Fluid removal (ultrafiltration) during dialysis

Ultrafiltration can only be performed at a maximum rate of 10-15 ml/kg/hour:

• Assessment of residual urine output. It is essential that this is regularly recorded as it is a vital piece of information for guiding individualised fluid intake guidance. It should be measured within a month of commencing chronic haemodialysis and every six months thereafter. Furosemide should be used to help maintain urine output. In addition, nephrotoxic drugs should be avoided in patients with residual kidney functions
• Insensible loss (e.g. fluid lost through sweating and gastrointestinal loss) is approximately 750 ml/day. This may be greater in hot weather or in patients with higher than average activity levels. Individualised fluid intake guidance should be developed. In an anuric patients this generally amounts to a 1000 ml/day fluid restriction but will obviously depend on the patient's size. This can be increased in a patient passing urine. In general fluid intake should be such that fluid gained between dialysis sessions is 2 litres or less and always such that weigh gain is <5% between even  a 3 day break. Dietetic advice should be given with regards to low salt intake in addition,
• Calculated fluid removal should be based on patient's dry weight. However ultrafiltration rates should not be higher than 10-15 ml/kg/hour. This is often misquotes as "1 litre per hour" but of course will depend on the patient dry weight  (a 50kg patient is very different from a 120kg patient) and other co-morbidities affecting tolerance to rate of fluid removal
• Effective estimation of dry weght is important and should be reviewed regularly. This can be difficult and should be based upon blood venous pressure, peripheral oedema, any symptoms of pulmonary oedema and bioimpedance measures if available.
• If fluids removal results in hypotension or symptoms hypovolemia, above dry weight various methods can be utilised to aid adequate fluid removal
• If patient is still not be able to tolerate removal of gained fluid, then consideration should be given increased frequency of dialysis