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The cause of the uremic syndrome remains unknown; the success of dialysis therapy suggests that retained, dialyzable, but unidentified toxic solutes may play a role. Since chronic peritoneal dialysis seems to prevent or improve uremic neuropathy as well as does hemodialysis, it has been suggested that retained solutes of "middle molecular weight" (500 to 5000 daltons) may be major toxins. Only body fluid concentrations of these larger solutes are presumed to be reduced by peritoneal dialysis as well as with hemodialysis, whereas small solute concentrations are relatively poorly controlled. There have been numberous hemodialysis studies to examine the toxic potential of "middle molecules" as compared with that of smaller solutes. Although the importance of "middle molecules" as toxins remains unproved, numberous factors influencing their concentrations in body fluid have been discovered. Studies have also shown a surprising tolerance of patients to many variations in dialysis strategies. Difficulties in defining adequate dialysis have been intensified.

We initiated a therapeutic program of continuous ambulatory peritoneal dialysis for patients with chronic renal failure. Our program resulted in many episodes of peritonitis arising from contamination due to the technical aspects of the procedure. Microbiologic evaluation showed that 73% of 97 episodes were culture positive, with gram-positive organisms causing most of the cases, especially early in dialysis. Gram-negative rods tended to occur later. Gram stains of dialysate effluent resulted in a disappointingly low yield of only 9% positivity. Cell counts were a dependable indicator of the presence of peritoneal inflammation and also of therapeutic success. Most patients responded well to intraperitoneal cephalothin, 125 mg/L for 10 to 14 d. The occurrence of peritonitis resulted in 0.93 years of hospitalization during the total of 15.45 patient-years on dialysis, which essentially negated the financial advantages of this method of treatment of chronic renal failure. For this to be a successful mode of therapy, advances in the prevention of peritonitis must be made.

Remissions of long-standing psoriasis have been reported in patients starting either chronic hemodialysis or peritoneal dialysis for renal failure. To see if dialysis influences the course of psoriasis in the absence of renal failure, we selected three patients with severe, refractory, long-standing psoriasis to undergo weekly peritoneal dialysis treatments. Two began to improve after the first dialysis, with nearly complete resolution after four and nine treatments, respectively. The third patient showed no objective changes after four dialyses. These findings add to increasing anecdotal reports of psoriasis improving with dialysis and extend the observations to patients without renal disease.

Sham and real trials of peritoneal dialysis were carried out in a double-blind crossover study design to test the efficacy of peritoneal dialysis as a treatment for psoriasis. The criteria for patients included having severe plaque-type psoriasis unresponsive to all conventional therapy including methotrexate. Patients were randomly assigned to 4 weeks of sham or real dialysis, 8 weeks of observation, 4 weeks of alternative real or sham dialysis and 8 weeks of observation. Topical therapy was continued during the trial. Real dialysis was done for 48 hours weekly with 1.5-hour cycle times and 2-litre exchanges by machine. Sham peritoneal dialysis was done recycling the same 2 litres of 1.5% continuous ambulatory peritoneal dialysis fluid with 1.5-hour cycle times for 48 hours weekly. After real dialysis, two patients completely cleared, two patients had greater than 75% clearing, and one patient had no substantial response. None of the five patients had a response to the sham dialysis procedure (p less than 0.01).

The technique of continuous ambulatory peritoneal dialysis was evaluated in nine patients during 136 patient weeks. The major objectives were to see if continuous ambulatory peritoneal dialysis would provide [1] acceptable control of serum chemistries by usual criteria, [2] adequate removal of sodium and water, [3] tolerable protein losses, and [4] a low prevalence of peritonitis with episodes responsive to therapy with continuing continuous ambulatory peritoneal dialysis. Preliminary findings suggest continuous ambulatory peritoneal dialysis represents an effective ambulatory, portable, internal dialysis technique. Larger-solute clearances per week may approach values six times greater than with most hemodialysis techniques. Small-solute clearances approach dialysate flow rate (8.3 ml/min) and are comparable to other dialysis techniques on a weekly basis. Edema is readily controlled and protein losses should be tolerable with adequate protein intake. Peritonitus occurs on the average every 10 weeks but responds to therapy promptly with continuing continuous ambulatory peritoneal dialysis. If the prevalence of peritonitis can be reduced, continuous ambulatory peritoneal dialysis appears to represent a very attractive dialysis technique.

Three years of clinical experience with continuous ambulatory peritoneal dialysis are summarized. Serum urea nitrogen, creatinine, hematocrit, nerve conduction velocity, calcium, inorganic phosphorus, serum proteins, and electrolytes have been maintained in acceptable ranges. Peritonitis, although reduced in incidence because of solutions in plastic bags and a new adapter, is still a problem. Excessive carbohydrate absorption, obesity, and high serum triglyceride concentrations may be long-term problems in some patients.