Resumo

CENTELLAS TRISTAN, María Teresa et al. Assessing dry weight and body water using bioimpedance vector analysis compared to the traditional method. Enferm Nefrol [online]. 2013, vol.16, n.1, pp.15-21. ISSN 2255-3517.  https://dx.doi.org/10.4321/S2254-28842013000100003.

Introduction: Electrical bioimpedance can be used to establish the hydration and nutritional state in haemodialysis. Assessing the hydration status of patients is habitually done as a "clinical art" using the concept of "dry weight". There are few studies that examine the concordance between dry weight estimated clinically and the dry weight deduced post-bioimpedance analysis. Material and methods: 36 patients were studied (26 men and 10 women). Electrical bioimpedance vector analysis was performed before and 30' after midweek dialysis, measuring weight, total water and its distribution, phase angle, Na/K ratio, and the position of each patient's vector in the sphere normogram: percentiles 50.75 and 95. Dry weight was estimated according to the subjective assessment of the nephrologist, nurse and patient. Furthermore, in 12 stable patients the bioimpedance analysis continued for 4 weeks. Results: The age was 69.6±12.5 (r=29-89). Weight was 73.1±14.1 predialysis, and 70.4±13.6 postdialysis. Total body water was 24.7±2.8 L/m (53.7±8.2% of weight); 22.1±3.0 L (56.2±5.9% of weight) corresponded to extracellular water and 17.4±3.8 L/m to intracellular water. Following haemodialysis, total water fell to 22.8±2.4 L/m (51.8±8.6% of weight) (23.5±2.2 L in men; and 21.5±3 L in women) of which 19.6±2.5 L (54.3±5.8% of weight) corresponded to extracellular water and 16.7±3.3 to intracellular water. One man and 5 women exceeded the highest reference value. Posthaemodialysis weight was 70.4±13.6, slightly higher than the established dry weight: 70.2±13.4 (p=0.02). The phase angle was <4 in 9 patients (25%) and Na/K exchange in 13 patients (36%) was >1.2, indicating malnutrition. The study of the ellipses showed 58.3% (21 patients) in the 50^th percentile. The rest were distributed in the 75^th percentile of overhydration: 9 (25%) and in the 95^th percentile, 5 (13.8%). In the 12 patients on whom series of bioimpedance analyses were carried out over 4 weeks, the results showed variations of little significance from the parameters studied. Conclusions: Although bioimpedance provides more accurate knowledge on body hydric composition and on the distribution of water, the dry weight established by clinical estimate continues to be of great value. Bioimpedance helps to detect small sub-clinical changes which could be more relevant in the longer term. Bioimpedance objectively shows the malnutrition present in almost half of haemodialysis patients.

Palavras-chave : Bioimpedance; Dry weight; Haemodialysis.

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