Epidural
Although use of ultrasound to locate the epidural space is increasing very
few people do real time ultrasonographic guided epidural block.
Mostly it is used to assist epidural or spinal block.
The uses are:
1. To locate the midline. In patients with high BMI it is sometimes very
difficult to feel the midline.
Ultrasound can help in finding the
midline.
2. To locate the correct interspace to do the block. The level of
intervertebral space can be easily determined by counting upwards from
the sacrum.
3. To measure the depth of epidural space and dura from the skin.
When we scan to locate the epidural space, essentially we are scanning
over bones (vertebrae) to find a gap inbetween the bones (intervertebral
space). Through this gap we try to see the ligamentum flavum, dura
and the epidural space.
Before we see how we can use ultrasound to see the epidural space, let us
first see how a bone looks under ultrasound.
Bone does not allow
ultrasound to pass through it.
Therefore all the ultrasound that
is incident on the bone gets reflected by the bone. The periosteum of
the bone which reflects the ultrasound back to the probe produces a
bright hyperechoic line.
Since no ultrasound travels beyond the
periosteum, the rest of the bone produces a dark shadow.
If a
structure is behind the bone, ultrasound will not be able to reach it
and thus that structure will not produce an image.
The image of the lumbar vertebra is from Gray's anatomy taken from
'Wikimedia commons' The image shows parts of the lumbar vertebra.
Let us see how lumbar vertebra will look under ultrasound:
Here we have immersed a plastic spine in water bath and scanned it using
a curvilinear ultrasound probe. This gives an idea of how a spine
will look under ultrasound.
Following video is from RA-UK explaining how to look for epidural space
using ultrasound:
Following is a presentation by Dr Sardesai on use of ultrasound to do
lumbar and thoracic epidural
https://1drv.ms/p/s!Aj1UiYRIfQtZgfl6zAhvoiieVrbu0Q?e=7Wapse
This file is slightly large. It is a power point presentation.
Either listen to the presentation or you can just scroll
through the slides. If you do use the presentation please acknowledge
the source.
