Bb Volatile Anesthetics

Front 1

What volatiles decrease MAP the least and which ones decrease it the most?

Back 1

decrease MAP the least: halothane
decrease MAP the most: des and iso

Front 2

How does ISO, DES and Halothane affect CO?

Back 2

ISO and DES: CO is unchanged due to inc HR
halothane: decreases CO

Front 3

How can you attenuate the increased CBF associated with iso and des?

Back 3

prior hyperventilation

Front 4

How does des affect the airway?

Back 4

1. airway irritation,
2. breath holding,
3. coughing,
4. excessive secretions,
5. laryngospasm

Front 5

Why do we heat the desflurane vaporizer?

Back 5

-due to high vapor pressure (near atmospheric pressure) small changes in liquid temperature or barometric pressure will greatly affect vaporizer output.
-Heating the vaporizer raises it's partial pressure so the vaporizer can be metered more accurately

Front 6

How much isoflurane vapor can be generated by one mL of liquid isoflurane?

Back 6

200 mL of isoflurane vapor

Front 7

How does N2O affect HR, CO, MAP, CBF, PAP?

Back 7

maintains HR, CO, MAP
increases CBF
increases PAP

Front 8

Where in the body will an air bubble expand the most rapid with N20?

Back 8

blood (less barriers to diffusion)

Front 9

When is N2O contraindicated?

Back 9

1. air embolus (also congenital heart disease),
2. bowel obstruction,
3. COPD-emphysema,
4. cor pulmonale,
5. cardiac dysfxn (severe LV depression)
6. eye and ear surgery of certain types,
7. PTX,
8. pneumocephalus,
9. trauma in the presence of head or chest wall trauma

Front 10

What does N2O expand faster an air embolus or a PTX?

Back 10

air embolus

Front 11

What volatile anesthetic would be the most beneficial in aortic or mitral stenosis? Why?

Back 11

Halothane - do not want to increase heart rate or decrease SVR

Front 12

Which volatile anesthetic is most beneficial with regurgitant cardiac lesions? Why?

Back 12

Isoflurane - increases HR, decreases SVR

Front 13

Rank isoflurane, enflurane and halothane by greatest to least respiratory depression

Back 13

Enflurane > halothane > isoflurane

Front 14

What do you see on the EEG with halothane and isoflurane and at what dose?

Back 14

burst suppression at 2MAC iso and 4MAC halo

Front 15

What are some renal manifestations of flouride toxicity?

Back 15

1. polyuria,
2. decreased urine concentrating ability

Front 16

How does cold affect induction with volatiles?

Back 16

cold increases solubility and slows induction

Front 17

How does mainstem intubation affect induction with volatiles?

Back 17

-for very soluble agents induction is not delayed,
-for insoluble agents induction is delayed

Front 18

How is induction affected in neonates and pregnant patients with volatiles?

Back 18

increased ratio of minute ventilation to FRC which accelerates induction

Front 19

How does CHF or cirrhosis affect metabolism of volatiles?

Back 19

may decrease the magnitude of overall metabolism

Front 20

How can halothane be metabolized?

Back 20

2 pathways:
-oxidative (normal pathway) -> triflouracetic acid, bromide and chloride;
-reductive (hepatic hypoxia or obesity) -> fluoride, chlorodifluoroethylene, chlorotrifluoroethane

Front 21

What are the blood gas solubilities of the volatile anesthetics?

Back 21

des 0.42,
N20 0.47,
sevo 0.6,
iso 1.4,
halothane 2.3

Front 22

What are the vapor pressures of the volatile anesthetics?

Back 22

sevo 160,
iso 238,
halothane 240,
des 665

Front 23

if a machine is calibrated at sea level and then taken to higher elevation what happens to the amount of anesthetic delivered?

Back 23

vapor pressure remains the same, barometic pressure decreases thus VP/BP increases and the delivered concentration is higher than appears on the dial

Front 24

Why do we see frost on the N2O cylinder?

Back 24

expansion of fresh gas absorbs heat resulting in frost in the cylinder

Front 25

How do you calculate how much N2O is in a cylinder?

Back 25

weigh the cylinder
44 gms/mole,
22.4 liters/mole

Front 26

how do you deal with a tipped anesthetic vaporizer?

Back 26

set vaporizer at low concentration and flush with oxygen at 10 L/min for 30min

Front 27

What decreases MAC?

Back 27

1. PaO2 <40mmHg,
2. severe hypotension,
3. hypothermia,
4. Hb<4,
5. age,
6. alpha methyldopa,
7. PaCO2 >90mmHg,
8. drugs - benzos, barbs, cholinesterase inhibitors, chronic amphetamines, narcotics, ketamine, reserpine, guanethidine, clonidine, lithium
9. pregnancy,

Front 28

What does not change MAC?

Back 28

1. duration of anesthesia
2. sex or species
3. hypocarbia or hypercarbia (PaCO2 <90 mmHg)
4. alkalosis or acidosis
5. hypothyroidism or hyperthyroidism

Front 29

What increases MAC?

Back 29

1. chronic alcoholism
2. hyperthermia
3. hypernatremia
4. drugs increasing catecholamines - ephedrine, acute cocaine, acute amphetamines, MAOIs

Front 30

How does hyperthyroidism effect CO? What is its implications?

Back 30

-CO is increased in pts with hyperthyroidism
-this necessitates a higher concentration of volatile anesthetic bc the rate of rise of alveolar concentration is decreased

Front 31

How does MAC change in neonates to adults?

Back 31

MAC is greater in neonates than adults and rises further until about 1 yr old, when it begins to fall progressively for the rest of life

Front 32

How does ISO, DES and Halothane affect SVR?

Back 32

-Iso and Des decrease SVR
-halothane has little effect on SVR

Front 33

How does ISO, DES and Halothane affect HR?

Back 33

-Iso and Des inc HR
-Halo no change

Front 34

How is myocardial oxygen consumption effected by volatile anesthetics?

Back 34

-Halothane decreases myocardial O2 consumption the most compared to other volatiles

Front 35

What other effect does halothane have on the heart?

Back 35

sensitizes the heart to the effects of catecholamines and can result in dysrrhythmias

Front 36

Which is the newest volatile anesthetic? How was it produced?

Back 36

Desflurane - substituting flourine for the single chlorine in isoflurane

Front 37

What is one major drawback of sevoflurane?

Back 37

It is significantly biotransformed and can result in serym fluoride concentration which exceed the threshold for renal toxicity

Front 38

Which is more of a myocardial depressant, sevoflurane or enflurane?

Back 38

sevoflurane

Front 39

What is compound A?

Back 39

AKA vinyl ether
-compound formed by the degradation of sevoflurane by soda lime and baralyme that is nephrotoxic in rats

Front 40

How does nitrous effect myocardial contractility?

Back 40

It is a dose dependent myocardial depressant but tends to cause sympathetic stimulation so HR, CO, and MAP are all maintained

Front 41

What is coronary steal?

Back 41

Represents a diversion of blood flow from the coronary vasculature distal to a critical coronary stenosis
-vessels distal to the critical stenosis are already maximally vasodilated so if the vasculature around them is vasodilated blood flow is "stolen" from them

Front 42

Which volatile anesthetic may possible cause coronary steal?

Back 42

Isoflurane - probably insignificant at concentrations <0.5%

Front 43

What effect on hypoxic ventilatory drive do volatile anesthetics have?

Back 43

Depress it

Front 44

What effect do volatile anesthetics have on oxygen consumption and work of breathing with spontaneous ventilation?

Back 44

both are increased

Front 45

What effect do volatile anesthetics have on SSEP?

Back 45

Above 1MAC, VAs cause a decrease in amplitude and an increase in the latency of the waveform

Front 46

Effect of VAs on CBF?

Back 46

Above 0.5 MAC, a dose dependent increase

Front 47

Which decreases CMRO2 more, iso or halo/

Back 47

Iso

Front 48

What effect do VAs have on CSF?

Back 48

-iso does not increase or decrease CSF production, but may decrease the resistance to absorption, thus decreasing total volume of CSF

Front 49

How is halothane hepatitis diagnosed?

Back 49

It is a diagnosis of exclusion

Front 50

What are the 2 types of halothane hepatitis?

Back 50

1. self-limited post op hepatotoxicity (less severe, MC)
2. life threatening (very severe, less common)

Front 51

What % of pts repeatedly anesthetized with halothane will show elevations of LFTs?

Back 51

20%

Front 52

What is the mechanism leading to halothane hepatitis?

Back 52

Unknown, but eosinophilia, rash, fever, and arthralgia suggest an immune mediated response
-pts plasma contains antibodies against specific halothane induced liver antigens called neoantigens
-thought to be formed by a reaction of a halothane metabolite (trifluoroacetyl halide) with hepatic proteins

Front 53

What are the genetic effects of nitrous oxide?

Back 53

inhibition of methionine synthetase a vit B12 dependent enzyme

Front 54

What concentration of fluoride can cause renal toxicity?

Back 54

when they exceed 50-80 uM/L

Front 55

What factors affect anesthetic gas uptake?

Back 55

1. delivery - fraction inspired and alveolar ventilation
2. uptake - CO, solubility, change in alveolar to venous blood concentration
3. second gas effect

Front 56

How does CO effect anesthetic uptake?

Back 56

-The greater the CO, the slower the rate of rise of alveolar concentration
-The lower the CO, the faster the rate of rise of alveolar concentration

Front 57

How does solubility of inspired gas affect anesthetic uptake?

Back 57

-The greater the solubility, the slower the rate of rise of alveolar concentration
-The lower the solubility, the faster the rise o alveolar concentration

Front 58

With what anesthetics is the rate of rise in alveolar (Fa) anesthetic concentration the most rapid?

Back 58

the least soluble anesthetics like nitrous and desflurane

Front 59

What are the advantages of isoflurane?

Back 59

1. induction and elimination are relatively rapid bc of low B/G partition coefficient
2. low metabolism results in minimal toxicity
3. associated with good muscle relaxation

Front 60

What is the percentage of metabolism of volatile anesthetics?

Back 60

-Methoxyflurane: 40%
-Halothane: 20%
-Sevoflurane: 5%
-Enflurane: 2%
-Isoflurane: 0.2%
-Desflurane: <0.2%

Front 61

What is metabolism of volatile anesthetics dependent upon?

Back 61

Cytochrome P450 enzzymes located in the endoplasmic reticulum of hepatocytes
-these enzymes mediate both oxidative and reductive metabolism of inhaled anesthetics

Front 62

What are the metabolites of isoflurane?

Back 62

1. difluoromethanol - degraded to minute quantities of fluoride
2. trifluoroacetic acid

Front 63

Order of fluorination for volatile anesthetics

Back 63

"Me So Hap-E I Declare"
M = methoxyflurane
S = sevoflurane
H = halothane
E = enflurane
I = isoflurane
D = desflurane

Front 64

Order of liver metabolism for volatile anesthetics

Back 64

"Me Have Sinned Enough I Declare"
M = methoxyflurane
H = halothane
S = sevoflurane
E = enflurane
I = isoflurane
D = desflurane

Front 65

What is MAC a measure of?

Back 65

Anesthetic potency
-the lower the MAC, the greater the potency

Front 66

The % of an anesthetic delivered increases with...

Back 66

increasing vapor pressure

Front 67

What is the liters, pressure, and critical temp for oxygen E cylinder?

Back 67

L 625-660
Press 2200
critical temp -120

Front 68

What is the liters, pressure, and critical temp for nitrous E cylinder?

Back 68

L 1590
Press 745
Crit temp 36

Front 69

What is the critical temp?

Back 69

temp above which a substance cannot be liquified regardless of the pressure placed upon it

Front 70

When all the nitrous liquid in a tank is vaporized, how much nitrous in liters remains?

Back 70

When all the liquid is vaporized, only then does the pressure begin to fall and approximately 75% of the total has been exhausted = 215L

Front 71

What are the physical properties of nitrous oxide?

Back 71

1. ammonium nitrate + heat => nitrous oxide + water
2. nitrous oxide supports combustion: at temps < 450 deg, nitrous breaks down into nitrogen + oxygen

Front 72

At low flows through a flow meter, gas flow varies according to ____.

Back 72

viscosity of gas

Front 73

At high flows through a flow meter, gas flow varies according to ____.

Back 73

density of gas

Front 74

What can cause inaccuracies with flowmeters?

Back 74

1. large temp fluctuations
2. barometric pressure decreases at high flows - high flow density of gas decreases and delivered flow is greater than what flow meter is reporting
3. the greater the flow, more error in actual flow delivered
4. floats must be properly aligned
5. length of the tube makes no difference to accuracy

Front 75

Which method of checking for an oxygen flowmeter leak is most sensitive?

Back 75

negative pressure (bulb) check test

Front 76

Once isoelectric EEG is achieved with isoflurane, do further decreases in CMRO2 occur?

Back 76

No

Front 77

What is the critical CBF at which EEG evident ischemia occurs with isoflurane vs halothane?

Back 77

-iso 10 mL/min/100gm
-halo 18-20 mL/min/100gm

Front 78

For every cm the head is elevated above the heart, how much does CBF change?

Back 78

CBF decreases 0.7 mmHg

Front 79

When can systemic toxicity occur with SNP?

Back 79

dose > 7 mg/min

Front 80

The oil/gas coefficient is directly related to...

Back 80

anesthetic potency

Front 81

Is nitrous teratogenic?

Back 81

Yes - higher rate of spontaneous abortion in OR personel

Front 82

What is inhalational anesthetic uptake determined by?

Back 82

1. pulmonary blood flow
2. solubility of agent
3. alveolar-venous partial pressure difference

Front 83

Explain the alveolar-venous partial pressure difference.

Back 83

-Occurs as a result of anesthetic uptake by the tissues
-arterial blood has an anesthetic partial pressure equal to that of the alveolus
-arterial blood distributes the anesthetic to tissues where tissue uptake occurs
-venous blood returning to the right heart and lungs through the pulmonary artery has a lower anesthetic partial pressure and an alveolar-venous partial pressure difference exists, allowing uptake at the alveolus to occur

Front 84

The higher the tissue-blood flow, the ___ the amount of anesthetic delivered to the tissue in a given amount of time.

Back 84

greater

Front 85

What are the 4 tissue groups according to their perfusion?

Back 85

1. vessel rich group- brain, heart, splanchnic bed
2. muscle group - includes skin
3. fat group
4. vessel poor group - bones, ligaments, cartilage, tendon

Front 86

What are the 2 components of the 2nd gas effect? Explain.

Back 86

1. an increase in tracheal inflow caused by the uptake of gases in the alveolus that creates a void, drawing more gas down the trachea
2. concentration effect - since nitrous is given in high concentration at induction, uptake of nitrous reduces volume of the alveolus, thereby concentrating the remaining gases in a small volume. with the next inspiration, the alveolus is re-expanded to its original volume with the same gas mixture. result is augmentation of the concentration of the second gas.

Front 87

What controls airway smooth muscle tone? How is this effected by inhaled anesthetics?

Back 87

It is controlled by both sympathetic and parasympathetic systems
-these systems mediate their efffects via cyclic GMP and cyclic AMP in the bronchial smooth muscle
-volatiles cause bronchodilation by possibly increasing cAMP as well as depression of airway reflexes