N16/17 - Anesthetics (Zhu) Flashcards
Types of local anesthetics (chemical property)
Esters
Amides
local anesthetic that mainly exists in neutral form (pka 3.5)
Benzocaine
hydrophobicity of most effective LAs
moderate
2 changes due to binding of LA to binding site
occlusion
restriction of conformational change
- AP generation is blocked (prevented channel opening)
- AP conduction is blocked (prolonged refractory period)
modulated receptor hypothesis
Low binding affinity at resting state
High binding affinity at:
- intermediate closed state
- open state
- inactivated state: LA stabilizes channel in innactivated state, channel cannot be reopened even after repolarization
channel states when LAs have major effect
Intermediate closed - prevents opening
Inactivated - extends refractory period
attenuates effectiveness of LAs
hypocalcemia - increased Na excitability
Potentiates the effectivenss of local anesthetics
Hyperkalemia - membrane is persistently depolarized
General blockade order
First pain
Second pain
Temperature
Touch, proprioception (pressure, position, stretch)
Motor function
blocks pain, without significant motor block
Epidural bupivacaine
A-gamma fibers
muscle tone
A-delta fibers
First pain & temperature
C fibers
second pain & temperature
to avoid systemic absorption of LAs
co-administration of vasoconstrictors
Co-administered vasoconstrictor:
Except in which areas?
epinepherine
Except in: fingers, toes, ears, nose, penis
Pain relief
oral, nasal, laryngeal, rectal disorders, surgery
Topical: Mucous membrane application
Tx: pruritus
poison ivy, insect bites, eczema, venipuncture, chickenpox, etc
topical anesthesia: skin application
suturing wounds
removal of foreign bodies
dental procedures
Infiltration LA - intradermal or subq
Lidocaine, procaine, bupivacaine
toxicity due to
systemic absorption
systems affected by LA toxicity
CNS - excitement followed by depression (inhibition of inhibitory pathways, then both excite & inhib)
Cardiovascular - vasoconstriction, then vasodilation
Acts as antiarrhythmic at very low concentration
Lidocaine
hypersensitivity
Ester-type LAs
met. product = p-aminobenzoic acid (PABA)
cautioned use for potentiation of neuromuscular blockers
Myasthenia gravis
(use great caution)
Vasoconstriction
cardiotoxicity
CNS stimulation
Tx: opthalmic, nasal surgery (blocks bleeding), topical
Cocaine
(Ester-type)
nasal surgery
Cocaine
No topical application
Procaine (Novocain)
Chloroprocain (Nesacaine)
(Ester-type)
High hydrophobicity
Fast onset
High potency
Long acting
Spinal & topical
Tetracaine
(Ester-type)
Weak
Used in nonprescription topicals
Benzocaine
(Ester-type)
Risk for hypotension & cardiotoxicity
Bupivacaine
Similar to bupivacaine
less cardiotoxicity
Levobupivacaine
Ropivacaine - structural analog
Mepivacaine - structural analog
(Amide-type)
Amide-type drugs - name hint
2 I’s
Ester-type drugs: name hint
1 “I” in name
Topical & infiltraion anesthesia
Prilocaine
Infiltration and nerve block anesthesia
Etidocaine
Amide-type with ester group
dental procedures
Articaine
Lidocaine + Prilocaine combo
Topical - Venipuncture, lumbar, dental
EMLA (Eutectic mixure of local anesthetic)
Contain halogens in chemical structure
Inhaled anesthetics
(except nitrous oxide)
Contain ether bond in chemical structure
Intravenous anesthetics
Stage I anesthesia
Analgesia
Stage II anesthesia
Excitement
Stage III anesthesia
Surgical anesthesia
- unconscious
- regular respiration
- decreased eye movement
Stage IV anethesia
Medullary depression
- respiratory arrest
- cardiac depression & arrest
- no eye movement
AVOID THIS STAGE - REVERSE STAGES IN RECOVERY
Ion channel hypothesis
Potentiation of inhibitory channels
- GABA(A) receptors
Glycine receptors
No significant action on GABA(A) or glycine receptors
Ketamine
Nitrous oxide
Inhibits excitatory channels - NMDA glutatmate receptors
ketamine
Activates K channels
inhalational anesthetics
Partial pressure
P = (# Mol. of gas A / # Mol. of mixture) x 760 mmHg
coefficient correlated directly with potency
inversely correlated with minimal alveolar concentration (MAC)
Oil : gas partition coefficient
Coefficient inversely related with anesthesia induction rate
No relation to potency
Blood : gas partition coefficient
Meyer-Overton rule
Anesthetics with larger oil/gas are more potent
Most common cause of malignant hyperthermia
Halothane
Tx: Dantrolene
Driving force for equilibrium
alveolar partial pressure gradient
NOT blood concentration
Speeds up induction
High partial pressure of anesthetic
High ventilation rate
- agents with high blood/gas are affected most
Smaller blood:gas partition coefficient =
faster induction
Larger blood:gas partition coefficient =
slower induction
Low cardiac output
high induction rate
high cardiac output
low induction rate
Reflects tissue uptake of drug
venous blood partial pressure
Drug significantly metabolized by the liver
Halothane
Inversely proportion to blood:gas
delayed w/ increased duration of anesthesia
profoundly decreased w/ long duration & high blood/gas
recovery rate
malignant hyperthermia
halothane
maintenence of in-patient anesthesia
pungent odor
isoflurane
fluoride ions formed from metabolism may cause renal toxicity
enflurane
outpatient surgery
not for induction
usually used with IV agent
desflurane
outpatient surgery
anesthesia induction in children
sweet-tasting
“compound A” may be renal toxic
Sevoflurane
diffusional hypoxia
nitrous oxide
primarily used as adjuct
dental procedures when full anesthesia isnt needed
nitrous oxide
N2O diffuses from blood to alveoli,
reduces PO2 in lung
diffusional hypoxia
upon discontinuation of N2O
100% O2 to avoid hypoxia
contraindications to nitrous oxide use
air-filled cavities (embolus, pneumothorax, etc)
Vit B12 deficiency
Most potent inhaled anesthetic
halothane
Least potent anesthetic
nitrous oxide
most analgesic of inhaled anesthetics
nitrous oxide
least analgesic of inhaled anesthetics
halothane
barbiturate
contraindicated w/ variegate prophyria
hepatic metabolism
renal excretion
not analgesic
hypotension
Thiopental
Rapid onset & recovery even w/ repeat dosing
Anti-emetic action
short day-surgery procedures
Propofol
young or head-injured patients
higher-dose infusions
metabolic acidosis, hyperlipidemia, rhabdomyolysis, liver enlargement
propofol infusion syndrome (PRIS)
minimal cardiovascular effects
etomidate
anesthesia induction in patients with cardiovascular diseases
etomidate
dissociative anesthesia - awake with profound analgesia and amnesia
ketamine
cardiovascular stimulating effects
bronchodilation
ketamine
benzodiazepines
midazolam
diazepam
lorazepam
opioids
morphine
fentanyl
sufentanil
pre-operative anti-anxiety and anterograde amnesia
benzodiazepines
anestesia with a combination of several inhaled and/or IV anesthetics, and adjuvant drugs
balanced anesthesia