Depth/Magnification

Depth is indicated on the monitor by a line of cm markers.

The depth control should be set to demonstrate the whole region of interest during an initial survey of the area (Fig 1).

During interventions that may be guided by ultrasound, such as central line placement, it is often more important that the needle tip misses innocent bystanders, rather than the target structure being reached on first pass (Fig 2).

However, setting the depth inappropriately deep loses temporal resolution (Fig 3).

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Fig 1	Fig 2	Fig 3

Learning bite

Initial depth settings should be set to demonstrate all of the relevant anatomy, not just the most superficial structures, but no deeper than the area of interest.