Support - FAQ's

The USCOM device is a sophisticated continuous wave (CW) Doppler ultrasound device designed for simple, high fidelity, non invasive assessment and management of circulation. The device uses unique algorithms, signal processing and software to provide a simple, accurate and cost-effective tool for non-invasive cardiovascular assessment. USCOM provides non-invasive, real time, beat to beat quantitative measures of cardiac haemodynamics.

Circulatory Optimisation: optimising the circulation can be critical. In multiple clinical applications haemodynamic optimisation has been demonstrated to decrease mortality, morbidity and hospital cost by as much as 35% in adults and children. Objective assessment of treatment and Early Goal Directed Therapy (EGDT): In routine clinical practice incredible resources are spent managing haemodynamics despite no objective assessment of efficacy. In an evidence based era the use of a device to measure the effects of fluid and drugs (inotropes and vaso-actives) on the circulation non-invasively is critical. USCOM provides accurate and non-invasive assessment of haemodynamics in all clinical environments and is ideal for quantifying haemodynamic goals and monitoring therapy and taking advanced haemodynamics beyond the ICU. Replace invasive methods: In critical environments where invasive catheters and probes are currently used for assessing cardiac function, USCOM provides a more immediate, accurate and safe alternative, while in more routine clinical environments USCOM can be both effective and litigation defensive.

Anyone in whom knowledge of cardiovascular performance is important; this includes patients in whom a Pulmonary Artery Catheter (PAC) may be contemplated, through to those in whom you would make a simple blood pressure or pulse measurement. USCOM can confirm normal or abnormal function, and monitor changes associated with therapy or disease with high sensitivity.

USCOM is a sophisticated CW Doppler ultrasound device. CW Doppler has been used safely and reliably for over 20 years in clinical practice in multiple clinical applications and CW Doppler is a recommended method for measuring Cardiac Output (CO) by the ASE, ACC and AHA. USCOM is one of the most accurate and well validated devices for measuring CO available. It has been validated in subjects from 26 weeks gestational age to 85 years old and in COs ranging from 0.12 to 18.7 l/min. USCOM results have been positively compared to flow probes in haemodynamic models and animals, against PAC thermodilution (bolus and CCO) FICK, MRI, and echocardiography in humans at rest and during exercise.

USCOM is unique by being both non-invasive and accurate unlike other methods of haemodynamic monitoring. USCOM uses a specialised CW Doppler with improvements to increase sensitivity and reproducibility, and simplify its use. As USCOM is less expensive than other methods when considering capital and maintenance costs, consumables, learning and accreditation, it has high levels of cost-effectiveness. Swan-Ganz (PAC) catheterisation is invasive, of questionable accuracy, associated with negative outcomes and remains a method of last resort. PiCCO is an invasive pulse pressure measurement method with CO calibrated to transpulmonary thermodilution. Pulse pressure is an analogue of blood pressure and not CO, or else simple non-invasive blood pressure would be desirable, while transpulmonary thermodilution has all the limitations of conventional thermodilution. This method remains slightly less invasive than PAC and less reliable, being more difficult to use and requiring frequent recalibration. Bio-impedance is simpler to perform, but with unproven accuracy, particularly in heart failure; a critical application for any monitoring method. Transoesophageal methods are only feasible for short term monitoring, require sedation and obstruct the pharynx. Doppler monitoring of the descending thoracic aortic (DTA) flow, although sometimes useful for intra-operative applications, does not measure CO. Transoesophageal echo is user dependent and expensive, requiring extensive training and experience, with high capital costs and consumable expenses. ECG remains the most extensive cardiac monitoring method but makes no measure of haemodynamics.

Echo is a diagnostic test that evaluates morphology and haemodynamics, but is expensive and difficult to use accurately, requiring extensive training. USCOM has improved the echocardiographic method of haemodynamic measurement by making it simpler to use, more accurate and less expensive.

The magnitude of changes in CO which can be detected by single repeated CW Doppler measurement, determined by 95% confidence intervals, are generally considered to be 10-15%. However if repeated and consecutive measures are made, this sensitivity can theoretically be improved to 5%. The use of USCOM anthropometric algorithms may improve the accuracy of conventional echocardiography resulting in detection of clinical changes of CO in the order of 10% or less.

USCOM takes about 30 cases to achieve reliable results, but like other methods optimal use of USCOM depends on training and experience; the more you do the better you get!

CW Doppler is the most reproducible of echocardiographic measurements with most data suggesting 5% or less variability between and across observers. The FlowTracer digital auto signal profiling increases reproducibility significantly by eliminating the variability associated with manual profile tracing.

Both Stroke Volume (SV) and CO can be reliably determined from the spectral flow profile as a product of the velocity time integral (vti) times cross sectional area (CSA), and, for CO, times heart rate (HR). This method has been in use reliably for over 20 years in clinical practice.

Optimising the Doppler profile shape, intensity, velocity and sound is important in acquiring optimised USCOM signals. As a method Doppler can only under measure haemodynamic values, so always use the largest stable signals. Some training is necessary to highlight the correct profile attributes.

Once the acoustic window is located, and the transducer orientated across the pulmonary or aortic valve, signal will continue until the transducer is moved. In clinical practice the transducer may move or the heart move with respiration and the signal diminish. This can simply be corrected by re-orientating the beam across the valve until the audio signal and visual display are optimised in both velocity and density.

The Doppler equation (?f = 2fv cosø /c) determines that flow and velocity are related by a factor of cosø. This means that when ø = 0° or 180° signal is optimised (cosø = 1), however as ø approaches 90° or 270°, cosø approaches 0, as does the Doppler signal. In practice an error of ±20° is acceptable resulting in less than 6% error in velocity calculations. Occasionally in clinical practice, due to anomalous anatomy, this ideal cannot be achieved. This is not a problem, as change will be detected regardless of the inherent error of measurement, provided the transducer position does not change. Additionally, the CO signal can be referenced to the contralateral USCOM measured output, or an alternate method (conventional echo, Swan-Ganz, etc.).

Cross sectional area (CSA) of flow is essential to measurement of Doppler flow volume. However other measures such as minute distance (MD) are more sensitive than volumetric measures to detect change in CO. USCOM has three methods of dealing with flow CSA;
a. Use CSA independent parameters such as vti or minute distance (MD). b. Measure the valve diameter using another imaging method (2D, MRI, etc) and recognise the valve diameter doesn’t change significantly after maturity.
c. Apply anthropometric algorithms to determine valve diameter and CSA.
While the diameter of the pulmonary artery (PV) and aorta (AV) vary during systole and diastole with changing pressures, the valvular annulae remain relatively constant in diameter and provide an accurate measure of flow CSA.

USCOM flow volumes depend on calculation of the CSAs by a height referenced algorithm. This is a very accurate method for estimating CSA, but depends on measurement of height. Across the normal values a 10cm change in height is associated with a 1mm change in valve diameter; the spatial resolution of ultrasound. Or to put it differently a 10cm error in subject height assessment is equivalent to an acceptable 2D ultrasound measurement.

The pulmonary artery is aligned at approximately 60-80° to the aorta, so when parasternal imaging of the pulmonary artery is optimised, detection of aortic flow will be negligible (cosø ? 0 where ø = 80°). Conversely, apical or suprasternal imaging of aortic flow will barely register pulmonary flow. In conventional echocardiography cross signal registration is insignificant.

Transthoracic echocardiography is routinely performed on many people each year, and CO is a routine part of these examinations. Occasionally these valves are not accessible. Results generally improve with experience, with right and left flows attainable in almost all subjects. Post thoracotomy examinations may be obstructed by intra-thoracic air, which is usually reabsorbed within 12 hours. Certainly changing acoustic access and patient examination position from supine to head up and left lateral decubitus can be useful to improve signal. Successful results have been reported from as low as 80% in difficult post cardiac surgical subjects to 100% in neonates and children.

Suprasternal access is almost universally possible, while auscultation can be used to locate difficult parasternal and apical acoustic windows. In rare cases 2D ultrasound may be required to locate optimal insonation access from the parasternal and apical windows, with skin marking used to aid accurate transducer re-positioning. Right suprasternal, right parasternal and subcostal imaging may also be used while raising the head or positioning in the left lateral decubitus position may help.

Signal is continuous while the probe is orientated across the valve, however in some subjects with anomalous anatomy, pulmonary disease or during ventilation, signal can be interrupted with respiration. Even under these conditions serial measure of 3 to 5 consecutive cycles provides a highly sensitive window for detecting changes in cardiovascular function.

USCOM has the same limitations as conventional Doppler ultrasound. Sound is poorly transmitted through air and bone (lung and ribs), so these obstructions limit signal. USCOM is a specialised CW Doppler device, so the signal is more robust than the CW Doppler on conventional multi-purpose devices, and significantly more robust than 2D imaging. Soft tissue attenuates ultrasound by approximately 1 dB/cm/MHz, meaning the more tissue to penetrate the less the signal. Anomalous anatomy and complex multi-valvular haemodynamic abnormalities can also be confusing. However as most of these subjects will have baseline echocardiograms, USCOM monitoring can be used to accurately monitor haemodynamic change. In cases of single sided pathology such as stenosis (commonly aortic), comparison with the contralateral output is useful. Locating the appropriate acoustic window may be difficult in some patients, however auscultation and 2D echo can be of assistance (see k). In subjects with irregular rhythm multiple cycles should be averaged from representative signals; the greater the variability the greater the number of signals to be averaged.

ECG provides an electrical map of the activation of the heart and is historically well accepted in clinical practice however, it has many limitations and makes no measure of CO. USCOM directly measures intracardiac flow.

Swan-Ganz and similar intracardiac or intra-arterial catheters provide clinicians with invasive estimates of haemodynamics. PACs are associated with increased mortality, morbidity and hospital costs, while there is a well documented association of infections with increased venous and arterial lines and growing dwell times; NO lines are the desired number. Recent evidence suggests USCOM can replace PAC in many ICU applications. Alternatively USCOM can be used to decrease the number patients with PACs and the duration of monitoring. In a litigation sensitive environment where the incidence and severity of infections is increasing, and the accuracy of catheters is being questioned, a safe and accurate alternative is increasingly important.

In developing the science and improving the sensitivity of transcutaneous CW Doppler monitoring, USCOM has developed a unique auto Doppler tracing system, FlowTracer, which provides instantaneous, beat to beat readout of haemodynamic parameters. The system operates with real time intelligence to provide mathematically accurate beat to beat Doppler flow profile tracing. In extremely irregular rhythms, or in extreme environments of electronic interference, the FlowTracer may not establish a reliable trace, in which case the manual TouchPoint outline method can be selected as an option. While FlowTracer accurately traces the Doppler signal, this does not indicate the accuracy of the Doppler flow profile so manual review of Doppler profiles is recommended.

USCOM has minimal consumables, requiring only a simple water soluble gel to operate optimally. This means the incremental cost per measure is negligible. However appropriate disinfection of the transducer is recommended between uses.

USCOM is HL7 compatible.

Uscom has a commitment to research and development and will continuously release new software to supplement functionality of the USCOM. These upgrades will be based on the current product platform. Additionally Uscom has a product development path and a number of allied patents, designed to improve the cost effectiveness of cardiovascular patient care.