Umbilical Artery Catheterization 

Umbilical artery catheterization is a common procedure in the neonatal intensive care unit (NICU) and has become the standard of care for arterial access in neonates.[1] The umbilical artery can be used for arterial access during the first 5-7 days of life, but it is rarely used beyond 7-10 days. Placement of an umbilical artery catheter is easy in principle but often challenging in practice.

Umbilical artery catheterization affords direct access to the arterial blood supply and allows accurate measurement of arterial blood pressure, serves as a source of arterial blood sampling, and provides intravascular access for fluids and medications.[2]

Indications for umbilical artery catheterization include the following:

• Continuous arterial blood pressure monitoring
• Arterial blood gas sampling
• Blood sampling for other laboratory tests and studies
• Exchange transfusion
• Angiography
• Infusion of maintenance fluids when other routes are not available

Contraindications for umbilical artery catheterization include the following:

• Omphalocele
• Omphalitis
• Cord anomalies
• Peritonitis
• Necrotizing enterocolitis
• Vascular compromise to the kidneys, buttocks, or lower limbs

Best practices

Before the procedure, it is necessary to determine the insertion depth of the umbilical artery catheter. Various methods have been proposed to accomplish this, and graphs, based on the neonate’s height and weight, have been published.[3, 4]  An umbilical artery catheter can be placed in either the high position or the low position, though the high position is associated with lower complication rates.

In the high position,[5]  the catheter tip lies above the diaphragm, between thoracic vertebrae T6 and T9. This position is above the celiac artery (T12), the superior mesenteric artery (T12-L1), and the renal arteries (L1). For the high position, the insertion depth can be calculated by using the following formula, developed by Shukla[4] :

• Umbilical artery catheter depth (cm) = (birth weight [kg] × 3) + 9

Wright et al proposed a slightly different formula, as follows[6, 7] :

• Umbilical artery catheter depth (cm) = (birth weight [kg] × 4) + 7

Gupta et al described an alternative approach that relied on morphometric measurements—specifically, the distances from umbilicus to nipple (UN) and from umbilicus to symphysis pubis (USp)—to determine insertion length, rather than on birth weight.[8]  They found that the formula (UN – 1 cm) + 2USp was better correlated with appropriate umbilical artery catheter insertion length than the Shukla formula was (92% estimated correct insertion length vs 57%); this formula was also more accurate in very low birth weight infants than the Wright formula was (94% vs 68%).

In the low position, the catheter tip lies above the aortic bifurcation (L4-L5) between lumbar vertebral bodies L3 and L4. In this position, the tip of the catheter lies near the origin of the inferior mesenteric artery (L3-L4). A Cochrane review from 2000 found no evidence to support the use of umbilical artery catheters placed in the low position.[9]  Umbilical artery catheters placed in the high position are associated with a lower incidence of clinical vascular complications without an increase in any adverse sequelae.

In a 1-year prospective observational study, Lean et al compared the accuracy of 11 published formulae for guiding umbilical artery catheter placement in 103 patients in a tertiary NICU.[10]  The gold standard insertion distance was defined as the distance from the abdominal wall to the mid-descending aorta, at the level of T8 on radiography (range, T6-10). The highest success rates for accurate catheter placement were achieved when formulae involving body measurements were used; however, even the most accurate method resulted in more than 25% of catheters requiring manipulation for optimal positioning.

A study using data from the Canadian Neonatal Network database examined the association between umbilical catheters and a composite outcome of mortality or major neonatal morbidity in extremely preterm infants.[11]  The study included infants born before 29 weeks' gestational age and admitted to 29 NICUs, who received (1) no umbilical catheters, (2) umbilical venous catheters, (3) umbilical artery catheters, or (4) both venous and arterial catheters. The presence of either catheter was associated with mortality or major morbidity, and the association was stronger when both catheters were present.

An umbilical catheter insertion tray should be available that includes the following:

• Syringe, 1 mL
• Syringe, 3 mL (2)
• Syringe, 5 mL (2)
• Hypodermic needle, 20 gauge
• Mosquito hemostat, straight, 5 in. (12.7 cm)
• Mosquito hemostat, curved, 5 in. (12.7 cm) (2)
• Vessel dilator probe, 5.5 in. (14 cm)
• Iris forceps, full curve, 4 in. (10 cm)
• Iris forceps, half curve, 4 in. (10 cm)
• Iris forceps, straight, 4 in. (10 cm), 1 × 2 teeth
• Straight forceps, smooth
• Hemostat needle holder, 5 in. (12.7 cm)
• Straight Iris scissors
• Safety scalpel with No. 11 blade
• Silk suture, 4-0, with curved cutting needle
• Umbilical tape, 15 in. (38 cm)
• Measuring tape
• Drape with 6-cm orifice
• Gauze pads, 4 × 4 in. (10 × 10 cm) (6)
• Gauze pads, 2 × 2 in. (5 × 5 cm) (6)

Additional equipment used in the procedure includes the following:

• Single-lumen umbilical artery catheter, 3.5 French (neonate weight < 1500 g) or 5 French (neonate weight >1500 g)
• Stopcock, three-way
• Additional syringes, 5 mL (2)
• Heparinized flush (0.45% sodium chloride plus 1:1 heparin)
• Skin preparation solution (4% chlorhexidine gluconate or povidone iodine)
• Sterile surgical towels (4)
• Surgical mask
• Surgical gown
• Sterile gloves
• Arterial pressure transducer

Anesthesia

Anesthetic agents are not required, because the umbilical cord is devoid of nerve fibers.

Small preterm neonates can be placed in soft arm and leg restraints to prevent movement during the procedure; anesthesia to prevent struggling is not usually required. Full-term and larger preterm neonates can also typically be restrained but may require sedation with intravenous midazolam or fentanyl to decrease struggling.

Positioning

The neonate should be placed in a supine position under a radiant warmer. The head of the neonate should be positioned toward the top of the warmer.

Care must be taken to ensure adequate thermal support during the procedure, especially in neonates with extremely low birth weight.

Umbilical artery cannulation

Before beginning the procedure, determine the insertion depth of the catheter as outlined previously (see Technical Considerations).

Restrain the neonate under the radiant warmer using soft arm and leg restraints.

Prepare the catheter under sterile conditions by connecting the three-way stopcock to the end of the catheter. Connect one prefilled 5-mL syringe to each port of the stopcock. Flush the system with heparinized solution (0.45% sodium chloride plus 1:1 heparin). Ensure that no air bubbles are present in the system. Turn the stopcock off to the catheter.

An assistant should hold the umbilicus upright with the cord clamp (see the image below) while the physician cleans the cord and an area of surrounding skin (~3-5 cm around the cord base) in sterile fashion with 4% chlorhexidine gluconate or povidone-iodine solution.

Drape the neonate’s abdomen with sterile towels, allowing adequate exposure to the umbilical cord and base.

Place the umbilical tape at the base of the umbilicus (see the image below). Tie a square knot around the base of the cord as close to the abdominal wall as possible. Tighten the knot securely to avoid bleeding after the umbilical stump is cut. Do not overtighten the umbilical tie, because this makes advancement of the catheter past the knot difficult and may impair blood flow to the skin distal to the tie at the umbilical base.

Cut the umbilical stump to within 1-2 cm of the abdominal wall using a No. 11 scalpel blade (see the image below). Use a straight cut across with a gentle sawing motion.

Identify the vessels in the freshly cut cord (one large thin-walled umbilical vein and two small muscular arteries). (See the image below.) Vessel identification and isolation are made easier by holding the edges of the cord with the curved 5-in. (12.7-cm) mosquito hemostats.

Isolate one umbilical artery, and carefully dilate the lumen using curved Iris forceps (see the image below). Insert the tip of the forceps into the lumen as deeply as possible, then allow the forceps tips to spread open over 15-30 seconds while holding the tips in the vessel lumen. Remove the Iris forceps tips from the lumen and repeat the dilation procedure. Perform the dilation technique two or three times until the lumen of the vessel appears dilated enough to accept the catheter.

Grasp the end of the catheter, approximately 1 cm from the tip, with the half-curve Iris forceps (see the image below). Hold the vessel lumen open with the full-curve forceps, and gently insert the catheter into the dilated umbilical artery lumen.

Once the catheter is advanced into the lumen to a depth of 2 cm, remove the half-curve Iris forceps. If it is not possible to advance the catheter to 2 cm, withdraw it and dilate the vessel again.

Continue to advance the catheter to a depth of 4-5 cm, and aspirate to verify position in the lumen (see the image below). If blood is easily aspirated, the catheter is within the lumen. Clear the catheter of blood by injecting 0.5 mL of heparinized flush.

If resistance is met prior to this depth, try to loosen the umbilical tie. If a “popping” sensation is encountered while advancing the catheter, the catheter has likely exited the lumen and created a false tract. If this occurs, remove the catheter and use the second vessel for catheterization.[12]

Continue to advance the catheter to the predetermined depth. Once there, again aspirate to verify position in the aorta and flush the catheter. The catheter should draw and flush easily.

If resistance is encountered in the first 5 cm during advancement, apply gentle steady pressure for 30-60 seconds to allow the vessel to relax.[12]

If blood is not easily aspirated after insertion, the catheter is likely outside the vessel in a false tract.

Once the catheter has been advanced to the predetermined depth, confirm placement with chest and abdominal radiography. The catheter tip should lie above the level of the diaphragm between T6 and T9.

On radiography, the catheter should be seen entering the umbilical cord and then proceeding inferiorly to connect with the internal iliac artery (see the image below). The catheter should be seen curving cephalad to enter the aorta and proceeding in a straight line to the left of the vertebral column.

If the catheter is found to be in the femoral artery or gluteal artery, pull it back to a depth of 4-5 cm and attempt reinsertion (see the image below). The femoral and gluteal arteries are not suitable sites for sampling, infusion, or blood pressure monitoring.

Once correct positioning is verified on radiography, secure the catheter in place using a purse-string suture through the umbilical cord stump (not through the skin or vessels). This is done by taking two or three bites through the cord in an in-to-out manner. Secure the catheter to the stump by wrapping the tails of the suture snugly around the catheter and then tying securely with a surgical instrument tie (see the images below).

Further secure the catheter by means of a self-made or commercially available umbilical catheter bridge affixed to the abdominal wall (see the image below).

Once the catheter is secured, loosen and remove the umbilical tape. Connect the arterial pressure transducer, and verify a good arterial waveform.

To remove the umbilical artery catheter, stop fluid infusion, cut the retention suture, and pull the catheter back to a depth of 1-2 cm. Wait at least 5-10 minutes to allow the umbilical artery to constrict before removing the catheter. If bleeding occurs, use umbilical tape secured around the base of the cord. Alternatively, pressure can be applied to the iliac artery to control bleeding. Keep the neonate supine for 30-60 minutes after umbilical artery catheter removal to allow easy monitoring of bleeding.

Procedural pearls

Fold drapes so as not to obscure the neonate’s face and upper chest. This allows an assistant access to the neonate’s airway in case of emergency and allows visualization of chest rise and work of breathing during the procedure.

Avoid false-tracking the catheter. Make sure the catheter is in the lumen of the vessel, not in the wall.

Take time to dilate the vessel. This increases the likelihood of success and decreases the chance of exiting the vessel and causing a false tract.

The catheter should never be forced. If advancing the catheter is difficult within the first 2-4 cm, check that the umbilical tape is not too tight. Also, the entire cord can be pulled toward the neonate’s head to facilitate passage of the catheter at the angle between the cord and the abdominal wall.[12]

If the vessel spasms, apply slow steady pressure for 30-60 seconds to allow the artery to dilate.

If vessel spasm is encountered during insertion, 2% lidocaine hydrochloride without epinephrine can be used as a vasodilator.[12]  To apply, insert the catheter 2 cm into the vessel lumen and then drip 0.5 mL of lidocaine into the vessel. Apply constant pressure until the vessel dilates.

To avoid air embolism during insertion, always withdraw before flushing and carefully observe for bubbles in syringes, tubing, and stopcock.

Never advance a catheter once it is placed and secure. Doing so greatly increases the risk of infection by introducing a length of contaminated catheter into the vessel.[12]

Placing a radiograph plate under the neonate before beginning the procedure avoids having to move the neonate to place film once the catheter is in place.

The umbilical vein, not the umbilical artery, is the preferred route for medication and fluid administration during neonatal resuscitation. For more information, see the Resuscitation Resource Center, as well as Umbilical Vein Catheterization.

Complications of umbilical artery catheterization that are related to catheter malpositioning include the following:

• Vessel perforation ^[13]
• Refractory hypoglycemia (if glucose-containing fluids are being infused and the catheter tip is near the celiac axis)
• Peritoneal perforation
• Sciatic nerve damage

Complications that are related to vascular accidents include the following:

• Thrombosis ^{[14, 15]}
• Embolism/infarction
• Vasospasm
• Loss of extremity
• Hypertension
• Paraplegia
• Heart failure (from aortic thrombosis)
• Air embolism

Equipment-related complications include the following:

• Broken catheter
• Transection of catheter ^[16]

Other complications include the following:

• Hemorrhage
• Infection ^{[17, 18]}
• Necrotizing enterocolitis
• Intestinal necrosis or perforation (related to a vascular accident or infusion of hypertonic solution)
• Cotton fiber embolus
• Wharton-jelly embolus
• Hypernatremia (true or factitious)