Management of sodium disorders during continuous haemofiltration

In patients with acute kidney injury and concomitant severe hyponatraemia or hypernatraemia, rapid correction of the serum Na+ concentration needs to be avoided. The present paper outlines the principles of how to adjust the Na+ concentration in the replacement fluid during continuous renal replacement therapy to prevent rapid changes of the serum Na+ concentration.


Introduction
Continuous venovenous haemofi ltration (CVVH) is an established treatment for patients with acute kidney injury. During CVVH, serum electrolyte concentrations tend to equilibrate with their concentrations in the replacement fl uid. Th e rate at which this happens depends on the diff erence in their concentrations between serum and replacement fl uid, and on the rate of treatment.
Patients presenting with acute kidney injury may have concomitant severe hyponatraemia or hypernatraemia. Over-rapid correction of the serum Na + concentration is associated with pontine myelinosis and/or cerebral oedema [1,2]. If CVVH is needed, the Na + concentration in the replacement fl uid (usually 140 mmol/l) needs to be adjusted in order to avoid rapid changes of the serum Na + concentration. In the present paper we provide some guidance on how to make these adjustments for CVVH. Th e same principle could be applied for continuous haemo dialysis or diafi ltration.

Acute kidney injury and hypernatraemia (Na + >155 mmol/l)
Free water hydration is the fi rst-line therapy if possible. If CVVH is necessary, the Na + concentration of the replacement fl uid should be increased by adding concentrated NaCl solution (Table 1).
Generally, it is not considered safe to lower the serum Na + concentration by more than 8 to 10 mmol/l over 24 hours, especially in the setting of chronic hypernatraemia [1]. Usually, a stepwise correction of the patient's serum Na + concentration is planned using replace ment fl uid made up to successively lower Na + concentrations.
If the serum Na + decreases by >2 mmol/l in 6 hours, either the rate of fi ltration should be decreased or the fl uid bags should be changed to bags with a higher Na + concentration.
Th e volumes of 30% NaCl added are small and will not aff ect the concentration of other electrolytes in the solution signifi cantly.

Acute kidney injury and hyponatraemia (Na + <125 mmol/l)
If CVVH is needed, the Na + concentration of the replacement fl uid should be reduced by adding sterile water (Table 2). Generally, it is not considered safe to increase the serum Na + concentration by more than 8 to 10 mmol/l over 24 hours, especially in chronic hyponatraemia [2]. Usually, a stepwise correction of the patient's serum Na + concentration is planned using replacement fl uid made up to successively higher Na + concentrations.
If the serum Na + concentration has increased by >2 mmol/l in 6 hours, either the rate of fi ltration should

Abstract
In patients with acute kidney injury and concomitant severe hyponatraemia or hypernatraemia, rapid correction of the serum Na + concentration needs to be avoided. The present paper outlines the principles of how to adjust the Na + concentration in the replacement fl uid during continuous renal replacement therapy to prevent rapid changes of the serum Na + concentration.  Final Na + concentration in replacement fl uid 140 mmol/l 145 mmol/l 150 mmol/l 155 mmol/l 160 mmol/l Eff ect of adding diff erent volumes of 30% NaCl (≈5 mmol/ml) to a 5 l bag of replacement fl uid containing a Na + concentration of 140 mmol/l. be decreased or the fl uid bags should be changed to bags with a lower Na + concentration. Th e concentration of bicarbonate and potassium in the fi nal solution will also be reduced, and the patient may need additional supplementation.