What is anesthesia

Question 1

Ether historically:

Answer 1

• First publicly used in 1846 by William TG Morton

* Standard of care until 1960s

Question 2

Chloroform historically:

Answer 2

Effective, but reports of arrhythmias, resp. depression, and hepatotoxicity

Question 3

Nitrous oxide historically:

Answer 3

Still used today, but low potency; “second gas effect”  N2O use can decrease amount of anesthetic needed

Question 4

Flourinated hydrocarbons historically:

Answer 4

Halothane (1956)
Isoflurane (1981)
Desflurane (1992)
Sevoflurane (1994)

Question 5

Father of Anesthesia

Answer 5

John Snow - british . Anesthesiology came into being mid-1900s.

Question 6

Cocaine historically

Answer 6

Cocaine from coca plants used topically (for eye surgery) in 1884
Later that year, cocaine was injected intradermally for local nerve blocks
1898: first spinal (cocaine)

Question 7

IV Induction agents historically

Answer 7

• Barbs used first in 1920s (barbital > hexobarbital > thiopental >methohexital)
• Benzos: used for induction, but also pre-medication, supplementation of anesthesia, and IV sedation
• Ketamine (1970)
o Minimal cardiac and respiratory depression
• Etomidate (1972)
• Propofol (1989)

Question 8

Meyer-Overton Rule

Answer 8

the potency of inhalation agents directly correlates with their lipid solubility

Question 9

Anesthesia is 4 things:

Answer 9

1. Analgesia
2. Amnesia
3. Reversible loss of consciousness
4. +/- Muscle relaxation

Question 10

FGF =?

Answer 10

Fresh Gas Flow - determined by vaporizer and flowmeter settings

Question 11

Inspired gas determined by?

Answer 11

Fi - determined by: FGF rate+circuit volume+ circuit absorption.

Question 12

Alveolar gas determined by?

Answer 12

FA - determined by uptake+ventilation+concentration effect+ 2nd gas effect. FA/Fi

Question 13

Arterial gas determined by?

Answer 13

Fa - determined by V/Q mismatching

Question 14

High solubility?

Answer 14

High solubility (ex: halothane) so quickly taken up by blood so takes longer for FA to rise so slower induction

Question 15

Low solubility?

Answer 15

Insoluble (ex: nitrous oxide) so slowly taken up by the blood so FA rises quicker so faster induction

Question 16

Partition coefficients of 5 volatile agents, starting at most insoluble (i.e fastest)

Answer 16

Partition coefficients:

Desflurane (0.42)

Question 17

How does high CO affect induction speed?

Answer 17

High CO –> higher uptake of anesthetic –> takes longer for FA to rise –> slower induction

Question 18

How does low CO affect induction speed?

Answer 18

Low CO can cause overdose of soluble agents because fast induction

Question 19

Factors determining transfer of anesthetic gas from machine to alveoli

Answer 19

• Inspired partial pressure

* Alveolar ventilation

Question 20

Factors determining transfer of inhaled anesthetic from alveoli to arterial blood

Answer 20

• Blood-gas partial coefficient
• Cardiac output
• Alveolar-to-venous partial pressure difference

Question 21

Factors determining transfer of inhaled anesthetic from arterial blood to brain

Answer 21

• Brain-blood partition coefficient
• Cerebral blood flow
• Arterial-to-venous partial pressure difference

Question 22

Factors that that speed recovery from anesthetic (also speed up induction):

Answer 22

• Elimination of rebreathing
• High FGF
• Low circuit volume
• Low circuit absorption
• Decreased solubility
• High cerebral blood flow
• Increased ventilation

Question 23

MAC =?

Answer 23

MAC = the alveolar concentration that prevents movement in 50% of patients in response to a surgical incision

Question 24

3 facts about MAC

Answer 24

o MAC mirrors brain partial pressure
o MAC allows comparisons of potency between agents
o MAC values for different anesthetic agents are roughly additive
0.5 MAC Nitrous oxide (53%) + 0.5 MAC Halothane (0.37%) = 1.0 MAC Isoflurane

Question 25

Nitrous Oxide: MAC, potency, smell...?

Answer 25

``` MAC ~105% -> cant ever get 1 MAC. Low potency. The only inorganic gas used. Gas at room temp. (liquid with pressure) Nonflammable Colorless/odorless Low solubility -> rapid onset Eliminated via exhalation, irreversibly oxidizes vit B12 (Inhibits enzymes that need B12) BM suppression with prolonged exposure Teratogen ```

Question 26

Isoflurane: MAC, potency, smell...?

Answer 26

MAC 1.2%, second most potent. Pungent. Vasodilator: lower BP, increase CBF and ICP. Nonflammable. Metabolized to trifluroacetic acid. Isomer of enflurane.

Question 27

Sevoflurane: MAC, potency, smell...?

Answer 27

MAC 1.8%, about half as potent as Iso. Sweet smell. Bronchodilator. Metabolized by P450 Potential for nephrotoxicity because of increased fluoride ions

Question 28

Desflurane: MAC, potency, smell...?

Answer 28

MAC ~6.6%, low potency, very pungent. Increases sympathetics: HTN if rapid. Boils at room temp because high vapor pressure, so requires special vaporizor. Low solubility so fastest in/out. Degraded by desiccated carbon dioxide to carbon monoxide so check ABG for carbohemoglobin.

Question 29

Variables Decreasing MAC

Answer 29

1. Hypo or Hyper thermia 2. Elderly 3. Acute EtOH 4. Anemia 5. Hypoxia/Hypercarbia 6. Hypotension 7. Hypercalcemia 8. Hyponatremia 9. Pregnancy

Question 30

Variables Increasing MAC

Answer 30

1. young age 2. chronic EtOH 3. Hypernatremia 4. acute amphetamines 5. Cocaine 6. Ephedrine

Question 31

Halothane MAC, potency...?

Answer 31

MAC 0.75, most potent. Liquid at room temp. Nonflammable Alkane derivative Oxidized by P450 in liver - trifluoroacetic acid. Rare halothane hepatitis (in middle age obese women)

Question 32

Stages of anesthesia

Answer 32

Stage 1. Analgesia: pt loses pain sensation but remains conscious Stage 2. Excitement: pt may experience delirium, become violent. BP: increased and irregular RR: increased Stage 3. Surgical Anesthesia: point at which surgery can begin.  Relaxed skeletal muscles  Regular breathing  Eye movements slow then stop Stage 4. Medullary Paralysis: occurs if primordial brainstem functions stop working

Question 33

How can Stage 2 of anesthesia be bipassed?

Answer 33

STAGE 2’s effects can be bypassed by giving a barbiturate!

Question 34

When should stage 4 of anesthesia be reached?

Answer 34

NEVER - it can cause death!

Question 35

What do inhaled anesthetics do to BP and SVR?

Answer 35

decrease BP (nothing for NO)

Question 36

What do inhaled anesthetics do to CO?

Answer 36

Decrease, or nothing for NO, Iso, sometimes Des.

Question 37

What do inhaled anesthetics do to HR?

Answer 37

Halothane - decrease. Isoflurane - increase. Desflurane - increase or nothing. Else- nothing

Question 38

What do inhaled anesthetics do to RR, PaCO2, and TV?

Answer 38

Increase RR and PaCO2. | Decrease TV.

Question 39

What do inhaled anesthetics do to CBF, ICP, and seizure threshold.

Answer 39

Increase CBF and ICP. | Decrease seizure threshold.

Question 40

What do inhaled anesthetics do to metabolic rate?

Answer 40

Decrease metabolic rate. | Except NO which increases metabolic rate.

Question 41

What do inhaled anesthetics do to renal blood flow, GFR, UOP?

Answer 41

Decrease all

Question 42

What do inhaled anesthetics do to hepatic blood flow?

Answer 42

decrease

Question 43

3 factors that affect anesthetic uptake?

Answer 43

1. blood solubility (less solubility means faster induction) 2. alveolar blood flow 3. diff in partial pressure b/w alveolar gas and venous blood

Question 44

Which inhaled anesthetic can cause BM depression?

Answer 44

NO

Question 45

Which states predispose patients to overdosage with soluble agents?

Answer 45

Low output states. Rise in alveolar concentration is increased.

Question 46

Greater uptake of an agent means...?

Answer 46

The greater the uptake of agent: the greater the diff between inspired and alveolar concentartions and slower rate of induction

Question 47

Which inhaled anesthetic has the least effect on BP?

Answer 47

NO. but sevo also has small decrease in BP.