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

The use of umbilical artery catheters for infusion of amino acids to enhance protein supply in infants born at extremely low gestational age has been described. ^[3]

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. ^{[4, 5]}  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, ^[6]  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). The insertion depth for the high position can be calculated by using the following formula, developed by Shukla ^[5] :

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

Wright et al proposed a slightly different formula, as follows ^{[7, 8]} :

• 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. ^[9]  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. ^[10]  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. ^[11]  The gold standard insertion distance was defined as the distance from the abdominal wall to the midportion of the 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 having to be manipulated for optimal positioning.

An observational study by Stuttaford et al stated that the current formulae for estimating insertion length of umbilical catheters are not sufficiently reliable and suggested that the use of a different external length measurement, the sternal notch to umbilicus length, might allow the development of a more reliable formula for the insertion of umbilical artery and umbilical vein catheters to an adequate length. ^[12]

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. ^[13]  The study included infants born before 29 weeks' gestational age and admitted to 29 NICUs, who received (1) no umbilical catheters, (2) umbilical vein 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.