The ultrasound guide allows direct visualization of the vessels of interest and surrounding anatomical structures. It also allows  to choose the best "target vessel", determine its depth and the optimal place to approach the puncture₍₃₎. This technique improves the safety of the procedure and reduces involuntary injuries. (Fig. 1)

Fig. 1: The ultrasound guide allows you to choose the best "target vessel", determine its depth and the optimal place to approach the puncture

ADVANTAGES OF EMPLOYMENT OF ECOGRAPHY IN THE PLACEMENT OF CENTRAL CATHETERS

If we add to that, its low cost, reproducibility and availability, the importance of  the use employment is multiplied.

BEFORE THE PROCEDURE

 INDICATIONS (Fig. 2)

Fig. 2: Indications for the placement of a central line.

 CONTRAINDICATIONS (Fig. 3)

Fig. 3: Contraindications for the placement of a central line

DURING THE PROCEDURE

¤ TECHNICAL CONSIDERATIONS

• TRANSDUCER CHOICE

To facilitate vascular access, broadband transducers are normally used (5-15 MHz). Higher frequencies provide better resolution, are more suitable for surface structures, and allow to unify and avoid vulnerable adjacent structures (example: small arteries and nerves). ₍₃₎ 

• ULTRASOUND TECHNIQUE (Fig. 4)

The vessels can be located in transverse ("out of plane") or longitudinal ("in plane") position.

• The transverse plane is safer since it allows continuous observation of the vein with respect to the artery and facilitates placement in smaller vessels.
•  The longitudinal plane,  has the disadvantage of not observing artery and vein in the same plane, being usually lateral to each other, it allows to observe the advance of the tip of the needle in the vein reducing the possibility of crossing the posterior wall.

Fig. 4: The vessels can be located in transverse ("out of plane") or longitudinal ("in plane") position.

The ultrasound guided placement must be in real time, we will have the position of the artery controlled at all times while we can visualize the entrance of the guide in the vein.

¤ PROCEDURE (mono -bi operator)

• The general literature highlights the importance of the generalization of the choice of the mono-operator as the best way of placing central catheters, with the understanding that it is the same person who manages the ultrasound and who performs the procedure of catheter placement.

• However, even in many places, the procedure is bi-operator, where the process can be made more difficult, especially because of the need for coordination to carry out the procedure. Being the most influential of all, the experience and skill of the ultrasound operator, which provides greater security to the bi-operator procedure.

¤ TYPES OF CATHETERISMS IN PEDIATRICS PACIENTS

⇒   Umbilical arterial catheter (UAC) (Fig. 5)

Umbilical artery catheterization is a common procedure in the neonatal intensive care unit. The umbilical artery can be used as arterial access during the first 5-7 days of life and rarely beyond 7-10 days, since spontaneous thrombosis of the umbilical vessels usually occurs after the week.

Fig. 5: Graph of the correct location of Umbilical Arterial Catheters (UAC)

⇒  Umbilical venous catheter (UVC) (Fig. 6)

The umbilical vein, such as the artery, can be used as central accesses until the first 7-10 days of life, because later they are obliterated.

It is a venous route widely used in neonatology since its channeling is very simple due to its wide caliber and accessibility. This contrasts with other veins that in infants and premature infants can be very difficult to access because they have a very small diameter, because they are fragile and deep.

Fig. 6: Graph of the correct location of Umbilical Venous Catheters (UVC).

⇒  Central venous catheter (CVC) (Fig. 7)

They are intravenous catheters that are located in a central vein. Unlike UAC and UVC, these catheters may be implanted for a long time.

In addition, theoretically they will present a lower incidence of complications due to the greater caliber of the vessel.

Among the most used central catheters in pediatrics we have:

• The PICC (peripheral central venous catheter of peripheral access).
• Hickmann catheter (tunneled catheter).
• Port-a-cath (catheter with reservoir). 

Fig. 7: Graph of the correct location of Central Venous Catheters (CVC).

⇒  Peripheral arterial catheter (PAC) 

The arterial catheter can also be used to obtain repeated blood samples, when it is necessary to frequently measure the levels of gases (oxygen and carbon dioxide) in the blood flow. It is also known as "arterial route"

AFTER THE PROCEDURE

¤ EVALUATION OF THE LOCATION IN NON-GUIDED PROCEDURES

(Fig. 8)

After placement of the CVC in neonates and pediatric population, their position is usually verified by chest radiography. Although this process is usually more delayed, less evaluable and most importantly, it radiates to the patient.

Fig. 8: Wrong position. 2 months with subclavian catheter with abnormal positioning through the internal jugular vein and distal cavus in the temporal jugular fossa. US shows pericateter echogenic material, in relation to pericateter thrombus.

⇒  IMMEDIATE COMPLICATION ASSESSMENT

• Pneumothorax (Fig. 9)

Frequent complication in “blind” procedures, detestable by ultrasound and X-ray, potentially fatal.

Fig. 9: Pneumothorax by ultrasound. On suspicion of complication, ultrasound is useful for the diagnosis of pneumothorax.

• Accidental puncture or cannulation of an artery/vein (Fig. 10)

Very frequent complication during “blind” placement may increase the risk of the appearance of arterial thrombosis.

Its detection is easy by ultrasound where the location of the distal end in the arterial vessel is identified, the Doppler and Spectral mode can also be used. 

Fig. 10: Accidental puncture or cannulation of an artery. It is usually found after a procedure not guided by ultrasound, "blindly"

• Puncture site hematoma (Fig. 11)

In the same way, its detection is by ultrasound. It consists of extravasation of catheter content with secondary formation of extraluminal collections. 

Fig. 11: Juxta-jugular hematoma secondary to CVC placement.

• Retroperitoneal hematoma (Fig. 12)

It happens when the lesion is produced in the intra-abdominal path of the affected vessels. Elevates morbidity and mortality. Its suspicion is essential and its detection can be done by ultrasound. It should be confirmed with other diagnostic methods (Angiography / AngioCT / AngioMR). 

Fig. 12: Retroperitoneal hematoma. Uncommon complication secondary to femoral canalization at high sites and difficult implementation

• Gas embolism (Fig. 13)

Secondary to the inadequate manipulation of the catheterization elements and the involuntary introduction of air volumes that can trigger fatal consequences in patients.

⇒  LATE COMPLICATION ASSESSMENT

• Arterial and / or venous thrombosis (Fig. 13)

They are also secondary to the endothelial lesion, can be arterial or venous and can generate secondary parenchymal infarctions

The EcoDoppler is the Gold Standard for detection 

Fig. 13: Venous thrombosis Pericateter thrombus is observed adjacent to the distal end of the CVC in a septic patient

• Local infection and / or distance (thrombophlebitis)

Generally associated with infectious (septic) thrombosis in patients with prolonged use of catheters.

• Pseudoaneurysms (Fig. 14)

Secondary to vascular lesion. They are easily visualized on Doppler ultrasound, they should always be suspected after arterial catheterization.

Fig. 14: Pseudoaneurysm Secondary to vascular injury due to improper catheter placement. Show turbulent flows

• AV fistula (Fig. 15)

It is clinically suspected by the local frémito or thrill and is confirmed by Doppler Ultrasound, by the presence of “pulsatile” venous flows. Secondary to any traumatic cause.

Fig. 15: AV fistula The color Doppler examination shows turbulent arterial flows of low resistance and pulsatile venous flows.

• Catheterization material migration (Fig. 16)

It is frequently associated with rupture of the material due to its bad handling, especially during the removal of the material 

Fig. 16: Catheterization material migration. 8 years, a catheter rupture occurs when removed. Material is observed in the lumen of vascular structure.