Rudolph's Pediatrics, 22nd Ed.

CHAPTER 478. Chronic Dialysis

Stuart L. Goldstein

Chronic dialysis therapy should be initiated for children with chronic kidney disease (CKD) who are unable to maintain safe electrolyte homeostasis, blood pressure control, fluid balance, and/or energy level with appropriate dietary restriction and medication management. Although no absolute serum creatinine or blood urea nitrogen concentration serves as an absolute indication for dialysis initiation, a creatinine clearance of ≤ 15 mL/min/1.73 m2 should also prompt consideration of dialysis initiation for children who do not expect to receive expeditious renal transplantation.1 In addition, dietary restriction should not be made so severe as to prevent growth in an effort to forestall dialysis initiation.

The need for dialysis should be anticipated in order to allow for proper patient and family education on treatment modalities, patient and parent training, and creation of a functioning vascular or peritoneal access even before dialysis is required. Whenever possible, dialysis should not be initiated as an emergency procedure because this usually necessitates placement of a temporary vascular access for hemodialysis (HD). Precautions such as avoidance of cephalic vein intravenous lines, subclavian catheter placement, and salvaging of nondominant arm vessels should be taken to preserve these vessels for future vascular access.1

Peritoneal dialysis (PD) and hemodialysis (HD) have both become standard maintenance treatments for children with end-stage renal disease (ESRD). Either modality provides effective treatment for children with ESRD, although each modality may have advantages for certain pediatric subpopulations.

PERITONEAL DIALYSIS

Peritoneal dialysis (PD) is preferred for smaller patients because it is provided without an extra-corporeal blood circuit. The advantages of PD include relatively stable serum biochemistries and blood pressure and fewer restrictions on dietary and fluid intake because dialysis is performed daily; simplicity of the procedure permits dialysis to be done at home, thus allowing greater flexibility of the dialysis regimen, infrequent interruptions of the school schedule, and decreased reliance on the dialysis center. Thus, PD is most suited for infants and young children, patients with severe cardiovascular disease or with vascular access difficulties, and those who live far from the dialysis center.

 CONTRAINDICATIONS

Absolute contraindications for peritoneal dialysis (PD) include peritoneal membrane failure, presence of extensive abdominal adhesions that obstruct dialysate flow, surgically uncorrectable mechanical defects that prevent effective PD or increase the risk of infection (omphalocele, gastroschisis, diaphragmatic hernia, bladder extrophy), and inability to identify a person (usually a parent) who can be trained for PD if the patient is incapable of performing PD. Relative contraindications for PD include newly placed abdominal foreign bodies (ventriculoperitoneal shunt), peritoneal leaks, body size limitations, inability to tolerate exchange volumes required to achieve adequate clearance or fluid removal, inflammatory or ischemic bowel disease, morbid obesity, and severe malnutrition. In addition, the parental and familial stress incurred from providing in-home life-saving medical treatment can lead to stress.2,3 Thus, adequate support systems must be established so that home-based dialysis care can be provided without compromising the family integrity.

 DIALYSIS ADMINISTRATION

Peritoneal dialysis (PD) is a process that facilitates transport of solutes and fluid between the capillary blood and the dialysate fluid through the peritoneal membrane, which lines the inner surface of the abdominal wall and reflects over the visceral organs. The procedure requires repeated instillation and drainage of dialysate solution into the abdominal cavity through a PD catheter surgically placed through the abdominal wall. Continuous dialysis can be delivered manually (via continuous ambulatory peritoneal dialysis [CAPD]) or through an automated cycler machine (via continuous cycling peritoneal dialysis [CCPD] or automated peritoneal dialysis [APD]), although the majority of patients in the United States prefer APD. In CAPD, the patient or the parent connects a bag of dialysate solution to the PD catheter, and the dialysate solution is instilled into the peritoneal cavity using exchange volumes that range between 900 and 1100 mL/m2 or 35 to 45 mL/kg. After 4 to 6 hours, the dialysate is drained into the same bag, which is disinfected, and a new bag is attached. Three or four such exchanges are done during the day, and an additional 6- to 8-hour exchange is carried out at night. The CCPD/APD technique is performed using a machine. It generally involves 5 to 10 short-dwell exchanges over 10 to 12 hours at night and may include a long exchange during the day.

PD removes nitrogenous waste products such as urea and creatinine through the process of diffusion, whereby solutes move from a greater concentration to a lesser concentration (eg, from the blood compartment to the dialysate compartment) across the peritoneal membrane. Convection or solvent drag also contributes to solute transfer. High glucose concentrations (1.5–4.25%) in the dialysis fluid solution create an osmotic gradient that facilitates net movement of water into the peritoneal cavity (ultrafiltration). Additional fluid is absorbed by the subdiaphragmatic lymphatic system, however, so that the net fluid removal is the difference between ultrafiltration and lymphatic drainage. The dialysis fluid glucose concentration is adjusted to achieve the desired amount of ultrafiltration. Dialysate solutions also contain electrolytes in physiologic concentrations to correct acid-base and electrolyte abnormalities, except potassium or phosphorous to facilitate their removal during dialysis. The buffer present in most commercially available peritoneal dialy-sate solutions is lactate (40 mEq/L), which is rapidly converted to bicarbonate in patients with normal liver function.

 COMPLICATIONS

The main complications of peritoneal dialysis (PD) are peritonitis and catheter-related infections. On average, one peritonitis episode occurs every 1 to 1.5 patient-years,4 and more frequently in younger children. Peritonitis is suspected when the patient presents with cloudy peritoneal fluid, abdominal pain, and/or tenderness. Fever is usually a late sign of peritonitis. Patients/parents are trained to obtain dialysate fluid for cell count, Gram stain, and culture before starting intraperitoneal antibiotics. A dialysate white blood cell (WBC) count ≥ 100/μL with at least 50% polymorphonuclear cells is suggestive of peritonitis. Most patients are treated successfully with intraperitoneal antibiotics as outpatients. Patients with severe symptoms or persistently cloudy fluid should be hospitalized to ensure proper intraperitoneal antibiotic treatment. Most infections are caused by gram-positive organisms and, to a lesser extent, by gram-negative organisms.5 Fungal peritonitis occurs infrequently, but is often difficult to eradicate, necessitating PD catheter removal. Other infectious complications of PD include infection at the catheter exit site, which presents as exudate and erythema of the skin, and tunnel infection, which manifests as erythema, tenderness, and swelling of the subcutaneous pathway of the catheter and may be associated with purulent discharge. The most common organisms are Staphylococcus species, followed by gram-negative organisms. Daily topical administration of mupirocin or gentamicin to the PD exit site may reduce the incidence of exit site/tunnel infections as well as peritonitis episodes.6-8 However, resistance to these medications may be of concern. A tunnel infection, however, may require catheter removal, especially when it results in peritonitis.

HEMODIALYSIS

Hemodialysis (HD) is the more common maintenance dialysis modality provided to children in the United States, especially in adolescent patients with end-stage renal disease (ESRD).9 Reasons for choosing HD include shorter treatment time and freedom from dialysis responsibilities, and the main contraindication for HD is failure to maintain vascular access. Although HD can be offered in very young children, it is technically more challenging because of patient size, high rate of vascular access thrombosis or failure, and need for skilled and experienced dialysis personnel. More recent pediatric experience has been reported with more frequent HD (defined as HD provided more the thrice weekly), using varying intensities in-center10 or at home3 with conventional dialysis machines and water treatment systems, or at home using a self-contained dialysis machine with sterile industry-prepared dialysis solutions in bags.11 Patients receiving more frequent HD demonstrate improved blood pressure profiles, growth, and nutrition parameters with fewer medications requirements and dietary restrictions.

 DIALYSIS ADMINISTRATION

Hemodialysis (HD) is a process whereby excess fluid and toxins are removed by the extracorpo-real circulation of blood through a dialyzer. Blood is pumped from the patient to the dialyzer and then returned back to the patient via a central catheter or arteriovenous (AV) fistula. Diffusion occurs through a semipermeable membrane that separates the blood and the dialysate fluid. Because the direction of blood flow is opposite to that of the dialysate flow (counter-current flow), the concentration gradient between the two compartments is maintained. The pressure gradient across the membrane (transmembrane pressure) and the ultrafiltration coefficient (permeability of membrane to water) of the membrane regulate fluid removal from the blood to the dialysate compartment (ultrafiltration). As in peritoneal dialysis (PD), the dialysate solution used in HD contains electrolytes in physiologic concentrations to normalize the acid-base and electrolyte abnormalities. Dialy-sate sodium concentration is usually 140 mEq/L to prevent hypotension and cramps from rapid fluid removal. Dialysate potassium concentration is adjusted based on the serum potassium level. Bicarbonate (35 mEq/L) is the major buffer, which avoids blood pressure instability associated with acetate use. Similar to PD, HD solutions contain calcium (2.0–2.5 mEq/L) to avoid negative calcium balance. HD is required three to four times a week in most patients, with each procedure lasting 3 to 4 hours and preferably performed in a facility with experience caring for children and adolescents.

Hemodialysis (HD) requires vascular access that allows sufficient blood flow to support the extracorporeal circuit. Creation of an AV fistula between the radial artery and cephalic vein (Brescia-Cimino) has been standard practice in adult HD patients because of longer patency rate and lower rates of thrombosis and infection.12 In pediatric patients, however, this technique should be reserved for patients > 20 kg in size who are not expected to receive a kidney transplant within a year.1 Ideally, placement of an AV fistula should be done a few months before the expected need for dialysis to allow maturation of the fistula and to avoid placement of a temporary HD catheter. In younger children, other options include placement of either an AV graft using synthetic material (polytetrafluoroethylene) or cuffed dual-lumen permanent catheter. Catheters should be placed in the internal jugular vein rather than in the subclavian vein, if possible, because of attendant risk of subclavian vein stenosis and/or thrombosis.

 COMPLICATIONS

Access malfunction and infection are major complications of hemodialysis (HD). Long maturation time and primary failure are problems associated with arteriovenous (AV) fistula placement in children. Stenosis at the venous anastomosis site can be detected with noninvasive ultrasound dilution flow methods,13,14 and can be treated with angioplasty or surgical correction. Thrombosis of the HD catheter may be treated initially with intraluminal administration of thrombin plasminogen activator, but persistent dysfunction may require catheter stripping or replacement. Local infections are treated initially with antibiotics against gram-positive and gram-negative organisms, and the antibiotics are adjusted based on culture results. More extensive infection of the AV graft may require resection of the infected portion of the graft. Persistent bacteremia may require catheter removal. Other access complications include AV fistula aneurysm and arterial steal syndrome.

The other complications of HD are associated with the rapid rate of fluid and solute removal. Ultrafiltration of large volumes of fluid over a short period increases the likelihood of hypotension, especially in patients with poor cardiac function. More recent data demonstrate the utility of noninvasive monitoring of hematocrit changes to help guide ultrafiltration and decrease intradialytic hypovolemic signs and symptoms, improve blood pressure profiles and decrease the need for antihypertensive medications.15,16 Rapid solute shifts potentially precipitate cerebral edema and dialysis dysequilibrium, which is characterized by headache, nausea, vomiting, or even seizures and coma, and can be prevented by avoiding rapid solute removal and by administration of mannitol, particularly during the first few dialysis sessions, in patients with markedly elevated blood urea nitrogen (BUN) levels.