Infant Hemodialysis

Vascular Access

Hemodialysis requires a central venous catheter, and in infants, this poses technical challenges because of their smaller vessel size and the likelihood that they may require vascular access throughout their lifetime if end-stage renal disease is present. Dialysis catheters are stiff, allow for high rates of blood flow, and are relatively larger than other central lines. Thus, use of central lines other than those designed for dialysis is not recommended. Historically, umbilical lines were sometimes used for infant hemodialysis access, but this has fallen out of favor with the availability of small-diameter hemodialysis lines. If umbilical vessels are used, the umbilical artery must have at least a 5-Fr (French) catheter and the umbilical vein, at least a 7–8-Fr catheter. In this case, the tip of the umbilical vein catheter should be above the diaphragm, and the tip of the umbilical artery catheter should be below the renal arteries. If umbilical catheters are used for dialysis, the arterial and venous lines cannot be reversed.

The choice of a temporary (uncuffed, nontunneled) versus semipermanent (cuffed, tunneled) hemodialysis catheter depends on whether the infant is expected to require short- or long-term therapy. However, even if the infant is expected to require long-term dialysis, many will be transitioned to PD, and thus in the acute setting, a temporary catheter (uncuffed) is often placed. Placement of a hemodialysis catheter should be performed under fluoroscopy to confirm placement. The line with the largest possible gauge should be placed in order to allow for optimum blood flows. However, placement of a line that is too broad can result in occlusion of the vessel. Available catheters may differ across institutions. Typically, the smallest catheter that can be used for hemodialysis and still maintain adequate blood flow is 7–8 Fr.

Options for the location of the HD catheter in infants include internal jugular (IJ), subclavian, and femoral veins. Catheter insertion sites should be determined individually as each infant requiring hemodialysis may have specific circumstances precluding one site or another. Use of the subclavian vein should be avoided if a line can be placed in the IJ, as occlusion of the subclavian vein may preclude creation of an arteriovenous fistula when the child is older and may require additional dialysis access. Ideally, the tip of the catheter should be at the right atrium/superior vena cava junction when placed in the IJ or subclavian. Catheters in the femoral vein should have the tip as central as possible. Femoral catheters are associated with an increased risk of infection and thus should not be used long-term. With noncentral placement of catheters, there is an increased risk of recirculation as well as blood flow limitations.

Complications of hemodialysis access include infection, clotting, venous outflow obstruction, and failure of the access, which may be related to mal-positioning or movement, kinking, or breaking of the line. Because these complications result in an inability to provide dialysis and may require surgical replacement of the line, only trained dialysis staff should use dialysis lines. Anticoagulation is used during dialysis to maintain patency of the lines, and the details of this are reviewed in Chapter 74 . Additional information regarding access may be found in Chapter 72 .

Equipment/Preparation

Equipment for hemodialysis includes dialysis machines, blood lines, and dialyzers. Each must be carefully considered to provide the safest and most efficient treatment for the infant. Many dialysis machines will now allow low blood flows, although none provides specific indications for infant dialysis, and thus provision of infant dialysis is an off-label use of the machine. Use of newer machines created for infants is typically geared toward continuous renal replacement therapy (CRRT), which is discussed elsewhere. Of critical importance in selecting a dialysis machine to use for the infant is the availability of accurate control of ultrafiltration. In the infant, even small volumes of ultrafiltration may result in hemodynamic changes. The ordering clinician should know the margin of error for ultrafiltration for each type of machine used.

One must have accurate information regarding the priming volume of the blood lines and the dialyzer. This should be available on standard packaging. The priming volume of the dialyzer and blood lines should never exceed 10% of patient's blood volume. For small patients, use of blood to prime the circuit may be required to avoid hemodynamic compromise and hemodilution. Use of neonatal lines may allow the clinician to reduce or avoid blood primes. If a blood prime is required, an aliquot of packed red blood cells should be diluted to achieve a priming hematocrit of 35%–45%. Consideration when using blood primes includes the potential for sensitization when exposing an infant to multiple blood donors, which may complicate future transplantation. Donated blood is anticoagulated with citrate, which may lead to hypocalcemia in the infant, and thus, serum calcium should be assessed and supplemental calcium provided if indicated. Blood primes also contain a significant amount of potassium, and, if possible, one should use fresh blood or washed red cells to avoid hyperkalemia. At the end of a treatment initiated with a blood prime, blood in the lines is not returned to the patient as this would represent a large-volume transfusion and can lead to hypervolemia, hypertension, and/or pulmonary edema. If the prime volume is less than 10% of the blood volume, 5% albumin may be used for priming. Lines may need to be warmed to prevent hypothermia in the infant undergoing hemodialysis. Frequent temperature monitoring is required.

For infants undergoing hemodialysis, typically, the smallest dialysis filter available is appropriate, as smaller filters will still allow for adequate clearance given the low total blood volume. There are a wide variety of filters with various blood volumes available, and each institution may have its own preferable filters based on local experience. Given the low number of small children receiving hemodialysis each year, there are no formal studies comparing the safety and efficacy of different dialysis machines and filters in infants.