Laser Doppler Needle Probe Insertion: A Technique for Real-time Quantification of Blood Flow within the Spinal Cord in a Porcine Model

Start by prepping an anesthetized pig in a lateral position. Flex the animal's back to expand the intervertebral spaces. Now, make a midline dorsal incision along the thoracolumbar region.
Incise the muscles around the thoracic vertebrae. Then, retract the muscles on both sides of the vertebral column to expose the spinous processes and lamina.

Now, remove the lamina - a small section of the spinal bone between the thirteenth and fourteenth thoracic vertebra. This creates a space between the vertebrae. Insert a vein catheter into this gap. This procedure punctures the spinal cord and positions the vein catheter laterally in the spine.

Remove the inlay needle of the catheter and replace it with a laser Doppler needle probe. Then, connect the probe to the laser Doppler hardware and acquisition system. This system allows the real-time evaluation of blood flow velocity in the microvessels of the spinal cord.

Start the laser Doppler machine to allow light from a monochromatic low-energy laser source to illuminate the area of interest. When light collides with moving red blood cells, there is a change in its frequency called the Doppler shift. The average Doppler frequency shift corresponds to the velocity at which the red blood cells move. This technique can help determine impaired blood flow in spinal cord injury.

After confirming an appropriate level of sedation in a three-month-old 40-kilogram pig, place the animal in the right lateral position, and flex the animal's back to widen the space between the vertebrae. Surgically expose the paravertebral area for the preparation of spinous processes in vertebral arches, and place a vascular 14-gauge peripheral vein catheter paramedian into the spinal cord at the level of thoracic vertebrae 13 / 14 or lumbar vertebrae 1 / 2 between two vertebral arches.

Replace the needle with the laser Doppler needle probe, and connect the probe to the designated hard- and software to test the signal quality. A stable signal with a moderate pulsatility should be observed. Carefully fix the probe with sutures, and use padding to prevent the probe from dislocating or kinking.