By Peter Laird, MD
Dialysis patients know their monthly hemoglobin levels, albumen, phosphorus, potassium and Kt/V but today, ultrafiltration rates are not published for the patients to review and understand. Sadly, excessive ultrafiltration rates are one of the major sources of morbidity and mortality for dialysis patients, yet CMS does not require dialysis units to report these figures to patients. Many recent studies articulate the risks of taking off too much fluid too rapidly leading to myocardial ischemia and stunning.
Associations between UFR and All-cause and CV Mortality
Overall, 871 deaths occurred during 5,233 patient-years of at-risk time; 343 of these deaths were due to CV causes. The median survival time was 2.5 years. Compared with UFR ≤10 ml/h/kg, UFR >13 ml/h/kg was significantly associated with all-cause mortality: unadjusted hazard ratio (HR) (95% confidence interval (CI)) 1.20 (1.03–1.41) (Figure 1). When multivariable adjustment was used to account for baseline differences between groups, this association was greatly potentiated: HR (95% CI) 1.59 (1.29–1.96). UFR 10–13 ml/h/kg bore an intermediate association with CV mortality that was not statistically significant: adjusted HR (95% CI) 1.06 (0.87–1.28). Results were similar when UFRs following the long interdialytic break were excluded from consideration, when the referent group was restricted to participants with UFR 8–10 ml/h/kg (data not shown), and when flux and Kt/V treatment group assignments were included as covariates in the statistical model (Supplementary Table SA online).
The effect on mortality of ultrafiltration rates increase dramatically once it is above 10 ml/hour/kg. The calculation is quite easy to do. Using an example of a dialysis patient who weighs 70 kg, dialysis for 4 hours and takes off 2 liters of fluid, we have: 2000 ml/4hr/70 kg = 7.14 ml/hr/kg. However, if we look at a 70 kg patient who dialysis for 3 hours taking off 3 L of fluid, the calculation changes drastically: 3000 ml/3hr/70 kg = 14.3 ml/hr/kg. Shortening the dialysis time and increasing the amount of fluid taken off with ultrafiltration now places the patient in a higher risk of cardiac and all cause mortality.
In order to more fully examine the threshold(s) at which UFR may become harmful, we
conducted analyses in which we examined the association of UFR, represented as a cubic spline, with CV and all-cause mortality. As demonstrated in Figure 3, the HRs for both CV and all-cause mortality rose sharply at values between 10 and 14 ml/h/kg, and to a less pronounced degree at higher values. Consistent with results of the primary analysis, the HR for CV mortality was greater than that for all-cause mortality at all values of UFR.
Just as all dialysis patients receive a monthly report showing URR, Kt/V, Alb, Potassium, Phosphorus and Hemoglobin levels, I believe that the UFR should be a monthly reported matrix as well that should also be tied into the QIP measures. After all, having normal labs and an "adequate" Kt/V and normal URR are meaningless if the patient undergoes concurrent dialysis sessions with excessive ultrafiltration rates that patients can easily calculate for themselves in the comfort of their own homes. I was speaking with Rich Berkowitz earlier today about this issue and he decided to develop a UFR calculator which he has posted on Home Dialyzors United:
Research has proven there is a definite relationship between how much fluid is removed per hour per kilogram of weight. This simple calculation will allow you to easily see how you compare to the Adjusted Hazard Ratio per the graph below. You can link to the specific Kidney International research paper HERE.
If your ultrafiltration rates exceed 10 ml/hr/kg, then please discuss these issues with your medical team on how you can avoid excessive risk of cardiovascular and all cause mortality. In addition, if you have an excessively high untrafiltration rate, you are most likely also at risk of feeling nauseous, vomiting, experiencing severe leg cramps and at risk of passing out during dialysis. In addition, if your ultrafiltration rate is high, many nephrologists will place you on a "sodium modeling program" where they add salt to your cleansing fluids that most patients retain after dialysis leading to severe thirst and headaches. In many ways, excessive ultrafiltration rates not only increase your risk of death, they also add greatly to the burden of symptoms associated with dialysis.
There is a better way to do dialysis and it all starts with longer, slower and gentler dialysis regimens. Short, fast and violent dialysis sessions leave patients feeling drained and at increased risk of heart attacks, chronic damage to the heart and severe discomfort during dialysis. The simple answer is to reduce ultrafiltration rates so that they don't exceed 10 ml/hr/kg. This simple calculation could save your life and make your dialysis sessions easier to tolerate. If your UFR is elevated, you may want to discuss the issues in the Medscape article and consider modifying your dialysis prescription or consider home hemodialysis where daily treatments or nocturnal almost completely eliminate this problem.