The publication of the National Cooperative Dialysis Study was a seminal moment in the history of Nephrology. It was on the basis of this RCT that dialysis time was deemed not to be an important predictor of outcomes (based on a p-value of 0.056), and the love affair with Kt/V(urea) effectively began. Nowadays, although Kt/V(urea) targets are slavishly met, hemodialysis patients continue to experience high rates of complications such as hypertension, LVH, CHF, hyperphosphatemia, malnutrition and death. Set this against the superior outcomes seen with longer treatments such as nocturnal HD, and you begin to wonder if they may be onto something in Tassin. There, longer dialysis times aren’t just instituted for their own sake; they permit the attainment of target dry weights that are almost impossible to reach in a shorter session i.e. it’s not the time that’s important, it’s what you do with it that matters. Here I’ll present some of their clinical pearls for achieving DW based on several review articles they have written on the subject:
First, a clinically meaningful definition of DW: “that body weight at the end of dialysis at which the patient can remain normotensive without antihypertensive medication, despite fluid accumulation, until the next dialysis.”
- At DW, a patient’s BP should remain in the normal range during the entire interdialytic period. If BP remains high after dialysis or is elevated before the next session, they are, by definition, above their DW.
- Dialysis session times of 5-6 hours are usually required, particularly when determining the DW for the first time. Trying to achieve the necessary ultrafiltration over a shorter time will cause hypotension and cramping, and lead to treatment failure.
- Go slowly! It takes 2-3 months to achieve DW in a new dialysis patient. During this time carefully controlled persistent UF and a strict low salt diet are used, while antihypertensive medications are weaned off entirely.
- It is essential that all BP medications be tapered down and stopped early in the process. Otherwise it will be impossible to achieve DW.
- Hypotension and cramping will often occur when nearing DW, and are a common cause of treatment failure. These symptoms do not indicate a patient has reached DW, rather the patient has hit their max refill capacity (Crit. lines predict hypotensive episodes, but do not assess dry weight for the same reasons). If a patient remains hypertensive while experiencing such symptoms, longer dialysis times are indicated to achieve UF goals.
- Be aware of the “lag phenomenon”. BP does not immediately change in response to changes in volume. Blood pressure may only normalize a few weeks after ECV has returned to normal.
- Do not wait for obvious signs of volume overload (oedema, hypertension, etc.). Pay attention to small signs such as headache or slight increase BP at the end of a session.
- Weight falls rapidly after initiating dialysis due to saline removal. However, as a rule of thumb, weight should return to pre-initiation levels after 1 year on dialysis due to muscle and fat build up, with BP now under control (see figure).
- In difficult cases, ambulatory blood pressure monitoring is an invaluable tool, as it gives the best estimate of the ‘true’ interdialytic BP (see point 1).