Inhalationsläkemedel

Question 1

Komponenterna av generell anestesi

Answer 1

1. Sömn
2. Anelgesi
3. Muskelrelaxation

Question 2

De första anestesigaserna

Answer 2

Eter.
Kloroform
Lustgas

Question 3

De halogenerade anestesimedlen är?

Answer 3

Halotan
Isofluran
Desfluran
Sevofluran

Question 4

En hypotes om halogenerade inhalationsgasernas farmakodynamik

Answer 4

Aktivering av GABA A-receptorer basalt o hjärnan som i sig dämpar noradrenerga systemet som styr sömn/vakenhet-relation

Question 5

Hur beskrivs ett inhalationsmedels potens?

Answer 5

MAC (minimal alveolar concentration)

MAC är den alveolära koncentrationen av ett medel som gör att hälften av populationen inte rör sig av att man lägger ett kirurgiskt hudsnitt.

Låg MAC betyder hög potens.

Question 6

Hur mycket MAC behövs för kirurgisk anestesi?

Answer 6

1,2-1,5 × 1

Question 7

Vilken fysisk faktor påverkar insomning/uppvaknande efter inhalationsanastesi?

Answer 7

Gasens löslighet i blod.

Question 8

Vilka gaser används inte för maskinduktion? Varför?

Answer 8

Isofluran och desfluran. De retar slemhinnorna i andningsvägarna. De ges först efter en sömngivande IV-injektion.

Halotan och sevofluran kan användas i maskinduktion.

Question 9

Lustgas metaboliseras i?

Answer 9

levern.

Question 10

Misstänkt toxicitet av halotan?

Answer 10

Metabolisering till levertoxiska ämnen.

Question 11

What factors determine the inspired gas concentration (Fi)?

Answer 11

1. Fresh gas flow rate.
2. Breathing system volume.
3. Any absorption by breathing system or circuit.

The higher the fresh gas ow rate, the smaller the breath- ing system volume, and the lower the circuit absorp- tion, the closer the inspired gas concentration will be to the fresh gas concentration.

Question 12

What factors affect the alveolar concentration?

Answer 12

1. Uptake
2. Ventilation.
3. The concentration effect and the second gas effect.

Question 13

How does uptake of anesthetic gas from alveoli relate to rate of induction?

Answer 13

The greater the uptake of anesthetic gas, the greater the difference between the inspired and alveolar gas concentration, and therefore the slower the rate of induction.

The uptake of a gas from the alveoli will slow the way to reach partial pressure steady state. We are striving for a partial pressure (fractional concentration (F)) equilibrium (steady state) , not a concentration equilibrium. The faster Alveolar F (Fa) approaches inspired F (Fi) the faster induction occurs.

Question 14

What factors affect the uptake of anesthetic gases from alveoli?

Answer 14

1. Solubility in the blood.
2. Alveolar blood flow.
3. Difference in partial pressure between alveolar gas and venous blood.

Question 15

What is partition coefficient?

Answer 15

The relative solubilities of an anesthetic in air, blood, and tissues are expressed as partition coefficients (Table 8–1). Each coefficient is the ratio of the concentrations of the anesthetic gas in each of two phases at steady state. Steady state is de ned as equal partial pressures in the two phases. For instance, the blood/gas partition coefficient (λb/g) of nitrous oxide at 37°C is 0.47. In other words, at steady state, 1 mL of blood contains 0.47 as much nitrous oxide as does 1 mL of alveolar gas, even though the partial pressures are the same. Stated another way, blood has 47% of the capacity for nitrous oxide as alveolar gas.

Question 16

What is alveolar blood flow equal to?

Answer 16

Cardiac output. That is in the case of no pulmonary shunting.

Question 17

How does change in cardiac output affect the uptake och anesthetic gas?

Answer 17

Increase in CO causes increased uptake of anesthetics from alveoli. This results in slowing of the rise of alveolar pressure, and induction is delayed.

Question 18

How does patients with low CO react to anesthetics and why?

Answer 18

Low-output states predispose patients to overdosage with soluble agents, as the rate of rise in alveolar concentrations will be markedly increased.

Question 19

What does the gradient of difference in partial pressure between alveolar gas and venous blood depend on?

Answer 19

Tissue uptake.

This in turn is affected by 3 factors similar to that of systemic uptake:

1. Tissue solubility of the agent. (tissue/blood partition coefficient)
2. Tissue blood flow.
3. Difference in partial pressure between arterial blood and tissue.

Question 20

How are the blood tissues grouped according to their perfusion?

Answer 20

1. Vessel-rich tissue (brain, heart, liver, kidney, and endocrine organs). First to reach steady state. Receives 75% of CO and 75% of perfusion (ml/min/100g).
2. Muscle and skin. 19% of CO and 3 % och perfusion. Uptake sustained for hours (until steady state is reached)
3. Fat. Only 6% of CO. 3% of perfusion. Anesthetics are 20x more soluble in fat than blood and muscle. Uptake will therefore be sustained for days.
4. Vessel-poor (bone and cartilage). Basically no uptake.

Question 21

How do gases equilibrate?

Answer 21

Gases equilibrate by partial pressure, not concentration. Thus a gas can be at different concentrations in different tissues and still at equilibrium because it has the same partial pressure. Concentration is affected by solubility.

Question 22

Describe how cardiac output can cause a positive feedback loop with induction?

Answer 22

When CO is low, alveolar blood flow decreases and therefore uptake decreases. This causes increase rate of induction which as a result lowers CO even further.

Question 23

Describe the concentrating effect?

Answer 23

A.k.a. overpressurization. Basically it states that if you administer higher concentration of a gas, it not only increases alveolar concentration, but also increases the rate of rise.