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AN INTRODUCTION TO CAPD

Shrirang Bichu

 
Patients with end stage renal failure (ESRF) require renal replacement therapy. The two main types of renal replacement therapies available are dialysis and kidney transplantation. Although transplantation is the best option, it may not be possible in all the patients for various reasons. In such patients in whom kidney transplantation is not possible and also in those who are awaiting transplant surgery, maintenance dialysis becomes essential. There are two types of dialysis therapies available. We all are familiar with haemodialysis. The other type is continuous ambulatory peritoneal dialysis or CAPD. An increasing number of patients in India are now opting for CAPD and hence I feel should know its basic oncepts. It has taken more than a century of painstaking research to make CAPD a successful treatment option. Ganter (1923) initiated several animal and human studies. Odel (1950) reviewed over a hundred patients treated with peritoneal dialysis between 1923 and 1948. Results were poor due to technical problems. In 1976, Popovich introduced the concept of CAPD which gained widespread popularity. Today about 20 per cent of the total world dialysis population is on CAPD.

Peritoneal dialysis is performed by introducing two to three litres of dialysis solution (dialysate) into the peritoneal cavity for three to four hours. By diffusion and ultrafiltration toxic materials from the blood move into the dialysate across the peritoneal membrane. This impure dialysate is then drained and fresh fiuid reinstilled. The dialysate is exchanged
(drained and reinstilled) 4-5 times a day. At night when the patient is in bed he still has dialysate in his peritoneal cavity. The metabolic wastes are thus excreted into the peritoneum continuously throughout the day and night. The patient is
ambulatory and can do his day to day work including attending office. Hence the name continuous ambulatory peritoneal dialysis. Once the patient opts for CAPD he has to have permanent Tenchoff catheter inserted in his peritoneal cavity by a specially trained surgeon. It has to be in the right position for free fiow of fiuid and for prevention of infection at the site where the catheter emerges out of the abdominal wall (exit site). Proper care of the catheter for the next few days until complete healing occurs is essential.

Following two weeks of the catheter insertion, the patient is trained to do the fiuid exchanges. The dialysate is marketed in plastic bags and the connecting system has various attachments to make the task of exchanging fluid user friendly. The main aim of the training is to keep the condition sterile and prevent peritonitis due to inadvertent introduction of organisms into the peritoneal cavity. The person is also taught to assess his body fiuid status and to use right dialysate concentration to get the right quantity of water out. Water removal from the body is essential part of dialysis treatment since most ESRF patients are oliguric and cannot excrete ingested fiuid.

Once the patient is fully trained to the satisfaction of the nephrologist he is allowed to do the exchanges on his own at home. He has to follow up regularly with his nephrologist, usually once a month. During this follow up changes are made in the dialysis prescription, if necessary.

CAPD has number of advantages over haemodialysis. The procedure does not require a machine, exchanges can be done at home or at work place, patient can make long distance travel and holiday plans, no strict dietary or fiuid restrictions are required and better blood pressure control is achieved. It is much better in patients with cardiovascular instability. It is the only option in patients with exhausted vascular haemodialysis assess sites. Diabetic patients can administer insulin intraperitoneally and the hypoglycaemic episodes are almost absent due to the dextrose content in the
dialysate. Unlike haemodialysis, there is no risk of cross infection with hepatitis B and C viruses. The prevalence of hepatitis B and C infection in haemodialysis population in India ranges between 20 per cent to as high as 60 per cent. These infected patients have an accelerated course leading to cirrhosis. In fact transplantation may have to be called off in those with chronic active hepatitis or cirrhosis. The long term success of transplantation is also jeopardized in patients with viral hepatitis. Finally, the hassles of travelling for many hours to and from the haemodialysis unit for patients
staying in remote areas is saved if they opt for CAPD. Particularly in children CAPD is preferred to haemodialysis.


Fig. 1 : An elderly man doing a CAPD exchange in his bathroom
CAPD should not be prescribed to patients who have had previous extensive abdominal surgeries and to those with stomas e.g. ileostomy, ureterostomy. It is relatively contraindicated in
psychotic, mentally retarded and blind patients unless they have motivated and dedicated attendants who are willing to take up the responsibility. Other relative contraindications include abdominal
hernias, severe airway disease, diverticulosis and chronic low backache. Some patients just do not want the daily hassle of performing the exchanges and are happy to visit the haemodialysis centre three times a week while remaining free for the rest of the time.
A few complications may arise in CAPD patients. Chief amongst these is peritonitis which can be prevented by following the instructions meticulously. Improvement in the connecting
systems has also brought down its incidence dramatically. In India, in early days, due to the dusty and unclean conditions there was unfounded fear of high incidence of peritonitis amongst the
nephrologists. Now it is clear that the incidence is no higher than that in the developed world. Most of the peritonitis episodes are easily treatable by intraperitoneal antibiotics but a few ones particularly resistant pseudomonas and fungal infections may
require removal of the catheter. One should know that the peritonitis is never as severe as surgical peritonitis since the peritoneal cavity is always filled with fiuid and gets washed with each exchange.

The other less serious complications include leaks, scrotal and labial swelling, catheter malfunctioning with infiow and outfiow obstruction, abdominal wall hernia and backache.

There have been many innovations and modifications in peritoneal dialysis. Many different types of connection sets and solutions are available. Details of these is beyond the scope of this article. Patients can change over from haemodialysis to CAPD and vice-versa. Thus for example, a patient who is on CAPD for two to three years may switch over to haemodialysis for one to two years, then have a transplant and on failure of the renal allograft may desire to go back on CAPD while awaiting a second transplant. Although CAPD is an excellent form of dialysis the major drawback is the exorbitant cost. It costs approximately Rs.40000 a month!! This includes the cost of dialysis, medicines and tests. Only
miniscule number of our patients can afford this sort of an expense. We really hope the cost of this excellent therapy comes down at least to a level at par to that of haemodialysis.
 

CHARMED BY ANGIOTENSIN-RECEPTOR BLOCKERS

`Candesartan in the treatment of chronic heart failure offers the opportunity to further reduce cardiovascular mortality in... our ageing population'

Despite the effectiveness of treatments for heart failure, such as angiotensin-converting-enzyme (ACE) inhibitors and b blockers, the prevalence of heart failure continues to rise. Angiotensin-II type 1-receptor blockers show potential as additional inhibitors of the renin-angiotensin-aldosterone system to improve outcomes for patients with heart failure. The CHARM investigators assessed the effects of the angiotensin-receptor blocker candesartan versus placebo in three subgroups of patients with heart failuer in separate trials - patients with low left-ventricular ejection fraction (LVEF) already taking (2548 patients) or intolerant to (2028 patients) ACE inhibitors, and patients with chronic heart failure but preserved LVEF (> 40%, 3023 patients). The primary composite outcome in all the studies was cardiovascular death or hospital admission for chronic heart failure. Overall, candesartan was generally well tolerated and significantly reduced cardiovascular deaths and hospital admissions for heart failure. Ejection fraction or treatment at baseline did not alter these effects. In the two ACE-inhibitor studies, candesartan had beneficial effects on the primary outcome, and in the preserved LVEF study, a moderate effect on hospital admissions for heart failure was noted. In an accompanying Commentary, Harvey White notes that, since a mortality reduction has not previously been observed among patients treated with angiotensin-receptor blockers, the CHARM findings will provoke debate about whether these drugs have a class effect. For patients, White comments that the consistency of the results lends support to the use of angiotensin-receptor blockers for patients who have low LVEF, in addition to other treatments for heart failure. For patients who have preserved LVEF, he suggests that this class of drug could be considered, but that further evidence of the treatment effects would be useful.


Lancet, 2003; 754, 759, 767, 772, 777.


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