Computer simulations of peritoneal fluid transport in CAPD

To model the changes in intraperitoneal dialysate volume (IPV) occurring over dwell time under various conditions in continuous ambulatory peritoneal dialysis (CAPD), we have, using a personal computer (PC), numerically integrated the phenomenological equations that describe the net ultrafiltration (UF) flow existing across the peritoneal membrane in every moment of a dwell. Computer modelling was performed according to a three-pore model of membrane selectivity as based on current concepts in capillary physiology. This model comprises small "paracellular" pores (radius approximately 47 A) and "large" pores (radius approximately 250 A), together accounting for approximately 98% of the total UF-coefficient (LpS), and also "transcellular" pores (pore radius approximately 4 to 5 A) accounting for 1.5% of LpS. Simulated curves made a good fit to IPV versus time data obtained experimentally in adult patients, using either 1.36 or 3.86% glucose dialysis solutions, under control conditions; when the peritoneal UF-coefficient was set to 0.082 ml/min/mm Hg, the glucose reflection coefficient was 0.043 and the peritoneal lymph flow was set to 0.3 ml/min. Also, theoretical predictions regarding the IPV versus time curves agreed well with the computer simulated results for perturbed values of effective peritoneal surface area, LpS, glucose permeability-surface area product (PS or "MTAC"), intraperitoneal dialysate volume and dialysate glucose concentration. Thus, increasing the peritoneal surface area caused the IPV versus time curves to peak earlier than during control, while the maximal volume ultrafiltered was not markedly affected. However, increasing the glucose PS caused both a reduction in the IPV versus time curve "peak time" and in the "peak height" of the curves. The latter pattern was also seen when the dialysate volume was reduced. It is suggested that computer modelling based on a three-pore model of membrane selectivity may be a useful tool for describing the IPV versus time relationships under various conditions in CAPD.     

Peritoneal dialysate volume determined by indicator dilution measurements

Dialysate volume was simultaneously determined by two different indicator dilution technique as a function of dwell time in a rabbit model of peritoneal dialysis using isotonic, hypertonic and hypotonic solutions. After a single injection of a large molecular weight index solute (SIIS) to the dialysis solution at a known concentration, the first indicator dilution technique determined dialysate volume by the change in the index solute concentration. In the second technique, dialysate volume was determined after multiple injections of a different index solute (MIIS) by measuring the change in concentration of the index solute two minutes after its injection into the dialysis solution. The volumes determined by SIIS were similar during isotonic, but larger during both hypertonic and hypotonic exchanges, than those determined by MIIS. Drained volume was dependent upon the peritoneal catheter used, was not different from that determined by MIIS, but was significantly smaller than that determined by SIIS. The present results suggest that systematic errors in volume measurements when using indicator dilution result from the loss of the index solute from the peritoneal cavity and are greater for SIIS than for MIIS. A model for fluid transfer during peritoneal dialysis showed that dialysate volumes determined by SIIS were useful, however, when estimating the rate of fluid movement across the peritoneal membrane.     

A quantitative description of solute and fluid transport during peritoneal dialysis.

To investigate the relationship between dialysate glucose concentration and peritoneal fluid and solute transport parameters, 41 six-hour single dwell studies with standard glucose-based dialysis fluids containing 1.36% (N = 9), 2.27% (N = 9) and 3.86% (N = 23) anhydrous glucose were carried out in 33 clinically-stable continuous ambulatory peritoneal dialysis (CAPD) patients. Intraperitoneal dialysate volumes (VD) were determined from the dilution of 131I-albumin with a correction applied for its elimination from the peritoneal cavity (KE, ml/min). Diffusive mass transport coefficients (KBD) were calculated from aqueous solute concentrations (with a correction applied for the plasma protein concentration and, for electrolytes, also for the Donnan factor) during a period of dialysate isovolemia. The intraperitoneal amount calculated to be transported by diffusion was subtracted from the measured total amount of solutes in the dialysate, yielding an estimate of non-diffusive solute transport. The intraperitoneal dialysate volume over time curve was characterized by: initial net ultrafiltration (lasting on average 92 min, 160 min and 197 min and with maximum mean net ultrafiltration rates 6 ml/min, 8 ml/min and 14 ml/min, respectively, for the 1.36%, 2.27% and 3.86% solutions); dialysate isovolemia (lasting about 120 min for all three solutions) and fluid reabsorption (rate about 1 ml/min for all three solutions). KBD for glucose, potassium, creatinine, urea and total protein did not differ between the three solutions and the fractional absorption of glucose was almost identical for the three glucose solutions, indicating that the diffusive transport properties of the peritoneum is not influenced by the initial concentration of glucose or the ultrafiltration flow rate. About 50% of the total absorption of glucose occurred during the first 90 minutes of the dwell. The mean percentage of the initial amount of glucose which had been absorbed (%GA) at time t during the dwell could be described (r = 0.999) for all three solutions using the experimental formula %GA = 85 - 75.7 * e-0.005*t. After 360 minutes, about 75% of the initial intraperitoneal glucose amount had been absorbed corresponding to a mean (+/- SD) energy supply of 75 +/- 6 kcal, 131 +/- 18 kcal and 211 +/- 26 kcal for the three solutions. Non-diffusive (that is, mainly convective) transport was almost negligible for the less hypertonic solutions while it was estimated to account for 30 to 40% of the total peritoneal transport of urea, creatinine and potassium during the first 60 minutes of the 3.86% exchange.     

Mass transfer of calcium across the peritoneum at three different peritoneal dialysis fluid Ca2+ and glucose concentrations

BACKGROUND: In peritoneal dialysis, the rate of ultrafiltration has been predicted to be a major determinant of peritoneal calcium (Ca2+) removal. Hence, dialysis fluid glucose concentration should be an important factor governing the transperitoneal Ca2+ balance. The aim of this study was to test the effect of various dialysate glucose levels and selected dialysate Ca2+ levels on Ca2+ removal in peritoneal dialysis patients. METHODS: Patients (N = 8) received, during a 7-week period, 2 L of lactate (30 mmol/L)/bicarbonate (10 mmol/L)-buffered peritoneal dialysis solutions containing either 1.5% glucose and 1.0 mmol/L Ca2+ or 2.5% glucose and 1.6 mmol/L Ca2+, or 4% glucose and 2.5 mmol/L Ca2+, respectively, provided in a three-compartment bag (trio system). Patients underwent standardized (4-hour) dwells, one for each of the three dialysates to assess permeability-surface area product (PS) or mass transfer area coefficients (MTAC) for ionized and "freely diffusible" Ca2+, lactate, glucose, bicarbonate, phosphate, creatinine, and urea. RESULTS: There was a clear-cut dependence of peritoneal Ca2+ removal on the rate of ultrafiltration. For large peritoneal to dialysate Ca2+ gradients (2.5 mmol/L Ca2+ in 4% glucose) a close fit of measured to simulated data was predicted by the three-pore model using nonelectrolyte equations. For low transperitoneal Ca2+ concentration gradients, however, directly measured Ca2+ data agreed with the simulated ones only when the peritoneal Ca2+ PS was set lower than predicted from pore theory (6 mL/min). CONCLUSION: There was a marked ultrafiltration dependence of transperitoneal Ca2+ transport. Nonelectrolyte equations could be used to simulate peritoneal ion (Ca2+) transport provided that the transperitoneal ion concentration gradients were large. Based on our data 1.38 mmol/L Ca2+ in the dialysis fluid would have created zero net Ca2+ gain during a 4-hour dwell for 1.5% glucose, whereas 1.7 and 2.2 mmol/L Ca2+ would have been needed to produce zero Ca2+ gain for 2.5% glucose and 3.9% glucose, respectively.     

Peritoneal ultrafiltration and fluid reabsorption during peritoneal dialysis

Peritoneal ultrafiltration and fluid reabsorption characteristics for 18 patients undergoing continuous ambulatory peritoneal dialysis (CAPD) were investigated in single dwell studies of 6 h duration with 21 of 3.86% glucose dialysis fluid. Dialysate volumes were determined in situ using radioiodinated serum albumin (RISA) as volume marker with a correction applied for the total elimination of RISA from the peritoneal cavity. The RISA elimination rate was calculated as 2.1 +/- 0.5 ml/min. The true dialysate volume after 360 min was on average 28% less than the apparent volume calculated without correction for the elimination of RISA. The mean maximum true volume plus sampling losses was 3255 ml at 240 min, corresponding to a mean net ultrafiltration volume of 762 ml between 3 min and 240 min. The mean net fluid reabsorption rate between 240 min and 360 min was 1.2 +/- 0.7 ml/min. This study of standard dialysate volume/time curves in clinically stable CAPD patients using hypertonic dialysis fluid shows that about 90% of the total net ultrafiltration is achieved during the first 90 min of the dwell. After an extended period of dialysate isovolaemia, usually lasting as long as between 120 min and 240 min, fluid reabsorption is observed in all patients.     

Pharmacokinetics of icodextrin in peritoneal dialysis patients

Pharmacokinetics of icodextrin in peritoneal dialysis patients. BACKGROUND: Icodextrin is a glucose polymer osmotic agent used to provide sustained ultrafiltration during long peritoneal dialysis (PD) dwells. A number of studies have evaluated the steady-state blood concentrations of icodextrin during repeated use; however, to date the pharmacokinetics of icodextrin have not been well studied. The current study was conducted to determine the absorption, plasma kinetics and elimination of icodextrin and metabolites following a single icodextrin exchange. METHODS: Thirteen PD patients were administered 2.0 L of solution containing 7.5% icodextrin for a 12-hour dwell. Icodextrin (total of all glucose polymers) and specific polymers with degrees of polymerization ranging from two to seven (DP2 to DP7) were measured in blood, urine and dialysate during the dwell and after draining the solution from the peritoneal cavity. RESULTS: A median of 40.1% (60.24 g) of the total administered dose (150 g) was absorbed during the 12-hour dwell. Plasma levels of icodextrin and metabolites rose during the dwell and declined after drain, closely corresponding to the one-compartment pharmacokinetic model assuming zero-order absorption and first-order elimination. Peak plasma concentrations (median C peak = 2.23 g/L) were observed at the end of the dwell (median Tmax = 12.7 h) and were significantly correlated with patients' body weight (R2 = 0.805, P < 0.001). Plasma levels of icodextrin and metabolites returned to baseline within 3 to 7 days. Icodextrin had a plasma half-life of 14.73 hours and a median clearance of 1.09 L/h. Urinary excretion of icodextrin and metabolites was directly related to residual renal function (R2 = 0.679 vs. creatinine clearance, P < 0.01). In the nine patients with residual renal function, the average daily urinary excretion of icodextrin was 473 +/- 77 mg per mL of endogenous renal creatinine clearance. Icodextrin metabolites DP2 to DP4 were found in the dialysate of subsequent dextrose exchanges, contributing to their elimination from blood. Changes in intraperitoneal concentrations of icodextrin metabolites during the dwell revealed a dual pattern, with a progressive rise in the dialysate concentration of smaller polymers (DP2 to DP4) and a progressive decline in the dialysate concentrations of the larger polymers (DP5 to DP7), suggesting some intraperitoneal metabolism of the glucose polymers. This increase in dialysate metabolite levels, however, did not contribute significantly to dialysate osmolality. In addition, some diffusion of maltose (DP2) from blood to dialysate may have occurred. There were no changes in serum insulin or glucose levels during icodextrin administration, indicating that icodextrin does not result in hyperglycemia or hyperinsulinemia as occurs during dextrose-based dialysis. Serum sodium and chloride declined in parallel with the rise in plasma levels of icodextrin, supporting the hypothesis that these electrolyte changes are the result of the increased plasma osmolality due to the presence of icodextrin metabolites. CONCLUSIONS: The pharmacokinetics of icodextrin in blood following intraperitoneal administration conforms to a simple, single-compartment model that can be approximated by zero-order absorption and first-order elimination. A small amount of intraperitoneal metabolism of icodextrin occurs but does not contribute significantly to dialysate osmolality. The metabolism of absorbed icodextrin and the resultant rise in plasma levels of small glucose polymers (DP2 to DP4) do not result in hyperglycemia or hyperinsulinemia, but may result in a small decrease in serum sodium and chloride.     

Volume stress-induced peritoneal endothelin-1 release in continuous ambulatory peritoneal dialysis

In long-term peritoneal dialysis, functional deterioration of the peritoneal membrane is often associated with proliferative processes of the involved tissues leading to peritoneal fibrosis. In continuous ambulatory peritoneal dialysis (CAPD), failure to achieve target values for adequacy of dialysis is commonly corrected by increasing dwell volume; in case of ultrafiltration failure, osmolarity of the dialysate gets increased. In a prospective study, the impact of increasing dwell volume from 1500 ml to 2500 ml per dwell (volume trial) or changing the osmolarity of the dialysate from 1.36 to 3.86% glucose (hyperosmolarity trial) on the peritoneal endothelin-1 (ET-1) release was analyzed. ET-1 is known to exert significant proliferative activities on a variety of cell types leading to an accumulation of extracellular matrix. A highly significant difference in the cumulative peritoneal ET-1 synthesis was found between the low- and high-volume exchange, whereas differences in the hyperosmolarity setting were only moderate. Sixty minutes after initiating dialysis, the cumulative ET-1 synthesis was 2367 +/- 1023 fmol for the 1500 ml versus 6062 +/- 1419 fmol for the 2500 dwell (P < 0.0001) and 4572 +/- 969 fmol versus 6124 +/- 1473 fmol for the 1.36 and 3.86% glucose dwell (P < 0.05), respectively. In conclusion, increasing dwell volume leads to a strong activation of the peritoneal paracrine endothelin system. Because ET-1, apart from being a potent vasoactive peptide, contributes to fibrotic remodeling, this study indicates that volume stress-induced ET-1 release might contribute to structural alteration of the peritoneal membrane in long-term peritoneal dialysis.     

Evaluation of peritoneal dialysis solutions with amino acids and glycerol in a rat model.

In this study a simple rat model for evaluating the ultrafiltration by peritoneal dialysis solutions is described. Anaesthetised male Sprague-Dawley rats were injected intraperitoneally with dialysis solutions. Zero, 1, 3, or 6 h later, the dialysate volume was determined directly: the abdomen was carefully opened, the intraperitoneal liquid was withdrawn with a syringe and its volume was measured. Good recovery of dialysate, highly reproducible results, and the similarity between the ultrafiltration profiles in rats and published profiles in CAPD patients for control solutions, indicate that the model is valid. The model was then used to evaluate peritoneal dialysis solutions containing a mixture of glycerol and amino acids. Both osmotic agents are chemically compatible and these mixtures provide amino acids and carbohydrates in a single solution. For three mixtures, intraperitoneal dialysate volume were determined as a function of dwell time and the formulation with the desired ultrafiltration could be selected.     

Peritoneal clearances with different dialysis regimens in children undergoing continuous cycling peritoneal dialysis

Peritoneal clearances and dialysate protein losses occurring in paediatric patients undergoing different continuous cycling peritoneal dialysis (CCPD) regimens have not been well defined. We, therefore, evaluated 10 children aged 15.8 +/- 2.5 (SD) years who were maintained on home peritoneal dialysis for 20.5 +/- 10 months. All patients had at least 3 months of CCPD. The patients were admitted to the Clinical Research Center for 48 hours and allocated to five different dialysis protocols. In protocol I, the frequency of exchanges was 10 per 10 hours; in Protocol II it was 5 per 10 hours; and in Protocol III it was 3 per 10 hours. Protocol II D and III D had, in addition, a daytime dwell of one-half the night-time volume. A 1.5% glucose dialysate solution was used for night-time dialysis, and 4.25% glucose dialysate solution for the daytime dwell. The mean inflow dialysate volume per exchange was 36.7 +/- 5.6 ml/kg body weight and was constant in each patient for each study protocol. BUN and creatinine clearances for each protocol were calculated and dialysate protein losses were measured. The data indicate that hourly night-time dialysis (Protocol I) provides best solute clearance. A daytime dwell further enhances the total solute clearance and should be used preferably in anuric patients. Residual urine output contributes significantly to the total solute clearance. Protein losses are maximum with low-frequency exchanges and a daytime dwell. No significant differences in the serum albumin concentrations were found during the different protocols; however, the long-term effect of the protein loss on the nutritional status of the patients requires further evaluation.     

Long-term changes in transperitoneal water transport during continuous ambulatory peritoneal dialysis

9 patients were observed prospectively during 14-40 months 003 continuous ambulatory peritoneal dialysis (CAPD) treatment. From start of CAPD, each patient recorded dwell time, drained ultrafiltration volume (delta V), initial glucose concentration in dialysate, dialy fluid intake, body weight and blood pressure on a special form. These data, together with monthly values for albumin, urea, creatinin, phosphate, glucose and beta 2-microglobulin in plasma and in instilled dialysate, were later fed into a specially designed computer program to compare changes in the monthly mean (+/- SEM) values. During 5 episodes of peritonitis, daily changes in delta V were also computed. A long-term increase in delta V was found in 4 and a decrease in 5 patients. In all 9 patients delta V changed intermittently. All changes were most pronounced for long dwell times as compared to shorter dwell exchanges. The decrease in delta V started within the first 12 months of treatment. In the daily routine were aware of decreased ultrafiltration capacity in 3 patients only. Intermittent monthly changes in delta V could partly be correlated to changes in daily fluid intake. No correlations were found between long-term changes in delta V and fluid intake. All except 1 patient gained progressively in body weight, but without correlations to fluid balance, blood pressure and plasma albumin concentration. At the start of the observation period, most patients loosing delta V during this study appeared to have a more permeable membrane with a higher absorption rate of glucose and higher equilibration ratios for creatinine and beta 2-microglobulin in 5-hours drained dialysate as compared with the other patients. However, this was not statistically different between the two groups of patients. During the observation period, most patients with decreased delta V also increased transperitoneal solute transport, while the solute transport decreased in patients with increasing delta V, but these changes were only significant for some patients. During peritonitis, delta V decreased significantly 1 day before any other signs of peritonitis. All changes in delta V were most pronounced for long dwell times as compared with short dwell times. It is suggested that changes in ultrafiltration can be related to altered permeability of the peritoneal membrane, which appear earlier and more frequent than suggested by others, and any loss of delta V can be explained by a more permeable ('open') peritoneal membrane. It is also possible that different diseases act differently on the permeability of the peritoneal membrane.     

Kinetic Modeling of Continuous Flow Peritoneal Dialysis

Kinetic models have been derived for analysis of the effects on peritoneal urea clearance ( K _p) of continuous single-pass flow of fresh peritoneal dialysate and continuous flow of peritoneal dialysate recirculating through an external dialyzer. Generalized solution of the models shows that both predict K _p to be a well-defined function of the peritoneal mass transfer coefficient (MTC) and the dialysance ( D ) of the external dialyzer, while the MTC is a function of the rate and distribution of dialysate flow. Thus the models should be useful to guide studies to optimize CFPD. Analysis of reported in vivo data indicate that with dialysate flow rate and D both in the range of 200 ml/min, MTC levels of 60–70 ml/min and K _p levels of 50 ml/min can be achieved. If the model predictions are verified in vivo, 8-hour overnight CFPD 6 nights/week could provide the average-size anephric patient a weekly stdKt / V of 3.2 which is competitive with daily hemodialysis. Kinetic modeling of ultrafiltration indicated ultrafiltration rates 0.2–0.3 L/hr should be achieved with 1.0–1.25% dextrose dialysate. The model shows average rates of glucose absorption can theoretically be reduced by 33% compared to CAPD with the same amount of fluid removal.     

The peritoneal equilibration test in children.

The peritoneal equilibration test (PET) has been recommended in adults as a standardized means of estimating solute transport. Based on results of the PET, adult peritoneal permeability has been classified as high, high average, low average, and low. We performed a PET on 32 children aged 0.8 to 17.8 years (mean 9.3) using a dwell volume of 32 +/- 5 ml/kg of 2.5% dialysate. Dialysate to plasma (D/P) ratios for creatinine, urea, and sodium were calculated at two and four hours as were the ratios of dialysate glucose at two and four hours to the dialysate glucose at time 0 (D/Do). Stepwise logistic regression identified only the patients' age and D/Do glucose values at two hours as significant predictors of ultrafiltration. Net ultrafiltration after a four hour dwell could be predicted for 75% of children above 9.3 years, or whose D/Do glucose value at two hours was greater than 0.45. The mean and standard deviation values for D/Do glucose and D/P creatinine at four hours were 0.31 +/- 0.17 and 0.71 +/- 0.12, respectively. When children are characterized according to adult standards, at least 70% fall into the high or high average permeability categories.     

低分子肝素对腹膜透析患者腹膜功能影响的观察

目的探讨低分子肝素对腹膜透析患者腹膜通透性、腹膜超滤量的影响。方法选择病情稳定的腹膜透析患者22例,采用双盲交叉对照设计,将患者随机分成2组,分别于腹膜透析液中加入低分子肝素和生理盐水,治疗3个月,再经1个月的洗脱期后交换处理因素,分别观察患者的腹膜通透性、超滤量及各凝血指标的变化。结果低分子肝素处理期,透析液肌酐／血肌酐和透析液尿素／血尿素比值较处理前和生理盐水处理期均明显降低,差异均有统计学意义（P〈0．05）。低分子肝素处理期透析液白蛋白／血白蛋白比率较处理前和生理盐水处理期明显降低,差异均有统计学意义（P〈0．05）。低分子肝素处理期4h、0h透析液葡萄糖比率及24h超滤量均较处理前和生理盐水处理期明显升高,差异均有统计学意义（P〈0．05）。所有患者观察期间均未出现腹腔出血并发症。结论腹膜透析患者腹膜透析液中加入低分子肝素可降低腹膜小分子的通透性,增加腹膜超滤量,而不增加出血的风险。     

肝细胞生长因子对维持性腹膜透析患者腹膜微炎症状态及超滤量的影响

目的：观察肝细胞生长因子（HGF）对腹膜透析微炎症状态和超滤量的影响。方法：选择稳定的持续非卧床腹膜透析（CAPD）患者20例,采用双盲交叉对照设计,患者随机腹透液内分别加入HGF或生理盐水治疗3个月,再经1个月的洗脱期后交换处理因素,分别观察患者的腹膜微炎症状态、腹膜通透性和超滤量的变化。结果：与处理前和生理盐水处理后相比,HGF可降低透析液CRP、IL-6、TNF-α和TGF-β的水平（P〈0．05）,降低透析液肌酐／血肌酐（D/PCr）比值,降低透析液尿素／血尿素（D／Purea）比值以及透析液白蛋白／血白蛋白比率。HGF可增加4h、0h透析液葡萄糖比率（D4／D0 glucose）及24h超滤量（P〈0．05）,患者周总KT／V和总Ccr／ml无明显变化（P〉0.05）。结论：PD患者腹透液内使用HGF可改善腹腔微炎症状态,降低腹膜对小分子通透性,增加腹膜的超滤量。     

Effect of amino acid based dialysis solution on peritoneal permeability and prostanoid generation in patients undergoing continuous ambulatory peritoneal dialysis.

The acute effect of amino acid based dialysis solution on peritoneal kinetics of amino acids and plasma proteins in comparison to conventional glucose-based dialysate was studied in 9 patients with end-stage renal failure on continuous ambulatory peritoneal dialysis. Instillation of 2.6% amino acid solution resulted in raised plasma concentrations of all essential amino acids included in the dialysis fluid (p less than 0.005). The amino acid solution induced an augmented leakage of plasma proteins into the dialysate at all dwell times investigated (1-8 h). After a dwell time at 8 h, the dialysate total protein increased from 2.62 +/- 0.45 g with glucose dialysate to 3.85 +/- 0.42 g with amino acid solution (p less than 0.05). Corresponding results were obtained for beta 2-microglobulin, albumin, transferrin, IgG, and for the non-essential amino acids alanine, citrulline, and glutamine (p less than 0.025) not included in the initial amino acid composition of the dialysis fluid. During the use of amino acid based dialysis fluid, the effluent prostaglandin E2 concentration increased by more than 80% in comparison to glucose dialysate (p less than 0.025). The augmented loss of proteins induced by the amino acid solution was positively correlated with increased dialysate prostaglandin E2 (r = 0.8894; p less than 0.001). Peritoneal ultrafiltration was not affected by the use of amino acid based dialysate fluid. The present results indicate that amino acid based dialysis fluid enhances the peritoneal permeability for plasma proteins and amino acids, probably mediated by locally generated prostanoids.     

Effect of increased dialysate volume on peritoneal surface area among peritoneal dialysis patients

Large dialysate volumes are often required to increase solute clearance for peritoneal dialysis patients. The resulting increase in solute clearance might be attributable to an increased plasma-to-dialysate concentration gradient and/or to an increased effective peritoneal surface area. One of the factors affecting the latter is the peritoneal surface area in contact with dialysate (PSA-CD). The aim of this study was to estimate the change in PSA-CD after a 50% increase in the instilled dialysate volume for patients undergoing peritoneal dialysis. PSA-CD was estimated by using a method applying stereologic techniques to computed tomographic (CT) scans of the peritoneal space. The peritoneal cavity of 10 peritoneal dialysis patients was filled with a solution containing dialysate, half-isotonic saline solution, and contrast medium. Peritoneal function tests and CT scanning of the abdomen were performed twice for each patient (with an interval of 1 wk), after instillation of a 2- or 3-L solution. Scanning of thin helical CT sections was performed, and 36 random sections of the abdomen were obtained after reconstruction. A grid was superimposed on the sections. The surface area was estimated by using stereologic methods. After instillation of the 2-L solution, the volume of the peritoneal solution at the time of CT scanning was 2.32 +/- 0.05 L. The PSA-CD was 0.57 +/- 0.03 m(2), ranging from 0.41 to 0.76 m(2). The use of the 3-L solution increased the peritoneal volume by 46 +/- 2%. PSA-CD increased by 18 +/- 2.3% to 0.67 +/- 0.04 m(2) (range, 0.49 to 0.84 m(2); P < 0.01). Creatinine mass transfer increased from 112 +/- 10 mg to 142 +/- 11 mg (P < 0.0001). The slope of the change of the plasma-to-dialysate creatinine concentration gradient with time decreased from -2.26 +/- 0.23 x 10(-2) to -1.97 +/- 0.16 x 10(-2) (P = 0.01). K(BD-0) (permeability-surface area product or mass area transfer coefficient at time 0 of the dwell) increased from 10.6 +/- 0.7 to 13.6 +/- 1.2 ml/min (P < 0.02). These data demonstrate that increasing the instilled dialysate volume by 50% for peritoneal dialysis patients results in significant increases in the PSA-CD and K(BD).     

High peritoneal residual volume decreases the efficiency of peritoneal dialysis

BACKGROUND: Wide variation in peritoneal residual volume (PRV) is a common clinical observation. High PRV has been used in both continuous ambulatory peritoneal dialysis (CAPD) and automated peritoneal dialysis to minimize the time of a dry peritoneal cavity and to achieve better dialysis. However, the impact of PRV on peritoneal transport is not well established. In this study, we investigated the effect of PRV on peritoneal transport characteristics. METHODS: Peritoneal effluents were collected in 32 male Sprague-Dawley rats after a five-hour dwell with 1.36% glucose solution. Forty-eight hours later, a four hour dwell using 25 ml of 3.86% glucose solution and frequent dialysate and blood sampling was done in each rat with 125I-albumin as a volume marker. Before the infusion of the 3.86% glucose solution, 0 (control), 3, 6, or 12 ml (8 rats in each group) of autologous effluent (serving as PRV) was infused to the peritoneal cavity. RESULTS: After subtracting the PRV, the net ultrafiltration was significantly lower in the PRV groups as compared with the control group: 13.4 +/- 0.5, 12.0 +/- 1.0, 11.7 +/- 1.7, and 8.9 +/- 0.4 ml for 0, 3, 6, and 12 ml PRV groups, respectively (P < 0.001). The lower net ultrafiltration associated with higher PRV was due to (a) a significantly lower transcapillary ultrafiltration rate (Qu) caused by a lower osmotic gradient, and (b) a significantly higher peritoneal fluid absorption rate (KE) caused by an increased intraperitoneal hydrostatic pressure. No significant differences were found in the diffusive mass transport coefficient for small solutes (glucose, urea, sodium, and potassium) and total protein, although the dialysate over plasma concentration ratios values were higher in the high-PRV groups. The sodium removal was significantly lower in the PRV groups as compared with the control group (P < 0.01). CONCLUSION: Our results suggest that a high PRV may decrease net ultrafiltration through decreasing the Qu, which is caused by a decreased dialysate osmolality, and increasing the KE caused by an increased intraperitoneal hydrostatic pressure. The high volume of PRV also decreased the solute diffusion gradient and decreased peritoneal small solute clearances, particularly for sodium. Therefore, a high PRV may compromise the efficiency of dialysis with a glucose solution.