Central venous (CV) access is a commonly performed procedure with multiple indications in routine and emergent situations. Access to the internal jugular vein (IJV),  subclavian vein (SV),  and femoral vein (FV) has typically been described in the emergency medicine and critical care literature using the traditional landmark-based approach. Studies using landmark-based methods have reported failure rates and complication rates as high as 30%  and 18.8%, respectively. One study looked at femoral venous access during cardiopulmonary resuscitation (CPR) and found that 31% of catheters were not in the femoral vein. 
The use of ultrasonography for CV access was first described in 1978;  Doppler localization was used to mark the skin overlying the IJV. Not until 1986 was the use of real-time ultrasonographic guidance for IJV cannulation reported.  In 2001, an Agency for Healthcare Research and Quality Evidence Report listed bedside ultrasonography during CV access as one of 11 practices with "strength of evidence for supporting more widespread implementation."  In the 2008 Emergency Ultrasound Guidelines from the American College of Emergency Physicians (ACEP), ultrasonographic guidance for CV access was listed as a "core or primary emergency ultrasound application."  In 2010, Ortega et al elaborated the methodology to employ ultrasonography for locating the IJV, underlining the safety and reliability of the technique.  The authors also detailed the intraoperative use of sterile ultrasonography.
Guidelines and practical advice for ultrasound-guided CV access have been published by the European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB). They recommend real-time ultrasound (RTUS) for central venous access as a key safety measure, as well as for detecting complications of vascular access and treatment of arterial pseudoaneurysms. [10, 11]
Check the equipment and its function during preparation.
Optimize the B-mode picture of the target vessel.
Optimize positioning of the patient (eg, Trendelenburg position), of the examiner, and of the US device relative to the puncture site (aim for a comfortable working environment for the interventionalist).
Choose the most appropriate head position in order to locate the target vein laterally rather than anterior to the artery.
Skills training on appropriate phantoms and in normal patient conditions prior to emergency situations.
In hypovolemic patients, give intravenous fluid before puncture.
The indication for central lines must be well considered—sometimes peripheral vascular access meets the needs of the condition.
The use of ultrasonographic guidance during CV line placement has been demonstrated to significantly decrease the failure rate, complication rate, and number of attempts required for successful access. [12, 13, 14, 15] A recent randomized, multicenter trial using point-of-care limited ultrasonography assistance of CV cannulation reported that ultrasonographic guidance had an odds improvement of 53.5 (6.6-440) times higher than landmark-based technique for success of cannulation.  The average number of attempts and the average time to cannula placement were also significantly lower in the ultrasonographically guided group.
Ultrasonographic guidance can aid in the establishment of CV access from multiple sites.  Ultrasonographic guidance is most useful for cannulation of the IJV and FV. [18, 19] Beaudoin et al found anatomic variability of the femoral vasculature where landmark-based FV cannulation is often attempted. They suggested that ultrasound guidance would improve cannulation and reduce complications during the procedure.  A recent prospective trial of ultrasound-guided femoral CV access demonstrated a trend toward a decreased rate of complications. 
Access to the SV is more difficult because of its deeper location and the presence of the overlying clavicle, which can prevent the transmission of ultrasound waves. However, ultrasonographic guidance at the midpoint of the clavicle, using the long-axis approach, has been described, as has the supraclavicular approach. A 2010 observational study suggested that using ultrasonographic guidance to cannulate the IJV may result in fewer adverse events than a landmark-guided approach to the SV. 
Additionally, infraclavicular axillary vein cannulation, performed a few centimeters lateral but otherwise in a similar fashion to the infraclavicular approach to the SV, can be performed using either long-axis or short-axis ultrasound. A recent ultrasound phantom-based study of this approach found that the long-axis approach was associated with greater first attempt success and fewer arterial punctures. 
Central venous access is indicated in the following cases:
Other peripheral sites are unavailable or inaccessible.
A large-bore venous catheter is needed for rapid administration of fluid or blood products in emergent situations.
A CV catheter is needed for the infusion of vasopressors, sclerosing agents, or hyperalimentation fluids with less risk to the vein.
CV access is needed for placement of a pulmonary artery catheter or transvenous pacemaker or for performance of hemodialysis or plasmapheresis.
CV access is needed for continuous CV pressure and CV oxygen saturation monitoring during resuscitation.
Site-dependent contraindications include the following:
IJV or SV access in severely coagulopathic individuals in whom femoral access is preferred (SV and IJV cannulation in severely coagulopathic patients poses risk because of its noncompressible nature and the risk of accidental carotid puncture, respectively. In such patients, the femoral vein approach is preferred.)
Local infection over the intended site
Patient-dependent contraindications include the following:
Inability of patient to tolerate supine positioning
Lack of patient cooperation
Morbid obesity of patient
Mechanical contraindications include the following:
Contralateral pneumothorax or hemothorax
Inability of patient to tolerate ipsilateral pneumothorax
Current or prior vessel injury
High-pressure ventilator settings
Trauma patients with cervical spine collars in place (IJV access is prohibited by the placement of a cervical spine collar.)
Presence of Greenfield or IVC filter in FV cannulation (Potential exists to snag the filter with the central line guidewire.)
Most of the above-mentioned contraindications are relative, especially in the case of emergent access. Additionally, the use of ultrasonography has been demonstrated in numerous studies to reduce the rate of complication. A recent meta-analysis demonstrated that the relative risk of complications decreased by 57% when ultrasonography was used. 
The following equipment is used for CV access :
High-frequency (6-10 MHz) linear transducer, as shown in the image belowHigh-frequency linear transducer.
Some studies have described the use of an endocavitary transducer for short-axis approach of the IJV. The benefit of using this probe is its small footprint. 
Alternative use of the curvilinear probe has been described, but its usage is limited by its large footprint and the lower-resolution images yielded by lower frequencies.
A sterile barrier is necessary for use during real-time, dynamic visualization.  Sterile transducer covers are commercially available, although sterile gloves can also be used as a barrier.
The use of mechanical guides has been described, though experienced operators may not need to use them. Mechanical guides come in 2 forms: built-in needle slot on the transducer and guides that may be fitted onto the transducer.
A commercially available central venous guidewire catheter kit or catheter-over-needle device is also required. The kit typically contains a triple lumen catheter, a vessel dilator, a spring guidewire with insertion device, a thin-walled percutaneous entry needle, various gauge needles, various syringes, sterile drapes, No. 11 blade scalpel, lidocaine, and silk suture.
For IJV and SV access, patients should be placed in a slightly Trendelenburg position. The head should be in a neutral position (maximum head rotation of 30°). A randomized trial comparing neutral head position to 45° neck rotation did not demonstrate any difference in rate of complications. Venous access time for the two groups was also similar. 
For femoral vein access, the patient should be placed in a neutral position.
For operator-assisted IJV ultrasonographic guidance, the operator should stand on the ipsilateral side of the patient. The procedure should be performed from the head of the bed and the indicator of the probe should be kept pointing to the operator's left (this corresponds to the left side of the patient's body and is opposite of our traditional orientation). For cannulation of the right IJV, this probe orientation ensures that the vessel positions in the patient's neck (carotid to left, IJV to right) share the same orientation on the ultrasound display. The operator should have a clear view of the ultrasound image.
Begin the procedure with hand-washing and universal precautions, including sterile gloves, gown, mask, cap, and protective eyewear.
Cleanse the patient’s skin with an antiseptic such as a povidone iodine solution, chlorhexidine gluconate, hexachlorophene, or a combination of these.
Vascular cannulation may be accomplished with a catheter-over-needle device or the catheter-over-guidewire technique, which is more commonly known as the Seldinger technique.
The vessel to be cannulated may be located with ultrasonography via several accepted variations, including the dynamic (real-time) method and the static (indirect) method, both of which are described below.
Dynamic (real-time) method
The dynamic method, shown below, is typically performed by a single operator, although it can also be performed with the aid of an assistant.
A sterile sheath, commercially available, or glove with transmission gel (any sterile gel/lubricant may be used) inside should be unrolled over the ultrasound probe.
Additional sterile transmission gel is then placed on the outside of the probe cover.
The probe is then placed on the patient's skin and the target vessel is identified.
The vein is identified with several techniques, including phasic respiratory pulsations, ease of compressibility, and increased filling using the Valsalva maneuver.
The vein to be cannulated should be centered on the ultrasound screen.
Once the anticipated path of the needle is identified, the path can be anesthetized with lidocaine under ultrasonographic guidance. This anesthesia minimizes patient discomfort.
Next, the skin is punctured with a thin-walled percutaneous entry needle. Do not focus on the ultrasound monitor until the needle has entered into the skin. Focusing on the monitor prior to needle entry can lead to inadvertent needle sticks.
Visual focus is then directed to the ultrasound monitor, where the needle appears sonographically as an echogenic line with reverberation or ring-down artifact. Often, the needle is not directly visualized; however, tenting of each tissue plane can be appreciated. See the image below.
In the short-axis view, scan back and forth with the probe over the needle to locate the needle tip. Often, a longitudinal view can help localize the needle tip.
After the needle is seen puncturing the vessel and a flash of blood is seen in the syringe, the ultrasound transducer may be set aside. The remainder of the procedure can be completed without ultrasonographic guidance.
Visualization of the guidewire using the longitudinal view within the target central vein verifies intravenous placement. This view minimizes the risk of puncture of the posterior vessel wall.
In the event that the location of the wire cannot be verified (eg, in cases in which back-wall puncture of the vessel is suspected), the guidewire can be partially withdrawn and the curvature of the distal "J" portion of the guidewire can be visualized within the target vessel.
After needle puncture of the vessel and guidewire placement, the entry needle is withdrawn, and the puncture site is enlarged with a No. 11 scalpel blade.
A dilator may then be used to facilitate placement of the catheter.
Venous blood return and easy flushing suggest accurate placement. Ultrasonography can also visualize the catheter and its relative location to the vein.
After the catheter is in place, it is secured with either simple interrupted sutures or staples.
Postprocedural chest radiography is necessary to confirm placement and evaluate for complications such as pneumothorax. Bedside ultrasonography can also be used to help assess for possible pneumothorax. The absence of lung sliding is greater than 90% reliable for the identification of a pneumothorax. 
If cannulation is unsuccessful, chest radiographs must be obtained before repeat attempts on the contralateral side to rule out complications.
Static (indirect) method
The indirect method (see the image below) involves the least amount of ultrasonographic guidance.
The vessel is identified and centered on the ultrasound screen.
A temporary mark is then placed on the skin to indicate where the needle is to be inserted. This mark can be made by indentation or with a sterile marker.
A second mark is then placed distal to this mark along the course of the vessel to use as a guide to direct the path of the needle.
Axis of visualization
Additional considerations in the use of ultrasonography for CV access include the axis of visualization. Reported approaches include short-axis, long-axis, and a combined approach. 
In the short-axis, or transverse, approach, shown below, the vessel is centered under the transducer. The needle is then inserted at a 45° angle, using the midpoint of the transducer as a reference site.
In the long-axis, or longitudinal, approach, shown below, the greatest anterior-posterior diameter of the target vessel is visualized. The needle is then inserted at a 30° angle along the axis of the transducer.
The "ski lift" approach to ultrasound-guided vascular access has been suggested to improve successful line placement.  The authors use the long-axis view to visualize the entire needle and vessel concurrently, which is purported to minimize puncture of the posterior wall, in addition to facilitating placement.
Advantages of each method
The short-axis approach is useful for concomitant visualization and avoidance of the adjacent arteries, for cannulation of smaller peripheral veins, and when space is limited (eg, when cannulating the IJV).
The long-axis approach enables better visualization of the advancing needle, threading of the guidewire, and avoidance of inadvertent puncture of the posterior vessel wall.
New technique - Wire-in-needle (WIN)
A novel ultrasound-guided vascular access technique has been described by Stone et al, involving the use of a needle preloaded with the guidewire, without the use of a syringe. 
Insertion of the needle containing the tip of the guidewire is performed using the long-axis technique under dynamic ultrasound guidance. After the tip of the needle is seen entering the vessel, the wire is subsequently advanced into the vessel.
Several advantages to this technique include eliminating the risk of dislodging the needle tip when the syringe is removed from the needle as in the classic Seldinger technique, as well as increased echogenicity of the needle containing the wire on ultrasound imaging. One potential complication of this technique is misidentification of the target vessel, resulting in inadvertent cannulation of the carotid artery, for example.
Ultrasonographic guidance of FV cannulation during CPR has demonstrated that chest compressions are associated with changes in venous diameter.
This finding suggests that the pulsations appreciated during CPR are actually venous. 
When using the landmark-based approach for FV cannulation during CPR, needle insertion medial to the arterial pulsation may be misleading.
Ultrasonographic guidance may also be used for peripheral venous cannulation in patients who need intravenous access but have no visible or palpable veins.
Echogenic polymer–coated needles, used during ultrasonographically guided biopsy and ultrasonographically guided egg retrieval for in vitro fertilization, may be useful during central line placement because of the enhanced visibility of the needle tip on the ultrasound. 
CV access, in general, carries multiple potential complications, including the following:
The most serious and most common complications include pneumothorax, arterial puncture and cannulation, and local infection.
Potential complications during anesthesia administration include inadvertent venous or arterial infusion of lidocaine with or without epinephrine or subcutaneous air instillation that obstructs view during ultrasonographic guidance.
Studies have shown that ultrasonographically guided CV access decreases the associated complication rate by as much as 75%. Also, simulation-based ultrasound training helps inexperienced operators achieve greater successful central line placement rates with an improved safety profile. 
Patient Education and Consent
Consent should be obtained from the patient or family member, unless emergent circumstances otherwise dictate.  The reason the procedure is being performed (suspected diagnosis); the risks, benefits, and alternatives of the procedure; the risks and benefits of the alternative procedure; and the risks and benefits of not undergoing the procedure. Allow the patient the opportunity to ask any questions and address any concerns they may have. Make sure that they have an understanding about the procedure so they can make an informed decision.
The patient should be counseled about the risks of allergic reaction to the local anesthesia, vascular injury (air embolus, damage to adjacent vessels, pericardial tamponade, catheter embolus, arteriovenous fistula, mural thrombus formation, hematoma), infection (localized cellulitis, generalized sepsis, osteomyelitis), dysrhythmias, catheter malposition. For the subclavian and internal jugular approaches, counsel the patient about the risk of pneumothorax, hemothorax, chylothorax, hemomediastium, neck hematoma and tracheal obstruction, tracheal perforation, phrenic nerve injury, brachial plexus injury, and cerebral infarct. For the femoral approach, counsel the patient about the risk of psoas abscess, bladder perforation, and femoral artery injury.
Reassure the patient that the use of the ultrasound will help reduce many of these risks and help guide the physician in locating the correct vessel.
The patient should also be counseled that even if there are no complications, the procedure may not be successful and that a diagnosis still may not be obtained from the procedure. Discuss with the patient the possibility that the catheter may be placed in the wrong position and may need to be repositioned. Also instruct them that it is possible that the procedure may need to be repeated.
Discuss how these risks can be avoided or prevented (eg, use of the ultrasound, proper positioning, ensuring that the patient remains as still as possible during the procedure, adequate analgesia).
Lidocaine with or without epinephrine may be infiltrated locally under ultrasonographic guidance. For more information, see Local Anesthetic Agents, Infiltrative Administration.
Instillation of anesthetic with ultrasonographic guidance allows for more precise placement and improved analgesia.
Inadvertent air instillation in the overlying tissues is important to avoid, as it may cause a reverberation or free air artifact that obscures the ultrasound image.