In PD the peritoneal cavity is used as a container for 2 to 2.5 liters of sterile, usually glucose-containing, dialysis fluid, which is exchanged four to five times daily by permanently indwelling catheter.
The peritoneal membrane, via the peritoneal capillaries, acts as an endogenous dialyzing membrane.
CAPD
PD is usually provided 24 h/day and 7 days/wk in the form of continuous ambulatory peritoneal dialysis
APD
sometimes also referred to as continuous cycling peritoneal dialysis (CCPD), in which nightly exchanges are delivered via an automatic PD cycler.
Absolute contraindications
If patients or their caregivers are competent to undertake PD
large diaphragmatic defects,
excessive peritoneal adhesions,
surgically uncorrectable abdominal hernias
acute ischemic or infectious bowel disease.
PD is best used for patients with some residual renal function, although anuric patients may do very well.
Most patients who start PD will eventually, after several years, transfer to other modalities of renal replacement therapy (RRT), such as hemodialysis (HD), if adequacy cannot be maintained or as a result of other complications, such as recurrent peritonitis or exit site or catheter problems.
Only rarely do HD patients transfer to PD, most commonly because of failure to maintain adequate vascular access.
Advantages of PD :
slow, physiologic removal of small solutes and body water
no vascular access
maintenance of residual renal function
Disadvantages
including increased workload for patients and families
increased risk for dyslipidemia
relatively high glucose load when glucose-based solutions are used
tendency to mild chronic volume overload.
Adult patients usually tolerate 2 to 2.5 liters of instilled volume, with larger volumes typically possible at night when the patient is supine.
an increased fill volume implies a more efficient exchange with regard to both small-solute exchange and UF, the latter being much more pronounced for hypertonic solutions.
In CAPD, 2 to 2.5 liters of dialysis fluid is instilled into the peritoneal cavity four or five times daily.
APD is usually performed with use of a cycler overnight (8 to 10 hours), during which large volumes (10 to 20 liters) can be exchanged. During daytime the APD patient usually has a so-called wet day—that is, a long dwell, usually with icodextrin as the osmotic agent in the dialysis fluid.
The exchange volume should be adjusted according to the patient’s size. Adult patients weighing less than 60 kg should start with 1.5-liter bags. The average patient (60 to 80 kg) should receive 2-liter exchanges, and for patients weighing more than 80 kg, 2.5 liters should be used.
The majority of PD fluids used today have the composition of a lactate-buffered, balanced salt solution devoid of potassium, with glucose (1.36% or 1.5%, 2.27% or 2.5%, 3.86% or 4.5%) as the osmotic agent. The K+ concentration in PD fluids is zero to aid control of potassium balance. Lactate is used as a buffer instead of bicarbonate, because bicarbonate and Ca2+ may precipitate (to form calcium carbonate) during storage. In current PD fluids the concentrations of Na+, Cl−, Ca2+, and Mg2+ are selected to be close to the serum concentration.
Glucose is the principal osmotic agent used for fluid removal (UF) in PD. Alternative commercially available osmotic agents are amino acids and icodextrin. icodextrin is preferable for long dwell exchanges, for example, overnight, and particularly for patients who tend to absorb glucose rapidly( fast transporters).
The net removal of solutes and fluid during PD, in excess of residual renal excretion, can be measured by evaluating the drained dialysate. For this purpose the concentrations of urea and creatinine are measured in dialysate and plasma. The dialysate-plasma concentration ratios (D/P) of either of these solutes multiplied by the daily drain volume gives the 24-hour clearance. Weekly creatinine and urea clearances are obtained by multiplying these figures by 7. For comparison among patients, creatinine clearance is conventionally standardized to body standard surface area (1.73 m2), and urea clearance (mostly for comparison with HD) is expressed as Kt/V (where Kt is the weekly clearance and V the volume of distribution of urea).
UF can be assessed with a 24-hour collection.
The PET yields approximate estimations of the rate of peritoneal transport of small solutes and of UF capacity.
1. Two liters (warm) 2.27% fluid instilled for 10 minutes with the patient supine and rolling from side to side every 2 minutes.
2. Exactly at 10 minutes after start of the infusion, 200 ml is drained into the bag. Draw 5 ml (discard); the next 5 ml taken for creatinine and glucose determination.
3.After 2 hours, new samples collected as in 3.
4. After 4 hours (exactly), collect drainage over 20 minutes. Note total bag weight. Subtract empty bag weight. Take samples (after mixing) for creatinine and glucose.
5.Glucose D/D0 (the ratio of dialysate glucose at 4 hours and at time zero) and creatinine D/P (the ration of dialysate and serum creatinine at 4 hours) are plotted versus time (as shown in Fig. 96.8). Record the total drain volume.
The night bag (8 to 12 hours) must be 1.36% or 2.27% glucose, drained for 20 minutes with patient sitting.
Rapid transporters:
increased peritoneal vascularity
transport small solutes quickly
losses glucose osmotic gradient quickly
problems with UF
PD peritonitis can lead to transient rapid transporter state due to increased inflammation
Management of rapid transporters :
reinforce salt and water restriction
use more hypertonic dialysate
icodextrin can be very helpful
push residual urine output ( diuretics )
APD with dry day or drain out at lunch ( if enough RRF )
once anuric, monitor closely for volume overload > transition to HD
slow transporters :
slow rate of small solute removal
better UF
Amount of UF depends on :
1) tonicity of dialysate : 4.25 % > 2.5 % > 1.25 %
2) duration of dialysate dwell : after osmotic equilibration, fluid starts to absorbed
3) peritoneal membrane permeability to glucose: osmotic gradient dissipates faster in more permeable membrane
UF Failure :
rule of 4 , failure to UF > 400 ml using 4.25 % dextrose bag after 4 hours dwell
Residual renal function
assessed by collecting all urine over a day and assessing the urine concentrations of urea and creatinine and total urine volume.
Because renal creatinine clearance, as a result of tubular secretion, yields an overestimate of the glomerular filtration rate (GFR) (by 1 to 2 ml/min) when the GFR is 10 ml/min or lower, and renal urea clearance yields an underestimate of GFR (by 1 to 2 ml/min) in the same interval of (reduced) GFR.
a good estimate of actual GFR can be calculated as the average of renal creatinine clearance and urea clearance.
weekly KT/V [combine renal + PD] > 1.7
weekly creatinine clearance above 50 l/1.73 m2
CAPD = multiple exchanges during the day + night dwell
APD = cycler at night with day dwell ( morning or evening )
CCPD = cycler at night + all day dwell
NIPD= cycler at night ( no day dwell )
increase clearance :
increase number of exchanges ( fast transporter)
increase volume/exchange( low or average transporter)
Increase UF :
increase dextrose concentration in dialysate
ESI :
prophylaxis: mupirocin or gentamicin topical exit site daily
(treatment : exit site infection, excluding tunnel and peritonitis) : clindamycin , tmp-smx, cephalexin = 2-3 w
BM : miralax 17 g d or lactulose 20 g tid or mineral oil enema
PD PERITONITIS :
PD effluent ( dialysate) after 2 hours dwell : cell count, differential , culture
effluent WBC > 100 cells/ul w > 50 % neutrophils
IP/IV vancomycin and Ceftazidime = 2 weeks
daily effluent counts
fluconazole prophylaxis
d/c gram negative coverage if culture is negative and improving effluent count
