesthetics A. Pharmacology 1. Mechanism of Action -Stable electrical potential across nerve cell membrane maintained by Na/K gradient. -Electrical alteration of membrane opens Na channel producing depolarization. -Blockage of nerve impulses by local anesthetics starts by displacement of calcium at receptor sites which alter Na permeability preventing depolarization. -Hypercalcemia and hypernatremia and hypokalemia states diminish effect of local anesthetics. -Local anesthetic spread into nerve is by diffusion. Large nerves, myelinated nerves, nerves enclosed in fibrous bundles require higher concentration. -Sensation will be lost in order of cold, warmth, pain, touch, pressure, vibration, proprioception and motor function. 2. Chemistry -Same molecular nucleus with either ester or amide linkage. -Made water soluble by mixing with HCl. Free base (unionized form) penetrates neural membranes while ionized form active. 3. Esters -Cocaine, Procaine, Chloroprocaine, Tetracaine -Metabolized in tissue or circulation by a cholinesterase and excreted by kidney. -Allergic reaction much more common with esters. -Is a paraminobenzoic acid (PABA) derivative; can cross-react 4. Amides -Lidocaine, Mepivacaine, Bupivacaine, Etidocaine -Metabolized in liver -Allergy extremely rare and hard to document. B. Topical Anesthetics 1. Cocaine -4% concentration, maximum dose 200mg; 5cc of 4% -Immediate onset of action with 120 minute duration -Only topical to produce vasoconstriction -Mechanism by preventing re-uptake of nor-epinephrine at synapses. -Addition of epinephrine has no effect on duration or absorption. -Used primarily in nasal surgery 2. Tetracaine (pontocaine) -1% concentration, maximum 200mg: 2ml of 1% -Onset slow topically, but duration 45 minutes -used primarily for as topical anesthetic 3. Dyclonine (dyclone) -not ester or amide -0.5% and 1% solutions; 200mg maximum dosage -Usual dosage 5-10mls gargled; 10-15ml swallowed for esophogoscopy -Also available as gel for oral lesions -Onset in 10 minutes, duration 1 hour -used for topical mucosal anesthesia only; not recommended for nose 4. Lidocaine (xylocaine) -Topical 2%, 4% and 10% concentrations; Maximum 10ml of 2%, 2ml of 10% solution (10mg metered spray); 300mg in single dose. -Should not be repeated in less than 2 hours. -Onset within minutes, duration only 10-15 minutes. C. Injectable Local Anesthetics 1. Lidocaine -0.5%, 1%, 2% concentrations; maximum 300mg (5mg/kg; 30ml of 1%) and 500mg (7mg/kg; 50ml of 1%) with epinephrine. -Onset almost immediate with infiltration; duration 1 hour with 0.5% (2 hours with epinephrine) and 1.5 hours with 1% (3.5 hours with epinephrine) 2. Procaine (novocaine) -Principle anesthetic for years, replaced by lidocaine. -ester linkage -Short-acting, extremely low toxicity 3. Bupivacaine (marcaine) -Amide linkage -0.25% and 0.5% concentrations; maximum 175mg (70ml of 0.25%) and 225mg (90ml of 0.25%) with epinephrine. Not to be repeated within 3 hours with maximum 8mg/kg in 24 hours. -Onset slow at 10-20 minutes lasting 3 hours, 6 hours with epinephrine. Nerve blocks usually 7 hours, sometimes 15 hours. 4. Etidocaine (duranest) -0.5% concentrations; maximum 300mg (4mg/kg) -amide linkage -Onset slightly longer than lidocaine with duration a little more than bupivacaine. -Less toxic than bupivacaine because less rate of absorption and increased volume of distribution. 5. Mepivacaine (carbocaine) -1%, 1.5% and 2% concentrations; maximum 400mg (7mg/kg, 80ml of 0.5%) -Onset similar to lidocaine with longer duration of action. -Only local anesthetic to produce vasoconstriction instead of vasodilation. -No drowsiness or amnesia sometimes seen with lidocaine. D. Adverse Reactions 1. Hypersensitivity -Extremely rare -use of test dose not predictable -Topical application for prolonged period can lead to sensitivity with esters. 2. Systemic -Most common cause of toxic reaction is inadvertent intravascular injection. -Reaction similar for all local anesthetics. -Central nervous system and cardiovascular systems affected -CNS: initially restlessness, circumoral paresthesia, tinnitus, tremors, shivering (stimulation); then seizures. -higher levels produce CNS depression. -Diazepam will control seizures; some advocate its use prophylactically. -Cardiovascular: bradycardia, hypotension, heart block. Develops well after CNS symptoms. -Treat with fluids and vasopressors like ephedrine (10-25mg IV). -Epinephrine can also produce systemic effects of anxiety, restlessness, palpations, tachycardia, dizziness and headache. 3. Local -Most common is contact dermatitis with ester types in people who have be frequently exposed. E. Drug Interactions -No local anesthetic should be used in the presence of monoamine oxidase inhibitors or phenothiazines. -MAO inhibitors create a pool of endogenous catecholamines which can cause hypertensive crisis. -Phenothiazines are irreversible blockers of alpha adrenergic receptors that when combined with the vasodilatory effects of all local anesthetics can lead to profound hypotension. -Tricyclics and tetracyclics block the reuptake of catecholamines and in the presence of exogenous epinephrine can produce prolonged hypertensive crisis and dysrhythmia. MAO Inhibitors: Phenelzine, Isocarboxazid, tranylcypromine Tricyclics: Imipramine, Amitriptyline, Amoxapine, Desipramine, Doxepin, Nortriptyline, Protriptyline, Trimepiamine, Carbamazepine (Tegretol), Cyclobenzapine (Flexeril) Tetracyclics: Maprotiline II. Local and Regional Anesthesia A. Preparation of Patient -Fear of the Unknown -Well rested: use minor sleeping aid -Preoperative sedation B. Local Infiltration and Field Block -Select anesthetic agent: many use combination of lidocaine and marcaine (10cc of 2% lidocaine with epinephrine 1:100,000 and 10cc of 0.5% marcaine with 1cc of 1:1000 epinephrine added to give 20cc 1% lidocaine/ 0.25% marcaine with 1:75,000 epinephrine.) -With patient comfortable raise wheal in dermal-subcutaneous junction as first injection. -use 27-30 gauge needle at 30-40 degree angle with bevel down. -For intraoral injections begin with topical anesthetic. -Little chance of intravascular injection if injecting while needle in motion during infiltration. -Minimize discomfort by: -slow injection (1cc/minute) -use plain anesthetic with fresh epinephrine added prior to use (Plain solution has higher pH.) -use buffered lidocaine or mepivacaine. -10:1 dilution with Na bicarbonate -must mix prior to use then discard -must not add too much base or agent will precipitate C. Scalp and Forehead -Ring of anesthetic injected subcutaneously along circumference of skull at level of eyebrow provides anesthesia superior to this line. -For forehead only end line at lateral eyebrows. -Can use less anesthetic and produce less pain by specifically blocking the supraorbital, supratrochlear, zygomaticotemporal and auriculotemporal nerves by injecting glabella, eyebrows and preauricular region. D. Auricle -Innervated by 4 cranial nerves and cervical plexus. Cervical plexus supplies posterior ear and lateral 2/3 of anterior. Trigeminal supplies remaining 1/3 and part of EAC. Facial, glossopharyngeal and vagus supply remaining canal and concha. -Field block beginning inferiorly, then concha and canal in 4 quadrants. E. Nose -Supplied by infratrochlear and external nasal branches of V1, infraorbital and anterior spinous branches of v2. -Anesthesia best with field block and nerve block with critical injection areas nasal root between innercanthi, nasal tip, infraorbital foramina and base of columella. -Begin by blocking infraorbital since anesthetizes greatest area. -Infraorbital nerve terminal branch of maxillary division of trigeminal supplies nose, cheek, upper lip and upper lid. -Located 1 cm below orbital rim at midpupillary line. -No attempt should be made to enter the foramen. -Intranasal block easily accomplished by application of topical anesthetics. Must have applicator directly under dorsum and one posterior middle meatus. F. Mental Nerve -Supplies chin and lower lip -Located 2.5cm lateral to midline; more superior in elderly; usually under second bicuspid -Aspiration important; incidence positive aspiration 10%. G. Mandibular Nerve -Highest failure rate at 15-20% in experienced hands. -Will block pharyngeal, buccal, preauricular, mandible and anterior 2/3 of tongue. -Most easily approached in the infratemporal fossa posterior to pterygoid plate. -Insertion below zygomatic arch midway between coronoid process and condyle. Advanced at right angle until contacts pteryoid plate at depth of 3-4cm. Then withdrawn few millimeters and redirected 20 degrees posteriorly until paraesthesias. Inferior Alveolar and Lingual Nerve -Insertion made in retromolar trigone region 1cm above and parallel to occlusal plane at 45 degree angle to mandibular teeth. Needle advanced between ramus and muscles covering internal surface about 1-2cm or until resistance met. -Hematoma not infrequent, almost always self-limiting. H. Maxillary Nerve -Produces profound anesthesia of premaxilla. -Lateral and anterior route described, but anterior approach considered easier. -Anterior approach: Locate anterior border of coronoid process and the inferior margin of the malar bone. 22 gauge needle inserted perpendicular until contact with maxilla. Then withdrawn and redirected superiorly and posteriorly to enter the pterygomaxillary fossa 1 cm farther than the original contact for insertion of 5 to 6 cm. III. Analgesia and Sedation A. Premedication for Local Anesthesia -Goals: relief of anxiety, analgesia, amnesia -Proper drug and dosage depends on patient taking into account age, physical state, weight, level of anxiety, history of past responses. -No premedication frequently in elderly, severe pulmonary disease or pediatric patient 1. Barbiturates Secobarbarbital (seconal) 100 - 150mg IM Pentobarbital (nembutal) 100-150mg IM -Advantages: good sedation with minimal respiratory or circulatory depression. Does not induce nausea or vomiting. -Disadvantages: Limited by lack of analgesic effect and occasional association with disorientation. -Contraindicated in patient with acute intermittent porphyria. 2. Narcotics Meperidine (demerol) 50 - 100mg IM Morphine 5 - 15mg IM -Advantages: Historically most commonn premedication. Provides comfortable and reliable sedation and perioperative analgesia. Readily reverible with naloxone. -Disadvantages: Strong respiratory depressant, provides no amnesia, can induce orthostatic hypotension and nausea and vomiting, causes smooth muscle contraction and occassional dysphoric reaction. 3. Benzodiazipines Diazepam (valium) 10mg po Lorazepam (ativan) 2 - 4mg po/IM Midazolam (versed) 5mg po/IM -Valium levels peak 30 - 90 minutes after po, while ativan peaks at 2.5 hours. Versed fastest onset and shortest duration with effect at 15 minutes after po and peak 30 - 60 minutes. -Advantages: Strong antianxiety effect and considerable amnestic (most with ativan). No caridovascular or respiratory depression in premed dose. Does not induce nausea or vomiting. -Disadvantages: Long duration, can cause depression in elderly,reduces esophogeal sphincter tone. -Ativan should not be combined with scopalamine because of increased sedation, hallucinations and irrational behavior. No problem with versed or valium. B. Approach to Premedication -Sleep aid night before beneficial (Dalmane 15 - 30mg) -On day of surgery preanesthetic administered IM 1 - 2 hours before surgery. (Valium best administered po 2 hours before surgery) -Combination frequently used (nembutal 100mg IM and ativan 4mg po or demerol 100mg with vistaril 25mg and valium 10mg po.) C. Intraoperative Sedation -Should have calm, comfortable and responsive patient after premed on arrival to OR. -Use of IV sedation requires close patient monitoring. Minimal requirement is EKG and serial vital signs. Pulse oximeter becoming standard of care. Must be able to stop procedure to address untoward effects. If not anesthesiologist is a must. 1. Narcotics Meperidine (10 - 25mg increments, 10 minute intervals) Morphine 1 - 2mg increments, 15 minute intervals) Fentanyl (0.5 - 1.0ml increments, 3 minute intervals) -Total amount and frequency titrated to patient response. -Note fentanyl short duration with slow onset. a. Cardiovascular Effects -Hypotension, bradycardia possible; most likely in hypovolemic or hypertensive patient. Readily treated with intravenous fluids and trendelenburg position. Bradycardia results from vagal stimulation. (most likely with morphine) Treat with atropine. -Meperidine is a stronger myocardial depressant and causes venodilation. This is a rare problem if medicine administered in increments with BP monitoring. b. Respiratory Effects -All narcotics cause dose related respiratory depression. -Initial phases patient exhibits decreased respiratory rate while maintaining normal tidal volume. Therefore, important to monitor rate. -Respiratory depressant effect additive with other depressants. -Older patients display greater sensitivity. -Pain functions as a physiologic antagonist. Therefore, unstimulated patient (ie. recovery room) needs rate watched closely. -If rate drops significantly can partially reverse narcotic with narcan intravenously in small incremental doses (0.05 - 0.1mg) allowing 2 -3 minutes for effect. c. Miscellaneous Effects -Can cause significant nausea and vomiting even in small doses. -Can induce biliary colic from spasm of sphincter of Oddi. -Bronchospasm can result from direct action on smooth muscles and indirect action through release of histamine. -Rapid administration, especially fentanyl, can precipitate chest wall rigidity. 2. Ultra-Short-Acting Thiobarbiturates Thiopental (pentothal) 50 - 100mg every 30 - 40 seconds till effect Methohexital (brevital) 5 - 12ml of 1% at 1ml/5 seconds -Should only be used with anesthesiologist. -Not useful for maintaining sedation. -Always begin with 2ml test dose of fresh solution. -Pentothal most common used. -In suffiently large doses produces sedation, hypnosis and amnesia. -Small doses actually produce increased sensitivity to pain. -Laryngotracheal reflexes remain intact until deep anesthesia achieved. -Reaches peak brain concentration in one circulation time, then rapidly diffuses out reaching 1/2 peak concentration in 5 minutes. Metabolism is much slower, so can accumulate. -Adverse Reactions: -Causes dose dependent cardiovascular depression and vasodilation. -Potent respiratory depressant. Depth of respiration decreased as opposed to rate as seen with narcotics. 3. Benzodiazepines Diazepam (valium) 2.5mg IV every 30 seconds to effect Midazolam (versed) 1.5 - 2.5mg IV allow at least 2 minute interval Lorazepam (ativan) 1 - 2mg IV -Valium dosage will vary depending on patient and premedication; usually will require 5 to 30mg with endpoint light sleep, nystagmus or slurred speech. -Versed half-life 2 hours, while valium 20 hours. All with rapid onset IV with sedation in 3 - 5 minutes. Onset of lack of recall delayed 20 - 30 minutes. -Versed must be administered slowly or brief period of apnea likely. (1mg/min) -Advantages: No cardiovascular effect, no emetic effect. -Disadvantages: Potentiates respiratory depression of narcotics. In sedative doses can produce mild respiratory depression with decrease in tidal volume with small increase in rate. 4. Butyrophenones (Major Tranquilizers) Droperidol (inapsine) 2.5 - 5mg IM premedication 1.25mg IV -Induces a strong state of apparent apathy and mental detachment. -No analgesic properties, but patient is placid, drowsy and indifferent. -When used alone frequently produces dysphoria and patients, although cooperative at surgery, afterwards describe feelings of anxiety and apprehension. -When used as a premed should always be combined with a narcotic. -Most noted for antiemetic activity. -Frequently combined with narcotic to produce neuroleptanalgesia which is a syndrome characterized by patient apathy, immobility and analgesia. -Most common combination is fentanyl and droperidol 0.05mg/2.5mg per cc (innovar) . -Advantages: Protects from epinephrine induced arrhythmias by lengthening the refractory period of the pacemaker. -Adverse Reactions: Causes moderate alpha adrenergic blockage with decreased peripheral and pulmonary vascular resistance which can lead to hypotension. Postural hypotension frequently occurs. Causes vasodilation which can increase bleeding. Extrapyramidal side effects may manifest as various degrees of dyskinesias especially of the face, neck and pharyngeal muscles. This usually responses promptly to IV diphenhydramine (benadryl) or benztropine (cogentin). ---------------------------------------------------------------------- BIBLIOGRAPHY Christoph, R., et al; Pain Reduction in Local Anesthetic Administration Through pH Buffering, Ann Em Med, 17:2, Feb. 1988, pp. 117-120. Corssen, G., et al; Intravenous Anesthesia and Analgesia, Lea and Febiger, 1988. Eriksson, E.; Illustrated Handbook in Local Anesthesia, 2nd ed.,W. B. Saunders, 1980. Klein, J.; Anesthesia for Liposuction in Dermatologic Surgery, Derm Surg Oncol, 14:10, Oct. 1988, pp. 124-1132. Pratt, J.; Analgesics and Sedation in Plastic Surgery, Clinics in Plastic Surgery, vol. 12, no. 1, Jan. 1985, pp.73-83. Scott, D.; Techniques in Regional Anesthesia, Appelton and Lange, 1989. Stiff, J., et al; Anesthesia in Otolaryngology, Otolaryngology, English, vol. 5, chpt 64, pp. 1-22. Stromberg, B.; Regional Anesthesia in Head and Neck Surgery, Clinics in Plastic Surgery, vol. 12, no. 1, Jan. 1985, pp.123-136. Verlander, J., et at; The Clinical Use of Cocaine, Otolaryngologic Clinics, Aug. 14:3, 1981. Winton, G.; Anesthesia for Dermatologic Surgery, Derm Surg Oncol, 14:1, Jan. 1988, pp. 41-54. ----------------------------------END------------------------------------------