Reply to Ravivarma Rao Panirselvam: Is 5% dextrose an effective osmole?

Reply to Ravivarma Rao Panirselvam: Is 5% dextrose an effective osmole?

E.S.Prakash, Editor, Medical Physiology Online, e-mail: medicalphysiologyonline@gmail.com

A 5% dextrose solution in water has roughly the same osmolality (280 mOsm/Kg H20) as that of normal human plasma. When small amounts of 5% dextrose solution are administered intravenously to an individual whose plasma osmolality is within normal limits, initially, there is little change in plasma osmolality; however, dextrose is taken up by cells and metabolized. Thus, the steady state effect is that of adding water which dilutes plasma [1]. Thus, some water would enter cells. This is why a 5% dextrose solution is used for replenishing intracellular fluid volume. In this instance, water flux across the cell membrane is not due to the restriction of dextrose on one side of the cell membrane – in other words, dextrose does not work as an effective osmole.

However in a diabetic with profound hyperglycemia (example, plasma glucose 400 mg/dL), the entry of glucose into cells is limited by the deficiency of insulin. In this instance, glucose in ECF would function as an effective osmole and bring about water shifts into the ECF resulting in intracellular dehydration.

The principle here is that glucose would function as an effective osmole if glucose transport into cells is a rate limiting step [2].

References:

[1] Ganong WF. Review of Medical Physiology, Mc Graw Hill, International edition, 2005.

[2] Davids MR. Lin SH, Edoute Y et al. Hyponatremia and hypoglycemia during laparoscopic surgery. Quarterly Journal of Medicine 2002; 95: 321 – 330.

Conflict of interests: none

This submission was not peer reviewed.