Excess interdialytic sodium intake is not always dietary

Colin C. Geddes, Marion Houston, Lynne Pediani, Angela Munday and Y. Mun Woo

Renal Dialysis Unit Inverclyde Royal Hospital Greenock UK Email: colin.geddes.wg{at}northglasgow.scot.nhs.uk

Sir,

In recent reviews in this journal, Shaldon [1] and Tomson [2] both emphasise the importance of dietary sodium intake to achieve drug-free control of blood pressure and to limit interdialytic fluid gain. A patient attending our centre for haemodialysis illustrates this and emphasises the importance of considering medication as a significant source of sodium.

A 72-year-old female with end-stage chronic renal failure due to analgesic nephropathy who has been on thrice weekly hospital haemodialysis since January 2001 was admitted to a nursing home for long-term care in December 2001. She subsequently developed persistently high interdialytic fluid gains. The nursing home was contacted on several occasions and we were assured that the prescribed low sodium diet was being adhered to. In June 2002 we discovered that after admission to the nursing home her family practitioner had prescribed a regular combined analgesic in effervescent form (co-codamol; a combination of codeine and paracetamol). The preparation is soluble because of the presence of 18 mmol sodium bicarbonate in each tablet. She was receiving eight tablets per day in four divided doses (144 mmol sodium per day). After substituting the effervescent co-codamol with an insoluble analgesic the mean interdialytic weight gain reduced from 1.20 to 0.41 kg per day (P<0.0001; unpaired t-test) as shown in Figure 1Go. This is consistent with the notion that the sodium intake from the effervescent medication was driving the intake of an extra 800 ml of water per day to maintain extracellular sodium concentration. The average pre-dialysis mean arterial pressure in the same time period fell from 105.0 to 79.4 mmHg in the absence of any antihypertensive medication (P<0.0001).



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Fig. 1.  Interdialytic weight gain before (closed circles) and after (open circles) stopping regular effervescent analgesia.

 
The administration of a known quantity of sodium every day in a nursing home environment in this case provides a valuable demonstration of the message that interdialytic fluid gain will diminish if sodium intake is reduced. Patients with high interdialytic weight gains should be asked specifically about the intake of effervescent medications before being labelled ‘non-compliant’.

References

  1. Shaldon S. Dietary salt restriction and drug-free treatment of hypertension in ESRD patients: a largely abandoned therapy. Nephrol Dial Transplant2002; 17:1163–1165[Free Full Text]
  2. Tomson CRV. Advising dialysis patients to restrict fluid intake without restricting sodium intake is not based on evidence and is a waste of time. Nephrol Dial Transplant2001; 16:1538–1542[Free Full Text]




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