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Lindsays Flashcardlet > RE2: Chapter 7: Pharmacokinetics of Inhalation Anesthetics > Flashcards

RE2: Chapter 7: Pharmacokinetics of Inhalation Anesthetics Flashcards

0
Q

What is the Blood/Gas Partition Coefficient at 37C for Sevo, Iso, Nitrous Oxide, and Des?

A

Sevo: 0.6
Iso: 1.4 (slowest)
Nitrous: 0.47
Des: 0.42 (fastest)

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1
Q

What is the MAC for Sevo, Iso, Nitrous Oxide and Desflurane?

A

Sevo: 2
Iso: 1.15
Nitrous Oxide: 105
Des: 5.8

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2
Q

What is the Oil/Gas Partition Coefficient at 37C for Sevo, Iso, Nitrous and Des?

A

Sevo: 50
Iso: 99
Nitrous: 1.4
Des: 18.7

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3
Q

What are factors that influence absorption of inhalation agents?

A
  1. Ventilation (directly related)
  2. Uptake into the blood
  3. CO (inversely related)
  4. Solubility in the blood
  5. Alveolar-to-venous blood partial pressure difference
  6. Conc. and second gas effect also play a role
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4
Q

Partial pressure of anesthetics in the lungs is the same as the partial pressure in the ________.

A

brain

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5
Q

What are two machine related factors that affect uptake early in anesthetic administration?

A
  1. drug solubility in the rubber and plastic machine parts

2. total machine liter flow of gases chosen

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6
Q

Due to residual trace amts of gases in the machine parts, what are the appropriate steps avoid exposure of residual gases to a patient with MH?

A
  1. Flush machine with 100% O2 at 10L/min for at least 20min
  2. Replace breathing circuit and canister
  3. Drain or inactivate vaporizers or removal of vaporizers
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7
Q

Oil/gas solubility coefficient is an indicator of ________.

A

Anesthetic potency

Higher coefficient = more potent agent

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8
Q

Define Blood/Gas Solubility.

A

How much the inhalational agent is in the liquid (blood) phase compared to the gas phase.

Ex. Iso has a b/g solubility of 1.4 or 1.4:1. Therefore 1.4 molecules stays in the blood for every 1 molecule that enters the tissues/brain and produces anesthesia.

Ex. Des has a b/g solubility of 0.42 or 0.42:1. Therefore only 0.42 molecules stay in the blood for every 1 molecule in the tissue/brain.

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9
Q

Blood gas solubility coefficient indicates the speed of ______ and __________.

A

uptake and elimination

Higher coefficient = slower anesthetic
Lower coefficient = faster anesthetic

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10
Q

The more soluble (higher coefficient) the agent, the slower/faster the brain and spinal cord uptake and slower/faster induction.

A

slower
slower

*Soluble drugs stay in the blood in greater proportion than less soluble drugs and less of the drug is released in the early/rapid uptake phase of induction

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11
Q

The lower the blood/gas solubility the faster or slower the rise in lung concentration.

A

faster

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12
Q

Is the rate of rise (FA/FI) of low solubility agents (nitrous and des) greater or less than moderately soluble agents (iso)?

A

Greater

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13
Q

Why does Nitrous have a higher FA/FI compared to des?

A

This is due to the concentration effect. Nitrous is usually given at much higher concentrations (50-70%) than des (3-9%)

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14
Q

What is the ventilation effect?

A

The faster and more deeply a patient is ventilated, the faster the patient losses consciousness and emerges at the end.

OR

The greater alveolar concentration - faster patient achieves anesthesia

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15
Q

How can you compensate for V/Q deficits or poor lung fxn during inhalational agent administration?

A

Increase the concentration of the insoluble (fast) agents or increase ventilation with the soluble (slow) agents.

16
Q

Define overpressuring or the concentration effect.

A

During the first minutes of gas administration, a higher conc. of the drug than necessary for maintenance, or a loading dose, is delivered to speed initial uptake.

More effective for more soluble (slower) agents
Less effect on the insoluble (faster) agents

17
Q

What is the induction dose and maintenance dose for Nitrous, Iso, Des and Sevo

A

Induction % Maint %
Nitrous 50-70 50-70
Iso 1-4 0.5-2
Des 3-9 2-6
Sevo 4-8 1-4

18
Q

What is the second gas effect?

A

Simultaneous administration of a slow agent (iso) with a fast agent (nitrous) in high concentrations can speed onset of the slower agent

19
Q

Oil/gas solubility coefficient is an indicator of ________.

A

potency

20
Q

The higher the solubility, the more or less potent the drug due to higher lipid solubility.

A

more

**Remember Mac is inversely related to potency and potency is directed related to lipid solubility

21
Q

The cardiovascular system exerts what two major influences on uptake and distribution?

A
  1. Majority of blood leaving the lungs is normally distributed to the vital organs (aka. vessel rich group). The longer the agent is given, the greater the saturation of all the body compartments
  2. During induction, increases in CO slow onset. Increased CO removes more anesthetic from the lungs, which slows the rise in lung and brain concentration.;
22
Q

What agents are the least metabolized and do not result in toxicity from metabolism?

What agent is metabolized, but no clinically significant toxicity has been noted?

A

Nitrous, Des and Iso

Sevo

23
Q

What are the average metabolisms of the anesthetic agents?

A

Sevo: 3-6%
Nitrous: <1%
Iso: <1%
Des: <0.1%

24
Q

During emergence, the difference b/t anesthetic agents are small, but significant and the most exaggerated during the final _____% of elimination.

A

10%

25
Q

Define Diffusion Hypoxia.

A

Occurs when high concentrations of N20 are administered. When high conc. of a fast (insoluble) anesthetic like nitrous are given and the drug exits quickly through the lungs it is replaced by less soluble nitrogen in air and may transiently dilute respiratory gases such as oxygen and carbon dioxide. Hypocarbia and hypoxia may occur.

Administrating 100% O2 for several minutes when anesthesia is terminated entirely avoids this problem

26
Q

Air containing spaces are normally rich in nitrogen, which is ____times less soluble than nitrous oxide.

A

34

27
Q

What are examples of spaces that will expand by increases in volume with the administration of Nitrous?

A

air embolism, pneumothorax, acute intestinal obstruction, intraocular air bubbles from sulfur hexafluoride gas injection and pneumoperitoneum

28
Q

What are some examples of rigid spaces that will undergo an increase in pressure with administration of Nitrous?

A

Tympanic membrane grafting after ear procedures and intracranial air during neuro procedures

29
Q

Why is the uptake of anesthetic agents faster in children compared to adults?

A

Due to the higher alveolar ventilation per weight

30
Q

Pediatrics have a higher CO which slows the onset of anesthesia. Why is this minimal?

A

The increased CO to the vessel rich group and peds have a lower muscle mass that allows more agent to accumulate in the vital organs and promotes uptake to the brain

Lindsays Flashcardlet (27 decks)

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