LowFlowO2, The Circle-Absorber System

8/3/2019 LowFlowO2, The Circle-Absorber System

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Low Fresh Gas Flow

Oxygen and Agent Considerations

James H. Philip, M.E.(E.), M.D.

Copyright 1985 - 2004, James H Philip. All rights reserv


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Low Fresh Gas Flow



Anesthesiologist andDirector of Technology Assessment

Brigham and Women's HospitalAssociate Professor of Anaesthesia

Harvard Medical SchoolBoston MA


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Low Fresh Gas Flow






Everything profitable I ever invented is owned by Brigham and Womans Hospital(Edwards Vigilance CCO, Baxter-Bard InfusOR Pump, Cardinal-IVAC-Alaris Signature PuPerkin-Elmer Life Watch CO2 Monitor)


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Low Fresh Gas Flow






I have a financial interest in Gas Man

and Med Man Simulations, Inc.I have performed funded research on Desflurane and SevofluraneI am a frequent speaker for Baxter and Abbott


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Safety Impact of Low Fresh Gas Flow

You will learn that low fresh gas flow can predispose to certainhazards and that these can be averted through knowledge andskills in clinical practice.

After attending this program, you will understand that:

1 Flows are low in some hospitals

2 Toxic substances dont build up in low flow or closed circuits3 Hypoxia can happen but we must not let it

4 Circuit gas composition approaches the composition of the

net flow of gases into the circuit5 The net flow of gases into the circuit includes patient uptake

of oxygen and anesthetic


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Flows are low at at BWH

PERIOD FGF (LPM) SD

Before education 2.4 1.1Immediate after 1.8* 1.0

Later (6 months) 1.9* 1.1

Fractional Reduction 21%

Body SC, Fanikos J, DePeiro D, Philip JH, Segal SB.

Individualized feedback of volatile agent use reduces fresh gas flow ratebut fails to favorably affect agent choice. Anesthesiology 90(4): 1171-7, 1999


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Recent meeting have taught meWe are spending > $400,000 per year on vapors

BWH would like us to reduce costsRobert Goldszer, Asst. CMO is shepherd

We must do one or more of the following:

Lower Fresh Gas Flow

Switch from Desflurane and SevofluraneSwitch to Isoflurane

Switch to other inexpensive drugs


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Flow Technique Nomenclature (EU)

High Flow > 1000 mL / minLow Flow 1000 mL / min

Minimal Flow 500 mL / min

Metabolic (closed) 250 mL/min by the book

Metabolic (closed) 140 - 180 mL/min typical

Uptake (titration) 140 - 180 mL/min typical


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Why Low Flow ?Low waste

Low expenseSafe

Effective

Planet-friendlyWarm patient

Moist CO2 absorbent


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Cost of three inhalants

as a function of FGF

$0

$10

$20

$30

0 1 2 3 4 5 6

HourlyCost US

FGF

L/min

Isoflurane

Desflurane

( Using Gas Man )

Sevoflurane

Low Flow

Closed

Circuit


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Low FGFMore rebreathing

Inspired more dependent on ExpiredInspired less dependent on Fresh Gas

OxygenAgent

Nitrous Oxide

View the Breathing Circuit

The Circle-Absorber System

Long story


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Sampled

Exhaust

Expired

CO2

Ab-sorb-ant

200 mL/min

InspiredFresh

Gas Flows

Rebreathed


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Sampled

Exhaust

Expired

CO2

Ab-sorb-ant

200 mL/min

InspiredFresh

Gas Flows

Rebreathed


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Sampled

Exhaust

Expired

CO2

Ab-sorb-ant

200 mL/min

InspiredFresh

Gas Flows

Rebreathed


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Sampled

Exhaust

Expired

CO2

Ab-sorb-ant

200 mL/min

InspiredFresh

Gas Flows

Rebreathed


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Sampled

Exhaust

Expired

CO2

Ab-sorb-ant

200 mL/min

InspiredFresh

Gas Flows

Rebreathed


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Sampled

Exhaust

Expired

CO2

Ab-sorb-ant

200 mL/min

InspiredFresh

Gas Flows

Rebreathed


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Sampled

Exhaust

Expired

CO2

Ab-sorb-ant

200 mL/min

InspiredFresh

Gas Flows

RebreathedOxygen


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Sampled

Exhaust

Expired

CO2

Ab-sorb-ant

200 mL/min

InspiredFresh

Gas Flows

RebreathedAgent


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Sampled

Exhaust

Expired

CO2

Ab-sorb-ant

200 mL/min

InspiredFresh

Gas Flows

RebreathedCO2

No


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Sampled

Exhaust

Expired

CO2

Ab-sorb-ant

200 mL/min

InspiredFresh

Gas Flows

Rebreathed

OxygenAgent


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Sampled

Exhaust

Expired

CO2

Ab-sorb-ant

200 mL/min

Inspired

Fresh

Gas Flows

RebreathedOxygen

Agent


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Sampled

Exhaust

Expired

CO2

Ab-sorb-ant

200 mL/min

Inspired

Fresh

Gas Flows


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Low Flow Oxygen Considerations


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Hypoxia can happen

But we must

avoid it.Always.

No matter what!

Q ti


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QuestionStandard anesthesia machine

Everything works(CO2 absorbent,..)

FGF = 1 L/min Air

No other flowsPatient is awake and breathing

Will the patient live or die ?

Assume Oxygen consumption = 0.21 L/minAnswer

Past {Live : Die answers = 98:1}


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Subject is me

Two Residents two pulse oximeters


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Two Residents, two pulse oximeters

B f l k d dl l


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Beware of leak around needle valvesSometimes nitrous oxide sneaks into circuit

I cancelled first attempt (I felt funny)Second attempt, I disconnected nitrous oxide


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Begin with 80% oxygen in circuit

10 min


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Quick recovery(my steady handheld the camera)

10 min


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Compute expected gas concentrations

Conservation of mass applies but is not necessary to computeequilibrium conditions.

No matter what the starting concentrations of gases in the circuitthe circuit concentration will head toward and eventually reach

the concentration of the

net flow of gases into the breathing circuit.The concentration of gases in the circuit will change toward the n

inflow concentration.

Key word is netNet = what goes in (FGF) minus what goes out (uptake)

N t Fl


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Net Flows

1) FGF is comprised of individual flows ofoxygennitrous oxide

airvapor

2) Patient removal is comprised ofoxygen consumptionnitrous oxide uptake

nitrogen uptakevapor uptake


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Net flows in Clinical Practice

FGF Oxygen - patient uptake (200 mL/min) = O2 in

FGF Nitrogen - patient uptake (0 mL/min) = N2 in

FGF Nitrous oxide - uptake (100 mL/min) = N2O in


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Low Flow Air (1 L/min)

Name Flow N2 O2

FGF Air 1.0 0.8 0.2Pt - 0.2 - 0.0 - 0.2

---------------------------------------------------

Net 0.8 0.8 0.0FIO2 = 0.0 / 0.8 = 0.0

Result = Deathafter falling FIO2, then falling SpO2

and lots of alarms sounding


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Add 200 mL O2 to Low Flow Air

Name Flow N2 O2

FGF Air 1.0 0.8 0.2FGF O2 0.2 0.0 0.2

Pt - 0.2 - 0.0 - 0.2---------------------------------------------------

Net 1.0 0.8 0.2

FIO2 = 0.2 / 1.0 = 0.2 = airResult = Life

with stable FIO2, and adequate SpO2N2O


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High Flow Nitrous Oxide

Name Flow N2O O2FGF 8.0 6.0 2.0

Pt - 0.3 - 0.1 - 0.2--------------------------------------------------------

Net 7.7 5.9 1.8FIO2 = 1.8 / 7.7 = 0.233 = 23% 25%

Result = Life, as expected

Error usually not noticed or ignored


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Common Flow Nitrous Oxide

Name Flow N2O O2FGF 1.0 0.5 0.5

Pt - 0.3 - 0.1 - 0.2--------------------------------------------------------

Net 0.7 0.4 0.3FIO2 = 0.3 / 0.7 = 0.43 = 43% 50%

Result = Life

Concern with FIO2 monitor


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Low Flow Nitrous Oxide

Name Flow N2O O2

FGF 0.8 0.6 0.2Pt - 0.3 - 0.1 - 0.2

--------------------------------------------------------

Net 0.5 0.5 0.0FIO2 = 0.0 / 0.5 = 0.0

Result = Deathafter falling FIO2, rising FIN2O, then finally,

falling SpO2

Correct for Uptake


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Correct for Uptakewith Low Flow Nitrous Oxide

Name Flow N2O O2

FGF 0.6 0.3 0.3Pt - 0.3 - 0.1 - 0.2

-------------------------------------------------------

Net 0.3 0.2 0.1FIO2 = 0.1 / 0.3 = 0.33

Result = Lifewith stable FIO2, stable FIN2O,

and adequate SpO2all this with still lower FGF = 0.6 L/min

Correct for Uptake


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Correct for Uptakewith Low Flow Nitrous Oxide

Name Flow N2O O2

FGF 0.6 0.3 0.3Pt - 0.3 - 0.1 - 0.2

-------------------------------------------------------

Net 0.3 0.2 0.1FIO2 = 0.1 / 0.3 = 0.33

50 /50 = N2O / O2 Flow rates67 / 33 = N2O / O2 Concentrations

Common observation


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Closed Circuit - Dont add excess gas

Name Flow N2O N2 O2

FGF 0.2 0.0 0.0 0.2Pt - 0.2 - 0.0 - 0.0 - 0.2

---------------------------------------------------------------------

Net 0.0 0.0 0.0 0.0FIO2 = 0.0 / 0.0 = 0 / 0 = indeterminate

Result = No change in circuit conc.Stable FIO2, stable FIN2O, stable FIN2,

and stable SpO2all this with closed circuit FGF = 0.2 L/min

Consider rebreathed agent


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Consider rebreathed agent

Sampled

Exhaust

Expired

CO2

Ab-sorb-ant

200 mL/min

Inspired

Freshgaswithvaporizer

Agentconc.

Rebreathed

gaswith

expired

Agent

conc.


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Expired Agent Concentration is important


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Expired gas rebreathing

Dilutes Inspired Concentration

toward Expired ConcentrationSo, The lower the expired concentration

the greater the dilution it causes,the higher my vaporizer must be set,

and the harder it is to use low FGF.Low solubility has the advantageof high Expired Concentration

We see this by viewing the Alveolar Curve

Alveolar Curve - note Height and


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300

Minutes of administration

300


Inf

1

Des

Sev

Iso

Hal

Zero

0.42

0.67

1.3

2.4

0.00

Name

Alveolar Curve

AlveolarTensionFractionConcentration

divided by

Inspired[same]

A/I



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300


300


Inf

1

Des

Sev

Iso

Hal

Zero

0.42

0.67

1.3

2.4

0.00

Name =Blood/GasSo

lubility

Alveolar Curve


divided by

Inspired[same]



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300


300


Inf

1

Des

Sev

Iso

Hal

Zero

0.42

0.67

1.3

2.4

0.00

Name

F

V

I OA 1

1 +C

A

= F(t)

.

Alveolar Curve


divided by

Inspired[same]



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300


300


Inf

1

Des

Sev

Iso

Hal

Zero

0.42

0.67

1.3

2.4

0.00

Name

F

V

I OA 1

1 +C

A

= F(t)

.

Alveolar Curve


divided by

Inspired[same]

Alveolar Deficiency - Initial


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0 Minutes of administration

1

0

Zero

Alveolar Deficiency - Initial

Des

Sev

Iso

Hal

Inf

46%

34%

62%

76%

100%

A/I

AlveolarDeficiency

30

Des

Sev

Iso

Hal

Alveolar Deficiency - Late


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Des

Sev

Iso

Hal

300 Minutes of administration 300

1.0ZeroA/I

Alveolar Deficiency Late

0.88

0.71

0.56

0.83

A/IAlveolaDeficien

12%

17%

29%

44%


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Low solubility facilitates low FGF

Allows low FGF.

Expired gas concentration is high,

Expired admixture is not a problem,

Inspired follows the vaporizer, and

Expired follows inspired.


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Low Flow Practice

Desflurane Example:Make inspired tension rise slowly

by using low fresh gas flowSave money

More convenient than adjustingvaporizer several times

Package Insert typical anesthetic - Desfluran


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Package Insert typical anesthetic - Desfluran

Adjust Vaporizer - increase slowly

Use high FGF for tight control

FGF = 5 L/min air or oxygen

Vaporizer set to 3, 4, 5, 6, 7, 8, 9 %

Inspired rises over 5 - 7 minutes

Expired rises over 5 - 7 minutes

Clinical Low Flow Technique - Desflurane


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Simple

Very Inexpensive


Vaporizer set to 18%

Inspired rises over 5 - 7 minutes

Expired rises over 5 - 7 minutes



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Simple

Very Inexpensive


Vaporizer set to 18%

Decrease vaporizer &/or FGF when

Inspired = 7% or so, and

Expired = 6%

Patient is deep enough!

Then,

Gas Man Examples


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Gas Man Examples

FGF Comparison

High FGF5 L/min O2Progressively increase vaporizer setting

Low FGF1 L O2/minAir + O2Set vaporizer to 18%Watch, wait,Readjust when circumstances merit

$7.80 for $0.75 in body

$2.90 for $0.75 in body


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Clinical Example


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1 L / min Air+ Oxygen

for induction


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I

E


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Desflurane

5 min

I

E


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Datex-Ohmeda AS/3/5 much better

Datex AS 3 Monitor


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Datex AS 3 Monitor

Zoom In


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Zoom In

Inspired and Expired rise smoothly.


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This Controls the rate of Desflurane rise

CO2

Desflurane

This avoids the sympathetic activity


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that might otherwise be seen

CO2

Desflurane


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GEMS IT(Marquette)

SAM Module

Fabius GS

Anes Machwith at 1 LPM

Replacing circuit gas loss with oxygen


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SAM with rising Oxygen


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Clinical Techniques

Yes

Clinical Technique with Desflurane


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C ca ec que t es u a e

Avoid Tachycardia and Hypertensionincrease inspired and expired slowly5 minutes (1 L/min does this!)

Avoid coughing on induction -

IV induction and secure airway with ET tube or LMA

Avoid coughing on emergence -

Wake up fast

High FGFNormal Ventilation

Extubate as early as practical

No re-anesthetization

Desflurane works well with LMA


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Desflurane works well with LMA

Similar profiles for maintenance

Similar profiles for emergence exceptDesflurane a bit faster for emergence

Similar profiles for recovery exceptDesflurane a bit faster for measures of early recoveryDesflurane much better for return to activities

Full activity next day Des 28/31 vs Sevo 15/29

Mahmoud NA, Rose DJK, Laurence AS. Desflurane or sevoflurane for gynaecological

day-case anaesthesia with spontaneous respiration? Anaesthesia 56:171-182, 2001.

Wshima RW, Maurer A, King T, Lin BK, Heavner, Bogetz MS, Kaye AD. A comparisoof airway responses during desflurane and sevoflurane administration via a laryngeal

mask airway for maintenance of anesthesia. Anesth Analg 96:701-5, 2003.


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Other Points


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Other Points

With very low FGF,it it good to returnsampled gas

to the breathing circuit

Pictures


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SampledGas

With high FGF

is usuallyevacuated.


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Evacuating sampled gas

wastes

200 mL/min


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Sample gas exhaust(Datex Monitor)


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can be returned to the breathincircuit when using low flo


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Reusable sample return deviceare bette


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Permanent

sample gasreturnis best


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Closed Circuit


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Closed Circuit

is the limitwhen FGF is reduced

to just meet the bodys needs.

Nothing is wastedbecause nothing leaves the circuit

but, flow = 200 mL/min oxygen

Anything more is

minimal flow or low flowClosed Circuit

Closed Circuit


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140 - 250 mL/min O2

for maintenance

Closed Circuit

Keep bellows away from the top


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Con

stant

Concen

tratio

ns


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Con

stant

Concen

tratio

ns


93/137

getCo

nstan

t

Vital

Signs


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Do not ress O Flush to fill Bellows

Do not press O2 Flush to fill Bellows


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Liquid to Vapor

Volume relationshipWhat happens when

I inject 1 mL liquid agent?


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Vapor / LiquidVolume Ratio

HalIso

195

EnfSev Des

207 226196182

200

mL VapormL Liquid

Agent

Derive

Dimensional analysis for liq -> vap


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Given: Molar Volume = 22.4 L at STP



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V = 1 mL Liq



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V =

22.4 L Vap

mole1 mL Liq



101/137


V =

22.4 L Vap

mole gGMW

mole

1 mL Liq



102/137


V =

22.4 L Vap

mole gGMW

mole

mL Liq

d g

1 mL Liq



103/137


V =

22.4 L Vap

mole gGMW

mole

mL Liq

d g 1000

L

mL

1 mL Liq



104/137


V =

22.4 L Vap

mole gGMW

mole

mL Liq

d g 1000

L

mL

1 mL Liq



105/137


V =

22.4 L Vap

mole gGMW

mole

mL Liq

d g 1000

L

mL

1 mL Liq



106/137


V =

22.4 L Vap

mole gGMW

mole

mL Liq

d g 1000

L

mL

1 mL Liq



107/137


V =

22.4 L Vap

mole gGMW

mole

mL Liq

d g 1000

L

mL

1 mL Liq



108/137


V =

22.4 L Vap

mole gGMW

mole

mL Liq

d g 1000

L

mL

1 mL Liq



109/137


V =

22.4 L Vap

mole gGMW

mole

mL Liq

d g 1000

L

mL

1 mL Liq



110/137


V =

22.4 L Vap

mole gGMW

mole

mL Liq

d g 1000

L

V =

22.4

GMW

d 1000

mL

1 mL Liq

mL Va

1.0



111/137


V =

22.4 L Vap

mole gGMW

mole

mL Liq

d g 1000

L

V =

22.4

GMW

d 1000

mL

1 mL Liq

mL Va

1.0

V = 22.4 GMWd

10001.0



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V =

22.4 L Vap

mole gGMW

mole

mL Liq

d g 1000

L

V =

22.4

GMW

d 1000

mL

1 mL Liq

mL Va

1.0

V = 22.4 GMWd

10001.0 = 22,400 GMWd

Temperature correction for liq -> vap


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V =

22.4 L Vap

mole gGMW

mole

mL Liq

d g 1000

L

V =

22.4

GMW

d 1000

mL

1 mL Liq

mL Va

1.0

V

22.4 GMW

d

10001.0 = 22,400 GMWd

T = V0C273.15

273.15 + Tx

V =

Temperature correction for liq -> vap


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V =

22.4 L Vap

mole gGMW

mole

mL Liq

d g 1000

L

V =

22.4

GMW

d 1000

mL

1 mL Liq

mL Va

1.0

V

22.4 GMW

d

10001.0 = 22,400 GMWd

T = V0C273.15

273.15 + Tx V 20C = V0C x 1.073

V =

Dimensional analysis for liq -> vapd


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22,400 GMW

d

V =0C

Dimensional analysis for liq -> vap yields:d


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GMW d 0 C

Sevoflurane 200.1 1.52 170

Desflurane 168.0 1.46 195

Isoflurane 184.4 1.50 182

Halothane 197.4 1.87 212

Enflurane 184.4 1.52 184

22,400 GMW

d

V =0C

Dimensional analysis for liq -> vap yields:d


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GMW d 0 C 20 C

Sevoflurane 200.1 1.52 170 182

Desflurane 168.0 1.46 195 208

Isoflurane 184.4 1.50 182 195

Halothane 197.4 1.87 212 227

Enflurane 184.4 1.52 184 198

22,400 GMW

d

V =0C


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Real InjectionsReal Circuits

Why inject in the inspired limb?

Otherwise too slow for clinical care

1.0 mL injections of liquid Isoflurane


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in a Closed Circuit

0 20 30Time

I

E E

(minutes)

Liquid Injections: I = Inspired limb, E = Expired Limb

0

1

2

3%

IS

O

I

10


120/137

I mL Desflurane injectedinspired limb


121/137

Flush, Inject


122/137

Syringe must always point up


123/137

10

So onlyvapor is lost

Syringe must always point up


124/137

10

10


Otherwise,liquid is lost,

208 times as fast

Syringe must always point upS l


125/137

10

10


Otherwise,liquid is lost,

208 times as fastVaporizatio

Desflurane does not disappear


126/137

Evaporates slowly

Absorbing Heat of Vaporization as it goes

Fast from the floor

Slow from the table top

Fast in the breathing circuit

Baxter packs bottle in a plastic cover anyway

just in case the bottle breaks

We will test this today at 5,700 feet where

Vapor pressure = Atmospheric pressure


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How much anesthetic?

Initial Vapor Uptake


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Vapor Uptake Initial =Alv Conc x Blood/Gas Solubility x CO =

F x MAC x Blood/Gas Solubility x CO =

Numbers

Desflurane Vapor Uptake Initial =

0.06 x 0.42 x 5000 mL/min =

1 x 0.06 x 0.42 x 5000 mL/min =

126 mL vapor / minute =

36 mL liquid / hour (for 5 minutes only)

Other Agents, other Solubilities


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g ,

Uptake = Pump Setting ( mL/hr )

Early Middle Late Never

Agent >ALV >VRG >MUS >FAT

Des 36 9 2 0

Sev 22 5 1 0

Iso 22 5 1 0

Enf 49 12 3 0

Hal 26 6 2 0

Time 5 min 120 min 12 hours

Agent Cost for closed circuit infusion


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g

$ / hour

Agent >ALV >VRG >MUS >FATDes $11 $3 $1 $0

Sev $16 $4 $1 $0Iso $10 $2 $1 $0

Enf $25 $6 $2 $0Hal $2 $0 $0 $0

Desflurane: $0.29 per mL Isoflurane: $0.30 per mL

Agent Cost for closed circuit infusion


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g

$ / hour

Agent >ALV >VRG >MUS >FATDes $10.55 $2.53 $0.63 $0.00

Sev $16.11 $3.87 $0.97 $0.00Iso $ 9.87 $2.37 $0.59 $0.00

Enf $24.65 $5.91 $2.37 $0.00Hal $1.77 $0.42 $0.11 $0.00

Desflurane: $0.29 per mL Isoflurane: $0.30 per mL


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Uptake Summary

Uptake = alveolar concentration x solubility x CO

Later, uptake is carried away at 1/4 the initial rate.

Liquid agent can be used instead of vapor

Inject liquid in inspiratory circuit limbA pump can be used for liquid circuit injection

For { >Alv, > VRG, >MUS, >FAT }, Des = 36, 9, 2;Isof = 22, 5, 1; Sevo = 22, 5, 1; Hal = 26, 6, 2 mL/hr

How do you know if FGF is sufficient ?


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Check your gas monitorfor Oxygen

for Agent Concentration

Record Vaporizer, Inspired, ExpiredRead and think about what you write

Avoid changes in inspired and expiredwhen you want depth constant

Cost reduction is up to you


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$0

$10

$20

$30

0 1 2 3 4 5 6

HourlyCost US

FGF

L/min

Isoflurane

Desflurane

Sevoflurane

Low Flow

Closed

Circuit

Cost reduction is up to you


135/137

$0

$10

$20

$30

0 1 2 3 4 5 6

HourlyCost US

FGF

L/min

Isoflurane

Desflurane

Sevoflurane

Low Flow

Closed

Circuit

Think carefully about oxygenAlways replace uptake


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Thank you


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Documents

LowFlowO2, The Circle-Absorber System