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
What is the local anesthetic of choice in pregnant women?
Lidocaine
Which local anesthetic carries a risk of methemoglobinemia and why is this important to remember?
Prilocaine, risk highest in those w/ G6PD and those <1y/o
Important b/c it is in the commonly used EMLA topical anesthetic
What two amide local anesthetics should not be used in pregnancy and why?
Mepivacaine: fetal bradycardia
Bupivacaine: fetal bradycardia
What is the longest activing amide anesthetic?
Bupivacaine (if combined w/ epi) –> often added to lido for long mohs cases
Ropivacaine is the longest acting anesthetic w/o epi
What are the sx’s of mild lidocaine overdose?
*sx’s loosely follow EtOH toxicity
Mild = restlessness, euphoria, talkativeness, lightheadedness, “funny tingling” around mouth/hands, metallic taste, and circumoral numbness
What are the sx’s of moderate lidocaine toxicity?
Nausea, vomiting, psychosis, tinnitus, muscle twitching/tremors, blurred vision, slurred speech, and confusion
What are the sx’s of severe lidocaine toxicity?
Seizures and cardiopulmonary depression
What is the easiest way to differentiate anaphylaxis and vasovagal responses to anesthesia?
Compare HR and BP
Vasovagal: Low pulse low BP
Analaphylaxis: high pulse/low BP (shock)
What intervention should be performed for mild lidocaine toxicity?
Observation
What intervention should be performed for moderate lidocaine toxicity?
Diazepam; airway maintenance
Management for severe lidocaine toxicity?
Respiratory support, cardiopulmonary support, life support, etc –> advanced care setting
What intervention should be done for vasovagal reaction?
Trendelenburg, cold compress and reassurance
What are the signs/sx’s of vasovagal reactions?
Excess parasympathetic reaction; diaphoresis, hyperventilation, and nausea
What are the sx’s of excessive epinephrine dosing?
Alpha and Beta receptor stimulation: palpitations, muscle tremors, and nervousness
What occurs with the BP and HR of epinephrine overdose?
High HR and high BP
What is the intervention for epinpehrine overdose?
Usually just observation (resolves in minutes). Severe cases: phentolamine and propranolol
What is the maximum amount of lidocaine + epi that should be used on a digital block?
3 mL on each side (6 mL in total)
What does EMLA stand for?
Eutectic mixture of local anesthesia
What anesthetics are in EMLA?
2.5% prilocaine and 2.5% lidocaine
What are some cautions for using EMLA?
Can cause methemoglobinemia (in infants and those w/ G6PD from prilocaine) and can cause corneal injury (don’t use near eye)
What histologic changes can EMLA cause?
Artificial swelling and vacuolization of upper epidermis and basal layer split
What is the only anesthetic that causes vasoconstriction?
Cocaine (esther) –> this is why epi is used in the others, they cause vasodilation
What topical anesthetics are used for eye numbing?
Proparacaine and tetracaine
What topical ester anesthetic is often used on the mucosa?
Benzocaine
When is post-operative pain worst after a procedure?
The night of the surgery day, drops dramatically each additional day after surgery
What should be considered if pain persists for >4 days after surgery?
Consider infection, hematoma, or drug-seeking behavior
What is the most common concentration of epinephrine in lidocaine?
1:200,000
What concentration of epinephrine is used in tumescent lidocaine?
1:1 million
What area is injected for an ulnar nerve block?
Just lateral to flexor carpi ulnaris
Which anesthetics are most likely to be cardiotoxic?
Bupivicaine (most) and ropivacaine (second)
What are two preservatives that can cause allergy in amide anesthetics?
Sodium metabisulfite and methyl-paraben
What topical anesthetic is most likely to cause contact dermatitis?
Benzocaine
What is the order of sensation loss when an anesthetic is injected?
Temperature, pain, touch, pressure, vibration, proprioception, motor
