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Pharmacology > Inhaled Anesthetics > Flashcards

Inhaled Anesthetics Flashcards

0
Q

Which is the most potent of the volatile anesthetics in clinical use?

A

Isoflurane

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1
Q

What are the major determinants of the speed of induction?

A

The inspired concentration and the blood:gas solubility

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2
Q

Which is the least soluble of the volatile anesthetics in clinical use?

A

Desflurane

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3
Q

Which is the least irritating of the volatile anesthetics in clinical use?

A

Sevoflurane

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4
Q

What is a vapor pressure?

A

Most volatile agents are liquids at ambient pressure and temperature. If the system in which the volatile liquid resides is a closed container, molecules of the substance will equilibrate between the liquid and gas phases. At equilibrium, the pressure exerted by molecular collisions of the gas against the container walls is the vapor pressure.

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5
Q

What is the boiling point?

A

The boiling point of a liquid is the temperature at which its vapor pressure exceeds atmospheric pressure in an open container.

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6
Q

What is the solubility of a gas in a solution?

A

It is the tendency of a gas to equilibrate with a solution, hence determing its concentration in solution.

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7
Q

What is the Henry’s law?

A 
Henry's law expresses the relationship of concentration of a gas in solution to the partial pressure of the gas with which the solution is in equilibrium:
C=kP
C- concentration in solution
K- solubility constant
P- partial pressure of the gas

The concentration of anesthetic in the blood depends on the partial pressure at equilibrium and the blood solubility.

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8
Q

What is the partial pressure of a gas in a solution?

A

The partial pressure of a gas in a solution represents the pressure that the gas in equilibrium with the liquid would have if a gas phase existed in contact with the liquid phase.

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9
Q

What is a partition coefficient.

A

The ratio of dissolved gas (by volume) in two tissue compartments at equilibrium.

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10
Q

Which of the inhaled anesthetics are true gases and what are the others?

A

Nitrous oxid and xenon are gases. The rest are vapours of volatile liquids

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11
Q

What is the goal of delivering inh. anesthetic agents?

A

To produce the anesthetic state by establishing a specific concentration of anesthetic in the CNS.

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12
Q

What is the fractional volume of a gas?

A

Fractional volume is equal to the partial pressure divided by ambient pressure

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13
Q

How much of CO is delivered to VRG?

How much does the VRG comprise of body mass?

A

75 %, 75 ml/ min/100g

10 % of body mass

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14
Q

How much of CO is delivered to muscle?

How much does the muscle comprise of body mass?

A

19%, 3 ml /min/100g

50 %

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15
Q

How much of CO is delivered to fat?

How much does the fat comprise of body mass?

A

6 %, 3 ml/min/100g

20% of body mass

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16
Q

What is the vessel rich group?

A

Tge VRG includes the brain, heart, kidney, liver, digestive tract, glandular tissues.

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17
Q

What is the Daltons law?

A

The sum of partial pressures of each gas in a mixture of gases equals the total pressure of the entire mixture.

or

Each gas in a mixture of gases at a given volume and temperature has a partial pressure that is the pressure it would have if it alone occupied the volume.

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18
Q 
Blood:gas partition cefficients for
Sevoflurane
Desflurane
Isoflurane
Enflurane
Halothane
N2O
A 
0,65
0,42
1,46
1,9
2,5
0,46
19
Q

What is the importance of FA/FI on the speed of induction?

A

The faster the Fa rises relative to Fi, the faster the speed of induction since Fa is proportional to Pa (Fa=Pa/Pbarometric) and Pa=Pblood=Pcns.

20
Q

How is the concentration rising in the circuit?

A

According to first order kinetics.

21
Q

What is the time constant?

A

Time constant is simply the volume or “capacity” of the circuit (Vc) divided by the fresh gas flow.

22
Q

What is the most important factor in the rate of rise of Fa/Fi?

A

Uptake of anesthetic from the alveoli into the bloodstream.

23
Q

What is overpressurization?

A

It is analogous to intravenous bolus: administration of a higher partial pressure of anesthetic that the alveolar concentration actually desired for the patient.

24
Q

What is a second gas effect?

A

Along with the concentration of potent agent in the alveoli via its uptake there is further concentration via the uptake of N20, a process called the second gas effect.

24
Q

How does ventilation affect the rise in Fa/Fi?

A

For more soluble anesthetics, augmentation of anesthetic delivery by increasing ventilation also increases the rate of rise in Fa/Fi. With very low tissue solubility there is very little room to improvement with increased ventilation.

24
Q

How does perfusion affect the rate in rise of Fa/Fi?

A

For less soluable agents changes in co do not affect the rate of rise in fa/fi to a great extent bur for more soluable agents the effect is noticable: the smaller the CO the faster the rise in fa/fi

25
Q

What is sevoflurane metabolized to?

A

An acyl halide (hexafluoroisopropanol)

26
Q

What is compound A?

A

Sevoflurane breakdown product in the presence of carbon dioxide absorber. It has been shown to be a dose-dependent nephrotoxin in rats but has not been associated with renal injury in human volunteers or patients with or without renal impairment even when FGF are less that 1l/min or less

28
Q

What is MAC?

A

Minimum alveolar concentration of an inhaled anesthetic at one atmosphere that prevents movement in response to a surgical stimulus in 50 % of patients.

29
Q

Factors that increase the MAC?

A

Increased central neurotransmitter levels ( MAO unhibitors, cocaine, levodopa, ephedrine)
Hypertermia
Chronic ethanol use
Hypernatremia

31
Q

What are the concentrations of inhaled anesthetics that provide loss of awareness?

A

0,4-0,5 MAC

32
Q

What is MAC-awake?

A

Alveolar concentration of anesthetic at which a patient opens his or her eyes to command, and it varies from 0,15 to 0,5 MAC

33
Q

What is MAC-BAR?

A

It is the alveolar concentration of anesthetic that blunts adrenergic responses to noxious stimuli. It has been approximated at 50% higher than standard MAC.

34
Q

Factors that decrease MAC?

A 
Increasin age
Metabolic acidosis
Hypoxia 
Induced hypotension ( MAP <50)
Decreased central neirotransmitter levels (alpha-methyldopa, reserpine, levodopa)
Alpha2-agonists
Hypothermia
Hyponatremia
Lithium
Hypo-osmolality
Pregnancy
Acute ethanol administration
Ketamine
Pancuronium
Opipids
Barbiturates
Diazepam
35
Q

How does age affect MAC?

A

Excluding patients <1 year of age (where MAC can be lower), there is a linear model that describes a change in MAC of approximately 6% per decade, a 22% decrease from age 40 to 80, and a 27% decrease in MAC from age 1to 40 years.

36
Q

What is the effect of inhalational anesthetics to blood pressure?

A

They decrease BP in a dose-related fashion with essentially no diffrences noted between the anesthetics at eqianesthetic concentrations.
Their primary mechanism to decrease BP is via a potent effect to relax vascular smooth muscle leading to decreases in regional and systemic vascular resistance. THEY HAVE ONLY MJNIMAL EFFECTS ON CARDIAC OUTPUT.

37
Q

How do the inhalational agents affect HR?

A

Sevoflurane up to AC fos not

Desflurane, isoflurane , endlurane result in 5-10% increase in HR. Underlying mechanism is likely pungency.

38
Q

Mechanism of action of inhalational agents?

A

The exact mechanism of action of volatile anaesthetic agents is at present unknown. Potency is, in general, related to lipid solubility (Meyer-Overton relationship, Table 1.3) and this has given rise to the concept of volatile agents dissolving in the lipid cell membrane in a non-specific manner, disrupting membrane function and thereby influencing the function of proteins, e.g. ion channels. However, it is now appreciated that volatile agents affect neuronal function as a consequence of binding to specific protein sites (e.g. GABAA receptor

39
Q

MAC of isoflurane in oxygen?

A

1,15

40
Q

The MAC of sevoflurane?

A

between 1.7 and 2% in oxygen

41
Q

Metabolism of sevoflurane?

A

Approximately 5% of the absorbed dose is metabolized in the liver to two main metabolites. The major breakdown product is hexafluoroisopropanol, an organic fluoride molecule which is excreted in the urine as a glucuronide conjugate. The metabolism of sevoflurane is catalysed by the 2E1 isoform of cytochrome P450 which may be induced by phenobarbital, isoniazid and ethanol and inhibited by disulfiram.

42
Q

The MAC of halothane?

A

The MAC of halothane in oxygen is approximately 1.1% in the neonate, 0.95% in the infant, 0.9% at 1–2 years, 0.75% at 40 years (0.29 in 70% nitrous oxide) and 0.65% at 80 years.

43
Q

MAC in oxygen of desflurane?

A

6%

44
Q

Metabolism of nitrous oxide?

A

Does not get metabolized, is excreted unchanged.

45
Q

What is the concentration effect?

A

The inspired concentration of nitrous oxide affects its rate of equilibration; the higher the inspired concentration, the faster is the rate of equilibration between alveolar and inspired concentrations. Nitrous oxide is more soluble in blood than is nitrogen. Thus, the volume of nitrous oxide entering pulmonary capillary blood from the alveolus is greater than the volume of nitrogen moving in the opposite direction. As a result, the total volume of gas in the alveolus diminishes and the fractional concentrations of the remaining gases increase. This has two consequences:

the higher the inspired concentration of nitrous oxide, the greater is the concentrating effect on the nitrous oxide remaining in the alveolus.

Pharmacology (5 decks)

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