6b Anesthesia

What are the 3 types of anesthesia?

1. Local
a) Regional
2. General
3. Monitored Anesthesia Care

What is local anesthesia?

- loss of sensation to limited region
- no loss of consciousness

What is regional anesthesia?

- loss of sensation to larger region
- no loss of consciousness

What is general anesthesia?

- loss of sensation to entire body
- loss of consciousness

What is monitored anesthesia care?

- varying levels of sedation
- no loss of consciousness
- used in diagnostic procedures or w local anesthesia for minor sx

What are some routes of local anesthesia?

- topical
- field block
- nerve block
- Intrathecal
- Epidural

What is the mechanism of action of local anesthetics?

- block voltage-gated Na channels
- inhibit motor and sensory neuronal signaling

How can you improve the duration of action of local anesthetics?

- administer with Epi
- alpha-1 agonist
- vasoconstriction --> restricts distribution --> remains at site longer

What are 2 local anesthetic drug classes?

1. Ester Anesthetics
2. Amide Anesthetics

What are some characteristics of ester anesthetics?

- metabolized in blood
- short half life
- pKa 8.6-8.9

What are some characteristics of amide anesthetics?

- metabolized in liver
- longer half life
- pKa 7.5-8.0

Which local anesthetic drug class is associated with a faster onset of action? Why?
a) Ester Anesthetics
b) Amide Anesthetics

- Amide Anesthetics
- 7.5 pKa is closest to physiological pH
- will be uncharged/lipid soluble and easily absorbed by nerve lipid membrane

Which requires a higher dose of anesthetic, epidural or intrathecal? Why?

- Epidural --> highly vascularized

- Intrathecal --> higher efficacy

Why is an epidural a common choice during child birth?

- administered below L1 w cauda equina --> decrease risk
- safer than intrathecal when in active labor

What is an example of a epidural?

- Bupivacaine (Marcaine)
- Visceral pain fibers (C fibers)

What fibers does bupivacaine effect more?

visceral & somatic pain fibers (C & A-gamma) more than motor fibers (A-alpha)

Why might intrathecal anesthetic be somewhat easier to administer?

clear endpoint

When in intrathecal typically used?

scheduled surgical procedures (C-section, TKR)

How do opioids work as regional analgesia?

- inhibit release of pain signaling NT
- decrease neuronal excitiability in brain

Why are opioids as regional analgesics a good choice for labor?

- very effective at visceral pain
- no impact on motor neurons (able to move)

Can opioids be used for surgical anesthesia?

- no
- local anesthetics are required for sx

What are some adverse effects of opioids?

- pruritus
- nausea and vomiting
- respiratory depression (always risk w opioids)

What is pruritus? How is it tx?

- extreme itching
- antihistamines

What are some adverse effects of epidural and intrathecal anesthesia?

- inadequate anesthesia (still in pain)
- backache
- infection
- arachnoiditis (allergic rxn)
- spinal h/a

What is a spinal h/a? How is it tx?

- after removal of catheter dura doesn't reseal
- leaks CSF
- brain rests on skull bone
- blood patch to puncture site

What are the four stages of GA?

1. Analgesia
2. Disinhibition
3. Surgical Anesthesia (hold here)
4. Medullary depression (lead to death)

What are the 6 goals of GA?

1. Analgesia
2. Sedation
3. Relaxation
4. Hypnosis (sleep)
5. Amnesia
6. Loss of reflexes

Why is balanced anesthesia used?

- no single drug can accomplish all 6 goals
- used combo of drugs

Why are IV anesthetics used?

- move quickly through stages 1 and 2
- decrease dose of inhaled anesthetic

What are the 4 drug classes of IV GA? Give examples of each

1. Barbiturates (propofol)

2. Benzodiazepines (midazolam)

3. Opioids (fentanyl)

4. Others (ketamine)

When are IV vs inhaled anesthetics used?

IV: Induce

Inhaled: Maintain

What are some characteristics of volatile liquids?

- low MAC (low [ ] needed)
- poor analgesic
- high safety profile

What are some characteristics of gaseous inhaled anesthetics (NO)?

- laughing gas
- no LOC
- strong analgesics

What are 4 things patients should be monitored for p/o?

- nausea & vomiting
- CNS depression
- respiratory depression
- Changes in vital signs