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The Use of SvO2 Monitoring in the The Use of SvO2 Monitoring in the Cardiac Intensive Care UnitCardiac Intensive Care Unit

Anthony Rossi, MDAnthony Rossi, MD

Director, Cardiac Intensive Care ProgramDirector, Cardiac Intensive Care Program

Congenital Heart Institute Congenital Heart Institute

Miami Children’s Hospital, Miami, FL USAMiami Children’s Hospital, Miami, FL USA

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Warning!!!!!!Warning!!!!!!

• My comments are completely biased• They are based on 21 years of clinical

experience with SvO2 monitoring in the CICU• They are based on some sound physiologic

principles• I believe in

– Early detection of hemodynamic derangements– Early correction of hemodynamic derangements– Goal oriented therapy in the critically ill

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The Value and Clinical Utility of The Value and Clinical Utility of Continuous SvO2 MonitoringContinuous SvO2 Monitoring

• This slide show will address– Relationship of DO2 to VO2– Goal Oriented therapy in the critically ill– Definition of SvO2– Use GDT and SvO2 monitoring in CHS– Pitfalls of other measures of cardiovascular

well-being in the critically ill

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Shock is a rest stop on the highway to death:

Last Exit before EternityLast Exit before Eternity

We must Identify shock states or impending shock states such as low cardiac output syndrome (LCOS) at the earliest possible moment.

a Last Exit before EternityLast Exit before Eternity

Irreversible shock

Warm shock

Cold shock

DEATH

Shock is a continuum

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The Constant Tug of War between DO2 and VO2

The Constant Tug of War between DO2 and VO2

Life is dependent on maintaining the most favorable relationship possible b/w VO2 and DO2

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DO2/VO2DO2/VO2

O2O2O2

O2O2

O2

In the relationship of DO2 and VO2, in fully saturated patients, 5 times as much oxygen is delivered to the tissues as utilized (in desaturated pts such as those with cyanotic heart disease, the situation is much more precarious*)..* Rossi et al. Congenit Heart Dis. 2006 Nov;1(6):294-9.

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Relation of DO2 to VO2Relation of DO2 to VO2Relation of DO2 to VO2Relation of DO2 to VO2

DO2

VO2

critical point of DO2critical point of DO2Lactate increasesLactate increases

52**

* * Decreasing CV Reserve

SVO2 decreases)

omega

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DO2 and Critical IllnessDO2 and Critical Illness

• Monitoring DO2 in the critically ill and developing treatment plans to optimize DO2, is a logical approach to pt management and has been shown to improve outcomes in a wide spectrum of critical illness

• Pts achieving a normal or supernormal level of DO2 have lower mortality, less end organ damage, lower morbidity and shorter hospital stays

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Goal of Post-Op Care: Maintain Optimal Goal of Post-Op Care: Maintain Optimal Tissue OxygenationTissue Oxygenation

Goal of Post-Op Care: Maintain Optimal Goal of Post-Op Care: Maintain Optimal Tissue OxygenationTissue Oxygenation

• Global• Regional

• splanchnic - the correction of unrecognized perfusion defects seems to be a desirable addition to the standard clinical management of critically ill patients with regard to preservation of organ function*

• coronary

* * J.-L. Vincent. Intensive Care Med (1996) 22:3

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Can You Measure DOCan You Measure DO22 Following Following

CHS?CHS?

Can You Measure DOCan You Measure DO22 Following Following

CHS?CHS?• CI usually impossible to measure

because of intracardiac shunting• small patient size makes CI

measurements impractical

Use indirect measures of DO2

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Indirect Indicators of Systemic DOIndirect Indicators of Systemic DO22

• pH

• HCO3

• BE

• SVO2 (Δ AVO2, OER)

• Δ CO2 (SvCO2-SaCO2)

• lactate

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Why not Measure CO?Why not Measure CO?

• Impractical in kids after CHS– Small size– Intra-cardiac mixing

• Not the most important piece of information!

• Only relevant when taken in context of patients oxygen requirements of demands (VO2).

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What does that CO measurement What does that CO measurement mean?mean?

• I implant an artificial heart in you and set it at a “normal cardiac output”

• Is that sufficient CO for the whole range of stresses in life or in the ICU?

• Wouldn’t it make sense to measure something that looks at the CVS ability to meet the metabolic needs of the body?

• *Data suggests that in some pt populations after CHS, the most important derangement in PO hemodynamics is not the decrease in CO but actually the increase in VO2. We need to measure the end product of this balance, not the individual components.– *Li et al. JTCVS 2006

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Common Cardiac Surgical Common Cardiac Surgical ProceduresProcedures

• Arterial switch operation• Repair of tetralogy of Fallot• VSD closure• ASD closure• AVC repair• Rastelli operation• Norwood operation• Bi-Glenn• Fontan• Repair IAA• BTS• Central shunt

• Ross• MV replacement• AV replacement• Aortic Valvotomy• Konno• Ross-Konno• Repair TAPVC• Repair coarctation• Repair DORV• Senning• Mustard• Double switch

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Single Goal of PO CareSingle Goal of PO Care

• Maintain optimal tissue oxygen delivery

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Goal Directed Therapy

• Therapy directed at specific end points, usually related to indices of DO2 in intensive care patients. Indices have traditionally included CO or SvO2.

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Psychological Benefits of GDTPsychological Benefits of GDT

• “Don’t mess up!”• “Keep ‘em alive till 8:05”• Goal oriented tasks keeps team

members focused• Little rewards (tangible results)

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Definition of SvO2Definition of SvO2Definition of SvO2Definition of SvO2

• Mixture of ALL the blood that has traversed the capillary beds capable of extracting oxygen.

• The mixed venous oxygen content will reflect the total body balance b/w DO2 and VO2 of perfused tissues.

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SvO2 MonitoringSvO2 MonitoringSvO2 MonitoringSvO2 Monitoring

• SvO2 Monitoring must occur at the site where all the venous blood in the body has pooled, such as the PA in pts with structurally normal hearts

• SVC monitoring better reflects cerebral blood flow physiology than global systemic blood flow

• IVC blood flow may best reflect splanchnic blood flow

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SvO2 MonitoringSvO2 MonitoringSvO2 MonitoringSvO2 Monitoring

• defines the relationship of DO2/VO2• estimate oxygen delivery (AVO2

difference, OER, OEF/omega)• estimate cardiac output trends• estimate Qp/Qs

– SaO2 poor indicator of Qp/Qs (low SvO2 will decrease SaO2 in face of large Qp/Qs)

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Causes of Low SVO2Causes of Low SVO2

1. Hypoxemia

2. Increased metabolic rate

3. Low cardiac output

4. anemia

11 22 33 44

SVO2 = SaO2 – (VO2/Q x Hb x 13)

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SaO2 does not predict SvO2 SaO2 does not predict SvO2 after Norwoodafter Norwood

Rossi et al. Am J Cardiol; 1994

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SaO2 and Qp/Qs after NorwoodSaO2 and Qp/Qs after Norwood

Rossi et al. Am J Cardiol; 1994

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OER and OEFOER and OEFOER and OEFOER and OEF

• OER = O2 consumption/O2 delivery• OER = O2 Sat art - O2 Sat sys ven

O2 Sat art• normal relationship of 5/1 DO2/VO2 • normal OER = 0.20• normal OEF = 5 (Ω = 5Ω = 5)

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AVO2 difference vs. OERAVO2 difference vs. OER

• AVO2 diff of 25 in pt with SaO2 100%– OER = 25/100 = 0.25– OEF = 4– DO2/VO2 = 4/1 (normal)

• AVO2 diff of 25 in pt with SaO2 65%– OER = 25/65 = 0.38– OEF = 2.5

–DO2/VO2 = 2.5/1 (DO2/VO2 = 2.5/1 (2/1 = critical point of DO2!2/1 = critical point of DO2!))

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OER in Infants following Heart Surgery

OER in Infants following Heart Surgery

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

admit 6 hours 24 hours

time

OE

R

survivors

nonsurvivors

Rossi, Seiden, Gross, et al. Annals Thorac Surg. 1999

normalnormal

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SvO2 Monitoring Decreases Morbidity and Mortality

SvO2 Monitoring Decreases Morbidity and Mortality

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Where to measure SvO2?Where to measure SvO2?Where to measure SvO2?Where to measure SvO2?

• PA: only true “mixed venous sat”• SVC: very dependant on cerebral BF• RA: not for pts with L to R shunt (HLHS)• IVC: lower body sat

– Could over estimate MvO2 because renal vein contribution

– Measures splanchnic BF– Should never be low

• Umbilical Vein• Femoral Vein

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Hierarchies of Organ HypoxiaHierarchies of Organ HypoxiaHierarchies of Organ HypoxiaHierarchies of Organ Hypoxia

VO2

Whole Body DO2

Who

le B

ody

Muscle

Liver

Intestine

Brain

From: Pathologic Foundations of Critical Care. Pinsky and Dhainhaut

MUSCLE IS THE FIRST ORGAN SYSTEM TO BE AFFECTED BY MUSCLE IS THE FIRST ORGAN SYSTEM TO BE AFFECTED BY LCOS. IT MAKES COMPLETE SENSE THAT WE SHOULDLCOS. IT MAKES COMPLETE SENSE THAT WE SHOULD

BE TARGETING THAT ORGAN SYSTEM FOR MONITORING!!!BE TARGETING THAT ORGAN SYSTEM FOR MONITORING!!!

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MEASURING REGIONAL OXYGEN DELIVERY MAY BE

MORE IMPORTANT THAN GLOBAL!!!!

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Redistribution of BF in Shock

• Early shock (or LCOS) is marked by a maldistribution of blood flow to critical organs (such as the brain and heart) and away from organs like the mesenteric bed or the limbs.

• It is intuitive that the earliest signs of LCOS (such as low venous O2 sat) would be found in the less critical organ systems, prompting earlier recognition and response by clinicians

• SVC or MVO2 monitoring MIGHT be considerably less valuable than IVC (esp. low IVC, which really measures venous saturation of lower extremities!)

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Alternatives to Continuous SvO2 Monitoring

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Lactate MonitoringLactate Monitoring

• Advantage: Lactate is measured and is not a derived variable

• Advantage: Association with outcomes in critical illness is clear

• Advantage: Goal oriented therapy targeted at lactate has been associated with improved outcomes

• Disadvantage: End product that is a result of very significant derangement in oxygen delivery/oxygen consumption equation

• Disadvantage: Intermittently monitored. Lots can happen b/w samples.

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How about Non-Invasive SvO2 Monitoring?

It sounds great but doesn’t exist!

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NIRS MonitoringNIRS Monitoring

• Advantage: Continuous monitoring technique• Advantage: Noninvasive• Disadvantage: what the heck is it really monitoring

and what is the physiologic significance of this monitored data?

• Requires the use of conformational bias in decision making.– All the data that is consistent with your assessment of the

pts underlying status is accepted.– Data that is in disagreement with your assessment is

rejected.

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Assumed SvO2=25Measured SvO2=52

Augment DO2Decrease VO2

Assumed SvO2=65

Measured SvO2=30

Decrease inotropesExtubate?

Can we be lead astray by the inaccuracies of NIRS monitoring?Two points circled here, one suggests SvO2 would be high when it is not, the second suggests SvO2 is pathologically low when it is not.

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aNIRS correctlypredicts low DO2

NIRS correctly predicts normal DO2

NIRS incorrectlypredicts low DO2

NIRS incorrectlyPredicts normal DO2

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Three site NIRS MonitoringThree site NIRS Monitoring

3 y.o. s/p subaortic membrane resection. SaO2 100%. What physiologic state is associated with an a-vO2 difference of 5 after CHS?

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Two Site NIRS MonitoringTwo Site NIRS Monitoring

7 mo s/p TOF repair. SaO2=100%Is the a-vO2 difference 31 or 5? Which number do you treat? Are the numbers truly reflective of the underlying physiology?

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Two Site NIRS MonitoringTwo Site NIRS Monitoring

NB with HLHS. Just off pump after S1P. LCOS or not?Using NIRS technology introduces cognitive dissonance and the need for applying conformational bias to resolve the conflict.

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We need the Canary in the CaveWe need the Canary in the Cave

The earliest warning sign that something is awry. Can monitoring splanchnic circulation or the venous oxygen sat from the major extremities in critical illness achieve this?

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ConclusionsConclusions

• Goal directed therapy is a valuable adjuvant to the management of critically ill patients, including those recovering after CHS

• SvO2 is an excellent hemodynamic parameter to target in GDT

• Monitoring individual, at risk tissue beds for hypoperfusion states may be of greater benefit than monitoring the admixture of all systemic venous blood

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ConclusionsConclusions

• Continuous monitoring of central venous oxygen saturation may be accomplished and of value in:– SVC– RA– Umbilical Vein – Femoral Vein

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No hemodynamic monitoring technique should ever be No hemodynamic monitoring technique should ever be considered a panacea or was intended to stand alone. considered a panacea or was intended to stand alone.

Hemodynamic techniques should be accurate, objective, timely Hemodynamic techniques should be accurate, objective, timely (in real-time if possible) and most importantly complimentary.(in real-time if possible) and most importantly complimentary.

Special Thanks To:Special Thanks To:MCH CICU TeamMCH CICU Team

Mt. Sinai Medical Center CICU TeamMt. Sinai Medical Center CICU TeamAmazing nursesAmazing nurses

Outstanding PA’s and ANP’sOutstanding PA’s and ANP’sRandall GrieppRandall GrieppRichard GolinkoRichard GolinkoRedmond BurkeRedmond BurkeRobert HannanRobert Hannan

Too many fellows to listToo many fellows to listEdwardsEdwards

All Children’s HospitalAll Children’s HospitalDavid CooperDavid Cooper

And of course….And of course….

Dave NelsonDave Nelson

Thanks for Listening!!!Thanks for Listening!!!