Background

Ultrasound-guided cannulation of the femoral artery is a crucial vascular access method frequently used in interventional operations, emergency medicine, and critical care. It improves arterial puncture safety and accuracy by using real-time (dynamic) ultrasound imaging to examine the femoral artery and surrounding tissues. The risks of hematoma, arterial damage, and unintentional venous cannulation that come with blind or landmark-based procedures are greatly decreased by this method.

The Seldinger technique, an effective technique that involves a series of steps, is usually used to perform the procedure. A flexible guidewire is inserted through the needle and advanced into the vessel lumen after the femoral artery has been punctured with a needle while being continuously visualized by ultrasound. After removing the needle, a catheter or sheath usually aimed at the distal aorta is inserted over the guidewire and into place.

Direct viewing of needle trajectory, vascular patency, depth, and anatomical changes is made possible by ultrasound guiding. Patients with challenging vascular architecture, obesity, hypotension, or those for whom several prior efforts have failed benefit greatly from this method. In many clinical settings, ultrasound-guided femoral artery cannulation has emerged as the preferred technique for arterial access due to the increased focus on safety and effectiveness in invasive treatments.

Indications

Patients in critical condition are the main candidates for ultrasound-guided femoral arterial cannulation, particularly those who have acute respiratory failure, refractory shock, or hemodynamic instability. For a variety of diagnostic and therapeutic applications, this technique offers safe and effective vascular access, especially in situations when peripheral access is insufficient or not recommended.

One of the main indications is the requirement for ongoing arterial blood pressure monitoring, which is crucial for unstable patients in order to evaluate their hemodynamic condition in real time and direct the use of vasopressors or fluids. The femoral arterial catheter also makes it possible to do repeated arterial blood gas (ABG) measurements, which are crucial for treating patients with respiratory failure or metabolic disorders because they provide vital data on ventilation (PaCO₂), oxygenation (PaO₂), and acid-base balance (pH).

In order to evaluate heart function in critically sick patients, the catheter is also utilized for continuous cardiac output monitoring, which provides a less invasive option than pulmonary artery catheterization. It makes it easier to draw blood often for lab testing, which is particularly helpful for patients who need to have their coagulation profiles, lactate levels, or biomarkers monitored serially.

Additionally, femoral artery cannulation is frequently carried out in situations involving significant fluid changes or blood loss, such as major surgery or trauma, where precise hemodynamic monitoring and quick volume resuscitation are required. Additionally, it is recommended for patients receiving therapeutic hypothermia, including induced hypothermia procedures, and during inotropic support.

This method is used in interventional and procedural settings outside of critical care, including hemorrhage control, therapeutic embolization, and angiography. It is noteworthy because it provides access for the insertion of a balloon catheter during resuscitative endovascular occlusion of the aorta (REBOA), a procedure that can save the lives of patients suffering from non-compressible thoracic bleeding.

Contraindications

Although femoral arterial cannulation under ultrasound guidance is a useful operation in critical care, there are a number of absolute and relative contraindications that need to be taken into account in order to prevent serious consequences.

Absolute contraindications include circumstances in which the technique is likely to fail or is intrinsically dangerous. Among these is insufficient operator education or expertise with ultrasound-guided vascular access, which raises the risk of problems considerably. If the artery is considered inappropriate because of thrombosis, severe atherosclerosis, or inaccessibility under ultrasonography, the surgery should not be undertaken. Since cannulating a non-evident artery raises the risk of unintentional harm, it is absolutely contraindicated in cases of trauma-related injury or suspected injury to the femoral artery or ipsilateral external iliac artery, as well as in the absence of a detectable or palpable artery.

Other absolute contraindications involve the presence of a local infection at the planned insertion site, full-thickness skin burns that affect the integrity of the area, severely impaired peripheral circulation as seen in conditions like Raynaud syndrome or thromboangiitis obliterans, and documented hypersensitivity to antibiotics used in antibiotic-coated catheters.

Before proceeding, consider the relative contraindications and do a risk-benefit analysis. These include coagulopathy, which can be caused by thrombocytopenia, genetic bleeding abnormalities, or the use of anticoagulants or antiplatelet medications. In such circumstances, the danger of bleeding must be balanced against the risks associated with reversing anticoagulation, such as thromboembolism. Other related contraindications include trauma-induced anatomic deformation, congenital anomalies, or excessive obesity that affects landmark recognition or catheter insertion. Previous operations or catheterizations in the same location might raise the risk of vascular damage, especially if there is a bypass graft or distal vascular insufficiency. Severe atherosclerosis and poor collateral circulation can increase the risk of limb ischemia. Finally, a lack of patient compliance is a difficulty; nevertheless, this may typically be overcome with suitable anesthesia.

Equipment

Sterile hats, masks, gowns, gloves, face shields: Maintain a sterile environment and reduce the risk of infection during the procedure.

Large sterile drapes and towels: Create a sterile field around the insertion site.

Antiseptic solution: Antiseptic solution like chlorhexidine-alcohol, chlorhexidine, povidone-iodine, or alcohol can cleanse the skin and reduce microbial flora at the insertion site to prevent infection.

Ultrasound machine with high-frequency (5 to 10 MHz) linear array probe: It provide real-time imaging to visualize the femoral artery and surrounding anatomy during cannulation.

Sterile and nonsterile ultrasound gel: It facilitate sound wave transmission during ultrasound imaging; sterile gel is used during the procedure.

Sterile probe cover and rubber bands (or sterile glove and drape): It maintain sterility of the ultrasound probe and cord during the procedure.

1% Lidocaine without epinephrine (~5 mL): It provide local anesthesia to minimize patient discomfort at the insertion site.

Small anesthetic needle (25–27 gauge, ~3 cm): Superficial infiltration of local anesthetic into the skin and subcutaneous tissue.

Large anesthetic needle (22 gauge, ~4 cm): Deeper infiltration of anesthetic around the femoral artery access site.

3- and 5-mL syringes (slip-tip): Draw and administer local anesthetic or confirm arterial blood return.

Femoral artery introducer needle (18 gauge, ~7 cm): Puncture the femoral artery under ultrasound guidance.

Guidewire (~30 cm long): Inserted through the introducer needle to maintain arterial access and guide catheter placement.

Scalpel (#11 blade): Make a small skin incision to facilitate catheter advancement.

Femoral arterial catheter (4 French or 18–20 gauge, ≥15 cm long): Inserted over the guidewire into the femoral artery to allow continuous pressure monitoring and blood sampling.

Sterile gauze (10 × 10 cm): Absorb blood and maintain a clean field during and after insertion.

Sterile saline: Flush the arterial catheter and tubing to ensure patency and prevent clotting.

Nonabsorbable suture (nylon/silk 3-0 or 4-0): Secure the catheter to the skin to prevent dislodgement.

Chlorhexidine patch and transparent occlusive dressing: Protect the insertion site and reduce infection risk.

Noncompliant arterial line tubing: Transmit arterial pressure signals accurately from the catheter to the monitor.

Blood pressure transducer and oscilloscope monitor: Display real-time arterial pressure waveforms for hemodynamic monitoring.

Two three-way stopcocks: Allow simultaneous flushing, sampling, and monitoring through the arterial line.

Continuous saline flush system (0.5 to 1 L saline, metered pump, flush device): Maintain catheter patency and allow continuous pressure monitoring without clot formation.

1 or 2 assistants: Aid in maintaining sterility, positioning the patient, handling equipment, and monitoring during the procedure.

Considerations

When performing ultrasound-guided femoral arterial cannulation, choosing the right ultrasound view and method is crucial for precise needle insertion and reducing problems.

The short-axis (transverse or cross-sectional) image is often easier to achieve and is extremely useful for recognizing arteries and veins, as well as their spatial orientation. This viewpoint is very beneficial for planning the vascular access site. However, monitoring the needle tip in the short-axis view might be difficult since it appears as a tiny, echogenic (bright) dot. To recognize the tip, carefully observe the dot’s disappearance and reappearance as the needle travels over the imaging plane. This method is most usually employed for steep needle angles of 45 degrees or greater, since it provides for clear sight of vascular location.

In contrast, the long-axis (in-plane or longitudinal) view shows the needle’s complete length, including the tip. This enables for more exact monitoring of the needle as it moves toward and inside the vessel. While more technically demanding (the ultrasound probe, vessel, and needle must all be aligned in the same imaging plane), it provides more control over needle trajectory. This procedure is particularly useful when inserting the needle at shallow angles, such as during axillary or subclavian access, or to ensure alignment during short-axis-guided insertions.

If a second cannulation effort is required, it is critical to utilize completely new sterile equipment, as earlier instruments may be clogged by blood or tissue, jeopardizing success or increasing infection risk.
Furthermore, doctors should exercise caution under situations such as cardiac arrest, hypotension, or hypoxia, when arterial blood may seem darker and less pulsatile, potentially misidentifying it as venous blood. Accurate identification using ultrasound and awareness of physiologic changes are essential in such scenarios.

Patient position

Proper patient positioning is essential to optimize vascular access, enhance visualization under ultrasound, and reduce complications during femoral arterial cannulation.

• Begin by raising the bed to a height that allows the operator to stand upright comfortably without bending, ensuring ergonomic stability throughout the procedure.
• Position the patient in the supine position, lying flat on their back, which exposes the femoral region and stabilizes the lower body.
• The leg on the side of the intended cannulation should be abducted (moved away from the midline) and externally rotated. This positioning helps expose the femoral artery, makes the inguinal area more accessible, and improves the ultrasound window.
• If a pannus (excess abdominal skin/fat) or a urethral catheter obstructs access to the inguinal region, it should be gently retracted. This can be done using adhesive tape or with the assistance of another person to ensure a clear, sterile working field.

Optimal patient placement improves vascular structure visibility as well as needle manipulation ease under ultrasound guidance, enhancing the chance of a successful and safe artery catheterization procedure.

Outcomes

Step1: Patient Preparation and Positioning

Step1: Patient Preparation and Positioning

Raise the bed to a comfortable height for easy access during the process.
Position the patient supine with the leg abducted and externally rotated to reveal the femoral area.
Use tape or help to retract pannus or urine catheters away from the groin and clean insertion site.
To limit infection risk, clip extra hair instead of shaving.

Step 2: Pre-Procedural Ultrasound Assessment

Verify the ultrasound machine’s orientation: Ensure the probe’s marker matches the screen’s side mark.
Perform a non-sterile ultrasound scan of the femoral region using a short-axis (transverse) view, about 2.5 cm below the inguinal ligament.
Identify the femoral artery, it appears round, thick-walled, non-compressible, and hypoechoic (black).
Use Color and Spectral Doppler to confirm pulsatile arterial flow and lumen patency.
Select an ideal puncture site where the artery is large and not overlapped by a vein.

Step 3: Equipment and Sterile Field Setup

Place all sterile supplies on a sterile tray.
Wear sterile hat, mask, gown, gloves, and face shield.
Use antiseptic solution to swab a wide area (from the anterior superior iliac spine to midline, extending 15 cm below the inguinal ligament).
Allow the solution to dry for at least 1 minute, then apply sterile drapes.

Step 4: Probe Preparation

Apply non-sterile gel on the probe tip.
Using a sterile probe cover, have an assistant hold the gelled probe while you insert it into the cover using your gloved hand.
Unroll the cover completely over the probe and cord using your non-dominant hand, avoiding contamination.
Wrap sterile rubber bands at the tip to secure the cover, and apply sterile ultrasound gel over it.

Step 5: Local Anesthesia

Using the short-axis view, center the artery under the probe.
Measure the depth to the artery on the ultrasound screen.
Insert a 25–27G needle at a 45° angle toward the artery using ultrasound guidance.
Inject 1% lidocaine into the skin and subcutaneous tissue along the insertion path, while tilting the probe gently to track the needle tip.

Step 6: Arterial Puncture

Insert the 18G introducer needle using the same trajectory and ultrasound view.
Advance the needle while applying negative pressure to the syringe.
Adjust the needle’s angle or position as needed to keep the tip centered above the artery.
Once the artery is punctured, look for pulsatile, bright red blood flashback.
Remove the syringe and immediately occlude the needle hub with your thumb to prevent bleeding and air entry.

Optional: Long-Axis View Confirmation

For better visualization, rotate the probe 90° to switch to the long-axis (in-plane) view.
This helps track the needle and confirm accurate arterial puncture.

Step 7: Guidewire Insertion

While keeping the needle stable, insert the J-tipped guidewire (curve facing up) into the artery.
Advance it smoothly to 8–10 cm under ultrasound guidance. Do not force if resistance is felt.
Never release your grip on the wire.
If resistance occurs during advancement or withdrawal, remove the entire assembly (needle + wire) as a unit to avoid wire shearing.

Step 8: Needle Removal

Hold the guidewire at the skin as you withdraw the introducer needle.
Reconfirm guidewire position in the artery using ultrasound (transverse and longitudinal views).

Step 9: Skin Incision

Use a #11 scalpel blade to make a small skin incision at the insertion site to facilitate catheter passage avoid contacting the guidewire.

Step 10: Catheter Insertion

Thread the femoral arterial catheter (4 Fr or 18–20G, ≥15 cm) over the guidewire.
Use a gentle corkscrew motion to advance it into the artery while holding the guidewire steady.
Reconfirm placement with ultrasound imaging.

Step 11: Guidewire Removal

Once the catheter is in place, remove the guidewire while maintaining catheter stability.
You should observe pulsatile blood from the catheter lumen.

Step 12: Tubing Attachment and Pressure Monitoring

Connect the pre-flushed arterial transducer tubing to the catheter hub.
Confirm a clear arterial pressure waveform on the monitor.
Ensure the transducer is leveled at the phlebostatic axis (4th intercostal space, midaxillary line).

Step 13: Dressing and Securement

If the patient is awake, anesthetize the suture site with lidocaine.
Place a chlorhexidine patch at the insertion site.
Suture the catheter securely and cover with a transparent occlusive dressing.
Warning and Common Errors

Never let go of the guidewire throughout the surgery to avoid wire embolism or misplacement. Don’t rely exclusively on the hue or pulsatility of blood flow. In cases of cardiac arrest, severe hypotension, or hypoxia, arterial blood may appear black and non-pulsatile, similar to venous blood.  Use an ultrasound or pressure waveform monitor to confirm artery placement.

To prevent air embolism during catheter removal, position the vascular access point above the heart (if possible). During catheter removal, instruct the patient to execute the Valsalva maneuver (if aware and able). Immediately apply occlusive pressure and sterile dressing following removal.

References

References