1. UPTAKE & DISTRIBUTION OF INHALATIONAL AGENTSGK
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2. INHALATIONAL AGENTS PATHWAY
AIRWAY
ALVEOLI
BLOOD STREAM
TISSUES
METABOLISM
ELIMINATION
UPTAKE
&
DISTRIBUTION
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3. U & D – Some basics
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4. SOME BASICS………
Gases/vapors move from one phase to another along a partial pressure gradient
Not along the concentration gradient
Not along the volume gradient
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5. SOME BASICS………
Vapor moves from alveoli pul.capillaries systemic circulation tissues along the partial pr gradient only i.e.
---more pr. phase to low pr. phase till the equilibrium reached
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6. PARTITION -COEFFICIENT
A ratio of volume of an anesthetic agent between two phases at equilibrium.
Eg. Blood gas P-C of halothane 2.4
……. Blood can hold 2.4 times of halo than alveoli at equilibrium
…….Pr gradient will be maintained between alveoli & blood till 2.4 times of volume of halo move from alveoli to blood
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7. PARTITION -COEFFICIENT
PC indicates….
Solubility of the agent in a medium / phase.
Relative affinity of the agent to a phase
Relative capacity of a phase to an agent. Eg. Blood gas P-C of halothane 2.4
……. Blood can hold 2.4 times of halo than alveoli at equilibrium
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8. U & D – Bird’s eye view
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9. INHALATIONAL AGENTS PATHWAY
AIRWAY
ALVEOLI
BLOOD STREAM
TISSUES
METABOLISM
ELIMINATION
RPG
75%C.O. MG
20%C.O. FG
5%C.O.
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10. equilibrium with in 10 min RPG BF- 75% c.o. MG 1-4hrs FG longer
AIRWAY vent LUNG
BF- 20% c.o. FG
longer
BF- 5% c.o.
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11. U & D Curve FA/FI 8 C AB-lung wash in B BC-RPG uptake phase
C∞- MG,FG uptake phase A
Time
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12. Brain anesthetic pr. Closely follows the alveolar pr.
Alveolar pr is an index of brain tissue pr.
Alveolar pr acts as a pressure head for maintenance of anesthetic tension at various sites.
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13. U & D – Closer view
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14. Factors concern with input Inspired anes.pr. Alveolar ventilation
Factors concern with uptake from alveoli
Uptake =λ Q (Pa-Pv)
λ-solubility
Q-cardiac output
(Pa-Pv)-partial pr.gradient
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15. Solubility-a prime factor
Expressed as partition coefficient
Depending on solubility,
Highly soluble-methoxyflurane15 > ether12
Moderately -halo2.5 > enflu1.8 > iso1.4
Poorly sevo.69 > N2o.47 > des.42
Alveolar pr .inversely prop to solubility
Induction inversely prop to solubility
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16. Solubility & Fa/Fi FA/FI Time Poor solubility Rapid induction
Moderate solubility
Fast induction
High solubility
Slow induction
Time
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17. Cardiac output AIRWAY ALVEOLI BLOOD STREAM TISSUES
CO removal from lung
Fa/Fi—slow induction
Fa/Fi—rapid induction
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18. Cardiac output & FA/FI FA/FI Time Low CO Rapid induction High CO
Slow induction
Time
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19. AV pressure gradient AIRWAY ALVEOLI TISSUES
Blood flow
TISSUES
AV pr gradient is due to Tissue uptake
AV pr gradient depends on
1.Tissue solubility [tissue blood PC]
2.Tissue BF
3.Arterial tissue pr. Gradient V A
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20. AV pressure gradient
AV pr gradient is “O”-no tissue uptake-equilibrium achieved- in sequence-RPG-MG-FG
Once brain tension equilibrated, uptake mainly by MG&FG tissues only.
So, maintenance of lung & brain tension mainly depends on the uptake of anesthetic agent in muscle& fat.
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21. U & D Curve FA/FI 8 C AB-lung wash in B BC-RPG uptake phase
C∞- MG,FG uptake phase A
Time
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22. U & D –A little more -concentration effect -second gas effect
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23. Concentration effect
The insp. anesthetic conc.[Fi] influences not only-the alveolar anesthetic conc.[Fa] but also the rate of rise of Fa
Rapid rise of Fa by 2 factors
1.concentrating effect
2.augmentation of inspired ventilation
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24. Concentration effect Concentrating O2 O2 O2 N2O O2 N2O N2O N2O 1% FG
60%
100%
100% 1%
1.7%
1.4% O2 O2 O2
31.7%
26.6%
19%
N2O O2
N2O
N2O
67%
N2O 1%
8o%
50% of N2O taken up-40%of total gas FG O2
19%
N2O
N2O
8o%
72%
Augmentation of ventilation
Concentration effect

25. Concentration effect
Uptake of half of N2O does n’t halve the concentration because the remaining gases are ‘concentrated’ in a smaller volume.[50% to 66.7%]
The N2O uptake is filled by drawing more gases in to the lung [augmentation of inspired ventilation] the final N2O conc is 72%
So, with 80% of N2O after 1 breath the alveolar conc[Fa] of N2O will be 72%[i.e. 90% of Fi]
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26. Concentration effect So, high Fi causes- Rapid rise of Fa
High value of Fa
The concentration effect clinically appreciated only in high concentration i.e. >20%
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27. Second gas effect
The uptake of large volume of a first gas accelerates the alveolar & there by arterial rate of rise of a second gas [passively] administered concomitantly.
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28. Second gas effect
The loss of volume due to the uptake of N2O concentrates the halothane-from1% to1.7%.
Replacement of gas taken by the inspiration will augment the amount present in the lung i.e. the Fa of halo will be 1.4%
The alveolar and brain tension of halo rise more quickly to wards the inspired tension when halo is given with N2O than With O2 only.
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29. Gases move from one phase to another along a partial pressure gradient
Partition Coefficient indicates solubility, relative affinity & relative capacityof a phase to particular agent
The intake of anesthetic agent determined by inspired pressure-Fi & alveolar ventilation
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30. The uptake = solubility × cardiac output × A-V pressure gradient
During induction Fa serves as pressure head for the anesthetic tension thro’out body
Highly soluble agent takes longer time to induce.
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31. Depending on perfusion, RPG will equilibrate with in 10 mins.
MG & FG will equilibrate / try to equilibrate .
Brain tension of an anesthetic agent almost always follows it’s alveolar tension {Fa} very closely &quickly.
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32. Recovery is just a reversal of what happens during induction.
In decreased cardiac output states, alveolar & brain tension rise rapidly.
Recovery is just a reversal of what happens during induction.
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33. Thank you
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