Local anesthetics and perioperative pain control Flashcards
What are the 3 main types of afferent sensory fibers?
- C fibers: small diameter, unmyelinated
- Adelta: medium diameter, lightly myelinated
- Abeta: Large, fast-conducting, myelinated fibers
What type of pain do c, Adelta, and Abeta fibers, transmit?
C: diffuse, dull, and aching pain
Adelta: Sharp, localized pain and temperature
Abeta: vibration and light pressure
What afferent sensory fibers respond quickest to lidocaine?
C fibers>Adelta>Abeta
The Abeta ones take awhile –> leads to the pt to feel something but not pain (pressure, movement)
What are the two broad groups of local anesthetics?
Amides (most common) and Esters
How are amides vs ester local anesthetics metabolized?
- Amides: Metabolized in the liver via the CYP 3A4 system in the liver
- Ester: Metabolized via pseudocholinesterases in the plasma; renally excreted
What is an easy way to identify an amide vs an ester local anesthetic?
If the drug name has two “i’s” = Amides (ex lidocaine, prilocaine, etc)
What is the most likely component of an amide anesthetic to cause an allergic reaction?
Methylparaben preservative
What should be done if an allergic reaction to an amide anesthetic occurs?
Most likely from the preservative (methylparaben) –> switch to preservative-free lidocaine
What is the most common allergen in allergies to ester anesthetics?
PABA
If a pt is allergic to an ester anesthetic, what else will they likely be allergic to?
PABA (frequent allergen in ester anesthetics) crossreact with the “PPPESTAA” allergens: Paraphenylenediamine (PPD), PABA, Para-aminosalicylic acid, Ethylenediamine, Sulfonamides, Thiazides, Anesthetics (esters), Azo dyes
What are contraindications to amide anesthetic usage?
End-stage liver disease
What are some contraindications to ester anesthetics?
Allergy to PABA or cross-reacting substances, pseudocholinesterase deficiency, and renal insufficiency
Is there any difference in efficacy between 1:200,000 vs 1:100,000 epinephrine in anesthetic?
No! These are equally effective and the more dilute (1:200,000) formulation has less toxicity
What are the contraindications for the usage of epinephrine in local anesthetics?
pheochromocytoma, and uncontrolled hyperthyroidism
Should local anesthetic + epinephrine be used on patients that are pregnant?
Can cause decreased uterine blood flow (pregnancy category C)
In what situations should epinephrine be used with caution in local anesthetics?
Pregnancy, severe CV disease, HTN, glaucoma, and drugs (B-blockers, TCAs, and MAO-I)
How does addition of sodium bicarbonate (8.5%) change anesthetic properties?
Bicarb raises pH to near physiologic levels –> majority of anesthetic remains natural/uncharged which allows the anesthetic to more rapidly cross nerve membranes
Speeds onset and decreases injection pain
What are the disadvantages of adding sodium bicarbonate to local anesthetic?
Decreased shelf-life (due to epinephrine degradation)
What impact does the addition of hyaluronidase to local anesthetic do?
Degrades hyaluronic acid, increases anesthetic diffusion and tissue distortion from fluid infiltration
Disadvantages: decreases the duration of anesthesia and anesthetic toxicity as a result of increased absorption and also contain contact allergy thimerosal
If a pt gets a reaction to lidocaine with hyaluronidase added, what is the most likely allergen?
Thimerosal
What are the adult maximum doses of lidocaine (w/o epinephrine, w/ epinephrine, and tumescent)?
4.5-5mg/kg, 7mg/kg, 55mg/kg
What are the pediatric maximum doses of lidocaine (w/o epinephrine, w/ epinephrine, and tumescent)?
1.2-2mg/kg, 3-4.5mg/kg, (tumescent not used)
these are approx. half of adult doses
What is the fastest onset local anesthetic?
Lidocaine (onset in <1min)
Which local anesthetic has the slowest onset of action?
Mepivacaine
