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What is local anesthesia?
- -Process of blocking the perception of
- pain and other sensations.
- -Renders part of the body insensitive
- without loss of consciousness
- -First local was cocaine in Peru
- -Reversibly block transmission of nerve impulses
- -Prevent or reverse acute pain
- -Treat symptoms of chronic pain
Is local Anesthesia reversible?
What is a syringe
-simple pump consisting of a plunger that fits tightly in a tube and expels a liquid or gas through an orifice at the open end of the tube
What is a commonly used gauge used in podiatry?
Describe Phosphate steroids
Describe Acetate Steroids
-Reserved for damaged joints
-Cloudy forms a precipitate
shake the vial with precipitate prior to injection
- 4-8 mg/ml
- Rapid onset, but short acting
- May increase glucose levels
- 10mg/ml or 40mg/ml
- long acting
How does a local work?
- Local anesthetic is injected as hydrochloride
- pH increases(tissue pH 7.4), drug dissociates and free base released
Lipid soluble free base
Inside the axon the pH is lower and free base re-ionized
portion then enters the Na+ channel
Ex. of a local with physiological pH
- do NOT use with infection because acidic environment will decrease efficacy
Local onset time near physiological pH(7.4)
- more un-ionized molecules in soluble form
- more rapid onset of anesthesia
Local with Higher pKa
- Higher pKa= more ionized molecules
- longer duration to onset of anesthesia
What comes first: sensory loss or motor loss?
Local low pKa characteristics
More unionized molecules
Better absorption into nerve tissue
RAPID ONSET OF BLOCK
Shorter duration of block
Local with High pKa (marcaine):
More ionized molecules
Slow entry into axon
MORE EFFECTIVE BLOCK
Onset of anesthesia slower
Time between onset of anesthesia and the time when patient begins to appreciate sensory stimuli again.
duration dependent on...
- More lipid soluble the more readily will
- cross lipid membranes and the greater the POTENCY and duration of the drug (ex Marcaine, tetracaine).
What could be added to decrease the rate of absorption and increase duration of a local?
Vasoconstrictors like epinephirin
Distribution of a local is dependent on:
- Volume administered
- Vascularity of the tissues
- barriers to diffusion
- Speed of injection
- Forces of injection
- Tissue planes/cavities
- increased volume will increase spread amongst tissues
- It WILL NOT not overcome poor injection technique
Time it takes from appreciation of sensation loss to complete return of sensory and motor function.
Cause of short Regression
drug has high vascularity components
How would you prolong the regression time of a local?
How would a local be toxic?
exceeded the dose
Why can anesthetics be toxic?
hydrophobic and hydrophilic= cross plasma membranes and intracellular membranes
What does local toxicity do?
CNS effects--> cardiac arrythmias and myocardial depression
What is the most cardiotoxic amine?
How do you convert %of solution into milligrams?
Step 1: Multiply the %concentration by 10
Step 2: Change % to mg/cc
- Step 3: Multiply by the amount of cc
Treatment for Local Toxicity:
- Airway management
- Seizure prevention
- ACLS and BLS as needed
- Avoid further local, vasopressin, calcium channel blockers and beta blockers
- IV lipid fluid bolus/infusion
- avoid propofol
- Monitor for greater than 12 hours
- VERY rare in foot and ankle
- Hydrolyzed in blood via pseudocholinesterases
- Esters only have one I in their name
- More prone to allergic reactions
•Hydrolyzed in the liver
•Amides have two I’s in their name**
- Onset: FAST (2-5 mins)
- Duration: SHORT (45-60 mins)
- Peak plasma levels: 15-30 min
- Toxicity: low 1
- Metabolized by liver
- pKa: 7.86
- Carbocaine and Polocaine
- ONset: MEDIUM (10 mins)
- Duration: MEDIUM (120-180 mins)
- Peak plasma level: 10-20 mins
- Toxicity: low 1.4
- Metabolized by liver
- pKa: 7.9
- Onset: 15-30 mins
- Duration: LONG (8-16 hrs)
- Peak Plasma levels: 10-20 mins
- Toxicity : HIGH CARDIO
- Met by liver
- Pka: 7.6
What nerves are most susceptible to locals?
c and A-deltas
Nerve susceptibility dependent on:
- inter nodal distance
- increase hemostasis
- Prolong anesthesia
- Used to decrease toxicity
- May increase pain of injection
- NOT used for foot/digits
- Don't use in vascular compromise
Epinephrine contraindicated in Patients who ...
blood pressure over 200 torr systolic or 115 torr diastolic
- severe cardiovascular disease including
- less than 6 months after a myocardial infarction or cerebrovascular accident
- daily episodes of angina pectoris or
- unstable angina
- cardiac dysrhythmias despite appropriate
medicated with β-blocker, monoamine oxidase inhibitors, or tricyclic antidepressants; or general anesthesia with a halogenated anesthetic like halothane, methoxyflurane, or ethrane.
injection of the anesthetic mixture into the space around the spinal cord, which is called the epidural space.
injection of a small amount of local anesthetic agent into the fluid surrounding the spinal cord; generally injected below the level L1/2
injection of a local anesthetic agents into the caudal portion of the epidural space through the sacral hiatus to anesthetize sacral and lower lumbar nerve roots
Infiltration- a local infiltration of anesthesia around a lesion .
What is it used for?
What can't infiltration be used with?
Peripheral Nerve block: how is it performed?
- -injecting a local anesthetic near the nerve, or nerves, that control sensation
- and movement to a specific part of the body
Is peripheral nerve block safe?
Yes, safer than general or spinal
What are some benefits of peripheral nerve block?
Safer than general or spinal anesthesia
Significantly reduce the risk of post-operative fatigue/confusion, nausea and vomiting
Earlier discharge from the recovery room and hospital and improved patient satisfaction
If other anesthesia necessary; less medication need to be administered with a peripheral block
- Better post-operative pain control (limiting the need for strong pain medications, which have
- complications of their own)
Common perineal block:
-Often times performed by anesthesia
-Can be ultrasound guided
- -Local infiltrated around common peroneal
- nerve proximal or near to the fibular neck
- Posterior Tibial
- Medial dorsal cutaneous
- Deep perineal
- Intermediate dorsal cutaneous
- Sural nerve
Posterior Tibilal block
Blocks tibial nerve and its distributions at level of ankle
1. Manually locate the posterior tibial nerve
2. Introduce needle just posterior to pulse aiming towards posterior medial malleoli
3. After negative aspiration inject anesthetic slowly
Used for surgical procedures, diagnostic, and analgesia
Usually3-5 ml of anesthesia if directly behind the nerve is sufficient
Saphenous Nerve block:
-Runs in subcutaneous tissue adjacent to saphenous vein
-Provides anesthesia along medial side of foot to 1st MTPJ
Medial and Intermediate dorsal cutaneous:
Provides anesthesia along dorsum of foot
Intermediate dorsal cutaneous ≈ 1.5cm lateral to tibialis anterior tendon at level of the ankle
Medial dorsal cutaneous located midway between malleoli at level of ankle joint
Deep Peroneal block:
- -Between the tendons of EHL and EDL
- -Just medial to dorsalis pedis artery
- - Anesthesia of skin to the dorsum of the 1st toe cleft and to the EDB muscle and tarsal joints in this area
Sural Nerve block:
-Follows course of small saphenous vein supplying lateral side of the foot
-Easily located between posterior lateral malleoli and lateral achilles tendon
Mayo Nerve Block:
- Bunion procedures
- for defined segments of the foot
- Anesthetizes: Saph, DPN, MDCN, MPN
Used in Hallux procedures
-1st dorsal digital proper nerve
-1st plantar digital proper nerve
-2nd plantar digital proper nerve
-Usually 3-5cc of local
- Used to block a digit
- Up to 3cc of local
- Anesthetizes: Dorsal digital proper nerves, plantar digital proper nerves
- Used to anesthetize:
- Common plantar digital nerves
- Common dorsal digital nerves
- usually 3-5 cc of local