Introduction to USCOM

Editor's Notes

• #2: Introduce self and USCOM: . USCOM is an Australian Company interested in completely non-invasive monitoring for management of haemodynamics.
• #3: Core Proposition: We know that stroke volume, heart rate, blood pressure and vascular resistance are all important for managing cardiovascular haemodynamics. Many current methods are invasive, expensive and technically difficult to do. Often we rely on “How do you feel?” There has been a need for a safer, accurate and rapid solution that is suitable for a range of patients from neonates to adults.
• #4: USCOM Solution: The USCOM 1A non invasive haemodynamic monitor is portable, simple to use, safe and accurate. It weighs < 8kgs. It allows for measurement of haemodynamics from both the left and right side of the heart. It is a technique that can be taught to doctors, nurses and paramedics alike. There are no consumables which makes it very cost efficient.
• #5: Applications: It can be used on patients that are awake or anaesthetised. From neonates to your larger patient. Also, animals from rats and lizards to sheep and horses. Taking serial measures and looking at change. It is currently used in all of these areas and specialities.
• #6: Product: The USCOM 1A non invasive monitor uses the reflected Doppler signal from red blood cells travelling through the aortic or pulmonary valve to determine the stroke volume of blood per heart beat. How is this done?
• #7: Cardiac Output: Let’s review the cardiac output formula: CO = SV x HR Stroke Volume = Valve Area x Stroke Distance The distance blood travels through the aortic or pulmonary valve in one beat is measured as stroke distance. . The area of the valve or outflow tract is calculated via an algorithm. The CW Doppler gives us the Stroke Distance.
• #8: VTI – Stroke Distance: Each systolic Doppler profile (vti) represents the stroke distance of the blood in that beat. The blue pixels represent red blood cells reflecting off the sound beam. The Doppler signal or profile is displayed on a Time / Velocity graph. The integral of the Doppler profile is measured in centimeters. In an enclosed circuit, flow is faster through a narrower area and fastest through the narrowest area. Think about when you use your finger to cover the opening of a hose. From the heart’s chamber to the main vessel, the narrowest area is the valve. Aortic on the left and pulmonary valve on the right. So, by obtaining the highest velocity with the Doppler probe we will obtain the distance that flow travels in each beat through the respective valve. Aiming the transducer directly in line with the blood flow will give the highest velocity. So we aim for the highest velocity obtainable. If we know the area of the valve then we can calculate the stroke volume .
• #9: OTD Algorithm: The Outflow Tract Diameter has a linear relationship with height. The algorithm is based on published research which shows that there is a linear relationship between height and aortic outflow tract diameter. This finding was used to establish the USCOM algorithm which determines the size of the Outflow Tract Diameter (OTD) based on a patient’s height. If the Left Ventricular Outflow Tract (LVOT) is known (measured on echo) that can be used to override the algorithm. For neonates, a weight based algorithm is used, as most neonates are difficult to measure length and weight is most commonly used. Regression equations can be calculated from populations studies to predict AV and PV annular diameters
• #10: Big Picture: Adjustment of preload, contractility and afterload to balance oxygen delivery with oxygen demand is core to haemodynamic management. Adjusting preload by adding or removing volume. Increasing contractility by using inotropes. Changing afterload, the pressure the left ventricle needs to eject blood into the aorta. Using different medication to alter preload, contractility or afterload can be confirmed by using the USCOM. Sample a baseline measure and then after the medication remeasure to see what objective value has been obtained. A number of studies have shown that circulatory optimisation reduces morbidity, mortality and hospital stay by approx 33%. Each of these alterations can be detected using the USCOM device.
• #11: Frank-Starling Curve: Frank and Starling described the relationship of myocyte stretch and contractility in the isolated heart. They observed that the more the myocyte was stretched, the greater the responding myocyte contraction, up to an optimal point. This is of clinical importance because it suggests that SV is dependent on preload or filling; the greater the filling, the greater the contraction and the greater the SV. Conversely, beyond a certain point, increasing the stretch results in decreased contractility, suggesting each myocyte has an optimal stretch.
• #12: Individual optimisation: Increasing preload by adding a fluid bolus will increase Stroke Volume. Monitoring the fluid challenge confirms optimal stroke volume. Once the change becomes less than approx. 10% adding more fluid will not benefit the patient. Each individual has a characteristic Frank-Starling curve reflective of their underlying myocardial morphology and function. For this reason, individual optimisation may not be achieved using standard targets, but rather it would be better to make serial observations of each patient’s cardiac output to determine preload, afterload and contractility.
• #13: Contractility: With increased contractility for a given preload, a higher SV and CO will be achieved. With a low contractility at the same preload, a lower SV and CO will result. The ‘number’ will reflect the individual patient.
• #14: Volume vs Pressure: The current clinical practice is to increase pressures such as central venous pressure (CVP) or mean arterial pressure to clinical targets. Optimising to a target pressure may not adequately optimise the volume status of every patient; one may be underfilled while another overfilled. Restoring blood pressure does not guarantee an adequate volume status. Restoring volume to a target value also does not ensure an adequate volume has been achieved, as each individual has a different capacity. There is no uniform response to adding fluid due to compliance of the heart muscle. In myocardium which is compliant, additional volume will stretch the myocytes and greater SV will be achieved. In a less compliant myocardium, a heart muscle that has had its myocytes over stretched (hypertrophied as in CHF), does not have the same recoil with the additional volume. Therefore SV may not increase or be able to be maintained. Think about a basketball and a balloon. When they are the same size and shape they will respond differently to volume and pressure. Due to its highly compliant nature, more air (volume) is needed by the balloon to reach the same pressure as the basketball. Adding extra volume will increase the pressure more rapidly in the basketball than in the balloon. When they contain the same volume, there is a higher pressure in the basketball.
• #15: Product: Technique: There are two main access points: suprasternal and parasternal. The method best used depends on the patient’s attributes and position. To gain access to flow from the aortic valve, the transducer needs to be positioned at the Suprasternal notch or at the supraclavicular area. To gain access to flow from the pulmonary valve, the transducer needs to be positioned on the left sternal edge at the 3 rd or 4 th intercostal space. As with any new technique there is a learning curve so it will take at approximately 30 patients, practicing SSN, Supraclavicular and LSE and regular use to start to become confident with the technique.
• #16: Aortic Approach: Lay the patient flat or with the head of the bed slightly elevated. The head and neck should be in a comfortable position. Lift the chin slightly, to gain access to the suprasternal notch (SSN). Sample around the neck while aiming the transducer toward the heart. Positioning the transducer under and parallel to the sternum. A triangular systolic Doppler profile is maximised with smaller manipulations of the probe. The aim is to acquire the peak velocity from the aortic valve.
• #17: Pulmonary Approach: Lay the patient flat or with the head of the bed slightly elevated. The muscles of the chest should be relaxed. The pulmonary valve is approximately positioned left of the sternum below the 2nd intercostal space. Begin the examination at this position . Sample in each intercostal space while aiming the transducer toward the heart. Position the transducer close to the sternum while rotating the transducer toward the head. A triangular systolic Doppler profile is maximised with smaller manipulations of the probe. The aim is to acquire the peak velocity from the pulmonary valve.
• #18: Product: Display & Features
• #19: Product Features: : 2hr battery. Large Hard Drive All software upgrades are done easily with a flashstick. The touchscreen interface is easy to navigate. The device automatically traces the Doppler profiles in real time and simultaneously calculates all of the parameters. Network connections for connecting to a network printer or download images or data with a Flashstick via the USB port. Researchers can download the spreadsheet.
• #20: Device: Let’s review each of these features.
• #21: Touchscreen Interface: The device is easily navigated with the stylus. All patient data is accessed via the ‘OPEN’ button. Patient names & IDs are listed . Patient studies are listed. Start by entering the patient information and then acquire the Doppler profiles. Display : The Examination screen shows: Haemodynamic values (V) acquired at each measure The difference (delta V) between the current and previous measurement Average (Avg) the average value of all cards. Exam Time & Date Transducer and Mode (Aortic or Pulmonary) Each Measure card represents each Doppler Flow Profile that was measured when in ALL or ONE select mode. Measure 3-5 profiles or a respiratory cycle. Each Measure card represents the average of all Doppler Flow Profiles that were measured at one acquisition when in GRP select mode.
• #22: Directly MEASURED INDICES: Vpk (Peak Velocity): Peak velocity of the systolic blood flow profile in metres per second. vti (Velocity Time Integral): Velocity time integral, or stroke distance. The distance a blood cell travels per cycle measured in centimeters. ET% (Ejection Time Percentage): The percentage of cycle duration occupied by systolic ejection. HR (Heart Rate): The number of cardiac cycles per minute. Pmn (Mean Pressure Gradient): The mean pressure change across the valve measured in millimeters of mercury. Derived CALCULATED INDICES (Dependent on CSA) SV (Stroke Volume) = Vti x CSA (CSA = Cross Sectional Area of Pulmonary Artery or Aortic Artery): The volume of blood ejected from the heart during one systolic beat. Measured in cubic centimetres (mls). The annular diameter of the valve is derived from a height referenced algorithm or directly entered from 2D echo measurements. CO (Cardiac Output) = SV x HR: The total volume of blood ejected from the heart in litres per minute. CI (Cardiac Index) = SV x HR/BSA (BSA = Body Surface Area): Cardiac Index adjusts the cardiac output to the individual persons body size by representing blood flow relative to a square metre of body surface area. Derived CALCULATED INDICES (Independent of CSA) MD (Minute Distance) = HR x Vti: The distance a blood cell travels per minute. Measured in metres per minute.
• #23: FlowTracer: The FlowTracer feature automatically traces the edge of the Doppler flow profile displayed on the examination screen. This allows automatic, beat to beat measurement of the profiles displayed. For easy viewing of the Doppler profile, the red traceline can be removed during acquisition. TRACE button is on the Examination screen. Note: The calculations continue even without the traceline being present! Individual beats can be deleted from the measurements. In difficult to trace rhythms TouchPoint manual measurement can be used.
• #24: SVR: Manual input of the blood pressure and CVP can be made for non invasive calculation of the Systemic Vascular Resistance.
• #25: Trending: As previously discussed, Frank and Starling described the relationship of myocyte stretch and contractility in the isolated heart. Adjustment of preload, contractility and afterload to balance oxygen delivery with oxygen demand is core to haemodynamic management using the USCOM. A graphic display of haemodynamic change is seen when serially monitoring a patient after each fluid challenge or medication change. In this example, fluid was given early and as the curve flattened, contractility drugs were given to improve CO.
• #26: Add Notes: Type notes to document change in interventions, fluids or medications. A date and time stamp will be attached automatically. These notes will be seen in the Report.
• #27: Exporting Data: Spreadsheets, Screenshots & Reports Insert a USB drive / flashstick into the USB port located on the back panel of the system. The displayed screen will be copied into a folder named ’Screenshots’ on the USB drive. The screenshot is a bitmap. The report will be copied into a folder named ‘Reports’ on the USB drive. The report is a .htm file. Spreadsheets are in .csv format and can easily be saved as .exl. The file can be transferred to a PC.
• #28: Care & Cleaning:: Transducer After completely cleaning the transducer head from gel and any foreign matter, the USCOM transducers and cables (not the connector) can be disinfected by submersing the head for up to 15 minutes in 0.55% orthophthalaldehyde (CIDEX OPA). DO NOT submerse the connector. The device can be wiped down with a damp cloth. Do NOT drip fluid on the screen.
• #29: QUICKSTART: RUN activates the QUICKSTART feature, this allows direct access to the Examination screen without the need to enter a patient’s details first. The Doppler trace will start automatically. Measurements not needing area will be displayed. Patient details can be added later allowing for all calculations to be made. Useful in urgent situations like Outreach, ED and retrieval situations.
• #31: Validation: There is extensive validation for Doppler done over the years. It has been used as standard clinical practice in echo labs for over 30 years. USCOM has been validated for flow velocity against the flow probe in the laboratory setting. It has been validated against flow probe in dogs and sheep. It has a number of validations from around the world comparing it to the pulmonary artery catheter in patients having undergone cardiac surgery. In neonates the algorithm for valve area has been validated against echo.
• #32: Validation: USCOM has been validated on neonates as small as 390gms at 26 weeks gestation.
• #34: Training: ON-Site Training Protocol: Background information is provided in booklet form prior to the training day, Basics and Quick Guide. An interactive PowerPoint presentation to introduce and review the science and technique is provided ahead of hands on training. Trainees can manipulate the unit in coordination with the presentation. ‘ Hands on’ training is usually started on 'normal' volunteers followed by patients. Review technique and answer questions on a ‘follow up’ visit. A 'Certificate' of Completion' will be sent to the trainee after filling out the log sheet with 30 studies and sending it to the USCOM head office. OFF-Site Training Protocol: This is provided at the AIU
• #35: Training: The concept model of Train the trainer works well as there is a hands on component to using the device. There is a learning curve of approx. 20 exams to get comfortable with the technique and then practice on real patients. Depending on the individual somewhere between 50-100 patients to become very comfortable.
• #36: Summary: USCOM is a safe, portable and non invasive haemodynamic monitor. We have reviewed the background of both the Stroke Volume equation and the properties of Doppler that are both relevant to acquiring haemodynamic information by the USCOM monitor. We have discussed the technique for acquisition of the Doppler profiles aiming to acquire the highest velocity flow from either the aortic or pulmonary valve. We have gone through the various screens and features of the USCOM and discussed haemodynamic optimisation of the individual. We have covered the various validation research that has been done. We have highlighted the training materials that can assist you and discussed the learning curve.
• #37: Conclusion: USCOM is a non invasive haemodynamic monitor. No blood, no needles, no consumables. The interface is easy to navigate and use. It is designed for individual fluid optimisation and management of haemodynamics and done noninvasively. It is a safe, accurate and efficient solution to haemodynamic monitoring.
• #38: THANK YOU for your attention. Questions please.