Acute hypernatraemia during bicarbonate-buffered haemodialysis

Five patients on maintenance haemodialysis were exposed to varying degrees of hypernatric dialysate, leading to acute hypernatraemia (plasma sodium concentrations 158 mmol/l to 179 mmol/l). With the exception of one patient, who developed pulmonary oedema, symptoms were minimal and in each case hypernatraemia was corrected without residual complications. The hypernatric dialysate resulted from a granular and less soluble batch of sodium bicarbonate powder. The extra effort required to dissolve the powder caused CO2 to be shaken out of solution, producing sodium carbonate and raising the pH. Mixing calcium from the 'acid' concentrate with excess carbonate in the 'bicarbonate' concentrate led to rapid precipitation of calcium carbonate on the conductivity monitoring cells. Dialysate conductivity was incorrectly sensed as low by the coated conductivity cells, so that an increasing amount of 'acid' concentrate, with its accompanying electrolytes, was delivered to the patient. When the granular powder was ground to a fine powder, passed through a 125 microns sieve and gently dissolved, the machine operated normally. We recommend that sodium bicarbonate powder is supplied with a sieve size no greater than 125 microns, kept dry to prevent the formation of large crystals, and dissolved gently.