FloTrac Algorithm Calculating stroke volume and cardiac output 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 pulse pressure technology is based on the basic principles of physics AP in mmHg is proportional to pulse pressure 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 vascular resistance and compliance through a MAP = mean arterial pressure 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 heart 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 heart rate 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, systole 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 vasoconstriction 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