oxygen pulse oximetry

7/31/2019 Oxygen Pulse Oximetry

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Standing guard over the flame of life

Oxygen Monitoring in Acute Medicine

Dave SainsburyStaff Anaesthetist, Women’s & Children’s Hospital

Adelaide, South Australia



1/25/2011 Oxygen Monitoring 2

n 2nd law of thermodynamics

n Entropy is time’s arrow

Entropy Life




CnHnOn

O2

CO2




1 5 91 4 9

1 0 09 2

4 0 4 0

2

0

5 0

1 0 0

1 5 0

Tissue Vein

Mitochondria

I

n

s

p

ir

e

d

T

ra

c

h

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A

l

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Monitoring Oxygen As a Gas

ª Inspired

ª Tracheal

ª

Alveolar

â Oxygen analyser

â Calculated from FIO2

â

Calculated: Alveolar air equationEnd tidal oxygen analyser




Ideal Oxygen Analyser

n Rapid response

n Continuous

n Robust

n

Low maintenancen Do no harm




Oxygen Analysers

n Polarographic sensor

n Fuel cell

n Paramagnetic analyzer – Robust

– Rapid response time

– Low maintenance




Paramagnetic Oxygen Analyser

Pressure transducer




Oxygram

Inspired

Expired

30%

20%

10%

0%




Alveolar Air Equation

n P A O2 = FIO2 * (Pb- 47) - PaCO2

n P A

O2 = FI

O2 * (Pb

- 47) - Pa

CO2 /R

n P A O2 = FIO2 * (Pb- 47) - PaCO2 /R(1-FIO2(1-R))




1 5 91 4 9

1 0 09 2

4 0 4 0

2

0

5 0

1 0 0

1 5 0

Tissue Vein

Mitochondria

I

n

s

p

ir

e

d

T

ra

c

h

ea

A

l

ve

o

l

u

s

A

rt

e

r

y




Partial pressure of oxygen (mmHg) O

x y g e n s a t u r a t i o n o f h a e m o g l o b i n ( % )

O x y g e n c o n t e n t o f b l o o d ( m l / 1 0 0 m l )

0

10

20

30

40

50

60

70

80

90

100

5

10

20

15

2010 806040 100 500300 600200 400

Artery

Vein

P50




Ideal blood oxygen monitor

n Indicate oxygen tension

n Indicate oxygen supply

– Haemoglobin concentration

– Haemoglobin saturation

– Blood flow

n Rapid response

n Continuous

n Safe

– Non-invasive

n Robust

n Low maintenance

n Stable calibration

n Affordable




Monitoring blood oxygen

ª Arterial tension

ª Arterial saturation

â Blood gas analyser

â Trans cutaneous

â Calculated from tensionCo-oximeterPulse oximeter




Blood gas analyser

n Polarographic

n Measures tension

n Calculates saturation (functional)

n Problems

– invasive

– intermittent




Functional Saturation

OxyHb(OxyHb+reducedHb)

7g OxyHb 1g reducedHb 2g metHb

Functional Saturation = 7/(7+1)

= 87%




Transcutaneous gas analyser

n Polarographic

n Measures tension

– persistent pulmonary hypertension

– diaphragmatic hernia

n Problems

– Delicate

– Heated

– Repositioning

– Recalibrating




Fractional Saturation

OHb(OHb+reducedHb+COHb +metHb)

7g OxyHb 1g reducedHb 2g MetHb

Fractional Saturation = 7/(7+1+2)

= 70%




Oximeters

• 1875 vonVierordt

• 1972 Takuo Aoyagi - "Pulse Oximetry"

• 1980's Nellcor

• 1988 pulse oximetry mandatory in Australia




Light absorption

due to tissuesArtery

(pulsatile tissue)

Non-arterial,

(non-pulsatile) tissu

Systole DiastoleLight absorption

due to arterial blood




Light wavelength (NM)

6 0 0 6 8 0 7 2 0 7 6 0 8 0 0 8 8 0 9 2 0 9 6 0 1 0 0 06 4 0 8 4 0

E x t i n c t i o n c

o e f f i c i e n t

.0 1

.1

1 .0

1 0

Red

Deoxyhaemoglobin

Oxyhaemoglobin

Infrared




O x y

g e n s a t u r a t i o n o

f h a e m o g l o b i n (

% )

0

10

20

30

4050

60

70

80

90

100

1.00.4 2.0 3.0 3.4

R =Red absorption

Infra-red absorption




Oximeter errors

n Signal artefact

n Light absorption artefact




Signal artefact

n Ambient light

n Poor perfusion

n Movement artefactn If R = 1 pulse oximeter shows 85%




Light absorption artefact

n carboxyHb

n metHb





6 0 0 6 8 0 7 2 0 7 6 0 8 0 0 8 8 0 9 2 0 9 6 0 1 0 0 06 4 0 8 4 0


o e f f i c i e n t

.0 1

.1

1 .0

1 0

Red

Deoxyhaemoglobin

Oxyhaemoglobin

Carboxyhaemoglobin

Infrared





6 0 0 6 8 0 7 2 0 7 6 0 8 0 0 8 8 0 9 2 0 9 6 0 1 0 0 06 4 0 8 4 0


o e f f i c i e n t

.0 1

.1

1 .0

1 0

Red

Methaemoglobin

Deoxyhaemoglobin

Oxyhaemoglobin

Infrared





n carboxyHb

– error showing low functional saturation

– error showing high fractional saturation

n metHb

– error toward 85%





n carboxyHb – reads low functional, high fractional

n metHb

– error toward 85%

n fetal Hb

n dyes

n nail polish

n bilirubin

n skin pigment




Monitoring oxygen

ª Tissue

ª Venous tension

ª Venous saturation

â Cytochrome oximeters

â Blood gas analyser

â Optical fiber oximeter




Monitoring Oxygen

•Oxygen supply is critical

•No single monitor of oxygen supply

•Oxygen tension versus haemoglobinsaturation

•Functional versus fractional saturation

oxygen pulse oximetry

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