Miscellaneous of Local Anesthetics Flashcards
What is the effect of sodium bicarbonate on a local anesthetic?
Speeds onset of action, especially commercially prepared epinephrine containing
What is the result of alkalinazation of local anesthetics?
Increases the % of unionized (free base) drug to cross the nerve membrane= speeds onset of action
What is the clinical use of alkalinization of LA?
Used clinically with epidural blocks or to reduce pain of subQ infiltration
What are locals ineffective in?
Acidotic infected tissue
1 mL of 8.4% sodium bicarbonate = _____ local anesthetic (except bupivacaine)
10 mL
What is the pH of commerically prepared LA usually between?
3.9-6.5
What is the relationship of dexmedetomidine and local anesthetics?
Dexmedetomidine has been used in local anesthetic admixtures and a central effect is proposed for prolongation of the local anesthetic effect
What is the relationship of intrathecal magnesium and local anesthetics?
has shown initial promising results (duration of spinal anesthesia was increased)
What does the addition of clonidine and ketamine to regional anesthesia have on pediatric patients?
- prolongs the actions of the local anesthetic
- Good pharmacokinetic and pharmacodynamic profiles of efficacy and safety
What is the relationship of epinephrine and local anesthetics?
Epinephrine (1:200,000 or 5 ug/ml) may be added to local anesthetic solutions to produce vasoconstriction
What is the goal of epinephrine use with LA?
vasoconstriction (goal: prolong duration, not onset as with alkalization)
What is the effect of epinephrine use with LA?
Limits systemic absorption and maintains the drug concentration in the vicinity of the nerve fibers to be anesthetized
What effect does epinephrine to a lidocaine or mepivacaine solution have?
prolongs the duration of conduction blockade and decreases systemic absorption of local anesthetics by 20-30% (less so with bupivacaine)
May be some analgesic effect with __________ properties of epinephrine
alpha-2
What is the principle side effects of local anesthetics?
effects are allergic reactions and systemic toxicity due to excessive plasma and tissue concentrations of local anesthetics
What is the systemic toxicity of LA?
in association with regional anesthesia is estimated to result in seizures in 1 to 4 per 1,000 patient exposures to local anesthetics
What is the most common LA associated with systemic toxicity?
Bupivacaine
What is the allergic reactions associated with LA?
rare, accounting for less than 1% of all adverse reactions to local anesthetics
Which LA are more likely to cause allergic reactions with LA?
Esters that produce metabolites related to PABA are more likely than amide local anesthetics to evoke an allergic reaction
What is a theory of the cause of allergic reactions of LA?
- may be due to methylparaben or similar substances used in preservatives in commercial preparations of ester and amide local anesthetics
- Preservatives are structurally similar to PABA
Cross sensitivity between local anesthetics reflects the common ___________
metabolite PABA
What is true about a patient with a known allergy to an ester LA?
can receive an amide local anesthetic without an increased risk of an allergic reaction
What is true about a patient with a known allergy to an amide LA?
An ester local anesthetic can be administered to a patient with a known allergy to an amide local anesthetic
What is true about LA solutions?
should be preservative free
What is the characteristic developments of Local Anesthetic Systemic Toxicity (LAST)?
Excess plasma concentration
- Inadvertent vascular injection
- Large amount absorbed into circulation from large volume blocks
- Continuous infusion or accumulation of metabolites
What is the magnitude of LAST depends on?
on dose administered, vascularity of injection site, presence of vasoconstrictor, & physiochemical properties of LA drug
How soon can LAST occur?
LAST can present more than 15 minutes after injection; monitoring should continue for at least 30 minutes after injection
What is the biggest culprit of Local Anesthetic Systemic Toxicity (LAST)?
Bupivacaine
What is the impact of neuraxial adjuncts/ opioids have?
way to prolong blocks and analgesia to use less LA
What is involved in systemic toxicity?
the CNS and cardiovascular system
What is the first CNS symptoms?
The CNS inhibitory neurons block first (voltage-gated Na+, K+, Ca++)
What occurs after CNS inhibitory neurons block from LAST?
Seizure (excitatory unchecked initially)
What is the CNS toxicity from LAST?
(from low plasma concentration to increased) : numbness of tongue & circumoral tissues, restlessness, vertigo, tinnitus, difficulty focusing, slurred speech
What occurs as a result of CNS toxicity with LAST?
Skeletal muscle twitching signals imminent tonic-clonic seizures
Review LAST progression effects.
Slide 79
______ can increase LA toxicity
Hyperkalemia
________ can lower seizure threshold
Increase PaCO2
_________ can lower seizure threshold of lidocaine
Increase in serotonin
What is a component of the cardiac symptoms of LAST?
requires greater plasma concentrations than needed for CNS symptoms
What are the inital cardiac symptoms of LAST?
- Increase heart rate
- increase blood pressure (Co-occuring with CNS sign)
What are other associated cardiac effects of LAST?
- dysrhythmias
- heart block
- hypotension, bradydysrhythmia
- reduced cardiac contractility
- asystole
What is true about higher doses of LA and LAST?
- At higher doses, LA also blocks cardiac Na+ channels
- Blocked Ca++ and K+ channels along with inhibition of cAMP production
LAST: ________ more sensitive and blocked first
CNS
What cardiac effects of Lidocaine and LAST?
prolongation of P-R interval and QRS complex
What are the characteristics of bupivacine that make it cardiotoxic?
Protein sites quickly saturated with IV injection leaving significant free form unbound (more cardiotoxic than lidocaine)
What are cardiac toxic side effects of bupivacaine?
Precipitous hypotension, cardiac dysrhythmias and AV block (PVC, QRS widening, VT).
Cardiac Toxicity of bupivacaine is plasma concentration: ________
8-10 mcg/ml
What can help to decreased the cardiac toxicity of bupivacaine?
Threshold for toxicity decreased with beta blockers and Ca++ channel blockers as well as epinephrine and phenylephrine
What are the characteristics of Levobupivacaine and ropivacaine?
prepared with less cardiac toxic S-isomer
What is the mnemonic for greatest systemic absorption to least?
BICEPS B-blood/tracheal I-intercostal C-caudal and para cervical E-epidurals P-perivascular brachial plexus S-sciatic/spinal S-subcutaneous
LAST Prevention: What should be used to avoid this side effect?
Use lowest effective dose of LA (volume & concentration)
LAST prevention: What is n injection technique to decrease the likelihood of occurring?
administer 3-5 ml aliquots pausing 15-30 minutes between each injection
LAST prevention: What needs to be done before each injection?
Aspirate the needle or catheter before each injection
LAST prevention: what needs to be done in potentially toxic doses of LA?
Use an intravascular marker
What is the result of epinephrine being injected into the intravascular space?
Adults: epinephrine 10-15 mcg will produce a 10-beat increase in HR or 15mmHg or greater increase in SBP
What is key to stopping LAST?
Early recognition is key/Stop LA administration
What are some theraputic interventions for LAST?
- Prompt airway support (oxygenate/ventilate)
- Circulatory support
- Treat seizures
What medications can be used for circulatory support with LAST?
epinephrine & amiodarone (avoid vasopressin, Ca++ channel blockers and beta blockers)
What medications can be used for seizure support with LAST?
with BZD (midazolam or diazepam – raise seizure threshold) or propofol (if tolerated); paralyze & intubate if refractory seizures
What is the treatment of LAST?
LIPID EMULSION RESCUE
What is the dose of LIPID EMULSION RESCUE?
1.5 ml/kg of 20% lipid emulsion followed by 0.25 ml/kg/min for at least 10 minutes until stabilized
What is the max dose of LIPID EMULSION RESCUE?
10 ml/kg over 30 minutes
What is a surgical intervention for the treatment of LAST?
Coronary pulmonary bypass immediately if not responsive
Permanent neurologic injury after spinal or epidural is _____
rare
What can neurotoxicity as a result of from placement of LAs into the epidural or subarachnoid space can lead to? (3)
- Transient Neurologic Symptoms
- Cauda Equina Syndrome
- Anterior Spinal Artery Syndrome
What is transient neurological symptoms?
Moderate to severe pain in lower back, buttocks, post; thighs 6-36 hrs after complete recovery of spinal anesthetic
What is transient neurological symptoms associated with which medication?
lidocaine spinal
What is the length of recovery for transient neurological symptoms?
usually takes 1-7 days
What is cauda equina syndrome?
Diffuse injury across lumbar-sacral plexus resulting in bladder and bowel dysfunction with bilateral lower extremity sensory and motor impairment (can be permanent
What is cauda equina syndrome most often associated with?
w/use of hyperbaric lidocaine 5% for continuous spinal anesthesia using microcatheters (28ga or smaller); possibly due to pooling of high concentration of LA in lithotomy position
What is the max dose of hyperbaric lidocaine?
spinal: 60mg
What is anterior spinal artery syndrome?
Transient spasm or thrombosis of anterior spinal artery; (elderly, peripheral vascular dz, +/- vasoconstrictor use)
What are the uses of LA classified by?
according to the following sites of placement of the local anesthetic solution
What are examples of classifications of regional anesthesia?
-Topical or surface anesthesia
-Local infiltration
-Peripheral nerve block (PNB)
IV regional anesthesia (Bier block)
-Epidural anesthesia
-Spinal (subarachnoid) anesthesia
Review dose guidelines for LA.
slide 87
Review Local Anesthetic Concentrations (and Epi).
Slide 88
Topical anesthesia is based on the priniciple of?
“Topicalization” of mucous membranes
What are some topical anesthesia used today?
Cocaine 4%, 10%
Tetracaine 1%, 2%
Lidocaine 2%, 4%
Lidocaine jelly 2%, lidocaine ointment 5%
What is topical cocaine used for?
for its vasoconstrictive properties (may sub with oxymetazoline/Afrin with lidocaine or tetracaine)
What is the max dose of Cocaine 4% solution?
Max 5 cc
What can topical lidocaine be used for?
nebulized to anesthetized for upper airway procedures
What is the systemic absorption of topical anesthesia similar?
Systemic absorption similar to IV (lidocaine > tetracaine)
What is EMLA cream?
Eutectic Mixture of Local Anesthesia: 2.5% lidocaine/2.5% prilocaine
What is a use for EMLA cream?
1-2 g per 10 cm2 INTACT skin, occlusive dressing
What satisfactory dermal analgesia for EMLA cream?
achieved 1 hour after application, reaches maximum at 2 to 3 hours, and persists for 1 to 2 hours after removal. (FDA)
What is true about EMLA cream and pediatric patients?
Caution children 3 months/age (methemoglobinemia)
What is not used for EMLA cream?
Not for use on mucous membranes or open wounds
What is the contraindication used for EMLA cream?
allergy to amides
What is local infiltration used for?
Subcutaneous placement
What are some local infiltration examples of LA?
port placement, pacemaker insertion, breast biopsy
What local infiltration is most commonly used?
Lidocaine most commonly used (0.25% bupivacaine too)
What is another dose of local infiltration?
Duration doubled (lidocaine) using 1:200,000 epinephrine (5 mcg/cc)
What LA with epinephrine should not be injected into? What can it cause?
Do NOT inject epinephrine containing LA into digits, ears, nose or penis – can result in vasoconstriction leading to ischemia & gangrene
What is peripheral nerve blocks?
Injection into tissues surrounding nerves/plexuses (i.e., brachial plexus)
What is the characteristics of peripheral nerve blocks?
Diffusion from outer surface of nerve/plexus of nerves toward center along a concentration gradient; usually result in a more proximal anatomic anesthesia followed by distal
What is the progression of blockade with peripheral nerve blocks?
Smaller sensory and autonomic fibers blocked first then larger motor and proprioceptive
What is the onset of Peripheral nerve blocks dependent on?
Rapidity of onset depends on pKa of LA used
What is the onset of lidocaine for peripheral nerve blocks?
onset in 3 minutes
What is the onset of Bupivacaine/Ropivacaine for peripheral nerve blocks?
onset in 15 minutes
What effects the dose of peripheral nerve blocks?
dose, lipid solubility, protein binding, use of vasoconstrictor
What effects duration of peripheral nerve blocks?
more safely by using epinephrine than increasing the dose to risk toxicity
What is a standard of care for peripheral nerve blocks?
Use of ultrasound guidance is becoming a standard of care (also provides documentation for reimbursement)
What is a common practice in some pain practices?
Use of indwelling, perineural catheters for continuous infusions a common practice in some pain practices (patients sent home to control postop pain)
What is true about adjuncts and additives?
not fully supported with evidence-based practice
What is the Bier block?
IV injection of a local anesthetic solution into an extremity isolated by a double tourniquet, producing a rapid onset of anesthesia and skeletal muscle relaxation
What is the common used medication for the bier block?
Lidocaine 0.5% methyl paraben free is most frequently used (Chloroprocaine causes thrombophlebitis)
Review examples of peripheral nerve block?
Slide 95
What is the components of a epidural block?
LA diffuses to spinal nerve roots, spinal cord, paravertebral nerves
What is the process of epidural diffusion?
Slow diffusion process 15-30 minutes
What is a common medication for lidocaine?
(1-1.5%) common drug
What is true about bupivacaine and epidural?
(0.5-0.75%) being replaced with its S-isomers (less cardiac toxicity)
What effect does ropivacine have with epidurals?
blocks motor fibers less than bupivacaine- advantage in laboring epidurals and with pediatrics
Epidural: Adding ______ improves analgesia
opioids
What is the components of epidurals and C sections?
Not uncommon to start with Chloroprocaine 3% in C-section (stat) for onset and then instill 2% Lidocaine for longer duration
What epidural medication is more problematic with fetus and neonates?
Mepivacaine
What is characteristics of highly protein bound medications and epidurals?
Highly protein-bound LA as bupivacaine cross placenta less (however bupivacaine a problem with ion-trapping with a fetus in distress)
What is the dose of epidurals?
Require larger doses than a spinal anesthetic - increased risk of systematic absorption
What is the blockade between motor and sensory?
Differential level of blockade between motor and sensory greater with epidural than spinal (motor block can average 4 segments below sensory level)
Review epidural and spinal differences
Slide 98
What is the dose of epidural?
High (10-20 mL)
What is the dose of spinal?
Low (1.5-2 mL)
What is the onset for epidurals?
Slow (25-30 min)
What is the onset for spinals?
Onset is fast (5 min)
What is spinal anesthesia?
Produced by injection of local anesthetic solutions into the lumbar subarachnoid space
What is the goal of spinal anesthesia?
Goal is to provide sensory anesthesia and skeletal muscle relaxation
What is the principle pharmcokinetics of spinal anesthesia?
Local anesthetic solutions placed into lumbar CSF act on superficial layers of the spinal cord, but the principal site of action is the preganglionic fibers as they leave the spinal cord in the anterior rami
What causes the zones of differential anesthesia to develop?
Because the concentration of local anesthetics in CSF decreases as a function of distance from the site of injection and because different types of nerve fibers differ in their sensitivity to the effects of local anesthetics, zones of differential anesthesia develop
What is true about SNS blockade with spinal anesthesia?
The level of sympathetic nervous system blockade during spinal anesthesia extends approximately two spinal segments cephalad to the level of sensory anesthesia
What is the relationship between the motor and sensory segments of spinal anesthesia?
The level of motor anesthesia averages two segments below sensory anesthesia
What effects the dosages of local anesthetics?
- The height of the patient, which determines the volume of the subarachnoid space
- Segmental level of anesthesia desired
- Duration of anesthesia desired
What is more important with spinal anesthesia?
The total dose of local anesthetic administered for spinal anesthesia is more important than the concentration of the drug or the volume of solution injected
What are the most common medications associated with SAB?
Tetracaine, lidocaine, bupivacaine, and ropivacaine
What does lidocaine produce?
- Lidocaine produces a higher incidence of transient neurologic symptoms than bupivacaine
- If lidocaine is selected, its dose should be limited to 60 mg
What is important regarding the injection of spinal anesthesia?
The specific gravity of local anesthetic solutions injected into the lumbar CSF is important in determining spread of the drug
What is hyperbaric?
The addition of glucose to local anesthetic solutions increases the specific gravity of LA solution above that of CSF
What is hypobaric?
Addition of distilled water lowers the specific gravity of LA solution below that of CSF
What is isobaric?
LA solutions with baricity of 1.000 are referred to
What is important about the duration of action of spinal anesthesia?
CSF does not contain significant amounts of cholinesterase enzymes, thus the duration of action of ester and amide local anesthetics is dependent upon the systemic absorption of the drug
What can occur with spinal anesthesia?
Cardiac arrest may accompany hypotension and bradycardia
In non-obstetric patients, the incidence of hypotension is ________ and the incidence of bradycardia is _________
33%; 13%
What increases the risk factors for hypotension with spinals?
Risk factors for hypotension include sensory anesthesia above T5 and baseline systolic BP<120 mm Hg
What increases the risk factors for bradycardia with spinals?
include sensory anesthesia above T5, baseline HR less than 60 bpm, prolonged PR interval, and concurrent use of beta blocking drugs
Upper abdominal surgery = dermatomal level of ________
T4
intestinal, gynecologic and urologic = dermatomal level of ________
T6
Transurethral resection of prostate surgery = dermatomal level of ________
T8
Vaginal delivery of a fetus and hup surgery surgery = dermatomal level of ________
t10
Thigh surgery and lower leg amputation = dermatomal level of ________
L1
Foot and ankle surgery = dermatomal level of ________
L2
perineal and anal surgery = dermatomal level of ________
S2 to S5 (Saddle block)
