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50 Cards in this Set

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What are local anesthetics?
Pain suppressors that block impulse conduction along axons. Conduction is blocked only in neurons located near the site of anesthetic administration. Entire CNS depression can be avoided. Less risky.
What are the two major groups of local anesthetics?
Esters & Amides
What's the characteristic chemistry of Esters?
Ester bond
What's an ester-type anesthetic?
Procaine
What's the incidence of allergic rxn's to ester anesthetics?
Low
What's the method of metabolism of ester anesthetics?
Plasma ensterases
What's the characteristic chemistry of Amide?
Amide bond
What's an amide-type anesthetic?
Lidocaine
What's the incidence of allergic rxn's to amide anesthetics?
Very low
What's the method of metabolism of amide anesthetics?
Hepatic enzymes
What's the mechanism of action of local anesthetics (L.A.)?
L.A. stop axonal conduction by blocking sodium channels in the axonal membrane
How selective are local anesthetics?
L.A. are non-selective & will block action potentials in all neurons (sensory & motor) they can access. Selectivity is achieved by localized administration.
Is blockage equal by local anesthetics on all neuron types?
No, small, nonmyelinated neurons are blocked more rapidly than large, myelinated neurons. Thus perception of pain is lost 1st then cold, warmth, touch & deep pressure
What 3 properties determine the ability of local anesthetics to penetrate an axon membrane?
1. Molecular size
2. Lipid solubility
3. Degree of ionization at tissue pH
What type of local anesthetics cross the axon membrane rapidly?
Small in size
High Lipid solubility
Low ionization
What type of local anesthetics cross the axon membrane slowly?
Big in size
Low Lipid solubility
High ionization
Which local anesthetics have a quicker onset on the pt?
L.A. that penetrate the axon most rapidly have a quicker onset
What's termination of local anesthetics?
L.A. molecules diffuse out of neurons & carried away by blood
How does regional blood flow affect duration of local anesthetics?
- Areas of high blood flow: L.A. carried away quickly
- Areas of low blood flow: L.A. more prolonged
What can be used to decrease regional blood flow and prolong the effects of local anesthetics?
L.A. is usually combined w/a vasoconstrictor (epinephrine) to prolong anesthesia and reduce risk of toxicity. If anesthesia is prolonged, less of it is needed.
Does the vasoconstrictor have undesired effects (adrenergic stimulation) on the pt?
Yes, palpitations, tachycardia, nervousness, hypertension. This can be controlled with alpha & beta adrenergic antagonists
What is the absorption & distribution of local anesthetics?
Absorbed by blood & distributed to all parts of the body.
What is the metabolism of local anesthetics?
Depends on class

If Ester-type: metabolized in the blood by esterases (enzyme)

If Amide-type: metabolized by hepatic enzymes

Metabolism for both types leads to inactivation
What are the Adverse Effects of local anesthetics in the CNS?
L.A. cause excitation followed by depression. Excitation phase can lead to convulsions. Depressant effects range from drowsiness to unconsciousness to death (2ndary to depression of respiration)
What are the Adverse Effects of local anesthetics in the Cardiovascular System?
L.A. can suppress excitability in the myocardium & conducting system leading to bradycardia, heart block, reduced contractile force & cardiac arrest.

L.A. can relax vascular smooth muscle leading to hypotension
What are the Adverse Effects of local anesthetics in the Immune System?
L.A. more commonly of the ester-type can cause relatively uncommon rxn's such as allergic dermatitis & anaphylaxis. Due to this, amide-types are used when injections must be used for administration.

Cross sensitivity is not observed between ester & amide types of L.A. Thus, allergic pt can be treated to one or another.
What are the Adverse Effects of local anesthetics in Labor & Delivery?
L.A. can prolong labor by depressing uterine contractility & maternal expulsion effort.

L.A. can cross the placenta & lead to bradycardia + CNS depression in the neonate
What's the prototype of the ester-type local anesthetics?
Procaine (Novocain)
How is Procaine administered?
- Not an effective topical drug. Must be injected
Is Procaine used often in the clinical setting?
No, due to allergic ADR's & development of newer agents
What's the prototype of the amide-type local anesthetics?
Lidocaine, which is the most widely used L.A.
How is lidocaine administered?
- Topical
- Injection
What are the benefits of using Lidocaine over Procaine?
A lidocaine dose is more rapid, intense & prolonged than the same does of procaine

Pts w/allergies to ester-type L.A. can safely use lidocaine (allergic rxns are rare)
What other uses does Lidocaine have other than anesthetic?
Commonly used to treat dysrhythmias due to cardiac excitability supression 2ndary to blockade of cardiac Na2+ channels
What type of local anesthetic is Cocaine?
Ester-type
What are the most common agents of topical administration? (3)
1. Lidocaine
2. Tetracaine
3. Cocaine
Which 2 topical anesthetics are mentioned in Dr. Robinson's slides?
1. Lidocaine: Duration: 1/2-1 hr (Short) (Amide-type)
2. Marcaine: Duration: 3-10 hr (Long) (Amide-type)

They are also WIDELY used in injection form
Where are topical agents applied?
Skin or mucous membranes (nose, mouth, pharynx, larynx, trachea, bronchi, vagina & urethra)
What are the effects of topical anesthetics?
Affects distal nerve endings, relieve pain or itching (loss of pain first, then warmth, pressure)
Can topical agents be toxic?
Absorption is proportional to surface area covered. Toxicity is greatest when surface area is large.

Absorption is greatest through mucous membranes than skin
How do we choose topical anesthetics?
Choice depends on duration of action:
- Short—1/2-1 hr (lidocaine)
- Intermediate—1-3 hr
- Long—3-10 hr (Marcaine)
- Some contain epinephrine—local vasoconstriction
Types of L.A. Injections: (5)
1. Infiltration Anesthesia
2. Nerve Block Anesthesia
3. Intravenous Regional Anesthesia
4. Epidural Anesthesia
4. Spinal (Subarachnoid) Anesthesia
Can local anesthetic injections be toxic?
Yes, injections delivered usually by anesthetist due to severe toxicity risk. Resuscitation equipment must be handy.
What's Infiltration Anesthesia?
Goes directly into immediate area of surgery or manipulation. Anesthesia can be prolonged w/epinephrine. HOWEVER, never use epinephrine in areas of end arteries (Toes, Fingers, Nose, Ears & Penis = Dr. Robinson's" "Fingers, Ears, Nose, Toes and OHs")
What's Nerve Block Anesthesia?
L.A. inj. into a near nerve supplying the surgical field, but at a site distant from the field itself. Less anesthesia needed.

Lidocaine used for short procedures- Marcaine (Bupivacaine) is used during longer periods.
What's Intravenous Regional Anesthesia?
Anesthesizes the extremities: hands, feet, arms, & lower legs, But Not Entire leg! Inj. into distal vein of an arm or leg. Blood must be removed from limb (gravity or Esmarch bandage) to prevent drug from entering the rest of the body. Lidocaine w/o epinephrine is preferred.
What's Epidural Anesthesia?
Inj. goes into the epidural space through a catherer. Blocks conduction in nerve roots & spinal cord by diffusion in the subarachnoid space. Drug easily reaches the rest of the body & is dangerous during delivery (neonatal depression). Lidocaine & marcaine are used. A risk of cardiac arrest to OB pts, limits how much marcaine can be used on them.
What's Spinal (Subarachnoid) Anesthesia?
Inj. into the subarachnoid space through the lumbar region. Lidocaine & Marcaine used commonly (preservative free)

ADR:
1. Hypotension (caused by vasodilation secondary to sympathetic nerve blockage). Placing pt 10 - 15 degrees in a head-down position will promote venous return to head; use of vasoconstrictors may be needed.
2. Autonomic blockade interrupts intestinal & urinary tract function. Cannot be released if cannot void.
3. Headaches (posture dependent. Pt should be supine & bedrest for 12x OR may occur due to suggestion). Usually only with larger loss of fluid. Pt is at High falls risk
What are the ADME's of local anesthetics?
Be Alert: When used in mouth can interfere with swallowing/gag reflex
- Viscous Xylocainefor sore throat
–Sprays given prior to endoscopy
What is the Nursing management when using Local Anesthetics?
–Monitor VS, watch for SE
–If mixed with epinephrine can cause ischemia in the area.
–Can be mixed with anti-inflammatory for dual action