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Anestesia Neuroassiale. Tutta l'Anatomia

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Looking at the patient's back with an

epidural anesthesia needle using

the median approach, what structures do we

cross? This exercise,

the needle passes through the skin and the

subcutaneous tissue, the supraspinous ligament,

then the interspinous ligament, the

yellow ligaments, and finally it must stop

in the

epidural space. Now we do this same

exercise but for spinal or

subarachnoid anesthesia. Again looking at the

patient's back, always using

the median approach, with a

spinal anesthesia needle. What structures do we

cross? The needle will pass through the skin,

the subcutaneous tissue, the

supraspinous ligament, and the interspinous ligament,

as before, the yellow ligament, the

epidural space, the duera mater, the

subdural space, the arachnid. Once past the arachnoid,

we are in the liquor

of the

subarachnoid space. When the tip of the needle

passes from the epidural space to the

subarachnoid space, crossing the

dual sac, therefore the duera and the arachnoid, the

transition can be described with a

click. The Pop click sensation is quite famous.

passing the

duera mater and the arachnoid the click is the

sensation that lets the anesthesiologists

know when to stop advancing

the needle and check for

CSF reflux But there are other

interesting sensations associated with the advancement of

the spinal needle through the

Uti tissues the supraspinous ligament gives a

strident sensation Some say

Crunch crunchy the

supraspinous ligament joins the posterior tips of

the adjacent spinous processes up to L3

L4 above the fourth

lumbar vertebra the fibers of the

supraspinous ligament are replaced by fibers

of the latissimus dorsi muscle the

interspinous ligaments the interspinous ligaments

connect the adjacent spinous processes

they extend from the supraspinous ligament

posteriorly to the ligaments flavum

anteriorly from the haptic point of view

the passage through the interspinous ligament

does not give rise to any particular sensations the

yellow ligaments the yellow ligaments

run between the lower margin of

one vertebral plate and the

upper margin of the underlying plate they are

rectangular in shape and Serrano the

spaces between one vertebral plate and

the other demarcating the

vertebral canal posteriorly i The yellow ligaments

may fuse in the midline but this

is not always the case and for this reason,

using a median approach to

spinal anesthesia, one cannot always

rely on the yellow ligament

as a perceptible resistance to the advancement of the or we

advancement of the or we

move to the epidural space

to identify the epidural space

freehand and with an epidural anesthesia needle,

two techniques can be used:

the loss of resistance and the

hanging drop. Despite the growing

interest in ultrasound-guided neuroaxial procedures,

the loss of

resistance technique is based on the different

density of the tissues when the needle passes

from the ligaments to the epidural space. The

most common and most used technique is the

syringe filled with a few milliliters

of saline solution. This resistance opposes a

certain resistance if the tip of the

epidural needle is engaged in the ligaments. This

resistance dissipates

suddenly when the needle enters the

epidural space. The hanging drop technique

is instead based on the

subatmospheric pressure of the epidural space

which is more pronounced and reliable

in the cervical and thoracic regions

than in the lumbar segments. A drop

of saline solution is placed in the

cone of the needle once it has entered the epidural space. this is

engaged in the ligaments the needle is

advanced and the entry into the

epidural space is signaled by the aspiration

of the drop in the transparent cone D lake

the epidural space in my imagination has

long been a cylinder of

continuous tissue of

uniform thickness that completely wrapped the

dura mater in reality the epidural fat

in the vertebral canal is organized in

discrete portions located at the

posterior and lateral level the

epidural fat does not adhere to the other

structures of the vertebral canal except at the

level of its vascular pedicles which

at the posterior level are on the

midline after the epidural space

the meninges begin for the meninges We

help ourselves with this image by looking at the

patient's back the first meninges we

encounter is the Dur mater here in

red the Dur mater has a thickness of about

about

0.35 mm and is made up of about 80

concentric laminae of collagen fibers

organized in all

spatial directions here I have only put three layers but you

have to imagine at least 80 it is

a relatively

permeable structure And since it is much thicker than the

other meninges the The dura mater has

long been considered the most

important obstacle to the diffusion of drugs

between the epidural space and the

central nervous system cerebrospinal fluid. However, it is the

very thin arachnoid membrane that

offers the most resistance to the diffusion

of drugs through the

spinal meninges, with a thickness of only 50-60

microns. The arachnoid is much thinner than

the dura mater but has

much more pronounced barrier properties due to the

lack of intercellular space between the

arachnoid cells, which are firmly connected to each

other by tight junctions and

desmosomes. The entire thickness of the

arachnoid layer is in blue. The black dots

indicate the plasma membrane of the

arachnoid cells. Looking at the

patient's back, after the dura mater but before

the arachnoid, there is nothing in

contradiction with the classic description

of the subdural space as a space.

Therefore, studies have shown that

between the dura mater and the arachnoid there is a

solid but delicate tissue

composed of specialized neuroglial cells.

Neuroglial cells

are also called dural border cells.

These elongated

and fusiform cells are fragile and

The weak cohesive forces between the

neuroglia cells and the lack of

collagen fibers facilitate

the widening of a fissure giving

the impression of a subdural space.

Therefore, the classic concept of a

subdural space is an iatrogenic artifact. The

subdural space is a potential space

that becomes real only after the

involuntary injection of fluid into its

structure with the destruction of the

weak intercellular junctions between the

neuroglia cells which allows the

injected fluids to accumulate in the

subdural space. The dimensions of the

acquired subdural space are

proportional to the volume of fluid

injected, smaller with the typical volumes

used with spinal anesthesia and

larger with the high volumes used with

with

epidural analgesia. This is for the arachnid towards the

dura on the other side towards the

subarachnoid space. The arachnoid sends thread

-like offshoots towards the surface

of the pia mater this creates the

spiderweb appearance which then gives it its name The name

of arachnoid The dura mater and the

arachnoid together form the

spinal dural sac They delimit the

spinal subarachnoid space filled with

spinal cerebrospinal fluid in which

the spinal cord is suspended and floats The

spinal cord is soaked In the cerebrospinal fluid it is

covered by the third and final meninx

The pia mater The pia mater is intimately

associated with the surface of the

spinal parenchyma Deep to the pia mater is

the glial limitans and beyond

this the glia and the neurons of the

spinal cord How an

epidural or peridural anesthesia works To date the only

experimentally demonstrated mechanism

that explains the movement of drugs between

the epidural space and spinal cerebrospinal fluid is

simple diffusion

through the spinal meninges The drugs you

inject into the epidural space

must pass through the dura mater and

the arachnid Disperse in the cerebrospinal fluid

Pass through the pia mater and reach the

spinal cord with

spinal anesthesia The drugs there inject

directly into the

subarachnoid space Since they are already there in the liquor, they

have to travel much less distance and

significantly smaller doses are needed. If the

drug we use is a

local anesthetic, its targets are the axons

of the white matter of both the

nerve roots and the spinal cord. If the

drug is an opioid, it must diffuse

through the white matter and

reach the gray matter 1-2 mm

from the spinal surface to reach

its biophase, which are the neurons of

lamina 2. The gelatinous substance of the

dorsal horns of the spinal cord and the

neurons of the dorsal root ganglia.

And that's all. I hope

you enjoyed this video and that it can be

helpful. If you haven't already done so, I

invite you to subscribe to my

YouTube channel and the podcast, the anesthetist. See you soon.

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Anestesia Neuroassiale. Tutta l'Anatomia