Continuous Ambulatory Peritoneal Dialysis

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Continuous Ambulatory Peritoneal Dialysis

Continuous ambulatory peritoneal dialysis (CAPD) is done to remove wastes, chemicals, and extra fluid from your body. During CAPD, a liquid called dialysate is put into your abdomen through a catheter (thin tube). The dialysate pulls wastes, chemicals, and extra fluid from your blood through the peritoneum. Thus, a typical CAPD patient could easily lose 132 to 198 mEq/day of sodium through the ultrafiltrate. A patient accus-tomed to restricted sodium intake during the course of chronic renal failure continues to consume a low-sodium diet during early periods of CAPD therapy.

 Consequently, CAPD patients become sodium depleted over the course of therapy due to a combination of dialysate sodium loss and restricted sodium intake. Initially, such sodium depletion is beneficial in controlling hypertension. Most CAPD patients require multiple antihypertensive agents for control of hypertension before starting CAPD, but gradually need fewer drugs and eventually discontinue needing drugs. This is the time to increase salt intake to minimize salt losses.

If dietary sodium intake is not increased, severe sodium depletion can lead to hypotension—especially in very compliant patients and with primary cardiac disease. Total body sodium depletion results in decreased vascular response to infusions of vasoconstrictor agents such as norepinephrine. Salt repletion in such patients results in restoration of the vascular pressor response, extracellular fluid volume, and blood pressure.

In certain CAPD patients, such as those with severe cardiac dysfunction, hypotension may occur readily after initiating CAPD. Surprisingly, many patients are asymptomatic despite a severe degree of hypotension. This degree of hypotension is possibly due to the lack of renin response from the native kidneys because most patients are functionally anephric.

 

In contrast, during peritoneal dialysis therapies (automated peritoneal dialysis, APD) with short-dwell exchanges of 1 to 2 hours, such as intermittent peritoneal dialysis (IPD), the dialysate sodium concentration decreases due to solute sieving and hypo-tonic ultrafiltration. This considerably diminishes sodium loss during the PD therapy. Consequently, hypertension control in patients on intermittent dialysis therapies is not as readily achieved.

 Most patients require continued fluid and dietary salt restriction, and many patients need severe salt restriction and medications to lower blood pressure. Hypotension, if it occurs, is generally transient as a result of rapid ultrafiltration during a dialysis session. The algorithm shown in Figure 45.1 depicts a systematic approach to a CAPD patient with hypotension.

CAPD is the abbreviation for continuous ambulatory peritoneal dialysis. Typically, patients manually infuse and drain 2 to 3 L of PD fluid three to four times a day. The PD fluid is allowed to dwell in the peritoneal cavity for a period of 4 to 6 hours per each of three daytime exchanges and 8 to 10 hours during the overnight exchange. Patients will usually carry PD fluid in the peritoneum continuously, 24 hours a day. Depending on the individual circumstance, a dry period may be allowed for reasons of patient comfort or convenience.

APD is the abbreviated term for automated peritoneal dialysis. This refers to use of a cycler (see Question 14) to assist in administration and drainage of PD fluid. Typically, this is utilized to administer several dialysis exchanges at night while the patient is sleeping, with a final filling of the abdomen in the morning before the patient disconnects from the device.

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With Regards,

David Paul

Editorial Assistant

Journal of Clinical Nephrology and Research