The use of invasive monitoring technologies and aggressive hemodynamic resuscitation protocols has increased. Therefore, the ability to gain rapid and accurate vascular access has become a skill that it is imperative for critical and emergency care physicians to possess.
Peripheral veins can be used to gain access to the central venous system. However, this requires the placement of long catheters via superficial veins that may be difficult to locate in emergency situations. The predictable anatomic locations of the internal jugular, subclavian, and femoral veins make them easy to cannulate in patients who are critically ill.
All routes of central venous access are associated with complications and possible failure. The less than ideal conditions under which such access is established also contribute to the incidence of complications. Compared with femoral site access, internal jugular or subclavian access was associated with a lower risk of catheter-related bloodstream infections (CRBSIs) in earlier studies, but subsequent studies (2008-2010) indicated that there were no differences among these three sites with regard to the rate of CRBSIs. 
One of the most common methods for gaining central venous access in emergency situations is via femoral vein cannulation. The technique of accurately placing a femoral vein catheter depends on appropriate patient selection and a sound knowledge of anatomy. As with most other central venous cannulations, the modified Seldinger technique is used.
For more information on subclavian vein cannulation, see Central Venous Access, Subclavian Vein, Subclavian Approach and Central Venous Access, Subclavian Vein, Supraclavicular Approach.
The following are generally accepted indications for femoral venous catheter placement:
Emergency venous access during cardiopulmonary resuscitation (CPR), in that it provides a rapid and reliable route for the administration of drugs to the central circulation of the patient in cardiac arrest
In hypotensive trauma patients, emergency access via the femoral route is recommended by some traumatologists immediately after two peripheral venous catheters are established; if peripheral access cannot be established expeditiously, femoral venous access is established immediately; femoral venous catheter placement is preferred to supraclavicular central venous access in patients with suspected superior vena caval injuries
Urgent or emergency hemodialysis access
Hemoperfusion access in patients with severe drug overdose
Central venous pressure monitoring
In 2012, a task force of the American Society of Anesthesiologists published a set of practice guidelines for central venous access. 
Absolute contraindications for femoral central venous access include the following:
Venous injury (known or suspected) at the level of the femoral veins or proximally (ie, iliac veins or inferior vena cava)
Known or suspected thrombosis of the femoral or iliac veins on the proposed side of venous cannulation
Ambulatory patient (because ambulation increases the risk of catheter fracture and migration)
Relative contraindications for femoral central venous access include the following:
Presence of bleeding disorders (innate or iatrogenic from the use of anticoagulants or thrombolytics)
Distortion of anatomy due to local injury or deformity
Previous long-term venous catheterization (which increases the risk of venous thrombosis)
Absence of a clearly palpable femoral artery
History of vasculitis
Previous injection of sclerosis agents
Previous radiation therapy
The femoral vein lies within the femoral triangle in the inguinal-femoral area (see the image below). The superior border of the triangle is formed by the inguinal ligament, the medial border by the adductor longus, and the lateral border by the sartorius. The apex of the triangle is formed by the sartorius crossing the adductor longus. The roof of the triangle is composed of the skin, subcutaneous tissue, the cribriform fascia, and the fascia lata. The concave floor is formed by the underlying adductor longus, adductor brevis, pectineus, and iliopsoas.
The neurovascular bundle consists of the femoral vein, artery, and nerve, which lie within the triangle in that order from medial to lateral. The femoral sheath encloses the femoral artery and vein, and the nerve lies outside the sheath. The femoral canal is a space within the femoral sheath and medial to the femoral vein.
The femoral artery lies at the midinguinal point, which is midway between the pubic symphysis and the anterior superior iliac spine. The surface anatomy of the femoral vein is identified for venipuncture by palpating the point of maximal pulsation of the femoral artery immediately below the level of the inguinal ligament and marking a point approximately 0.5 cm medial to this pulsation.
Distally in the leg, the femoral vein lies almost posterior to the artery. This is important because arterial puncture is more likely in the sites distal to the inguinal ligament. 
Many clinical situations necessitate placement of central venous catheters. The choice of site is dictated by the specific advantages and disadvantages of each access method in the clinical situation being considered.
The femoral site is advantageous in patients who are critically ill because the femoral area is relatively free of other monitoring and airway access devices. If a bedridden patient requires central venous access, the femoral site allows relatively free movement of arms and neck without impeding the access line. In patients with severe coagulopathy or profound respiratory failure, femoral access precludes the risks of a development of a hemothorax or pneumothorax, both of which are potential complications of supraclavicular venous access.
The disadvantage of the femoral site is that it presents a field that is potentially contaminated because of its proximity to the perineal area. However, this disadvantage is disputed by many investigators, who point out that the incidence of CRBSIs at the femoral access site is not significantly different from the incidence at the supraclavicular access site. [4, 5] The head and neck area is also potentially contaminated by excessive secretions in the critically ill patient who is intubated or has undergone a tracheostomy for airway access.