Probe Placement

ODM+ monitoring uses Doppler ultrasound technology to determine directly a patient’s central vascular blood flow and fluid status during the intra-operative period.

A probe is placed into the oesophagus, either orally or nasally and is similar to placing a nasogastric tube.

Easy to use and quick to focus, the device generates a low frequency ultrasound signal which is highly sensitive to changes in flow and measures them immediately.

Once in position the clinician is able to measure real time blood velocities within the descending aorta.

For more information, visit Deltex e-Learning or access the Training Workbook for a deeper understanding of how to use this technology.

How to Insert the Probe Orally

  • Lubricate tip of probe with plenty of water-based gel. Do not use oil-based products.
  • The technique is similar to that of placing an orogastric tube into the oesophagus.
  • Do not use force.
  • There are 3 depth markers on the adult probe. They are set at 35, 40 and 45cm from the tip. Using these depth markers and assessing the signal, will ensure the tip of the probe is at approximately T5/T6 area of the descending aorta. This is the region where the oesophagus and descending aorta will be closest.
  • For oral use in an adult, the incisors should be between maker 1 and 2. It may be acceptable for the incisors to be just outside of these markers by approximately 1 or 2 cm if the patient is particularly short or tall. Also consider the length of the torso if a signal cannot be found.  Start at the deepest marker to find the optimal focus.
  • It can be used together with a nasogastric tube, a temperature probe or even a transoesophageal echocardiogram (TOE) probe.
  • ODM probes have been used successfully with an LMA. It may be helpful to place the probe before the LMA is placed. Ensure the seal of the LMA is lubricated well and when inflated, it should easily accommodate the probe.


  • Abnormalities or surgery of the mouth, pharynx, aorta and oesophagus.
  • Base of skull fractures.
  • Coagulopathies.
  • Remove probe if patient having an MRI.
  • Remove probe or disconnect if cardioversion required.

The following may make locating an optimal signal difficult:

  • Coarctation of the aorta.
  • Use of intra-aortic balloon pump.
  • Anatomical abnormalities.

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