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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
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n 2nd law of thermodynamics
n Entropy is time’s arrow
Entropy Life
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CnHnOn
O2
CO2
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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
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r
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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
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Ideal Oxygen Analyser
n Rapid response
n Continuous
n Robust
n
Low maintenancen Do no harm
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Oxygen Analysers
n Polarographic sensor
n Fuel cell
n Paramagnetic analyzer – Robust
– Rapid response time
– Low maintenance
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Paramagnetic Oxygen Analyser
Pressure transducer
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Oxygram
Inspired
Expired
30%
20%
10%
0%
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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))
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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
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p
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T
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A
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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
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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
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Monitoring blood oxygen
ª Arterial tension
ª Arterial saturation
â Blood gas analyser
â Trans cutaneous
â Calculated from tensionCo-oximeterPulse oximeter
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Blood gas analyser
n Polarographic
n Measures tension
n Calculates saturation (functional)
n Problems
– invasive
– intermittent
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Functional Saturation
OxyHb(OxyHb+reducedHb)
7g OxyHb 1g reducedHb 2g metHb
Functional Saturation = 7/(7+1)
= 87%
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Transcutaneous gas analyser
n Polarographic
n Measures tension
– persistent pulmonary hypertension
– diaphragmatic hernia
n Problems
– Delicate
– Heated
– Repositioning
– Recalibrating
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Fractional Saturation
OHb(OHb+reducedHb+COHb +metHb)
7g OxyHb 1g reducedHb 2g MetHb
Fractional Saturation = 7/(7+1+2)
= 70%
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Oximeters
• 1875 vonVierordt
• 1972 Takuo Aoyagi - "Pulse Oximetry"
• 1980's Nellcor
• 1988 pulse oximetry mandatory in Australia
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Light absorption
due to tissuesArtery
(pulsatile tissue)
Non-arterial,
(non-pulsatile) tissu
Systole DiastoleLight absorption
due to arterial blood
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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
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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
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Oximeter errors
n Signal artefact
n Light absorption artefact
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Signal artefact
n Ambient light
n Poor perfusion
n Movement artefactn If R = 1 pulse oximeter shows 85%
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Light absorption artefact
n carboxyHb
n metHb
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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
Carboxyhaemoglobin
Infrared
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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
Methaemoglobin
Deoxyhaemoglobin
Oxyhaemoglobin
Infrared
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Light absorption artefact
n carboxyHb
– error showing low functional saturation
– error showing high fractional saturation
n metHb
– error toward 85%
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Light absorption artefact
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
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Monitoring oxygen
ª Tissue
ª Venous tension
ª Venous saturation
â Cytochrome oximeters
â Blood gas analyser
â Optical fiber oximeter
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