Raised ICP,the hyperosmolar therapy..Part2..Mannitol VS Hypertonic saline

There is no clear evidence of superiority of either mannitol or hypertonic saline at reducing intracranial pressure. One small trial suggested mannitol was better, others have favored hypertonic saline. The absolute differences of effects between agents have been quite small in these studies.

If a ventricular drain is placed, CSF can be removed and intracranial pressure can be measured directly; this invasive approach carries a slight infection risk and has not been shown to improve outcomes.

If a direct-pressure monitoring device is not in place, the goal of hyperosmolar therapy is to either:

• Increase the serum osmolarity initially to a target of 300-320 mOsm/L. Calculate osmolarity by (2 x Na) + (glucose / 18) + (BUN / 3), or use an osmolarity calculator, or your lab’s true measured osmolality.
• Increase serum sodium to 145-150 mmol/L.

Both these methods work whether using mannitol (an osmotic diuretic that causes generalized dehydration and hypernatremia) or hypertonic saline (which increases sodium concentration directly).

Mannitol sig: 20% mannitol bolus 0.25-1.0 grams / kg body weight q. 2-4 hours; use higher doses in emergencies, lower doses for maintenance. Check osmolarity 20 minutes after infusion. If there is an osmolar gap between measured and calculated osmolarity, mannitol is still circulating; wait and check again.

Hypertonic saline sig includes boluses of either:

• 3% NaCl (513 mmol/L) bolus 150 ml;
• 7.5% NaCl (1283 mmol/L) bolus 75 ml;
• 23.4% NaCl (4008 mmol/L) bolus 30 ml

Use boluses; don’t use continuous infusions of 3%, the author advises; it doesn’t work as well.

Use the formula to determine the number of millimoles of sodium to infuse to achieve the 145-150 mmol/L serum Na goal:

sodium needed in mmol = (lean body weight in kg × 0.5 for a woman or 0.6 for a man) × (target sodium − current sodium in mmol/L).

Divide the result of this (# of mmol) by the concentration of your NaCl solution (in mmol/L) to get a total volume (L) to bolus in measured aliquots (see above).

Hypertonic saline greater than 3% concentration should be infused through a central line.