The difference between hemofiltration and dialysis

With the progress of today's social life, many people have also suffered from uremia. However, with the advancement of medical care, uremia patients have more choices for dialysis methods, starting from hemodialysis to hemofiltration, and then to the current hemodialysis filtration. What are the differences in inheritance and development among these three? For the sake of health, it is necessary for us to understand them in detail.

Normal urine is produced mainly through glomerular filtration and tubular reabsorption and secretion. Blood filtration is designed to imitate the filtration principle of the nephron, but without the reabsorption function of the renal tubules. During the treatment, a large amount of fluid with similar composition to extracellular fluid needs to be supplemented to replace the function of the renal tubules.

The main difference between hemofiltration and hemodialysis is that hemofiltration removes solutes by convection, while hemodialysis removes solutes by diffusion. The former is similar to the principle of solute clearance by normal glomeruli, and has equal ability to clear medium and small molecular substances. However, hemodialysis has a better clearance rate for small molecular substances such as urea and creatinine, but a poorer clearance ability for medium molecular substances. The blood filtration method is to introduce the patient's arterial blood into a semipermeable membrane filter with good permeability and equivalent to the area of ​​the glomerular filtration membrane. Due to the transmembrane pressure gradient between the blood area and the outside of the membrane, when the blood passes through the filter, except for the formed elements such as proteins and cells in the plasma, water and most of the small and medium-sized molecules are filtered out, so as to achieve the therapeutic purpose of clearing excess water and solutes retained in the blood.

Hemofiltration is suitable for the following situations

1. Refractory hypertension: Patients with refractory hypertension that cannot be controlled by medication and hemodialysis will have their blood pressure return to normal after hemofiltration. This may be related to the removal of certain pressor substances in plasma during hemofiltration. It may also be related to the fact that the cardiovascular system and extracellular fluid are relatively stable during hemofiltration, which reduces the stimulation of the renin-angiotensin system.

2. Water retention and hypotension: For patients with water retention and hypotension, it is impossible to remove enough water through hemodialysis because hypotension and collapse occur early in the dialysis process. If these patients switch to hemofiltration, the symptoms of circulatory disorders will be significantly improved. The main advantage of hemofiltration is that it can remove large amounts of fluid without causing hypotension.

3. Hypervolemic heart failure: This type of heart failure often worsens during hemodialysis, but hemofiltration can alleviate or treat this type of heart failure because

①Hemofiltration can quickly remove excess water and reduce cardiac preload.

② Although dehydration is effective and reduces blood volume, it is isotonic dehydration, which increases peripheral vascular resistance and maintains blood pressure stability.

③ After clearing a large amount of water, the plasma albumin concentration increases relatively, which is beneficial for the surrounding tissue water to enter the blood vessels and reduce edema.

④ There is no need to use acetate dialysate, thus avoiding the vasodilation and inhibition of cardiac contractility caused by it. Due to the above advantages, hemofiltration is an effective treatment for patients with heart failure who are unresponsive to diuretics.

Although blood filtration has its advantages, it also has its disadvantages:

① Since a large amount of replacement fluid needs to be supplemented, the cost is high.

② Volume imbalance. If the filter does not have an automated volume balancing device and relies entirely on manual operation, either insufficient volume will cause hypotension, or excessive volume will increase the heart load.

③The clearance of small molecules is poorer than hemodialysis.