Umbilical arterial catheterization provides direct access to the arterial system, thus enabling arterial blood sampling as well as the measurement of the systemic arterial blood pressure. It is one of the commonly performed procedures in extremely premature neonates. The procedure is relatively easy to perform but requires practice.
The umbilical artery originates from the anterior division of the internal iliac artery. In fetal life, it traverses within the umbilical cord carrying oxygen-depleted blood from the fetus to the placenta. There are usually two umbilical arteries and one umbilical vein within the umbilical cord. In approximately 1% of pregnancies, one of the umbilical arteries may undergo atresia, aplasia, or agenesis resulting in a single umbilical artery. A single umbilical artery is an isolated finding in most cases, but if it is associated with other fetal anomalies, there is an increased risk of chromosomal abnormalities. The umbilical arteries are identified by their caudal location within the cord with thicker walls and smaller lumen.
The primary indications for umbilical artery catheterization include the need for frequent measurement of arterial blood gases, frequent blood sampling, or continuous blood pressure monitoring in the extremely low-birthweight infant or critically ill neonate. Occasionally, it can be used temporarily for the infusion of parenteral nutrition if alternate access is not available.
Omphalitis, necrotizing enterocolitis, omphalocele, gastroschisis, peritonitis are some of the contraindications for placement of an umbilical arterial catheter.
A physician or an advanced practitioner with adequate training should perform the procedure. Second personnel, such as a nurse, should also be present to help monitor the patient throughout the process.
After determination of the necessity for an umbilical arterial catheter, informed consent must be obtained as per the local institutional policy. Measures should be taken to avoid hypothermia in the infant while doing the procedure. These include the use of a radiant warmer and placement of an exothermic mattress under the infant, as necessary while performing the procedure. The three-way stopcock has to be attached to the desired catheter and flushed with saline solution. It is better to use 0.45% normal saline to avoid hypernatremia with the use of 0.9% normal saline. The flush syringe has to be left attached to the stopcock with the stopcock turned off. The length of the insertion of the catheter tip has to be determined before the insertion.
The ideal position of the catheter tip should be in the descending aorta above the origin of the celiac, mesenteric, and renal arteries to avoid occlusion of these vessels. This high position (thoracic vertebra level T6-T9) is preferred compared to the low position, i.e., below the renal arteries (lumbar vertebra level L3-L4) as it is associated with fewer complications of thrombosis. The catheter length is estimated from the formula [(birth weight in kg x 3) + 9] cm. Other methods for estimating the depth of insertion are also described. The length of the stump above the skin is added to this measurement.
Before starting the procedure, the infant has to be restrained to minimize movement. The umbilical cord and the surrounding skin are cleaned with an antiseptic solution. The cord is better cleaned with an assistant grasping the cord by the cord clamp or forceps and pulling the cord vertically out of the field. The area is then draped and an umbilical tie placed around the cord, tight enough to minimize blood loss but loose enough to allow catheters can be passed easily through the vessels. The cord is then cut horizontally 1 cm to 1.5 cm from the skin. The umbilical arteries are identified by their thick walls with a smaller lumen. The cord stump is grasped, and traction applied. The lumen of the artery is probed gently by introducing the closed tips of the iris forceps and then is dilated by allowing the forceps to spring apart, maintaining in this position for about 30 seconds. The catheter is then grasped with the curved iris forceps, or between the thumb and forefinger and inserted into the lumen of the dilated artery.
If there is any resistance to the advancement of the catheter, gentle, steady pressure must be applied. Repeated probing or excessive pressure can result in perforation of the vessel. If unsuccessful, catheterization of the other artery must be attempted. After advancing to the appropriate distance, the catheter is secured using purse-string sutures around the base of the cord, and the tie removed. Radiologic confirmation of the catheter tip must be obtained to confirm its location between the T6-T9 vertebra. The catheter can be retracted if needed, but it should never be advanced once it is secured, due to the risk of introducing infection. Infusion of a heparinized solution must be started as soon as the catheter tip is verified to be in an appropriate position.
Thromboembolism is a major concern with the use of umbilical arterial catheters. Occlusion of the mesenteric arteries can result in gut ischemia, bowel infarction, and necrotizing enterocolitis. Renal artery involvement can lead to hypertension or acute renal failure. Vascular accidents more distally can result in an ischemic injury of the back, buttocks, and lower extremities. Removal of the catheter must be considered at the first sign of any vascular compromise. Other complications, such as vessel perforation, peritoneal perforation, bladder injury, and false aneurysm, can occur during catheter insertion. Catheter-associated infection and bleeding are other frequently associated complications. Refractory hypoglycemia is a rare complication associated with high position umbilical artery catheters whose tip is near the celiac and mesenteric arteries.
An umbilical arterial catheter can be lifesaving in the management of critically ill neonates. However, due to the potential complications associated with its use, the risks and benefits must be carefully weighed before attempting the procedure. Extremely low birth weight infants (< 1000 g), preterm infants needing mechanical ventilatory support, infants with hypoxic-ischemic encephalopathy undergoing therapeutic hypothermia, critically ill late preterm or term infants requiring mechanical ventilation are some of the groups of neonates who might benefit from the use of umbilical arterial catheter owing to the need for frequent blood sampling. It is helpful to adhere to guidelines standardizing the use of umbilical catheters in neonates. There is a theoretical concern of necrotizing enterocolitis, while infants are enterally fed in the presence of an umbilical arterial catheter. However, there is no evidence to support this, and withholding enteral feeds while an infant has an umbilical arterial catheter is not recommended anymore.
An interprofessional care team approach is essential for the successful insertion and maintenance of umbilical arterial catheterization. As discussed earlier, communication and coordination between the physicians/advanced practitioners and nurses are very important. The necessity of the catheter must be evaluated every day by the healthcare team, including the nurse, and it must be removed when no longer necessary. [Level 2] Continuation of the umbilical arterial catheter beyond five days is not recommended due to the risk of infection and thrombosis associated with its prolonged use. [Level 2]
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