Quick Course in Inhalant Kinetics

The Alveolar Tension Curve

Written forBWH Anesthesia Sunrise Lecture Series 2008 - 2009

© Copyright 1995 - 2008, James H Philip, all rights reserved.

Dr. James Philip has performed funded research on Isoflurane, Sevoflurane, and Desfluraneand is often supported by the manufacturers of these drugs to teach about these drugs.

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Quick Course in Inhalant Kinetics

The Alveolar Tension Curve

James H. Philip ME(E) MD

Anesthesiologist and Director of BioengineeringDepartment of Anesthesia Brigham and Women’s Hospital

Associate Professor of Anaesthesia, Harvard Medical SchoolPresident, Med Man Simulations, a nonprofit organization

that distributes Gas Man®, worldwide

AlveolarTensionCurve

Focus on the

Alveolar response to an Inspired Step

Alveolar Tension Curve

The time course of alveolar tension = PA

in response to a step change ininspired tension = PI

=

PI PA

Alveolar Tension is important

Tension = Partial Pressure

Tension equalizes when Concentration equilibrates

Concentration does not drive molecular motion

Tension drives molecular motion

Inspired Tension drives Alveolar Tension

Alveolar Tension drives Arterial Tension

Arterial Tension drives Tissue Tension

Brain it the important tissue for Anesthesia

Brain Tension drives depth of anesthesia

Alveolar Tension is important

Tension = Partial Pressure

Tension equalizes when Concentration equilibrates

Concentration does not drive molecular motion

Tension drives molecular motion

Inspired Tension drives Alveolar Tension w loss + delay

Alveolar Tension drives Arterial Tension = approx

Arterial Tension drives Tissue Tension w delay

Brain it the important tissue for Anesthesia

Brain Tension drives depth of anesthesia

If we know Alveolar Tension, we know the hard part

Gas Man® Picture shows path of anesthetic tension

I BrA a V

Axes and Labels

0 1 20.0

1.0

A / I

3 minutes (time)

0 1 20.0

1.0

A / I

3 minutes (time)

Alveolar response to a stepchange in inspired agent

Inspired Step

0 1 20.0

1.0

A / I

3 minutes (time)

Inspired Step

0 1 20.0

1.0

A / I

3 minutes (time)

Pure Lung wash-inWithout Uptake into Blood

is the same as

Cardiac Output = zero ( CO = 0) or

Drug solubility in blood = zero ( = 0)

Call this Zerothane

Inspired Tension

Alveolar Tension

Alveolar response to a stepchange in inspired Zerothane

is an

exponential curve

0 1 20.0

1.0

A / I

3 minutes (time)

0.63

0.5 min =

Alveolar Tension

Inspired Tension

Time constant, tau ( )is the time required to achieve

63% of the final value*

0 1 20.0

1.0

A / I

3 minutes (time)* Derive in long course

Now, add uptake into blood

Uptake into bloodproduces

an Alveolar TensionPlateau

Inspired Tension

0 1 20.0

1.0

A / I

3 minutes (time)

Pure Lung wash-inWithout Uptake into Blood

Alveolar Tension Plateau

Plateau

0 1 20.0

1.0

A / I

3 minutes (time)

Inspired

Alveolar

Plateau is produced by Removal by Blood

Tail

Alveolar Tension Plateau

Plateau

0 1 20.0

1.0

A / I

3 minutes (time)

Inspired

Alveolar

Delivery

Removal

Tail

Alveolar Tension Plateau

Plateau

0 1 20.0

1.0

A / I

3 minutes (time)

Inspired

Alveolar

Delivery = VA

Removal = CO •

Hal Enf

Iso

SevoN O 2

Des

Zerothane

Infinithane

0 1 20.0

1.0

A / I

3 minutes (time)

Alveolar Plateaus

Alveolar Plateau Heights

.38

.54

.66

Ht 1

.24

.00

Hal Enf

Iso

SevoN O 2

Des

Zerothane

Infinithane

0 1 20.0

1.0

A / I

3 minutes (time)

Alveolar Plateau Heights and solubilities

.38

.54

.66

Ht 1

.24

.00

Hal Enf

Iso

SevoN O 2

Des

Zerothane

Infinithane

0 1 20.0

1.0

A / I

3 minutes (time)

1.3

.67

.42

0

2.4

Inf.

Alveolar Plateau Height Equation

.38

.54

.66

Ht 1

.24

.00

Hal Enf

Iso

SevoN O 2

Des

Zerothane

0 1 20.0

1.0

A / I

3 minutes (time)

1.3

.67

.42

0

2.4

Inf.V I .O A 1

1 + C Plateau Ratio = A

=

Tail

Venous Return converts Plateau

Plateau

0 1 20.0

1.0

A / I

3 minutes (time)

Inspired

Alveolar

Plateau produced by Removal by Blood

0 1 20.0

1.0

A / I

3 minutes (time)

Venous Return converts Plateau into Tail

Plateau

TailAlveolar

Inspired

Alveolar

0 1 20.0

1.0

A / I

3 minutes (time)

Alveolar Tension Curve sections named

Inspired

Initial Rise

Knee

Tail

Plateau

Real drugs and real curvesNext,

Des

Sev

Iso

Hal

300 Minutes of administration 300

PI

PA

1.0

Yasuda & Eger, 1991

Real drugs and real curves

A / I

Des

Sev

Iso

Hal

300 Minutes of administration 300

PI

PA

1.0

What is the similarity among these curves?

A / I

Des

Sev

Iso

Hal

300 Minutes of administration 300

PI

PA

1.0

Initial rise follows the same Zerothane curve

ZeroA / I

Des

Sev

Iso

Hal

300 Minutes of administration 300

1.0

What is the difference between these curves?

ZeroA / I

Des

Sev

Iso

Hal

300 Minutes of administration 300

1.0ZeroA / I

Plateau Height is the only kinetic difference !

Des

Sev

Iso

Hal

Des

Sev

Iso

Hal

300 Minutes of administration 300

1.0ZeroA / I

And, plateau height is determined by

DesSev

Iso

Hal

1.3

.67

.42

0

2.4

inf.

.38

.54

.66

1

.24

.00

Ht

Inf

Blood / Gas Solubility

Dominates Inhalation Kinetics

Determines

how closely

Expired Tension

approaches

Inspired Tension

in the first few minutes of anesthesia

The endof

The Alveolar Tension Curvein its first few minutes