BLOOD AND DIALYSATE PUMPING AND FLOW SYSTEMS IN RENAL DIALYSIS: CURRENT AND PAST ISSUES
Researched by: Tarek Ghanameh
RIVEW OF BLOOD AND DIALYSATE CIRCULATION SYSTEMS:
The complete dialysis procedure lasts a multiple of weeks over three to four sessions a week, every appointment takes between 4 – 5 hours to be efficiently completed. The dialysis machine readjusts and balance back the levels of water and salts in the blood by functioning as a temporary replacement kidney. It is crucial for the system setup to be accurate in order to replace the kidney as if there is no kidney or such replacement at present, urea and other waste materials will aggregate in the blood causing an overload of harmful products in the blood that has a high chance of killing the patient. 1
The Dialysis machine has two main systems, The extracorporeal circuit tubes (alongside to its sub-systems of haemodialysis needles, a blood pump, blood thinners and a bubble trap) and the dialysis machine’s artificial kidney, the dialysate delivery system.
To understand the devices and systems more accurately, it is best to discuss them in the order of the haemodialysis procedure.
The first step of the haemodialysis procedure is when a vascular access site is created by numbing the area with local anaesthesia and creating an arteriovenous graft. The fist main system of the dialysis machine, the extracorporeal blood circuit, is used next. It is the system that is in charge of implementing the blood transport from the patient to the dialysis machine and back while simultaneously monitoring and maintaining the bloods flow rate. The extracorporeal circuit functions without harming the cell components of the blood or contaminating it from environmental microorganisms. All of the system’s devices are rigid, extremely compatible biologically, purified and sterilized before packaging and delivery to clinics and hospitals. 2
From the circuit, cannulation begins when two needles are inserted in the fistula (which is a direct link from the artery to the vein) or graft allowing blood access and circulation between the patient and the machine. The first needle which is known is the arterial needle is injected into the vascular domain which transport the blood from the patient to the dialysis machine, while the second venous needle transport the processed blood back to the patient. The second needle helps in removing any blood clots and aids the bubble chamber in clearing trapped air bubbles. 5
Extracorporeal circuit needles have multiple types, the sharp metal one is the most common in the United States of America. This type of needles is manufactured from stainless steel and has a thin layer of silicon for a finer injection and lower flow resistance. It is delivered in either a blunt or a sharp beg upon request. The sharp begs have fine cutting ends which are more efficient if the rope ladder technique was performed. On the other hand, blunt needles have rounded edges which makes them more suitable for the button-hole injection procedure. There is also very uncommon type of needles that has tip with a sharpness intensity that lies between the sharp and blunt needles. 4
Many doctors suggest the use of Angiocatheters for the initial injection sessions as they help in reducing the risk of infiltration by the arm behaviour while performing the dialysis session. It would be ideal to use Angiocatheters in every single session. However, due to expensive prices it is harder for every hospital and clinic to follow this procedure. 7
Fistula Cannula is another popular type of needles. This type is manufactured specially for haemodialysis and is made from razer-sharp metal that is coated by a plastic envelope. The metal section injects the arteriovenous fistula and aids the release of the plastic envelope to the vessel. 6
Choosing the right needle gauge is thought to related to the age and expansion of the arteriovenous fistula. The first injection is the one that requires extra care than the following injections as there are no special requirements for selecting the gauge. However, the one crucial requirement is that the gauge and the blood flow rate are equivalent. The larger the gauge, the smaller the resistance flow. Thus, a slow flow rate of 200-250 ml/min needs a lower gauge needle.
Needle length also plays a role in choosing the appropriate needle for the procedure. It relies on how deep is the targeted area for injection is from the surface of the skin. Patients with high body mass index requires a needle that is longer than the regular needle and vice versa. 8
A black eye is a necessity for the arterial needle to expand the blood flow. 9
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