Correction of Fluid, Electrolyte, and Acid-Base Derangements by Peritoneal Dialysis in Acute Kidney Injury

Physical Aspects

Once the decision is made to initiate PD, a prescription must be formulated on the basis of the particular clinical situation and therapeutic goals ( Table 182.1 ). The details of the therapy instituted, in addition to fluid balance, should be recorded meticulously on flow sheets to facilitate future decisions about the patient's PD regimen. The PD prescription should be reviewed frequently and appropriate adjustments made on the basis of the patient's clinical parameters and laboratory investigations.

The length and the technique of PD must be determined. Session length can vary greatly depending on the cause and duration of AKI as well as the presence or absence of underlying chronic kidney disease. The length of the dialysis sessions also depends on the goals of fluid and solute removal. PD can be performed intermittently or continuously, either manually or with an automated cycling device. Techniques available for the treatment of AKI include acute intermittent PD, continuous equilibrating peritoneal dialysis, and high-volume PD.

Other components of the dialysis prescription include determination of the appropriate exchange volume and the dwell time. The exchange volume is influenced by several factors, including technique of PD being used, concomitant medical problems such as the presence of hernias or respiratory disease, the estimated size of the patient's peritoneal cavity, and any noted leakage of dialysate around the PD catheter. For example, in acute intermittent PD, an exchange volume for an average-size person without respiratory failure may be 2 L, whereas in a larger patient, it may be as much as 3.5 L. On the other hand, an exchange volume for a small person with acute respiratory distress syndrome may be only 0.5 to 1.5 L to prevent compromise of diaphragmatic excursion and respirations. Dialysis solutions should be warmed to body temperature before infusion to avoid discomfort and to enhance solute transport. The temperature of the dialysate can be especially advantageous in the management of hyperthermia and hypothermia.

The inflow period is the time required to instill the dialysate into the peritoneal cavity. For manual exchanges, gravity is the primary determinant of this period, although the exchange volume, elevation of the dialysate bag, and presence of inflow resistance also play roles. To maximize the efficiency of PD, the inflow period must be kept to a minimum. A typical inflow period is 10 to 15 minutes. The outflow period is defined as the time needed to drain the peritoneal cavity of the effluent dialysate, which averages 20 to 30 minutes. This period consists of an initial fast segment lasting a few minutes, in which time approximately 80% of dialysate is drained; this segment is followed by a slower segment in which the remainder is emptied. Like the inflow period, the outflow period also must be kept to a minimum and is determined primarily by gravity. The time between the inflow and outflow period is referred to as the dwell time: the period in which the exchange volume remains in the peritoneal cavity. The standard dwell time for acute PD is approximately 30 minutes, the time in which the gradients for fluid and urea are most favorable. For continuous equilibrating PD, the usual dwell time ranges from 3 to 6 hours; for high-volume PD dwell times of various duration can be applied, but the total number of exchanges is divided over 24 hours during several days.