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Renal Replacement Therapy for the Critically Ill Infant


Objectives

This chapter will:

  • 1.

    Explain special issues related to use of renal replacement therapy for infants.

  • 2.

    Identify specific risks and complications of renal replacement therapy in infants.

  • 3.

    Highlight advantages and disadvantages of different renal replacement modalities for the critically ill infant.

The expanding role of renal replacement therapy (RRT) in the care of critically ill children extends to the smallest pediatric patients. Infants with oliguria, volume overload, multi-organ dysfunction, and metabolic disorders can be treated successfully with techniques that have been established in larger children and adults. RRT for infants presents special challenges. Data regarding dialysis support for infants in the intensive care unit (ICU) are limited and recommendations often are based on clinical experience. Overall, the need is relatively uncommon, but dialysis is potentially lifesaving when circumstances warrant. Careful preparation, communication, and coordination between various hospital specialists, including nephrologists, neonatologists, surgeons, nurses, nutritionists, and pharmacists, can maximize the likelihood of success for these critically ill infants.

Renal Failure and Other Indications for Renal Replacement Therapy

Indications for RRT in the critically ill infant parallel those seen in older children and adults ( Box 206.1 ). Acute kidney injury (AKI) is a common complication seen in the neonatal period and has been reviewed recently. Causes for AKI in the newborn period can include urinary obstruction, so-called prerenal conditions with diminished perfusion, and complications of intrinsic renal diseases including congenital abnormalities. A majority of infants with AKI experience recovery without the need for therapy beyond supportive care. When conservative measures fail, RRT can be considered for the newborn with renal dysfunction. Renal replacement in this setting provides the parallel needs of metabolic control and fluid balance, identical to that required by an older child or adult with AKI. Rarely, an infant patient will require RRT for chronic kidney disease. Indications are similar to those for older children or adults with the additional need to begin treatment in the setting of suboptimal growth or inability to provide sufficient nutrition to the infant because of fluid limitations. Acute intoxication, either with endogenous toxins as seen with inborn errors of metabolism or exogenous toxins resulting from iatrogenic events, represents another clinical scenario that may require treatment by dialysis. Hemodialysis can remove toxins rapidly and is often the preferred therapy for severe intoxication in older children and adults. For infants, hemodialysis is similarly more efficient than peritoneal dialysis in this setting and should be considered for the treatment of intoxication.

Box 206.1
Potential Indications for Renal Replacement Therapy in Infants

  • Volume overload or metabolic/electrolyte abnormalities related to decreased kidney function

    • Diminished effective circulating volume (“prerenal” states):

      • Volume depletion

      • Hemorrhage/blood loss

      • Fluid redistribution (“third-space”)

      • Diminished cardiac output (e.g., congenital heart disease)

      • Hypotension/shock (e.g., sepsis syndrome)

    • Urinary obstruction (“postrenal” states):

      • Bladder outlet obstruction (e.g., posterior urethral valves)

      • Bladder dysfunction (e.g., neurogenic bladder)

      • Obstructing tumor or mass

      • Congenital obstruction of ureters

      • Solitary functioning kidney with obstruction

    • Intrinsic renal disease or injury (“intrarenal” states)

      • Ischemic injury

      • Tubular toxicity (e.g., drugs, myoglobin)

      • Vascular thrombosis

      • Hemolytic uremic syndrome

      • Congenital renal diseases (e.g., renal dysplasia)

      • Multi-organ dysfunction

  • Intoxication

    • Endogenous intoxication (e.g., hyperammonemia of the newborn)

    • Exogenous intoxication (e.g., drug intoxication)

  • Renal support

    • Suboptimal kidney function limiting delivery of nutrition and medical therapy

The concept of “renal support” has been applied to older patients to describe the use of renal replacement therapies before the development of absolute indications such as fluid overload or uremia. Fluid restriction as part of conservative management for a patient with mild renal dysfunction potentially may lead to reduced nutrition. RRT can reduce the total fluid burden related to daily fluid input and also permit maximal medical support. The infant with renal dysfunction can benefit from this approach as well; RRT should be considered early in the course of AKI.

Peritoneal Dialysis

Despite technologic improvements that have opened the possibility of use of all modalities of RRT in the critically ill infant, peritoneal dialysis (PD) remains an effective renal replacement modality and may represent a superior alternative for infants. Even the most experienced centers may have difficulty achieving vascular access in infants, limiting options for the use of hemodialysis and continuous RRT. Children with vascular abnormalities, certain types of cardiac disease, or hemodynamic issues may be suboptimal candidates for extracorporeal perfusion. In such circumstances PD can be the best choice for RRT.

Indications

PD is an effective method for achieving metabolic control and fluid balance in the infant with renal failure. The technique is relatively straightforward, and protocols for therapy in the newborn are well established. PD often is considered the preferred method of management for infants who have undergone cardiac surgery and can be a useful adjunct to maintaining fluid balance in those patients who have low cardiac output.

Technique

To perform PD, a dialysis catheter must be placed in the infant's abdomen. These catheters come in various sizes; smaller catheters are available for use in the newborn and small infant. Either a surgically placed catheter or percutaneously inserted temporary catheters may be used. Some evidence suggests fewer complications with surgically placed catheters. Local practice often determines who will insert the catheters when they are needed; the procedure requires expertise to ensure proper function of the catheter. Peritoneal dialysate comes in standardized concentrations that are available commercially. These formulations usually are acceptable for use in the critically ill infant. In the United States, peritoneal dialysate is available in standard dextrose concentrations of 1.5%, 2.5%, and 4.25%, with lactate used as the base; similar dextrose concentrations are available elsewhere.

Lactate absorption can lead to complications in critically ill infants. The hospital pharmacy may have to specially prepare dialysate with bicarbonate, although in our experience standard lactate-based dialysate is usually acceptable. Outside of the United States bicarbonate-based peritoneal dialysate is available commercially. Peritoneal dialysate should be warmed to body temperature before use in infants to prevent hypotension associated with cold dialysate infusion. Initial exchanges with a newly placed PD catheter should use relatively lower volumes of 10 to 20 mL/kg (200–500 mL/m 2 ) of dialysate to limit the chance of leak from the catheter insertion site. Low-volume PD can be an effective method in the infant, successfully achieving ultrafiltration goals. Exchanges of dialysate can be performed throughout the day in the ICU, thereby increasing time on dialysis compared with that typical when PD is performed in the ambulatory setting. This more frequent exchange helps achieve metabolic balance even with the use of lower dialysate volume. For those patients who require greater mass transfer after successful initiation, fill volumes may increase gradually to 1000 to 1100 mL/m 2 . Shorter dwell times often are used for infants in the critical care setting. Although longer dwell periods provide more time for equilibration of dialysate and for ultrafiltration, shorter dwell periods may permit more dialysis and ultrafiltration in a 24-hour period by allowing more exchanges per day. Initial dwell periods of 15 to 30 minutes in the newborn can be adjusted later based on clinical status.

Programming limitations may prevent the use of a cycler for infants who require very small fill volumes or very short dwell times. In such circumstances PD must be performed manually. Premade tubing systems for hand dialysis in the neonate are available commercially, or caregivers familiar with the modality may assemble extemporaneously a system using intravenous tubing. In either case, bedside care providers must be careful to maintain sterility through a closed system.

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