Evaluation and management of chronic anorectal and pelvic pain syndromes: Italian Society of Colorectal Surgery (SICCR) position statement.

Chronic pelvic pain is a hidden issue which needs to involve many different usually uncoordinated specialists. For this reason there is a risk that treatments, in the absence of well-defined pathways, common goals, and terminology, may be poorly effective. The aim of the present paper is to summarize the evidence on anorectal pelvic pain, offering useful evidence-based practice parameters for colorectal surgeons' daily activity. Analysis of chronic anorectal and pelvic pain syndromes, the diagnostic and clinical optimal needs for evaluation, and the innumerable low evidence treatments and therapeutic options currently available suggests that a multimodal individualized management of pain may be the most promising approach. The limited availability of dedicated centers still negatively affects the applicability of these principles.

Acute acalculous cholecystitis on a COVID-19 patient: a case report.

INTRODUCTION: We report an extremely rare case of acute acalculous cholecystitis on a COVID-19 patient. In our knowledge, this is the first report of laparoscopic cholecystectomy performed on a COVID-19 patient. PRESENTATION OF CASE: A COVID-19 patient was diagnosed with acute acalculous cholecystitis and a multidisciplinary team decided to perform a percutaneous transhepatic biliary drainage (PTBD) as the first treatment. SARS-CoV-2 RNA was not found in the bile fluid. Because of deterioration of the patient's clinical conditions, laparoscopic cholecystectomy had to be performed and since the gallbladder was gangrenous, the severe inflammation made surgery difficult to perform. DISCUSSION: Acalculous cholecystitis was related with mechanical ventilation and prolonged total parenteral nutrition, in this case the gangrenous histopathology pattern and the gallbladder wall ischemia was probably caused by vascular insufficiency secondary to severe acute respiratory distress syndrome of COVID-19 pneumonia. The percutaneous transhepatic gallbladder drainage (PTBD) was performed according to Tokyo Guidelines because of high surgical risk. Laparoscopic cholecystectomy was next performed due to no clinical improvement. The absence of viral RNA in the bile highlights that SARS-CoV-2 is not eliminated with the bile while it probably infects small intestinal enterocytes which is responsible of gastrointestinal symptoms such as anorexia, nausea, vomiting, and diarrhoea. CONCLUSIONS: Although the lack of evidence and guidelines about the management of patient with acute cholecystitis during COVID-19 pandemic, laparoscopic cholecystectomy, at most preceded by PTGBD on high surgical risk patients, remains the gold standard for the treatment of acute cholecystitis on COVID-19 patients.

Practice pattern and treatment options for kidney patients in a single North Italian nephrology center.

The experience and the current practice of a single center located in northern Italy is reported. The center of Vicenza is a self-standing nephrologic unit serving a population of about 300,000 individuals. The overall province counts approximately 800,000 individuals and some of them are referred to our center from peripheral hospitals for renal transplantation and/or particular pathologic conditions. The center offers an integrated approach to the treatment of uremia including hemodialysis (HD), peritoneal dialysis (PD), and renal transplantation. In HD and PD, the most peculiar aspect is the treatment personalization that leads to numerous types of applied therapies and technologies. The policy of the center is based on the belief that the nephrology team has a substantial influence on the outcomes of dialysis patients. A large number of treatment options are available. Special care is placed on the delivery of an adequate amount of dialysis, but the fractional clearance of urea in relation to volume (Kt/V) is seen as a prerequisite and other factors are considered important. Reduction in mortality and morbidity is largely dependent on beginning therapy early in the course of renal treatment. The attainment of appropriate hemoglobin concentrations, good nutrition, good control of calcium and phosphorus metabolism, lipids, and blood pressure, is considered of great importance. Beyond all these factors the time spent by the physician with the patient is considered one of the major factors influencing quality of care. The particularly low mortality of the center (6%/yr) may also be ascribed to a lower incidence of diabetes and other comorbidities.

Bioethical issues related to continuous renal replacement therapy in intensive care patients.

OBJECTIVE: To examine the ethical approach of intensivists and nephrologists to continuous renal replacement therapy (CRRT). DESIGN: A questionnaire. SETTING: The First International Course on Critical Care Nephrology. PARTICIPANTS: The participants in the course (around 500). RESULTS: Most participants think that establishing ethical criteria for managing CRRT is a medical task, as clinicians have adequate criteria for defining futility. However, many responders would grant the request of starting futile CRRT or would maintain it if requested by the family. Only 55% believe that informed consent is necessary for initiating CRRT; one out of four would start or maintain unwanted life-saving CRRT. In case of lack of equipment, the majority would select the patients, excluding the worst one or on a "first-come, first-served" basis. Withholding and withdrawing are regarded differently by most responders. Again, most think that every vital support should be withdrawn when futile, but practical and psychological aspects still influence the final decision. Responders think that ethics critical care committees can help in the management of ethical problems in ICU. CONCLUSIONS: Our results show that several ethical questions are still unsolved and that practical and psychological aspects of the treatment process can be stronger than bioethical principles.

Totally implantable venous access devices implanted surgically: a retrospective study on early and late complications.

BACKGROUND: The techniques used for the implantation of totally implantable venous access devices (TIVADs) are the percutaneous approach and surgical cutdown; however, the choice is still controversial. HYPOTHESIS: The surgical cutdown approach may be beneficial to reduce the rate of complications. DESIGN: Retrospective review. SETTING: A university hospital and a tertiary referral center. PATIENTS: Patients undergoing a TIVAD implant at the First Surgical Clinic of the University of Catania in Catania, Italy, between January 1995 and December 1999, were considered for the study. All of the devices were implanted in an operating room under fluoroscopic control. The vein of choice was the cephalic vein. When the cephalic vein was not suitable for implantation, the external jugular vein or the axillary vein and its branches were used. The percutaneous approach to the subclavian vein or internal jugular vein was considered a last resort to implant a catheter. RESULTS: During the study period, 346 TIVADs were implanted in 344 patients. The procedure was performed with local anesthesia in 341 cases (98.5%), and only 2 patients (0.6%) required sedation for psychological reasons. Three patients (0.9%) had their TIVAD placed during a laparotomy. In 326 patients (94.2%), the devices were implanted in the cephalic vein. In the remaining cases, other veins were used with surgical cutdown. The mean time for the procedure was 15 minutes. Percutaneous access was never used, and no early mechanical complications were recorded. Only 6 patients (1.8%) in our study group had late complications (1 case of migration of the catheter, 2 cases of infection, and 3 cases of withdrawal occlusion). The catheter life ranged from 6 to 1487 days (mean time, 348 days). CONCLUSION: Our results confirm the safety, speed, and low cost of the open cutdown technique. This surgical procedure avoids both early and late complications that frequently occur with percutaneous access. Surgical cutdown should be considered the technique of choice to implant the TIVAD, especially in cancer patients.

Hemodiafiltration with online regeneration of the ultrafiltrate.

The concept of regeneration of dialysis fluids and of ultrafiltrate in particular has been recently revisited. Hemodiafiltration with online regeneration of the ultrafiltrate allows the concomitant infusion of sodium, calcium, and bicarbonate. Here, we studied the adsorptive characteristics of an integrated two-step sorbent system relative to different solutes present in the ultrafiltrate: sodium, calcium, phosphate, bicarbonate, uric acid, creatinine, and beta2-microglobulin. In vitro studies were performed in order to differentiate the relative roles for each sorbent (mineral-activated charcoal or hydrophobic resin) in adsorbing a given solute. Ex vivo studies were performed in order to evaluate the presence of cytokines (interleukin-1 beta and tumor necrosis factor-alpha), of cytokine (interleukin-1 beta and tumor necrosis factor-alpha)-inducing activities, and of the cytokine release in response to exogenous bacterial lipopolysaccharide by normal whole blood incubated with ultrafiltrate samples obtained at 15, 120, and 240 minutes after the start of treatment. The results of the present studies show the presence of immunomodulatory substances in the ultrafiltrate and the significant (P < 0.01) increase in the lipopolysaccharide-induced release of both interleukin-1 beta and tumor necrosis factor-alpha. The biological relevance of the ultrafiltrate and the possible relevance of the online, endogenous reinfusion are discussed.

Use of adsorptive mechanisms in continuous renal replacement therapies in the critically ill.

The pathophysiology of sepsis is becoming a more complicated scenario. In sepsis, endotoxin or other gram-positive derived products induce a complex and dynamic cellular response giving rise to several mediators known to be relevant in the pathogenesis of septic shock, such as specific mediators. substances responsible for up- or down-regulation of cytokine receptors and cytokine antagonists, inactivators of nuclear factor-kappaB or signal transduction pathways, and precursor molecules. In this article, we delve into some new concepts stemming from the use of sorbents in continuous plasma filtration. The rationale is based on the assumption that the nonspecific removal of several mediators of the inflammatory cascade and cytokine network may improve outcome in a rabbit model of septic shock and hemodynamics in a pilot clinical study. The importance of looking for innovative treatments specifically targeted for the special needs of the critically ill patients rather than using concepts and technology applied to the treatment of chronic renal failure is underlined.

Favourable anatomical variation for the resection of a Klatskin tumour.

The liver and the biliary tract are rich in anatomical variations, knowledge of which is important for the surgeon. A case of an anatomical variation is reported, which allowed easy and oncologically correct resection of a Klatskin tumour. The variation consisted of abnormally long right and left extrahepatic ducts and an abnormal distal bifurcation, with a cystic duct joining the distal end of the right duct. A favourable modification of surgical strategy could be obtained by an oncologically correct resection of a Klatskin tumour avoiding a liver resection and also allowing easy reconstruction. Complete biliary exposure was necessary to reveal the rare, pre-operatively unrecognized, but favourable situation. In the absence of clear contraindications extended biliary dissection is to be recommended to avoid errors in the evaluation of the resectability of hilar biliary cancers.

The role of technology in hemodialysis.

The evolution of hemodialysis therapy has been characterized over the years by the search for reliable devices and supplies, for more efficient treatments and finally for a more tolerable therapy in long term dialysis patients. In this view, three steps can be identified: a) the first step was the creation of safe and reliable vascular access, dialyzers and machines. This step led to the birth of modern dialysis and treatment personalization was the logical consequence. Each patient is a single entity and he requires a specific therapy prescription and delivery. From this concept the search for adequacy and better outcomes has been generated, with the inevitable consequence that newer techniques were explored in the attempt to perform a more efficient and clinically tolerated dialysis therapy. b) The second step was the attempt to consider the intratreatment variations as possible source for dialytic morbidity. In this view, efforts were made to pre-set ultrafiltration and dialysate sodium profiles in the machine to counterbalance the negative effects of uncontrolled water and solute removal. However, this approach failed to provide significant results, because ultrafiltration and sodium profiles were predetermined and no adaptations could be made if the designed profile was inadequate. c) The third step in the evolution of dialysis was the understanding that on-line signals from the machine and from the patients were required in order to prepare and carry out the adequate response and variation of treatment parameters. For this reason a series of sensors have been developed including urea and blood volume sensors which are offering the most important signals from the patient. In this way, accurate responses could be made during treatment and from a simple manual feedback, we have today a completely automatic form of biofeedback. The question that now arises is where to find the financial resources to afford the upcoming technology. Another question is whether this new technology should be for everybody in routine dialysis or it should be designed for specific conditions. In other words, are these toys for nice experimental studies and speculations or are they tools to improve dialytic outcomes and morbidity? Probably, technology cannot be stopped in its evolution. What is exceptional today will probably be part of the routine of tomorrow. It seems that we are struggling more with the complex physiology of human body than with mechanical or electronic problems that certainly find their solution before or after. The increasing use of computers and the evolution of the applied software will certainly help in reducing the costs and improving the performances of our newer dialysis devices.

Brain density changes during renal replacement in critically ill patients with acute renal failure. Continuous hemofiltration versus intermittent hemodialysis.

Computerized tomography (CT) studies of the brain were made on 12 patients with acute renal failure from different origin. Patients were treated for two subsequent days in random sequence with intermittent hemodialysis (HD) (one 4-h session and Kt/V > or = 1) and continuous veno-venous hemofiltration (CVVH) (one 24-h session and Kt/V > or = 1). CT scans were done before and after the HD and CVVH session in each patient. In baseline conditions, the only macroscopic morphological alteration was a slight brain edema in some patients. Significant changes in the density of white and gray matter were observed after the HD session in all patients (gray matter from 52.3 +/- 5.2 to 38.9 +/- 5.3 and white matter from 36.7 +/- 3.5 to 24.8 +/- 3.2 Hounsfield units, average delta -26.7%). No changes were observed after CVVH. We conclude that intermittent HD involves a remarkable degree of "unphysiology", leading to increased water content in the brain after each session. In acute patients this may lead to a post-dialytic brain edematogenic state. The physiological stability provided by continuous therapies such as CVVH avoids this unwanted effect, and suggests that continuous renal replacement therapies should be a first choice in these patients.

Cannulation of the internal jugular vein: comparison of the classic Seldinger technique and an ultrasound guided method.

Central venous catheterization allows immediate and easy vascular access for hemodialysis. Accidental arterial puncture is the most frequent complication of central vein cannulation and may occur in up to 8% of cases with the classic Seldinger procedure. We compared the Seldinger technique which implies manual localization of the vascular access, and an ultrasound guided technique, to assess whether the latter is an improvement on the Seldinger procedure.

The effect of membrane permeability on ESRD: design of a prospective randomised multicentre trial.

The different permeability of high-flux and low-flux dialysis membranes results in different removal capacity, particularly for uremic toxins of middle and large molecular weight. High-flux dialysers have been evaluated in clinical and epidemiological studies for their effect on mortality, morbidity, dialysis-related amyloidosis, nutritional status, response to erythropoietin treatment, dialysis tolerance and the preservation of residual renal function. Many of these studies, however, lack a prospective design and randomised treatment allocation, or have too few patients and too short a follow-up. Therefore, this clinical trial was designed to prospectively investigate the long-term effect of membrane permeability on clinical outcome in a larger number of patients. The primary objective is to compare the effect of membrane permeability on mortality of patients on bicarbonate hemodialysis and treated with a minimum dialysis dose. Patients included in the study should have been on hemodialysis for no longer than one month and have serum albumin 4 g/dl or lower. Patients will be randomised to either the experimental or the control group. During the four-week run-in period the treatment parameters will be established in order to achieve the required dialysis dose. During the maintenance period of three to five years regular visits are scheduled to record clinical and laboratory parameters, to measure Kt/V and to adapt the treatment parameters. Altogether a minimum of 660 patients should be enrolled within a two-year recruitment period.

Continuous urea monitoring in hemodialysis: a model approach to forecast dialytic performance. Results of a multicenter study.

BACKGROUND: A urea biosensor, inserted into the ultrafiltrate collection-line of paired filtration dialysis (PFD), not only allows on-line dialysis quantification, but also forecasts final (Cend) and 30 min equilibrated urea concentration (Ceq), the most reliable value for calculating dialysis efficiency. The urea biosensor processes plasma ultrafiltrate continuously, delivering a large amount of data to the computer, which estimates the parameters by a mathematical model, thus predicting the whole urea profile with rebound. METHODS: A multicenter randomized trial on 41 patients was conducted to ascertain the ability of a two-pool variable-volume urea model to forecast Cend and Ceq at 60 and 90 min after the start of dialysis. Two alternative dialytic treatments, A or B, were chosen, the latter being more efficient. Each treatment included six serial PFD. The accuracy of forecasting was evaluated through four indices based on forecast errors, calculated as the difference between observed and forecasted urea values: mean percent error (MPE) (%), mean absolute deviation (MAD) (mg/dl), mean absolute percent error (MAPE) (%) and root mean squared error (RMSE) (mg/dl). RESULTS: Forecasted urea concentrations were lower than those measured by the biosensor. MPE for Cend was negligible in A (+1.2%) and much higher in B (+7.2%); both values improved at 90 min, +1.0% and +5.8%, respectively. MAD for Cend was similar in both treatments and improved slightly at 90 min, ranging from 4.9 to 5.9 mg/dl. MPE for Ceq was +4% in A and and more than doubled in B (+11.5%); both values improved at 90 min, +3.7% and +9.7%, respectively. MAD for Ceq was 7.5 mg/dl in A and 8.5 mg/dl in B; both improved at 90 min, 6.7 and 7.4 m g/dl, respectively. The other indices, MAPE and RMSE, showed similar results. Comparison between the errors of the two treatments with analysis of variance (ANOVA) for repeated measures gave no significant results. CONCLUSIONS: Our model forecasts of urea concentrations were overall lower than the measured ones: the bias was negligible for A-Cend, greater for the A-Ceq and when the more efficient treatment B was used. The 60 min predictions improved at 90 min. The comparison between the prediction errors in the two treatments were not statistically significant. The recirculation measurement would probably reduce the bias if it were properly incorporated into the model.

Laparoscopic resection of an abdominal wall desmoid using a modified suture traction technique: the "marionette trick".

Desmoids are rare mesenchimal tumors that may originate also inside the abdomen or in the abdominal wall. These tumors are biologically characterized by a tendency to local growth, and only rarely are they able to develop distant metastases. Surgical excision usually is the best treatment with a chance of a cure. In the few reports on intraabdominal or abdominal wall desmoids, open surgery always was performed. The first case of successful laparoscopic resection of a symptomatic anterior wall desmoid tumor with intraabdominal growth is reported. During the procedure, it was difficult to mobilize and grasp the mass using the common laparoscopic instruments, but with the help of the "marionette trick," modified suture traction technique, the tumor could be removed easily using only three trocars. With four traction sutures minimizing the wall trauma, the trick made it possible to mobilize the mass in at least, seven directions, according to the principles of physical forces and vectors. This simple trick can be helpful for other common laparoscopic procedures, avoiding the insertion of sometimes ineffective instruments through more traumatic trocars.

Uremic encephalopathy: an updating.

Uremic encephalopathy (UE) is a clinical syndrome, closely linked to the progression of renal failure. Many approaches can be utilized to diagnose it: EEG changes, somatosensory evoked potentials, choice reaction time test, cerebrospinal fluid (CSF) studies, brain computerized tomography, plasma and CSF amino acid concentration. On the basis of the data available at present, it is possible to postulate that UE could be caused by amino acid derangements (mainly glutamine, glycine, aromatic and branched-chain amino acids) and by the subsequent imbalance of neurotransmitters (mainly GABA, dopamine, serotonin). Disturbances of mental, neurologic, motor and hormonal functions could derive.

Role of antigenemia assay in the early diagnosis and treatment of CMV infection in renal transplant patients.

AIM: CMV antigenemia by direct pp65 antigen detection and quantification was monitored on a weekly basis during the first 3 months after kidney transplantation. SUBJECTS AND METHODS: Preemptive therapy with ganciclovir was started according to the following criteria: any positive antigemia in CMV-NEG subjects, a single determination > or = 30 cell or a two fold increase of positive cells in two consecutive specimens in CMV-POS and continued until pp65 was cleared. Overall, 109 patients were monitored. RESULTS: Among the 24 CMV-NEG patients, 13 (54%) developed a pp65 positive assay without symptoms and were treated. Ten patients remained CMV-infection free and one patient developed late onset (7 months) CMV disease (hepatitis). Among the 85 POS patients 15 (17%) developed a pp65 positive assay and were treated. Two of them developed CMV disease within 7 days of the onset of positive antigenemia and 13 were asymptomatic. The other 70 patients remained CMV-infection free. The interval between transplant and the onset of CMV infection was 39 +/- 13 days in the CMV-NEG group and 64 +/- 20 days in the CMV-POS group (p < 0.001). The peak antigenemia level was 193 +/- 175 cells in the CMV-NEG group and 55+/- 78 cells in the CMV-POS group (p < 0.001). The duration of treatment did not differ in the two groups (22 +/- 7days). A second course of therapy, due to a relapse of asymptomatic infection was performed in 11/13 (85%) treated CMV-NEG patients and in 2/15 (13%) treated CMV-POS patients. CONCLUSIONS: Among the total 28 treated patients, we observed only 6 episodes of mild creatinine increase and 9 episodes of mild neutropenia. In the overall population, we observed 8 systemic infections not related to CMV.

Preliminary technical and clinical evaluation of a new hollow fiber dialyzer with a 5 microns thick cuprophan membrane.

In vitro and in vivo studies were performed on 10 dialyzers with 5 microns thick cuprophan membrane to evaluate hydraulic properties and permeability to solutes. Inlet and outlet pressures of the filter were measured at different blood flows to assess the resistance of the device and the end-to-end pressure drop. Hysolated ultrafiltration was performed to evaluate the spontaneous filtration at increasing blood flows, the ultrafiltration rate at different transmembrane pressures and, finally, the sieving coefficients for solutes. Standard hemodialysis was also performed to study the clearances throughout a 4-h session. During hysolated ultrafiltration the UF rate was increased up to 37 ml/min showing a very high hydraulic permeability of the membrane. The spontaneous filtration rates related to blood flow were quite low. Since the end-to-end pressure drop in the filter was also relatively low at high blood flow we may conclude that the geometry of the device is able to dissociate the influence of blood flow on the hydrostatic pressure inside the filter. This results in a easy modulation of the membrane permeability to water. Sievings were surprisingly high and clearances were stable along the dialysis session (BUN = 196 ml/min, creatinine = 161 ml/min and phosphate = 163 ml/min).

Acid-base balance on peritoneal dialysis.

Forty studies of acid-base balance during intermittent peritoneal dialysis (IPD) and during continuous ambulatory peritoneal dialysis (CAPD) were performed on 20 patients who were receiving IPD with acetate buffer (5 patients), IPD with lactate buffer (5 patients), CAPD with acetate buffer (5 patients) and CAPD with lactate buffer (5 patients). Measurements of acetate, lactate and pyruvate levels in blood and dialyzate were taken at different times during dialysis; blood samples for blood gas analysis were drawn at the same times. Calculations of the kinetics of acetate, lactate and bicarbonate during IPD and CAPD were carried out according to the method of Tolchin [1977] but modified for PD. Thus it was possible to quantify the balance of the buffers, their mass transfer rates, bicarbonate generation and the percentage of buffer converted to HCO3. IPD kinetics of acetate and lactate were found to be similar, the main difference being a lower and significant percentage conversion of lactate to bicarbonate (45%) compared to that of acetate to bicarbonate (71%) (P < 0.005). On CAPD the kinetics of the two buffers was quite different: while the serum lactate level was always low (mean 0.97 +/- 0.33 mM/l), the acetate level was always high (mean 5.12 +/- 3.34 mM/l). Thus the utilization of the two buffers during "acute intermittent" treatment (IPD) and "continuous" treatment (CAPD) is different. On IPD there are no important differences between the two buffers, whilst on CAPD lactate seems to be better and safer than acetate; for instance, serum HCO3 values are relatively constant with lactate (27.7 +/- 2.13 mM/l) while with acetate there is a trend to exceed physiological values (29.5 +/- 1.7 mM/l). When acetate is used in the dialyzate for CAPD the concentration must be less than 38.5 mM/l.

Pancreas transplantation in the rat using Lee's technique: a reliable model in experimental microsurgery.

Numerous unresolved problems, both technical and immunological, in pancreas transplantation stimulate experimental studies. Dogs have been routinely used in experimental studies but today rats are more commonly used. However, pancreas transplantation in the rat presents complex technical problems and requires a good knowledge of microsurgical techniques. In 1983 Squifflet undertook an experimental study aimed at evaluating the technical aspects of pancreas transplantation in the rat and calculating the success rates using different methods. The comparison of four methods revealed to our surprise that 100% of the rats operated on using Lee's technique had complications, with a 0% survival rate. In our study we report our experience using Lee's technique which we had the opportunity of mastering directly under the supervision of Professor Lee. We performed 100 pancreas transplantations using Lee's technique and divided our study in two phases. In the first phase we performed 70 pancreas transplantations and overall survival, after 1 week, was 42 rats (60%). In the second phase on 30 rats diabetes was induced by administering 70 mg/kg of streptozotocin. These 30 diabetic rats underwent pancreas transplantation and overall survival, after 1 week, was 25 (83.3%). We believe that our successful survival rates could probably be explained by the close collaboration between Lee and our department. Moreover, we noted the importance of constant training in obtaining better results, and in our opinion Lee's technique of pancreas transplantation is a reliable experimental model which can be used to resolve problems linked to pancreas transplantation.

Factors affecting bicarbonate transfer with bicarbonate-containing CAPD solution.

OBJECTIVE: To evaluate bicarbonate fluxes across the peritoneal membrane and bicarbonate gain in patients treated with continuous ambulatory peritoneal dialysis (CAPD) using dialysis solutions with different bicarbonate concentrations. PATIENTS AND DESIGN: Ninety-seven exchanges, using different dwell times and glucose and bicarbonate concentrations were performed in 43 stable CAPD patients. Dialysate effluent bicarbonate concentration and volumes were measured at different dwell times. Net dialytic bicarbonate gain was calculated. Patients' acid-base status was determined at the middle of the dwell. RESULTS: In prolonged dwells (6-12 hours) the dialysate effluent bicarbonate concentration correlated with arterial plasma bicarbonate concentration (F = 129, p < 0.0001), but not with ultrafiltration rate or dialysis solution bicarbonate concentration. In 4-hour dwells, effluent bicarbonate concentration correlated with both plasma bicarbonate concentration and ultrafiltration rate (F = 32.52, p < 0.0001 and F = 4.4, p < 0.05, respectively). The effluent bicarbonate concentration may be predicted from the patient's plasma bicarbonate concentration and net ultrafiltration rate for either a 4-hour or prolonged (6-12 hours) dwell time. Net bicarbonate gain by the patient correlated with ultrafiltration rate, plasma bicarbonate, and dialysis solution bicarbonate concentration (F = 100.56, p < 0.0001 at 4 hours and F = 108.08, p < 0.0001 at 6-12 hours), with the ultrafiltration rate being the predominant parameter. CONCLUSIONS: The effluent bicarbonate concentration is related to plasma bicarbonate concentration, with ultrafiltration playing a marginal role only during short dwells. However, the ultrafiltration rate has a profound effect on net patient bicarbonate gain. Multiple linear regression analysis allows the prediction of the effect of acid-base status, ultrafiltration, dwell time, and dialysis solution bicarbonate content on net patient bicarbonate gain. It seems that bicarbonate content in the CAPD dialysis solution should be progressively increased with increasing solution osmolality.