Feline Peritoneal Dialysis1

Peritoneal dialysis (PD) is a medical technique that has been used to treat acute renal failure (ARF) in humans since 1923 (Boen, 1981).  PD has been, and is currently being utilised in the human and animal critical care context to remove systemic dialysable toxins (e.g. ethylene glycol (EG), ethanol, barbiturates, and salicylates), reduce severe metabolic derangements and treat severe conditions including: pancreatitis, peritonitis, uroabdomen, hypothermia, and hypervolaemia (Labato, 2000). Peritoneal dialysis is currently used world-wide to treat CRF in humans.

Renal transplantation is employed for CRF, in a limited capacity in veterinary medicine.  However, feline renal transplantation is associated with high complication rates, morbidity, mortality, and is prohibitively expensive for the vast majority of pet owners (Bernsteen et al., 1997). As treatment modalities, continuous ambulatory peritoneal dialysis (CAPD) and intermittent peritoneal dialysis (IPD) are rarely used in cats, presumably due to perceived technical difficulties. Thus, a dearth of data is available for IPD application in feline and canine CRF.  Until present, ARF has been the prevailing indication for dialysis in animals (Labato, 2001; Dzyban et al., 2000).  

Indications for IPD in veterinary medicine

Dialysis may be indicated in oliguric and anuric ARF, intoxication with dialysable substances such as ethylene glycol, systemic fluid overload, and in the decompensated CRF patient (Labato, 2001; 2000). Most animals with suspected ARF are treated in veterinary emergency medical centres.  Contemporary treatment includes a trial of IV fluid and diuretic therapy, dopamine if indicated, coupled with mannitol, dextran, or other plasma expanders, in cases of hypovolaemia (McClellan et al., 2006). The primary goal in companion animal ARF is to re-establish normal urine flow, of ≥ 2ml/kg/hr, and preclude prerenal azotaemia, prior to commencing dialysis (Ross, 2006). In cases of ARF and CRF which are refractory to fluid therapy: if the patient has hyperkalaemia, metabolic acidosis, and other metabolic derangements, these are addressed prior to placing the catheter for dialysis, which frequently requires general anaesthesia (GA) (McClellan et al., 2006). Several North American emergency veterinary hospitals and veterinary schools provide facilities for haemodialysis (HD) treatment of ARF, and CRF (Labato, 2001; Elliott, 2000; Hackner, 1998).  Dialysis is instituted in cases of ARF which are non-responsive to fluid, diuretic and renal vasodilatory therapy, after 12-24 hours (Hackner, 1998; Cowgill & Maretzki, 1995). 

Haemodialysis is prohibitively expensive for many clients and is associated with many medical complications in companion animals, including: septicaemia, right atrial thrombosis, chylothorax, bacteraemia, endocarditis, pulmonary oedema, ascites, and others (Langston, 2002; Cowgill & Elliott, 2000; Langston et al., 1997). The technique for veterinary PD has been described, though little information is available regarding IPD for CRF in companion animals. Complications have been reported infrequently, and the limited IPD data that has been documented has shown it to be successful in veterinary medicine, in treating both CRF and ARF (Labato, 2001; Labato, 2000; Lichtenberger & Kirby, 2000; Dzyban et al., 2000; Crisp et al., 1989; Rubin et al., 1983). 

Principles of Peritoneal Dialysis 

Peritoneal dialysis: the employment of the peritoneum surrounding the abdominal cavity as a dialysing membrane for the purpose of removing accumulated waste products or toxins.  In veterinary medicine, the main indication is acute, reversible renal failure.  Certain crystalloids such as urea, creatinine and electrolytes, and some drugs, such as the salicylates, bromides and barbiturates can be removed. Fluid equal in osmolarity and similar in chemical composition to normal body fluid is introduced to the peritoneal cavity via a catheter.  After a period of time (‘dwell time’) determined by the molecular weight of the substance being used as the dialysing solution the fluid is drained and the cycle repeated. -Professor D. Blood & Professor V. Studdert, 1994.

 On a fundamental level, dialysis is defined as the transfer of solutes across a semi-permeable membrane by the process of diffusion. The semi-permeable membrane in IPD is constituted by the parietal and visceral peritoneum. The transfer capacity and rate of a particle leaving the plasma and crossing the peritoneal membrane is dependent upon the size of the particle, the size of the pores in the peritoneum and vascular endothelium, the electrostatic charge of a molecule and stearic influence and / or hindrance and the composition of the dialysis solution (dialysate) in the peritoneal cavity (Scarpioni et al., 1978). The difference in chemical composition and osmolality between blood and the dialysate establishes a concentration gradient.  For any solute that can pass through the membrane pores, solute movement will occur from an area where it is present in high concentration to an area of lower concentration, via osmosis.  When there are equal amounts of solute in both plasma and dialysate, there is no additional net solute transfer (Sorkin & Nolph, 1981).

Dialysis solutions in contemporary feline CRF

Frequently, due to sterility, quality control and convenience, commercially available dialysates are utilised.  Some medical clinicians have experienced success creating their own dialysates, which are frequently composites of LRS and 1.5-4.5 % w/v dextrose.  The dextrose creates a hyperosmolar milieu, promoting mass motion of water across the peritoneum, or ultra filtration. High dextrose solutions are not indicated in IPD in dehydrated animals, as they exacerbate hypovolaemia (Labato, 2001).  Solutions containing 1.5% w/v dextrose are mildly hyperosmolar compared to feline plasma, and will cause some water to be removed from the patient.  These show the greatest promise for routine use in feline IPD, in which dehydration is a serious complication (Crisp et al., 1989). A 4.25 % w/v glucose dialysate has an osmolality of 486 mOsm/litre, which can quickly volume deplete the patient.  In the majority of human and veterinary IPD applications, 1.5% w/v dextrose containing solutions are considered appropriate (Labato, 2000).  Heparin, at doses of 500 to 1,000 IU is frequently added to each litre of dialysate, reducing clotting in the peritoneal catheter (Labato, 2001).

For a standard aseptic technique, all injection ports are scrubbed with a betadine solution. The transfer must be made aseptically to minimise the chance of contaminating the dialysate.  Parenteral antibiotics have been administered coincident with IPD in previous studies to prevent peritonitis (Labato, 2001). Most feline patients with renal failure have metabolic acidosis, and the lactate in commercial dialysis solutions specifically addresses the acid / base imbalance.

Dialysis technique

The volume of dialysate to be infused into the patient’s peritoneal cavity is dependent on body weight. From human data, the abdomen should be mildly distended; utilising an approximate dialysate volume of 30- 40 ml/kg (Labato, 2001; Sorkin & Nolph, 1981). In North American critical care facilities, in which PD is used for refractory ARF cases; PD is frequently performed with a commercial cycling machine which rapidly instills and removes small volumes of dialysate, several times an hour (Labato, 2000; Huxtable, 1998). Passive instillation and gravity dependent dialysate removal, as previously described, will be employed in this study.

Transfer of dialysate: mechanics & technique

Companion animal studies have shown that early in the course of dialysis, a rapid reduction in urea nitrogen, creatinine, and potassium is obtained by hourly exchanges of dialysate. Approximately 98% of urea (60 Daltons (Da)) and potassium (39 Da) equilibrate when the dialysate has been in the abdominal cavity for 60 minutes.  Creatinine (113 Da) and phosphate (95 Da), both larger molecules, are, intuitively and objectively equilibrated to 60-80% within 60 minutes (Sorkin & Nolph, 1981). The North American model of dialysate cycle frequency has been engineered on the basis of economics and labour factors (Labato, 2001). Too rapid a reduction in BUN can lead to dialysis disequilibrium syndrome, which is characterised by neurologic dysfunction (Parker, 1984). To change the dialysate, any clamps on the line must be opened, and the empty dialysis bag placed below the patient, allowing the dialysate to drain by gravity into the empty bag. With a well functioning intraperitoneal catheter, a litre of solution will drain within a period approximating 10 minutes, without requiring alteration of the patient's position.  Conversely, if the IPD catheter is partially or wholly obstructed, patient positional change is indicated to remove the used dialysate. Once the dialysate ceases flowing, the bag containing it is clamped at its neck, disposed of, and a new dialysate bag is attached to the catheter. The fresh dialysate is suspended above the patient to facilitate passive flow into the peritoneal cavity. The process is repeated. Each passively drained bag of dialysate is measured and weighed. Detailed patient data sheets must be meticulously maintained, to accurately assess the volume status of the patient.  The dialysis flow chart is to be utilised to direct the remainder of the patient's fluid therapy (Wilcox A., pers. comm., 2006).

Complications of IPD

The most common complication in both human and veterinary PD is hypoalbuminaemia (Crisp et al., 1989; Parker, 1984; Atkins et al., 1981; Thornhill, 1981). Major complications documented in veterinary PD literature include: peritonitis, subcutaneous leakage of dialysate, infection of the subcutaneous tract, and chronic malnutrition / poor healing / immunosuppression etc., associated with excessive loss of plasma proteins; albumin and globulins (Labato, 2001; Crisp et al., 1989; Thornhill et al., 1983; Atkins et al., 1981; Kaurczoglou et al., 1980). As most animals will attempt to chew out their catheter, IPD is the protocol elected in this study, as risk assessment of permanent catheter placement and maintenance show unfavourable outcomes, and potentiate serious medical complications (Labato, 2001; Dzyban et al., 2000). Given the commonality of hypoproteinaemia associated with human PD, it is advisable to monitor the feline patient’s serum proteins, and it may be necessary to increase the protein content of their diet to compensate for protein losses in the spent dialysate (Wilcox A, pers. comm., 2006; Labato, 2000, Nolph, 1979; Thomson et al., 1979). 

Each companion animal case is individualistic, and must be managed objectively at a holistic level, considering all historical, subjective, clinical, medical and pathological factors.

1. (C) Rebbecca Wilcox, 2007

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