thermodilution technique to estimate cardiac output to estimate

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Thermodilution technique Thermodilution technique to estimate cardiac outputto estimate cardiac output

ADVANTAGES AND LIMITATIONSADVANTAGES AND LIMITATIONS––THE AVAILABLE TECHNIQUES THE AVAILABLE TECHNIQUES

to estimate cardiac outputto estimate cardiac output

Azriel PerelP f d Ch iProfessor and Chairman

Department of Anesthesiology and Intensive CareSheba Medical Center, Tel Aviv University, Israel

Rome 2009

Disclosure

Th k t ith th f ll i iThe speaker cooperates with the following companies

BMeye

Drager-Siemens

Pulsion

[email protected]

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Cardiac Output Monitoring using Indicator Dilution Techniques:

Template for Review Article, Anesthesia & AnalgesiaCopyright © 2009 by the International Anesthesia Research Society

Basics, Limits, and Perspectives.

Daniel A. Reuter, MD, PhD+

Huang C*, Edrich T*, Shernan SK*, Eltzschig HK*°+ Department of Anesthesiology, Hamburg-Eppendorf University Hospital, Hamburg, Germany

• Department of Anesthesiology, Perioperative, and Pain Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, USA

° Department of Anesthesiology and Intensive Care Medicine, Tuebingen University Hospital, Tuebingen, GermanyDepartment of Anesthesiology and Perioperative Medicine, University of Colorado Denver, Aurora, CO, USA

Proceedings of the Würzburg Physikalische Medizinische Gesellschaft for July 9, 1870

Adolf Fick

“It is astonishing that no one has arrived at the following obvious method by which the amount of

blood ejected by the ventricle of theblood ejected by the ventricle of the heart with each systole may be

determined directly …”

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Researches on the circulation time and on the influences which affect it. IV. The output of the heart.

Stewart GN. Physiol 1897; 22: 159-83

In 1897 Stewart injected a bolus of a sodium chloride solution into the central venous circulation of anesthetized dogs and rabbits, and then collected blood samples containing diluted sodium chloride from a femoral artery catheter. An electric o a e o a a te y cat ete e ect ctransducer on the contralateral femoral artery sensed the arrival of diluted injectate.

A cardiac output measurement by indicator dilution has three principal phases:

(a) an indicator is brought into the circulation (injection)

(b) the indicator mixes with the bloodstream (mixing and dilution)

(c) the concentration of the indicator is determined downstream (detection).

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The StewartThe Stewart--Hamilton formulaHamilton formula

VCtVF 00/ F =C0 V0

∫

Contrary to his own observations, Stewart assumed in his formula that the indicator concentration at the collection site rises and declines in a stepwise

tCtVF

1

001 / ==

.

Fc(t)dt

t∫

collection site rises and declines in a stepwise manner over the collection interval.

The Hamilton formula (1928) introduced the concept of an explicit time-concentration curve.

F =C0 V0

c(t)dt∫

The StewartThe Stewart--Hamilton formula Hamilton formula (time-concentration curve)

CO =

( )t∫

area of dilution curve

amount of injected indicator

This technique, using indocyanine green as indicator and a continuous withdrawal of blood into a sensing cuvette, was the conventional indicator dilution method used to measure cardiac output in critically ill patients until the 1970’s.

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The thermodilution method adapts the indicator-dilution principle to injectates that cause changes in blood temperature detected downstream

The thermodilution (TD) method

blood temperature detected downstream.

An injectate of known volume and temperature is injected into the right atrium and the cooled blood traverses a thermistor in a major vessel branch downstream over a duration of time.

The cardiac output is inversely proportional to the p y p pmean blood-temperature depression and the duration of transit of cooled blood (i.e. area under the curve).

∫Δ−

==

tB

B

dtTKTTV

tVF 1001 )(

Catheterization of the heart in man with use of a flow-directed balloon-tipped catheter.Swan HJ, Ganz W, Forrester J, Marcus H, Diamond G, Chonette D. N Engl J Med 1970; 283: 447-51

A new technique for measurement of cardiac output q pby thermodilution in man. Ganz W, Donoso R, Marcus HS, Forrester JS, Swan HJ. Am J Cardiol 1971; 27: 392-6

Following the introduction of the pulmonary artery catheter (PAC) into clinical practice, the single-bolus thermodilution measurement of cardiac output has beenthermodilution measurement of cardiac output has been widely accepted as the “clinical standard” for advanced hemodynamic monitoring. In fact, it is still considered to be the clinical gold-standard against which new technologies are validated and compared.

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Pulmonary thermodilution (P-TD) with a PAC

The introduction of the cold injectate causes a rapid upslope to a peak, a gradual downslope, and an exponentialp , g p , pdecay of the thermal signal. The CO computer begins integration of the area under the TD curve until the exponential decay reaches a value of about 30%, and extrapolates the exponential decay to baseline in order to minimize artifacts due to recirculation of the indicator.

Sources of measurement error and variability (P-TD)

Loss of indicator prior to injection – when the actual amount of cold indicator entering the circulation is less than the “assumed quantity” the mean bloodis less than the “assumed quantity”, the mean blood-temperature depression (the AUC) would be smaller leading to overestimation of the true cardiac output.

Inaccurate filling of syringes

Occult warming of cold indicator prior to injection

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Loss of indicator during injection

The factors that determine loss of indicator during


ginjection include the intraluminal surface area, the dead space of the catheter lumen (0.7-1 ml), the injectate volume, temp gradient, and injection rate.

Dissipation of cold indicator through the warm intravascular portions of the catheter can be partially circumvented by measuring the temp of the injectatecircumvented by measuring the temp of the injectate immediately before entering the catheter and employing a corrective, catheter-specific computation constant.

For practical considerations, it is recommended to discard the first measurement because it is most prone to incorrect results.

Loss of indicator after injection

Conductive rewarming of indicator by surrounding


g y gtissue is more pronounced in low-flow states, or when the indicator travels longer distances en route to the arterial thermistor (TP-TD). The heat loss can lead to falsely elevated CO’s.

Diversion of cold indicator from its normal itinerary (e g right-to-left intracardiac shunt venovenous(e.g., right-to-left intracardiac shunt, venovenous extracorporeal lung assist, or certain instances of tricuspid regurgitation) may also cause falsely elevated CO’s.

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Variation of injectate temperature and volume

When room-temperature (RT) injectate is used,


p ( ) j ,less indicator is lost but the initial thermal signal is smaller than with iced injectate, magnifying the relative effect of lost indicator on the computed result.

RT injectate is less accurate in low and in high flow states The highest reproducibility of COflow states. The highest reproducibility of CO measurements by P-TD in critically ill patients was demonstrated with 10 ml iced injectate.

Cyclic changes in cardiac output

Spontaneous or mechanical ventilation affect the


pactual cardiac output, with stroke output variations (mainly RV) reaching 50% at various phases of the respiratory cycle.

Although successive thermodilution CO measurements are most reproducible when performed at the same point in the respiratory cycleperformed at the same point in the respiratory cycle, the averaging of multiple measurements at different phases of the respiratory cycle is recommended.

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Loss of indicator prior to injectionLoss of indicator during injectionL f i di t ft i j ti


Loss of indicator after injectionVariation of injectate temperature and volumeCyclic changes in cardiac outputTransient lowering of the heart rate during cold

indicator injectionRecirculation and detainment of indicatorTricuspid regurgitationFluctuations in baseline temperatureTruncation and extrapolation of TD curves

CO = amount of indicator injected/area of dilution curve

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Reliability of the thermodilution method in the determination of cardiac output in clinical practice

Stetz CW, Miller RG, Kelly GE, Raffin TA Am Rev Respir Dis 1982; 126: 1001-1004

The intrinsic limits on the reproducibility of pulmonary thermodilution cardiac output measurements require a measured change of approximately 22% (or 13% for triplicate measurements) for the difference to be statistically significant.

The acceptance of a new method for the measurement of cardiac output should be judged against the ±10-20% accuracy of the current reference method (e gaccuracy of the current reference method (e.g. thermodilution).

Consequently, we recommend that limits of agreement between the new and the reference technique of up to 30% be accepted.

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New methods for the measurement of CO are usually validated against the intermittent thermodilution technique, which has an assumed precision of ±20% or less.

The combination of this precision with an assumed similarThe combination of this precision with an assumed similar precision of the new technique, equates to a total error of ±28.3%, which is commonly rounded up to ±30%.

Clinicians therefore often use the 30% error as a cutoff in order to validate a new technique.

Comparison studies should however report the precision of the reference technique as it may be either more or less precise than would normally be expected.

A more precise reference technique may lead to an unjustifiable validation of an unacceptably imprecise new technique.

A less precise reference technique may lead to an unjustifiable rejection of an acceptably precise new technique.

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Advantages of P-TD

The standard method for CO measurement.

Good correlation with earlier methods.

Simple measurement technique.

Repeated measurements possible.

The PAC may provide calibrated CCO.

The PAC provides, in addition, PA pressures, PAOP, mixed-venous oxygen saturation, and optionally, RVEF and RVEDV.

Limitations P-TD

Intrinsic limitation of the reproducibility ofIntrinsic limitation of the reproducibility of measurements.

Inherent limits on the frequency and number of measurements.

Complications associated with placement and presence of a PAC.p

PAC-based CCO may not be clinically useful during periods of hemodynamic instability since it is averaged with time delay (not real-time).

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Pulmonary TD Transpulmonary TDPulmonary TD Transpulmonary TD

(PAC) (PiCCO) (PAC) (PiCCO)

Central venous catheterCentral venous catheter

The PiCCO The PiCCO

• FemoralFemoral

•• AxillaryAxillary

•• BrachialBrachial

• Radial (long)Radial (long)

ThermistorThermistor--tipped tipped arterial catheterarterial catheter

{

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lung

Transpulmonary Indicator Dilution Technique

bolus -Injection

aorta

0.0

0.1

0.2

0.3

−ΔT in °C

CVC

[s]0 10 20 30 40 50

Thermistor-tippedcatheter

Pulmonary (P) and transpulmonary (TP) thermodilution curves after injection of cold saline into the SVC

PP

TPTP

PP

The pulmonary artery TD curve appears earlier and has a higher peak temperature than the femoral artery TD curve. Thereafter, both curves soon re-approximate baseline.

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Measures of agreementStudy parameters

Investigators (year) PrecisionBiasrnNAgesPatient population

11%+1 9%0 931866224 66Liver transplantDella Rocca 2002

Comparisons of TP-TD to P-TD CO measurements using a single bolus of cold injectate

11%+1.9%0.931866224–66Liver transplantDella Rocca 2002

27.3%10.3%ni32529NiSevere heart failureFriesecke 2009

11%+4.9%0.932162441–81Cardiac surgeryGoedje 1999

7.3%+8.0%0.971092319–78BurnsHolm 2001

nini0.811131421–61BurnsKuntscher 2002

4 8%+4 3%ni60101 – 8PediatricsMcLuckie 1996 4.8%+4.3%ni60101 8PediatricsMcLuckie 1996

10%+4.1%0.911902027–79Intensive care unitSegal 2002

12%–4.7%0.9748210.5–25Cardiologyvon Spiegel 1996

7.6%+7.4%0.96361843–73Cardiac surgeryWiesenack 2001

12%–0.33%0.911601819–75ARDSZöllner 1998

CO determination by TPTD is reliable and agrees well with the results from pulmonary artery p y ythermodilution in patients with severe left ventricular dysfunction.

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Correlation of CO measured by the transpulmonary thermodilution technique and by the Fick method in small children.

Tibby SM et alI t i CIntensive Care Medicine 23:987-91, 1997

Monitoring Right-to-Left Intracardiac Shunt in ARDSMichard F et al. Crit Care Med 2004; 32:308

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Looking at Transpulmonary Thermodilution Curves:The Cross-Talk Phenomenon

Michard F. Chest 2004; 126:656

The use of venous and thermistor-tipped arterial catheterson the same side and of the same length should be avoided in patients monitored with transpulmonary thermodilution.

Sources of measurement error and variability (TP-TD)

The TP-TD CO is measured over a longer duration than P-TD and reflects LV output. As a result, TP-TD is less affected (i.e., is slightly higher than P-TD) by the cold-induced transient lowering of the heart rate during cold indicator injection, and by the respiratory variations in CO.

The longer distance between the injection and sampling sites may theoretically increase indicator loss and effects of recirculation. Yet about 96–97% of the indicator that reaches the pulmonary artery is recovered in the aorta. In addition,the pulmonary artery is recovered in the aorta. In addition, the effects of indicator loss and indicator recirculation tend to cancel one another.

Indicator loss may be increased when the EVLW is elevated, necessitating an increase in the amount of the injectate (automatically prompted by the PiCCO).

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P [mm Hg]

CCO by the pulse contour method

PCCO = cal • HR •⌠⌡P(t)SVR + C(p) • dP

dt( ) dt

t [s]

Area of pressure curve

Shape of pressure curve

⌡Systole

SVR (p) dt( )

ComplianceHeart rate

Patient-specific calibration factor (determined with thermodilution)

The pulse contour cardiac output of the PiCCO was demonstrated to agree with P-TD CO

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SV

Effects of increase in pacemaker rateWhy do we need Why do we need

realreal--time CCO?time CCO?

The intrinsic limited reproducibilityThe intrinsic limited reproducibility of intermittent TD CO measure-ments highlights the importance of continuously measured real-time CO in assessing the response to therapeutic or diagnostic events.

HR

CCOFluid loading

Inotropes

Passive leg raising

injectionc (I)

Advanced indicator dilution curve analysisAdvanced indicator dilution curve analysis

ln c (I)

injection

recirculation

AtMTt t

e-1

DSt

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ITTV = CO * MTtTDa RAEDV RVEDV LAEDV LVEDVPBV

EVLW

EVLW

EVLW

PTV = CO * DStTDa

ITBV* 1 25 * GEDV

GEDV = ITTV - PTV RAEDV RVEDV LAEDV LVEDV

PBV

EVLW

PTV

ITBV* = 1.25 * GEDV RAEDV RVEDV LAEDV LVEDVPBV

EVLW = ITTV-ITBVEVLW

EVLW

Advantages of TP-TD

Good correlation with P-TD.

Less invasive than the PAC, avoiding risks of PA rupture, pulmonary embolism, etc.

Most critically ill patients do have CVP and art line anyway.

Simple measurement technique; repeated measurements possible.

Less influenced by respiratory variations than P-TD.

Real-time (calibrated) CCO by the pulse contour method (+SVV).

The PiCCO provides several other important parameters (e.g., GEDV, EVLW, PPV; ScvO2 available).

May be used in children.

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Limitations of TP-TD

Inherent methodological and statistical limitations as th P TDthe P-TD.

Complications associated with placement and presence of a CV line and a (large) arterial line.

Smaller temperature changes necessitate steady baseline temp and the use of cold injectate (especially when EVLW is increased)when EVLW is increased).

Inherent limits on the frequency and number of measurements.

Does not provide PA pressure and SvO2.

Conclusions

The thermodilution method is the clinical gold-standard for the measurement of CO.

The P-TD and TP-TD are practically equal in their accuracy.

Each of these techniques offers additional information besides the CO.

The choice of monitoring technique isThe choice of monitoring technique is therefore largely affected by the additional information that is offered and by the presumed associated morbidity of each of these techniques.

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Thank you!

Special thanks to

Daniel A. Reuter, MD, PhD

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Intensive Care Med. 2006 ;32:919-22

CCO assessment by the PAC is an averaging technique. The value indicated by the device is a mean value reflecting the data collected in the past 3–6 min. Thus, more rapid changes in CO could not be reflected by CCO data.

thermodilution technique to estimate cardiac output to estimate

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