FREQUENTLY ASKED QUESTIONS
1. How easy is it to use ODM+?
The majority of new ODM+ users find the product easy to handle, place and manipulate the probes. Evidence suggests it takes up to 12 probe insertions to become competent, The manufacturer’s surveillance reports show that in more than 90% of cases, it takes less than two minutes to get a first good signal. In a typical major operation, of 3-4 hours duration, the total time spent interfacing with the monitor and probe is between three and four minutes. Calibration of the arterial CO takes approximately 10 seconds and is done simply at a button press.
2. Does ODM+ lead to excessive or inadequate fluid?
Neither is correct and ODM+ delivers the optimal amount of fluid to each patient – not too much and not too little.
Set fluid regimes are also incorrect. Individualised Doppler guided fluid management tailors the amount of fluid to the individual patient at any given time under various anaesthetic or sedation strategies. The goal is to ensure the patient receives the correct volume of intravascular fluids at the correct time. The final decision to give fluid or drugs based on ODM+ parameters lies with the clinician and should take into consideration the current clinical situation and any underlying comorbidities.
3. Is the ODM+ safe?
ODM+ has been used in over 400,000 patients worldwide. To date, there have been no serious adverse events associated with ODM+. In all, eight potential adverse incidents have been reported, however after investigation none of the eight were attributed to ODM+ use. The manufacturer’s instructions for use lists the contraindications. In summary, particular care should be taken in patients known to have existing oesophageal disease or injury or where multiple devices are placed in the oesophagus at the same time.
4. Can ODM+ be used in paediatrics?
Yes in most countries, but contact your Deltex Medical representative for further information. There are dedicated paediatric probes available (KDP), suitable for children of 2.5kg and above. A paediatric specific nomogram is integrated into the ODM+ monitors. The adult nomogram should not be used for children.
5. Are the probes reusable?
Not between patients, but probes can be reused for the same patient within the time frame of the probe. The DPn and I2n range of probes are all single patient use and are labelled accordingly.
6. Can ODM+ be used in awake patients?
The I2n range of probes are designed to be placed in unconscious patients (both anaesthetized and sedated) and then left in position after they wake up, providing the option to conduct post-operative fluid optimization. Experienced users also find these probes are well tolerated by fully conscious or lightly sedated patients. However, patients who are likely to attempt to dislodge other invasive devices, may also try to remove the ODM+ probe.
If an arterial line has been calibrated against the Doppler flow, a calibration period continues for monitoring in an awake stable situation.
7. Can ODM+ be used at the same time as:
- a. Insufflation of the abdomen?
Yes: ODM+ is unaffected by insufflation, however, changes in abdominal pressure and consequently venous return cause changes in blood flow in the descending aorta and therefore caution should be taken in interpreting these changes. Similar caution should be applied in the event of major positional change while awaiting the outcome of a fluid challenge (eg Trendelenburg).
- b. NG tubes?
Yes: occasionally when using ODM+ with a nasogastric (NG) tube, a somewhat diminished intensity of signal may be noticed. If it is in the path of the Doppler transmission, air in the NG tube can diminish the intensity of the Doppler signal (muted colours on screen). To avoid this, insert the probe before the NG tube, position the probe to the left of the already inserted NG tube, and/or flush the NG tube with saline.
- c. Epidurals?
Yes: however epidurals and spinal blocks cause different levels of vasodilation around the body and this may cause the derived values of stroke volume and cardiac output to change disproportionately. However, ODM+’s ability to report changes and trends accurately and in the right direction is unaffected. If in doubt, manage the patient’s haemodynamics using SD.
- d. Diathermy/electro-cautery?
Yes: certain models of diathermy equipment emit noise that can intermittently interfere with ODM+ probe, and may cause loss of signal on the monitor. If the noise is prolonged, then the average cycles per calculations can be reduced to maximize the data capture opportunity between the periods of diathermy. However, if the arterial line is calibrated against the Doppler CO, the pressure screen can be used to monitor during this period.
- e. Ultrasonic scalpels?
Yes: no interference reported to date.
- f. Vasopressors or vasodilators?
Yes: ODM+ responds instantly to the effects of vasoactive agents.
- g. MRI scanner?
No: the probes contain a metal spring.
- h. Defibrillators?
Yes: ODM+ is insulated to protect both patient and machine. Best practice is to remove or disconnect the probe during defibrillation.
- i. Prone position?
Yes: It may be useful to obtain some readings whilst in a supine position first to assess the approximate depth of optimal focus. There are likely to be intrathoracic pressure changes due to the change in position and therefore the data obtained from this period should not be compared to data outside of this.
- j. During atrial fibrillation?
Yes: Increase the average cycle time to between 10 and 20 to average over a longer period. SVV and PPV will not be valid during atrial fibrillation with any device.
8. How can I clean the probes?
Refer to the hospital policy regarding cleaning between use. Do not use the same probe on a different patient. See number 5 above.
9. Should we use the ODM+ in conjunction with CVP monitoring?
A CVP line is often used to administer drugs but is not necessary to monitor CVP at the same oesophageal Doppler monitoring. CVP should not be used for fluid management.
10. I like to know what the ejection fraction (EF) is. How can ODM+ help?
ODM+ cannot measure ejection fraction. However, a study by Monnet et al from 2013 showed that Peak Velocity (as Vpeak) (and to some extent Mean Acceleration as Acc) measured by the ODM/EDM correlated very well with EF. They suggest that “low values of Vpeak should alert the clinician that LVEF is probably low and should prompt an echocardiographic examination in order to confirm the presence of LV systolic dysfunction. The relatively good trending ability of Vpeak suggests that if inotropic therapy is initiated, then the relative changes in Vpeak could allow monitoring of its effects in an easier way than by repeating echocardiography.”
11. I don’t know the patient’s weight or height, what should I do?
The adult nomogram relies on the age of the patient and that should be accurate as possible. However if the weight and height are not known, a good estimate is acceptable. The paediatric nomogram is different and requires the height of the child.
12. What should I do if the patient is outside the nomogram limits?
When entering the patient data, if outside of the nomogram limits, that data will be displayed in red. If this data is accepted, no volumetric calculations will be available. Linear measurements will still be available on the flow screen and include FTc, PV, SD, HR. SD correlates well with SV and can be used as a substitute. Note that pressure cannot be calibrated unless there are volumetric calculations from flow available.
13. The Cardiac output is 5.6 L/m. Why should I worry about an FTc of 280?
FTc is inversely related to afterload and the most common cause is hypovolaemia. CO may be compensated by an increase in HR or contractility. An FTc less than 330ms is never normal but the upper limit depends on the clinical scenario.
14. Why can’t I find normal values?
There are some suggested normal values available in Doppler Specific Parameters. These are for healthy resting individuals and since most patients requiring haemodynamic monitoring are not in a ‘normal’ situation, it may be better to consider aiming for ‘optimal’ rather than ‘normal’ parameters but without accepting low parameters.
15. Restrictive vs. liberal fluids?
One person’s restrictive is another’s liberal. There are wide variations in traditional maintenance fluid regimens. Thus where large amounts of maintenance fluid is given ‘restrictive’ may simply mean less maintenance fluid with boluses. These terms are relative and should not be used to suggest that either optimisation is ‘liberal’ or that giving no boluses as ‘restrictive’. The best source of information is the Consensus Statement from the enhanced recovery partnership i.e. “Use fluid management technologies to deliver individualised goal directed fluid therapy. Avoid crystalloid excess (salt and water overload). ‘Maintenance’ fluid, if utilised, should be limited to less than 2 ml/kg/hr including any drug infusions. The use of isotonic balanced electrolyte solution (e.g. Hartmann’s) will minimise hyperchloraemic acidosis”.