Peritoneal dialysis

Dr Ejaz Ahmed

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Barrier to transport

• Mesothelium– Does not hinder transport

• Interstitium– Hinders transport to some extent

• Endothelium– Main barrier

Peritoneal transport principles

• Diffusion– Depends on concentration gradient

• Convection(filtration)– Depends on hydrostatic pressure and osmotic

pressure

Diffusion

• Dr=p×a×c

• Dr=diffusion rate• P=solute permeability• A=area of membrane• C=concentration gradient

Ultrafiltration

• UFr=p×a×(Hp+Op)

– UFr=ultrafiltration rate– P=permeability of water– A=surface area– Hp=hydrostatic pressure gradient– Op=osmotic pressure gradient

Material of catheter

• Silicone rubber– Milky white material

• Polyurethane– Clear material

Catheter design

• Three portions– Intraperitoneal– Extraperitoneal– External

• Cuffs– Dacron material– One or two

Placement of catheter

• Open surgical placement

• Peritoneoscopic placement

• Blind placement

Proper location of catheter

• Intraperitoneal portion– Directed towards pelvis

• Cuff– Deep: within medial or lateral border of rectus

sheath– Superficial: about 2 cms from skin exit

Sodium(mmol/L) 132-134

Potasium(mmol/L) 0-2

Calcium(mmol/L) 1.0-1.75

Magnesium(mmol/L) 0.25-0.75

Chloride(mmol/L) 95-106

Lactate(mmol/L) 35-40

Bicarbonate(mmol/L) 34

Bicarbonate/lactate 25/15

Glucose(g/dl) 1.36-4.25

lcodextrin(g/dl) 7.5

Amino acids(g/dl) 1.1

Composition of peritoneal dialysis fluid

Osmotic agents

• Low molecular weight– Glucose- 1.5%,2.5%,4.25%– Glycerol– Amino acids

• High molecular weight– Albumin– Glucose polymer– peptides

Clearance

• Theoretical concept• “Volume of plasma from which all the substance has been

removed and excreted into the urine per unit time”

Amount excreted = Urine volume x urine concentration

Excretion rate = Urine volume x urine concentration

Time

Clearance Example

Clearance of a substance x• Excretion rate = 100 mg/ml x 1 ml = 100 mg/min

1 minute• Concentration of substance x in plasma = 1 mg/ml• Amount of plasma cleared per minute =

100 mg/min = 100 ml

1 mg/ml

Clearance = U x V

T x P

Principles of Clearance

Principles of Clearance

Clearance of Inulin

Substance

(L/wk)

kidney H D

standard

H D

High flux

CAPD

Urea 750 130 130 70

Vit B12 1200 30 80 40

Inulin 1200 10 40 20

β2 Microg 1000 0 300 250

Small solute clearance

• Urea clearance (Kt/V)– Normalised to total body water

• Creatinine clearance (CrCl)– Normalised to body surface area

Total clearance

• Sum of– Residual renal clearance– Peritoneal dialysis clearance

Method of calculating dialysate clearance of urea

• 24 hr collection of peritoneal dialysate effluent

• Measure urea concentration in dialysate

• Estimate total urea content– Urea concentration × volume of effluent

• Calculate clearance– Kt = Urea content in dialysate

Serum urea level

Method of calculating renal clearance of urea

• Collect 24 hr urine

• Measure urea concentration in urine

• Estimate total urea content– Urea concentration × urine volume

• Calculate renal clearence of urea– Kt = Urea content in urine

serum urea level

Total and normalised clearance

• Total clearance– Dialysate clearance + renal clearance

• Normalised clearance (Kt/V)– Dialysate clearance + renal clearance

Total body water

Calculate clearance

• A 50 yr old man weighing 66 Kg has no urine output. He is on CAPD with four 2.5 L exchanges daily. His blood urea is 160 mg/dl and dialysate urea concentration of 24 hr collection is 140 mg/dl.calculate his daily clearance

Complications of peritoneal dialysis

• Mechanical complication of catheter– Catheter obstruction/inadequate drain– Perforation and laceration of organs– Peritoneal catheter leaks

• Infectious complications– Exit site infection– Peritonitis

Clinical presentation of peritonitis(percentages)

Cloudy fluid 98-100

Abdominal pain 67-97

Abdominal tenderness 62-79

Fever 34-36

Chills 18-23

Nausea 30-35

Vomiting 25-30

Diarrhoea 7-15

Route of entry for peritonitis

• Touch contamination

• Catheter related

• Enteric

• Haematogenous

• Gynaecological

Organisms causing peritonitis

• Gram-positive– Staphylococcus epidermidis– Staphylococcus aureus– Streptococcus– Enterococcus

• Gram-negative

• Fungal

• Mycobacterial

Differential diagnosis of cloudy effluent

• Infectious peritonitis

• Eosinophilic peritonitis

• Sclerosing peritonitis

• Chylous ascites

• Malignant ascites

• Pancreatitis

• Chemical peritonitis

Treatment of peritonitis

• Antibiotics– Intraperitoneal route

• Continuous• Intermitent

– Intravenous route

• Pain control

Outcome and sequelae

• Resolution-60-90%• Abscess formation-1%• Transfer to hemodialysis(technique failure)-30%• Sclerosing peritonitis-1-2%• Death-1-6%

Types of peritoneal dialysis

• Manual– CAPD-Continuous ambulatory peritoneal

dialysis

• Automated– CCPD-Continuous cyclic peritoneal dialysis– NIPD-Nocturnal intermittent peritoneal dialysis– TDP-Tidal peritoneal dialysis

TYPE Day

exchange

Night

exchange

Volume of exchange

CAPD 2-3 1-2 1-3

CCPD 1 3-4 1-3

NIPD 0 3-5 2-3

TDP 0 20 1-1.5

Peritoneal transport assessment

• PET test– Concentration of creatinine in dialysis solution

at four hrs– Concentration of creatinine in plasma at same

time– Ratio of dialysate creatinine to plasma

creatinine is calculated– Subject is classified into different transporter

group

Improving outcomes: equal or better survival in first 2–3 years

Better preservation of RRF versus HD

Higher haemoglobin levels; less erythropoietin use

Preservation of vascular access for HD

Provides continuous UF for improved blood pressure and volume control

Better outcomes post-transplant

Less risk of acquiring blood borne virus (hepatitis C)

Patient benefits including more flexible holidays and travel and higher employment rates; better quality of life than maintenance HD

Ability to expand patient numbers in a dialysis centre with limited need for resources and major capital investments

Lower staff to patient ratio than maintenance HD

Less costly than maintenance HD