Abstract

We inadvertently perpetuated a misconception about water requirements during parenteral nutrition. Concentrated glucose solutions containing as little as 75% water by volume should not lead to dehydration if all the glucose is catabolised, as the water produced is sufficient to bring their ‘effective’ water content to almost 100%.¹ If glucose is supplied faster than it can enter cells, plasma glucose rises and an osmotic diuresis may lead to dehydration.² If, however, more glucose enters cells (with the help of administered insulin if necessary) than can be catabolised, intracellular accumulation can lead to a state of intracellular overhydration clinically resembling dehydration. The two conditions should be distinguished:¹ extracellular dehydration requires fluid replacement, and intracellular overhydration calorie restriction. Calorie requirements are often overestimated, particularly in seriously ill patients, and too much can be harmful.³