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ODM Parameters Explained

Flow Parameters

The CardioQ-ODM monitor uses Doppler ultrasound technology to directly measure a patient’s central vascular blood flow velocity to deliver the following flow parameters:

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 ODM devices in possessing the ability to calculate Stroke Volume and so 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