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FloTrac Algorithm Calculating stroke volume and getting mL/beat from mmHg

Summary Traditional: CO = HR * SV

The FloTrac algorithm, an arterial pressure-based cardiac FloTrac system: APCO= PR x (sAP * x) output (APCO) method in which cardiac output can be Where x = M (HR, s , C(P), BSA, MAP, µ3 , µ4 ...) AP ap ap continuously calculated using an arterial catheter. This s = standard deviation of arterial pressure technology is based on the basic principles of physics AP in mmHg is proportional to and the application of a sophisticated algorithm. x = scaling multivariate parameter proportional Physics and physiology to the effects of vascular tone on pulse pressure Flow is determined by a pressure gradient along a M = multivariate polynomial equation vessel and the resistance to that flow (F=ΔP/R). The FloTrac algorithm uses a similar principle to calculate BSA =body surface area calculated by Dubois’ pulsatile flow by incorporating the effects of both equation for body surface area and compliance through a MAP = calculated by conversion factor known as Khi ( ). x taking sum of sampled pressure point values over 20 seconds and dividing it by the number Cardiac output is an important component of of pressure points global oxygen delivery (DO2) and is the most often manipulated variable when improving oxygen delivery. µ = statistical moments determined by skewness Cardiac output is calculated by multiplying rate (symmetry) and kurtosis (distinctness of a peak) by the stroke volume. The FloTrac algorithm uses these calculated along several mathematical derivatives same components but substitutes with the pulse rate (PR), capturing only truly perfused beats, Arterial pressure-based cardiac output and multiplies PR by a calculated stroke volume. Stroke The FloTrac algorithm is based on the principle that volume is calculated from the patient’s arterial pressure aortic pulse pressure is proportional to stroke volume to analyze the arterial pressure waveform using the (SV) and inversely related to aortic compliance. unique FloTrac algorithm. The FloTrac algorithm analyzes the pressure waveform at one hundred times per second Standard deviation of arterial pressure over 20 seconds, capturing 2,000 data points for analysis. Initially, the FloTrac algorithm assesses pulse pressure by These data points are used along with patient using the standard deviation of the arterial pressure demographic information to calculate the standard (sAP) around the MAP value, measured in mmHg, making it independent of the effects of vascular tone. This deviation of the arterial pressure (sAP). This (sAP) is proportional to pulse pressure (PP). The sAP is standard deviation of the pulse pressure is proportional multiplied by a conversion factor known as Khi (x) to the volume displaced or the stroke volume. This is which incorporates both the effects of resistance and calculated by analyzing the arterial pressure waveform compliance (vascular tone) and also converts sAP in over 20 seconds at 100 times per second, creating

(mmHg) into mL/beat. Therefore, with the variables 2,000 data points from which sAP is calculated. sAP and vascular tone (x), flow or stroke volume can be calculated. ARTERIAL PRESSURE-BASED CARDIAC - Large vessel compliance: Work reported by Langewouters OUTPUT found a direct correlation among age, gender, and MAP The FloTrac algorithm is based on the principle that aortic with respect to aortic compliance. An equation was pulse pressure is proportional to stroke volume (SV) and derived from these studies by which a patient’s inversely related to aortic compliance. compliance could be estimated with the inputs of age and gender. According to Langewouters et al, the arterial STANDARD DEVIATION OF ARTERIAL compliance (C), as a function of pressure, could be PRESSURE estimated using the following equation: Initially, the FloTrac algorithm assesses pulse pressure by using the standard deviation of the arterial pressure (σAP) around the MAP value, measured in mmHg, making it independent of the effects of vascular tone. This standard deviation of the pulse pressure is proportional to the volume displaced or the stroke volume. This is calculated by analyzing the arterial pressure waveform over 20 seconds at 100 times per second, creating 2,000 data points from which L = estimated aortic length.

σAP is calculated. Amax = aortic root cross sectional area maximum. P = arterial pressure. KHI AND THE CONVERSION OF MMHG TO ML/BEAT P0 = pressure at which compliance reaches its maximum.

The conversion of standard deviation of arterial pressures P1 = the width of compliance curve at half of (mmHg) into ml/beat is performed by multiplying it by a maximum compliance. Additional measures of weight and conversion factor known as Khi (χ). Khi is a multivariate height (BSA) were also found to correlate with vascular polynomial equation which assesses the impact of the tone and were added to enhance the calculation of aortic patient’s ever-changing vascular tone on pulse pressure. Khi compliance. is calculated by analyzing the patient’s pulse rate, mean - Skewness (a measure for lack of symmetry, μ ): arterial pressure, standard deviation of mean arterial 3ap Symmetry characteristics on arterial pressure can indicate pressure,Khi large-vessel and the conversion compliance of mmHgas estimated to mL/beat by patient • Skewness (a measure for lack of symmetry, µ3ap): The conversion of standard deviation of arterial pressures a changeSymmetry in vascular characteristics tone and/or on resistance. arterial pressure Two different can demographics, and skewness and kurtosis of the arterial (mmHg) into mL/beat is performed by multiplying it by a functionsindicate may a changehave the insame vascular mean andtone standard and/or deviationresistance; waveform. Khi is updated and applied to the FloTrac conversion factor known as Khi (x). Khi is a multivariate buttwo will different rarely have functions the same may skewness. have the For same example, mean algorithm on a rolling 60-second average. polynomial equation which assesses the impact of the an andarterial standard pressure deviation waveform but in will which rarely the have data thepoints same - Pulsepatient’s rate: The ever-changing patient’s pulse vascular rate tone is calculatedon pulse pressure. by increaseskewness; quickly for in example, andan arterial fall slowly pressure can result waveform as an countingKhi isthe calculated number of by pulsations analyzing in the a 20patient’s second pulse period rate, increasein which in thevasoconstriction data points increase and would quickly have in systoleincreased and mean arterial pressure, standard deviation of mean fall slowly can result as an increase in and extrapolated to a per minute value. skewness. arterial pressure, large-vessel compliance as estimated and would have increased skewness - Meanby arterial patient pressure demographics, (MAP): andAn skewnessincrease in and average kurtosis pressureof the often arterial indicates waveform. an increase Khi is updated in resistance, and applied and to Figure 1 - Decreased skewness low resistance vice versa.the FloTrac algorithm on a rolling 60-second average.

- Standard deviation of arterial pressure ( ): Pulse Decreased skewness - Standard• Pulse deviation rate: The of patient’s arterial pulse pressure rate is (calculatedσAP): Pulse by pressure is proportional to σ and to stroke volume. low resistance counting the number ofAP pulsations in a 20 second mmHG Increasesperiod and anddecreases extrapolated in the tostandard a per minute deviation value also provide information on pressure amplitude. When this pressure• Mean amplitude arterial pressureis correlated (MAP): with An increasekurtosis, in it Time compensates for differential compliance and wave average pressure often indicates an increase in Figure 2 - Increased skewness constant MAP high resistance reflectanceresistance, that vary and from vice one versa arterial location to another. - Kurtosis (a measure of how peaked or flat the pressure Since clinically available, the FloTrac system has been This then allows the monitoring of cardiac output from Increased skewness data points are distributed from normal distribution, validated against various cardiac output technologies different• Standard arterial locations.deviation of arterial pressure (sAP): Pulse Constant MAP pressure is proportional to and to stroke volume; μ ): Pressure data with high kurtosis has the pressure including thermodilution cardiac output. sAP 4apmmHG High resistance increases and decreases in the standard deviation rise and fall very quickly relative to the normal pulse also provide information on pressure amplitude; pressure and can be directly associated with large vessel NO MANUAL CALIBRATION NEEDED when this pressure amplitude is correlated with compliance. 1) A high kurtosisTime value will indicate a Other arterial pressure cardiac output devices (pulse kurtosis, it compensates for differential compliance distinct peak near the mean, with a drop thereafter, contour or pulse power) require calibration as they cannot and wave reflectance that vary from one arterial • Kurtosis (a measure of how peaked or flat the pressure followed by a heavy “tail”. 2) A low kurtosis value will auto correct for the patient’s changing vascular tone. Since location to another; this then allows the monitoring data points are distributed from normal distribution, tend to indicate that the function is relatively flat in the of cardiac output from different arterial locations μ4ap): Pressure data with high kurtosis has the pressure the FloTrac algorithm continuously adjusts for the patient’s regionrise of and its fallpeak very and quickly suggests relative decreased to the central normal tone, pulse as ever changing vascular tone, it does not require manual • Large vessel compliance: Work reported by is oftenpressure seen, andfor example,can be directly in the associatedneonatal vasculature. with large vessel calibration. As a component of the calibration, Khi auto Langewouters found a direct correlation among compliance; corrects for changes in vascular tone through a complex age, gender, and MAP with respect to aortic 1) A high kurtosis value will indicate a distinct peak waveform analysis. This feature also eliminates the need for compliance; an equation was derived from these near the mean, with a drop thereafter, followed a central or peripheral venous line, required for indicator studies by which a patient’s compliance could be by a heavy “tail” (Figure 3) dilution methods used in manual calibration. estimated with the inputs of age and gender; 2) A low kurtosis value will tend to indicate that the according to Langewouters et al, the arterial - Kurtosisfunction (a measure is relatively of how flat peaked in the orregion flat theof its pressure peak and SinceTECHNICAL clinically CONSIDERATIONS available, the FloTrac system has been compliance (C), as a function of pressure, could suggests decreased central tone, as is often seen, for data points are distributed from normal distribution, validated against various cardiac output technologies be estimated using the following equation: example, in the neonatal vasculature (Figure 4) The FloTrac algorithm is dependent upon a high fidelity μ4ap): Pressure data with high kurtosis has the pressure includingpressure tracing.thermodilution Attention cardiac to bestoutput. practice in pressure A riseFigure and 3 - fallHigh verycompliance quickly of largerelative vessels to the normal pulse monitoring is important by; priming with gravity, pressure ______max pressure and can be directly associated with large vessel NObag keptMANUAL to 300mmHg, CALIBRATION adequate NEEDEDI.V. bag flush volume, π • P 1 compliance. 1) A high kurtosis value will indicate a sensorOther arterialstopcock pressureis kept cardiaclevel to outputphlebostatic devices axis, (pulse and C(P)=L • ______distinct peak near the mean, with aHigh drop compliance thereafter, P - P 2 periodiccontour ortesting pulse of power) optimal require dampening calibration with asa squarethey cannot wave ______0 followed by a heavy “tail”. 2) A low kurtosisof large vessels value will 1 + ( ) mmHG test.auto FloTraccorrect sensorfor the kits patient’s are especially changing configured vascular tone.to optimize Since P 1 tend to indicate that the function is relatively flat in the frequencythe FloTrac response algorithm therefore continuously adding adjusts additional for the pressurepatient’s region of its peak and suggests decreased central tone, as tubingever changing or stopcocks vascular is highly tone, discouraged. it does not require manual L = estimated aortic length is often seen, for example, inTime the neonatal vasculature. calibration. As a component of the calibration, Khi auto Amax = aortic root cross sectional area maximum Figure 4 - Low compliance of large vessels LIMITATIONScorrects for changes in vascular tone through a complex P = arterial pressure KHI (χ) MMHG TO ML/BEAT Aswaveform of this analysis.publication, This the feature FloTrac also sensor eliminates is only the indicated need for Taking all of these variables into consideration, the FloTrac fora central adult oruse peripheral and has notvenous been line, validated required in patientsfor indicator with P0 = pressure at which compliance reaches its maximum algorithm continuously assesses the impactLow of compliancevascular tone ventriculardilution methods assist useddevices in manual or intra calibration. aortic balloon pumps. P = the width of compliance curve at half of maximum 1 on pressure every 60 seconds. The result ofof largethe analysis vessels is a Absolute values during aortic regurgitation may be affected compliance; additional measures of weight and height mmHG conversion factor known as Khi (χ). Khi is then multiplied TECHNICALalthough trending CONSIDERATIONS may be appropriate. Severe peripheral (BSA) were also found to correlate with vascular by the standard deviation of the arterial pressure to calculate tone and were added to enhance the calculation constrictionThe FloTrac duringalgorithm shock is dependentstates or hypothermicupon a high episodes fidelity stroke volume in milliliters per beat. This stroke volume is of aortic compliance Time maypressure influence tracing. valuesAttention with to radialbest practicearterial inlocations, pressure multiplied by the pulse rate to obtain cardiac output in liters considerationmonitoring is importantto femoral by; sites priming during with these gravity, episodes pressure or per minute. insertionbag kept ofto a 300mmHg,pulmonary arteryadequate catheter I.V. maybag beflush considered. volume, sensor stopcock is kept level to phlebostatic axis, and Stroke Volume (ml/beat) = σAP (mmHg)* χ (ml/mmHg) CONCLUSIONperiodic testing of optimal dampening with a square wave DEVELOPED WITH THE CLINICAL GOLD Edwardstest. FloTrac has sensor converted kits are the especially complexity configured and invasiveness to optimize STANDARD traditionallyfrequency response associated therefore with continuousadding additional cardiac pressure output tubing or stopcocks is highly discouraged. The vascular tone factor (Khi) was developed based on monitoring into the simplicity of utilizing only an arterial cardiovascular principles, advanced signal catheter. The ease of use of the FloTrac system allows for processing of the arterial pressure waveform, and LIMITATIONSearlier implementation of flow monitoring in critically ill KHI (χ) MMHG TO ML/BEAT comparative analysis with the clinical gold standard patients.As of this Clinicians publication, now the have FloTrac the option sensor to is monitor only indicated cardiac Taking all of these variables into consideration, the FloTrac thermodilution cardiac output. outputfor adult on useany patientand has who not currently been validated requires in an patients arterial withline. algorithm continuously assesses the impact of vascular tone ventricular assist devices or intra aortic balloon pumps. χ onKhi pressure ( ) was everymodeled 60 seconds.and compared The result across of athe wide analysis range is of a Absolute values during aortic regurgitation may be affected cardiacconversion output factor values, known patient as Khi (profiles,χ). Khi ispathologies, then multiplied and although trending may be appropriate. Severe peripheral hemodynamicby the standard conditions. deviation of the arterial pressure to calculate constriction during shock states or hypothermic episodes stroke volume in milliliters per beat. This stroke volume is may influence values with radial arterial locations, multiplied by the pulse rate to obtain cardiac output in liters consideration to femoral sites during these episodes or per minute. insertion of a pulmonary catheter may be considered.

Stroke Volume (ml/beat) = σAP (mmHg)* χ (ml/mmHg) CONCLUSION DEVELOPED WITH THE CLINICAL GOLD Edwards has converted the complexity and invasiveness STANDARD traditionally associated with continuous cardiac output The vascular tone factor (Khi) was developed based on monitoring into the simplicity of utilizing only an arterial cardiovascular hemodynamics principles, advanced signal catheter. The ease of use of the FloTrac system allows for processing of the arterial pressure waveform, and earlier implementation of flow monitoring in critically ill comparative analysis with the clinical gold standard patients. Clinicians now have the option to monitor cardiac thermodilution cardiac output. output on any patient who currently requires an arterial line. Khi (χ) was modeled and compared across a wide range of cardiac output values, patient profiles, pathologies, and hemodynamic conditions. Khi (x) mmhg to mmHg to mL/beat Limitations Taking all of these variables into consideration, the As of this publication, absolute values during aortic FloTrac algorithm continuously assesses the impact of regurgitation may be affected although trending may be vascular tone on pressure every 60 seconds. The result appropriate. Severe peripheral constriction during shock of the analysis is a conversion factor known as Khi (x). states or hypothermic episodes may influence Khi is then multiplied by the standard deviation of the values with radial arterial locations, consideration to arterial pressure to calculate stroke volume in milliliters femoral sites during these episodes or insertion of per beat. This stroke volume is multiplied by the pulse a catheter may be considered. rate to obtain cardiac output in liters per minute. The FloTrac system can be used in patients with

Stroke volume (mL/beat) = sAP (mmHg)* x (ml/mmHg) arrhythmias and who are spontaneously breathing. Arrhythmias and spontaneous breathing are NOT Developed with the clinical gold standard a limitation of the FloTrac algorithm in calculating The vascular tone factor (Khi) was developed based on cardiac output. cardiovascular hemodynamics principles, advanced signal processing of the arterial pressure waveform, and FloTrac system 4.0 comparative analysis with the clinical gold standard The FloTrac system algorithm has evolved based on thermodilution cardiac output. a broad and expanding patient database that allows ongoing system performance improvements. The Khi (x) was modeled and compared across a wide range following high-risk surgical patients were added to the of cardiac output values, patient profiles, pathologies, database including, but not limited to, gastrointestinal, and hemodynamic conditions. Since clinically available, esophageal, pancreaticoduodenectomy (whipple) and the FloTrac system has been validated against various esophagectomy. The expanded patient database has cardiac output technologies including thermodilution informed the algorithm to recognize and adjust for cardiac output. more patient conditions.

No manual calibration needed Additional physiologically-based variables were Other arterial pressure cardiac output devices (pulse added to the algorithm’s vascular tone Khi factor in contour or pulse power) require calibration as they order to adjust automatically for hyperdynamic and cannot auto correct for the patient’s changing vascular vasodilated patients. Once identified it accesses tone. Since the FloTrac algorithm continuously adjusts a specially designed algorithm to account for for the patient’s ever changing vascular tone, it does such conditions. not require external calibration. As a component of the calibration, Khi auto corrects for changes in vascular tone Figure 5 - Pulsatility of the wave through a complex waveform analysis. This feature also 140 eliminates the need for a central or peripheral venous 130 line, required for indicator dilution methods used in 120 external calibration. 110

P, (mmHg) P, 100 Technical considerations 90 FloTrac algorithm is dependent upon a high fidelity 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 pressure tracing. Attention to best practice in Time, (sec) pressure monitoring is important by; priming with Figure 6 - Pulsatility of the wave gravity, pressure bag kept to 300mmHg, adequate I.V. 140 bag flush volume, sensor stopcock is kept level to 130 phlebostatic axis, and periodic testing of optimal 120 dampening with a square wave test. The FloTrac 110 sensor kits are especially configured to optimize P, (mmHg) P, 100 frequency response therefore adding additional 90 pressure tubing or stopcocks is highly discouraged. 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 Time, (sec) In addition to a broader database the FloTrac system 4.0 algorithm adjusts for rapid changes in pressure that occur during vasopressor administration through Khi-fast. Khi-fast is assessed every 20 seconds and is inversely affected by pressure. Khi continues to assess vascular tone every 60 seconds and Khi-fast every 20 seconds resulting in a more physiologic response to changes in resistance.

Conclusion Edwards Lifesciences has converted the complexity and invasiveness traditionally associated with continuous cardiac output monitoring into the simplicity of connecting to an arterial catheter. The proven FloTrac system allows for earlier implementation of hemodynamic instability in surgical and critically ill patients.

Prepared by: John A. Frazier RN, RRT Feras Hatib, PhD Group Manager, Critical Care Technology & Discovery Edwards Lifesciences Edwards Lifesciences

Information contained in this document is based on the following references: 1. Pratt B, Roteliuk L, Hatib F, Frazier J, Wallen RD. Calculating arterial pressure-based cardiac output using a novel measurement and analysis method. Biomed Instrum Technol. 2007 Sep-Oct;41(5):403-11. 2. Cecconi M, Parsons AK, Rhodes A. What is a fluid challenge? Curr Opin Crit Care. 2011 Jun;17(3):290-5. 3. Monge García MI, Gil Cano A, Gracia Romero M. Dynamic arterial elastance to predict arterial pressure response to volume loading in -dependent patients. Crit Care. 2011;15(1):R15. 4. Monnet X, Rienzo M, Osman D, Anguel N, Richard C, Pinsky MR, Teboul JL. Passive leg raising predicts fluid responsiveness in the critically ill. Crit Care Med. 2006 May;34(5):1402-7. CAUTION: Federal (United States) law restricts this device to sale by or on the order of a physician. See instructions for use for full prescribing information, including indications, contraindications, warnings, precautions and adverse events. Edwards, Edwards Lifesciences, the stylized E logo, and FloTrac are trademarks of Edwards Lifesciences Corporation or its affiliates. All other trademarks are the property of their respective owners. © 2020 Edwards Lifesciences Corporation. All rights reserved. PP--US-5175 v1.0 Edwards Lifesciences • One Edwards Way, Irvine CA 92614 USA • edwards.com