Anesthesiology

Physics and Anesthesiology

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 Dynamics of Inhalational Anesthesia

 

6Blood: gas partition coefficients ( ratios)

Sevoflurane (Sevorane, Ultane)

Desflurane (Suprane)

Isoflurane (Forane)

Enflurane (Ethrane)

Halothane (Fluothane)

Nitrous oxide

0.65

0.42

1.46

1.9

2.4

0.46

 

6Brain: blood partition coefficients ( ratios)

Sevoflurane (Sevorane, Ultane)

Desflurane (Suprane)

Isoflurane (Forane)

Enflurane (Ethrane)

Halothane (Fluothane)

Nitrous oxide

1.7

1.3

1.6

1.4

1.9

1.1

 

6Fat:blood partition coefficients ( ratios)

Sevoflurane (Sevorane, Ultane)

Desflurane (Suprane)

Isoflurane (Forane)

Enflurane (Ethrane)

Halothane (Fluothane)

Nitrous oxide

47.5

27.2

44.9

36

51.1

2.3

 

Muscle:Blood partition coefficients ( ratios)

Sevoflurane (Sevorane, Ultane)

Desflurane (Suprane)

Isoflurane (Forane)

Enflurane (Ethrane)

Halothane (Fluothane)

Nitrous oxide

3.1

2.0

2.9

1.7

 3.4

1.2

Chemical Structures for the above Volatile Agents

Nitrous oxide

Halothane (Fluothane):  halogen substituted (Cl & F) ethane compound

Isoflurane (Forane): methyl ethyl ester

 

Desflurane (Suprane):  Similar to isoflurane except F substitues for a Cl

Enflurane (Ethrane): methyl ethyl ester

Sevoflurane (Sevorane, Ultane): methyl isopropyl ether

 

First-order Equations

  • First-order equations refer to a change in concentration of some molecule with time. More formally, we could write -d[A]/dt = k [A], so the rate of change in the concentration of A is set equal to a constant times the concentration of A

  • Integration of -d[A]/dt = k [A] results in an equation of the form ln[A] = -kt + C where C is a constant of integration established by setting boundary conditions such as when t = 0, [A] = [A]o where [A]o is the starting concentration of A. So when t = 0, ln [A]o = -k(0) + C or C= ln [A]o . Now we can substitute for C in ln[A] = -kt + C, obtaining ln[A] = -kt + ln [A]o . This last expression can be represented as:

    • ln ([A]/[A]o ) = -kt OR

    • [A]/[A]o = e(-kt)  OR

    • [A] = [A] e(-kt)  

  • This last expression, [A] = [A] e(-kt) ,   is of the form FI = FFGO (1-e-T/

  • One final point is that the integrated form of the relationship, ln[A] = -kt + ln [A]o is in the same form as the equation for a straight line (y = mx + b); in this case the y-value is ln[A], the slope m is -k, the x value is t and the y-intercept is ln [A]o. So, if the data were plotted, that is ln [A} vs. t, a straight line would be obtained with a slope = -k.

 

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