Fluid and electrolyte replacement in renal failure

Acute kidney injury (AKI) (acute renal failure, ARF)

Prompt resuscitation can restore blood pressure and renal perfusion in the majority of patients with acute renal failure. See acute renal failure for further management.

Fluid and electrolyte replacement in dialysis-requiring inpatients

The usual principles apply – daily requirements = losses + approx 500ml (for insensible losses). In anuric patients without extra losses this may mean that they only require 500mls daily, and almost no sodium, though this can be hard for other wards and units to remember.

After an acute illness in which large amounts of fluid have been required, it may be necessary to remove large excesses of extracellular fluid. This may require prolonged periods of ultrafiltration and often daily treatments will be best. Remember that patients may have lost significant flesh weight and their new dry weight may be significantly lower than before the illness.

Sodium restriction is as important as ever once patients are euvolaemic again. Look out for sodium-containing drugs – antibiotics and soluble/effervescent medications are common culprits.

Click for Fluid prescription principles (Edinburgh and South East Scotland guide) … link to follow
Click for Revision of fluid compartments and daily requirements in health.

Potassium supplementation

Is rarely necessary in patients with advanced CKD. Transient hypokalaemia after haemodialysis does not usually require supplementation. If recurrent, best to alter the [K] of the dialysate. This is safer than supplementation. If potassium supplementation is required, give small amounts and re-check.

Calcium supplementation

Acute hypocalcaemia; 1.7mmol/L or below usually justifies its administration. Higher limits post-parathyroidectomy.

IV dosing

  • Calcium Gluconate 10%w/v = 2.25mmol Ca2+/10ml
  • Calcium Chloride 10%w/v = 6.8mmol Ca2+/10ml (3 times the calcium content of Ca gluconate)
  • 10-30ml Ca gluconate can be given as intravenous bolus over 3-6 minutes (up to 10ml CaCl2).  Use large vein or greater dilution; ECG monitor recommended.
  • Calcium infusion can be used for persistent hypocalcaemia.  Add 100mls of 10% Ca gluconate to 150ml 5% dextrose to give a solution containing just under 0.1mmol/ml.  Infuse at 20-40 ml/h (2-4mmol/h).
  • Too rapid administration can cause nausea, vomiting, dysrhythmias, flushing, peripheral vasodilation, hypotension
  • Normal ionised [Ca] is 1.1-1.4 mmol/l.  So dialyis with normal dialysate (Ca=1.5mmol/l) delivers a calcium infusion to a normocalcaemic or hypocalcaemic patient.

Oral Preparations
Sandocal 400 effervescent tablets – 10mmol Ca2+ per tablet
Sandocal 1000 effervescent tablets – 25mmol Ca2+ per tablet
Typically two tablets of Sandocal 400 (20mmol Ca2+) 2-3 times a day prescribed outwith meal times.  This is not enough for hungry bones post-parathyroidectomy – typical starting dose Sandocal 1000, 6 daily.

Phosphate supplementation

Phosphate <0.3mmol/L or risk factors for phosphate depletion present. Risk factors include haemodialysis and re-feeding sydnrome.
If phosphate 0.5 – 0.7mmol/L with no clinical evidence of deficiency then there is no need for phosphate administration.

CAUTION: Administering phosphate, especially IV, risks calcium phosphate crystal deposition in the kidney and elsewhere. Peaks in serum concentration have been recorded (and associated wth acute phosphate nephropathy) after oral or rectal admin of phosphate for bowel preparation in patients with even mild-moderately reduced GFR.

Oral Phosphate
Phosphate Sandoz® each tablet contains phosphate 16.1mmol, sodium 20.4mmmol, potassium 3.1mmol. Causes diarrhoea. Note high sodium.  4 – 6 tablets daily depending on severity of deficiency.

IV Phosphate
Phosphate Polyfusor ® 500ml contains:

  • Phosphate 50mmol (i.e., 1mmol per 10ml)
  • Potassium 9.5mmol
  • Sodium 81mmol

100ml (10mmol PO4) is a typical first dose. This would raise ECF PO4 concentrate of a 70kg person by 1.0 in the absence of losses/uptake. Too much is dangerous! More may be needed in transplant patients or others with excessive losses or very hungry cells.  Be cautious in the presence of renal impairment.  If giving more than this, give slowly eg over 12-24 hours.

Magnesium supplementation

Acute or severe hypomagnesemia

Recommended Dose
25mmol Mg2+ per day until corrected

IV Magnesium

  • Magnesium Sulphate 50%w/v = 500mg/ml = 2mmol Mg2+/ml
  • Magnesium Chloride 40.6%w/v = 406mg/ml = 2mmol Mg2+/ml
  • 25mmol Mg2+ (12.5ml) in 500ml Glucose 5% given over 12-24 hours

Oral Preparations

  • Magnesium Glycerophosphate tablets 500mg (approximately 2mmol Mg2+/tablet) are available on a Named Patient Basis.
  • Recommended Oral Administration – 2 to 4 tablets three times daily (i.e., 12 – 24mmmol Mg2+ daily)

Some patients experience gastrointestinal side effect with oral magnesium supplementation.