Ultrasound Guided Thoracic Epidural

There are twelve thoracic vertebrae in humans. The spinous processes of thoracic vertebrae are inclined steepely in the upper and mid-thoracic region such that they almost overlap each other.  The tip of the spinous process of the vertebra above lies over the vertebra below. In the lower thoracic region the inclination is less steep.

This makes doing thoracic epidural by midline approach very difficult as the tuohy needle needs to be angulated extremely cephalad and negotiated through a smaller space between two spinous processes.

The best way to overcome this is by doing a thoracic epidural by the paramedian approach especially in high and midthoracic region.
In this approach once the intervertebral space for doing the epidural is identified, the tip of the spinous process of the vertebra above is felt and a point marked one centimeter lateral to it. 
Local anaesthetic is injected to the skin and towards the lamina below.  The tuohy needle is inserted at this point directed perpendicular to the skin to hit the lamina.  This will be the lamina of the vertebra below.  Once this is done the needle is slightly withdrawn and angled medially to so that the needle walks off the lamina towards the ligamentum flavum and then the epidural space. 
Loss of resistace to saline or air is used to identify the epidural space.

How can we use ultrasound for thoracic epidural?
To understand this we must first see how the thoracic vertebra looks under ultrasound and how it is different to lumbar vertebra.

The following video shows what can be seen when we scan over a thoracic vertebra.  Initially the probe is parallel to the long axis of the spine and then the probe is turned through 90 degrees so that the probe is perpendicular to the long axis of the spine


Ultrasound can be used in adults to assist us with thoracic epidural.
With ultrasound we can find out:
1. Midline
2. How deep the lamina is from the skin
3. In some thin adults how deep the dura is from the skin

Once this is determined we can do epidural using paramedian approach as described earlier without ultrasound.