Getting Started with the ODM+
Welcome to Deltex Medical’s CardioQ-ODM+ for measuring real time cardiac function.
The course objectives will give you an understanding of:
- How and why to use the paediatric probe with the monitor
- The Doppler waveform
- The physiological data being collected.
Tip: We advise you to choose a patient, who is likely to be relatively straight forward the first time that you use the oesophageal Doppler monitor. This course is for information only and is in no way intended to be a replacement for the Instructions for Use and the Operating Handbook, which should be referred to for full instructions.
Note: Local laws apply in all cases. The products shown in this course may not be available in all markets.
Haemodynamic Monitoring in Paediatrics
Central venous pressure may be a poor predictor of volume status in paediatrics.1
The clinical requirements of haemodynamic monitoring in paediatrics needs to tackle whether:2
- the patient is in a high, medium or low flow state
- flow is changed by a particular therapy
- flow is adequate for metabolic needs
Oesophageal Doppler monitoring was able to provide a clinically accurate estimate of Cardiac Output and monitor changes in flow, including those in response to therapy, such as inotropes and vasodilators.2,3
ODM in children shows the high precision of flow measurements observed in adults and is easy to use.4
Thus, changes in response to interventions are probably of greater significance than the actual value itself.4
1 Tibby et al. Intensive Care Med 2001,27:201-5.
2 Tibby et al. Crit Care Med 2000,28:2045-50.
3 Lechner et al. Pediatr Crit Care Med 2012,13:542-8.
4 Murdoch et al. Acta Paediatr 1995,84:761-4.
When to Monitor Children
Oesophageal monitoring is minimally invasive, reliable and useful for monitoring haemodynamic change within the operating theatre, accident and emergency, or critical care to assess cardiac function in children.2,5,6
2 Tibby et al. Crit Care Med 2000,28:2045-50.
5 Schubert et al. J Clin Monit Comput 2008,22(4):299-307.
6 Mohan et al. Pediatr Cardiol 2002,23(1):58-61.
CardioQ-ODM+ Monitor Screen
The Oesophageal Doppler Probe
Probes are for single patient use and are sterile with a latex-free silicone tube. They are held coiled inside the packaging by a clear plastic sleeve. Remove carefully from plastic sleeve before insertion.
The spring core makes probe placement easy and adds power to rotate the Doppler crystals inside the oesophagus. The action of the spring means that holding the probe towards the proximal end provides maximal rotational motion.
- Do not insert nasally
- Not for use in patients weighing less than 3 kg
- Do not use in close proximity to laser surgery
- Not for use in patients with pharyno-oesophago-gastric pathology and/or severe bleeding diatheses
- Remove probe prior to MRI scan due to the metal parts within the probe
- Always use the appropriate probe for children under 16 years
Probe placement may be contraindicated with:
- Carcinoma of pharynx, larynx, oesophagus
- Aneurysm of thoracic aorta
- Proximal coarctation of aorta
- Tissue necrosis of the oesophagus
- Intra-aortic balloon pumping
Note: Downs Syndrome children may have intrinsic narrowing of their hypopharyngeal structures preventing insertion of the probe.
Nomogram Your patient’s real time flow parameters are Flow Time and Peak Velocity, which together give you Stroke Distance (SD), also referred to as Velocity-Time Integral (VTI). These are converted to left ventricular Stroke Volume (SV) with a nomogram, based primarily on height and validated in children.2
If the patient’s characteristics fall outside of the nomogram limits, indicated by red numbers on the selection screen, this conversion cannot happen and volumetric calculations (e.g., CO, SV) will not be displayed.
2 Tibby et al. Crit Care Med 2000,28:2045-50.
The paediatric probe should be inserted orally. Tip: The probe may be connected to the monitor before or after insertion. However, if possible, ensure probe is inserted 10 minutes prior to use to allow a mucous bond to develop.The bond is important because ultrasound travels poorly through air.
Probe placement may be guided by the six markers at predefined distances from the tip of the probe (15, 20, 25, 30, 35, 40 cm). These should be aligned with the incisors at the shortest acquisition distance determined by patient height.
Note: A tape measure is supplied with each box of paediatric probes.
Add a New Patient
Focussing the Probe
Proficiency in signal location is rapidly developed with experience in probe placement. Lefrant commented on an adult study that: “A training period involving the first 12 patients made the operator self confident”.7 The optimal signal will be the tallest and brightest waveform together with the loudest, sharpest ‘whip crack’ sound located around the correct depth markers. Tip: Once found, remember the depth where the optimal signal occurred and always return to the same depth to refocus.
7Lefrant et al. Intensive Care Med 1998;24:347-52.
Doppler Signal Optimisation
Range will increase or decrease the size of the wave so that the top can be seen on the screen.
Once the best waveform has been found, the signal can be amplified by turning the Control Knob manually or by pressing the Auto gain button. The probe must be held steady for up to 45 seconds while Auto gain is adjusting the signal. Manual adjustment expedites the ideal signal strength: white and orange edges with a white trailing edge and a dark centre. However, too much or too little gain affects the picture.
Doppler Signal Optimisation 2
The Filter button will strip out low frequency signals, such as valve noise or wall thump. It should not be required for anything else.
The Peak Velocity Display draws a blue line that remains as a guide to the point of the highest velocity signal found during Focus mode.
Once the correct signal is displayed on the monitor, press the ‘Run’ button to begin data evaluation.
Check the cycle time displayed in the top right corner. The default is 5, where 5 waveforms are averaged and the results displayed. However, this can be increased to between 10 and 20 when there are fluctuations in the height of the waveform e.g., atrial fibrillation, or decreased to use each cycle (beat-to-beat)
Understanding your Signal
Optimal waveform: A strong orange and white edge with a trailing white edge and a dark centre. It will always have the loudest, sharpest ‘whip crack’ sound, accompanied by the tallest, brightest picture for that patient within markers.
Inadequate waveform 1
Inadequate waveform 1: This wave shows signal scattering and dispersion indicating incorrect probe placement: a dark centre is required to indicate the probe is facing the centre of the aorta. Do not use data until refocussed.
Inadequate waveform 2
The vertical lines represent valve noise. Refocus the probe and reduce gain to give a clearer picture. If a better signal is not found, use the filter. Do not use data until refocussed.
Inadequate waveform 3
Poor signal: Green follower unable to track a wave outline and arrows placed incorrectly. Do not use data until refocussed.
Coeliac axis signal is a wide waveform denoted by flow gradually reducing during diastole. Its sound will be less sharp than that of the descending T5/6 aortic and parameters may be implausible. Probe too far in – withdraw slightly and refocus. Do not use data – repeat until optimal signal is found.
If the probe is too high, the pulmonary artery may be detected below the line. Flow above the line at this depth may indicate flow from other vessels – advance the probe until as near as possible to the appropriate depth marker. Do not use data until refocussed.
Venous (azygous) signal: a ‘whooshy’ slower sound with a strong signal below the line as flow returns towards the probe. Refocus and/or withdraw slightly. Repeat until optimal signal is found. Do not use data until refocussed.
Intracardiac: a ‘galloping horse’ sound with signal above and below the line due to different flow directions through the heart – rotate the probe through 180 degrees and refocus. Change depth and refocus until optimal signal is found. Do not use data until refocussed.
Monitoring Cardiac Function
Run mode appears when pressing the ‘Run’ button, or automatically after using auto gain. It measures cardiac function and is indicated by the presence of a green follower, which outlines the wave. Three white arrows should appear at the peak and bottom corners of the waveform defining peak velocity and flow time.
If the arrows are placed incorrectly this will affect the data displayed. Once the green follower outlines the waveform and arrows are placed correctly, the parameters and the shape of the waveform can be evaluated on the monitor.
Blood flow as seen by the monitor
Once the correct waveform is located, blood flow velocity in the descending thoracic aorta is shown above the line. Signals below the line are moving towards the probe. Stroke Distance (SD) = the distance that a column of blood travels down the descending thoracic aorta (cm/s). The ODM+ demonstrates SD as the area under the triangular waveform. This is known as the velocity-time integral (VTI).
Basic Flow Parameters
The aortic wave shows two major indicators of cardiac function. The ability to determine preload, afterload and contractility from them is unique to Doppler: Peak Velocity (PV) = the fastest speed of red blood cells ejected during the cardiac cycle. Normal PV values are age related and are a good indicator of contractility. It is affected by ventricular loading and the resistance/afterload against which the heart is pumping.
More upright waveforms usually indicate good left ventricular (LV) function, whereas a flatter waveform usually indicates reduced ventricular function.
Flow Time = the duration of systolic blood flow and this is corrected for heart rate (FTc). Range: 330-360 ms in a healthy resting adult.
FTc is inversely related to afterload: If afterload/resistance increases,
- FTc is likely to decrease and may be due to hypovolaemia (preload decreases) or other causes, such as those due to vasoconstriction.
- FTc increases = low resistance state eg, sepsis, vasodilation due to anaesthesia or other drugs
Default Cardiac Function Parameters
Other parameters are available during monitor set up, such as: Oxygen Delivery (DO2), Systemic Vascular Resistance/Index (SVR/SVRI), Stroke Volume Variation (SVV), Cardiac Power/Index (CPO/CPI), Pulse Pressure Variation (PPV).
The shape of the waveform will change with an intervention or progression of illness.
Rules of thumb
- Preload – predominant change = FTc Flow time corrected (FTc) decreases as ventricular filling reduces resulting in a narrower waveform. Conversely, FTc increases as ventricular filling increases. The apex of the waveform, Peak Velocity (PV), doesnt change much unless hypovolaemia is very severe.
- Afterload predominant changes = PV+FTc As afterload increases PV gets smaller and FTc becomes shorter. This is especially noticeable in patients with a poor left ventricle that doesnt like pumping against a resistance and results in a fall in Stroke Volume. Conversely, PV raises and FTc becomes longer when afterload reduces because there is less resistance for the heart to pump against.
- Inotropy predominant change = PV PV decreases with myocardial depression and increases with inotropy.
The ‘Freeze’ button will provide a still image of the waveform and the associated parameters.
Rotate the Control Knob to select the waveform(s) to be placed in the red frame for capture as a Snapshot. Up to eight snapshots can be saved for each patient. Snapshots can be used as a reference point (or baseline) for comparison.
Physiological changes and interventions may alter the shape of the waveform and the parameters relative to your reference snapshot.
Arterial Line - an Optional Extra
Once the oesophageal Doppler signal has been set up, the arterial line can be used for Pulse Pressure Wave Analysis (PPWA) for continuous cardiac output monitoring. It is easily calibrated and re-calibrated against the Doppler signal. (Available when the arterial signal is fed into ADC socket at rear of monitor.) If you would like to know more about using PPWA, please visit our course on ‘Pressure Monitoring Mode’.
Paediatric Case Studies
The following case studies in babies and children illustrate how the ODM+ can be helpful in clinical practice. Fluid challenges may be given as directed locally.
Click on the links to select a case study.
All references from this course can be found at Peadiatric course references