Continuous ambulatory peritoneal dialysis (CAPD). CAPD was introduced in 1976 by Popovich and Moncrief and later modified by Oreopoulos as a wearable and portable form of dialysis, not requiring any equipment other than the disposable solution bags and a line to connect the bag to the patient's catheter. CAPD was based on the concept of equilibrium dialysis. Briefly stated, when 2 liters of dialysis solution are infused into the peritoneal cavity of an average adult and allowed to dwell for 4 - 6 hours, there is virtual equilibration of the concentration of small solutes between plasma and dialysate (D/P = 1). It was theoretically predicted that an average size anephric patient would maintain a steady-state BUN of approximately 28 mmol/l using CAPD and capable of achieving 10 L of equilibrated effluent. This lead to wide-spread use of the standard CAPD regimen consisting of 4, 2-L exchanges/day. The procedure involves the infusion of the solution (approximately 10 min), a dwell period (3 - 8 hours) and drainage of the dialysate (10 - 20 min).
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Since some patients have a large mass, do not equilibrate in 4 hours or cannot achieve a 2-L ultrafiltration/day with the standard CAPD prescription more frequent exchanges or larger infusion volumes may be used.
The simplicity of CAPD, its low cost and the associated freedom from machines made CAPD a very popular form of chronic PD. In addition, CAPD can maintain a steady physiological state, control fluid volume and blood pressure in most patients and simplify the control of glycemia in many diabetic patients through the use of intraperitoneal insulin.
Continuous cyclic peritoneal dialysis (CCPD). This modality of automated peritoneal dialysis (APD) was introduced in 1981 by Diaz-Buxo and Suki et al. to achieve higher solute and fluid removal than with CAPD and to automate the procedure with a simple cycler while the patient sleeps. The system gained immediate popularity to treat infants and children. During the last decade it has also become the most used modality for the treatment of adults in the United States and selected developed countries. CCPD allows greater flexibility in the number and volume of exchanges during the night without taxing the patients' time. Larger volumes are also better tolerated in the supine position. All connections and preparation of equipment usually takes place at bedtime. Consequently, there is better control of the environment and less patient fatigue. Many reports suggest lower peritonitis rates with CCPD compared to CAPD.
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Intermittent peritoneal dialysis (IPD). IPD was the first modality of APD for chronic use. It remained popular until the 1980's when more effective forms of PD were introduced. IPD generally consists of frequent, short cycles performed over 8 - 10 hours per session, three times weekly. The peritoneal cavity remains drained between sessions. If IPD is practiced on a nightly basis, it is referred to as nocturnal IPD (NIPD). The principal disadvantages of IPD are limited solute removal, especially of larger solutes and high cost due to large volumes of solution. NIPD is mostly reserved for patients with high solute transport and limited ultrafiltration, since the short cycles of NIPD can achieve better ultrafiltration than the longer cycles of CAPD or CCPD.
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PD Plus is basically CCPD with an additional exchange during the day. The breaking of the long diurnal dwell of CCPD improves both clearance and ultrafiltration. The last automated exchange provided by the cycler (last bag option) is the first diurnal cycle of PD Plus. The second diurnal exchange can either be a manual CAPD exchange or be performed by the cycler when used as a "docking station". This exchange is also commonly referred to as a "pause". Another benefit of this modality is that it makes use of lower volume day exchanges to improve patient comfort and larger exchange volumes in the supine position at night.
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In addition, CAPD with a limited number of automated, nocturnal exchanges has been used in order to breakup the long nocturnal dwell. The disadvantage of this modality is that it increases both the cost and complexity of CAPD and also requires that the patient be attached to a device while sleeping.
Tidal peritoneal dialysis (TPD). The procedure of TPD has been defined under tidal technique. The principal purpose of TPD was to enhance clearance of small solutes by reducing the normal loss of dialytic time that is associated with the inflow and drainage of solution of the intermittent technique. Unfortunately, the clinical experiences with TPD have not confirmed any advantage over APD in terms of clearance or ultrafiltration, except perhaps among patients with slow catheter drainage. The main disadvantages of TPD are its increased cost and complexity.
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Continuous flow peritoneal dialysis (CFPD). CFPD is a modality of PD that uses the continuous technique and two separate catheters or a double lumen catheter. It is generally performed with high dialysate flow rates. PD fluid is infused into the peritoneal cavity through an inflow catheter while the outflow catheter is clamped. Once the desired fill volume is achieved, the outflow catheter is opened and the inflow and outflow are maintained relatively constant at high flow rates (150 - 250 ml/min). CFPD requires very large volumes of PD solution. Since it is impractical and economically prohibitive to use dialysis bags, several methods have been employed to solve this problem. Spent dialysate can be regenerated with hemodialysis technology. In other words, spent peritoneal dialysis solution is being "hemodialyzed"; instead of plasma water. Peritoneal dialysate can also be regenerated using a sorbent cartridge. On-line generation of fluid is possible using hemodiafiltration technology or by mixing a concentrate with pure water. The potential advantages of CFPD are its very high clearances and possibly high ultrafiltration. While there has been much interest in CFPD for many years, the requirement of special peritoneal access and large volumes of solution have impeded its clinical application. Furthermore, several recent trials have failed to achieve adequate ultrafiltration.