6b Drugs for Local and General Anesthesia

What is anesthesia?

Loss of all sensations

What is the difference between anesthesia and analgesia?

Anesthesia is the loss of all sensation whereas analgesia is only the loss of pain sensations

What are the 3 types of anesthetics?

• Local

• General

• Monitored anesthesia care

What is local anesthesia?

Drugs intended to block sensations to local area with no loss of consciousness

What is regional anesthesia?

Loss of sensation to larger body area with no loss of consciousness

Hoe are regional anesthesia given (2)?

• Epidurals

• Spinal

What is general anesthesia?

Loss of sensation throughout the entire body, accompanied by loss of consciousness

What is monitored anesthesia care?

Varying levels of sedation, in which client remains responsive

When is monitored anesthesia care used?

Used during diagnostic procedures or in combination with local anesthesia for minor surgeries

Which type of anesthesia is good for claustrophobic pts in MRI?

Monitored anesthesia care

What are the different routes of anesthesia administration (5)?

• Topical

• Nerve block

• Infiltration

• Spinal

• Epidural

What is topical route?

Applied to the skin or mucous membranes that take a local effect

What is infiltration route?

Direct injection into tissue immediate to surgical site

What is nerve block route?

Direct injection into tissue that may be distant from operation side

What is spinal route?

Injection into CSF

What is epidural route?

Injection into epidural space of spinal cord

What is the common mechanism of action for most local anesthesthetics?

Blocks voltage gated Na+ channels to block all sensations (no opening of Na+ channels = No influx of Na+ = No depolarization = No propagation of signals)

Which neurons are the most susceptible to local anesthetics?

Active neurons - they bind to open Na+ channels first

How do we improve the biological effect of some local anesthetics?

Co-administration with epinephrine (adrenergic agonist)

What are 2 common local anesthetics?

• Procaine benzocaine

• Lidocaine bupivacaine

What type of anesthetic is procaine benzocaine?

Ester anesthetic

What type of anesthetic is lidocaine bupivacaine?

Amide anesthetic

Where is procaine benzocaine metabolized?

In bloodstream

Where is lidocaine bupivacaine metabolized?

In liver

What is the t1/2 of procaine benzocaine?

Short - 1-2 min

What is the t1/2 of lidocaine bupivacaine?

Long - 60-240 min (1-4 hours)

What is the pka of procaine benzocaine?

8.6-8.9

What is the pka of lidocane bupivacaine?

7.5-8.0

Which of the following is used for epidural and intrathecal anestheisa: procaine benzocaine or lidocaine bupivacaine?

Lidocaine bupivacaine

Which administration route is used for regional anesthesia (2)?

• Epidural

• Spinal

Why is bupivacaine commonly used in regional anesthesia for operative management fro pt in pain and sensation (2)?

• Longer t1/2

• Good at managing visceral pain fibers and somatic pain fibers than motor fibers and fibers related to sensation of pressure

What type of fiber conducts visceral pain?

C fiber

What type of fiber conducts somatic pain?

A-delta fiber

What type of fiber conducts motor?

A-alpha fibers

Why is the dose for epidural anesthesia greater than spinal?

Epidural space is highly vascularized which gives high opportunity for local anesthetic to move out of the space and disperse into other areas of the body

What happens if we properly apply epidural anesthesia?

Drug should predominantly affect the nerve roots passing through epidural space

Where is an epidural administered?

L2

Why is epidural administered at L2?

Cauda equina is located there - less chance of damaging a nerve

Where does the spinal cord end?

L1

Which is safer in labour: Spinal or epidural anesthesia?

Epidural

Why is epidural safer in labour (2)?

• Not inserting needle into CSF

• No danger if mother moves

Which is preferred for c-section when pt is not in labour: Spinal or epidural?

Spinal

Why is spinal preferred for c-section without labour?

Mother can stay still for the time that the needle and catheter are being inserted into CSF

When are epidurals administer during labour?

Between contractions

Why is spinal anesthesia easier to administer?

There is a clear endpoint - drawing on needle when applying traction allows us to get clear fluid out which indicates that we are in the CSF

What happens if spinal anesthesia is not inserted in midline of spine?

Pt may experience anesthesia on only one side of body - unconformable

Why does spinal anesthesia have higher rates of efficacy than epidural?

There is no blood supply that may spread the anesthetics to other parts of the body

What happens if a product that is supposed to be given epidurally is administered in the dura on accident?

Dose will enter CSF - this dose is too high for the CSF, causing migration of the product up the spinal column and results in analgesia and anesthesia in areas of the body that involve the cardio-respiratory system

How do products provided intrathecally not float upwards?

They have a specific gravity that prevents the product from floating upwards

Why do we not have specific gravity in epidural products like spinal ones?

Since we are administering the drug in epidural space rather than fluid filled space of cerebral spinal column

What do opioids manage?

Pain

Do opioids block sensations?

No

What is added to regional anesthesia?

Analgesics (opioids)

Why do we continue to give analgesia after anesthetics post op?

So that they do not feel pain

How are opioid analgesics more beneficial than local anesthetics for pain?

Opioids let them move unlike anesthetics which blocks all sensations - they will not be able to move

What is used more often as epidural in labour: Opioid analgesic or local anesthetic?

Opioid analgesic - so that they can move around

Does opioid analgesic administered epidural enter systemic circulation or breast milk?

No

What is the opioid analgesic mechanism (3)?

• Binds to presynaptic receptors in the dorsal horn of the spinal cord (substantia gelatinosa), inhibits release of pain signalling NTs

• Bind to postsynaptic receptors in the brain to decrease neuronal excitability

• No impact on activity of motor neurons

Does dose of anesthetic increase or decrease when we add analgesic?

Decrease

What are AEs of opioid analgesic (3)?

• Pruritus (intense itchiness)

• Nausea and vomiting

• Resp depression

What can be used to treat pruritus after opioid analgesic?

Antihistamines

When does nausea and vomiting occur after opioid analgesia?

If drug reaches postrema in brainstem

Is nausea and vomiting rare after opioid analgesia?

Yes

Is resp depression rare after opioid analgesia?

Yes

What are the AEs of epidural and intrathecal anesthesia (5)?

• Inadeuqate anesthesia

• Backache

• Infection

• Aeachnoiditis

• Spinal HA

When would inadequate anesthesia occur?

If anesthetic has not been properly administered (not on midline) - pt wil still feel pain on one side or both

What causes backache to occur after epidural or IT administration?

Actual injection of product

When can infection occur after epidural or IT administration?

If skin has not been prepped properly

How does infection occur after apidural/IT?

Organism that is part of normal flora can be brought into CSF - CSF is sterile (no WBCs present)

How would we treat infection in CSF?

IV antibiotics for 6-8 weeks

Are infections of CSF rare?

Yes

What is arachnoiditis?

Inflammation of arachnoid layer of the dura mater

Is arachnoiditis something that we can predict beforehand and why/how?

No, it is more of an allergic reaction

What are symptoms of arachnoiditis?

Pt complains of persistent backache and discomfort

What is the most common AE after epidrual/IT administration?

Spinal HA

How does spinal HA occur?

After we have finished from anesthesia/analgesia and we have removed the catheter, we can except the dura to cover up the hole we made from the catheter

For some patients, the resealing does not happen and the hole remains open - CSF leaks out of the hole

Brain that is floating in CSF starts to sink on the bony processes of the skull - PT will experience a severe headache that does not improve with rest, food, analgesics

How is spinal HA treated?

Blood patch - 15-20 mL of autologous blood transfusion to the puncture site (use pt blood)

What are the 4 stages of general anesthesia?

1. Analgesia - no pain

2. Disinhibition - hyperactivity due to reaction to medication

3. Surgical anesthesia - ideal stage to keep surgical patients

4. Medullary depression - can lead to death

What is the purpose of general anesthesia (6)?

• Analegesia

• Sedation

• Relaxed

• Hypnosis/sleep

• Amnesia

• Loss of reflexes

Can a single drug safely accomplish the 6 effects of general anesthesia?

No - multiple drugs need to be used

Which drugs are used to accomplish the effects of general anesthesia?

• Short-acting benzo

• Opioids (pain)

• General anestehtic

• NMBA (loss of reflex)

Why is it beneficial to have more than one drug for general anesthesia vs one drug?

The more medications we have, the lower the dose of each we can use in general anesthesia - lower doses = less risk for AE

How are general anesthetics given (2)?

• IV

• Volatile liquid

What is volatile liquid?

A liquid that evaporates quickly

What do IV anesthetics induce (4)?

• LOC

• Sedation

• Muscle relaxation

• Analgesia

What are volatile liquids used for?

Maintenance

What drug is administered first for general anesthesia?

IV anesthetic

What is administered after IV anesthetic?

Benzo

What is administered after benzo?

General anesthesia cocktail

What do IV anesthetics allow pt to do?

Move from stage 1-2 fast

When can IV anesthesia be used alone - without inhaled anesthesia?

If procedure takes less than 15 min

What IV anesthetic is used on its own for procedures less than 15 min (3)?

• Propofol

• Midazolam

• Opioids and ketamine

What does propofol look like?

Milky white

What is propofol good for?

Intubation

What does propofol do (3)?

• Hypnotic

• Muscle relaxation

• Amnesia

What does midazolam do (2)?

• Sedation

• Relaxation

What do opiods + ketamines do (2)?

• Hypnotic

• Inhibits pain

Are inhaled general anesthetics highly water or lipid soluble

Lipid