| Abstract|| |
Soon after its introduction, continuous ambulatory peritoneal dialysis (CAPD) became the choice mode of dialysis treatment for small children. With the advent of automated machines, continuous cycling peritoneal dialysis (CCPD) is now finding more favor in many centers. Initial cost of CCPD is higher due to the need for automated machines, but puts much less strain on the family. However, there is evidence that biochemical control is better with CAPD. Growth and nutrition in both groups are found to be similar. CCPD may have advantages over CAPD with regard to infection, since the former has fewer disconnections. The same is also true with regard to hernias and leaks. Some patients still prefer CAPD, since it allows more freedom in life style compared to CCPD.
Keywords: CAPD, CCPD, NIPD.
|How to cite this article:|
Balfe J W. Comparison of CAPD and CCPD in Children and their Limitations. Saudi J Kidney Dis Transpl 1994;5:173-8
Continuous ambulatory peritoneal dialysis (CAPD) was introduced in 1977 by Popovitch and Moncrief  . Soon thereafter, Oreopoulos demonstrated it could be applied practically with fewer episodes of peritonitis using plastic dialysis bags  . The technique was quickly incorporated into the management of children with end-stage renal disease (ESRD), and has continued to gain in popularity. Because maintenance of vascular access is a problem in children on haemodialysis, the advent of CAPD was most opportune. Because of its simplicity, it proved to be the dialytic mode of choice for small children.
Over the past five years, automated peritoneal dialysis has gained in popularity, Continuous cycling peritoneal dialysis (CCPD) has become the favored mode of peritoneal dialysis for children in many centers. It appears that the burden of CCPD is less than that of CAPD, and since there is no proven therapeutic advantage of CAPD over CCPD, many centers prefer the latter. The usual schedule for older children is to have five two-hour exchanges per evening, With one long diurnal exchange, using either a full or one-half exchange volume, depending on the tolerance of the patient. For younger patients, and especially those who are anephric, frequently it is necessary to prescribe more nocturnal exchanges (5 to 12 exchanges) to provide enough fluid removal so that adequate nutrition can be provided. In many centers CCPD has been modified in that the peritoneal cavity is left empty during the day, more accurately described as nighttime intermittent peritoneal dialysis (NIPD). Some patients do not tolerate the diurnal exchange, complaining of anorexia and/or vomiting. This is more often observed in smaller children. Some adolescents, especially females, are not happy with the cosmetic side-effects of the diurnal dwell, even when the volume is reduced. Therefore, for those patients on NIPD, more exchanges are prescribed during the night-time session. With the shortening of the dwell-time, there is less solute clearance. In addition, omission of the diurnal dwell, and reduced dwell-time during NIPD, there will be a reduction in the clearance of middle molecules with the theoretical biochemical disadvantages  . In the future, there will be modifications to CAPD; however, for this discussion, CCPD will include NIPD.
| Indications for CAPD versus CCPD|| |
CCPD is the preferred chronic peritoneal dialysis therapy for small children. The child lives a more scheduled life, and is in bed for a prolonged period. In addition, there is less work for the parent to maintain their child on CCPD. However for some adolescents, in spite of the reduced burden of CCPD, they prefer CAPD because it is less restrictive to their busy life schedule. Many young children have serious nutritional problems, and consequently are prescribed tube-feeding. The feedings can be delivered conveniently during the night while the child is being dialyzed. The cost of CCPD is also a consideration. The automated cycler is expensive, however if it reduces the number of costly complications such as infection, then the extra cost may not be a disincentive to its use. The intraabdominal pressure produced by the volume of dialysate is reduced when the patient is supine. Therefore, CCPD would be preferred for patients who are at risk to develop abdominal or inguinal hernias.
| Biochemical Control|| |
Alliapoulos et al  compared ten children on CAPD with 10 children on CCPD. There was no statistical difference in the serum creatinine, urea, or phosphates when comparing the two groups, although there was a trend to higher values for CCPD patients. In a larger series reported by the Southwest Pediatric Nephrology Study Group (SPNSG)  they noted statistically significant higher serum creatinine in the patients treated with CCPD compared to the CAPD patients. It would seem apparent that CAPD and CCPD should provide similar clearance of urea and creatinine, provided they received the same amount of dialysis. The concern is that the removal of creatinine and urea is flow or volume dependent, and therefore changes in CCPD which reduce the exchange volume or dwell-time produce less solute removal.
Fluid removal is an important component of chronic peritoneal dialysis. In the anephric patient, one is totally dependent on peritoneal dialysis for fluid removal. This is achieved by prescribing extra exchanges, or using a higher dextrose concentration in the peritoneal dialysis fluid. Fortunately, it is relatively easy using CCPD to alter the peritoneal dialysis schedule without imposing a difficult burden on the parent(s). In addition, it is possible to avoid the stronger peritoneal dialysis solutions.
| Growth and Nutrition|| |
It is difficult to assess the growth of children on chronic peritoneal dialysis (CPD). Frequently they are on CPD for short periods before receiving a renal transplant, and since meaningful assessment of growth requires 6 months of observation, many children are not assessable. The SPNSG evaluated growth in 34 patients receiving CAPD, and in 19 receiving CCPD, who had been treated for 6 months  . There was no difference in the growth for each group, and growth was considered acceptable for both groups. The standard deviation scores for height among these patients were -2.7+1.8 and -2.5+1.3 for CAPD and CCPD, respectively. There was no growth acceleration in either group. Prospective trials using growth hormone for such children are currently being conducted. Such studies are encouraging, however, effectiveness over the long-term needs to be established using prospective trials.
We have studied amino acid dialysis in children on CAPD and CCPD therapy  . We have noted that many children on chronic peritoneal dialysis have a low serum albumin level  . Approximately 80% of the amino acid delivered in the peritoneal dialysis fluid is absorbed. We observed no deleterious side-effects from amino acid dialysis, other than an elevated plasma urea concentration and a mild increase in the serum potassium level. However, it was not possible to definitely demonstrate improved nutrition in these children.
| Infection|| |
Peritonitis continues to be a serious problem for chronic peritoneal dialysis. When our program started in 1978, the incidence was one episode of peritonitis for every 13.6 months on CAPD. This rate has been maintained static through the intervening years. Now, with the popularity of CCPD in pediatrics, we can hope for reduced peritonitis rates, in view that CCPD requires fewer disconnections. It is difficult to compare CAPD to CCPD peritonitis rates in our patients since the CAPD numbers are decreasing, while CCPD numbers are increasing. However, there is an impression that the peritonitis rate on CCPD will be lower. Our results in 1991 had an overall rate of one episode of peritonitis per 29 treatment months, with CAPD having one episode in 15 and CCPD having one episode in 49 treatment months. Our most recent results are shown in the [Figure 1].
A number of pediatric centers have compared CAPD versus CCPD peritonitis rates, and were not able to show a difference ,,, . Diaz-Buxo has reported reduced peritonitis rates on adult CCPD patients  . Reassessment of CCPD peritonitis rates in a few years will be important and naturally, will include newer techniques such as "flush before fill" on CCPD, and the effect of a dry daytime period.
It is becoming increasingly apparent that exit-site infections (ESI) can have serious consequences. It is felt by many that ESIs are the major problem of CPD. Not only may they lead to a tunnel infection and consequent catheter loss, but they also can result in peritonitis. The pathogenesis of ESI is uncertain, but many factors have been proposed, such as mechanical irritation, hypersensitivity to silicone rubber, excessive sweating, and reduced tissue reactivity  . Infections may present from slight erythema around the catheter to purulent ulcerated skin erosion.
We reported our experience with fifty children on CAPD/CCPD  . There were 157 episodes of ESI during 950 patient months of dialysis, giving an incidence of one episode every six months. Of the 132 episodes where the ESI is described, 39 were purulent, whereas 71 were non-purulent. Staphylococcus aureus was the most common organism (46.2%) in both the purulent and non-purulent groups. Pseudomonas aeruginosa was less frequent (10.6%), yet the most common gram-negative organism in both groups. Predisposing risk factors such as gastrostomy-tube exit-sites, diapers, and pyelostomies were assessed and did not favor exit-site infections. Exit-site infections in diapered infants, surprisingly, were more commonly secondary to gram-positive infections, rather than fecal organisms. Of 132 episodes of ESI, 38 (28.7%) in patients were complicated by peritonitis. Of the 28 patients, 13 had the catheter removed because of recurrent or Pseudomonas peritonitis. Unfortunately, the incidence of ESI did not differ before and after catheter removal.
Thus, careful diligence to maintaining a clean exit-site is important. We were not able to demonstrate a difference in the rate of exit-site infections in CAPD versus CCPD patients. Fortunately, we have rarely observed tunnel infections in our patients.
| Hernias/Leaks|| |
Abdominal wall hernias are a frequent complication of CPD. The incidence in the pediatric population ranges from 22% to 40% , . In both groups they were children who had multiple hernias. Khoury  reported 28 hernias in 18 children, and Von-Lilien  reported 60 hernias in 37 children.
Filling the peritoneal cavity with peritoneal dialysis solution with the resultant increased intra-abdominal pressure, would be the usual cause of herniation. The processus vaginalis is patent in 90% of newborns, and declines to 15% patency in adult men  . The increased incidence of indirect inguinal hernias in CPD patients is 100 times higher than in the general population. The increased intra-abdominal pressure associated with peritoneal dialysis has the potential of converting an asymptomatic patent processus vaginalis into a clinically significant hernia. It appears that the hernia is likely to occur early in the course of CPD therapy, and seems to be more common in the younger age group. One would speculate that poor nutrition and previous use of corticosteroid would increase the incidence of hernia.
In Khoury's series  inguinal hernias were most commonly observed. There were 18 inguinal hernias (64% of the total number) occurring in 12 patients, 11 of whom were males. The average age of these boys was 5.2 years, and four were less than two years of age. Three of the six boys who had bilateral hernias were less than two years of age. Von-Lilien et al  reported that 36 of their 60 hernias (60%) were ventral, and 75% were surgically repaired. They observed only one incarcerated hernia and Khoury also observed only one incarcerated hernia, this being associated with an umbilical hernia.
Alliapoulos did show a trend towards reduction in the number of hernias and peritoneal leaks in patients treated with CCPD compared to CAPD  . We are not able to make such a comparison, however, we do favor CCPD for patients who are at risk for hernias or a peritoneal leak, because it provides reduced intra-abdominal pressure since the patient is dialyzed in the supine position. In addition, one is able to prescribe a small exchange volume, with gradual, incremental volumes, e.g., 10 to 20 ml per exchange.
| Leaks|| |
Dialysate can leak from the peritoneal cavity into various tissue planes, most often in the subcutaneous tissue around a previous surgical incision or into the genital area. Subcutaneous leaks usually begin as a dissection of very small amounts of dialysate into a tissue plane that begins at the site of an old or recent surgical incision, often after an episode of coughing or vomiting. The subcutaneous fluid collection enlarges as a consequence of the osmotic pressure of the hypertonic dialysate. Conservative management, such as converting a CAPD patient to CCPD, or temporary suspension of peritoneal dialysis, is frequently sufficient to allow these leaks to resolve.
A leak into the genital area can be difficult to distinguish from an inguinal hernia. Both CT scan  and scintillography  have been used for this purpose. Most of these patients can be managed conservatively by reducing exchange volume, prescribing bed rest, or switching from CAPD to CCPD with lower exchange volumes. If a processus vaginalis is present, it may require ligation to prevent recurrence of a genital leak.
| Prune-Belly Syndrome|| |
We reported our experience with seven boys with the Prune-Belly syndrome who required CPD  . Since these children lack abdominal musculature, there is concern about the feasibility of creating a water-tight peritoneal dialysis catheter. Although catheter leakage and tunnel infections can occur, we have demonstrated that CPD can be offered to these children. It is our impression that percutaneous insertion of the peritoneal dialysis catheter, using the peel-away quill catheter (Y.Tec®, Medigroup Inc., USA), permits a tighter entrance port to the peritoneal cavity, and thus a reduced tendency to leakage.
Pectus excavatum and small lungs are frequently associated with this syndrome. Over-distention of the peritoneal cavity with peritoneal dialysis solution could cause respiratory embarrassment. We have found that they tolerate the usual prescribed exchange volumes, and we have avoided over-filling these children, even though their peritoneal cavities can easily accommodate a larger volume. Such patients may find day time activity, such as running, difficult because of the excessive movement of dialysate in their peritoneal cavity. CCPD/NIPD consequently could be prescribed to avert this problem.
| Renal Transplantation|| |
Even though CAPD/CCPD provides good biochemical control, improved blood pressure control, healing of renal osteodystrophy, and in addition, the potential for regular school attendance and with less medical intervention on free time, renal transplantation remains the ultimate goal for renal replacement therapy in children. Initially there was a hesitancy to transplant chronic peritoneal dialysis patients for fear of infection, especially in those who had a previous episode of peritonitis. We encountered no serious complications in transplanting 23 children, managed with CAPD before the transplant  . Their actuarial graph survival rates were not different compared to patients receiving haemodialysis or no dialysis before surgery. There was a 30% (n = 7) incidence of ascites, which was managed by drainage through the peritoneal dialysis catheter. Scharer and Fine reported the results of a multicenter survey on pediatric renal transplant centers and provided suggestions for the management of such patients  . In their survey of 18 centers and 96 CAPD patients, there was an incidence of posttransplant peritonitis of one episode in 6.2 patient months. Leichter et al  had a similar rate of peritonitis.
We continue to encounter few problems directly related to chronic peritoneal dialysis after transplant at our center. Post-transplant peritonitis is rarely observed, and we have never encountered an abdominal abscess. Mild ascites is frequent; however, severe ascites is rare. We manage chronic peritoneal dialysis patients going for transplant as follows: for patients with chronic or a currently purulent exit-site infection, the catheter is removed at the time of transplantation. We rarely have need for post-translant dialysis and furthermore, a central venous line is routinely available for haemodialysis if it is required. For patients whose peritoneal dialysis catheter remains is situ, it is routinely flushed weekly with 10 ml/kg body weight of peritoneal dialysis fluid containing 500 units/L of Heparin. The catheter is preferably removed prior to discharge from hospital. For patients whose graft function is tenuous, and thus the possibility of returning to peritoneal dialysis, we continue to flush the catheter weekly as an out-patient. The catheter is not flushed after discharge from hospital for patients with good graft function. If the catheter is not flushed frequently, we fear biofilm will accumulate and a catheter flush could dislodge biofilm into the peritoneal cavity and cause peritonitis. Such catheters should be removed as soon as convenient, but preferably not longer than 90 days from the day of transplant.
| Conclusions|| |
CAPD/CCPD has now become the preferred mode of dialytic treatment at many pediatric centers. CCPD continues to gain in popularity over CAPD, at least in the treatment of children on chronic peritoneal dialysis. The burden of CCPD/NIPD is much less on the family, especially those who are caring for small children. Naturally, the cost of CCPD versus CAPD is a consideration. Both CAPD and CCPD have limitations, and the ultimate, and at present our best treatment, is a successful renal transplant. Nonetheless, while waiting and preparing the child for renal transplant, we must strive to reduce the limitations of CAPD/CCPD. Infection rates need to be reduced with improved catheter technology, and linear growth needs to be accelerated by better peritoneal dialysis solutions, improved efficiency of dialysis, better nutrition, and possibly, hormonal modulation. The true goal is the prevention of ESRD in children, but until then, we must improve renal replacement therapy.
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J Williamson Balfe
Professor of Pediatrics, University of Toronto, Clinical Director, Division of Nephrology, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, M5G 1X8