head injury

[dkduncan]

why should 5% dextrose water should not be administered to head injury patients?-----nurse Duncan R.N

[EmmaG, RN]

Think osmosis

Saline vs Colloid vs Dextrose

The brain is surrounded by a membrane separating it from the vascular space - the blood-brain barrier. This membrane will only allow water to pass through it. Therefore only fluid with the same concentration of sodium as plasma should be given intravenously. Otherwise, the plasma will become more dilute and water will pass from it into the brain, making the brain swell, and thus increase pressure further.

Normal Saline (0.9%) has a similar concentration of sodium and therefore is the fluid of choice for the brain. Colloid can be given if required to treat hypovolaemia due by major blood loss.

When Dextrose solutions in water (5% Dextrose, Dextrose 4%-Saline 0.18%) are given, the dextrose is metabolised leaving just the water or a very dilute saline solution. This "dilutes" the blood, reducing the concentration of sodium in the plasma. The water then passes into the brain where the concentration of sodium is higher. The brain then swells, and intracranial pressure will rise.