Principles of PD

PD utilizes similar principles as hemodialysis in that blood is exposed to a semipermeable membrane against which a physiologic solution is placed. In the case of PD, however, the semipermeable membrane is the peritoneal membrane, and a sterile dialysate is instilled into the peritoneal cavity. The peritoneal membrane is composed of a continuous single layer of mesothelial cells that covers the abdominal and pelvic walls on one side of the peritoneal cavity, and the visceral organs, including the GI tract, liver, spleen, and diaphragm on the other side. The mesothelial cells are covered by microvilli that increase the surface area of the peritoneal membrane to approximate body surface area (1-2 m2). Blood vessels that supply the abdominal organs, muscle, and mesentery serve as the blood component of the system.

The gaps between the mesothelial cells allow for large solutes to pass through into the bloodstream. Both the interstitium and endothelial cells of the blood vessels provide resistance to limit the solute size that is removed from the blood. Diffusion is the most important component of solute transport in PD, which is enhanced by the large surface area and volume of dialysate, as well as contact time with the peritoneal membrane. Ultrafiltration is achieved in PD by creating an osmotic pressure gradient between the dialysate and the blood. Traditionally, glucose has been used to create the osmotic gradient, but the solutions are not biocompatible with the peritoneal membrane, resulting in cytotoxicity of the cells. More recently, polymeric glucose derivatives, such as icodextrin, have been used to create a colloid-driven osmosis that results in ultrafiltration and convection of solute removal.

In PD, prewarmed dialysate is instilled into the peritoneal cavity where it "dwells" for a specified length of time (usually one to several hours, depending on the type of PD) to adequately clear metabolic waste products and excess fluids and electrolytes. At the end of the dwell time, the dialysate is drained and replaced with fresh dialysate. The continuous nature of PD provides for a more physiologic removal of waste products from the bloodstream, which mimics endogenous kidney function by decreasing the fluctuations seen in serum concentrations of the waste products. Sim ilarly, water is removed at a more constant rate, lessening the fluctuations in intravascular fluid balance and providing for more hemodynamic stability.

There are several types of PD that are used: Table 26-10 Management of Hemodialysis Access Infections lniii.il Jiiiihk/k dx^Ct ■JiiiLiltd.ilw.v* fiws injilYpGiilrvL' ui,H>iTi1.rniii:'.L|., u'i IK only Lin-

20 mgVkg I1/ with serum concentration monitonng or oefazolin JO mg/kg IV 3 x pe^ week) Grim-neQSHive fflWiJi 6 ¡ntfcciir<xJ ivirh di^Uit^ HIV infi^i [inn, prophetic valwvof Lhoit'receiving lirt*kir*Hupp(ieS5^4(^[4(jJMairicln 2 mg/ltg Wrtlli -t^rnm

Li«:ii intetiori Enx^* Mitibtirtc ((weiigefof oiirttossi^. an<J Entewoaut bo.

gentamicm plus vancomycin Ihen individualize aft« culture results become available);

Infii'i(jii knaliMd 14 l'JIhiU'i exit jit? Nn ttfainaQpr capital .iiiMiiurk"'. ft'*;, mmptcvin □irampnt)

Dijirliyr pflKint; GfJiTi pO^itiwC iCvtri^ (fjyu teiJioliri 20 my/ty IV 3 k pjtf wtrk)

Bacteremia with or without sys1emk: Gram positive coverage as above iyns.0« symutornn If Msble jrd MyiKplomaHc. change catheter and provide cuhwe-spedfk: inttHotk oovcuge

• Continuous ambulatory peritoneal dialysis (CAPD) is the most common. The patient exchanges 1 to 3 L of dialysate every 4 to 6 hours throughout the day with a longer dwell time overnight.

• Automated peritoneal dialysis (APD) procedures involve the use of a cycler machine that performs sequential exchanges overnight while the patient is sleeping.

• Continuous cycling PD (CCPD) performs three to five exchanges throughout the night. The final exchange remains in the peritoneal cavity to dwell for the duration of the day.

• Nightly intermittent PD (NIPD) performs six to eight exchanges throughout the night. The final exchange of dialysate is drained in the morning and the peritoneal cavity remains empty throughout the day.

• Nocturnal tidal PD (NTPD) is similar to NIPD, with the exception that only a portion of the dialysate is exchanged throughout the night. The final exchange is drained in the morning and the peritoneal cavity remains empty throughout the day.

Peritoneal Access

Access to the peritoneal cavity requires placement of an indwelling catheter with the distal end of the catheter resting in the peritoneal cavity. The central portion of the catheter is generally tunneled under the abdominal wall and subcutaneous tissue where it is held in place by cuffs that provide stability and mechanical support to the catheter. The proximal portion of the catheter exits the abdomen near the umbilicus (Fig. 26-8). There are several types of indwelling catheters available; the most common is the Tenckhoff catheter. Placement and handling of the catheter during PD exchanges requires a sterile environment to minimize the risk of infectious complications.

Risks Due Peritoneal Dialysis

FIGURE 26-8. Diagram of the placement of a peritoneal dialysis catheter through the abdominal wall into the peritoneal cavity. (From Foote EF, Manley HJ. Hemodialysis and peritoneal dialysis. In: DiPiro JT, Talbert RL, Yee GC, et al., eds. Pharmacotherapy: A Pathophysiologic Approach, 7th ed. New York: McGraw-Hill, 2008: Q110, with permission.)

FIGURE 26-8. Diagram of the placement of a peritoneal dialysis catheter through the abdominal wall into the peritoneal cavity. (From Foote EF, Manley HJ. Hemodialysis and peritoneal dialysis. In: DiPiro JT, Talbert RL, Yee GC, et al., eds. Pharmacotherapy: A Pathophysiologic Approach, 7th ed. New York: McGraw-Hill, 2008: Q110, with permission.)

Complications of Peritoneal Dialysis

Complications associated with PD include mechanical problems related to the PD catheter, metabolic problems associated with the components of the dialysate fluid, damage to the peritoneal membrane, and infections (Table 26-11). Strategies to manage infectious complications of PD are discussed below.

Peritonitis

Peritonitis is a leading cause of morbidity in PD patients, which often leads to loss of the catheter and subsequent change to HD as the treatment modality. However, recent advances with connectors used during instillation and drainage of dialysate and delivery systems have dramatically decreased the incidence of peritonitis. Peritonitis can be caused by chemical irritation or microorganisms.

Pathophysiology. Gram-positive organisms, namely S. epider-midis, are the most common cause of peritonitis. Other pathologic organisms include S. aureus, strepto-

coccal species, enterococcus species, Gram-negative organisms including Escherichia coli and Pseudomonas species, and fungal organisms. Peritonitis should be presumed if cloudy fluid is drained from the peritoneal cavity and the fluid should be evaluated by cultures. Antibiotic treatment should be initiated immediately, until cell counts and

cultures prove otherwise. Patients with peritonitis may also complain of abdominal pain, although pain may be absent in some cases.

Treatment. The International Society of Peritoneal Dialysis (ISPD) revised the recommendations for the treatment of PD-related infections in 2005 7 Drug selection for empiric treatment of peritonitis should cover both Gram-positive and Gram-negative organisms specific to the dialysis center and be based on the protocols and sensitivity patterns of organisms known to cause peritonitis, as well as the history of infections in the patient. First-generation cephalosporins, such as cefazolin, or vancomycin are recommended for empiric coverage of Gram-positive organisms. Appropriate coverage for Gram-negative organisms includes third- or fourth-generation cephalosporins, such as ceftazidime or cefepime, or aminoglycosides. Alternatives for Gram-negative coverage include oral fluoroquinolones. An example of an appropriate empiric treatment for peritonitis includes cefazolin in combination with ceftazidime, cefepime, or an aminoglycoside. If the patient has a cephalosporin allergy, vancomycin in combination with an aminoglycoside is an alternative empiric treatment.70

Table 26-11 Common Complications During Peritoneal Dialysis

Lose Weight Today With Yoga

Lose Weight Today With Yoga

Want to lose weight but don't know where to start? Transform Your Life With The Knowledge Of The Yogi's And Begin Losing Weight Today. This guide is one of the most valuable resources you can have when learning about yoga to lose weight.

Get My Free Ebook


Post a comment