Traumatic Brain Injury & Neurocritical Care
You’ve just intubated your traumatic brain injury patient and the repeat pupil exam shows signs of herniation. In addition to your other interventions (e.g., Reverse Trendelenburg positioning, optimization of sedation/analgesia), do you reach for the hypertonic saline or mannitol as osmotherapy? What risks and benefits come with either therapy? And what’s the evidence behind it all?
The 2016 Berger-Pelletier meta-analysis found that hypertonic saline did not improve mortality, intracranial pressure, or functional outcome when compared to other solutions, including mannitol. It is the most recent and largest systematic review on osmotherapy in TBI.1 Hyperosmolar therapies like mannitol or hypertonic saline are thought to work by drawing CSF out of the cranium, reducing intracranial pressure.2 More recent data suggests the action is via reduction in blood viscosity with improved microcirculatory flow.1
Without clear evidence guiding therapy, the mechanistic properties of each agent are worth contemplating. Mannitol’s osmotic load transiently increases volume but may ultimately have adverse diuretic/hypovolemic effects. Remember, cerebral perfusion pressure is the difference between mean arterial pressure and intracranial pressure. Though there is no clear evidence of benefit over mannitol, hypertonic saline may not cause such massive diuresis/hypovolemia. Furthermore, monitoring effect / status may be easier as serial sodium levels can aim for levels between 145 mEq/L and 155 mEq/L.3
Given the paucity of high-quality data available for meta-analysis, the most recent Brain Trauma Foundation guidelines do not make significant progress from the prior 2007 guidelines, stating that there is insufficient evidence available to meet current standards for guideline development.4 In short, it is unclear if hypertonic or mannitol hyperosmolar therapy is better.
1. Carney N, Totten AM, Oʼreilly C, et al. Guidelines for the Management of Severe Traumatic Brain Injury, Fourth Edition. Neurosurgery. 2016
4. Brain Trauma Foundation American Association of Neurological Surgeons Congress of Neurological Surgeons. Guidelines for the management of severe traumatic brain injury: hyperosmolar therapy. J Neurotrauma 2007; 24(Suppl 1):S14-20.