Diagrammatic representation of continuous ambulatory peritoneal dialysis (CAPD)
Choosing the PD modality takes into consideration both medically optimal adequacy and patient preferences. Patient preferences are considered for patient lifestyle, employment, family or caregiver support, residence circumstance, familiar with cycler technology, and so on. In the past, peritoneal transport status and its effect on fluid removal and solute clearance were considered to be crucial to choose PD modalities such as CAPD and the various types of automated PD (APD). However, recently patient preferences have been emphasized to decide PD modality.
Daytime ambulatory peritoneal dialysis (DAPD) is a modified method of CAPD in which patients carry out two to four exchanges during the daytime with dwell time of 3–4 h and an empty abdomen at night. DAPD is helpful of improving the quality of sleep and recovering peritoneal cells due to a dry abdomen overnight. However, this modality should be applied to patient with significant residual renal function who has high (or fast)-membrane transporters which reabsorb significant amounts of fluid with the long overnight dwell of CAPD.
12.2 Types of Automated PD
Automated peritoneal dialysis (APD) is referred to as all forms of PD that apply an automated device to perform in the instillation and drainage of the dialysis solution. Mechanized cyclers are used in continuous cyclic peritoneal dialysis (CCPD) , nocturnal intermittent peritoneal dialysis (NIPD) , tidal peritoneal dialysis (TPD) , intermittent peritoneal dialysis (IPD) , and continuous -flow peritoneal dialysis (CFPD). In addition, some patients on CAPD may perform one or more overnight exchanges with a night exchange machine. In the previous, APD has been recommended mainly for patient who had high (or fast) peritoneal transporters. However, these days, patient preferences have more emphasis on choosing PD modality, and improved technology of automatic machine, APD , using a cycler, has become very popular across the world over the past 10–15 years. The majority of PD patients especially in wealthier countries are treated with this method. Development of APD machine and newer APD schedules enable individualized treatment prescription and could enhance patient compliance to the prescribed regimens. Automation could handle some of the limitations of manual PD, including ultrafiltration failure, patient treatment fatigue, complications of increased intra-abdominal pressure, and failure to get treatment clearance goals.
The APD have some advantages compared with CAPD. APD had less number of on-off procedures needed each day, especially daytime. All preparation of apparatus and on-off procedures are usually performed in the private home. Therefore, patients feel more comfortable and less inconvenient with APD , which improves patient satisfaction and decreases patient fatigue. APD is a therapy of choice for active patients who would not be interrupted during their daily routine. APD is the modality of choice in children and adolescents, because it allows free daytime without bag exchanges, thereby not interrupting the daytime academic or work schedule of their parents. In addition, APD is also an attractive treatment option for patients who require support to perform their dialysis (e.g., the dependent elderly, healthcare residents, patient with visual impairments, and children). APD is a practical modality option for patients with increased intra-abdominal pressure complications (back pain , dialysate leaks, hernias, hemorrhoids, and uterine prolapse) (Negoi and Nolph 2006). The disadvantages of APD relative to CAPD are the need for an automated machine, the higher cost, and the complexity to deal with a cycler. Some patients may not tolerate the dependence on a machine or the prolonged confinement to bed overnight. Patients could have sleep disturbances by the cycler alarms. Additionally, sodium sieving and the consequent low sodium in the ultrafiltrate may bring about hypernatremia, poor blood pressure control, and increased thirst (Shen et al. 1978).
APD with the development of automatic machine is ready to deliver a dose range beyond traditional dialysis and to provide individualized composition of PD solution to meet individual requirements by online preparation or teledialysis technique (Ronco et al. 2006).
12.2.1 Continuous Cyclic Peritoneal Dialysis (CCPD)
Continuous cyclic peritoneal dialysis (CCPD) , also known as APD with a day dwell, is a continuous automated PD regimen. CCPD is a reversal type of CAPD where the shorter multiple exchanges are performed overnight, while the longer dwell are provided during the day. APD was introduced in the late 1970s with the purpose of attaining higher fluid and solute removal compared to CAPD (Diaz-Buxo et al. 1981). CCPD provides much flexible regimen and endures larger dwell volume due to decreased intraperitoneal pressure at a supine position. Figure 12.2 shows the diagrammatic feature of CCPD regimen. Typically, overnight dialysis is performed for 8–12 h with each dwell volumes of 1.5–3.0 L and 3–5 automated cycles. The total volume of instilled dialysis solution is 8–12 L. After the last overnight cycle, the automated machine is programmed to deliver a last bag fill (with 1.5–2 L of dialysis solution) for day dwell with hypertonic dialysis solution or non-glucose osmotic agent like icodextrin . Additional daytime exchanges can be performed in addition to typical CCPD (e.g., 2 daytime exchanges (CCPD-2)). These daytime exchanges could be carried out manually or by the cycler. CCPD could be the regimen of choice in patient with high membrane transporter who has ultrafiltration failure, especially without residual kidney function. In addition, this regimen is suitable for the employed workers or school children who have difficulty to perform multiple daytime exchanges. For patients who need assistance to conduct dialysis, CCPD could be better than CAPD . To achieve target clearance, dwell volume , dwell time, and number of exchanges can be manipulated. Detailed prescription methods to meet dialysis adequacy are described in Chap. 4.
Diagrammatic representation of continuous cyclic peritoneal dialysis (CCPD)
12.2.2 Nocturnal Intermittent Peritoneal Dialysis (NIPD)
Nocturnal intermittent peritoneal dialysis (NIPD) , also known as dry-day APD , is an intermittent dialysis regimen performed every night using a cycler (Fig. 12.3) (Twardowski 1990). Typically, dialysis is performed for 8–12 h with each fill volume of 2–2.5 L for average-sized patient. The total volume of dialysis solution used overnight is 8–12 L. To avoid insufficient solute clearance associated with dry abdomen in the daytime, time for each dialysate drainage should be limited to approximately 15 min. Large volume (up to 20 L) and extended dialysis hours (high-dose NIPD) may be needed for anuric patients. NIPD regimen has empty the abdomen during daytime; it is advantageous for patients suffering from various complications due to elevated intra-abdominal pressure. APD with dry day enhances patient daytime activity and decreases glucose absorption, leading to a better appetite. NIPD , a PD method that uses short dwells, is suitable for patients who have high membrane transporter and who have type I ultrafiltration failure. Patient with residual renal function could be initially started on PD with NIPD regimen. However, the “dry-day” NIPD , as compared to continuous PD modality, decreases at least 10–15% of small-solute clearance and almost 50% of middle-solute clearance which is highly time dependent (Gahl and Jorres 2000; Brophy et al. 1999). NIPD have limitations when prescribed for patients with large body surface area and those with low or low-average membrane transporter with no or minimal residual renal function, as dialysis adequacy cannot be fulfilled (Gahl and Jorres 2000). The average cost is higher than CAPD.
Diagrammatic representation of nocturnal intermittent peritoneal dialysis (NIPD)
12.2.3 Intermittent Peritoneal Dialysis (IPD)
Intermittent peritoneal dialysis (IPD) is the first APD modality and a classical PD regimen wherein several short-dwell exchanges are performed intermittently in a hospital or dialysis center. It had been widely used and remained popular until the 1980s when more efficient newer forms of PD such as CAPD and APD were introduced. During classical IPD , the patient generally receives frequent, short-dwell exchanges over 8–10 h per session with a high-dose dialysis volume (20–40 L), three times weekly (Fig. 12.4). The dialysis procedure is carried out manually or with cyclers. IPD has been no longer prevalent modality due to long duration and poor solute clearances. However, IPD could be the suitable option for elderly and multi-morbid dialysis patients who have failed hemodialysis (HD) (e.g., recurrent vascular access problems) or are unable to perform PD on their own and lacking social support at home (Fourtounas et al. 2009; Woywodt et al. 2008). IPD could also be an option for acute rescue PD as bridge therapy before long-term HD or PD and transient therapy for patients who have hernias or recently undergone abdominal surgery (Kleinpeter and Krane 2006; Shah et al. 2006). Lower dwell volume is recommended during postoperative periods. In addition, IPD regimen could be applied for those with congestive heart failure who have difficulty to achieve volume control on maximal medical treatment (Basile et al. 2009; Koch et al. 2012a). Long duration of dialysis needs longer nursing time, larger volume of dialysis fluid, and higher staffing costs. However, funding and insurance reimbursement may not fully cover the cost.
Diagrammatic representation of intermittent peritoneal dialysis (IPD) prescription
12.2.4 Tidal Peritoneal Dialysis (TPD)
Tidal peritoneal dialysis (TPD) is a modality combining intermittent and continuous-flow regimen (Fig. 12.5). The variant of APD was developed to increase solute clearance by maintaining a reserve volume in the abdominal cavity throughout all the cycles. It was considered that this might enable diffusive clearance to be sustained throughout the dialysis period without interruption. The prime purpose of TPD was to improve small-solute clearance by minimizing the interruption of diffusive clearance during the drainage of dialysis solution. Typically, initial volume is filled as large as possible without discomfort. The volume is determined according to patient body size but is usually 2–3 L. After initial volume is instilled, only a portion of solution is drained, leaving the rest of the solution (reserve volume or residual volume) in the peritoneal cavity. Then, the peritoneal cavity is refilled by fresh dialysis solution (tidal volume, usually 50% of initial volume, 50% TPD). For example, if 2 L is initially filled, the next fill volume (tidal volume) is 1 L, the next drain volume is approximately 1 L. TPD may be done with or without a daytime dwell. The ultrafiltration volume must be closely calculated and refilled with each exchange to maintain reserve volume unchanged. If ultrafiltration volumes are underestimated, lower volumes will be drained. Therefore, the reserve volume will gradually increase, potentially resulting in increased intraperitoneal pressure and abdominal discomfort. To reduce overfill risks (Fernando and Finkelstein 2006), the peritoneal cavity can be completely drained before cycling initiation or every third or fourth cycle. On the other hand, if ultrafiltration volumes are overestimated, the residual volume might be decreased. Initially, TPD have been developed to improve dialysis efficiency. However, TPD with usual fluid volumes does not improve solute clearances compared with similar amounts of PD fluid delivered by conventional APD (Perez et al. 2000; Juergensen et al. 2000). Small-molecule (Juergensen et al. 2000; Aasarod et al. 1997) and middle-molecule (Vychytil et al. 1999) clearances, blood pressure regulation (Balaskas et al. 1993), and sodium sieving (Perez et al. 2000) in TPD have found little differences from other APD regimen. Today, the most common indications for TPD are relieving infusion or drain pain and avoiding low-drain cycler alarm, especially with poor catheter function (Blake et al. 2014). Most automated cyclers use hydraulic suction, rather than gravity, to drain the dialysate (Neri et al. 2001). That leads to painful suction on the parietal peritoneum or visceral organs. TPD minimizes the time period with completely empty abdomen, thereby minimizing infusion or drain pain (Juergensen et al. 1999). However, TPD needs higher dialysis volume to improve small-solute clearance , and this is very expensive.
Diagrammatic representation of tidal peritoneal dialysis (TPD) prescription
12.2.5 Adapted APD
Adapted APD is a novel approach to the APD regimen to reach optimal PD prescription for improving solute and fluid removal (Fischbach et al. 2016). Reaching adequacy goals in PD for both clearance and ultrafiltration is challenging. Smaller fill volumes and shorter dwell times enhance the process of ultrafiltration (aquaporin exchange) and while large fill volumes and longer dwell times increase solute clearance (small pore exchange) (Fischbach et al. 2011). Adapted APD promotes ultrafiltration and solute clearance within one PD session. The adapted APD regimen consists of two different sequences of exchanges during one PD session (Fig. 12.6). The first sequence is short-dwell and small fill volume to facilitate ultrafiltration . The next sequence is longer dwell (longer diffusion time) with large fill volume (recruitment of wetted peritoneal membrane) to improve the removal of solute and uremic toxins . Dwell volume and dwell time are determined by the body surface area and the membrane transport characteristics of the patient, respectively (Fischbach et al. 1994; van Biesen et al. 2010). The short-dwell time in adapted APD may be established according to the membrane transporter status or directly evaluated from the crossing time point of the urea (D/P) and glucose (D/D0) curves on the peritoneal equilibrium test, also known as “optimal ultrafiltration dwell time” by accelerated peritoneal examination (APEX) test (Fischbach et al. 1996). The longer dwell time (90–240 min) may be prescribed as 3–4 times the APEX time (30–60 min). The large dwell volume is the highest fill volume endured in the supine position, not to be over an intra-abdominal pressure of 18 cm H2O (>14 cm H2O is associated with increased risk of hernia and leakage) (Durand et al. 1994; Fischbach et al. 2014). Small fill volume is one-half of the large volume. Proper dwell volume not exceeding the upper limit of intra-abdominal pressure should be applied (Fischbach et al. 2014). Further studies on the mechanisms of enhanced clearances and the outcomes of adapted APD are needed.
Diagrammatic representation of adapted APD prescription
12.2.6 Outcomes Between CAPD and APD
The choice of PD modality type is mostly based on peritoneal membrane type and patient preferences. Many investigators have compared these two submodalities—CAPD and APD.
Higher residual renal function is associated with improved solute and volume control and patient survival (Susantitaphong et al. 2012). APD, particularly in patients undergoing NIPD, has been described as an intermittent treatment more similar to HD. CAPD is regarded as more gradual, with performance at a near-constant rate over the 24-h period. Some reports showed that APD was associated with a faster decline in residual renal function (Hufnagel et al. 1999; Hamada et al. 2000; Hidaka and Nakao 2003). However, the majority of studies do not show a definite difference of residual renal function change by PD modality (Moist et al. 2000; Cnossen et al. 2011; Bro et al. 1999). In this considerations, whether APD brings about rapid decline in residual renal function is not convincing.
The number of connections and disconnections between PD catheter and the tubing system is regarded as an important factor of developing PD-associated peritonitis. Since APD required fewer connections and disconnections than CAPD, PD-associated peritonitis rates with APD were lower than with CAPD in the past. However, in connection systems of CAPD, not only APD has been improved dramatically. With the use of contemporary connection systems, there is no significant difference in the risk of PD-associated peritonitis between CAPD and APD (Nessim et al. 2009; Ruger et al. 2011). Further studies comparing the response, severity, and recurrence rates of peritonitis in CAPD versus APD are needed.
There are no significant differences in volume overload or blood pressure control between patients with CAPD and APD (Frankenfield et al. 1999; Van Biesen et al. 2011). Individualized and proper prescription of PD therapy can improve solute and water removal and achieve target clearance. There is no convincing evidence for a difference in the overall survival and technique survival between the two PD modalities (Mehrotra et al. 2009; Badve et al. 2008; Michels et al. 2009). In addition, there is no evidence that patients on APD have a better health-related quality of life (Balasubramanian et al. 2011; Michels et al. 2011). Therefore, there is no persuasive evidence of a significant difference in any clinically relevant outcomes between patients on CAPD and APD (Mehrotra et al. 2009; Bieber et al. 2014). Individualized and differential application of the two PD modalities is likely to continue according to patient preferences, peritoneal membrane type, and lifestyle.
12.3 Hybrid Dialysis (Bimodal Dialysis)
The basic role of dialysis is to maintain the adequacy of solute clearance and ultrafiltration . When patients on PD cannot meet target clearances, especially with decreasing residual renal function, the higher dialysis dose is needed . If increasing the dose by PD alone is limited, combined prescription of PD and HD can be considered. HD and PD have different techniques and advantages. PD enables slow continuous ultrafiltration without rapid hemodynamic changes but less efficient solute removal. On the other hand, HD enables efficient solute removal but rapid ultrafiltration and hemodynamic changes. Historically, both modalities have been considered as mutually exclusive. However, on the basis of the unique characteristics of the two modalities, combination therapy of both modalities simultaneously may be a good option for individual patient. This combination therapy with PD and HD is referred as “hybrid dialysis,” “bimodal dialysis ,” or “complementary dialysis” (McIntyre 2004; Kawanishi and Moriishi 2007). Combined regimen with PD and HD was first introduced in Japan in the 1990s by Watanabe and Kimura [abstract: Watanabe S, Kimura Y et al. Nihon Touseki Igakukai Zasshi. 1993;26(suppl 1):911]; it has been rapidly applied in Japan. In 2013, 20.4% of the patients on PD were receiving combined therapy with PD and HD (Masakane et al. 2015). Usual prescription is the addition of once weekly HD to established 5–6 days of PD prescription (CAPD or CCPD). Any combination of PD with HD schedule could be adjusted with clinical needs and psychosocial issues. Medical indications for hybrid dialysis are as follows: inadequate solute removal resulting in uremic symptoms ; loss of residual renal function resulting in unsatisfied dialysis goal; insufficient ultrafiltration , chronic volume overload, and difficult-to-manage fluid balance; avoiding an increased dialysate volume for preventing pressure-related problems such as hernia and hydrothorax ; peritoneal rest; and cardiovascular instability in HD patients (Kawanishi and Moriishi 2007; Agarwal et al. 2003). Psychosocial factors such as employment, work schedule, patient preferences, and patient or caregiver support also influence the choice of hybrid dialysis. In the previous studies, mostly based on retrospective analysis, hybrid regimen improved solute removal , increased serum albumin and hemoglobin, and improved patient quality of life (Agarwal et al. 2003; Suzuki et al. 2012). In other studies, patients with hybrid dialysis improved volume and blood pressure control with the same or decreased dose of antihypertensive drugs and reduced left ventricular mass index (McIntyre 2004; Tanaka et al. 2011). Other advantages of hybrid dialysis are permitting a “PD holiday” with peritoneal rest (with expectation of reducing glucose exposure and improving peritoneal function and glycemic control), achieving PD prolongation with a minimal change in lifestyle, and increasing flexibility of renal replacement therapy and seamless transition to single modality if access problem develops (Kawanishi and Moriishi 2007). However, the requirement for the formation of dual access is a potential drawback, exposing the patient to the possible complications of both. In addition, total solute clearance goals and methods for evaluating total clearance need to be standardized. Criteria for discontinuation of hybrid therapy (long-term PD therapy may increase the risk of encapsulating peritoneal sclerosis) are needed (Maruyama et al. 2014). Reimbursement issues may be a problem in the majority of cases. Further large, prospective studies are needed.