Local anesthetics 4 Flashcards
LAST is more common with ______________ than with ____________
peripheral nerve blocks than with epidural anesthesia
The risk of LAST is increased in the setting of
hypoxia, hypercarbia, acidosis, and hyperkalemia
___________ is the only local anesthetic with vasoconstrictive properties
Cocaine
_______________ is the primary risk of cocaine toxicity
Excessive SNS stimulation
Cocaine toxicity is best treated with
a vasodilator or a mixed alpha and beta antagonist such as labetalol
Cardiovascular toxicity causes
conduction block
depresses the myocardium
and reduces systemic vascular resistance
CNS complications such as seizures occur _________ CV complications with LAST.
before
_____________ is the exception because cardiac complications (myocardial depression, AV block, cardiac arrest) often occurs before a seizure.
Bupivacaine
Analgesia occurs at a plasma concentration of ________ mcg/mL of lidocaine
analgesia
At a plasma concentration of _________ mcg/mL of lidocaine, tinnitus, skeletal muscle twitching, numbness of lips and tongue, restlessness, vertigo, blurred vision, hypotension, and myocardial depression.
5-10 mcg/mL
At a plasma concentration of ______________ of lidocaine seizures and loss of consciousness may occur.
10-15 mcg/mL
At a plasma concentration of __________ of lidocaine coma and respiratory arrest can occur.
15-25 mcg/mL
At a plasma concentration of ___________ of lidocaine cardiovascular arrest can occur.
> 25 mcg/mL
How does hypercarbia increase the potential for LAST?
hypercarbia increases cerebral blood flow and increases drug delivery to the brain
decreases protein binding and increases the free fraction available to enter the brain
How does hyperkalemia increase the risk for LAST?
raises resting membrane potential, making neurons more likely to depolarize
How does metabolic acidosis increase the risk for LAST?
decreases the convulsion threshold and favors ion trapping inside the brain
Factors that decrease the risk of LAST include
hypokalemia, hypocarbia, and CNS depressants
What two features determine the extent of cardiotoxicity?
affinity for the voltage- gated sodium channel in the active and inactive states
rate of dissociation from the receptor during diastole
The risk of bupivacaine toxicity is increased with
pregnancy
beta-blockers
calcium channel blockers
digitalis
Rank the difficulty of cardiac resuscitation with local anesthetics:
bupivacaine> levobupivacaine> ropivacaine> lidocaine
Cocaine should be avoided with
MAOIs
TCAs
sympathomimetic drugs
Beta blockade in the setting of cocaine overdose is a questionable practice that allows for
unopposed alpha-1 stimulation. High SVR (alpha 1 stimulation caused by cocaine) and reduced inotropy (beta-1 antagonism) set the stage for congestive heart failure and CV collapse
What is the best tx for cocaine toxicity?
a vasodilator such as nitroglycerine is best but if given a list of beta-blockers than labetalol (or another mixed alpha and beta antagonist) is a reasonable choice
The maximum allowable dose for cocaine is
200 mg
The dose range for cocaine is
1.5-3.0 mg/kg
One minute following an interscalene block, a 62 kg patient has a seizure. How much 20% lipid emulsion should you administer?
93 mL
What are the steps to treating LAST?
- manage the airway
- treat seizures with a benzodiazepine
- ACLS w/ modifications
- administer 20% lipid emulsion therapy
- avoid beta-blockers and calcium channel blockers
- If the patient is unresponsive to modified ACLS and lipid emulsion therapy, prepare for cardiopulmonary bypass
What should you not give for seizures in the LAST patient?
propofol
What is the agent of choice for ventricular dysrhytmias for the patient with LAST?
amiodarone
What drugs should be avoided with LAST?
vasopressin
lidocaine
procainamide
epinephrine
Why should epinephrine be avoided with LAST?
epinephrine reduces the efficacy of lipid emulsion therapy
if you must give it, then limit the dose to <1 mcg/kg
For 20% lipid emulsion therapy what is the bolus and infusion dose for a patient over 70 kg:
bolus = 100 mL over 2-3 minutes
infusion = 250 mL over 15-20 minutes
if the patient remains unstable–> repeat bolus and/or double the infusion
For 20% lipid emulsion therapy what is the bolus and infusion dose for a patient under 70 kg:
bolus: 1.5 mL/kg of lean body weight over 2-3 minutes
infusion: 0.25 mL/kg/min.
if the patient remains unstable–> repeat bolus and/or double the infusion
LAST can be reduced by
using a test dose and incremental dosing with periodic aspiration
______ & ____________ will worsen the symptoms of LAST
hypoxia and acidosis
If benzodiazepines are ineffective to treat a LAST seizure,
a small dose of succinylcholine or a non-depolarizer should be given to stop muscle contraction
this minimizes O2 consumption, hypoxemia, and acidosis although it will not stop seizure activity in the brain
Why is propofol avoided for seizures in LAST?
larger doses of propofol augment myocardial depression
If epinephrine is used in last, the recommended dose is
below 1 mcg/kg
The maximum recommended dose of lipid emulsion is
12 mg/kg
The infusion of lipid emulsion should be continued for
a minimum of 15 minutes after the patient regains CV stability
Is lipid emulsion safe in pregnancy?
yes
What is a theoretical complication secondary to hyperlipidemia and hyperamylasemia after lipid emulsion therapy?
pancreatitis
The proposed MOA of lipid emulsion therapy includes?
lipid sink- sequesters LA and reduces the plasma concentration of LA
metabolic effect- enhanced myocardial fatty acid metabolism
inotropic effect- increased Ca+ influx and intracellular Ca+ concentration
membrane effect- impairs LA binding to Na+ channels
What is the MAXIMUM recommended dose for lidocaine during tumescent anesthesia?
a. 5 mg/kg
b. 7 mg/kg
c. 55 mg/kg
d. 75 mg/kg
C. 55 mg/kg
Tumescent anesthesia provides
comfort during liposuction
The plasma concentration of lidocaine peaks at __________ and is completely eliminated by _____________
12 hours; 36 hours
GA for liposuction is recommended if > ____________ of tumescent is planned
2-3 L
_______ & __________ may occur as a result of intravascular volume expansion when using tumescent lidocaine.
fluid overload
pulmonary edema
