【Health Lecture】Hyperphosphatemia: The "silent killer" of dialysis patients

Hyperphosphatemia is a common complication of chronic kidney disease, especially end-stage renal disease. The incidence rate in dialysis patients is as high as over 80%. Hyperphosphatemia can significantly increase the incidence of vascular calcification and cardiovascular and cerebrovascular events in dialysis patients, and is a "silent killer" of chronic kidney disease patients. Therefore, strictly limiting blood phosphorus levels is an important guarantee for improving the quality of life of dialysis patients and prolonging their lives.

1. Causes of hyperphosphatemia

The blood phosphorus concentration of normal people is relatively stable. The normal range of serum phosphorus in adults is 0.87-1.45mmol/L. Hyperphosphatemia can be diagnosed when the blood phosphorus concentration exceeds 1.45mmol/L. Food intake is an important source of blood phosphorus, and excretion mainly depends on the kidneys. Excretion pathway of phosphorus: 30% is excreted by the intestines of normal people, and 70% is excreted by the kidneys. Due to decreased renal function, maintenance hemodialysis (MHD) patients will have insufficient excretion of phosphorus and retain it in the extracellular fluid, resulting in the accumulation of phosphorus in the body and the formation of hyperphosphatemia.

2. Target range for controlling hyperphosphatemia

The KDOGI guidelines recommend that blood phosphorus be controlled at 0.87-1.45mmol/L in hemodialysis patients. The consensus of Chinese experts recommends that blood phosphorus be controlled at 0.87-1.78mmol/L in hemodialysis patients. It is difficult for most patients with uremia to control blood phosphorus below 1.45mmol/L. The guidelines recommend that the target value for blood phosphorus in patients with end-stage renal disease undergoing maintenance dialysis treatment be 1.13-1.78mmol/L, and blood phosphorus levels should be monitored regularly.

How to control hyperphosphatemia

1. Diet: Phosphorus-restricted diet

(1) KDIGO guidelines recommend that daily phosphorus intake should not exceed 1000 mg, and try to choose foods with a low phosphorus/protein ratio. Foods with a phosphorus/protein ratio of >12 mg/g are "high-phosphorus foods", and foods with a phosphorus/protein ratio of <12 mg/g are "low-phosphorus foods". It should be noted that foods with a low phosphorus/protein ratio cannot be eaten at will. Patients with end-stage renal disease should eat any food in moderation.

(2) Reducing phosphorus through cooking: When boiling eggs, discard the egg yolk and eat the egg white; boil meat in water (discard the broth and eat the meat).

(3) Avoid consuming processed foods, food additives, preservatives, beverages, phosphorus-containing drugs, etc.

(4) Common foods high in phosphorus: nuts, beans, dairy products, grains, mushrooms, animal offal, etc.

2. Dialysis: Adequate dialysis

Too strict dietary control can easily lead to malnutrition, because protein is the main source of organic phosphorus. Although reducing protein intake can reduce phosphorus intake, the body's essential amino acids will also be reduced, leading to malnutrition. How can we ensure adequate dietary intake while controlling blood phosphorus? At this time, two other principles are involved, adequate dialysis (Dialysis) and the use of phosphorus-lowering drugs (Drugs). Patients who have entered dialysis need regular hemodialysis treatment. Regular dialysis (3 times a week, 4 hours each time) can remove 800-1000 mg of phosphorus, but it is not sufficient. At the same time, the use of high-flux dialysis membranes, increasing the number of dialysis times, and adjusting the dialysis mode (hemodiafiltration, hemoperfusion) can increase phosphorus removal to varying degrees. 3. Drug: Drug treatment

If the disease cannot be controlled by a restricted phosphorus diet and adequate dialysis treatment, it is necessary to take phosphate-lowering drugs. Therefore, it is very important for patients who have been on dialysis to cooperate with phosphate-lowering drugs. Patients who have not yet entered dialysis treatment need to cooperate with phosphate-lowering drugs due to toxin metabolism disorders. So how should phosphate-lowering drugs be selected and used? Existing phosphate binders mainly increase intestinal phosphorus excretion. Its mechanism of action is that the drug combines with phosphorus in food and is excreted with the stool, reducing the absorption of phosphorus by the intestine. Therefore, phosphate-lowering drugs are most effective when taken during meals. They cannot be taken on an empty stomach. Currently, phosphate-lowering drugs are divided into 4 types: aluminum-containing phosphate binders, calcium-containing phosphate binders, iron-containing phosphate binders, and calcium-free phosphate binders. The characteristics and methods of taking representative drugs are as follows: Hyperphosphatemia should be selected according to different blood phosphorus and blood calcium conditions of patients. Although they are all phosphate binders, the dosage and method of taking the drugs are different. The correct method of taking the drugs can achieve the best effect. For patients who still have persistent hyperphosphatemia and severe secondary hyperparathyroidism after 3D treatment, parathyroidectomy should be considered.

4. How to prevent hyperphosphatemia

1. Drink less "old-fashioned delicious soup". "Old-fashioned delicious soup" does not contain much nutrition, but contains a lot of purine, potassium and phosphorus. It is not conducive to controlling weight gain between dialysis sessions, so it is not advisable to drink too much.

2. Don't eat too much food containing food additives. Bad eating habits, such as eating snacks, drinking beverages, and heavy flavors, will cause the blood phosphorus level in the body to remain high. Kidney patients should "say goodbye to donuts, pearl milk tea, instant noodles, say goodbye to caffeine, and quit cola and greasy food."

3. Regularly monitor "electrolytes, PTH" Long-term hyperphosphatemia can lead to secondary hyperparathyroidism (SHPT). SHPT often occurs silently. When some people feel that there are signs in their bodies and go for a check-up, soft tissue and cardiovascular calcification may have occurred, which greatly increases the incidence of cardiovascular accidents. Kidney disease patients need to regularly monitor electrolytes and PTH, correct low calcium, high phosphorus, and high PTH early, and adjust the dosage of phosphorus-lowering drugs, vitamin D and its analogs, calcimimetics, etc. according to the test results. In short, if blood phosphorus is not controlled, it is easy to have skin itching, secondary hyperparathyroidism (promote bone mobilization and intestinal absorption of phosphorus, aggravate calcium and phosphorus metabolism disorders), cardiovascular calcification (increase in cardiovascular events and mortality), renal osteodystrophy (bone pain, fractures), etc., and severe cases can lead to disability or even death.

Therefore, it is very important to control blood phosphorus.

Unit: Shanghai Tongren Hospital

Image: Qianku.com

About the first author:

Li Fang, head nurse, college graduate, works in the hemodialysis room of Shanghai Tongren Hospital. She has been engaged in blood purification for more than 20 years and is good at blood purification nursing and arteriovenous fistula puncture for difficult patients.