Getting started with the ODM+
The course objectives will give you an understanding of:
- How and why to use the adult 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 straightforward 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.
Welcome to E-learning with Deltex Medical
ODM+ can be used in haemodynamic monitoring protocols within the OR, ER or critical care to assess cardiac function. Its high precision allows you to govern fluid therapy strategies safely for patients at high risk of blood loss or undergoing ‘restrictive’ fluid protocols, as well as guiding the use of vasoactive and inotropic drugs to support ventricular function.
CardioQ-ODM+ Monitor Screen
This graphic shows what is displayed on different areas of the ODM+ screen in flow monitoring mode.
The Oesophageal Doppler Probe
The oesophageal Doppler probe stores the date, time, patient’s characteristics and calibration data.
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.
Probe placement may be contraindicated with:
- Carcinoma of pharynx, larynx, oesophagus
- Aneurysm of thoracic aorta
- Proximal coarctation of aorta
- Tissue necrosis of the oesophagus or nasal passage
- Nasal injury, facial trauma, nasal polyps
- Where there is a risk of brain damage (nasal insertion)
- Intra-aortic balloon pumping
- 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
Note: Oesophageal Doppler probes are for patients 16 years and over.
Your patient’s real time flow parameters are Flow Time and Peak Velocity, which together give you Stroke Distance (SD).
These are converted to left ventricular Stroke Volume (SV) with a nomogram, based mainly on the patient’s age.
The ODM+ incorporates an adult nomogram, derived from the patient’s age, weight and height, to convert the descending aortic blood flow velocity to total left ventricular SV.1
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. However, since SD correlates well with SV, this can be used as a substitute for guiding fluid and vasoactive drugs.2
1 Singer et al. Curr Opin Crit Care 2009;15:244-8.
2 Singer et al. Crit Care Med 1989;17:447-52.
The probe can be inserted via the mouth or nose depending on user preference, or factors related to individual patients.
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.
Nasal insertion is usually preferred in patients who are awake. As with a nasogastric tube, patients may eat, drink and walk around with the tube in situ and secured by a clip as shown.
Markers are at a predefined distance from the distal probe: 1 = 35 cm, 2 = 40 cm, 3 = 45 cm. Align markers 1-2 with with the incisors for oral use and markers 2-3 with the nostril for nasal use.
No oesophageal Doppler monitoring-related adverse incidents have occurred in over 800 thousand placements.1
1 Deltex Medical. Data on file.
Add a New Patient
Focussing the Probe
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
Tip: If you are having difficulty visualising the optimal waveform, Peak Velocity Display (PVD) can be a useful tool.
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).
Cycle time is changed by pressing ‘Data input & recording‘ followed by ‘Cycles for calculation‘. The Control Knob can then be rotated to select the appropriate cycle time.
Understanding your Signal
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
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.
Pulmonary artery wave
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.
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. It is affected by ventricular loading and the resistance/afterload against which the heart is pumping.
More upright waveforms usually indicate better 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 healthy resting individuals.
FTc is inversely related to afterload:
- If afterload/resistance increases, FTc is likely to decrease = the most common cause of hypovolaemia (preload decreases) a low circulating blood volume causes vasoconstriction and subsequent reduced FTc with prompt splanchnic response. Then consider LV, then right ventricular (RV) issues.
- FTc increases = low resistance state eg, sepsis, vasodilation due to anaesthesia or other drugs.
Default Cardiac Function Parameters
As with any drug administered to a patient, fluid also has a therapeutic window. While cardiac output parameters are robust indicators of volume responsiveness, when giving fluid, the bigger haemodynamic/clinical picture should be considered.
Greater than or equal to 10% increase in SV indicates fluid responsiveness.
A fluid bolus can be used to assess circulating blood volume. Infuse 200 or 250 mls rapidly, i.e., in less than 5-minutes and then measure the change in stroke volume (SV) 5-10 minutes later.
Unique to Doppler is the 10% rule. The high precision of the ODM+ means you can be 99% sure that these changes in volume are real1:
- If the change in SV is 10% or more, then the patient may not be haemodynamically optimised and a further bolus(es) may be administered.
- A response of less than 10% may indicate that the left ventricle may not be responsive which may be due to:
1 Singer et al. Crit Care Med 1989;17:447-52.
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), doesn’t 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 doesn’t 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.
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)
Complications Determine Long-term Survival
Complications may become apparent clinically only in the days following surgery.1
However, these complications may reduce median survival by 69% independent of a patient’s preoperative risk.2
1 Singer et al. Crit Care Med 1989;17:447-52.
2 Khuri et al Ann Surg 2005;242:326-41.
Improving Patient Outcome
Doppler-guided fluid management leads to clinically significant reductions in major complications. (OR: p=0.00002, AHRQ Technology Assessment 2007; p<0.00001, Hamilton 2011)1,2
This benefit has been seen in clinical trials, which showed significant reductions in major complications, nausea and vomiting, length of hospital stay and overall treatment costs associated with ODM+ use.3-8
Oesophageal Doppler monitoring uses ultrasound to give a direct measurement of blood flow velocity in the descending thoracic aorta.
An understanding of this signal provides early recognition of systemic and cardiac problems. Too much fluid can be as detrimental as too little. Intraoperative fluid management is about optimising circulating volume based on individual patient need.
1 AHRQ Technology Assessment. Agency for Healthcare Research and Quality 2007.
2 Hamilton et al. Anesth Analg 2011;112:1392-402.
3 Gan et al. Anesthesiology 2002;97:820-6.
4 Mythen and Webb. Arch Surg 1995;130:423-9.
5 Noblett et al. Br J Surg 2006;93:1069-76.
6 Pillai et al. J Urol 2011;186:2201-6.
7 Scheeren et al. J Clin Monit Comput 2013;27:225-33.
8 Wakeling et al. Br J Anaesth 2005;95:634-42.