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ODM+ Parameters Explained

Pressure Parameters

The CardioQ-ODM+ uses the proven Doppler technology to control both its Flow Monitoring Mode of use and the calibration of the chosen Pulse Pressure Waveform Analysis (PPWA) algorithm for its Pressure Monitoring Mode of cardiac output (CO). Pressure parameters and flow based parameters are available on the CardioQ-ODM+ monitor.

Flow Based Parameters

Stroke Distance (SD)

Stroke Distance is a Doppler flow based parameter only. SD is simply the distance the blood ejected by the left ventricle travels down the aorta every beat. It is measured in centimeters per second. If the aorta approximates to a cylindrical pipe then the SD can be represented a series of cylinders of blood moving down the aorta as each pulse of the left ventricle propels them into the bodies arterial system.

Stroke Distance (SD)

Stroke Distance (SD)

The CardioQ-ODM is distinct from other devices in possessing the ability to calculate Stroke Volume and Cardiac Output from its own patient nomogram. The patient nomogram was created as a result of research by Prof. Mervyn Singer. The patient nomogram is a calibration of Stroke Distance against the total Cardiac Output as measured by a Pulmonary Artery Catheter (PAC) for patients of both genders and various races, ages, weights and heights.

SD is the basic parameter for IOFM and Stroke Volume (SV) is automatically calculated by the monitor. The patient’s age, weight and height are input during the monitor set up. This information accesses the nomogram which effectively provides the dynamic aortic root diameter.

SV = SD x Aortic Root Diameter

As a result ODM has been found to be equivalent in terms of accuracy to a PAC. However it is the precision of ODM in tracking change that is key to recognising how and why ODM guides Stroke Volume Optimisation (SVO) so effectively which has resulted in an unparalleled evidence base.

Stroke Volume (SV)

Stroke Volume is the amount of blood in millilitres pumped from the human heart every heart beat. It is the volume ejected from the left ventricle due to the contraction of the heart muscle which compresses the left ventricle. Stroke Volume can be calculated as a Doppler Flow Based Parameter by CardioQ-ODM and CardioQ-ODM+.

The CardioQ-ODM calculates Stroke Volume by multiplying the Stroke Distance by a constant accessed from the built in patient nomogram. The patient nomogram was created as a result of research by Prof. Mervyn Singer. The patient nomogram is a calibration of Stroke Distance against the total Cardiac Output as measured by a Pulmonary Artery Catheter (PAC) for patients of various ages, weights and heights. The calibration factor is functionally the dynamic aortic root diameter for typical patient of the input age, weight and height.

Stroke Volume

Stroke Volume

Heart Rate (HR)

Heart Rate is displayed on the CardioQ-ODM and CardioQ-ODM+ from Doppler based measurement. From the Doppler the heart beats per minute is calculated from the analysed waveform.

The monitor updates the heart rate display after each calculation period depending on the number of cycles set.

Cardiac Output (CO)

The CardioQ-ODM and CardioQ-ODM+ can calculate Cardiac Output in Doppler flow mode.

Cardiac Output is the volume of blood being pumped by the left ventricle in the time interval of one minute. The units of Cardiac Output are litres per minute (l/min). The CardioQ-ODM calculates the Cardiac Output based on the setting of ‘cycles for calculation’. If set at ‘every beat’ the individual Stroke Volume in millilitres of each beat is multiplied by the Heart Rate at that time and is displayed in litres per minute.

Cardiac Output = Stroke Volume x Heart Rate

Peak Velocity (PV)

Peak Velocity is a Doppler only parameter and is available on both the CardioQ-ODM and CardioQ-ODM+ as the maximal velocity of the blood.

PV is an indicator of contractility and typical values change with age. The peak velocity of 20 year old may be 90 – 120 cm/s whereas at age 90 it may only be 30 – 60 cm/s. Thus a PV markedly below the typical expected value may be an indicator of increased afterload or decreased cardiac function. A higher than normal PV may be indicative of decreased afterload.

Minute Distance (MD)

Minute Distance is a Doppler only parameter and is available on both the CardioQ-ODM and CardioQ-ODM+. MD is simply the distance blood moves in one minute down the aorta.

Minute Distance = Stroke Distance x Heart Rate

Peak Velocity

Peak Velocity

Flow Time corrected (FTc)

Flow Time corrected is a Doppler only parameter and is available on both the CardioQ-ODM and CardioQ-ODM+. Flow Time (FT) is the duration of time of the flow from the left ventricle during systole.  Flow Time corrected (FTc) is Flow Time duration of blood flow in the aorta normalised to 60 beats/min using Bazett’s equation.

Corrected Flow Time

Corrected Flow Time

Typically FTc is one third of the cardiac cycle. When standardised to 60 beats/min one cycle is one second. FTc is then 0.33 seconds or 333 milliseconds.

Thus typical values for normally hydrated resting healthy individuals is 330 – 360 milliseconds. This can be used as an indicator of hypovolaemia.

FTc is inversely related to afterload/resistance and the most common cause of an increased afterload/resistance is hypovolaemia.  Other causes of increased afterload/resistance should be considered.  High FTc is usually seen in low afterload/resistance states such as the vasoactive effects of drugs and sepsis.

Flow Time to peak (FTp)

Flow Time to peak is a Doppler only parameter and is available on both the CardioQ-ODM and CardioQ-ODM+. Flow Time to peak is the time in milliseconds from the start of systole to the point of peak velocity. Flow Time to peak is when combined with Peak Velocity and Mean Acceleration, a parameter for evaluating cardiac contractility and the effects of preload and afterload.

Flow Time to Peak (FTp)

Flow Time to Peak (FTp)

Cardiac Index (CI)

The CardioQ-ODM and CardioQ-ODM+ can calculate Cardiac Index in Doppler flow mode.

Cardiac Index relates the Cardiac Output to body surface area (BSA), thus relating heart performance to the size of the individual. The unit of measurement is litres per minute per square metre (l/min/m2).

Cardiac Index = Cardiac Output/Body Surface Area.

Stroke Volume Index (SVI)

Stroke Volume Index is the amount of blood in millilitres pumped from the human heart every heart beat indexed for body surface area. Stroke Volume Index can be calculated as a Doppler Flow Based Parameter by CardioQ-ODM and CardioQ-ODM+.

Stroke Volume Index relates the Stroke Volume to body surface area (BSA), thus relating heart performance to the size of the individual. The unit of measurement is millilitres per square metre (ml/m2).

Stroke Volume Index = Stroke Volume/Body Surface.

Stroke Volume Variation (SVV)

The CardioQ-ODM and CardioQ-ODM+ can calculate Stroke Volume Variation in Doppler flow.

Stroke Volume Variation is widely considered as a useful indicator of fluid responsiveness. The mechanism of generation of this parameter relates to the observation of variations in left ventricular ejection volumes (Stroke Volume).  It has been shown that return blood flow through the thorax is affected by the positive pressure of the ventilator.  As the ventilator cycles it creates varying periods of higher and lower flow. These fluctuations traverse the lung and are manifest as variations in stroke volume of the heart.

These variations can be detected as variations in flow and pressure. The CardioQ-ODM uses these variations in flow to calculate the percentage variation between the maximum stroke volume and the minimum.

The limitations of this parameter is that the patient must meet the following criteria: Fully mechanically ventilated, sinus rhythm, tidal volume ≥ 7-8 mL/kg and higher tidal volumes elicit higher variations. Increasing PEEP will result in higher variations. HR: Respiratory rate ratio ≥4. Changes in lung or chest compliance, or patient position and right ventricular dysfunction or  abdominal insufflation may affect readings.

Caution is advised and clinicians need to be aware of the particular ‘cut off’ or ‘grey zone’ threshold values for the technology being used and the limitations described in the literature.

Stroke Distance Variation (SDV)

Stroke Distance Variation is a linear mode only parameter and is an indicator of fluid responsiveness when patients are outside the nomogram range of the CardioQ-ODM (typically in bariatric surgery).

The mechanism of generation of this parameter is identical to that of Stroke Volume Variation and relates to the observation of variations in left ventricular ejection volumes (Stroke Volume) due to variations in ejection volumes.

The limitations of this parameter is that the patient must meet the following criteria: Fully mechanically ventilated, sinus rhythm, tidal volume ≥ 7-8 mL/kg and higher tidal volumes elicit higher variations. Increasing PEEP will result in higher variations. HR: Respiratory rate ratio ≥4. Changes in lung or chest compliance, or patient position and right ventricular dysfunction or  abdominal insufflation may affect readings.

Systemic Vascular Resistance (SVR)

Systemic Vascular Resistance can be calculated as a Doppler Flow Based Parameter.

Systemic Vascular Resistance is the resistance to blood flow due to the peripheral vascular system. The formula used in the CardioQ-ODM is as follows:

SVR = 80 (MAP-CVP)
CO

Where MAP is the Mean Arterial Pressure, CVP is the Central Venous Pressure and CO the Cardiac Output.

The Cardiac Output is automatically provided from the flow readings calculated from Stroke Volume and Heart Rate. The user is required to input the MAP and CVP from other sources. The monitor then provides the measurement continuously as the CO is derived.

Systemic Vascular Resistance Index can be calculated as a Doppler Flow Based Parameter by CardioQ-ODM and CardioQ-ODM+.

Systemic Vascular Resistance Index (SVRI)

Systemic Vascular Resistance Index is the resistance to blood flow due to the peripheral vascular system indexed for patient body size. The formula uses the Body Surface Area as calculated from the input weight and height is as follows:

SVRI = SVR x BSA

Where BSA is the Body Surface Area.

The SVRI is automatically updated as SVR changes with CO calculated from the flow readings calculated from Stroke Volume and Heart Rate.

Delivered Oxygen (DO2)

Delivered Oxygen can be calculated as a Doppler Flow Based Parameter by CardioQ-ODM and CardioQ-ODM+.

Delivered Oxygen is the amount of oxygen in the blood delivered to the body’s tissues. The CardioQ-ODM and CardioQ-ODM+ can calculate this parameter but require the user to input measurements of haemoglobin concentration and the saturated oxygen concentration. The Cardiac Output as calculated by the monitor is automatically updated as DO2 changes with CO calculated from the flow readings, the formula used is as follows:

DO2 = 1.34 x Hb x SaO2 x CO

Where Hb is the concentration of haemoglobin, SaO2 is the saturation of haemoglobin and the amount of dissolved oxygen all multiplied by the Cardiac Output (CO).

Delivered Oxygen Index (DO2I)

Delivered Oxygen Index can be calculated as a Doppler Flow Based Parameter by CardioQ-ODM and CardioQ-ODM+.

Delivered Oxygen Index is the amount of oxygen in the blood delivered to the bodies tissues indexed for patient body size. The CardioQ-ODM and CardioQ-ODM+ can calculate this parameter but require the user to input measurements of haemoglobin concentration (Hb) and the saturated oxygen concentration (SaO2). The Body Surface Area (BSA) is calculated by the monitor from the input patient weight and height and this used to automatically updated as DO2 changes with CO calculated from the flow readings, the formula used is as follows:

DO2I = DO2
BSA

Pressure Based Parameters

Stroke Volume (SV)

Stroke Volume is the amount of blood in millilitres pumped from the heart during every heart beat. It is the volume ejected from the left ventricle due to the contraction of the heart muscle. Stroke Volume can be calculated as a Doppler Flow Based Parameter by the CardioQ-ODM+ (when in flow-monitoring mode). In addition the CardioQ-ODM+ also calculates SV from the arterial pressure wave using the Liljestrand and Zander algorithm (when calibrated and in pressure-monitoring mode).

The CardioQ-ODM+ first calibrates the arterial pressure wave signal against the Doppler Flow Based calculation of Stroke Volume. During calibration the mean Stroke Volume of a minimum of 10 Doppler flow waveforms is established, alongside simultaneous measurements of mean systolic and diastolic pressures.

The CardioQ-ODM+ then applies the Liljestrand and Zander formula (with the constant (k) generated during the calibration period), to calculate beat-by-beat Stroke Volume (SV) from the arterial pressure waveform via the following equation:

SV = k (Ps – Pd)
(Ps + Pd)

Stroke Volume Index (SVI)

Stroke Volume Index is the amount of blood in millilitres pumped from the human heart every heart beat indexed for body surface area. Stroke Volume Index can be calculated as a Doppler Flow Based Parameter by CardioQ-ODM and CardioQ-ODM+ and after calibration of the PPWA algorithm CardioQ-ODM+ can calculate this parameter as a Pressure Based Parameter Stroke Volume Index relates the Stroke Volume to body surface area (BSA), thus relating heart performance to the size of the individual. The unit of measurement is millilitres per square metre (ml/m2).

Stroke Volume Index = Stroke Volume/Body Surface Area

The typical value for Stroke Volume Index is 50 ml/ m2 with arrange of between 35 ml/m2 to 65ml/ m2).

Heart Rate (HR)

Heart Rate as displayed on the CardioQ-ODM and CardioQ-ODM+ from Doppler based measures and the CardioQ-ODM+ can also calculate Heart Rate from the ABP waveform. From the Doppler the heart beats per minute is calculated from the analysed waveform. The number of beats used to make the calculation can be set by the user from ’every beat’ to a maximum of 20. If set to ‘every beat’ the time in milliseconds of the complete cardiac cycle is measured and then this is divided into 60,000 (milliseconds in a minute) to give the number of beats per minute. If the monitor is set to 20 cycles for calculation then the time in milliseconds for 20 full cycles would be used as the basis of the parameter calculations.

The monitor updates the heart rate display after each calculation period depending on the number of cycles set.

The CardioQ-ODM+ can also calculate the Heart Rate from the ABP waveform. The system uses the same method as described for the Doppler as it measures the length of the cardiac cycle in milliseconds and divides this into one minute to give the number of beats per minute.

Cardiac Output (CO)

Cardiac Output is the volume of blood being pumped by the heart, in particular by the left ventricle in the time interval of one minute. The units of Cardiac Output are litres per minute (L/min).

The CardioQ-ODM and CardioQ-ODM+ calculate Cardiac Output in Doppler flow mode. Additionally, after the calibration of the Stroke Volume, the CardioQ-ODM+ can simultaneously calculate the Cardiac Output from the arterial pressure waveform.

The CardioQ-ODM+ averages the Cardiac Output based on the setting of ‘cycles for calculation’, ranging from beat-by-beat estimation of cardiac output, to Cardiac Output based on Stroke Volume averaged over 20 cycles.

Cardiac Output = Stroke Volume x Heart Rate

Cardiac Index (CI)

The CardioQ-ODM and CardioQ-ODM+ can calculate Cardiac Index in Doppler flow mode and CardioQ-ODM+ can additionally calculate this from the Pulse Pressure Waveform Analysis algorithm.

Cardiac Index relates the Cardiac Output to body surface area (BSA), thus relating heart performance to the size of the individual. The unit of measurement is litres per minute per square metre (l/min/m2).

Cardiac Index = Cardiac Output/Body Surface Area

Typical values for Cardiac Index are between 3.5-4.5 L/min/m2

“Low cardiac output syndrome” is typically associated with CI values < 2.5 L/min/m2.

Stroke Volume Variation (SVV)

The CardioQ-ODM and CardioQ-ODM+ can calculate Stroke Volume Variation in Doppler flow mode and CardioQ-ODM+ can additionally calculate this from the Pulse Pressure Waveform Analysis algorithm.

Stroke Volume Variation is widely considered as a useful indicator of fluid responsiveness. The mechanism of generation of this parameter relates to the observation of variations in left ventricular ejection volumes (Stroke Volume).  It has been shown that return blood flow through the thorax is affected by the positive pressure of the ventilator.  As the ventilator cycles it creates varying periods of higher and lower flow. These fluctuations traverse the lung and are manifest as variations in stroke volume of the heart.

These variations can be detected as variations in flow and pressure. The CardioQ-ODM uses these variations in flow to calculate the percentage variation between the maximum stroke volume and the minimum.

The limitations of this parameter is that the patient must meet the following criteria: Fully mechanically ventilated, sinus rhythm, tidal volume ≥ 7-8 mL/kg and higher tidal volumes elicit higher variations. Increasing PEEP will result in higher variations. HR: Respiratory rate ratio ≥4. Changes in lung or chest compliance, or patient position and right ventricular dysfunction or  abdominal insufflation may affect readings.

Caution is advised and clinicians need to be aware of the particular ‘cut off’ or ‘grey zone’ threshold values for the technology being used and the limitations described in the literature.

Systemic Vascular Resistance (SVR)

Systemic Vascular Resistance can be calculated as a Doppler Flow Based Parameter by CardioQ-ODM and CardioQ-ODM+ and after calibration of the PPWA algorithm CardioQ-ODM+
can calculate this parameter as a Pressure Based Parameter

Systemic Vascular Resistance is the resistance to blood flow due to the peripheral vascular system. The formula used in the CardioQ-ODM is as follows:

SVR = 80 (MAP-CVP)
CO

Where MAP is the Mean Arterial Pressure, CVP is the Central Venous Pressure and CO the Cardiac Output.

The Cardiac Output is automatically provided from the flow readings calculated from Stroke Volume and Heart Rate. The user is required to input the MAP and CVP from other sources. The monitor then provides the measurement continuously as the CO is derived.

Systemic Vascular Resistance Index (SVRI)

Systemic Vascular Resistance Index can be calculated as a Doppler Flow Based Parameter by CardioQ-ODM and CardioQ-ODM+ and after calibration of the PPWA algorithm CardioQ-ODM+ can calculate this parameter as a Pressure Based Parameter

Systemic Vascular Resistance Index is the resistance to blood flow due to the peripheral vascular system indexed for patient body size. The formula uses the Body Surface Area as calculated from the input weight and height is as follows:

SVRI = SVR x BSA*

*Where BSA is the Body Surface Area.

The SVRI is automatically updated as SVR changes with CO calculated from the flow readings calculated from Stroke Volume and Heart Rate.

Delivered Oxygen (DO2)

Delivered Oxygen can be calculated as a Doppler Flow Based Parameter by CardioQ-ODM and CardioQ-ODM+ and after calibration of the PPWA algorithm CardioQ-ODM+ can calculate this parameter as a Pressure Based Parameter

Delivered Oxygen is the amount of oxygen in the blood delivered to the body’s tissues. The CardioQ-ODM and CardioQ-ODM+ can calculate this parameter but require the user to input measurements of haemoglobin concentration and the saturated oxygen concentration. The Cardiac Output as calculated by the monitor is automatically updated as DO2 changes with CO calculated from the flow readings, the formula used is as follows:

DO2 = 1.34 x Hb x SaO2 x CO

Where Hb is the concentration of haemoglobin, SaO2 is the saturation of haemoglobin and the amount of dissolved oxygen, all multiplied by the Cardiac Output (CO).

Delivered Oxygen Index (DO2I)

Delivered Oxygen Index can be calculated as a Doppler Flow Based Parameter by CardioQ-ODM and CardioQ-ODM+ and after calibration of the PPWA algorithm CardioQ-ODM+ can calculate this parameter as a Pressure Based Parameter

Delivered Oxygen Index is the amount of oxygen in the blood delivered to the bodies tissues indexed for patient body size. The CardioQ-ODM and CardioQ-ODM+ can calculate this parameter but require the user to input measurements of haemoglobin concentration (Hb) and the saturated oxygen concentration (SaO2). The Body Surface Area (BSA) is calculated by the monitor from the input patient weight and height and this used to automatically updated as DO2 changes with CO calculated from the flow readings, the formula used is as follows:

DO2I = DO2
BSA

Pulse Pressure Variation (PPV)

Pulse Pressure Variation is available only on the CardioQ-ODM+ as a pressure based parameter only. PPV has been reported to be a useful predictor of fluid responsiveness.

Intermittent Fluid Loading

Intermittent Fluid Loading

As with Stroke Volume Variation the mechanism of generation of this parameter relates to the observation of variations in pulse pressure due to variations in ventricular ejection volumes. It has been shown that return blood flow through the thorax is affected by the positive pressure of the ventilator.

These fluctuations traverse the lung and are manifest as variations in pulse pressure and stroke volume of the heart.

The CardioQ-ODM+ uses the measured variations in pulse pressure to calculate the percentage variation between the maximum and minimum pulse pressures. The effect of the thoracic pressure changes due to ventilation (PAW) creates a respiratory swing in the magnitude of the pulse pressure wave (PA). The resulting PPMax and PPMin measurements are the basis of calculating the PPV.

image_9

Publications have shown that the sampling plan used for collecting the data and the formula have a significant bearing on the sensitivity of the PPV methodology.

The CardioQ-ODM+ uses a state of the art method where PPMax values are calculated separately for each of three successive breaths. The resulting %PPV has improved accuracy as a result. The formula used is as follows:

PPV = (2(PPmax1 – PPmin1)) + 2(PPmax2 – PPmin2) + 2(PPmax3 – PPmin3) ÷ 3 x 100%
(PPmax1 + PPmin1) (PPmax2 + PPmin2) (PPmax3 + PPmin3)

The limitations of this parameter is that the patient must meet the following criteria: Fully mechanically ventilated, sinus rhythm, tidal volume ≥ 7-8 mL/kg and higher tidal volumes elicit higher variations. Increasing PEEP will result in higher variations. HR: Respiratory rate ratio ≥4. Changes in lung or chest compliance, or patient position and right ventricular dysfunction or  abdominal insufflation may affect readings.

Caution is advised and clinicians need to be aware of the particular ‘cut off’ or ‘grey zone’ threshold values for the technology being used and the limitations described in the literature.

Mean Arterial Pressure (MAP)

The Mean Arterial Pressure (MAP) is the average blood pressure of an individual and is measured in mmHg. It is the average arterial blood pressure during a single cardiac cycle. In ‘Pressure Monitoring Mode’ the CardioQ-ODM+ calculates the MAP from the systolic and diastolic pressures of each heart beat.

MAP is considered to be the perfusion pressure required to perfuse thecells with oxygen.

The following formula can be used:

MAP = (2 X diastolic pressure) + systolic pressure
3

Curve of the arterial pressure during one cardiac cycle (sourced from Wikipedia).

Curve of the arterial pressure during one cardiac cycle (sourced from Wikipedia)

Blood Pressure (BP)

Blood pressure (BP) is the pressure exerted by the circulating blood upon the walls of the blood vessels and is created from the pumping action of the heart. Blood pressure decreases as the circulating blood moves away from the heart through the vascular system.

BP is measured in mmHg and consists of systolic pressure (SP) and diastolic pressure (DP) displayed as SP/DP. The systolic pressure is the pressure created when the heart contracts and diastolic pressure is the resting pressure when the heart relaxes.

Various factors influence BP and will include blood volume, resistance and viscosity.

Increased circulating blood volume allows more blood to return to the heart ready to be pumped to the organs and cells, which therefore influences cardiac output and the pressure required to achieve this.

Resistance is related to vessel radius, vessel length and it’s smoothness and also to blood viscosity. The larger the radius, the lower the resistance and the longer the vessel area, the higher the resistance. Vasoconstrictors can reduce the radius of a vessel thereby increasing BP, while vasodilators can increase the radius causing the BP to fall.

Viscosity is the thickness of the fluid and refers to the red cell concentration. If viscosity increases, resistance will increase.

Cardiac Power Output (CPO)

Cardiac Power Output requires flow and pressure to be measured simultaneously and describes the pumping ability of the heart. This be easily achieved with the CardioQ-ODM+ since flow is measured by the oesophageal Doppler probe at the same time as arterial pressure from the arterial waveform. The formula for Cardiac Power Output is as follows:

CPO = MAP x CO
451

CPO has been found to be the strongest independent haemodynamic correlate of in-hospital mortality in patients with cardiogenic shock and chronic heart failure, following the review of the SHOCK trial results (2000). A cut off value of 0.53 watts had a predictive value for in hospital mortality. Patients with a value below 0.53 watts had a 71% probability of in hospital mortality, whereas those with a value above 0.53 watts had a 58% probability of mortality before discharge. Increasing age and female gender are independently associated with a lower CPO.

Cardiac Power Index (CPI)

Cardiac Power Index as with CPO require flow and pressure to be measured simultaneously. This be easily achieved with the CardioQ-ODM+ since flow is measured by the oesophageal Doppler probe at the same time as arterial pressure from the arterial waveform.

CPI = MAP x CI
451

CPI is similar to CPO where cardiac output has been substituted for cardiac index. Women had a lower CPI than men and there was an inverse correlation between CPI and age.