Local and Regional Anesthesia (Mod 3) Flashcards
General traits of local anesthesia?
Prevents transmission of information to and from the CNS
- They aren’t selective to pain fibres; they block sensory, motor, autonomic fibres as well as skeletal and cardiac muscles
What is Nociception?
Nociception is the activation of primary sensory nerve fibers (nociceptors) by noxious stimuli such as:
- High temps
- Mechanical perturbations (trauma)
- Harsh chemicals
Where are Nocicepters located?
Nociceptors are free (bare) nerve endings found in all levels of skin (Figure 6.2), muscle, joints, bone and viscera.
- Tissue damage is the primary stimulus for nociceptors
- They are absent in certain areas, such as the lung and brain
Nociceptor transmission?
Nociceptors transmit impulses from the periphery to the spinal cord, where information is transmitted to the various parts of the brain
How is pain transmitted?
Electrical signals jump between fibers
- Myelinated fibres transmit impulses much faster than nonmyelinated fibers
Myelinated fibers vs. nonmyelinated fibers
First pain is derived from?
Myelinated fibers
- quick, sharp, and stinging pains
- highly localized
- Require weaker stimulus for excitation
Second pain is derived from
Nonmyelinated fibers are responsible for second pain
- Slower developing, longer lasting
- dull, throbbing, burning pain
- Present post stimulus removal
- Require stronger stimulus for excitation
Why is there a delay in topical anesthetics?
Has to work through layers of skin, muscles and fats.
- Recall the muscle bundle image (slide 8)
Why is a high concentration of anesthetic used for local anesthetics?
Only a fraction of molecules reach the target site (has to work through the layers of skin, fat, and muscles)
add slide 9
What is the general order in which a functional blockade occurs?
- First pain
- Second pain
- Temperature,
- Touch
- Proprioception (pressure, position, or stretch)
- Skeletal muscle tone and voluntary tension
What is differential functional blockade?
The general order in which a functional blockade occurs:
- First pain
- Second pain
- Temperature,
- Touch
- Proprioception (pressure, position, or stretch)
- Skeletal muscle tone and voluntary tension
What is often administered together w/local anesthetics?
Vasoconstrictors like Epinephrine
Why are vasoconstrictor agents administered in conjunction with local anesthetics
These agents reduce blood flow causing smooth muscles of the vessel to contract, slowing the rate of removal of the anesthetic
- Extend duration of anesthetic affect in the area
- Vasoconstrictors increase the concentration around the nerve (enhances the affect)
- Decreases systemic toxicity via slower distribution of anesthetic into circulation
- Secondary effect = reduces bleeding at injection site
What is a secondary affect of using a vasoconstrictor in conjunction with local anesthetics?
To reduce bleeding at the site of injection
Risks of vasoconstrictors with local anesthetics?
Decreases systematic toxicity as the local anesthetic is more slowly distributed to the circulatory system
- Could stop flow when trying during procedures such as ABG pokes (poking itself could also vasoconstrict the vessel)
SLide 12
What do topical drugs have to overcome?
The epidermal layer, once across topical anesthetics are absorbed rapidly into circulation
WHen would you provide topical anesthetics vs percutanous?
Topical anesthetics provide short term pain relief when applied to mucous membranes or skin
When is infiltration anesthesia used?
To numb an area of skin via injection
- The anesthetic is injected intradermally or subcutaneously, often at several neighboring sites near the area to be anesthetized
- Onset of action is much faster than topical anesthesia
When would Regional Anesthesia be used?
To anesthetize a large area of the body, such as extremities or the abdomen
- Regional anesthesia allows a procedure to be completed w/o the use of general anesthesia
- i.e a whole shoulder, c section, or leg would be regional
What are the risks of regional anesthesia
- Infection (low)
- Hematoma
- Systemic toxicity
- nerve injury
- wrong sided block
Add slides 17 and 18
- What are the risks of regional anesthesia
What are the 2 subcategories for peripheral nerve blocks?
- Minor nerve blocks
- Major nerve blocks
When is Intravenous Regional Anesthesia used?
Anesthetize an extremity
How is Intravenous Regional Anesthesia different from a a regional method i.e ultrasound guided needle?
Area if isolated and flooded with anesthesia
- A peripheral vein is cannulated to introduce an anesthetic
- Tourniquets, BP cuffs, and a distally located elastic band are applied an elevated extremity leading to partial exsanguination of the limb
- The tourniquet is inflated and the band removed.
- A large amount of diluted local anesthetic in injected into the vein. The tourniquet prevents systematic toxicity by limiting blood flow to and form the extremity
Difference between a central nerve block and spinal block?
Central nerve blocks don’t inject into the actual spinal cord, its actually in the dura space under the spinal cord, or in the epidural space.
- The drug penetrates and can act within the spinal cord
- Results in a large area being anesthetized
What are a central nerve blocks? (2)
A nerve block where a drug is inserted near the spinal cord; Also called Neuraxial block
- Epidural Anesthesia
- Spinal (Intrathecal) Anesthesia
What are 2 types of central nerve blocks?
Epidural Anesthesia
Spinal (Intrathecal) Anesthesia
How do Central Nerve Blocks work?
The early effects of these procedures result primarily from impulse blockade in spinal roots
- In later phases the drug penetrates and can act within the spinal cord
When would central nerve blocks be used?
- Surgery
- Obstetrics,
- Post op pain management
- Chronic pain clinics
When would single injection spinal or epidural anesthesia be commonly used for
- Lower abdomen surgery
- Pelvic procedures (prostrate)
- Lower limbs
- Cesarean deliveries
When would continuous cather based epidural infusions be used for?
- Obstetrics
- Post op pain relief (can be used for days)
When would you use a spinal block?
Useful for procedures of known duration that involve the lower extremities, perineum, pelvic girdle and lower abdomen
- Also used when consciousness is indicated for a procedure such as increased risk involved with general anesthesia (Severe respiratory disease or Difficult airway)
How are spinal blocks different from epidurals?
Spinal anesthesia requires a small amount of drug to produce rapid, profound, reproducible, but finite sensory analgesia
where does the spinal cord end?
L1-L2
Where should spinal cord injections be avoided?
Above L1 and L2
Where should Spinal Blocks be inserted?
At the level of the Cauda Equina
- L2-L3
- L3-L4
- L4-L5
edit slide 25 and slide 27
Spinal block procedure?
Needle is inserted (after infiltration anesthesia of the area) at a slight cephalad angel, 10-15 degrees, through the skin, subcutaneous tissue and the supraspinous ligament to reach the interspinous ligament.
The needle, is advanced slowly until the characteristic change in resistance is noted at the needle passes through the ligamentum flavum and dura
On passing through the dura, a pop sensation occurs
What happens when the pop sensation occurs in terms of spinal block procedure ?
Resistance decreases because the needle has entered an open space
For spinal blocks, what is the range of anesthesia dependant on?
The amount of anesthetic given
- To anesthetize dermatomes (the area of tissue supplied by nerves from a single spinal root) that lie high on the spinal cord (above area of insertion) more anesthetic is required
What are dermatomes?
The area of tissue supplied by nerves from a single spinal root
Side effects of Spinal blocks?
- break this card up
The side effects of the anesthetics depends on the amount of anesthetic given and the health status of the patient
- Cardiovascular (Reduced SVR and CO)
- Respiratory (Reduced VC due to paralysis of abdominal muscles and reduced function of the diaphragm)
- Post dural puncture headache (PDPH)
How do Epidurals differ from Spinal Blocks?
Allows for prolonged surgical anesthesia by catheter-based local anesthetic delivery; and the insertion depth aka epidural space vs spine
What affects the height of epidural blocks?
The level of injection affects the height of the epidural block
- Cervical region: Spread is caudal (tail region)
- Midthoracic: Spread is equally cephalad and caudal
- Low thoracic: Spread is mostly cephalad
- Lumbar: Spread is mostly cephalad
Important landmarks for epidurals?
- L4-L5: Hip, lower extremity, Obstetrics
- T7: Upper abdominal Sx, Colectomy, anterior resection
- T3: Thoracic Sx
- C7: Steroid injections for neck, shoulder girdle and upper extremities
What can be used to identify correct thoracic space and cervical space for Epidural injection (guide epidural basically)
Ultrasound, interventional radiology and fluoroscopy
Add slide 35 and 37 on Epidural procedure factors
Which nerves are affected by local anesthetic agents?
Local anesthetics provide a generalized of all peripheral nerves (4)
- Afferent
- Efferent
- Autonomic
- Somatic
Whats a Minor nerve block
For a distal extremity, could involve the radial nerve
Whats a major nerve block?
A major block for the entire arm, would involve the brachial plexus
When would a Intravenous Regional Anesthesia route like a Bier Block be used?
To provide complete, local anesthesia that’s safe and simple.
- Ability to perform the block with little additional equipment so its also cheap
- Basically just a tourniquet is used to stop blood flow to an area while anesthetic agents are flooded in the area
What do Neuraxial blocks affect?
- Early effects result form impulse blockades in spinal routes
- Later phases the drug penetrates and can act within the spinal cord
- Remember, its a central nerve block
What areas are affected by spinal blocks?
The lower extremities
- Perineum
- Pelvic girdle
- lower abdomen
Where is the Perineum?
The area between the anus and the scrotum or vulva
Which block would be best suited for a procedure with increased risk involved with general anesthesia?
Severe respiratory distress and difficult airways
What should you expect when inserting a needle through the dura?
A pop sensation to occur
First pain Transmission rate?
5-25 m/s transsmion rate
Second pain transmission rate
1 m/s transmission
What level of blockade do local anesthetics provide?
Local anesthetics provide a generalized blockade of all peripheral nerve fibers (afferent, efferent autonomic, somatic)
- Give larger doses bc only some of it gets to the site of action
- There is no anesthetic that isolates only efferent nerves
What is the differential functional blockade dependent on?
Dose given, the larger the dose, the larger the block. keep in mind goals of care for the patient,
- Goal might not necessarily be ot hit all 6, depending on the procedure?
- i.e Epidurals aim to help with 1st and 2nd pain, temp is typically reduced but we want them to feel touch, proprioception and skeletal muscle tone.
Spinal block insertion site?
L2-L5
What membrane do topical anesthetics have to bypass to achieve therapeutic affect?
The epidermal barrier
- The stratus corneum (outer most layer) presents the major obstacle to site of action
Infiltration anesthesia vs topical anesthesia?
Infiltration anesthesia is much faster than topical
Risks associated with Infiltration Anesthesia?
Areas that are being anesthetized will have blood bringing nutrients and taking away the anesthetics –> Risk of toxicity as the anesthetic is spread to the rest of the body
Why is a tourniquet used when injecting peripheral veins (IV regional anesthesia)
Tourniquet also prevents systemic toxicity by limiting blood flow to and from the extremity
- Anesthetic that is picked up by blood is taken to the liver for metabolism to break it down
- Is used when a ultrasound isn’t available
What color should CSF be?
Clear
- If it is not clear or is viscous = infection
How much analgesia do spinal blocks provide
Finite sensory analgesia, but require a small amount of drug to produce rapid, profound, reproducible blockages
Central blocks vs spinal blocks?
- Epidurals typically use less meds per dose compared to spinal blocks because they are injected into a larger space outside the dura mater and are intended to provide longer-lasting anesthesia with a more diffuse spread.
- Spinal blocksinvolve a more concentrated injection directly into the CSF, resulting in a more intense and rapid onset of anesthesia with a smaller volume of medication.
If CSF does not flow after insertion of needle, what does that indicate?
An obstruction or wrong placement
How do you anesthetize a rea higher up via spinal block?
Increase dose, it will spread up and down the spinal cord.
- if you want to spread it up = large dose
Why do Post Dural puncture (PDPH) headaches occur from spinal blocks?
Results from a disruption of normal CSF homeostasis.
- Loss of CSF via a leak reduces pressure around the brain and spinal cord = traction/pulling on meninges of brain = headache
- Head = severe and can involve entire head, neck, and shoulders.
- Neck stiffness is also associated with PDPH as well as N&V, hearing loss , pain and paresthesia in the extremities, vertigo and dizziness
How can Post Dural puncture (PDPH) symptoms be alleviated/reduced
Lying down can help reduce the symptoms of PDPH
Absolute contraindications for Spinal block
- Sepsis
- Severe ICP
- Patient inability to maintain stillness via the procedure
- Allergy to anesthetic
Relative contraindications for Spinal block
Risk/benefit analysis must be performed for these contraindications:
- Myelopathy (any disorder affecting spinal cord or peripheral neuropathy aka nerves outside the spinal cord/brain)
- Spinal stenosis
- Previous spinal Sx
- MS
- Spina Bifida
- Aortic stenosis
- Hypovolemia
Where is the epidural space located?
Epi = area before the dura and not the dura
- allows for prolonged surgical anesthesia by catheter based local anesthetic delivery
Epidural Complications?
- Paraplegia (loss of function in the lower half of body)
- Nerve injury
- PDPH
- Transient neurological systems
- CV effects (Hypotension + brady)
- Resp paralysis/depression (if opioids used)
- Infection and Pruritus (itchy skin)
- Shivering (only in epidurals not spinal)
Contraindications for epidural?
Absolute and relative are the same as spinal
