Hypertonic saline is used to treat elevated intracranial pressure in children with traumatic brain injury.
What is it and how does it work?
Technically hypertonic saline is any sodium chloride solution with a greater concentration than normal saline (0.9%, which has 154 mEq/L of NaCl). Available concentrations include 3% (513 mEq/L), 5% (856 mEq/L) and 23.4% (4000 mEq/L). Believe it or not the blood brain barrier is very impermeable to sodium. Giving saline with a NaCl concentration far in excess of the plasma sodium will exert an osmotic effect that will help shift fluid out of the cranial vault – overcoming this baseline lack of permeability. This, can lower intracranial pressure. Aside form the osmotic effect there are also potential benefits on inhibiting inflammation, stimulation of atrial natriuretic peptide and increased cardiac output (maybe by restoring resting membrane potentials?). The effectiveness of hypertonic saline is greatest in the first hour then wanes a bit as sodium rapidly equilibrates across the blood brain barrier.
How do you give it?
There are various strategies and dosing regimens. The effective dose for acute usage – which is how you’ll use it in the Emergency Department on kids – is between 6.5 and 10 mL/kg. The dose I’ve used is:
In general you can expect 3% saline to increase serum sodium by 1 mEq/L for each mL/kg you give. Experts recommend aiming for a serum sodium of 155 mEq/L. You hit a ceiling in decreasing ICP once the serum sodium gets to ≥160 mEq/L. In ICU settings continuous infusions of 3% saline are given at a rate of 0.5 – 1.5 mL/kg/hr. This is in conjunction with ICP monitoring with a goal of <20 mmHg.
Three percent can be given through a peripheral IV. The higher concentrations may be more caustic and are better given through central venous access.
What’s the evidence?
This is by no means a complete listing of all studies on hypertonic saline – but I did limit the choices to humans, and display them here to illustrate some of the evidence, and also highlight that it isn’t quite “ironclad.” They are presented in chronological order.
J Neurosurg Anesthesiol. 1992 Jan;4(1):4-10.
This was a randomized controlled crossover trial of only 18 patients and compared 3% and 0.9% saline. ICP was compared over two hours following dosing and patients in the 3% arm had lower ICP and needed fewer “interventions” – thiopental and hyperventilation. A serum sodium increase of approximately 7 mEq/L was noted in the 3% group. The authors did not control for many confounding variables unfortunately.
A prospective, randomized, and controlled study of fluid management in children with severe head injury: lactated Ringer’s solution versus hypertonic saline
Simma B, Burger R, Falk M, Sacher P, Fanconi S.
Crit Care Med. 1998 Jul;26(7):1265-70.
A randomized controlled trial of 35 patients that compared lactated ringers (a hypotonic solution) with hypertonic saline (1.7%) as a continuous infusion over 3 days. The outcomes included ICP, cerebral perfusion pressure, need for other interventions, fluid requirements, intensive care unit length of stay and survival rate. Unfortunately this study was not blinded, but it did show the following;
- No difference between groups in survival rate and length of hospital stay
- Hypertonic saline required fewer interventions to maintain ICP control (p=0.01)
- Hypertonic saline had shorter length of ICU stay (p= 0.04)
- Hypertonic saline had shorter duration of mechanical ventilation (p =0.10)
- Hypertonic saline had fewer complications (p=0.09 for ≥2 complications)
Peterson B, Khanna S, Fisher B, Marshall L.
Critical Care Medicine, 2000
This was a retrospective chart review of 68 patients who received continuous hypertonic saline infusions to reduce ICP by ≤20 mmHg. The authors noted a higher survival rate than expected by injury severity scores (they predicted 41% but 58% survived) and did not see what at the time was called central pontine myelinosis (osmotic demyelination syndrome), subarachnoid hemorrhage or rebound ICP increases.
Use of hypertonic saline in the treatment of severe refractory posttraumatic intracranial hypertension in pediatric traumatic brain injury
Khanna S, Davis D, Peterson B, Fisher B, Tung H, O’Quigley J, Deutsch R.
Critical Care Medicine, 2000
A prospective study of 10 children with elevated ICP resistant to conventional therapy (HOB 30 degrees, normothermia, sedation/analgesia/paralysis etc,.). Children got continuous infusion of 3% saline to keep ICP <20 mmHg. The authors noted a “statistically significant decrease in ICP spike frequency at 6, 12, 24, 48, and 72 hrs (p < .01).” Two of the ten patients developed acute renal failure – but this was also because they were both septic. Ultimately this study is harder to interpret in the context of the ED, since it was focused on patients refractory to other interventions.