Local And Regional Anesthetics Flashcards
Esters - hydrolysis, examples, do they have allergic rxn?
- Hydrolysis by pseudo cholinesterase enzyme
- Cocaine, chloroprocaine, procaine, tetrocaine
- Yes, they are known for allergic reactions
Amides (local anesthetics) - metabolism, examples, allergic rxn?
Liver metabolism CYP450
Lidocaine, bupivicaine, ropivicaine, etidocaine, mepivicaine
Lidocaine:
Weak base - pKa of 7.8
Mainly ionized at physiological pH
1h duration
2h duration w/ adrenaline
CNS and CVS toxicity
Max dose:
- 200mg (20ml of 1%)
- 500mg (50ml of 1%)
Bupivicaine:
Dose
Max of 150mg (30ml of 0.5%)
Selective cardiotoxicity
Highly plasma protein bound
Tachyphylaxis is rare
What is tachyphylaxis?
Appearance of progressive decrease in response to a given dose after repetitive administration of the drug
Does increased fraction of unionized drug increase the onset of action?
Yes
Factors increasing potency and duration of action of local anesthetics?
Greater oil/water partition coeffectient = greater lipid solubility = greater potency
Greater protein binding = greater greater duration of action
What to do in systemic toxicity with local anesthetics?
Lipids and CPR
Lidocaine toxicity starts at?
3 Ug/mL with circumoral and tongue numbness
Goes all the way to coma, respiratory collapse and CVS collapse
Main disadvantage of regional anesthesia? The others are easy to guess
Hypotension
Spinal injection properties?
Lumbar region only
Brief but high block quality
Epidural injection qualities?
Can be done anywhere on spinal cord
Longer but less ecfdcfice block
Requires 5-6x higher dosage
Type of local anesthetic blocks?
Motor - muscle paralysis, weakness
Sensory - total anesthesia
Sylpathetics - hypotension, bradycardia
Sequence of events with regional anesthetics:
- 1 - sympathetic block - vasodilation
- 2 - loss of pain and temperature sensation
- 3 - loss of proprioception
- 4 - loss of touch and pressure sensation
- 5 - loss of motor function
Chloroprocaine:
Use of vasoconstrictors is contraindicated
Good short duration spinal procedure
Lidocaine:
60 to 90 mins
Sensory and motor block
60-75mg
Transient neurologic symptoms in 1/3
Bradycardia is caused by blockade where?
T1 to T4
Which regional anesthetic is greatly affected by vasoconstrictors?
Tetracaine
Spinal injection for sylpathetics block vs motor block
Motor block is 2 dermatomes lower
Hyperbaric anesthetic is mixed with?
Hypobaric?
Dextrose
Sterile water
Absolute spinal injection contraindications?
Sepsis
bacteremia
Skin infection
Hypovolemia
Coagulopathy
Anticoagulation
Increase ICP
Lack of consent
Relative spinal injection contraindication:
Peripheral neuropathy
Heparin
Psychosis
Aspirin or antiplatelet
Demyelunated CNS disease
Cardiac lesion
Emotional instability
Prolong surgery
Surgical team resistance
Epidural anesthesia location?
Widest L2
Narrowest C5
Prefer L3-L4
Skin to epidural space is 4-6cm
Anesthetic test:
3mL lidocaine 1.5% with epinephrine 1:200,000
Epidural techniques
Midline
Paramedian
Taylor L5-S1
Caudal - pediatrics single shot
Lower pKa effect on local anesthetics:
-> Un-ionizes faster -> faster onset of action
Also why adding sodium bicarbonate (NaHCO3) increases speed of onset
Regional anesthesia advantages:
Cheap
High patient satisfaction
Maintain patient airway
Decreased blood loss
Selective muscle relaxation
Decreased incidence of DVT and PE
Regional anesthesia disadvantages:
Hypotension
Risk of toxicity
Many patients prefer to be asleep
Skills required
Patient can talk
Patient anxiety
Not reliable
Location of spinal and epidural anesthesia:
Spinal - Lumbar only, subarachnoid space
Epidural - Along spinal cord, epidural space
Where does the spinal cord end in the vertebral column in adults and infants?
- Adults - L1/L2
- Childern - L3
Dura and arachnoid end at?
S2
Chlorprocaine:
- 11mg/kg -> up to 13 w/ E
- CONTRAINDICATED WITH VASOCONSTRICTORS
- Enhanced by fentanyl and clonidine
- Used in short procedures
Lidocaine:
- 5mg/kg -> up to 7 w/ E
- 60 - 90 mins
- Good sensory and motor block
- Transient neurological symptoms in a third of patients
- Used in short procedures
Bupivicaine:
- 2.5mg/kg -> up to 3mg/kg w/ E
- 90-120 mins
Tetracaine:
- 2.5mg/kg -> up to 3mg/kg w/ E
- 90 - 120 mins
- Effect is doubled with vasoconstrictors
Blockade where causes bradycardia?
T1-T4
Most ideal patient position for regional anesthesia:
- Regional anesthesia
Complications for spinal anesthesia:
- Failed block
- Back pain
- Hypotension
- Local anesthesia toxicity
- High blockade
- Urinary retention
- Local infection
- Meningism
- Epidural hematoma
- Spinal headache
Factors affecting distribution of spinal anesthesia:
- Level of injection
- Shape of spinal column
- Patient height
- Angulation of needle
- Volume of CSF
- Characteristics of local anesthetic (density, specific gravity, baricity)
- Dose
- Patient position
Absolute contraindications of spinal anesthesia:
- Sepsis
- Back pain
- Skin infection
- Severe hypovolemia
- Coagulopathy
- Therapeutic anticoagulation
- Increase intracranial pressure
- Lack of consent
Relative contraindications of spinal anesthesia:
- Peripheral neuropathy
- Mini-dose heparin
- Psychosis
- Aspirin or other antiplatelet drugs
- Demyelinated CNS diseases
- Certain cardiac lesions (aortic stenosis)
- Emotional instability
- Prolong surgery
- Sirgical team resistance
Verterbal canal is widest at ____
Narrowest at ____
Preferable location of administration _____
Distance from skin to epidiral space ______
L2
C9
L3-L4
4-6cm (can be from 3-8cm)
Epidural test (dose, explain)
3mL lidocaine 1.5% w/ epinephrine
- Test for intravenous or intrathecal catheter placement
Positive test:
- Tachycardia
- High BP
- Light headedness
- Metallic taste in mouth
- Ringing in ears
- Facial numbness
Does patient position affect epidural anesthesia?
NO
Complications of epidural administration:
- Penetration of blood vessels
- Hypotension
- Nausea and vomiting
- Headache
- Back pain
- Intravascular catheterization
- Dural puncture
- Infection
