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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