Apd

Peritoneal dialysis has been used as an intermittent form of clinic-bound treatment since the 1960s and was largely replaced at the end of the 1970s by continuous outpatient peritoneal dialysis at home (Geberth 2011).

Descriptions of the first cycler - a device required for APD (Keller 2010) - can be found in the early 1960s by Fred Boen et al. The first automatic cycler described in 1966 by Norman Lasker et al. was the forerunner of today's automated peritoneal dialysis (Gokal 2000).

Automated peritoneal dialysis (APD) is one of the machine-assisted procedures of peritoneal dialysis (PD). It is a generic term for all types of peritoneal dialysis performed with a cycler. The cycler serves to automate the filling and emptying process (Hörl 2004).

With APD, higher volumes of dialysate are used than with CAPD (Continuous Ambulatory Peritoneal Dialysis) and the dialysis time is shorter. However, since higher molecular weight parts cannot be completely eliminated with the short retention time, an additional dialysate filling/d with a long retention time is usually required.

The precursor of APD is intermittent peritoneal dialysis (IPD). (Geberth 2011)

ODA procedures include (Hörl 2004):

• Intermittent peritoneal dialysis in a centre (IPD). IPD is one of the oldest forms of APD. It takes place in special centres 2 - 4 times a week. The peritoneal cavity remains empty between treatments (Hörl 2004).
• Night-time intermittent PD (NIPD). NIPD is performed by the patient himself or by an assistant in a home environment. The dialysate is changed at night by the cycler, as is the complete emptying of the abdominal cavity in the morning (Geberth 2011). Advantages of NIPD for the patient are unrestricted mobility during the day, hardly any cosmetic impairments and the possibility of continuing to work and travel (Herold 2020).

• Continuous cyclical peritoneal dialysis (CCPD). CCPD is also performed at home by the patient himself or by an assistant. The dialysate is changed at night by the cycler, but the last morning filling remains in the abdomen during the day, so that the abdominal cavity is constantly filled with dialysate. (Geberth 2011).

A distinction is made between two forms of cycler therapy:

• 1st standard APD: At the end of the dialysis cycle, the entire dialysate (both the filling volume and the ultrafiltrate) is removed from the peritoneal cavity. The peritoneum only comes into contact with the dialysate to a small extent (during inflow and outflow) (Jiang 2012).

• Tidal peritoneal dialysis (TPD): Tidal peritoneal dialysis can be performed in all three of the above procedures (Jiang 2012). It is preferred for patients with dialysate outflow problems (Vychytil 2005) and when high flow rates of > 5l / h are required (Kuhlmann 2015). In TPD, the dialysate is only partially removed by the cycler after the first filling of the peritoneal cavity. Only the so-called tidal volume is emptied, which usually makes up between 50 % and 80 % of the filling volume. The remaining 20 % - 50 % remain in the abdominal cavity during the entire cycler treatment. During the next cycle, only the missing volume is refilled. Thus, part of the filling volume is in contact with the peritoneum during the entire treatment period. At the end of the treatment, the entire abdominal cavity is also emptied (Jiang 2012).

In Germany, peritoneal dialysis is used for about 6 % of patients requiring dialysis (Kasper 2015), worldwide for about 10 % (Herold 2020).

However, the proportion of APD treatments has increased in industrialized countries compared to continuous peritoneal dialysis (Moor 2018).

In recent years, the concept of "integrated care" has been developed to reduce mortality among dialysed patients, and this has been confirmed in studies. This concept initially involves peritoneal dialysis and then switches to HD (haemodialysis) (Herold 2020).

In APD, the peritoneum is the dialysis membrane.

Through the capillaries of the peritoneum, substances from the blood accumulate in the dialysis solution by diffusion and are eliminated.

Small molecular parts can either diffuse or be transported by convection into the dialysis solution or peritoneal cavity.

Large-molecular parts leave the capillaries by convection. This usually requires a longer residence time of the dialysate (Geberth 2011).

The water, on the other hand, is primarily removed osmotically by the hypertonic dialysis solution (Moor 2018).

Complications of the APD:

• APD- associated peritonitis
  • the contamination can be intraluminal, periluminal (along the catheter [Geberth 2011]) or gastrointestinal
  • These are predominantly gram-positive germs (especially staphylococci)
  • the patients complain of abdominal pain, cloudy dialysate; the dialysate contains a laboratory chemical detection of > 100 leukocytes / µg with > 50 % granulocytes and positive dialysate cultures
  • the therapy consists of broad-spectrum antibiotics with adjustment after receipt of the antibiogram, administration is preferably intraperitoneal, otherwise i. v.
  • the dose of the antibiotic should be adjusted to the residual renal function
  • Therapy duration at least 2 weeks; for S. aureus, enterococci and Gram-negative pathogens at least 3 weeks
  • intraperitoneal heparin should be administered due to the risk of adhesion and catheter obstruction
• exit- side infections
  • this leads to a purulent secretion with or without redness, swelling and crusts
  • the diagnosis is made clinically
  • the systemic antibiosis should be carried out after the smear according to the antibiogram (Kuhlmann 2015)
• Tunnel infections
  • in so-called tunnel infections, infections of the abdominal wall occur in the area of the tissue surrounding the catheter with swelling, redness, pain and purulent secretion (Kuhlmann 2015)
  • the frequency of both exit side infections and tunnel infections varies between 0.1% - 1% episodes / year
  • the diagnosis is made sonographically (low-echo area around the catheter and / or the socket)
  • after a germ smear, antibiotic treatment adapted to the antibiogram
  • the follow-up should also be sonographic (Herold 2020) The application of silver nitrate, which used to be common to prevent tunnel infection, is no longer recommended because silver nitrate attacks the catheter material (Kasper 2015).
• unintentional weight increase due to overwatering
• metabolic disorders
• Hyperkalemia is very rare in peritoneal dialysis, however, because the dialysate solutions are potassium-free (Kasper 2015)

For peritoneal dialysis, a catheter is surgically, laparoscopically or percutaneously implanted into the abdominal cavity approximately 2 weeks before the start of dialysis using the Seldinger technique (Geberth 2011).

Indications for APD:

• Dependence of the patient, e.g. children, adults in need of help or elderly people
• Patient preference
• Continued professional activity of the patient (here the night-time APD is preferred)
• decreasing ultrafiltration (as for example in the case of the high transporter status proven by the peritoneal equilibration test (PET) ) (Kuhlmann 2015)
• Inadequate clearances in continuous ambulatory peritoneal dialysis(CAPD)
• Complications in CAPD due to increased intraperitoneal pressure (Vychytil 2005)
• Patients with infectious diseases such as hepatitis C, HIV etc. (Hepp 2009)

Advantages of an APD:

• the risk of peritonitis is lower with APD than with other forms of peritoneal dialysis
• Improvement of the quality of life, e.g. through social integration, continued possibility to work or attend school
• the dialysis effectiveness is increased
• an increase in ultrafiltrationis also found
• the intra-abdominal pressure is reduced (Fusshoeller 2006)
• the dialysis fluid causes less discomfort (Moor 2018)

Disadvantages of an APD:

• APD causes the residual excretion to diminish more quickly
• a higher apparatus, personnel and logistical effort is required
• cost overrun
• lower peritoneal removal of sodium and phosphate (Moor 2018)
• late detection of peritonitis (Fusshoeller 2006), as higher dialysate volumes and sales lead to a dilution of the leukocytes and thus the cloudiness of the dialysate is less detectable (Geberth 2011)
• higher cardiac load than in CAPD
• Patients sometimes complain of sleep problems during nightly dialysate changes (Moor 2018)

Contraindications of peritoneal dialysis are e.g.:

• existing diseases with an increased risk of peritonitis
• chronic inflammatory bowel disease (CED)
• COPD
• non-curable hernias
• Protein deficiency
• Psychoses (Herold 2020)
• diverticulitis known from medical history
• body weight > 90 kg
• Lack of hygienic behaviour
• Difficulties in material storage (e.g. due to cramped housing conditions)
• Colostoma
• Nephrostoma
• high renal protein loss with malnutrition
• numerous preliminary operations with adhesions
• very large cystic kidneys (Hepp 2009)

Carrying out PD at home: Before bedtime, the patient connects via the PD catheter to the cycler, which carries out multiple dialysate exchanges during the eight-hour night's rest at the pre-programmed run-in and run-out times.
Dialysate exchange of up to 20 l is possible during this time, but the exchange volume is usually only 10 l. (Gebert 2011)

The dialysate itself often consists of glucose containing solutions with a low concentration of glucose degradation products = GDPs (Herold 2020). For APD, pH-neutral dialysate solutions are preferred because they improve acidosis balance and dialysate inlet pain (Vychytil 2005).

The peritoneum is the semi-permeable membrane with an exchange surface of about 1m2. (Herold 2020)

Quality indices of PD treatment: In the case of APD, functional tests should be performed at regular intervals (see below). These include the peritoneal equilibration test and the determination of residual renal function:

1) Peritoneal equillibration test: The peritoneal transport properties should be checked regularly using the so-called combined modified peritoneal equilibration test (PET) . According to the recommendation, the first test should be performed 4 weeks after the start of therapy, then once a year (Herold 2020) and additionally after every case of peritonitis (Kasper 2015). The test is performed with a 3.68 % glucose solution. The ultrafiltration properties of the peritoneum, the sodium sieving and the free water transport are examined. A decrease in sodium sieving and free water transport are currently the best available parameters for early detection of encapsulating peritoneal sclerosis (EPS). A marker for peritoneal fibrosis is the decrease of free water transport (Haag- Weber 2017).

2. determination of residual renal function: In patients with existing urinary excretion, residual renal function should be determined at least every six months (Herold 2020), as this contributes significantly to detoxification and drainage. Since residual renal function correlates inversely with patient mortality, all measures to maintain renal function should be taken. These include:

• Avoidance of higher doses of non-steroidal anti-inflammatory drugs.
• Avoidance of nephrotoxic antibiotics such as cephalosporins, penicillamine, sulfonamides, etc. [Weckmann 2019])
• Avoidance of large doses of contrast medium (Haag- Weber et al. were able to prove in a study that small amounts of contrast medium do not lead to any significant impairment of residual renal function) (Kuhlmann 2015)

Mortality: Peritoneal dialysis (PD) has a lower mortality in the first 2-3 years compared to haemodialysis (HD), but with long-term PD the mortality is higher compared to HD. In order to reduce mortality, the so-called "integrated care" concept has been developed, in which peritoneal dialysis is initially used and later switched to HD (Herold 2020).

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