Femoral Vein Cannulation
The Seldinger technique is the most commonly used method of gaining central venous access. It was initially described in 1953 by Seldinger as a vascular access method for percutaneous arteriography.  Although the Seldinger technique requires multiple sequential steps, intravascular access can be rapidly and reliably gained once these steps are mastered. 
Place the patient in the supine position, with the inguinal area adequately exposed to allow identification of anatomic landmarks. Decontaminate the area by painting it widely with povidone-iodine or chlorhexidine solution. Chlorhexidine is preferred because of its prolonged residual antiseptic effect (up to 6 hours after initial application). Use sterile drapes to isolate the femoral area.
After donning the gown, mask, cap and sterile gloves, identify the surface landmarks by palpation (see the image below). Identify the inguinal ligament and the femoral arterial pulsations. Identify a point approximately 1 cm below the inguinal ligament and 0.5-1 cm medial to the femoral arterial pulsation. Mark this point as the site to percutaneously access the femoral vein.
Ultrasound guidance, involving either plain two-dimensional (2D) ultrasonography or Doppler ultrasonography, has been considered as an alternative to identification of anatomic landmarks for determining the insertion site. A 2015 Cochrane review of 13 studies (2341 patients; 2360 procedures) found that 2D ultrasound guidance had small advantages in safety and quality over an anatomic landmark technique in femoral vein cannulation for central access.  No certain conclusions were reached regarding Doppler ultrasound guidance versus an anatomic landmark technique.
Once the site has been determined, infiltrate the skin and subcutaneous tissue overlying the venipuncture site with 2-5 mL of 1% lidocaine solution (see Patient Preparation).
Identify the vein and gain initial access. Many advocate the use of a small (26-gauge) exploratory or “finder” needle on a 5-mL syringe to accurately identify the vein and gain initial access. However, experienced operators often omit the finder needle, instead using a 20- to 22-ga needle on a 10-mL syringe for the initial venipuncture.
Insert the finder needle so that enters the skin at an angle of approximately 45º in a cephalic direction. Maintain a small amount of negative suction by elevating the plunger of the syringe. As the vein is punctured, a flash of dark venous blood into the syringe indicates that the needle tip is within the femoral vein lumen.
Next, place the larger (20- to 22-gauge) needle immediately adjacent to the finder needle, and enter the femoral vein again. Thread the flexible J-tip guide wire through the lumen of the needle and into the vein lumen. Then, gently advance the guide wire until approximately one fourth to one third of its length (ie, 8-10 cm) is within the lumen of the vein.
If resistance is encountered in advancing the guide wire, rotate it gently and then advance. Continued resistance indicates misplacement of the wire. Under no circumstances should force be used to advance the wire.
Remove the needle by threading it backward over the wire. Next, take the No. 11 scalpel and make a nick medial to the wire at the skin to permit easier passage of the dilator device. Thread the dilator device over the wire, and use it to create a tract in the skin and the subcutaneous tissue so as to facilitate passage of the catheter.
Remove the dilator device, and thread the catheter over the wire until the wire emerges from the distal end of the catheter. Grasp the distal end of the wire, and thread the catheter forward to an intravenous position. Withdraw the wire simultaneously to maintain constant control of the distal end.
Once the catheter is in an intravenous position and the guide wire has been completely withdrawn, secure the catheter with 3-0 or 4-0 nylon to suture the flanges to the skin. Confirm the intraluminal placement of the catheter tip by aspirating venous blood from the ports and flushing these with sterile saline solution.
The FLUSH (Flush the Line and UltraSound the Heart) test may be a useful alternative for confirming correct intravenous placement. In this test, the heart is visualized via a subxiphoid ultrasonic view while the central catheter is flushed with agitated saline solution. Horowitz et al found the FLUSH test to be a simple and reliable technique that appeared capable of accurately confirming femoral venous line placement. 
Apply antibiotic ointment at the site of skin entry, followed by sterile dressings.
A less commonly used technique used for percutaneous venous access is the catheter-over-needle method. In this technique, the vein is accessed by using a solid needle over which a short single-lumen catheter is already in place. Once the vein is cannulated, the catheter is threaded over the needle into an intraluminal position, and the needle is withdrawn, leaving the catheter in place.
A helpful mnemonic to remember the location of the femoral vein is VAN (Vein, Artery, Nerve) which indicates the order in which the three structures are encountered from medial to lateral.
Another helpful mnemonic is NAVEL (Nerve, Artery, Vein, Empty space, inguinal Ligament), which describes the anatomy of the femoral region from lateral to medial.
The chest compressions given during cardiopulmonary resuscitation can produce venous pulsations. In this case, attempts to locate the vein by aspirating medial to the perceived femoral arterial pulsations may fail. Direct venipuncture over the pulsations should be attempted, because these may be venous pulsations.
To prevent needle displacement after the femoral vein is punctured, the needle can be stabilized with a hemostat when the syringe is being removed.
In difficult cases, a handheld Doppler ultrasound device can be used to identify the location of femoral arterial pulsations. Venipuncture can then be attempted medial to these pulsations.
If Doppler ultrasonography is unsuccessful, a duplex ultrasound device with visual display can be used. The device most commonly used is a 7.5-MHz real-time mechanical sector transducer with an attached needle guide. The transducer is covered with a sterile sheath, and the femoral vessels can be identified on the attached monitor. The femoral vein can then be punctured under direct visualization. 
The complications associated with femoral venous cannulations are generally less severe than those associated with access via jugular or subclavian veins.  This is largely because the risk of traumatizing intrathoracic structures is avoided. The following complications are commonly associated with femoral venipuncture [14, 9, 7] :
Arterial puncture - This is more common when the femoral arterial pulsations are not pronounced, as in low-flow states, during circulatory arrest, or when due to iliac or femoral arterial stenosis
Hematoma formation - This can be a result of arterial puncture venous perforation and is generally self-limited, except in coagulopathic patients, where it could extend to the retroperitoneal area
Bowel penetration - This is more likely in patients with femoral hernias; although the bowel injury is generally self-limiting, the potential vascular contamination with intestinal flora can lead to sepsis
Bladder puncture - This is more likely to occur with a distended bladder; like bowel injury with a needle, it is generally self-limited, but the potential for vascular contamination poses a serious risk
Psoas abscess - This complication is a result of penetration and contamination of the underlying psoas fascia
Septic arthritis - This is more common in infants and is a result of puncture and contamination of the hip capsule
Femoral nerve injury with resulting paresthesias
Thrombosis of the femoral or iliac veins