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Benefits of Systemic Lidocain (3):
- Central Analgesic Effect (Blocks Na channel in central nociceptive neurons)
- Prokinetic (GIT)
- Antioxident/Inflammatory modulators
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Used appropiately, Local Anaesthetics provide ____ analgesia
Absolute
-
Local Anasthetics are classified as:
-
Most common Amide LA's (3):
- Lidocain
- Bupivicaine
- Mepivicaine
-
Most common Ester LA's:
Tetracaine
-
Tetracaine is often used for...
ocular anaesthetics
-
Ester Vs Amide LA (1/2 Life and stability):
- Ester= unstable, 1/2 life is a few mins
- Amides= Stable, 1/2 life is a few hours
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LAs are transported in the plasma, and are bound to _____& ____. The ____ is active
- Alpha Glycoproteins
- Albumin (minimally)
- Unbound drug
-
What property affects the potency of LA's
Increasing Lipid Solubility
-
What property affects the duration of action of LAs
Protein Binding
-
What property affects the rapidity of onset of LAs?
Low pKa= Rapid onset
-
What LA's have a rapid onset?
-
Rate of Diffusion is dependent on (4):
- pKa of Drug
- pH of nerve
- Amount of LA
- Vascular Removal
-
Successful impulse blockade is dependent on
- Sufficient concentration of anesthetic within and along axon
- Na/K channel density
- Na/K channel susceptibility
-
As a rule of thumb, ________, the greater concentration of LA required to produce blockade
the greater the diameter of nerve fiber
-
Which neuron type is unmyelinated?
C
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How does dosage affect an anasthetic block?
- Rapidity of Onset
- Intensity
- Duration
-
How does volume affect an anasthetic block?
- Spread
- Dermatomal Distribution of neural blockade
- DOES NOt DETERMINE SPEED OF ONSET, INTENSITY, OR DURATION
-
How does pH affect an anasthetic block?
The closer the pKa to physiological pH, the better it penetrates the membrane
-
How can pH of LA be alkalinized?
Add Sodium Bicarbonate
-
Repeated blocks can cause...
Tachyphylaxis, especially when pH ~pKa
-
Local Anesthetic Side Fx Occur when...
high plasma concentrations are achieved
-
LA plasma concentrations are determined by (6):
- Quantity(dose)
- Route
- Rate of Absorption
- Acid-Base Status
- Rate of Metab
- +/- Epi
-
Lidocaine TOXIC dose, IV:
10mg/kg
-
Never give more than ___mg/kg Lidocaine IV
4
-
Bupivicaine TOXIC dose, IV:
4mg/kg
-
Never give more than ___mg/Kg Bupivicaine IV
2
-
What must be considered when combining local anaesthetics?
Toxicity of each is additive
-
CNS effects of LA OD (2)
- CNS Depression
- Followed by Agitation, Muscle Twitching and convulsions
-
Cardiovascular Effects of LA OD (2):
- Myocardial Depression (Bradycardia and Decreased CO)
- Hypotension
-
Which is harder to tx Lidocaine or Bupivacaine OD? Why?
Bupivacaine- High binding affinity for cardiac myocytes (70x)
-
Tx for a Local Anesth OD(5) :
- Treat Sympotoms
- Seizures= Valuim PRN
- Cardiovascular= Fluids, O2, Ionotropes, Antimuscarinics if Bracycardic
-
Precautionary steps to avoid Local Anest OD (4)
- Caution w/ small animals
- Double check weight
- Diltute LA
- Draw back before injecting
-
Which LA has antiarrhythmic properties?
Lidocaine
-
Which LA is more potentially cardiotoxic?
Bupivacaine (cardiotoxic before neurotoxic)
-
Which LA is used for nerve blocks in horses?
Mepivicane
-
Less irritating alternative to Lidocaine
Mepivicaine
-
Benefits of using Ropivicaine over Bupivacaine (5):
- Longer Duration
- Less Cardiotoxic
- Less Arrythmogenic
- Selective for Sensory Nerve Fibers (over A alpha motor fibers)
- Dissociates more rapidly from Na channels (less accumulation)
-
Which LA has a longer duration of action than Lidocaine?
Bupivicaine (2-6 hours)
-
Which LA is a more potent alternative than Lidocaine?
Bupivicaine
-
Which LA can cause tachyphylaxis?
Lidocaine
-
What is a safer alternative to Xylocaine spray in cats?
2% Lidocaine WITHOUT adrenaline, spray directly on Vocal Cords
-
Rec Dosage for: Lidocaine, Mepivicaine, Bupivacaine & Ropivicaine
- Lidocaine: 4mg/kg, but 2mg/kg is sufficient
- Mepivacaine: 4mg/kg, but 2mg/kg is sufficient
- Bupivacine: 2mg/kg
- Ropivacaine: 2mg/kg
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