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SSAI Gothenburg November 2019
Transpulmonary indicator dilution method
Per Werner Möller – M.D.•Head of section Operating theatres and Anaesthesia, Department of Anaesthesiology and Intensive Care Medicine, Östra sjukhuset, Sahlgrenska University Hospital, Gothenburg•Department of Anaesthesiology and Intensive Care Medicine, Institute of Clinical Sciences at the Sahlgrenska Academy, University of Gothenburg, Sahlgrenska University Hospital, Gothenburg, Sweden•Visiting Investigator, Department of Intensive Care Medicine, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland
Continous pulse contour cardiac output monitoring
• AUC of systolic part of pulse curve is proportional to SV• Thermodilution gives instantaneous CO and actual SV is calculated from HR• Arterial impedance (a combination of vessel tree resistance and compliance)
is calculated• Under the assumption of unchanged impedance, the system provides beat-to-
beat SV from continous pulse contour analysis
Volumetric measures derived from transpulmonary thermodilution• Global End-Diastolic Volym; GEDV• Extravascular Lung Water; EVLW
The software takes into account the individual aortic compliance and
systemic vascular resistance based on the following considerations.
During systole, more blood is ejected from the left ventricle into the aorta
than actually leaves the aorta. During the subsequent diastole, the volume
remaining in the aorta flows into the arterial network at a rate
determined by the aortic compliance (C), systemic vascular resistance (R),
and the blood pressure (Windkessel effect)
The shape of the arterial pressure curve after the dicrotic notch is
representative for this passive emptying of the aorta (exponential decay
time = R × C). The systemic vascular resistance, R, is determined by the
quotient of mean arterial pressure (MAP) and cardiac output measured by
the reference method (R = MAP ⁄ CO). As the decay time and R are
known, the compliance, C, can be computed.
Thermodilution curves
Higher flow
Reference curve dashed
Lower flow
Reference curve dashed
Larger amount of indicator…
… or smaller distribution volume for indicator
Reference curve dashed
m = amount of indicatorAUC = area under the curve
Example:10 mg of indicator is injectedand concentration over time is determined down stream
Modified for temperature as indicator:
Factor K:corrects for differences in heat conductance and heat capacitance between injectate and blood
Transit time for particle 1, travelling with flow Q1 equal to:
…distribution frequency histogram of transit times
MTt = mean transit time
Distribution volume for indicator
For intravascular indicator:
For thermal indicator:
The distribution volume for a thermal indicator extends beyond the vessel bed
Dilution curve with exponential decay
Lin-log transformation allows circumvention of the problem with recirculation
Time, linear
Time, linear
Time, linear
Small distribution volume
Large distribution volume
Slope is proportional to distribution volume and flow
Small
Large
The flow thru the system and the size of the largest distribution volume will decide the properties of the dilution curve…
…it is irrelevant where in the series the ”bathtub” is located
In transpulmonary thermodilution, the single largest distribution volume is Pulmonary Thermal Volume (PTV)
Therefore, it is PTV and CO that determines the slope of the indicator dilution curve
PTV is pulmonary blood volume and surrounding structures involved in thermal equilibrium
Circulation 1951;4;735-746
Down Slope Time, DSt = the time that multiplied with CO gives PTV
• AUC and known amount of indicator gives CO
• MTt×CO = ITTV = total distribution volume
• DSt×CO = PTV = largest included volume
ITTV = CO ×MTt
PTV = CO×DSt
ITBV = CO ×MTt ICG
Intrathoracic blood volume
ITBV = GEDV+PBV+part of caval vein+part of aorta to tip of catheter
A volumetric measure of central blood volume
Method dependent rather true anatomical definition
Determined by use of intravascular indicator; ITBV = CO×MTt ICG
intrathoracic blood volume
Several studies demonstrate how ITBV correlates to SV or CO
Whereas CVP and PAOP does not;
•In septic shock
•In hemorrhage
•Intraoperatively for different types of surgery
RA RC PBV LA LC
Comparison Between Intrathoracic Blood Volume and Cardiac
Filling Pressures in the Early Phase of Hemodynamic Instability of
Patients With Sepsis or Septic Shock
Sakka et al. Journal of Critical Care, Vol 14, No 2 (June), 1999, pp 78-83
Can this really be true?
There is a physiological relation between GEDV and PBV
…in porcine models of extreme hemorrhage
…for different rates of cathecholamine infusion
…not affected by infusion of dobutamine
…not affected by concomitant pulmonary hypertension
After pulmonary resection, the ratio of PBV/GEDV is changed;Pulmonary blood volume decreases in relation to GEDV
ITBV is overestimated by approx. 10% after pulmectomy
Extravascular lung water (EVLW) is underestimated
Extravascular lung water
A measure of the amount of water in the lung...
…or the amount of tissue in the thorax, other than ITBV, involved in thermal equilibrium
EVLW normally <7mL/kg (Predicted Body Weight)EVLW >7mL/kg indicates hydrostatic or inflammatory edema
EVLW increases: in pneumoniain pulmonary edemain alveolar fluidin ARDS
…alternatively PTV-PBV=EVLW
Prognostic value?
In an ICU population the mortality was 65% for EVLW>15mL/kg
and 33% for EVLW<10mL/kg
The prognostic value of EVLW at ICU admission was highar than APACHE
II score
Diagnostic value?
To better characterize patients with ARDS
The ratio of EVLW/ITBV (or EVLW/GEDV) is significantly higher in
”permeability edema” than in hydrostatic edema
Therapeutic value?
Hemodynamic management based on fluid restriction guided by ITBV (or
GEDV) and EVLW vs. therapy guided by PAOP gave fewer days on
ventilator and fewer days in the ICU
Potential sources of error
Experimentally - EVLW is underestimated by obstruction of pulmonary vessels with
diameter >0.5 mm
thermal indicator does not get access to the ”true” distribution volume
However – temperature is excellently conducted in water and can reach equilibrium
in spite of vascular obstruction
Clinically, obstruction of smaller pulmonary vessels is more problematic (compare
ARDS or PEEP effect)
•High levels of PEEP (in respect to central blood volume) can induce perfusion
defects (West zone 1) leading to underestimation of EVLW
•Recruitment maneuvers can open pulmonary perfusion and thereby give the thermal
indicator access to to higher Vd reporting higher EVLW
•But of course, PEEP also give CO or PAOP and decrease EVLW
…in summary PEEP can affect the measurement and the prevalence of EVLW
Potential sources of error
Focal pulmonary injury from ALI or acte cardiac edema gives a severely diminished
HPV;
therefore pulmonary flow is not so much deviated away from the injured
areas and this makes the method robust
ITTV=CO*MTt
PTV=CO*DSt