Solute and Water Transport during Continuous Arteriovenous Hemofiltration (CAVH)

The transport mechanisms governing solvent and solute removal during CAVH were elucidated on the basis of in vitro and in vivo observations.

Using a typical hemofilter (Diafilter D-20, AMICON), filtration rate rose with inlet blood flow rate until an asymptote was reached at blood flows of approximately 150 ml/min. The onset of the asymptote coincided with transition from a regime controlled by oncotic pressure (filtration pressure equilibrium), to one governed by simple Darcy's law filtration behaviour. Subsequent measurements showed that under clinical conditions, CAVH is generally in the pre-asymptotic regime and operates at filtration pressure equilibrium.

These observations offer the theoretical bases for a new design for CAVH hemofilters.

As a possible corollary, middle-molecule sieving coefficients were found to be stable with time during CAVH in vivo, whereas in chronic mechanical hemofiltration they declined significantly during clinical treatment. The sieving coefficients, however, were lower in mechanical hemofiltration from the beginning of the session.

These observations suggest that the measured sieving coefficient for a membrane is not necessarily a constant directly and solely related to the membrane standard reflection coefficient for a given solute. Concentration polarization and the ultrafiltration rate per unit of surface area may in fact have a major effect on the final concentration of solutes in the ultrafiltrate.

The “Ronco” Catheter for Continuous Flow Peritoneal Dialysis

To perform CFPD, a two way access must be available in order to allow continuous inflow and outflow of the solution. This is most likely achieved with a double lumen peritoneal catheter. To design a double lumen catheter does not necessarily mean to increase the size of the tube or to increase the discomfort of the patient. However, the real challenge is to find a design in which minimal re-circulation is experienced. The two tips of the catheter must be positioned such that a maximal exposure of the peritoneal surface to the fluid is guaranteed during one single passage of the fluid from one lumen to another.

Double lumen catheters with one short branch and another long of straight and of spiral shape were originally designed. Ash and coworkers have designed a catheter with a t-shape configuration in order to distantiate to the maximum the tips of the two lumens. Recently we have designed a novel catheter for CFPD equipped with a thin walled silicone diffuser used to gently diffuse the inflow dialysate into the peritoneum. The holes on the round tapered diffuser are positioned to allow dialysate to perpendicularly exit 360 degrees from the diffuser. The diffuser design and hole locations disperse the high-flow dialysate fluid at 360 degrees, reducing trauma to the peritoneal walls and allowing the dialysate to mix into the peritoneum. The dispersed fluid infused into the peritoneal cavity is then drained through the second lumen whose tip is placed into the lower Douglas cavity. The new catheter with diffuser is also equipped with a special removable hub that allows for easy creation of the subcutaneous tunnel without increasing the size of the skin exit site. The results so far achieved seems to offer advantages in terms of high flows, minimal pressure regimes and negligible recirculation.

The Vicenza “Short” Peritoneal Catheter: A Twenty Year Experience

Dislocation of peritoneal dialysis catheters is one of the major causes of technique failure. We evaluated 701 Vicenza catheters, implanted since 1985 in 365 males, mean age 53 ± 16 yrs, range 24 - 87, and 336 females, mean age 51 ± 17 yrs, range 21 - 82. The Vicenza catheter is defined “short” since it consists of a classic straight double cuff PD catheter having however an inner segment (the portion located in the peritoneal cavity) much shorter than any other type of catheter. It is implanted in the lower abdomen, just a few centimeters above the pubis. The analysis of our results obtained in a large PD population displayed good device survival at 2 and 5 years (94.3% and 91.5% respectively), a low dislocation rate (4%) and an exit-site infection rate similar to other double cuffed catheters. There was no selection of patients receiving this catheter since from 1985 we have used this catheter in every incident patient. Due to its lower implantation site this catheter demonstrates excellent wearability and good body image acceptance.

Controlling the alien hand through the mirror box. A single case study of alien hand syndrome

Disruption of motor control in the alien hand syndrome might result from a dissociation between intentions and sensory information. We hypothesized that voluntary motor control in this condition could improve by restoring the congruency between motor intentions and visual feedback. The present study shows that, in one patient with right alien hand syndrome, the use of a mirror box paradigm improved motor speed. We speculate that the visual feedback provided by the mirror increases the sense of congruence between intention and sensory feedback, leading to motor improvement.

[Health-related quality of life in patients with chronic kidney disease]

Assessment of quality of life in patients with different degrees of chronic kidney disease is an important issue because of its impact on clinical decisions and financial resource management in the health-care system. The aim of this study was to assess whether a generic instrument like the SF-36 questionnaire is able to discriminate three different populations of patients with different degrees of renal disease (pre-ESRD, ESRD, TxR). Five hundred sixty-three patients from 12 Italian nephrology units completed the SF-36 scales by themselves. The results from these samples were compared with those from the general population. Univariate analysis and multivariate regression were used. The generic SF-36 questionnaire proved to be a powerful instrument to discriminate populations with different degrees of chronic renal failure. The quality of life of patients on dialysis is significantly worse than that of the normal population and other patients with less severe renal function impairment.