Principles of Ultrasound Guided Venous Access in Children

Introduction:

Ultrasound-guided venous access has proved to be more successful than the landmark-guided technique. In addition, it has been shown to cause fewer complications in adults and children. An anesthesiologist must have solid knowledge and skill in this technique and be well-experienced in performing the procedure on difficult age groups of patients, such as pediatric patients. Venous access in children has certain factors to consider, like greater variability in anatomy, smaller vessel size, smaller equipment size, a child's anxiety and fear, and superficially placed vessels.

What Are the Advantages of an Ultrasound-Guided Technique in Venous Access?

1. Accurately visualize the vessel location, diameter, patency, orientation, direction, and relation to the neighboring structures.

2. Safely used in patients with deviation from normal anatomy.

3. Increases the chance of successful cannulation in children and reduces the incidence of complications.

4. Easily inserted and well tolerated by potentially uncooperative children.

5. Immediate recognition of some complications.

6. Correct placement of a catheter into the right vessel by a guidewire can be confirmed.

7. Precisely guides the puncture site's location and needle approach angle to the target area to avoid errors.

What Are the Drawbacks of Ultrasound-Guided Venous Access Techniques?

• It is a complicated procedure, and so requires good hand skills. An anesthesiologist should have good coordination between hand and eye movement.

• The equipment is expensive and should be well maintained.

• The smaller probe size requirement for children had limitations in usage.

• The ultrasound-guided technique has some errors, such as a reverberation artifact that makes the needle tip appear deeper than it is.

What Is the Working Principle of an Ultrasound Device?

An ultrasound device functions on low-frequency ultrasound waves and the piezoelectric effect. Ultrasound waves have frequencies in the range of 3 to 10 MHz, above the audible frequency of the human ear. The vibration of piezoelectric crystals present in the probe of an ultrasound device produces these sound waves. When an electric current activates the probe, it produces short sound waves. This phenomenon is called the piezoelectric effect. Now, these waves strike the target organ and reflect their source. Different organs reflect these waves at different directions and depths because each organ has a different impedance for these waves. These variations are converted into digital images on the screen. Thus, ultrasound is used to visualize the internal structure of organs.

What Are the Common Venous Access Sites for Ultrasound-Guided Techniques in Children?

Vascular access can be done by venous, arterial, and intraosseous access. Venous access can be central or peripheral. The common access sites for peripheral venous access in children are:

• Scalp veins include the frontal vein, superficial temporal vein, and posterior auricular vein.

• External jugular vein.

• Antecubital vein.

• Umbilical vein.

• Dorsal venous plexus of hands.

• Dorsal venous plexus of the foot.

The common site for central venous access in children are:

• Internal jugular vein.

• Subclavian vein.

• Femoral vein.

What Are the General Principles of Ultrasound-Guided Venous Access in Children?

Short-Axis Versus Long-Axis Visualization:

Depending upon the orientation of the ultrasound image plane relative to the blood vessel, the plane can be short axis (out of plane) and long axis (in the plane). In the short axis view, the ultrasound image is at a right angle to the course of the blood vessels and needle. In the long-axis view, the image is parallel to the course of the blood vessel. Short axis view helps to reach the center of a vein. The vessel is seen as an anechoic (dark) circle, with the tip as a hyperechoic (bright) spot. Whereas in a long-axis view, the entire needle shaft and tip can be visualized. Long axis view is easier and suitable to use in larger veins like in central veins where tip location is important.

A. Identification of Vein and Artery

Both the retired vascular vessel and the veins appear similar on an ultrasonic image. Both vessels appear anechoic (dark). But there are a few differences. Arteries are a little hyperechoic and appear brighter. Also, veins are more compressible than arteries. Doppler imaging can also be used to distinguish between arterial blood flow and venous blood flow.

B. Static Versus Dynamic Ultrasound Technique

There are two ways to carry out a procedure, static and dynamic. In the static approach, ultrasound is used to locate the vessel and assess its patency, direction, and surrounding structures. After locating the site of the vessel, the procedure is performed based on the imaging done before the real-time ultrasound. In the dynamic approach, a live ultrasound is used during the procedure to visualize the access point and advancement of the needle into a vein.

C. One-Person Versus Two-Person Technique

During dynamic visualization, one person will hold the needle in one hand and the ultrasound probe in another and perform the procedure with coordinated eye movement and hand by looking at the imaging screen. But in a two-person approach, one person will direct the needle through ultrasound guidance, and the other will carry out the procedure. So, it requires an assistant to be present and should be well-trained.

D. Selection of Site and Preparation

Various factors like vein size, depth, course, anatomic variations, related structure, and underlying pathology decide the site for puncture for venous access. After locating the site, the patient and equipment are prepared. The patient is administered with local anesthesia, either intravenous or topical. The site is restricted by sterilizing the skin and creating a barrier. The ultrasound probe is covered with a sterile sheath. Ultrasound gel is used inside and outside the probe, and sterile gel is applied only on the outside.

E. Cannulation

Firstly, the axis of the vein should be determined. Then the path of insertion of the needle or catheter should be decided. Both paths should coincide. The depth of the vein to be cannulated is measured using ultrasound, and the needle's point of entry should also be the same. The entry angle is 45 degrees and should be at a distance from the probe equal to the vein's depth.

If the angle is less than 45 degrees, the needle is placed nearer to the probe, and if it is more than 45 degrees, the needle should be farther away. Throughout the procedure, the tip of the needle should be traced with the help of ultrasound. Care must be taken in not going beyond the posterior wall of the vein. If the posterior wall is entered, a flash of blood is seen in the needle. The needle should not be withdrawn to the center of the vein. After the successful entry of the needle into the vein, it is confirmed if it is placed correctly, and then a guidewire, a line, or a dilator is placed.

F. Postoperative Use of Ultrasound

Now, after the placement of the needle and a guide wire or catheter, ultrasound is used to confirm its location and identify if any compilation arises. A postprocedural flush is performed with a saline solution less than ten milliliters in volume and is agitated with air. If the placement is right, saline flush creates a hyperechoic image within the vessel.

Conclusion:

The introduction of ultrasound-guided venous access has made it very easy to place catheters and guidewires and to minimize complications like malpositioning, thrombosis, and pneumothorax, especially in children. Peripheral venous access is commonly performed in children. Scalp veins or the umbilical vein are used for venous access in neonates. Patient positioning, the access of the ultrasound probe, and its side orientation are important so that the left side of the ultrasound image on the screen indicates the left side of the body.