Umbilical Artery Catheterization

Suna Seo

Umbilical artery catheterization is performed in critically ill neonates, often soon after birth. The umbilical arteries are patent for 7 to 14 days, but are often accessible only in the first day or two after birth, after which vasoconstriction and clotting make access difficult.

A. Indications

Primary

1. Frequent or continuous (see Chapter 11) measurement of lower aortic blood gases for oxygen tension (PO₂) or oxygen content (percent saturation)

2. Continuous monitoring of arterial blood pressure

3. To provide a port for frequent blood sampling in the extremely low birth weight infant

4. Angiography

5. Resuscitation (use of umbilical venous catheter is the first choice)

Secondary

1. Umbilical arterial catheter is not usually recommended for infusion of maintenance glucose/electrolyte solutions or medications, but has been used for this purpose (1)

2. Exchange transfusion

C. Equipment

Sterile

1. Sterile gown and gloves

2. Cup with antiseptic solution

3. Surgical drape with central aperture

4. Catheter

a. Single hole

(1) Reduces surfaces for potential thrombus formation

(2) Recorded pressure tracing will change when hole is occluded

b. Made of flexible material that does not kink as it follows the curves of vessels

c. Relatively rigid walls with frequency characteristics suitable for accurate measurement of intravascular pressure

d. Small capacity (minimum volume of blood to be withdrawn to clear catheter prior to blood sampling)

e. Radio-opaque: The need to visualize the catheter position on x-ray film outweighs the theoretical risk of increased thrombogenicity related to a radioopaque strip (3)

f. Smooth, rounded tip (4), nonthrombogenic material (5)

g. 5-Fr gauge for infants weighing >1,200 g

h. 3.5-Fr gauge for infants weighing <1,200 g

5. Three-way stopcock with Luer-Lock

6. 10-mL syringe

7. 0.45 to 0.9 normal saline (NS) flush solution (saline with heparin, 1 to 2 U/mL)

a. In very small premature infants, particularly in the first week of life, hypernatremia may result from
receiving excess sodium in flush solutions. In these infants, 0.45 NS rather than more concentrated saline solutions is recommended

b. The use of hypotonic (0.25 NS) or dextrose solutions has been associated with hemolysis of red blood cells and should be avoided if possible (6)

c. Use of heparinized flush solution is common practice (7, 8, 9, 10, 11)

Heparin decreases the incidence of thrombotic complications (12), and a Cochrane Database Review found that the use of as little as 0.25 U/mL heparin in the infusate decreases the likelihood of line occlusion (13)

8. Tape measure

9. 20-cm narrow umbilical tie

10. No. 11 scalpel blade and holder

11. 4- × 4-in gauze sponges

12. Two curved mosquito hemostats

13. Toothed iris forceps

14. Two curved, nontoothed iris forceps

15. 2% lidocaine HCl without epinephrine

16. 3-mL syringe and needle to draw up lidocaine

17. Small needle holder

18. 4-0 silk suture on small, curved needle

19. Suture scissors

Nonsterile

1. Cap and mask

D. Precautions

1. Avoid use of feeding tubes as catheter (associated with higher incidence of thrombosis) (14)

2. Fold drapes so as not to obscure infant’s face and upper chest, allowing access to airway and visual monitoring of infant’s respiratory status during the procedure

3. Take time and care to dilate the lumen of the artery before attempting to insert catheter

4. Catheter should not be forced past an obstruction

5. Never advance catheter once placed and secured

6. Loosen umbilical tie slightly upon completion of procedure and obtain radiographic confirmation of position

7. Avoid covering the umbilicus with dressing. Dressing may delay recognition of bleeding or catheter displacement

8. Always obtain radiographic (including a lateral view) or ultrasound (15) confirmation of catheter position (16, 17)

9. Be certain that catheter is secure, and examine frequently when infant is placed in prone position, because hemorrhage may go unrecognized

10. Take care not to allow air to enter the catheter. Always have catheter fluid filled and attached to a closed stopcock prior to insertion. Check for air bubbles in catheter before flushing or starting infusion

11. When removing catheter, cut suture at skin, not on the catheter, to avoid catheter transection

12. Catheters should remain in place only as long as primary indications exist. Because of the risk of complications, catheters should usually not remain in place for more than 7 to 10 days

E. Technique (

Video 31.1: Umbilical Vein and Artery Catheterization)

Anatomic note: The umbilical arteries are the direct continuation of the internal iliac arteries (Fig. 31.1). Their diameters at their origins are 2 to 3 mm. As they approach the umbilicus, their lumina become small and the walls thicken significantly. A catheter introduced into the umbilical artery will usually pass into the aorta from the internal iliac artery. Occasionally, a catheter will pass into the femoral artery via the external iliac artery or into one of the gluteal arteries (see Fig. 31.15D). The latter two sites are unsuitable for sampling, pressure measurement, or infusion.

FIGURE 31.1 Anatomic relations of the umbilical arteries, showing relationships with major arteries supplying buttocks and lower limb.

1. Placement of UAC in high position should be used exclusively (18, 19). In rare cases, if high position is not successful, a low position may be used (Fig. 31.2).

a. High position (14,19): Level of thoracic vertebrae T6-T9 (Fig. 31.3); catheter tip above origin of celiac axis.

b. Low position (14,19): Level of lumbar vertebrae L3-L4 (Fig. 31.4).

(1) Catheter tip is below major aortic branches such as renal mesenteric arteries.

(2) In most newborns, this position coincides with the aortic bifurcation at the upper end of the fourth vertebra.

FIGURE 31.2 The aorta and branches.

FIGURE 31.3 UAC in satisfactory high position at the level of the ninth thoracic vertebral body on anteroposterior (A) and lateral (B) projections.

FIGURE 31.4 Anteroposterior (A) and lateral (B) radiographs showing satisfactory low position of a UAC. Catheter tip is at the level of the superior margin of the fourth lumbar vertebral body, which in newborns usually corresponds to the aortic bifurcation.

2. Make external measurements as necessary to estimate length of catheter to be inserted (Table 31.1) (see Fig. 31.5) (20, 21, 22, 23, 24, 25, 26).

a. There is no universal formula, measurement, or nomogram to accurately predict the UAC insertion length for infants of all birthweight and gestational ages (27, 28).

(1) Use Shukla (Table 31.1) for infants with birthweight >1,500 g (23).

(2) Use Wright formula for infants with birthweight <1,500 g (24, 26, 28, 29).

TABLE 31.1 Available Formulae to Estimate UAC Insertion Length (cm)

FORMULA AUTHOR (PUBLICATION YEAR)	CALCULATION OF UAC INSERTION LENGTH (cm) FROM ABDOMINAL WALL
Dunn (1966) (20)	Graph reference using shoulder-umbilicus distance (Fig. 31.5 (a))
Rosenfeld et al. (1980)(21, 22)	Graph reference using total body length
Shukla and Ferrara (1986) (23)	[3 × weight (kg)] + 9
Wright et al. (2008) (24)	[4 × weight (kg)] + 7
Vali et al. (2010) (25)	1.1 × [xiphisternum to ASIS + ASIS to umbilicus] + 1.6
Gupta et al. (2015) (26)	(Umbilicus to nipple – 1) + (2 × umbilicus to symphysis pubis) (Fig. 31.5 (b and c))
UAC, umbilical arterial catheter; ASIS, anterior superior iliac spine.

(3) Published precision performance comparisons of the formulae are inconsistent and inconclusive (27, 29, 30).

(4) Morphometric measurement-based formulae may be more suitable for extremely preterm infants (25, 26, 31).

3. Prepare as for major procedure (see Chapters 5 and 6).

4. Attach stopcock to hub of catheter and fill system with flush solution (see Section C7). Turn stopcock to catheter “off.”

FIGURE 31.5 White dashed line indicates the base of the umbilicus. (a) Shoulder to umbilicus length measurement (20); (b) Umbilicus to nipple length measurement (26); (c) Umbilicus to symphysis pubis measurement (26).

5. Place sterile gauze around umbilical stump and elevate out of sterile field or have an assistant grasp the cord by the cord clamp or forceps and hold the cord vertically out of the sterile field.

6. Prepare cord and surrounding skin with antiseptic solution to radius of approximately 5 cm. The use of chlorhexidine in infants <2 months of age is not recommended (32, 33).

7. Drape area surrounding cord.

8. Place umbilical tie around umbilicus and tie loosely with a single knot.

a. Tighten only enough to prevent bleeding and, if possible, place around Wharton jelly rather than skin.

b. It may be necessary to loosen the tie when inserting the catheter.

9. Cut cord horizontally at 1 to 1.5 cm from skin with scalpel (Fig. 31.6).

(Note: Need longer length of umbilical cord for alternative technique—see Lateral Arteriotomy below.)

FIGURE 31.6 Traction is being placed on cord in the direction of the arrow. Operator is about to make a horizontal cut across cord.

10. Avoid tangential slice. Control bleeding by gentle tension on umbilical tape.

11. Blot surface of cord stump with gauze swab. Avoid rubbing, as this damages tissue and obscures anatomy.

12. Identify cord vessels (Fig. 31.7).

FIGURE 31.7 The vessels of the umbilical cord. Thin-walled umbilical vein at 12-o’clock position is indicated by a white arrow. The two umbilical arteries are directly below the vein at 4- and 6-o’clock positions.

a. Vein is easiest to identify as large, thin-walled, sometimes gaping vessel. It is most frequently situated at the 12-o’clock position at the base of the umbilical stump.

b. Arteries are smaller, thick-walled, and white and may protrude slightly from cut surface.

c. Omphalomesenteric duct is rarely present.

13. Grasp cord stump, using toothed forceps, at point close to (but not on) artery to be catheterized. If available, it may be helpful to have an assistant scrub and assist.

a. Apply two curved mosquito hemostats to Wharton jelly on opposite sides of the cord, away from the vessel to be cannulated.

b. Apply traction to stabilize cord stump.

14. Introduce one of the points of the curved iris forceps into the lumen of the artery and probe gently to a depth of 0.5 cm.

15. Remove forceps and bring points together before introducing them once more into the lumen.

16. Probe gently to a depth of 1 cm (up to the curved “shoulder” of the forceps), keeping the points together.

17. Allow the points to spring apart and maintain forceps in this position for 15 to 30 seconds to dilate vessel (Fig. 31.8). Time spent in ensuring dilatation prior to catheter insertion increases the likelihood of success.

FIGURE 31.8 An iris forceps is pointed into the umbilical artery in order to dilate the lumen of the artery.

18. Release cord and set aside toothed forceps, while keeping curved forceps within artery.

19. Grasp catheter 1 cm from tip, between free thumb and forefinger or with curved iris forceps.

20. Insert catheter into lumen of artery, between prongs of dilating forceps (Fig. 31.9).

FIGURE 31.9 A: Inserting the catheter into the artery between the prongs of dilating forceps. Note that the umbilical tape has been tied around the skin of the umbilicus; this should be loosened once the catheter is secured in place. B: Close-up photo of the umbilical stump with the arterial catheter in place.

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