Regional Lecture Test Flashcards
What reverses a local anesthetic?
Time
What are the three characteristic segments all local anesthetics have?
- intermediate carbon group (ester/amide)
- unsaturated ring system
- amine end
What is the most prominent problem of local anesthetics?
inadvertent vascular injection
What is responsible for the classification of a local anesthetic and why?
- The ester or amide linkage
- the only difference between the aromatic ring and amine end
How can you differentiate between an ester and amide by looking at the name?
- Esters have one i (procaine,cocaine)
- Amides have two i’s (lidocaine, mepivacaine)
What does lipid solubility relate to?
High lipid solubility is proportional to potency of a local anesthetic
Definition of Lipophilic/Hydrophobic
Lipophilic-fat loving
Hydrophobic-water fearing
Why does lipid solubility affect potency?
Nerve sheath covering is lipid based so other lipids pass through easily
What type of binding is related to the duration of action?
Protein Binding
Between duration of action and potency, which is more related to lipid solubility?
Potency
Sodium channels have what three functional states?
Resting (closed)
Inactive
Open
What are the two parts to a local anethestic?
Nonionized (fat soluble
Ionized (water soluble)
How does LA work? Part 1
- -Once injected LA dissociates into its active(non-charged) and inactive(charged) forms
- -the non-charged(lipid soluble) part passes through the lipid soluble membrane
How does LA work? Part 2
- -the lipid portion that passes through, binds with minerals in axoplasm
- -the reassociated LA blocks the action potential by blocking Na pump and prevents the pain stimulus from moving down the nerve
What is the definition of pKa?
pKa is the pH at which 50% of the drug is in the charged (ionized, inactive) form and the remaining half is the uncharged (active) state
What is the correlation of pKa and potency?
–the lower the pKa the greater the potency
How does pKa work?
- -the lower the pH of the environment the drug is placed into compared to it pKa, the more ionized (inactive) it becomes
- -so the higher the pKa the more inactive it becomes
- -the lower the pKa the more active drug left to work
Why are vasoconstrictors added to LA’s?
To decrease the spread , vascular uptake of the drug
What 4 helpful things happen when adding a vasoconstrictor to the LA?
- higher local concentration of the LA
- longer duration of effect
- reduced systemic absorption
- hemostasis for improved visualization
When should we not use a vasoconstrictor?
- fingers
- toes
- nose
- hose
What drug reverses the negative results of a vasoconstrictor in a given area?
-phentolamine 1.5-5mg
How are LA with epi packaged?
Red top with red lettering on label
What does adding NaHCO3 do to the LA?
- stored at pH of 4-6 for shelf life (decreases unionized/active form)
- buffering with NaHCO3 increases the unionized/active form to increase speed of penetration to nerve tissue
All LA, except which three, produce vascular smooth muscle relaxation?
- Cocaine (topical)
- Ropivacaine (parenteral)
- Lidocaine (parenteral)
If VSM relaxation occurs, it increases the risk of ________?
toxic effects
Which type of tissue receives the most amount of LA if it enters blood stream and why?
Muscle because it is highly perfused
How are esters metabolized?
- Ester hydrolysis occurs through esterase
- Occurs in plasma, RBC’s, and liver
- Primarily, Plasma Cholinesterase rapidly metabolizes LA
How are amides metabolized?
- occurs primarily in liver
- microsomal cytochrome P-450 enzyme
- dependent on hepatic blood flow and enzyme availability
What are the two most common ways that toxicity occurs?
- inadvertent intravascular injection
- absorption of large amounts of drug from a nerve block that requires large volume
LAST stands for what and what 5 things are affected?
- Local anesthetic systemic toxicity (seen 5-10min)
- CNS
- CV
- Allergic Reaction
- Methemoglobinemia
- Local tissue
CNS effects of LAST
Mild = tongue numbness, apprehension, restlessness
Moderate = peri-oral tingling, tremors, slurred speech, drowsiness
Severe = Seizures, cardiorespiratory depression, coma, death
CV LAST effects
- palpitations
- HTN
- ventricular dysrhythmias
- myocardial depression
- bradycardia
- hypotension
- CV collapse
PVS LAST effects
- low concentrations-vasoconstriction and increased SVR
- as doses increases significant vasodilation and hypotension occurs
Arrythmias with LAST
-LAST effects electrophysiologic and contractile forces
- increased PR interval and QRS durations
- complete AV block, bradycardia, cardiac arrest
What preservative is associated with allergic reactions to LA?
More common in esters due to para-aminobenzoic acid
Which three LA can cause Methemoglobinemia?
- Prilocaine (citanest)
- Benzacaine
- Cetacaine
What is the metabolite that causes methemoglobinemia and what are the s/s?
- o-toluidine oxidizes hgb to met-hgb
- tachypnea
- metabolic acidosis
- brownish-gray cyanosis
Met-Hgb treatment
- Spontaneous is 2-3 hrs
- methylene blue 1mg/kg
LAST treatment
- Airway mgt
- seizure suppresion
- CPR
- alert nearest facility with bypass capabilities
- give IV intralipid
Intralipid dosing
- Bolus: 20% intralipid 1.5ml/kg over 1 min
- Cont: 0.25ml/kg/min
- Double infusion if BP returns but stays low
- Continue infusion for a minimum of 30 min
