The modern technique to access the vascular system through a peripheral vessel was introduced by Dr. Sven Seldinger using a two-piece (needle and stylet) 18-G needle.
The Arterial puncture can be performed in two different ways: double or single-wall.
The double-wall puncture is the most common and the most frequently used; the needle is completely advanced into the body, the stylet is removed and the needle is withdrawn until brisk pulsatile backflow or blood appear. Then a 0.035 guidewire can be introduced into the artery.
The single-wall puncture is performed using an open-tip needle. Once the needle reaches the arterial lumen and blood comes out from the needle, the wire can be advanced.
Different vascular approaches:
- femoral
- axillary
- brachial
- radial
can be used to perform a carotid stenting.
The retrograde femoral access is generally the most frequent  Fig.1
The puncture must be done in the common femoral artery (CFA) at the level of the middle portion.
A too low puncture (superficial femoral artery) must be prevented to avoid the risk of complications, especially pseudoaneurysms and hematoma correlated more with the inefficacy of the compression against soft tissue than against bone.
A too high puncture may result in retroperitoneal bleeding since the puncture site is uncompressible and absence of local tissue doesn't help compress bleeding once it has grown to sufficient size. The correct puncture site is located at the level of the femoral head, 1-2 cm below the inguinal ligament.
The axillary artery access is performed when  femoral access is impossible or in those cases with severe angulation of the aortic arch (type III or IV). Fig.2
Puncture should be performed along the axillary fold over the proximal humerus so that the underlying bone provides support during the manual compression.
Hematoma causing compression of the brachial plexus is the most frequent complication and for this reason the brachial approach is generally preferred. Fig.3
The radial approach is a useful alternative access site Fig.4
This technique is associated with a very low incidence of bleeding complications and a rapid patient ambulation.
As radial artery occlusion can occur in 1-5% of patients after trans-radial procedures, before performing a trans-radial puncture, blood flow must be assessed  the hand.
If adequate collateral circulation to the hand is present, with a patent ulnar artery, thrombosis or occlusion of the radial artery does not endanger the blood flow of the hand.
Factors that contribute to radial artery occlusion include small artery size, severe arterial spasm, prior radial artery intervention and prolonged compression with a hemostasis device.
The artery must be reached 1-2 cm proximal to the styloid process of the radius, where the radial pulse can be easily palpated in the wrist. A common mistake is to access the artery in the wrist too distally where the vessel is more tortuous.
Puncture should be performed using a 20G open-tip needle and a  0.025" guide-wire. A long introducer, 25 cm, no greater than 6 Fr. must be inserted.
Radial access failure has been reported in 3-7% of cases correlated with the presence of a small artery diameter , to arterial spasm and the presence of a radial-ulnar loop.
Another possible approach is represented by the direct cervical approach Fig.5 that should be selected when no other arterial access is possible.
Puncture of the common carotid artery, using a 21-G fine needle, should be performed as low as possible to provide enough space to an introducer sheath inserted below the carotid bifurcation.
However, a pre-procedure evaluation using USCD is recommended to get a precise map of the carotid anatomy. Sometimes a very low level of the carotid bifurcation may preclude direct cervical access for CAS.
External compression can be difficult, ineffective and uncomfortable for the patient and may often cause hematoma or hemorrage

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