Plasma ionized calcium in the critically ill on total parenteral nutrition.

Eight patients were monitored three times daily for 3 consecutive days. Plasma calcium fluctuated slightly, whereas phosphate varied more and in two patients fell below 0.08 mmol/I. Necessary calcium and phosphate supply for adults was estimated to be 0.15 and 0.25 mmol per kg body mass per day, respectively. Plasma ionized calcium could be estimated form total calcium, albumin and pH with a standard deviation of 0.05 mmol/l. This is 5 times higher than by direct measurement with a new combined pH-pCa electrode system.