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THE AVAILABLE TECHNIQUES – ADVANTAGES AND LIMITATIONS
Thermodilution technique
to estimate cardiac output
Azriel Perel
Professor
P
f
and
d Ch
Chairman
i
Department of Anesthesiology and Intensive Care
Sheba Medical Center, Tel Aviv University, Israel
Rome 2009
Disclosure
Th speaker
The
k cooperates
t with
ith the
th following
f ll i companies
i
BMeye
Drager-Siemens
Pulsion
[email protected]
1
Template for Review Article, Anesthesia & Analgesia
Copyright © 2009 by the International Anesthesia Research Society
Cardiac Output Monitoring using
Indicator Dilution Techniques:
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, Germany
Department 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 the
heart with each systole may be
determined directly …”
2
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
¾ 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
o a femoral
e oa a
artery
te y cat
catheter.
ete An e
electric
ect c
transducer 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).
3
The Stewart
Stewart--Hamilton formula
F =V1 / t =
F=
C0V0
C1 t
C0 V0
∫ c(t)dt
t
¾ Contrary to his own observations, Stewart assumed
in his formula that the indicator concentration at the
collection site rises and declines in a stepwise
manner over the collection interval.
¾ The Hamilton formula (1928) introduced the concept
of an explicit time-concentration curve.
The Stewart
Stewart--Hamilton formula (time-concentration curve)
F=
C0 V0
()
∫ c(t)dt
t
amount of injected indicator
CO =
area of dilution curve
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.
4
.
The thermodilution (TD) method
¾ The thermodilution method adapts the indicatordilution principle to injectates that cause changes in
blood temperature detected downstream
downstream.
¾ 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.
¾ The cardiac output
p is inversely
yp
proportional
p
to the
mean blood-temperature depression and the duration
of transit of cooled blood (i.e. area under the curve).
F=
V1 V0 (TB − T0 ) K1
=
t
∫ ΔTB dt
t
Catheterization of the heart in man with use of a flowdirected 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
q for measurement of cardiac output
p
by thermodilution in man.
Ganz W, Donoso R, Marcus HS, Forrester JS, Swan HJ.
J Cardiol 1971; 27: 392-6
Am
Following the introduction of the pulmonary artery
catheter (PAC) into clinical practice, the single-bolus
thermodilution 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.
5
Pulmonary thermodilution
(P-TD) with a PAC
The introduction of the cold injectate causes a rapid upslope
to a p
peak,, a g
gradual downslope,
p , and an exponential
p
decay 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)
¾ Loss of indicator prior to injection – when the
actual amount of cold indicator entering the circulation
is less than the “assumed quantity”
quantity”, the mean blood
bloodtemperature depression (the AUC) would be smaller
leading to overestimation of the true cardiac output.
¾ Inaccurate filling of syringes
¾ Occult warming of cold indicator prior to injection
6
Sources of measurement error and variability (P-TD)
¾ Loss of indicator during injection
¾ The factors that determine loss of indicator during
g
injection include the intraluminal surface area, the dead
space of the catheter lumen (0.7-1 ml), the injectate
volume, temp gradient, and injection rate.
¾ Dissipation of cold indicator through the warm
intravascular portions of the catheter can be partially
circumvented by measuring the temp of the injectate
immediately before entering the catheter and employing a
corrective, catheter-specific computation constant.
¾ For practical considerations, it is recommended to
discard the first measurement because it is most prone to
incorrect results.
Sources of measurement error and variability (P-TD)
¾ Loss of indicator after injection
g of indicator by
y surrounding
g
¾ Conductive rewarming
tissue 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.
¾ Diversion of cold indicator from its normal itinerary
(e g right-to-left intracardiac shunt
(e.g.,
shunt, venovenous
extracorporeal lung assist, or certain instances of
tricuspid regurgitation) may also cause falsely
elevated CO’s.
7
Sources of measurement error and variability (P-TD)
¾ Variation of injectate temperature and volume
¾ When room-temperature
p
((RT)) injectate
j
is used,,
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.
¾ RT injectate is less accurate in low and in high
flow states
states. The highest reproducibility of CO
measurements by P-TD in critically ill patients was
demonstrated with 10 ml iced injectate.
Sources of measurement error and variability (P-TD)
¾ Cyclic changes in cardiac output
p
or mechanical ventilation affect the
¾ Spontaneous
actual cardiac output, with stroke output variations
(mainly RV) reaching 50% at various phases of the
respiratory cycle.
¾ Although successive thermodilution CO
measurements are most reproducible when
performed at the same point in the respiratory cycle
cycle,
the averaging of multiple measurements at different
phases of the respiratory cycle is recommended.
8
Sources of measurement error and variability (P-TD)
¾ Loss of indicator prior to injection
¾ Loss of indicator during injection
¾ Loss
L
off indicator
i di t after
ft injection
i j ti
¾ Variation of injectate temperature and volume
¾ Cyclic changes in cardiac output
¾ Transient lowering of the heart rate during cold
indicator injection
¾ Recirculation and detainment of indicator
¾ Tricuspid regurgitation
¾ Fluctuations in baseline temperature
¾Truncation and extrapolation of TD curves
CO = amount of indicator
injected/area of dilution curve
9
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.
¾ 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
(e.g.
g
thermodilution).
¾ Consequently, we recommend that limits of agreement
between the new and the reference technique of up to
30% be accepted.
10
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 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.
11
Advantages of P-TD
¾ The standard method for CO measurement.
¾ Good correlation with earlier methods.
¾ Simple measurement technique.
¾ Repeated measurements possible.
¾ The PAC may provide calibrated CCO.
¾ The PAC provides, in addition, PA pressures, PAOP,
mixed-venous oxygen saturation, and optionally, RVEF
and RVEDV.
Limitations P-TD
¾ Intrinsic limitation of the reproducibility of
measurements.
¾ Inherent limits on the frequency and number of
measurements.
¾ Complications associated with placement and
p
presence
of a PAC.
¾ PAC-based CCO may not be clinically useful during
periods of hemodynamic instability since it is averaged
with time delay (not real-time).
12
Pulmonary TD
(PAC)
Transpulmonary TD
(PiCCO)
The PiCCO
Central venous catheter
• Femoral
Thermistor-tipped
Thermistorarterial catheter
• Axillary
• Brachial
• Radial (long)
13
{
Transpulmonary Indicator Dilution Technique
lung
aorta
CVC
−ΔT in °C
0.3
0.2
bolus Injection
0.1
0.0
0
10
20
30
40
50
[s]
Thermistor-tipped
catheter
Pulmonary (P) and transpulmonary (TP) thermodilution
curves after injection of cold saline into the SVC
P
TP
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.
14
Comparisons of TP-TD to P-TD CO measurements using a
single bolus of cold injectate
Study parameters
Investigators (year)
Measures of agreement
Patient population
Ages
N
n
r
Bias
Precision
Della Rocca 2002
Liver transplant
24 66
24–66
62
186
0 93
0.93
+1 9%
+1.9%
11%
Friesecke 2009
Severe heart failure
Ni
29
325
ni
10.3%
27.3%
Goedje 1999
Cardiac surgery
41–81
24
216
0.93
+4.9%
11%
Holm 2001
Burns
19–78
23
109
0.97
+8.0%
7.3%
Kuntscher 2002
Burns
21–61
14
113
0.81
ni
ni
McLuckie 1996
Pediatrics
1– 8
10
60
ni
+4 3%
+4.3%
4 8%
4.8%
Segal 2002
Intensive care unit
27–79
20
190
0.91
+4.1%
10%
von Spiegel 1996
Cardiology
0.5–25
21
48
0.97
–4.7%
12%
Wiesenack 2001
Cardiac surgery
43–73
18
36
0.96
+7.4%
7.6%
Zöllner 1998
ARDS
19–75
18
160
0.91
–0.33%
12%
CO determination by TPTD
is reliable and agrees well
with the results from
pulmonary
p
y artery
y
thermodilution in patients
with severe left ventricular
dysfunction.
15
Correlation of CO
measured by the
transpulmonary
thermodilution
technique and by the
Fick method in small
children.
Tibby SM et al
I t
Intensive
i Care
C
Medicine
23:987-91, 1997
Monitoring Right-to-Left Intracardiac Shunt in ARDS
Michard F et al. Crit Care Med 2004; 32:308
16
Looking at Transpulmonary Thermodilution Curves:
The Cross-Talk Phenomenon
Michard F. Chest 2004; 126:656
The use of venous and thermistor-tipped arterial catheters
on 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)
¾ 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 coldinduced transient lowering of the heart rate during cold
indicator injection, and by the respiratory variations in CO.
¾ 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 effects of indicator loss and indicator recirculation tend to
cancel one another.
¾ Indicator loss may be increased when the EVLW is
elevated, necessitating an increase in the amount of the
injectate (automatically prompted by the PiCCO).
17
CCO by the pulse contour method
P [mm Hg]
t [s]
⌠
PCCO = cal • HR • ( P(t) + C(p)
(p) • dP ) dt
⌡ SVR
dt
Systole
Patient-specific Heart
calibration factor rate
(determined with
thermodilution)
Area of
pressure
curve
ComplianceShape of
pressure
curve
The pulse contour cardiac output of the PiCCO was
demonstrated to agree with P-TD CO
18
Effects of increase in
pacemaker rate
Why do we need
real--time CCO?
real
SV
The intrinsic limited reproducibility
of intermittent TD CO measurements highlights the importance of
continuously measured real-time
CO in assessing the response to
therapeutic or diagnostic events.
¾ Fluid loading
CCO
¾ Inotropes
¾ Passive leg raising
HR
Advanced indicator dilution curve analysis
c (I)
injection
recirculation
ln c (I)
e-1
At
MTt
19
DSt
t
EVLW
ITTV = CO * MTtTDa
RAEDV
RVEDV
PBV
LAEDV
LVEDV
LAEDV
LVEDV
LAEDV
LVEDV
EVLW
EVLW
PTV = CO * DStTDa
PBV
PTV
EVLW
GEDV = ITTV - PTV
RAEDV
RVEDV
ITBV* = 1.25
1 25 * GEDV
RAEDV
RVEDV
PBV
EVLW
EVLW = ITTV-ITBV
EVLW
Advantages of TP-TD
¾ Good correlation with P-TD.
¾ Less invasive than the PAC, avoiding risks of PA
rupture, pulmonary embolism, etc.
¾ Most critically ill patients do have CVP and art line
anyway.
¾ Simple measurement technique; repeated
measurements possible.
¾ Less influenced by respiratory variations than P-TD.
¾ Real-time (calibrated) CCO by the pulse contour
method (+SVV).
¾ The PiCCO provides several other important
parameters (e.g., GEDV, EVLW, PPV; ScvO2 available).
¾ May be used in children.
20
Limitations of TP-TD
¾ Inherent methodological and statistical limitations as
th P-TD.
the
P TD
¾ Complications associated with placement and
presence of a CV line and a (large) arterial line.
¾ Smaller temperature changes necessitate steady
baseline temp and the use of cold injectate (especially
when EVLW is increased).
increased)
¾ Inherent limits on the frequency and number of
measurements.
¾ Does not provide PA pressure and SvO2.
Conclusions
¾ The thermodilution method is the clinical
gold-standard for the measurement of CO.
¾ The P-TD and TP-TD are practically equal
in their accuracy.
¾ Each of these techniques offers additional
information besides the CO.
¾ The 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.
21
Thank you!
Special thanks to
Daniel A. Reuter, MD, PhD
22
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.
23