Pharmacological Behavior Guidance Flashcards
Olfactory (I) sensory
Nose
Optic (II) sensory
Eye
Oculomotor (III) motor
All eye muscles except those supplied by IV and VI
Trochlear (IV) motor
Superior oblique muscle
Trigeminal (V) sensory and motor
Sensory: face, sinuses, teeth, etc.
Motor: muscles of mastication
Abducent (VI) motor
External rectus muscle
Facial (VII) motor
Muscles of the face
Vestibulocochlear (VIII) sensory
Inner ear
Glossopharyngeal (IX) motor and sensory
Motor: pharyngeal musculature
Sensory: posterior part of tongue, tonsil, pharynx
Vagus (X) motor and sensory
Motor: heart, lungs, bronchi, gastrointestinal tract
Sensory: heart, lungs, bronchi, trachea, larynx, pharynx, gastrointestinal tract, external ear
Accessory (XI) motor
Sternocleidomastoid and trapezius muscles
Hypoglossal (XII) motor
Muscles of the tongue
Branches of the trigeminal nerve
- V1: Ophthalmic branch
- V2: Maxillary branch
- Superior alveolar nerve - V3: Mandibular branch
- Inferior alveolar nerve
- Lingual nerve
How does local anesthetic work?
- Blocks sodium channels reversibly
- Inhibit depolarization and conduction of action potentials (at least 3 nodes of Ranvier must be blocked)
- LA must enter the nerve, therefore must be fat soluble
- Only possible with non-ionized molecule
Local anesthetic composition
- Lipophilic (substituted benzene ring) —> penetration of anatomic barriers
- Intermediate chain (amide or ester)
- Hydrophilic (amino terminus) —> ensures drug will not precipitate in interstitial fluid
Composition of articaine
Contains a thiopene ring with an ester group
Are local anesthetic bases or acids?
- All common LAs are weak bases (pKa 7.5 to 9.5), prepared in salt form by addition of HCl
- Only basic form can diffuse into the nerve
What happens when pKa = pH?
50% of the LA is uncharged
Meaning of low pKa?
Low pKa —> more non-ionized molecules = more effective
Result of low pH in areas of infection on LA
Low pH in areas of infection will decrease non-ionized %
Mental (anesthesia)
“Soft tissue” block
Posterior superior alveolar nerve block
- May not always anesthetize the mesiobuccal root of the 1st maxillary molar
- In conjunction with palatal anesthesia?
Conventional IA injection technique
- Palpate deepest portion of coronoid notch
- Insert needle between pterygomandibular raphe and deep tendon of temporalis
Long buccal nerve
- Will sometimes innervate primary and permanent molars —> anesthetize buccal to the last tooth to be treated
Mandibular foramen in a child
- Slightly below the plane of occlusion
- More anterior than in adults
- Growth is downward and forward at condyles and along the posterior surface of the ramus
- The distance from lingula to anterior border is fairly stable with growth, while other dimensions change
Injection pain causes
- Mechanical trauma from needle penetration
- Distention of tissue from cartridge contents
- Anesthetic properties (temperature, pH, etc.)
Needle gauge
- Larger is less likely to break
- Larger is easier to aspirate through
- Larger is less likely to deflect
What determines anesthesia?
- LA proximity to nerve
- Degree of ionization
- Concentration of solution
- Volume injected
- Time
Name the ester local anesthetics
- Novocaine
- Tetracaine
- Benzocaine
- Cocaine
- Procaine
Where are ester local anesthetics metabolized?
Hydrolized in plasma by pseudocholinesterase.
Major metabolite of ester anesthetics
PABA is a major metabolite, responsible for most allergic reactions
Name the amide local anesthetics
- Lidocaine
- Mepivacaine
- Bupivicaine
- Prilocaine
- Ropivacaine
Where are amide local anesthetics metabolized?
- Metabolized by liver in cytochrome P450.
Most common topical anesthetic
- 20% benzocaine
Precaution with benzocaine
- Large dose may cause methemoglobinemia in young children, however has been reported after a single dose
- Consult healthcare professional for use under age 2
pKa of Lidocaine
7.8
Lidocaine
- Gold standard
- 1:100,000 epi standard, 1:50,000 for some surgical procedures
- 2% (20mg/mL)
- Duration pulpal anesthesia (45 min), soft tissues (2-3 hours)
Prilocaine
- 4% plain
- 3% with 1:200,000 epinephrine
- pKa 7.8
- Methemoglobinemia
- Shouldn’t use in pregnant women (risk of methemoglobinemia in unborn child)
Methemoglobinemia
- Induced by metabolite, ortho-toluidine
- Methemoglobin contains the ferric (Fe 3+) form of iron.
- The affinity for oxygen is impaired.
Precaution with G6PD patients (LA)
Prilocaine
Treatment for methemoglobinemia
Methylene blue
Mepivacaine
- 3% plain
- 2% with 1:20,000 levonordefrin
- pKa = 7.7
Articaine
- 4% with 1:100,000 epinephrine
- pKa = 7.8
- High tissue diffusion (liposolubility) due to thiophene substitution for benzene ring
- Only amide LA to contain an ester group
- Metabolism 90% plasma, 10% liver = more rapid removal from circulation that other LAs
Can articaine substitute for block anesthesia?
- 30 patients (4-8 years) were randomly assigned to receive nerve block with Lidocaine or infiltration with articaine
- Procedures were pulpotomies or pulpectomies
- Researchers recorded Pain and Sound/Eye/Motor (SEM) scores
- Pain scores were higher for block injections during administration and during pulp extirpation
Vasoconstrictors
- Longer duration, requiring less volume
- Anesthetic stays local
- Less bleeding during procedures
Vasoconstrictors counteracts ____ of amide
Vasodilation
Vasoconstrictors _____ due to slower release of drug into bloodstream
Decreases systemic toxicity
Maximum dosage of vasoconstrictor
- Epinephrine (1:100,000 = 10 microgram/mL)
- Max dose 200 microgram (approximately 11 cartridges 2% lido with 1:100,000 epinephrine)
Epinephrine effects on the cardiovascular system
Increased:
- Systolic and diastolic pressure
- Cardiac output
- Stroke volume
- Heart rate
- Contraction strength
- Myocardial oxygen consumption
Use of epinephrine in cardiac patients
- Generally not associated with any significant cardiovascular effects in healthy patients or those with mild to moderate heart disease
- Reduced dosages or local anesthetics without vasoconstrictors are indicated for patients with more significant disease
- Epinephrine-impregnated retraction cord should be used cautiously or avoided in certain situations
Recommended max dose for articaine with epi (AAPD)
7 mg/kg
Recommended max dose for lidocaine with epi (AAPD)
4.4 mg/kg
Recommended max dose for mepivicaine (plain or with epi) [AAPD]
4.4 mg/kg
Recommended max dose for prilocaine (plain or with epi) [AAPD]
6 mg/kg
Local anesthetic overdose
- Local anesthetics are not selective, and may interfere with impulse transmission in any excitable tissue (e.g. central nervous system)
- Inhibitory cortical neurons or synapses are highly susceptible to transmission block
- Disruption of these pathways may result in disinhibition of excitatory neurons
Symptoms of a local anesthetic overdose
- Generalized tonic-clinic seizures
- CNS depression
- Hypotension
- Bradycardia
- Respiratory depression
Management of a local anesthetic overdose
- Place in supine position
- Administer oxygen
- CPR as necessary if cardiac function disrupted
Pharmaceutical management of local anesthetic overdose
- Seizure management with benzodiazepines (e.g. IV midazolam 0.1-0.2 mg/kg)
- 20% lipid emulsion (1.5 mL/Kg over 1 min, traps unbound amide LA)
- Fluid bonus of 10-20 mL/kg balanced salt solution and phenylephrine (0.1 mcg/kg/, min)
OraVerse (Phentolamine Mesylate)
- Reduces anesthesia time by approximately 50%
- 0.4mg/1.7mL
- Maximum recommended dose
- 2 cartridges for adults and adolescents 12 years of age and older
- 1 cartridge for patients 6-11 years of age and over 66 lbs
- 1/2 cartridge for children 3-11 years of age and weighing 33-66 lbs
OraVerse is not recommended for this age group
- Children <3 years of age or under 33 lbs (15 kg)
- A dose of more than 1 cartridge has not been studied in children <4 years
FDA pregnancy risk category A
Adequate and well-controlled studies have failed to demonstrate a risk to fetus
FDA pregnancy risk category B
Either:
1) Adequate and well-controlled studies have failed to demonstrate a risk, but animal studies have shown adverse effect
OR
2) Human studies are lacking, but animal studies have failed to demonstrate risk
FDA pregnancy risk category C
No adequate and well-controlled studies have been performed in pregnant women, but animal studies are lacking or have shown risk to fetus. Potential benefit may warrant use despite potential risk.
Local anesthetics that are category A
Sodium fluoride ** not anesthetic
Local anesthetics that are category B
- Lidocaine
- Prilocaine
Local anesthetic that are category C
- Articaine
- Mepivacaine
- Bupivacaine
Blood/gas coefficient of nitrous oxide
0.47 —> poorly soluble in blood
Is nitrous oxide flammable?
Nonflammable, but supports combustion in presence of O2.
Minimum alveolar concentration of nitrous oxide
104
Minimum alveolar concentration of sevoflurane
3.3
Minimum alveolar concentration of isoflurane
1.2
Minimum alveolar concentration of halothane
0.87
Nitrous oxide
- No noxious smell
- Mild myocardial depressant, mild sympathomimetic effects cancel each other
Sevoflurane
- Somewhat pungent
- Allows very rapid induction
- HIgher rate of emergence excitement
- Decreases respiratory rate and tidal volume
- Increases heart rate, no change in BP
Isoflurane
- Pungent noxious smell
- Inexpensive
- Greater incidence of laryngospasm, coughing
- Used for maintenance
Halothane
- No noxious smell
- Allows rapid induction
- Inexpensive
- Used for maintenance
- Decreases tidal volume, increases respiration
- Decreases BP, no change in HR
Anesthetic properties of nitrous oxide
- Low blood solubility results in rapid induction and awakening
- MAC approximately 104% (incapable of full anesthesia by itself)
- Used in anesthesia to achieve more rapid induction/recovery because MAC is additive with other, slower-acting anesthetics
- Minor depression in cardiac output + slight increase in peripheral resistance = little change in BP
Stage I of Guedel’s stages of anesthesia
- Patient relaxed, able to follow instructions
- Some pain reduction
- Four planes (from analgesia to hallucinations and loss of consciousness)
Stage II of Guedel’s stages of anesthesia
- Deepended CNS depression
- Excitement/delirium/jerky movements
- Laryngospasm may occur
Stage III of Guedel’s stages of anesthesia
- Patient unconscious, laryngeal and pharyngeal reflexes inactive
- Used for major surgical procedures
- Four planes