Focusing the Probe

Securing the Probe

  • Many users do not secure the probe because peristalsis in the esophagus may cause the probe to move internally.
  • If the user wishes to secure the probe with tape or a nasal clip, then ensure the probe can be manipulated to check focus.

Focusing the Probe

How to get the optimal focus

  • It is useful to place the probe as early as possible (for instance immediately after intubation) so that a settling-in period can be achieved where the probe sits comfortably against the esophageal wall (the patient’s secretions will aid signal acquisition)
  • Insert the probe to appropriate depth
  • Turn up the sound on the monitor
  • Choose this depth and rotate slowly all way round without letting go
  • If no signal is seen at this depth, pull out slightly (by approximately 1 cm at a time) and rotate again slowly without letting go
  • Repeat these changes of depth followed by rotations until a signal is found
  • Do not pull and rotate at the same time as this will cause a spiral effect and the appropriate area may be missed

The qualities of a good signal:

  • The loudest, sharpest ‘whipcrack’ sound
  • The tallest waveform
  • The brightest waveform
  • A well-defined triangle with a black center surrounded by red with white in the trailing edge. This indicates an equal distribution of red blood cell velocities at a given point in time and the probe is facing the center of the aorta. (note that if the waveform has no black center, this is called spectral dispersion and may indicate that the probe is not facing the centre of the aorta)
  • The incisors will be as close to the appropriate depth marker as possible.

Find a signal that meets the above requirements and it may be useful to recheck at different depths once more to ensure the optimal signal has not been missed.

Check the gain manually or use autogain. This will help to adjust the signal quality.

When in run mode, check the cycle time. The default is “5” but this can be increased for arrhythmias or decreased if there is noise interference.

Ensure the green follower line is set tightly against the waveform and the white arrows are placed on the triangle.

To refocus:

  • Ensure the probe is at the same depth when the optimal signal was found
  • Turn up the volume
  • Rotate slowly without letting go to find the appropriate signal again before evaluating the parameters

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