Pharmacology Review: Q & A for Local

Anesthetics

John M. O'Donnell CRNA, MSN

What is the mechanism of local anesthetic action?

What ‘kind’ of block is achieved by giving the local anesthetic?

How is the block referred to…

Name two theories explaining local anesthetic activity

Describe neuronal impulse conduction in both myelinated and unmyelinated fibers

Name the types of nerve fibers from largest to smallest and from fastest to slowest conducting

What effect do locals have on the threshold and resting membrane potentials of the neuron?

Name at least two receptors beyond the Na+ channel receptor that are affected by LA

Draw a diagram of the structure of LA and name the parts

Name at least three areas of impact of the structure of locals on day to day practice?

What do we mean when we say that some local anesthetics are left or right ‘handed’ and that this results in a reduction in toxicity?

Describe amide local metabolism and indicate which specific enzyme may be responsible for metabolism of many of the amides

How are ester locals metabolized?

What is minimum blocking concentration with respect to local anesthetics?

To what inhalation anesthetic concept is Cm analogous?

Give three examples of differential blockade and explain why this occurs

Describe the concept of critical blocking length or spread with regard to LA infiltration

Name 3 physical or chemical properties that govern the activity of local anesthetics?

Name three determinants of ionization

Describe how a low pH of the site of injection specifically changes the ionization of a LA molecule.

Is the intrinsic structure of local anesthetics acid or base?

What is pKa?

Do esters or amides have higher pKas (in general)?

How does the relative degree of ionization affect onset speed?

What does it mean when we say we plan to alkalinize our LA prior to injection. Describe how this would be done.

Name two other substances that may be added to local anesthetics prior to infiltration

Why is lipid solubility important and how does it

affect choice of local or concentration?

How is lipid solubility assessed chemically?

What is the relationship between local anesthetic potency and toxicity?

Why are ropivacaine and L-bupivacaine potentially revolutionary new drugs?

Describe the onset of systemic LA toxicity in terms of symptoms as they will most likely appear

What pharmacokinetic situation leads to rapid onset of CNS symptoms of local anesthetic toxicity in the clinical setting?

Name three variables which affect systemic absorption of LA

How would you treat a LA toxicity reaction?

Name 4 risk factors for LA toxicity

From least to most, name the sites of injection related to local anesthetic toxicity

Name the effect of LA on vascularity

Name two pharmacokinetic determinants of LA duration

What is the relationship between protein binding and duration of LA?

What is the relationship between lipid solubility and LA duration?

What two situations/conditions are associated with neuronal damage post LA administration?

What is Cauda Equina Syndrome and what causes it?

What is transient radicular irritation and what causes it?

What is methemoglobinemia and how is it treated? (must name the dose)

Name at least two local anesthetics associated with methemoglobinemia

Name all of the ester locals commonly used

Name at least one key characteristic or fact about Procaine excluding chemical structure

Name at least one key characteristic or fact about Chloroprocaine excluding chemical structure

Name at least one key characteristic or fact about Tetracaine excluding chemical structure

Name at least one key characteristic or fact about cocaine excluding chemical structure

Name at least 6 amide local anesthetics

Name at least one key characteristic of lidocaine aside from chemical structure

Name at least one key characteristic of mepivacaine aside from chemical structure

Name at least one key characteristic of bupivacaine aside from chemical structure

Name at least one key characteristic of l-bupivacaine aside from chemical structure

Name at least one key characteristic of etidocaine aside from chemical structure

Name at least one key characteristic of prilocaine aside from chemical structure

Name at least one key characteristic of ropivacaine aside from chemical structure

Name at least one key characteristic of dibucaine aside from chemical structure

Name at least one key characteristic of articaine aside from chemical structure

Epidural Block Question

You are managing a fem-pop bypass caseEpidural anesthesia is plannedSelect an agentWhat dermatome level of block is neededAssuming L3-4 injection site, what is a

reasonable 1st dose in volume?Should you bolus or run an infusion?

What are the rates or amounts needed?

Axillary Block Question

You are performing an axillary block for ORIF of a compressed fracture of the wrist Total duration of the surgery will be 1-2 hours

Select an agent and dose (name 2 others that could be used) What dermatomes need to be blocked? How would you assess efficacy?

Name two complications of intravascular injection

Spinal Block Question

Patient for appendectomyWhat dermatome level is needed?What 5 agents are typically used

Name doses and durations for each with and without epinephrine

Name three complications associated with local anesthetics in the SAB

Test Dosing

What drugs are used for test dose in Epidural anesthesia

What is the reason a test dose is performed?

What is the total dosage of the drugs used and what is the typical concentration and volume?

What symptoms would you observe in the event of SA injection? Intravascular?

What is the toxic dose of bupivacaine with and w/o Epi?

If you are using bupivacaine 0.25% in a 10 kg patient, how many milliliters injected would represent the toxic dose threshold?

What is the toxic dose threshold for 2-Chlorprocaine?

Give at least one reason why it is much higher than many other locals.

Which drug used in spinal anesthesia enjoys the biggest increase in duration with addition of epinephrine?

Give at least two reasons why conduction block affects sensory and motor fibers differently.

Explain why higher doses of LA result in dense sensory AND motor block.