oxygen transport calculations – m . l. cheatham, md...

Oxygen Transport Calculations – M. L. Cheatham, MD, FACS, FCCM

Revised 01/14/2009 1

OXYGEN TRANSPORT OXYGEN TRANSPORT CALCULATIONSCALCULATIONS

S lS l DemandDemand

Michael L. Cheatham, MD, FACS, FCCMMichael L. Cheatham, MD, FACS, FCCMDirector, Surgical Intensive Care UnitsDirector, Surgical Intensive Care Units

Orlando Regional Medical CenterOrlando Regional Medical CenterOrlando, FloridaOrlando, Florida

SupplySupply DemandDemand

IN REVIEW…IN REVIEW…

•• There are four primary monitoring questionsThere are four primary monitoring questions–– Is intravascular volume or “preload” adequate?Is intravascular volume or “preload” adequate?–– Is blood flow adequate?Is blood flow adequate?–– Is vascular resistance appropriate?Is vascular resistance appropriate?–– Is oxygen transport balance appropriate? Is oxygen transport balance appropriate?

•• Volumetric assessment of preload status is Volumetric assessment of preload status is superior to pressuresuperior to pressure--based measurementsbased measurements

•• Continuous hemodynamic monitoring provides an Continuous hemodynamic monitoring provides an improved understanding of patient illness and improved understanding of patient illness and response to therapyresponse to therapy

OXYGEN TRANSPORT BALANCEOXYGEN TRANSPORT BALANCE

•• The foremost question in critical care is not:The foremost question in critical care is not:a)a) What is the perfect PAOP or EDVI?What is the perfect PAOP or EDVI?b)b) What cardiac output ensures patient survival?What cardiac output ensures patient survival?c)c) What systemic vascular resistance is optimal?What systemic vascular resistance is optimal?

•• The ultimate question is:The ultimate question is:d)d) Is tissue oxygen delivery sufficient to meet Is tissue oxygen delivery sufficient to meet

cellular oxygen demand?cellular oxygen demand?


•• Failure to provide sufficient oxygen to meet cellular Failure to provide sufficient oxygen to meet cellular demands leads todemands leads to–– Cellular ischemiaCellular ischemia–– Bacterial translocationBacterial translocation

S iS i–– SepsisSepsis–– Worsening shockWorsening shock–– Organ dysfunctionOrgan dysfunction–– Multiple system organ failureMultiple system organ failure–– DeathDeath

DEFINITIONSDEFINITIONS

•• Oxygen delivery (DOOxygen delivery (DO22))–– The amount of oxygen pumped to the tissues by The amount of oxygen pumped to the tissues by

the heartthe heart

•• Oxygen consumption (VOOxygen consumption (VO22))yg p (yg p ( 22))–– The amount of oxygen consumed by the tissues The amount of oxygen consumed by the tissues

•• Oxygen demandOxygen demand–– The amount of oxygen required by the tissues to The amount of oxygen required by the tissues to

function aerobicallyfunction aerobically–– May exceed both oxygen delivery and May exceed both oxygen delivery and

consumption during critical illnessconsumption during critical illness

ASSESSING OXYGEN TRANSPORTASSESSING OXYGEN TRANSPORT

•• To assess the adequacy of a patient’s oxygen To assess the adequacy of a patient’s oxygen transport balance, four more questions must be transport balance, four more questions must be consideredconsidered–– Does oxygen delivery meet the patient’s needs?Does oxygen delivery meet the patient’s needs?–– Is cardiac output adequate for consumption?Is cardiac output adequate for consumption?Is cardiac output adequate for consumption?Is cardiac output adequate for consumption?–– Is oxygen consumption adequate for demand?Is oxygen consumption adequate for demand?–– Is the patient’s hypoxemia due to a pulmonary Is the patient’s hypoxemia due to a pulmonary

problem or to a low flow state? problem or to a low flow state?


Revised 01/14/2009 2


•• If oxygen delivery and oxygen consumption are If oxygen delivery and oxygen consumption are balancedbalanced–– “Supply” equals “demand”“Supply” equals “demand”–– The cellular requirements of the body are metThe cellular requirements of the body are met

N l t b li d i hibit dN l t b li d i hibit d–– Normal metabolic processes proceed uninhibitedNormal metabolic processes proceed uninhibited–– Anaerobic metabolism is minimizedAnaerobic metabolism is minimized

“A Happy Pea Monster”“A Happy Pea Monster”

The wellThe well--known fable of the “Pea known fable of the “Pea Monster” will be used to illustrate Monster” will be used to illustrate

the key concepts of oxygen the key concepts of oxygen transport balancetransport balance


•• If oxygen demand exceeds delivery, shock is presentIf oxygen demand exceeds delivery, shock is present–– Cellular oxygen is deficientCellular oxygen is deficient–– Energy is produced via anaerobic metabolism with Energy is produced via anaerobic metabolism with

lactic acid (lactate) as a byproductlactic acid (lactate) as a byproductL t t t b tili d d l tL t t t b tili d d l tLactate cannot be reutilized and accumulates Lactate cannot be reutilized and accumulates leading to:leading to:–– Metabolic acidosisMetabolic acidosis–– Cellular injury Cellular injury –– Cellular deathCellular death

“A Sick Pea Monster”“A Sick Pea Monster”

•• Oxygen consumption may just meet oxygen demandOxygen consumption may just meet oxygen demand–– Requires a high extraction of oxygen from bloodRequires a high extraction of oxygen from blood–– Places patient at risk for rapid Places patient at risk for rapid decompensationdecompensation

Little physiologic reserve is presentLittle physiologic reserve is present


Organs with high baseline oxygen extraction, Organs with high baseline oxygen extraction, such as the heart, are at high risk for ischemiasuch as the heart, are at high risk for ischemia

“An Unhappy Pea Monster”“An Unhappy Pea Monster”


•• Patient survival is improved by optimizing oxygen Patient survival is improved by optimizing oxygen delivery to ensure that…delivery to ensure that…

1)1) Oxygen demand is met at baselineOxygen demand is met at baseline

AND AND

2) There is an adequate physiologic oxygen reserve 2) There is an adequate physiologic oxygen reserve to cope with acute increases in oxygen demandto cope with acute increases in oxygen demand

OXYGEN CALCULATIONSOXYGEN CALCULATIONS

•• Knowledge of the oxygen transport equations is Knowledge of the oxygen transport equations is essential to understanding the pathophysiology essential to understanding the pathophysiology and appropriate treatment for the various shock and appropriate treatment for the various shock statesstates

•• Pulmonary artery and central venous Pulmonary artery and central venous oximetryoximetrycatheters provide the ability to monitor oxygen catheters provide the ability to monitor oxygen transport balance at the bedsidetransport balance at the bedside–– Continuous mixed venous Continuous mixed venous oximetryoximetry (SvO(SvO22))–– Continuous central venous Continuous central venous oximetryoximetry (ScvO(ScvO22))–– Intermittent calculation of oxygen delivery Intermittent calculation of oxygen delivery

(DO(DO22I) and oxygen consumption (VOI) and oxygen consumption (VO22I)I)

MEASURED PARAMETERSMEASURED PARAMETERS

•• Arterial oxygen tension (PaOArterial oxygen tension (PaO22))

•• Arterial carbon dioxide tension (PaCOArterial carbon dioxide tension (PaCO22) )

•• Arterial oxygen saturation (SaOArterial oxygen saturation (SaO22 or SpOor SpO22) )

•• Mixed venous oxygen saturation (SvOMixed venous oxygen saturation (SvO22))

•• Central venous oxygen saturation (ScvOCentral venous oxygen saturation (ScvO22))

•• Venous oxygen tension (PvOVenous oxygen tension (PvO22) )

•• Hemoglobin (Hgb) Hemoglobin (Hgb)

•• Cardiac output (CO)Cardiac output (CO)


Revised 01/14/2009 3

CALCULATED PARAMETERSCALCULATED PARAMETERS

•• Cardiac index (CI)Cardiac index (CI)•• Pulmonary capillary oxygen content (CcOPulmonary capillary oxygen content (CcO22))•• Arterial oxygen content (CaOArterial oxygen content (CaO22))•• Venous oxygen content (CvOVenous oxygen content (CvO22))Venous oxygen content (CvOVenous oxygen content (CvO22))•• ArterialArterial--venous oxygen content difference (Cavenous oxygen content difference (Ca--vOvO22))•• Oxygen utilization coefficient (OUC)Oxygen utilization coefficient (OUC)•• Oxygen delivery index (DOOxygen delivery index (DO22I)I)•• Oxygen consumption index (VOOxygen consumption index (VO22I)I)•• Intrapulmonary shunt (Qsp/Qt)Intrapulmonary shunt (Qsp/Qt)

VASCULAR CIRCUITVASCULAR CIRCUIT

•• Central to any assessment Central to any assessment of oxygen transport is the of oxygen transport is the ability to calculate the ability to calculate the amount of oxygen in the amount of oxygen in the blood at any point in the blood at any point in the

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y py pbodybody

•• Such calculations are Such calculations are dependent upon both the dependent upon both the measured oxygen tension measured oxygen tension and oxygen saturation at and oxygen saturation at each pointeach point

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CALCULATING OXYGEN CONTENTCALCULATING OXYGEN CONTENT

•• To calculate the oxygen content of blood, one must To calculate the oxygen content of blood, one must recognize that:recognize that:1.1. Oxygen can be either “bound” or “unbound”Oxygen can be either “bound” or “unbound”2.2. Each gram of Each gram of HgbHgb can carry up to 1.34 can carry up to 1.34 mLmL of oxygenof oxygen

Thi b i f i t iThi b i f i t iThis number varies from species to speciesThis number varies from species to species3.3. The solubility of oxygen in blood is 0.0031 The solubility of oxygen in blood is 0.0031 mLmL//dLdL4.4. The amount of oxygen carried by The amount of oxygen carried by HgbHgb depends upon depends upon

its saturationits saturationThis varies depending upon the patient’s inspired This varies depending upon the patient’s inspired oxygen fraction (FiOoxygen fraction (FiO22) and the presence of any ) and the presence of any mixed, mixed, unoxygenatedunoxygenated bloodblood

–– Also known as “intrapulmonary shunt”Also known as “intrapulmonary shunt”

OXYGEN CONTENTOXYGEN CONTENT

•• Oxygen contentOxygen content= oxygen bound to = oxygen bound to HgbHgb + oxygen dissolved in plasma+ oxygen dissolved in plasma

•• Oxygen boundOxygen bound== HgbHgb concconc x oxygenx oxygen HgbHgb can carry xcan carry x HgbHgb saturationsaturation HgbHgb concconc x oxygen x oxygen HgbHgb can carry x can carry x HgbHgb saturationsaturation

•• Oxygen dissolvedOxygen dissolved= oxygen tension x solubility coefficient of oxygen= oxygen tension x solubility coefficient of oxygen

CC OO22 = (1.34 x = (1.34 x HgbHgb x Sx S OO22) + (P) + (P OO22 x 0.0031)x 0.0031)

where “where “ ” signifies the location of the blood” signifies the location of the blood(“c” for end(“c” for end--capillary, “a” for arterial, or “v” for venous)capillary, “a” for arterial, or “v” for venous)

CALCULATING OXYGEN CONTENTCALCULATING OXYGEN CONTENT

•• To calculate the oxygen content of To calculate the oxygen content of blood as it leaves the alveolus blood as it leaves the alveolus (C(CccOO22), remember that:), remember that:1.1. HgbHgb should be fully saturated should be fully saturated

(i e S(i e SAAOO22=1 0 if F=1 0 if FiiOO22 > 0 21) as> 0 21) as

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SAO2(i.e., S(i.e., SAAOO22 1.0 if F1.0 if FiiOO22 > 0.21) as > 0.21) as it leaves the alveolusit leaves the alveolus

2.2. The alveolar oxygen tension The alveolar oxygen tension (P(PAAOO22) must be determined ) must be determined using the Universal Gas Lawusing the Universal Gas Law

PPBB = P= PAAOO22 + P+ PAACOCO22 + P+ PAANN22 + P+ PH2OH2O

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ALVEOLAR OXYGEN TENSION (PALVEOLAR OXYGEN TENSION (PAAOO22))

•• Assuming an FAssuming an FiiOO22 of > 0.30 (i.e., Sof > 0.30 (i.e., SAAOO22=1.0)=1.0)

PPAAOO22 = F= FiiOO22 x [(Px [(PBB--PPH20H20))--(P(PaaCOCO22/RQ)]/RQ)]

where Pwhere PBB = barometric pressure, P= barometric pressure, PH2OH2O = water vapor = water vapor pressure RQ = respiratory quotientpressure RQ = respiratory quotientpressure, RQ = respiratory quotientpressure, RQ = respiratory quotient

PPAAOO22 = 0.30 x [(760 = 0.30 x [(760 torrtorr -- 47 47 torrtorr) ) -- (40 (40 torrtorr / 0.8)]/ 0.8)](assuming normal values)(assuming normal values)

PPAAOO22 = 0.30 x 663 = 0.30 x 663 torrtorr = 199 = 199 torrtorr

PPAAOO22 can also be approximated rapidly at the bedside can also be approximated rapidly at the bedside as 700 as 700 torrtorr x FiOx FiO22 -- 50 50 torrtorr


Revised 01/14/2009 4

PULMONARY ENDPULMONARY END--CAPILLARY OXYGEN CAPILLARY OXYGEN CONTENT (CcOCONTENT (CcO22))

•• TheThe oxygenoxygen contentcontent ofof pulmonarypulmonary endend--capillarycapillary bloodblood asasitit leavesleaves thethe alveolusalveolus

CCccOO22 = (1.34 x Hgb x 1.0) + (P= (1.34 x Hgb x 1.0) + (PAAOO22 x 0.0031)x 0.0031)(oxygen bound)(oxygen bound) (oxygen dissolved)(oxygen dissolved)( yg )( yg ) ( yg )( yg )

= (1.34 mL O= (1.34 mL O22/gm x 15 gm x 1.0)+(199 torr x 0.0031)/gm x 15 gm x 1.0)+(199 torr x 0.0031)

= 20.1 ml O= 20.1 ml O22/dl blood + 0.6 ml O/dl blood + 0.6 ml O22/dl blood/dl blood

== 2020..77 mlml OO22/dl/dl bloodblood

•• Note again that alveolar (PNote again that alveolar (PAAOO22) and not arterial (P) and not arterial (PaaOO22) ) oxygen tension is used in this equationoxygen tension is used in this equation

20.7 20.7 mLmL//dLdL199 199 torrtorr

1.01.0

PULMONARY ENDPULMONARY END--CAPILLARY OXYGEN CAPILLARY OXYGEN CONTENT (CcOCONTENT (CcO22))

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SAO2 1.01.0

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ARTERIAL OXYGEN CONTENT (CaOARTERIAL OXYGEN CONTENT (CaO22))

•• Oxygen content of arterial blood leaving the heartOxygen content of arterial blood leaving the heart–– 98% of arterial oxygen is bound to 98% of arterial oxygen is bound to HgbHgb–– 2% of arterial oxygen is dissolved in plasma2% of arterial oxygen is dissolved in plasma

CCaaOO22 = (1.34 x= (1.34 x HgbHgb x Sx SaaOO22) + (P) + (PaaOO22 x 0.0031)x 0.0031)CCaaOO22 (1.34 x (1.34 x HgbHgb x Sx SaaOO22) (P) (PaaOO22 x 0.0031)x 0.0031)

= (1.34 x 15 gm x 1.0) + (100 = (1.34 x 15 gm x 1.0) + (100 torrtorr x 0.0031) x 0.0031)


= 20.4 ml O= 20.4 ml O22/dl blood/dl blood


1.01.0

ARTERIAL OXYGEN CONTENT (CaOARTERIAL OXYGEN CONTENT (CaO22))

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SAO2 1.01.0

20.4 mL/dL20.4 mL/dL100 torr100 torr

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CcOCcO22 vs. vs. CaOCaO22

•• Question:Question:–– So if the So if the CcOCcO22 was 20.7 was 20.7 mLmL, in this example, and , in this example, and

the CaOthe CaO22 is now 20.4 is now 20.4 mLmL, where did the other 0.3 , where did the other 0.3 mLmL of oxygen go??? The blood hasn’t even of oxygen go??? The blood hasn’t even made it out of the heart yet???made it out of the heart yet???made it out of the heart yet???made it out of the heart yet???

•• Answer:Answer:–– A small amount of oxygen is used by the lung A small amount of oxygen is used by the lung

and heart before being pumped to the bodyand heart before being pumped to the body–– This deoxygenated blood is returned to the left This deoxygenated blood is returned to the left

heart and contributes to intraheart and contributes to intra--pulmonary shunt pulmonary shunt (stay tuned!)(stay tuned!)

VENOUS OXYGEN CONTENT (CvOVENOUS OXYGEN CONTENT (CvO22))

•• Oxygen content of blood returning to the heartOxygen content of blood returning to the heart–– >99% of arterial oxygen is bound to Hgb>99% of arterial oxygen is bound to Hgb–– <1% of venous oxygen is dissolved in plasma<1% of venous oxygen is dissolved in plasma

CCvvO2O2 = (1.34 x Hgb x S= (1.34 x Hgb x SvvOO22) + (P) + (PvvOO22 x 0.0031)x 0.0031)CCvvO2 O2 (1.34 x Hgb x S (1.34 x Hgb x SvvOO22) (P) (PvvOO22 x 0.0031)x 0.0031)PvOPvO22 can be measured with a venous blood gas, can be measured with a venous blood gas,

or estimated as 35 torr with high accuracyor estimated as 35 torr with high accuracy

= (1.34 x 15 gm x 0.75) + (35 torr x 0.0031) = (1.34 x 15 gm x 0.75) + (35 torr x 0.0031)




Revised 01/14/2009 5


1.01.0

VENOUS OXYGEN CONTENT (CVENOUS OXYGEN CONTENT (CvvOO22))

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SAO2 1.01.0


1.01.0


0.750.75 SYSTEMIC

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ARTERIALARTERIAL--VENOUS OXYGEN VENOUS OXYGEN CONTENT DIFFERENCE (CaCONTENT DIFFERENCE (Ca--vOvO22))

•• The difference in oxygen content between arterial The difference in oxygen content between arterial and venous bloodand venous blood–– Represents the amount of oxygen used during Represents the amount of oxygen used during

one pass of blood through the bodyone pass of blood through the bodyCan be used as an estimate of the patient’sCan be used as an estimate of the patient’s–– Can be used as an estimate of the patient s Can be used as an estimate of the patient s physiologic oxygen reservephysiologic oxygen reserve

CCaa--vvOO22 = C= CaaOO22 -- CCvvOO22

= 20.4 ml O= 20.4 ml O22/dl blood /dl blood ––15.2 ml O15.2 ml O22/dl blood/dl blood



ARTERIALARTERIAL--VENOUS OXYGEN VENOUS OXYGEN CONTENT DIFFERENCE (CaCONTENT DIFFERENCE (Ca--vOvO22))

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SAO2


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0.750.75

5.2 mL/dL5.2 mL/dL

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So you now have the ability to measure or calculate the oxygen So you now have the ability to measure or calculate the oxygen content and tension at any point in the body!content and tension at any point in the body!

OXYGEN DELIVERY INDEX (DOOXYGEN DELIVERY INDEX (DO22I)I)

•• Volume of gaseous oxygen pumped from the left Volume of gaseous oxygen pumped from the left ventricle per minute per meter squared BSAventricle per minute per meter squared BSA

DODO22I I = CI x C= CI x CaaOO22 x 10 x 10 dLdL/L/L

The 10The 10 dLdL/L corrects for the fact that CI is measured/L corrects for the fact that CI is measuredThe 10 The 10 dLdL/L corrects for the fact that CI is measured/L corrects for the fact that CI is measuredin L/min/min L/min/m22 and oxygen content is measured in ml/dland oxygen content is measured in ml/dl

= 4.0 L/min= 4.0 L/min--mm22 x 20.4 ml Ox 20.4 ml O22/dl blood x 10 /dl blood x 10 dLdL/L/L

= ~800 ml O= ~800 ml O22/min/min--mm22

•• This is a very important resuscitation endpoint for This is a very important resuscitation endpoint for ensuring adequate oxygen delivery to the tissuesensuring adequate oxygen delivery to the tissues

OXYGEN CONSUMPTION INDEX (VOOXYGEN CONSUMPTION INDEX (VO22I)I)

•• Volume of gaseous OVolume of gaseous O22 returned to the right atrium returned to the right atrium per minute per meter squared BSAper minute per meter squared BSA

VOVO22I I = CI x C= CI x Caa--vvOO22 x 10 x 10 dLdL/L/L

1010 / f f C/ f f CThe 10 The 10 dLdL/L corrects for the fact that CI is measured/L corrects for the fact that CI is measuredin L/min/min L/min/m22 and oxygen content is measured in ml/dland oxygen content is measured in ml/dl

= 4.0 L/min= 4.0 L/min--mm22 x 5.2 ml Ox 5.2 ml O22/dl blood x 10 /dl blood x 10 dLdL/L/L

= ~200 ml O= ~200 ml O22/min/min--mm22

OXYGEN UTILIZATION COEFFICIENT (OUC)OXYGEN UTILIZATION COEFFICIENT (OUC)

•• Percentage of delivered oxygen which is consumed Percentage of delivered oxygen which is consumed by the bodyby the body–– Also known as the oxygen extraction ratio (OAlso known as the oxygen extraction ratio (O22ER)ER)

OUCOUC = VO= VO22I / DOI / DO22II22 22

= 200 ml O= 200 ml O22/min/min--mm22 / 800 ml O/ 800 ml O22/min/min--mm22

= ~0.25= ~0.25

•• If SaOIf SaO22 is maintained at > 0.92, OUC can be is maintained at > 0.92, OUC can be approximated as 1approximated as 1-- SvOSvO22


Revised 01/14/2009 6


1.01.0

OXYGEN UTILIZATION COEFFICIENT (OUC)OXYGEN UTILIZATION COEFFICIENT (OUC)

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SAO2 1.01.0


1.01.0


0.750.75

5.2 mL/dL5.2 mL/dL0.250.25

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MIXED VENOUS OXYGEN SATURATION (SvOMIXED VENOUS OXYGEN SATURATION (SvO22))

•• Provides a continuous “online” indication of the Provides a continuous “online” indication of the relative balance between VOrelative balance between VO22I and DOI and DO22II

•• It is the "flowIt is the "flow--weighted average" of the venous weighted average" of the venous saturations from all saturations from all perfusedperfused vascular bedsvascular beds–– Does not reflect oxygen transport adequacy of Does not reflect oxygen transport adequacy of

nonnon--perfusedperfused vascular beds vascular beds –– A “normal” SvOA “normal” SvO22 therefore does not mean that therefore does not mean that

all tissues are adequately oxygenatedall tissues are adequately oxygenated–– Does not yield information about the adequacy Does not yield information about the adequacy

of perfusion of any individual vascular bedof perfusion of any individual vascular bed


•• Can be used…Can be used…–– As an "early warning signal" to detect the onset As an "early warning signal" to detect the onset

of oxygen transport imbalance before clinical of oxygen transport imbalance before clinical deterioration occursdeterioration occursTo evaluate the efficacy of therapeuticTo evaluate the efficacy of therapeutic–– To evaluate the efficacy of therapeutic To evaluate the efficacy of therapeutic interventions such that physiologic endinterventions such that physiologic end--points points are reached more quicklyare reached more quickly

–– To identify potentially detrimental consequences To identify potentially detrimental consequences of “patient care” (suctioning, positioning, etc.) of “patient care” (suctioning, positioning, etc.) that might otherwise go unnoticedthat might otherwise go unnoticed


•• If SIf SvvOO22 decreases…decreases…–– Consumption (VOConsumption (VO22I) is increasing ORI) is increasing OR–– Delivery (DODelivery (DO22I) is decreasingI) is decreasing

•• If SIf SvvOO22 increases…increases…If SIf SvvOO22 increases…increases…–– Consumption (VOConsumption (VO22I) is decreasing ORI) is decreasing OR–– Delivery (DODelivery (DO22I) is increasing ORI) is increasing OR–– Blood is being shunted without releasing its Blood is being shunted without releasing its

oxygen ORoxygen OR–– Oxygen uptake by the tissues is decreasingOxygen uptake by the tissues is decreasing


•• As a general rule…As a general rule…

A “low” SA “low” SvvOO22 is always badis always bad

A “normal” SA “normal” SvvOO22 is not necessarily goodis not necessarily good

A “high” SA “high” SvvOO22 is usually badis usually bad


•• The four determinants of SvOThe four determinants of SvO22

–– Hemoglobin (Hemoglobin (HgbHgb))–– Cardiac output / index (CO / CI)Cardiac output / index (CO / CI)–– Arterial oxygen saturation (SaoArterial oxygen saturation (Sao22))–– Oxygen consumption index (VOOxygen consumption index (VO22I)I)

•• The four main causes of low SvOThe four main causes of low SvO22

–– AnemiaAnemia–– Low cardiac outputLow cardiac output–– Arterial Arterial desaturationdesaturation–– Increased VOIncreased VO22II


Revised 01/14/2009 7


•• Two common sources of error in SvOTwo common sources of error in SvO22

–– Inadequate calibrationInadequate calibrationPerform inPerform in--vitro calibration prior to catheter vitro calibration prior to catheter insertioninsertionP f iP f i i lib ti i i di lib ti i i dPerform inPerform in--vivo calibration via mixed venous vivo calibration via mixed venous blood gasblood gas

–– Catheter malpositionCatheter malpositionIf the catheter tip is against the wall of the If the catheter tip is against the wall of the pulmonary artery, the light reflected back to pulmonary artery, the light reflected back to the catheter will be amplified artificially the catheter will be amplified artificially increasing the SvOincreasing the SvO22 measurementmeasurement


•• A sensitive “online” monitor of the adequacy of A sensitive “online” monitor of the adequacy of balance between oxygen delivery and oxygen balance between oxygen delivery and oxygen consumption consumption

•• Not a specific indicator of the cause for oxygen Not a specific indicator of the cause for oxygen transport compromisetransport compromise

•• Accurately predicts potentially detrimental Accurately predicts potentially detrimental changes in patient status before they become changes in patient status before they become clinically apparentclinically apparent–– Allows appropriate therapeutic interventions to Allows appropriate therapeutic interventions to

be initiated prior to development of severe be initiated prior to development of severe changes in cardiorespiratory statuschanges in cardiorespiratory status

FOUR PRIMARY QUESTIONSFOUR PRIMARY QUESTIONS

•• Is DOIs DO22I adequate to meet the patient’s needs?I adequate to meet the patient’s needs?

•• Is CI adequate to support VOIs CI adequate to support VO22I?I?

•• Is VOIs VO22I appropriate for oxygen demand?I appropriate for oxygen demand?

•• Is the patient’s hypoxemia due to a pulmonary Is the patient’s hypoxemia due to a pulmonary problem or to a low flow state? problem or to a low flow state?

FUNDAMENTAL QUESTIONSFUNDAMENTAL QUESTIONS

•• Question #1Question #1–– Is DOIs DO22I adequate to meet the patient's needs?I adequate to meet the patient's needs?

DODO22I should be at least 500 ml OI should be at least 500 ml O22/min/min--mm22

–– Higher levels do not change outcomeHigher levels do not change outcomeIf lower, check the SvOIf lower, check the SvO22

–– < 0.65 suggests that oxygen supply is barely < 0.65 suggests that oxygen supply is barely meeting oxygen demandmeeting oxygen demand

Ensure that the patient’s Ensure that the patient’s HgbHgb is appropriate is appropriate –– Consider transfusion of packed red blood Consider transfusion of packed red blood

cells if DOcells if DO22I is inadequateI is inadequate»» HgbHgb level has the greatest impact on DOlevel has the greatest impact on DO22I I

OXYGEN SUPPLY DEPENDENCYOXYGEN SUPPLY DEPENDENCY

•• When DOWhen DO22I exceeds oxygen demand, VOI exceeds oxygen demand, VO22I will I will “plateau” and no longer rise in response to DO“plateau” and no longer rise in response to DO22I I –– The goal in oxygen transport resuscitationThe goal in oxygen transport resuscitation

•• When DOWhen DO22I no longer meets oxygen demand, VOI no longer meets oxygen demand, VO22I I 22 g ygg yg 22becomes “supply dependent”becomes “supply dependent”–– So called “critical DOSo called “critical DO22””–– Patients should be maintained to the right of Patients should be maintained to the right of

“critical DO“critical DO22I”I”

OXYGEN UNLOADINGOXYGEN UNLOADING

•• Judicious amounts of Judicious amounts of acidemiaacidemia, , hypercarbiahypercarbia, and , and fever all produce a right shift fever all produce a right shift in thein the oxyhemoglobinoxyhemoglobin

•• The optimal The optimal HgbHgb concentration is unknownconcentration is unknown

in the in the oxyhemoglobinoxyhemoglobinassociation curve and may association curve and may improve tissue unloading of improve tissue unloading of oxygenoxygen

•• These factors should be kept These factors should be kept in mind when attempting to in mind when attempting to improve oxygen delivery to improve oxygen delivery to the tissuesthe tissues


Revised 01/14/2009 8


•• Question #2Question #2–– Is CI adequate to support VOIs CI adequate to support VO22I?I?

Check the CaCheck the Ca--vOvO22

Check the heart rate and stroke volumeCheck the heart rate and stroke volume



Check the CaCheck the Ca--vOvO22

–– If < 5 ml OIf < 5 ml O22/dl blood, CI is sufficient to /dl blood, CI is sufficient to t th b d ' d d ft th b d ' d d fmeet the body's demands for oxygenmeet the body's demands for oxygen

»» A large percentage of blood returned to A large percentage of blood returned to the heart is still oxygenatedthe heart is still oxygenated

–– If > 5 ml OIf > 5 ml O22/dl blood, an abnormally high /dl blood, an abnormally high percentage of oxygen is being extracted percentage of oxygen is being extracted from the blood from the blood

»» Attempts to increase CI and DOAttempts to increase CI and DO22I I should be undertakenshould be undertaken



Check the heart rate and stroke volumeCheck the heart rate and stroke volume–– CI = SVI x HRCI = SVI x HR–– High heart rates may reduce diastolic High heart rates may reduce diastolic

filling time impairing stroke volumefilling time impairing stroke volume–– Patients with tachycardia may benefit fromPatients with tachycardia may benefit from

»» Fluid resuscitationFluid resuscitation»» Judicious betaJudicious beta--blockadeblockade»» Correction of abnormal rhythmsCorrection of abnormal rhythms


•• Question #3Question #3–– Is consumption appropriate for demand? Is consumption appropriate for demand?

Check a lactic acid levelCheck a lactic acid level–– If > 2.0 If > 2.0 mmolmmol/L, anaerobic metabolism is /L, anaerobic metabolism is

ttpresentpresent»» CI and DOCI and DO22I should be optimizedI should be optimized»» If SvOIf SvO22 is normal, lactic acid is probably is normal, lactic acid is probably

due to prior anaerobic metabolismdue to prior anaerobic metabolism»» If SvOIf SvO22 is low, anaerobic metabolism is is low, anaerobic metabolism is

likely still occurringlikely still occurring


•• Question #4Question #4–– Is the patient's hypoxemia due to a pulmonary Is the patient's hypoxemia due to a pulmonary

problem (i.e., increased intrapulmonary shunt) problem (i.e., increased intrapulmonary shunt) OR to a low flow state (i.e., low CaOR to a low flow state (i.e., low Ca--vOvO22)?)?

Calculate the patient's intrapulmonary shuntCalculate the patient's intrapulmonary shuntCalculate the patient s intrapulmonary shunt Calculate the patient s intrapulmonary shunt (Q(Qspsp/Q/Qtt) )

INTRAPULMONARY SHUNT (INTRAPULMONARY SHUNT (QspQsp/Qt)/Qt)

•• Also known as "venous admixture“Also known as "venous admixture“

•• Blood which does not pass through ventilated Blood which does not pass through ventilated portions of the lung and leaves the lung portions of the lung and leaves the lung desaturateddesaturated

•• Normal intrapulmonary shunt is 2Normal intrapulmonary shunt is 2 5%5%•• Normal intrapulmonary shunt is 2Normal intrapulmonary shunt is 2--5%5%

•• May exceed 50% in patients with severe acute May exceed 50% in patients with severe acute respiratory distress syndrome (ARDS)respiratory distress syndrome (ARDS)

•• Commonly estimated using PCommonly estimated using PAAOO22--PPaaOO22

–– The “alveolarThe “alveolar--arterial” or “Aarterial” or “A--a gradient”a gradient”


Revised 01/14/2009 9

NORMAL INTRAPULMONARY SHUNTNORMAL INTRAPULMONARY SHUNT

•• There are three primary sources of normal There are three primary sources of normal QspQsp/Qt /Qt (i.e., deoxygenated blood leaving the left heart)(i.e., deoxygenated blood leaving the left heart)–– Bronchial artery blood which enters the Bronchial artery blood which enters the

pulmonary veins after giving up some of its pulmonary veins after giving up some of its oxygen to the bronchioxygen to the bronchioxygen to the bronchioxygen to the bronchi

–– DesaturatedDesaturated blood which enters the left ventricle blood which enters the left ventricle via the via the ThebesianThebesian veins after veins after perfusingperfusing the the myocardiummyocardium

–– Normal alveolar collapse in the apices of the Normal alveolar collapse in the apices of the lungs (West’s Zone I lung)lungs (West’s Zone I lung)

ABNORMAL INTRAPULMONARY SHUNTABNORMAL INTRAPULMONARY SHUNT

•• There are a number of sources There are a number of sources of of QspQsp/Qt in the critically ill/Qt in the critically ill–– AtelectasisAtelectasis–– Lobar pneumoniaLobar pneumonia

I h l ti i jI h l ti i j–– Inhalation injuryInhalation injury–– DrowningDrowning–– Acute Respiratory Distress Acute Respiratory Distress

Syndrome (ARDS)Syndrome (ARDS)–– Abdominal Compartment Abdominal Compartment

Syndrome (ACS)Syndrome (ACS)

INTRAPULMONARY SHUNTINTRAPULMONARY SHUNT

•• RepresentsRepresents anan "oxygen"oxygen refractory"refractory" hypoxemiahypoxemia–– Shunted blood is not exposed to ventilated alveoli Shunted blood is not exposed to ventilated alveoli –– CannotCannot bebe improvedimproved withwith supplementalsupplemental oxygenoxygen

regardlessregardless ofof thethe oxygenoxygen fractionfraction administeredadministered

O2

SvO2=0.75 SvO2=0.751.0 0.75

0.88

O2

INTRAPULMONARY SHUNT EQUATIONINTRAPULMONARY SHUNT EQUATION

•• Knowing how Knowing how QspQsp/Qt is calculated is important/Qt is calculated is important

•• DefinitionsDefinitions–– Qt = total cardiac outputQt = total cardiac output–– Qs = shunted portion of cardiac outputQs = shunted portion of cardiac outputQs shunted portion of cardiac outputQs shunted portion of cardiac output–– QnsQns = normal pulmonary end= normal pulmonary end--capillary blood capillary blood

flow that is not shunted past abnormal alveoliflow that is not shunted past abnormal alveoli

•• Therefore,Therefore,

Qt = Qs + Qt = Qs + QnsQns

Total blood flow = shunted + nonTotal blood flow = shunted + non--shunted bloodshunted blood


•• Further definitionsFurther definitions–– Qt * CaOQt * CaO22 = total oxygen delivered to the body= total oxygen delivered to the body

The equation for oxygen delivery (DOThe equation for oxygen delivery (DO22))–– Qs * CvOQs * CvO22 = total oxygen within shunted blood= total oxygen within shunted blood

No oxygen is added; content remains CvONo oxygen is added; content remains CvO22

–– QnsQns * CcO* CcO22 = total oxygen within end= total oxygen within end--capillary bloodcapillary blood

•• Therefore,Therefore,

Qt (CaOQt (CaO22) = Qs (CvO) = Qs (CvO22) + ) + QnsQns (CcO(CcO22))

Total oxygen delivered = sum of the oxygen within Total oxygen delivered = sum of the oxygen within shunted and nonshunted and non--shunted bloodshunted blood


Qt (CaOQt (CaO22) = Qs (CvO) = Qs (CvO22) + (Qt ) + (Qt -- Qs)(CcOQs)(CcO22) )

Substituting (Qt Substituting (Qt -- Qs) for Qns…Qs) for Qns…

Qt (CaOQt (CaO22) = Qs (CvO) = Qs (CvO22) + Qt (CcO) + Qt (CcO22) ) -- Qs (CcOQs (CcO22))

Rearranging…Rearranging…

Qs (CcOQs (CcO22 -- CvOCvO22) = Qt (CcO) = Qt (CcO22 -- CaOCaO22))

Further rearranging…Further rearranging…

QsQs (CcO(CcO22 -- CaOCaO22))Qt Qt (CcO(CcO22 -- CvOCvO22))

==

The “Shunt Equation”The “Shunt Equation”


Revised 01/14/2009 10


•• For those of you who are still awake, you will no For those of you who are still awake, you will no doubt remember the following fable from your doubt remember the following fable from your preschool days...preschool days...

The Pea MonsterThe Pea MonsterA Fable of pea eating A Fable of pea eating

monsters and oxygen transportmonsters and oxygen transport

Once upon a time, there was a pea eating monster who Once upon a time, there was a pea eating monster who lived near a pea factory. A train delivered the peas to lived near a pea factory. A train delivered the peas to the monster day and night. As long as the villagers the monster day and night. As long as the villagers delivered enough peas to the monster, he remained delivered enough peas to the monster, he remained

happy and didn’t terrorize the countryside.happy and didn’t terrorize the countryside.

NORMAL PEA DELIVERYNORMAL PEA DELIVERY

•• The train made 5 trips between the pea factory and The train made 5 trips between the pea factory and the monster every minute. Each train consisted of the monster every minute. Each train consisted of 5 cars with each car holding 40 peas.5 cars with each car holding 40 peas.

•• Therefore…Therefore…–– 5 trips per minute5 trips per minute–– 5 cars per train5 cars per train–– 40 peas per car40 peas per car–– 200 peas per train200 peas per train–– 1000 peas per minute1000 peas per minute

NORMAL PEA CONSUMPTIONNORMAL PEA CONSUMPTION

•• The pea monster ate 10 peas The pea monster ate 10 peas from each car as it passedfrom each car as it passed

•• Therefore, he consumed…Therefore, he consumed…–– 10 peas per car10 peas per carp pp p–– 50 peas per train50 peas per train–– 5 trains per minute5 trains per minute–– 250 peas per minute250 peas per minute

NORMAL PEA UTILIZATIONNORMAL PEA UTILIZATION

•• The villagers created the “pea utilization ratio” and The villagers created the “pea utilization ratio” and the “train car pea saturation” to monitor the monsterthe “train car pea saturation” to monitor the monster

Pea Utilization Ratio Pea Utilization Ratio = = Pea ConsumptionPea ConsumptionPea DeliveryPea Delivery

250 i250 i== 250 peas per min250 peas per min1000 peas per min1000 peas per min

= = 0.250.25

Train car pea saturationTrain car pea saturation == Delivery Delivery -- ConsumptionConsumptionDeliveryDelivery

== (1000(1000––750) peas per min750) peas per min1000 peas per min1000 peas per min

== 0.750.75


Revised 01/14/2009 11

NORMAL PEA RETURNNORMAL PEA RETURN

•• Peas delivered Peas delivered = 200 peas per train= 200 peas per train

•• Peas returned Peas returned = 150 peas per train= 150 peas per train

•• Peas consumed Peas consumed = 50 peas per train= 50 peas per train

POTENTIAL PROBLEMSPOTENTIAL PROBLEMS

•• If the Pea Monster gets hungry If the Pea Monster gets hungry and eats more peas, fewer and eats more peas, fewer peas are returned and the peas are returned and the factory may not be able to fully factory may not be able to fully y y yy y yload the train cars before the load the train cars before the train leaves the factory againtrain leaves the factory again

•• As a result, there will be fewer As a result, there will be fewer peas to deliver to the monster peas to deliver to the monster during the next tripduring the next trip


• The monster has short arms that limit how many peas he can reach. The first 10 peas (25%) are scooped off easily.


• The second 10 peas (50%) can be plucked out, but with some difficulty.


• The monster’s arms are too short to reach the bottom of the car and he cannot remove the bottom 20 peas!

PEA DELIVERYPEA DELIVERY

•• May be augmented by:May be augmented by:–– Increasing the number ofIncreasing the number of

Peas per carPeas per car–– Up to a point that the cars are fullUp to a point that the cars are full

Cars per trainCars per train–– More cars can be added to the trainMore cars can be added to the train

Trains per minuteTrains per minute–– The train can travel fasterThe train can travel faster

–– Improving the ease of pea removalImproving the ease of pea removal–– Increasing the rapidity of pea loadingIncreasing the rapidity of pea loading


Revised 01/14/2009 12

WHEN THE MONSTER’S NEEDS ARE MET…WHEN THE MONSTER’S NEEDS ARE MET… WHEN THE MONSTER’S NEEDS ARE WHEN THE MONSTER’S NEEDS ARE NOTNOT MET…MET…

Ever heard of my Ever heard of my cousin “Godzilla”??cousin “Godzilla”??

CAUSES OF AN UNHAPPY MONSTERCAUSES OF AN UNHAPPY MONSTER

•• Hungry monsterHungry monster

•• Too few carsToo few cars

•• Train too slowTrain too slow

•• Cars not full of peasCars not full of peas

•• Too few peasToo few peas

•• Wrong peasWrong peas

•• Peas missing carsPeas missing cars

•• Train missing loaderTrain missing loader

HUNGRY MONSTER HUNGRY MONSTER

•• 5 cars per train5 cars per train•• 5 trains per minute5 trains per minute•• 10 10 20 20 peas eaten per car peas eaten per car •• 50 50 100 100 peas eaten per trainpeas eaten per trainxxxx

•• 250 250 500 500 peas eaten per minutepeas eaten per minute•• 1000 peas delivered per minute1000 peas delivered per minute

Pea utilizationPea utilization = = 500500 peaspeas = = 0.500.501000 peas1000 peas

xx

TOO FEW CARSTOO FEW CARS

•• 5 trips per minute 5 trips per minute •• 5 5 44 cars per traincars per train•• 10 10 12.512.5 peas eaten per carpeas eaten per car•• 50 peas eaten per train50 peas eaten per train

xxxx

•• 200 200 160 160 peas delivered per trainpeas delivered per train•• 1000 1000 800 800 peas delivered per minutepeas delivered per minute

Pea utilizationPea utilization = = 250 peas250 peas = = 0.310.31800800 peaspeas

xxxx

•• 5 5 44 trips per minutetrips per minute•• 5 cars per train5 cars per train•• 10 10 12.512.5 peas eaten per carpeas eaten per car•• 50 50 62.562.5 peas eaten per trainpeas eaten per train

TRAIN TOO SLOWTRAIN TOO SLOW

xx

xxxx

•• 250 peas eaten per minute250 peas eaten per minute•• 1000 1000 800 800 peas delivered per minutepeas delivered per minute

Pea utilizationPea utilization = = 250 peas250 peas = = 0.310.31800800 peaspeas

xx


Revised 01/14/2009 13

HUNGRY MONSTER & SLOW TRAINHUNGRY MONSTER & SLOW TRAIN

•• 5 5 44 trips per minutetrips per minute•• 5 cars per train5 cars per train•• 10 10 20 20 peas eaten per carpeas eaten per car•• 50 50 100 100 peas eaten per trainpeas eaten per train

xx

xxxx

•• 250 250 400400 peas eaten per minutepeas eaten per minute•• 1000 1000 800 800 peas delivered per minutepeas delivered per minute

Pea utilizationPea utilization = = 400400 peaspeas = = 0.500.50800800 peaspeas

xxxx

•• 5 5 44 trips per minutetrips per minute•• 5 5 44 cars per traincars per train•• 40 40 3030 peas per carpeas per car

1010 11

HUNGRY MONSTER, SLOW TRAIN, HUNGRY MONSTER, SLOW TRAIN, TOO FEW CARS, CARS NOT FULLTOO FEW CARS, CARS NOT FULL

xxxxxxxx•• 10 10 15 15 peas eaten per carpeas eaten per car

•• 250 250 320320 peas eaten per minutepeas eaten per minute•• 1000 1000 480 480 peas delivered per minutepeas delivered per minute

Pea utilizationPea utilization = = 320320 peaspeas = = 0.660.66480480 peaspeas

xxxxxx

THE MORAL OF THE FABLE…THE MORAL OF THE FABLE…

•• Never heard of the “Fable of the Never heard of the “Fable of the Pea Monster”???Pea Monster”???–– Your preschool education Your preschool education

was obviously deficientwas obviously deficient

•• So what is the moral of the So what is the moral of the fable?fable?

LungsLungs

CellularCellularTissueTissue

HeartHeartHemoglobinHemoglobin

OxygenOxygen

THE MORAL OF THE FABLE…THE MORAL OF THE FABLE…

•• Hungry monsterHungry monster Increased consumptionIncreased consumption•• Too few carsToo few cars Low hemoglobinLow hemoglobin•• Train too slowTrain too slow Low cardiac outputLow cardiac output•• Cars not full of peasCars not full of peas Low oxygen saturationLow oxygen saturation•• Too few peasToo few peas Low FiOLow FiO22

•• Wrong peasWrong peas CarboxyhemoglobinCarboxyhemoglobin•• Peas missing carsPeas missing cars V/Q mismatchV/Q mismatch•• Train missing loaderTrain missing loader Intrapulmonary shuntIntrapulmonary shunt

If only it were that simple…If only it were that simple…


Revised 01/14/2009 14

CONCLUSIONSCONCLUSIONS

•• Assessment of oxygen transport balance through Assessment of oxygen transport balance through calculation of oxygen delivery, consumption, and calculation of oxygen delivery, consumption, and utilization is an essential part of utilization is an essential part of patient resuscitationpatient resuscitation

•• The oxygen transport parameters are useful The oxygen transport parameters are useful resuscitation endpoints in titrating therapy to ensureresuscitation endpoints in titrating therapy to ensureresuscitation endpoints in titrating therapy to ensure resuscitation endpoints in titrating therapy to ensure adequate tissue perfusion and oxygenationadequate tissue perfusion and oxygenation

oxygen transport calculations – m . l. cheatham, md...

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