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Uf endnote download12/21/2023 ![]() One potential solution to the problem of size inequity in UF warning levels is to consider using the “raw” UF ( i.e., simply in terms of milliliter per hour). A similar size bias can be seen for the body mass index quintile rows ( Table 1). The magnitude of higher mortality risk was 1.165 for men in the two smaller quintiles of body surface area versus 1.265 for men in the two larger surface area quintiles for a “size inequity” factor of 1.265/1.1265=1.09. ![]() The higher mortality risk in larger versus smaller women is about 133/120=1.11, very similar to that when UF was scaled to body weight. In women, in the two smaller versus two larger quintiles of body surface area, the relative mortality risk of exceeding the UF warning value is 1.20 for the smaller women versus 1.33 for the larger women. Their data for body surface area–scaled UF rate show a similar pattern of body size inequity. ![]() ( 4) used a cutoff UF rate value on the basis of body surface area of 500 ml/h per meter 2. ( 4) for body surface area ( Table 1) are similar to those for body weight. ![]() What does this mean? It means that UF rate is not flagged in larger patients until their UF-associated incremental mortality risk is 11%–13% higher compared with the risk in lighter patients exceeding the same weight-based UF warning level. Again, the relative risk of exceeding the UF warning value in heavier versus lighter men is 129/114=1.13. However, in the highest two weight quintiles of men, exceeding the weight-scaled UF warning level is associated with a relative mortality risk of 1.29, very similar to the magnitude of higher risk in the two largest weight quintiles of women. For smaller men, again averaging the risk for the two lowest weight quintiles in Table 1, a relative mortality risk of 1.14 is observed when the 13–ml/h per kilogram UF warning level is exceeded. This means that by the time the UF cutoff is reached in larger women, the relative mortality risk compared with smaller women exceeding the warning level is about 129/116 or 1.11. For example, for body weight scaling where the warning level UF rate was 13 ml/h per kilogram, for smaller women, the mean relative risk of exceeding this level is 1.16, compared with 1.29 for larger women (highest two quintiles of body weight averaged). If one considers their data in Table 1 and averages the mean relative mortality risk in the lowest two quintiles of body weight versus the highest two quintiles, one finds that the change in mortality risk is higher in the heavier patients when the warning level UF rate is exceeded. ( 4) suggest that a UF rate warning value on the basis of any of these body size measures is not optimal. I would argue that the data by Flythe et al. ( 4) have responded to this suggestion by pointing out that mortality risk is higher with higher UF rates in both men and women of different body sizes and that this is true whether body size is expressed as postdialysis weight, body mass index, or body surface area ( Table 1). Daugirdas and Schneditz ( 3) have argued that, on the basis of physiologic measurements such as those related to blood volume, the UF rate might be better scaled to body surface area than to body weight. On the basis of observational data, guidelines and quality assurance metrics have been proposed, suggesting a maximum allowable UF rate, such as 13 ml/kg per hour, although it has been recognized that the higher mortality risk associated with UF rate might be more or less continuous. There have been no randomized trials examining this issue and very few interventional trials. These associations have been derived from observational dataset reports, with all of their known shortcomings. It is now well established that higher ultrafiltration (UF) rates during a hemodialysis session are associated with a higher propensity to intradialytic hypotension, cardiac stunning, and mortality ( 1, 2).
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