Why do maintenance hemodialysis patients need to control their water intake? Before starting to prepare for long-term hemodialysis, physicians and nurses caution their patients and friends to control their water intake and not to gain more than 3 kg of weight between dialysis sessions. Some of our patient friends are very confused and think that they can easily dehydrate more than 3 kg each time by setting the hemodialysis machine parameters. Plus some patients with low urine output are very uncomfortable at the beginning after strictly controlling water intake. Therefore some of our patient friends gain 4 or 5 kg or even more before each hemodialysis. Then why is it necessary to control the weight gain? Actually, the change of weight in a short period of time mainly reflects the accumulation of water in the body. If you are already urine free and drink too much water, it will basically be retained in your body, leading to an excessive increase in intravascular volume load and significantly increasing the burden on your heart. The result is severe left heart insufficiency, even life-threatening, right before the next hemodialysis. Since the capillary refill rate, i.e., the rate at which extravascular water returns to the vasculature, is limited in each individual, it is approximately 0.25 ml/kg/min. If there is more weight gain between dialysis sessions, more dehydration per hour in order to reach the target weight, and when the refill rate is exceeded, dialysis hypotension may easily occur, and it may also cause adverse reactions such as limb cramps, muscle spasms, and post-dialysis weakness. Therefore, it is recommended that the hourly ultrafiltration should not exceed 1% of body weight, and each hemodialysis ultrafiltration should not exceed 4~5% of body weight. Assuming that the patient weighs 60 kg, dehydration should not exceed 3 kg per hemodialysis. If you still have some urine, that means the kidneys still have some residual function. Residual kidney function is important because the kidneys can excrete some medium-molecule toxins through urine, which are difficult to remove by ordinary hemodialysis, thus compensating to some extent for the lack of ordinary hemodialysis. If too much water is removed from each hemodialysis, the blood volume fluctuates too much and the hemodynamics are unstable, which is not conducive to the protection of residual kidney function and can easily lead to a significant decrease in urine output or even anuria. So, how can we better control water intake? Usually eat less thin rice, noodles, soups and fruits when eating, and eat more high-quality protein as well as dry rice. The amount of water intake can be different for each person, but generally the daily water intake is limited to urine volume plus 500 ml or less. The water intake can be slightly relaxed in summer when it is hot and you sweat a lot.