Peritoneal dialysis (PD) offers several advantages over hemodialysis (HD) at least during the first 2–3 years of treatment. Which one of the following statements regarding PD is FALSE?

PD has been shown to have a better survival than HD during the first 2 years of dialysis treatment. The cost of PD is much less than HD. Also, the rate of infection-related complications has been declining over the last decade in patients on PD than patients on HD. Thus, many nephrologists offer PD as the first choice of renal replacement therapy.

One of your 52-year-old female patients with an eGFR of 12 mL/min comes to your office with complaints of fatigue and poor appetite due to metallic taste in the mouth for the last 2 years. She has no chest pain or hyperkalemia. Her BP is 130/80 mmHg. Her serum [HCO₃ ⁻] is 20 mEq/L. During her previous visit 3 months ago, you discussed about the choice of her future renal replacement therapies, including transplantation. After prolonged discussion, she feels that PD is a reasonable choice in view of her daily work in the school . Based on her clinical history, which one of the following choices is MOST appropriate regarding the management of her symptoms and selection of dialysis modality is CORRECT?

This patient has no either PD catheter or an arteriovenous fistula or graft ; therefore, HD using a CVC or femoral catheter is a default modality for dialysis initiation. This is usually the practice in unplanned mode of treatment for acute dialysis. However, this patient expressed PD as her choice of dialysis. If she agrees to PD, a PD catheter can be placed and acute PD can be started to improve her symptoms. Then she can be trained for CAPD. Thus, choice C is correct. Option A is the usual treatment for patients with no prior follow-up by the nephrologist; however , this patient prefers PD. Moreover, PD catheters have low infection rates than CVCs. A study by Koch et al. showed that initiation of PD within 12-h after PD catheter insertion for unplanned dialysis had a lower rate of infection compared to HD catheters. A study from the USA also showed that PD for unplanned dialysis is safe, efficacious, and feasible alternative to unplanned initiation of HD . Therefore, choice A is incorrect. Other choices are also not appropriate.

A 65-year-old woman with diabetic nephropathy preferred PD, and her granddaughter is trained to do automated peritoneal dialysis (APD) with four exchanges at night without daytime dwell (“dry day”). The patient is brought to the emergency department with complaints of fever and chills. Her admission labs: Na⁺ 130 mEq/L, K⁺ 4.1 mEq/L, HCO₃ ⁻ 17 mEq/L, creatinine 12.6 mg/dL, BUN 72 mg/dL, and glucose 172 mg/dL. Which one of the following factors can maximize PD clearance of a solute?

The solute and fluid clearance occurs by three processes in PD: diffusion, convection, and fluid reabsorption. The best accepted model of peritoneal transport is the three-pore model. In this model, the peritoneal capillary, which is the only barrier to the peritoneal transport, consists of three pores of different sizes. The smallest pores (<0.5 nm) represent aquaporin-1 channels that allow only water to pass through them, and solute transport is inhibited. The following figure shows three-pore model of capillary transport and water and solute movement from capillary lumen to the interstitium and then into the dialysate (Fig. 10.1 ).

All of the above factors are involved to increase the peritoneal clearance of small solutes during APD. Increasing dialysate dwelling time (no dry time) with frequent exchanges which increases the concentration gradient will increase solute clearance.

In addition, larger dwell volumes increase the peritoneal surface area and maximum fluid removal by increasing the osmotic gradient with 4.25 % dextrose can improve fluid removal and solute clearance. Thus, E is correct.

One of your 50-year-old male patients with CKD 5 is considering PD as one of his choices for renal replacement therapy. He asks you about indications and contraindications about PD. Which one of the following choices is a contraindication for PD?

All of the above choices are contraindications to PD (E is correct). The contraindications can be absolute or relative. The following table summarizes these contraindications for PD (Table 10.1 ).

There are some indications for PD, which are shown in Table 10.2 .

A 50-year-old diabetic woman is on PD for 1 year. Her ultrafiltrate Na⁺ concentration is 128 mEq/L 1-h after instillation of 2 L of 4.25 % dextrose into the peritoneum. Simultaneous determinations of plasma Na⁺ concentration is 144 mEq/L. Which one of the following statements regarding the difference in Na ⁺ concentration between plasma and ultrafiltrate is CORRECT?

All of the above statements are correct (E). During the first hour dwell of hypertonic (hyperosmolar) dialysis solutions such as 2.5 % and 4.5 % dextrose solutions, the osmotic pressure in the peritoneum is higher than in the peritoneal capillaries. This osmotic gradient causes water movement from blood into the peritoneum and dilutes Na ⁺ concentration. This water movement is a process of diffusion via aquaporin-1 channels. These channels are stimulated by dialysate osmolality. Na ⁺ does not move with aquaporin-stimulated water movement. Therefore, Na ⁺ concentration in blood increases due to water movement into the dialysate. This process is called sieving of Na ⁺ (A is correct).

Because of an increase in plasma Na ⁺ and a decrease in dialysate Na ⁺ , the D/P ratio decreases during the first hour of dwell. If the dwell time increases to four or more hours, there is an equilibration, and water movement decreases across the transcellular pores (see figure in question 2) and convection increases through other pores. As a result, Na ⁺ and other solutes as well as water move into the peritoneal cavity, and the D/P _Na ratio reaches unity (B is correct).

When sieving of Na ⁺ occurs (Na ⁺ dip), it is an indication of adequate aquaporin function . On the other hand, failure to decrease Na ⁺ concentration in the dialysis solution (ultrafiltrate) during the first hour of dwell is an indication of aquaporin deficiency. This causes ultrafiltration failure .

Icodextrin is a glucose polymer derived from starch, and is isoosmotic. Unlike dextrose, icodextrin does not stimulate aquaporin channels in the three-pore model of transport. Therefore, sieving of Na ⁺ does not occur. Icodextrin creates a colloidal osmotic pressure (similar to albumin) with resultant water and solute movement across the small and large pores. There the D/P _Na ratio does not alter, and Na ⁺ dip does not occur (D is correct).

It should be noted that Na ⁺ sieving causes hypernatremia, thirst, and hypertension, which are seen with hyperosmolar dialysis solutions.

The osmotic agents that are commonly used in clinical practice are glucose-containing solutions, usually referred to as dextrose solutions. It is, therefore, important for the nephrologists to be familiar with the concentrations, osmolarities, and the expected rate of ultrafiltration with these different glucose solutions (see Table 10.3 below)

A 54-year-old man is started on continuous ambulatory peritoneal dialysis (CAPD) 6 weeks ago. You ask your PD nurse to perform a test to evaluate the peritoneal membrane transport characteristics to prescribe appropriate PD therapy for the patient. Which one of the following is MOSTLY used tests in this incident patient?

There is insufficient evidence to suggest that one test is superior to another test to evaluate peritoneal membrane characteristics. However, the traditional (original) test, which was introduced by Twardowski et al. in 1987, is the most widely test used in clinical practice. This test uses a 2 L of 2.5 % dextrose solution, and a sample of dialysate is taken immediately after completion of instillation, then at 2- and 4-h. The samples are sent for determinations of urea, creatinine, glucose, and Na ⁺ . A blood sample is taken at 2-h and sent for urea, creatinine, glucose, and Na ⁺ . At the end of 4-h, the dialysate is drained, and its volume is recorded. Blood for creatinine is also collected. Dialysate to plasma (D/P) ratios are calculated. Glucose samples are drawn immediately after instillation (0 time) and then at 2- and 4-h to calculate D/D ₀ ratio.

Based on 4-h D/P ratios of creatinine and glucose, the patients are classified into four groups of transporters, as shown in Table 10.4 . Other ratios are also used to evaluate the membrane characteristics.

The above traditional test does not quantify ultrafiltration rate, because it does not involve Na ⁺ sieving. Therefore, use of 4.25 % dextrose is recommended. With this test, ultrafiltration ((UF) can be calculated. The PET is done 4–6 weeks following initiation of PD .

The fast PET is a simplified test of the traditional PET. In this test, only 4-h dialysate and blood creatinine and dialysate glucose are measured after instillation of 2.5 % dextrose. The volume of drained dialysate is measured. Typical values for fast PET are shown in Table 10.5 . The fast PET is criticized for not having internal controls, and also difficult to interpret data in diabetic subjects.

A modified PET is introduced in some patients who have UF failure. In this test, 2 L of 4.25 % dextrose is used. After 4-h dwell, the volume is drained. UF failure is defined as an UF volume <400 mL. This suggests that the peritoneal membrane has lost its UF capacity, and a decision can be made to switch to HD for volume control. This incident patient has not shown any UF failure yet.

DATT is used by some centers to evaluate membrane permeability. This test requires 24-h drainage in a CAPD patient and blood sample on the day of drainage for creatinine to calculate D/P _Creatinine ratio. Studies have shown reasonable correlation between PET and DATT .

Of all the above tests, the traditional PET is preferred in incident PD patients; therefore, the appropriate answer is A.

The above patient is on CAPD with 2 L of 2.5 % dextrose with a dwell time of 4-h. He had a traditional PET 5 weeks after initiation of PD, and the following values were obtained:

D/P_Creatinine 0.91 and D/D_{0 Glucose} 0.2

Based on the above ratios, the patient is a fast (high) transporter. Approximately 15 % of patients will be fast transporters at the initiation of PD . Rapid transporters have high rates of diffusive transport for small solutes like urea, creatinine, and glucose. As a result, these patients reabsorb glucose at a rapid rate, leading to dissolution of the osmotic gradient between the dialysate and blood. This causes slow diffusion and convection of water and solutes. The net result is less ultrafiltration (UF) and resultant fluid accumulation. Systemically these patients develop volume-dependent HTN and LV hypertrophy. This cardiac stress leads to high mortality. It was estimated that for every 0.1 increase in D/P ratios of creatinine , there was an increase in the relative risk of death of 1.15 (CI 1.07–1.23). In low transporters, this risk diminishes.

This patient who is a rapid transporter will benefit from APD with shorter dwell times (1.5-h or less). Thus, D is correct.

CAPD with longer dwell times is not indicated for fast transporters because of dissipation of osmotic gradient and low UF . For low transporters, CAPD with longer dwell time, or continuous cycling PD with less overnight exchanges, may be appropriate. Thus, choices other than D are not appropriate for this patient.

It should be noted that PET does not provide information on adequacy of dialysis, which is obtained from K _t / V _Urea . This requires appropriate adjustments in the number of exchanges.

One of your patient’s choices for renal replacement therapy is PD. He read CAPD and APD from the internet, but he could not understand completely the survival advantage of any of these modalities. Which one of the following statements you would make regarding the risk of survival between CAPD and APD?

Most of the studies on mortality in CAPD and APD patients are observational. These studies showed no difference in mortality between these two modalities. Also, a small randomized study did not find any difference in mortality, indicating that survival is similar between CAPD and APD patients. Thus, choice C is correct. Similarly, no difference in peritonitis , volume management, and technical failure were observed between these two modalities. Larger randomized studies are needed to confirm the results of observational studies.

In selecting the modality of PD, which one of the following major considerations is important?

Selection of either CAPD or APD is dependent mostly on the patient preference. These preferences may include lifestyle, time for social activities, employment, ability to perform PD with or without support, unwillingness to sleep with cycler, and freedom from cycler. Although peritoneal membrane characteristics are an important consideration in the selection of PD, emphasis is placed on patient preferences. Finally, cost is an important consideration. CAPD is cheaper than APD, and frequently the patient has to bear the additional cost. Thus, all of the above choices are correct.

PD adequacy is expressed as K _t / V _Urea , which is the clearance of urea (K) per unit time (t) in relation to its volume of distribution or total body water (V). Which one of the following choices regarding K _t / V is CORRECT?