EDM+

EDM+

Only the CardioQ-EDM+ has the precision and responsiveness to guide the clinically proven >10% change Stroke Volume Optimization (SVO).

The clinical benefits of the EDM+ stem directly from the use of a low frequency ultrasound sound signal to measure blood flow directly in the central circulation.

The EDM+ is the world’s first hemodynamic monitoring system to measure both flow and pressure directly.

An exciting new upgrade to the proven Doppler technology, the EDM+ combines Doppler measurement of blood flow with Pulse Pressure Waveform Analysis (PPWA). This provides users with:

  • “Flow Monitoring Mode” : to guide intervention – with proven and highly senstive measurement of flow
  • “Pressure Monitoring Mode” : for extendended continuous monitoring – using proven Doppler for the simplest calibration yet devised

Previous hemodynamic monitors have either been ideal intervention devices, fast precise responsive flow based measurement but non-continuous, or less responsive pressure based continuous monitors requiring complex calibration and frequent recalibration to be effective. In bringing together simple, minimally invasive esophageal Doppler monitoring (EDM) flow based technology with a PPWA system, the EDM+ provides an unparalleled range of functional hemodynamic parameters. Patients can be continuously monitored for extended periods between intervention and calibration episodes. Designed for surgical and intensive care applications, Deltex Medical has chosen the most stable and extensively researched PPWA algorithm currently available.

View the EDM+ Product Brochure

EDM+ Technical Specification

A technical specification for the EDM+ monitor can be accessed here

Monitor Mounting Arms

There are a range of mounting arms available from GCX which attach the monitor to anesthesia stations.  You can view the full range available here GCX Mounting Solutions

Interface Cables

When making a connection to the EDM+ to the High End Monitor (HEM), an interface cable is required.  Deltex Medical provide a Blood Pressure (ABP) Cable Guide which is available here; Cable Guide

For further information relating to probes or for any sales enquires please call (864)- 527-5913 or email the Corporate Office

 

In surgery the CardioQ-EDM+ offers the following advantages:
  • Only surgical CO monitor offering both EDM & PPWA
  • Ease of PPWA calibration and recalibration
  • Continuous monitor ‘bridge’ during diathermy episodes
  • ‘Bridge’ in surgical cases where esophagus is displaced or removed
  • Only device able to guide 10% SVO (Doppler guided)
  • Offers fluid responsiveness parameters including:
    • Corrected flow time (FTc)
    • Stroke volume variation (SVV –  flow and pressure)
    • Pulse pressure variation (PPV)
  • Provides post operative monitoring for 6 to12 hrs in awake patients in recovery/ICU (dependent on probe type)
In the Intensive Care Unit CardioQ-EDM+ offers the following advantages:
  • Only critical care monitor offering both EDM & PPWA
  • Ease of PPWA calibration and recalibration
  • Continuous monitor capability
  • Only device able to guide 10% SVO (Doppler)
  • Offers fluid responsiveness parameters including:
    • Corrected flow time (FTc)
    • Stroke volume variation (SVV flow and pressure)
    • Pulse pressure variation (PPV)
  • Offers Cardiac power output (CPO) and Cardiac power index (CPI), combined flow and pressure parameters (German regulations indicate a benefit in managing and monitoring patients at risk of Cardiogenic shock)

How it Works

How the EDM works

The EDM is unique in its ability to directly measure central blood flow with a minimally invasive disposable probe. The probe is placed in the patient’s esophagus and uses Doppler ultrasound to measure the velocity of blood flow in the descending aorta. The esophagus is easy to access for placement of the ultrasound probe as it is close to the patient’s aorta at the level of T5/T6.

Ultrasound explained

Ultrasound emitted by the probe is directed into the aortic blood flow at angle of 45o. The ultrasound will be reflected by the blood’s red cells. As the blood is moving away from the probe tip each reflected wave is emitted from a position further from the observer than the previous wave, so the arrival time between successive waves is increased, reducing the frequency. The distance between successive wave fronts is increased, so the waves “spread out”. The EDM receives the reflected frequency shifted wave and compares its frequency to that of the transmitted wave. The result of this calculation is that the velocity of the blood can be measured during each cardiac cycle.

Ultrasound Waveform

The ultrasound waveform is displayed in red and white with a dark center and it is encapsulated by a green line, which follows the maximal velocity at that point in time. The monitor places three arrows on the screen; the first at the start of systole (on the baseline); the second at the peak velocity (at the top of the waveform) and the third at the end of systole (on the baseline).

EDM+

The EDM+ directly measures central blood flow in the same way as the EDM. In addition, the device also takes the standard Arterial Blood Pressure (ABP) measurement and calculates a range of Pressure Based Parameters. It is unique in that it can take the Cardiac Output as measured by Doppler flow to calibrate a Pulse Pressure Waveform Analysis (PPWA) algorithm. The PPWA algorithm provides secondary pressure based measures of Stroke Volume (SV) and Cardiac Output (CO) as well as new flow and pressure combined parameters.

By combining both flow and pressure based measurements, the EDM+ allows the user to reduce the inherent weaknesses of PPWA with a quick and simple calibration and recalibration from the Doppler flow based measurements of CO.

For further information relating to probes or for any sales inquiries please call 864-527-5913 or email our Corporate Office

Accuracy & Precision

Accuracy

Many publications cite device performance in terms of accuracy. Accuracy in this context is simply the ability to measure the actual Stroke Volume (SV) in millilitres.

The basic measurement of Stroke Distance (SD) by EDM has an accuracy on a single waveform of ±3%. The conversion of this extremely accurate SD uses a nomogram (a constant using age, weight and height) to calculate a more familiar parameter of SV.

Only Doppler has the precision to guide a 10% SV optimization protocol. EDM has the ability to detect change in sequential measurements. In this case the effect of a small fluid challenge on SD or SV. Precision is the ability to measure the same result repeatedly with minimal error.

Precision

EDM’s strength is in its precision, using Doppler to measure flow directly at the source, the decending aorta.

The precision of a technology dictates its ability to guide fluid management. The 10% SV change algorithm used to optimize SV is specific to the EDM and is evidence-based. Other technologies that are less precise may not be as effective in guiding fluid management based on this algorithm.

Prof. Singer established that the error of repeatability of measuring SD for the EDM was 3.8% [1]. For an individual patient the diameter of the aorta will be a constant thus the SV precision will be equal to the known error for SD. [SV = SD x Aortic Root Diameter (from patient nomogram)].

This precision/repeatability error can then be used to determine the least significant change in SD/SV required to ensure confidence in measuring a real hemodynamic change and not just measurement error. With its calculated error of 3.8%, the user can be 99% confident that a measured change in SD/SV of >10% is real (this is based on 99% of normally distributed data points falling within 2.5 standard deviations of the mean).

 

_________________________
1Singer, M., J. Clarke, and E.D. Bennett, Continuous hemodynamic monitoring by esophageal Doppler. Crit Care Med, 1989. 17(5): p. 447-52

Flow Parameters

The EDM monitor uses Doppler ultrasound technology to directly measure a patient’s central vascular blood flow velocity to deliver the following flow based 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)

The EDM is distinct from other 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 EDM has been found to be equivalent in terms of accuracy to a PAC. However it is the precision of EDM in tracking change that is key to recognising how and why EDM guides Stroke Volume Optimization (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 EDM and EDM+.

The EDM 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

Heart Rate (HR)

Heart Rate is displayed on the EDM and EDM+ 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 EDM and EDM+ 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 EDM 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 EDM and EDM+ 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 EDM and EDM+. MD is simply the distance blood moves in one minute down the aorta.

Minute Distance = Stroke Distance x Heart Rate

Peak Velocity

Flow Time corrected (FTc)

Flow Time corrected is a Doppler only parameter and is available on both the EDM and EDM+. 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 normalized to 60 beats/min using Bazett’s equation.

Corrected Flow Time

Typically FTc is one third of the cardiac cycle. When standardized 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 hypovolemia.

FTc is inversely related to afterload/resistance and the most common cause of an increased afterload/resistance is hypovolemia.  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 EDM and EDM+. 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)

Cardiac Index (CI)

The EDM and EDM+ can calculate Cardiac Index in Doppler flow mode.

Cardiac Index relates the Cardiac Output to body surface area (BSA), 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 EDM and EDM+.

Stroke Volume Index relates the Stroke Volume to body surface area (BSA), 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 EDM and EDM+ 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 EDM 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 EDM (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 EDM 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 EDM and EDM+.

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 EDM and EDM+.

Delivered Oxygen is the amount of oxygen in the blood delivered to the body’s tissues. The EDM and EDM+ can calculate this parameter but require the user to input measurements of hemoglobin 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 hemoglobin, SaO2 is the saturation of hemoglobin 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 EDM and EDM+.

Delivered Oxygen Index is the amount of oxygen in the blood delivered to the bodies tissues indexed for patient body size. The EDM and EDM+ can calculate this parameter but require the user to input measurements of hemoglobin 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 Parameters

The EDM+ 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). Flow based parameters are also available on the EDM+ monitor.

The direct flow Doppler EDM, is preferred for guidance of intervention with fluid and drugs. EDM can do this effectively in the hemodynamically challenging environment of the Operating Theatre, where anesthesia and surgery result in rapid and frequent changes in compliance. Pressure based technologies are useful in stable postoperative patients but are limited in their ability to guide interventional treatment.  A combination of both technologies, EDM+ is the best of both worlds.

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 EDM+ (when in flow-monitoring mode). In addition the EDM+ also calculates SV from the arterial pressure wave using the Liljestrand and Zander algorithm (when calibrated and in pressure-monitoring mode).

The EDM+ 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 EDM+ 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 EDM and EDM+ and after calibration of the PPWA algorithm EDM+ can calculate this parameter as a Pressure Based Parameter Stroke Volume Index relates the Stroke Volume to body surface area (BSA),  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 EDM and EDM+ from Doppler based measures and the EDM+ 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 EDM+ 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 EDM and EDM+ calculate Cardiac Output in Doppler flow mode. Additionally, after the calibration of the Stroke Volume, the EDM+ can simultaneously calculate the Cardiac Output from the arterial pressure waveform.

The EDM+ 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 EDM and EDM+ can calculate Cardiac Index in Doppler flow mode and EDM+ 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 EDM and EDM+ can calculate Stroke Volume Variation in Doppler flow mode and EDM+ 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 EDM 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 EDM and EDM+ and after calibration of the PPWA algorithm EDM+ 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 EDM 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 EDM and EDM+ and after calibration of the PPWA algorithm EDM+ 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 EDM and EDM+ and after calibration of the PPWA algorithm EDM+ 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 EDM and EDM+ 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 hemoglobin 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 EDM and EDM+ and after calibration of the PPWA algorithm EDM+ 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 EDM and EDM+ can calculate this parameter but require the user to input measurements of hemoglobin 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 EDM+ as a pressure based parameter only. PPV has been reported to be a useful predictor of fluid responsiveness.

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 EDM+ 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 EDM+ 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 EDM+ calculates the MAP from the systolic and diastolic pressures of each heart beat.

MAP is considered to be the perfusion pressure required to perfuse the cells 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).

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 EDM+ since flow is measured by the esophageal 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 hemodynamic 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 EDM+ since flow is measured by the esophageal 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.

Arterial Lines

This section highlights the importance of maintaining and calibrating an Arterial Line

Incorrect setup of pressure readings can lead to inappropriate treatment.

Prior to any transduced pressure readings and then subsequent use with an EDM+, it is essential that the transducer has been:

Levelled to the phlebostatic axis to eliminate the effects of hydrostatic pressure on the readings:

  • The phlebostatic axis is on the 4th intercostal space along the mid axilla line.
  • The phleblostatic axis is relevant for supine and up to 60 degrees of head-up tilt.
  • The transducer should not be levelled to the site of arterial catheter access.
  • If the transducer has not been levelled to the phlebostatic axis, pressure readings will be either falsely high or falsely low.
  • It is not suitable for an abnormal shaped thorax.
  • Levelling should be done at every handover, prior to pressure and EDM+ readings and at any time where there is doubt about the readings. The literature suggests that for consistent readings of pressure trends, the patient bed should be at the same angle each time.

Zeroed to eliminate the effects of atmospheric pressure on the readings. It is sometimes known as calibration:

  • The transducer has to read zero when there is no pressure against it.
  • It is described as being similar to zeroing a set of scales before weighing.
  • This should be done at every handover, prior to pressure and EDM+ readings, if the line is disconnected from the patient monitor and at any time where there is doubt about the readings.

Tested for damping:

  • Damping in the pressure line system acts as shock absorber (like a car suspension).
  • In order to test the system dynamics, the user should carry out the Square Test.
    • The Square Test assesses how fast the system vibrates in response to a pressure signal.
    • Allows the transducer to ‘feel’ some of the 300mmHg in the pressure bag.
    • The user should squeeze the flush valve on the transducer for a few seconds and then let go.
      • Waveform should rise sharply, plateau and drop off sharply when released (Figure 1).

Inaccurate damping can lead to inappropriate treatment:

Overdamping (This is defined when the oscillations following the downstroke are sluggish and can underestimate systolic pressure or overestimate diastolic pressure) Causes include:

  • Loose connections
  • Air bubbles
  • Kinks
  • Blood clots
  • Arterial spasm
  • Narrow tubing

Underdamping (This is defined when the oscillations are too pronounced and can lead to a false high systolic or a false low diastolic pressure):

  • Catheter whip or artefact
  • Stiff non-compliant tubing
  • Hypothermia
  • Tachycardia or dysrhythmia

Technical Review

The Technical Review US is ideal for those seeking a deeper understanding of the EDM technology and contains information on:

  • A short history of the development of esophageal Doppler monitoring
  • How esophageal Doppler measures blood flow velocity in the aorta
  • Comparative results compared to pulmonary artery catheter data
  • Accuracy of measurement
  • Probe placement and focussing
  • Waveform and parameter explanation
  • A summary of Fluid Management
  • Results of clinical application
  • Limitations of use