Oxygen uptake-to-delivery relationship: a way to assess adequate flow

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Oxygen uptake-to-delivery relationship a way to
assess adequate flow

• Critical Care 2006
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O2 uptake (VO2)

• The importance of VO2
• VO2 is inversely related to the risk for cell
  dysfunction and to the severity of shock
• Among the hemodynamic parameters, VO2 is the most
  strongly related to death
• Once cell necrosis occurred, organ function
  recovery is not always possible, even when
  aadequate VO2 restoration

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O2 uptake (VO2)

• Hemodynamic flow-monitoring must be aimed at
  early adaption of VO2 to metabolic needs
• Its usefulness has been challenged due to
  theoretical and practical limitations at the
  bedside
• These limitation have been over-stated
• No need to continuous VO2 measurement to meet the
  patients need
• Monitoring V related variables (CO/SvO2) is
  acceptable compromise, and less invasively

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Respiratory Gas Parameters

• O2 delivery (DO2)
• DO2 Q CaO2 Q (1.34 Hb SaO2) 10
• O2 uptake (VO2)
• VO2 Q 13.4 Hb (SaO2-SvO2)
• O2 extraction ratio (O2ER)
• O2ER VO2/DO2 100
• Q cardiac output SV HR

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Fundamental basis

• Energy depends on oxidative reactions that
  require nutrition and oxygen
• O2 is used for oxidative mechinisms.
  Non-oxidative system have lower affinity for O2
  than do cytochrome oxidative system.
• Non-mitochondrial oxidative system activity can
  only be present when there is no more dysoxia

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• Matching the bodys needs.
• Regional of global?
• Cellular level or organ level?
• Invasive or non-invasive?
• The first priority is to consider the balance
  between whole body VO2 and nVO2

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Several equations

• VO2 DaO2 EO2
• nVO2 nDaO2 nEO2 (n needed)
• oVO2 oDaO2 oEO2 (o observed)
• oVO2/nVO2 oDaO2/nDaO2 oEO2/nEO2
• Any change in oDaO2/nDaO2 must be balanced by an
  inverse change in oEO2/nEO2 to maintain
  oVO2/nVO2 1 and vice versa. If oVO2/nVO2 1
  cannot be maintained, dysoxia occurs.

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• oVO2/nVO2 (global performance)
• If the ratio lt1, it indicates shock
• oDaO2/nDaO2 (Circulatory performance)
• If the ratio lt1, it indicates circulatory failure
• oEO2/nEO2 (Tissue performance)
• If the ratio lt1, it indicates tissue failure

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Matching oxygen uptaketo the patients needs
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Is oxygen uptake equal to the patients needs?

• Clinical improvement
• It is a good indicator of adequate resuscitation
• In practice, the nVO2 is usually met by
  decreasing metabolic requirement, optimizing the
  hct, and arterial SaO2, and increase blood flow
  empirically.

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Is oxygen uptake equal to the patients needs?

• A clear improvement of lactate clearance
• Single lactate value fails to discriminate
  between dysoxia and aerobiosis
• The time course of lactate levels is not an ideal
  marker
• DM, liver dysfunction, tissue reperfusion
  pyruvate dehydrogenase inhibition may cause
  marked increase in blood lactate level

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Is oxygen uptake equal to the patients needs?

• An evaluation of oVO2 and nVO2
• oVO2 can be measured at the bedside using expired
  gases
• If the oVO2 plateau is reached at a value close
  to the estimated needed, the patients real needs
  are probably met.

How may we estimate the needed VO2?
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How may we estimate the needed VO2

• Basal metabolism
• Age-specific sex-specific
• Additional metabolism
• Body temperature ( 13 for each 1? )
• Pathologic situation
• Severe sepsis respiratory failure
• nVO2 the sum of the above

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How may we estimate the needed VO2

• Biphasic relationship diagram

1. Inadequate oxygen supply DO2 increases with
an VO2 increases 2. Adequate oxygen supply DO2
increases with an stable VO2 value a.lactate
level decrease b.lactate level increase -gt other
mechanism limites VO2
O2 supply independency EO2 changes proportionally
Critical point
O2 supply dependency Increased
Lactate Activation of anaerobiosis
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Right ward shift of critical point
Needed VO2 are excessive VO2 plateau is at
higher level
The VO2/DO2 slope is decrease O2 tissue
diffusion is impaired
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Right ward shift of critical point

• nVO2 of kidney/stomach/muscle increased
  proportional to flow (or CO)
• Infusion of inotropic agents increases myocardial
  oxygen uptake
• Conformance is a decrease in the metabolic needs
  of cells that occurs in response to gradual
  decline in available oxygen.

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Recent generation of device
New devices Continuous CO monitoring and blood
gas analysis minimize the measurement
variability VO2/DO2 vsVO2/time to finding out
the ciritical point
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First conclusion

• It may be concluded that oVO2 nVO2 when one or
  several of the following factors is present
  clinical improvement, decreased in blood lactate,
  and oVO2 inside the expected range of oVO2 / DO2
  curve

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Targeting a pre-established value

• Targeting a pre-established value for DO2, CO, or
  SvO2 does not meet the needs of an individual
  patients.
• These pre-established values were derived from
  normal findings or survivors in selected
  populations.
• Determination of the needed values must take into
  consideration that they are specific to the
  patient

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No less and no more

• In some conditions, such as coronary disease,
  efforts to increase CO in order to normalize
  the cardiac index to more than 2.5 l/min per m2
  or the SvO2 value to more than 70 can be
  harmful.
• An excessive oxygen supply may be deleterious,
  either via the useless metabolic cost of an
  excessive increase in DO2 or via activation of
  nonoxidative systems.

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Add VO2 into the normogram
Corrected VO2 value (Age/Sex-specific Disease/str
ess) As individualized therapeutic guidance
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Clinical sample 1

• Aortic valve replacement post OP and cold
  extremities
• H0 nVO2 90
• H2 nVO2 119

oVO2 nVO2 There is no need to hemodynamic
support
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Clinical sample 2

• Sudden shock hyperkinetic state
• nVO2 216

oVO2 lt nVO2 He need hemodynamic support
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Practical Guidelines

• Early detection of shock states
• Matching oxygen consumption to needs is the first
  objective
• To reach this objective, the best compromise must
  be identified, mostly on metabolic cost

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Conclusion 1

• Matching the VO2 and nVO2 is a crucial objective
  in critically ill patients
• In most conditions, targeting a clinical
  improvement, a decreased blood lactate level, or
  a pre-established value for CO, SaO2 or SvO2 is
  an accetable means of achiving an adwquate VO2

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Conclusion 2

• In complex conditions, by plotting VO2/DO2 over
  time during a DO2 challenge, the critical DO2
  value can be rapidly identified as the inflection
  point on the curve, and resuscitation efforts can
  then be limited

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Conclusion 3

• Flow monitoring is one of major interest in terms
  of stabilizing the macrocirculation.
• A stabilized macrocirculation is a global
  prerequisite, and must be achived before one
  looks at the local microcirculation