Many studies and recommendations exist concerning the vasopressor choice in neurogenic shock, but most are Class III recommendations. No great prospective, randomized, placebo-controlled trials exist on the subject. Neurogenic shock usually presents with hypotension and a relative bradycardia after acute spinal cord injury, usually corresponding to a level of at least T6 or higher. You must be very careful not to automatically say a trauma patient who is tachycardic and hypotensive is in neurogenic shock, as patients with decompensated hemorrhagic shock will have the same vitals signs. Just because they’re not hemorrhaging externally in front of your eyes doesn’t mean they don’t have internal hemorrhage and it doesn’t mean there wasn’t a lot of blood at the scene of the injury!
There is no clear-cut favorite for choice of vasopressor, although most authors tend to lean toward norepinephrine or dopamine (remember dopamine is the precursor of norepinephrine and they both act on alpha-1 and beta-1 receptors). Some studies used dobutamine with good results as well. Vasopressin is not used because of the anti-diuretic effects, which can lead to water retention and hyponatremia. Phenylephrine acts only on alpha-1 receptors and can theoretically cause worsened hypotension by a reflexive bradycardia without another beta agonist on board. No matter which pressor you use, the goal for MAP is generally regarded to be 85 mmHg, although several studies have shown no mortality difference between MAP of < 85 mmHg and MAP of <90 mmHg. The goal is to have higher MAPs than other forms of shock in order to increase spinal perfusion.
Again, I can’t stress this enough…shock in a trauma patient should be presumed to be secondary to hemorrhage until proven otherwise. If you’re certain it’s neurogenic shock, then optimize BP with crystalloid fluids, followed by a pressor as above to increase your MAPs and increase spinal perfusion.
Muzevich KM, Volis SA. Role of vasopressor administration in patients with acute neurologic injury. Neurocritical Care. 11(1):112-9, 2009.
Ploumis A, Yadlapalli N, et al. A systematic review of the evidence supporting a role for vasopressor support in acute SCI. Spinal Cord. (2010) 48, 356–362
Stratman, Weisner, et al. Hemodynamic Management After Spinal Cord Injury. Orthopedics. March 2008;31(3):252.