Thirst and xerostomia

One of the major problems we struggle with in haemodialysis patients is excess, volume, inter-dialytic weight gain and ultrafiltration. Despite constant reminders by nursing staff, physicians and nutritionists, patients seem to find it extremely hard to restrict their fluid intake to what we’d like it to be.


The reasons for this are variable and include social and cultural differences, habit, psychological diagnoses, medications and likely the very dialysis procedure itself by means of salt-loading. One of the clinical manifestations that is important to differentiate from thirst (a central mechanism driven by tonicity) is xerostomia (dry-mouth).


Xerostomia has a broad differential of possible causes and includes medications (particularly those with anti-cholinergic effects), anxiety, radiation therapy, connective tissue disease and rarely, autonomic disease. It is important to examine the long list of medications prescribed to our patients for possible culprits contributing to dry mouth and the excessive fluid intake that results from it.


I came across a small study of 43 HD patients followed for two years in Holland (not the most robust study, but interesting nonetheless). Unstimulated and chewing-stimulated 5 minute saliva collections were performed at baseline and at 2 years, along with a formal xerostomia inventory and thirst questionnaires. Then a formal dental examination was performed on each patient examining for decay, oral hygiene and periodontal disease.


Twenty patients were transplanted during follow-up. The most interesting finding was that those who were transplanted experienced an increase in salivary flow rate from 0.3ml/min to 0.44ml/min (p=0.002) and a decrease in thirst score from 10.6 to 8.1 (p=0.02); there were no significant changes over the 2 years for those who remained on dialysis. Also, there were no detectable differences in oral health between the 2 groups and the 2 time-points.


It’s possible that there is something peculiar about the state of ESKD that alters salivation and contributes to the symptom of dry mouth (supported by the observation of improvement after renal transplantation). Perhaps attention to the medication history and trying to distinguish the symptoms of thirst from dry-mouth may help us to help our patients in their ongoing battle with inter-dialytic weight gain.

The Secrets of Tassin

No, this is not the title of the next Dan Brown novel (although the quality of the writing may sometimes compare, you will not find phrases like “the famous man looked at the red cup” here). I’m referring to Tassin, France, a location famous in Nephrology circles for the fact that 95% of dialysis patients there achieve normotension without antihypertensive medication. Nephrologists in Tassin firmly believe in the importance of scrupulous attainment of dry weight (DW) using increased dialysis times. Maybe they have something to teach us.


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."

1. 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.
2. 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.
3. 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.
4. It is essential that all BP medications be tapered down and stopped early in the process. Otherwise it will be impossible to achieve DW.
5. 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.
6. 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.
7. 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.
8. 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).
9. 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).

The road to an accurate determination of DW is hard and long. Expect some lightheadedness, cramping and bouts of intense frustration. For the patient, it can be even worse. However, as a great man once said, “Everything is possible. The impossible just takes longer…”