DIALYSIS AND KIDNEY TRANSPLANTATION
AN INTRODUCTION TO HAEMODIALYSIS
INTRODUCTION D ialysis is a procedure for cleansing the blood using semi-permeable membranes to ?lter out waste elements. Dialysis is one of the options available to the renal failure patient in whom sustenance of useful and meaningful life is dependent upon renal replacement therapy. The availability of a form of therapy that can replace, albeit incompletely, the failed kidneys, is indeed a matter of considerable relief to the patient who stares deaths in the face. The advent of dialysis therapy has brought salvation to the ailing patient. This therapeutic modality has seen modi?cations and improvements over the years since its inception, making it a viable alternative. The innovations that have been incorporated have made one dream of a machine capable of providing individualized, need-based therapy. Sophisticated equipment now provide for safer and more effective haemodialysis. The rotating drum and the coil dialyzer have given way to the more compact, ef?cient hollow ?ber dialyzers. Long hours on dialysis have been substituted by more truncated dialysis sessions.
Dialysis therapy does not achieve total replacement of the kidney functions but functions incompletely, replacing the excretory function primarily - a ‘laundry’ job.
HAEMODIALYSIS In haemodialysis, blood is allowed to flow through a machine with a special device (dialyzer or filter) that removes wastes and extra fluids. The clean blood is then returned to the body. In haemodialysis, solute transport across the membrane pores, takes place through two different mechanisms: diffusion and ultrafiltration (convention). In diffusion, transport takes place along the concentration gradient whereas in ultra?ltration or convection transport, pressure differences across the membrane move water molecules or solvent.
Solutes that are small are swept along with the water in a process called solvent drag.
The haemodialysis procedure requires the following components:
1. A vascular access : a portal through which blood can be drawn from and returned to the individual’s systemic circulation. 2. A dialysis machine that pumps blood through the extracorporeal circulation, monitors and provides for safe dialysis, assists in waste and ?uid removal with features permitting control of the dialysis procedure. 3. The haemodialyser or arti?cial kidney which actually performs the cleansing process with removal wastes. The contemporary dialysers, comprise of membranes drawn into hollow ?bres which are externally bathed by a ?uid
of dialysate of appropriate composition so that the waste removal is achieved and appropriate corrective changes are brought about in the blood.
VASCULAR ACCESS The need for a vascular access may be either temporary (ranging from several hours to several weeks) or permanent (months to years). Temporary access involves percutaneous insertion of a cannula into a large vein (femoral, subclavian or jugular). These cannulae have either a single or a doublelumen (one lumen functions as the ‘arterial blood pathway that carries blood away from the body (vein) to the dialyser and the other ‘venous’ blood pathway returns blood to the blood stream. When one single lumen catheter is used for dialysis, the extracorporeal dialysis circuitry as well as the single patient dialysis system need to be adapted/modi?ed. Temporary access placement, has its share of complications which range from complications that arise at the time of catheter placement (haemorrhage due to puncture of neighbouring vessels, pneumothorax or haemothorax) or subsequently (infection, catheter clotting, vessel thrombosis or stricture). A newer access Permacath, constructed from silicone, incorporating a Dacron cuff and requiring either surgical or percutaneous placement technique, has become available. The subcutaneous Dacron cuff location lowers the infection rates and permits longer residence of the catheter at the implantation site. The Quinton- Scribner arteriovenous shunt has been rendered obsolete by the new venous cannulae mentioned above. The shunts, connecting externally the artery and the vein, are located in the forearm or just above the ankle. The disadvantage of this access is related to the fact that two good vessels need to be permanently sacri?ced. The shunt being external, infection, clotting and accidental dislodgement
of the shunt with exsanguinating haemorrhage is possible.
Permanent vascular access may be obtained by anastomosing the artery and the vein, usually the radial artery and cephalic vein subcutaneously in the forearm. Occasionally, such a ?stula is constructed more proximally between the brachial artery and the cephalic vein. The non-dominant arm is usually selected. Needles are placed in two arterialised veins to gain ‘access’ to the bloodstream in readying the patient for dialysis. Poor ?ows, thrombosis, ischaemia of the hand, oedema, pseudoaneurysm of the venous limb, infections and congestive heart failure (in large ?stulae) are observed complications. The native arteriovenous ?stula is the ?rst choice for permanent access placement. In instances wherein, a native AV fistula cannot be constructed (poor veins in forearm), it becomes necessary to use grafts (autogenous saphenous vein graft or PTFE grafts). The long term patency rates of grafts ismuch inferior to that of native AV ?stulae. These grafts may be placed in the forearm as either loop or straight grafts. Graft infection, stenosis and thrombosis, aneurysm or pseudoaneurysm, limb ischaemia, oedema and congestive heart failure may complicate matters. Dialysis Machines The modern dialysis machine comprises a blood pump, a dialysis solution delivery system and appropriate safety monitors. The blood pump aids in the circulation of blood in the extracorporeal circuit - from access site to dialyser and back to access. The appropriate dialysate is prepared within the machine using concentrate solutions admixed with treated and puri?ed water. The more sophisticated machine have facilities to modify the dialysate solution for individual patient needs. Dialysis machines can provide variable sodium, bicarbonate and on-line monitoring of dialysis delivered. The machine is also capable of determining the rate and quantity of ?uid removed during a dialysis session by varying pressures within the internal circuitry through strategically located pumps. Dialysis has become safer because of the built-in monitoring devices that monitor the temperature, rate of ?uid removal, the pressures, the presence of air in the blood circuit, the appropriateness of the dialysate and the occurrence of blood leak due to the loss of integrity of the dialyser. Haemodialyser The rotating drum, the coil dialyser, Kill dialyser, the plate dialyser have all given way to the contemporary dialyser - the hollow ?bre or capillary dialyser. The dialyser has two compartments: the blood compartment (blood passing through the capillary lumen) and the dialysate compartment wherein the dialysate flows. The outside of the hollow-?bres is bathed by the dialysate solution and exchange takes place across the hollow-?bres is bathed by the dialysate solution and exchange takes place across the hollow-fibre membrane. These hollow fibres, numbering thousands, are manufactured from materials which in initial days comprised cellulose-based materials but in recent times is made up of synthetic materials that are more biocompatible and efficient. Though the manufacturers label the product (dialyser) for ‘single-use only’, reuse of dialysers has been practised widely. The reuse practices have advantages and disadvantages. Though standardized, there needs to be quality control and quality assurance practices in place in the dialysis unit. The performance of various dialysers is available from the manufacturers. Choice of a dialyser (material, size, etc) can be individualized. Other requirements for Dialysis 1. Water for Dialysis : Dialysis water needs to be purified, rendered contaminant-free and sterile, pyrogen-free so that dialysis patients are not exposed to impure water that could produce long-term complications. AAMI (Association for the Advancement of Medical Instrumentation) standards have been prescribed for purity of haemodialysis water. 2. Dialysis solutions : Dialysis solution concentrates are broadly bicarbonate containing or acetate-containing. Minor modifications are possible and utilized in individuals requiring the same. 3. Anticoagulation : To maintain the ?uidity of the blood through the extracorporeal circulation, anticoagulants such as heparin are used. Heparin is administered either intermittently after an initial bolus injection or as a continuous infusion
using the heparin pump present on the dialysis machines. In patients with bleeding disorders, a regional anticoagulation may be practised. Regional heparinisation utilizing heparin-protamine or a regional citrate anticoagulation may be utilized. Another option in patients with a bleeding tendency is the intermittent saline flushes employed to clear the blood from the extracorporeal circuit intermittently and prevent clotting.
Dialysis prescriptions Prescriptions are determined for individual patients though some broad guidelines exist. The acute haemodialysis prescription differs from that of a chronic dialysis patient. Factors that are considered other than that mentioned above include, membrane size and efficiency, fluid removal, dialysate composition, anticoagulation and duration of dialysis. The duration of dialysis is usually 4 hours though shorter or longer dialysis sessions may be prescribed depending on the need, dialyser used etc. Dialysis prescriptions too may range from sessions twice a week to short daily dialysis, the common prescription being thrice a week. Compications on haemodialysis Complications could be encountered during or post dialysis, early after initiation of dialysis or late (after many years on dialysis). Hypotension, dialysis disequilibrium, cramps, nausea and vomiting, headache, chest pain, back pain, itching and fever and chills comprise the common complications on dialysis. Some of the complications are related to the dialyser reactions. Others may be due to ?uid shifts/removal, pyrogen reactions (contaminated dialysate). Less common complications include arrhythmias, cardiac tamponade, intracranial bleeding, seizures, haemolysis, air embolism, dialysis associated neutropenia and complement activation and dialysis associated hypoxaemia. In patients who have been on maintenance haemodialysis, bone disease, dialysis dementia, neuropathy, etc may occur. Quality-of-life on dialysis
The adequacy of dialysis may be monitored by periodic laboratory studies to calculate URR or Kt/V. Since dialysis incompletely replaces renal function, it becomes essential to provide for the unreplaced functions viz: active Vitamin D provision, erythropoietin use in addition to ?uid and diet controls, iron and vitamin supplements, antihypertensive medications, etc.
With adequate dialysis, disciplined lifestyles, rHuEPO administration, the quality of life patients has improved tremedously. However, one may query whether this could be ever achieved in the socioeconomic conditions existent today in our country.