(The original language of this article is French, and the graphs are shown from actual screenshots in the original language)
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Kidney failure is a pathology characterized by a progressive decrease in the kidney’s filtration capacity¹. Initially, therapeutic management aims to maintain kidney function; however, ultimately, the degradation becomes so significant that it is necessary to compensate for it through dialysis protocols² or kidney transplantation¹. One of the main consequences of kidney failure is a significant increase in fluid volume, particularly in the extracellular compartment³. The goal of dialysis is to replace the kidney by filtering the blood and removing excess water that cannot be eliminated normally by the kidneys. Therefore, it is necessary to 1) detect an excessively high fluid volume and/or fluid imbalance and 2) precisely calculate the volume of water to be removed during dialysis. In this context, bioimpedance analysis is a relevant tool for fluid monitoring during dialysis⁴, a use that will be studied in this case study.
| Sex | Female |
| Age | 82 years |
| Height | 158 cm |
| Weight | 52,10 kg |
| BMI | 20,07 kg/m2 |
| Pathologies | Kidney failure |
Pre-dialysis quick analysis
First, we can observe that this patient has an excess water volume of 2.37 L, which led to the decision to perform dialysis despite a seemingly normal fluid balance. We can also observe that this patient has a fat mass deficit of 4.80 kg and a skeletal muscle mass 200 g above her reference. Considering the age and pathology of this patient, these values seem consistent with a potential state of moderate malnutrition observed in patients with kidney failure⁵.
Hydratation
As mentioned earlier, this patient has a total water volume of 32.27 L, with an additional volume of 2.40 L, corresponding to a fat-free mass hydration rate of 79.18%, indicating an extremely overhydrated fat-free mass. We also observe an excess of 2.37 L when considering fat-free hydration, confirming the presence of an excessively high fluid volume in this patient. The small difference between the two values is mainly explained by her low fat mass percentage, as fat-free hydration corresponds to the total water volume minus the water contained in adipose tissue, which is approximately 15% of the total water volume.
Focusing on water balance, we observe that the majority of the water is at the intracellular level with 59.61% of the total water volume, while only 40.40% of this volume is in the extracellular space. This result is confirmed by the fat-free water balance measurement, where we observe a higher water volume at both the intra- and extracellular levels, with a predominance of intracellular water.
Active Cellular Mass, Fat-Free Dry Mass, and Fat Mass
In the quick analysis, fat mass and muscle mass data suggested slight malnutrition in this patient, so to verify this hypothesis, it is pertinent to focus on active cellular mass, fat-free dry mass, and fat mass at constant hydration. Although fat-free mass is recommended for malnutrition screening⁶, overhydration, particularly intracellular, can bias the interpretation of results. In this case, since this patient has significant intracellular overhydration, it is more relevant to use active cellular mass, which accounts for this phenomenon, allowing us to verify that she does not have malnutrition. Here, this patient has an active cellular mass 1.59 kg above her reference, but this value could be explained by cellular overhydration. However, it seems that active cellular mass is sufficient with normal hydration, partly confirmed by the fat-free dry mass, which does not show a reduction in the total amount of proteins and minerals. Thus, it appears that this patient does not have malnutrition. However, it should be noted that this patient’s fat mass remains relatively low compared to her reference, which could be a consequence of her pathology.
Post-dialysis Body Composition
Weight is a commonly used indicator to verify the volume of water removed during dialysis, assuming that weight variation is caused by changes in water volume. Here, we observe a loss of 2 kg of mass associated with a 2.7 L decrease in total water. These differences can be explained by several factors:
- This patient is in a nursing home, so weighing is not systematically performed before and after dialysis. In this case, the pre-dialysis weight corresponds to the weight measured at the last weighing, and the post-dialysis weight was estimated by the dialysis device. Therefore, these weight values may not be accurate compared to the patient’s actual weight.
- The bioimpedance measurement was performed directly at the end of dialysis, so the physiological changes induced by this intervention could also slightly modify the results obtained by bioimpedance analysis. Indeed, dialysis involves removing body water with a machine that then redistributes part of this water to the body to avoid too rapid volume changes for the organism. Therefore, it is a procedure that causes transient instability in water distribution, which can influence the results obtained.
Despite these differences, we can see that the variations observed in these two parameters go in the same direction with similar amplitudes. However, they highlight that it is necessary to perform measurements in individuals in a stable physiological state. In this case, it would be necessary to wait about ten minutes post-dialysis to perform the measurement.
Hydratation
Regarding hydration, we can observe that the total water volume is 29.58 L and a fat-free mass hydration of 76.80%, indicating that the volume of water removed would be insufficient to return to a normal hydration state. This observation is confirmed by the fat-free hydration, which remains 3.5% higher than an ideal hydration rate.
The water balance shows that the 2.7 L of water removed during dialysis is composed of 1.35 L of extracellular water and 1.33 L of intracellular water. If we analyze the fat-free water balance, we can observe a return to balance at the extracellular level, but the intracellular overhydration persists. Thus, it appears that the dialysis volume was calculated based on the extracellular volume, allowing a return to balance in this space but not in the intracellular space. This can be explained by the fact that the techniques commonly used to monitor the hydration state specifically measure the extracellular compartment⁴, thus omitting the intracellular space. Therefore, in this patient’s case, the return to normal at the extracellular level, combined with the physiological regulation of water balance, keeps part of the water in the intracellular space, resulting in overhydration.
Conclusion
This case study confirms that bioimpedance measurement is relevant in evaluating the dialysis volume and checking the hydration status of individuals post-dialysis, particularly regarding the balance between intra- and extracellular spaces. However, it is necessary to follow standard measurement conditions and perform them in individuals in a stable physiological state, especially after the dialysis protocol.
