Ingen bildrubrik

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Oxygenation in patients with exceptionally high
oxygen demand - and the role of hemotherapy
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Problem An increased oxygen demand reflects an
increased overall metabolism - useful or not. An
increased oxygen demand is often seen in patients
with severe circulatory impairment. An increased
oxygen demand must be matched by an adequate
oxygen transport.
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Terminology Oxygen demand/consumption VO2 Oxyg
en transport DO2 Oxygen extraction rate O2ER
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Oxygen transport / Oxygen flux (DO2)
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Arterial oxygen content (CaO2)
20/100 ml O2
/ml blood
0,2 ml O2
/ml blood
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Oxygen consumption (VO2) Amount of oxygen
transported out to the tissues minus amount
of oxygen transported back to the heart. Out CO
x SaO2 x Hb x 1.39 Back CO x SvO2 x
Hb x 1.39 VO2 CO x (SaO2 - SvO2) x Hb
x 1.39
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Oxygen demand/consumption VO2
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Oxygen extraction rate O2ER Relative amount of
oxygen extracted from the blood during one
passage through the tissues. Out CO x SaO2
x Hb x 1.39 Back CO x SvO2 x Hb x
1.39 O2ER (SaO2 -SvO2)/SaO2 x 100
Example SaO2 95 and SvO2 70 gives O2ER
(95-70)/95 26
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Oxygen extraction rate O2ER Varies in different
vascular beds Highly extracting beds liver gut
mucosa hippocampus Global O2ER is about 25 ,
i.e. DO2/VO2 is about 41
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From Nunn JF, Applied Respiratory Physiology
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From Vincent JL et al. In Pathophysiology of
Shock, Sepsis and Organ Failure, Ed Schlag
Redl, Springer, 1993
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Oxygen demand/consumption VO2
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How do we know that oxygen transport is
adequate? Global vs local assessment
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How do we know that oxygen transport is
adequate? Global vs local assessment Adequate
where???
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• Global assessment of adequacy of oxygen transport
• Blood lactate
• related to survival in sepsis
• Oxygen saturation in mixed venous blood

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Local assessment of adequacy of oxygen
transport Hypothesis Deficient oxygen transport
to a certain vascular bed is related to success
of therapy Liver? Gut? Brain? Gut
tonometry Liver vein SO2
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DO2 -dependent DO2 -independent
Anaerobic metabolism
Aerobic metabolism
VO2
Critical DO2
DO2
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DO2 -dependent DO2
-independent
Anaerobic metabolism
Aerobic metabolism
VO2
Critical DO2
DO2
-- normal -- sepsis
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General strategy Improve oxygen
transport When in doubt determine! (CO and
O2ER) CO? Hb? optimal viscosity (Hct close to
33) BV? CVP (LAP) ? vasoactive amines
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Burn injury Massive activation of all cascade
systems Major effects of circulating and
locally acting cytokines Major metabolic
consequences, oxygen demand may increase to
200-300 cytokine effects SIRS compensation
for heat loss
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Strategy for adequate oxygenation in
burns Diminish oxygen consumption diminish
water loss diminish heat loss diminish
shivering diminish fever Optimize oxygen
transport
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How to monitor the acute intravenous
treatment? The dream is to monitor by the
parameter that gives the best information about
the patients condition after 24 hours. -least
risk for organ ischemia (e.g. kidneys) - least
risk for bacterial translocation - least risk
for causing progression of the burn Circulatory
parameter (CVP?, MAP?, HRlt120?) Oxygen transport
parameter (SaO2?) Kidney perfusion parameter
(hourly urinary output?) Other metabolic
parameter (blood lactate?) Gut perfusion
parameter (pHi?)