Aug 18, 2015
A trauma patient with persistent, yet unexplained hypotension may be suffering from neurogenic shock. What's that? Anand Swaminathan joins the show to help break down the diagnosis and treatment.
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**Correction: the original title of this post was "spinal shock" which, of course, is a different entity than neurogenic shock. The term spinal shock is also used interchangibly with neurogenic shock during the conversation. The entity we are referring to in this show is indeed neurogenic, and not spinal shock.
Neurogenic shock is a form of distributive shock unique to patients with spinal cord injuries. Fewer than 20% of patients with a cervical cord injury have the classic diagnosis of neurogenic shock upon arrival to the emergency department, and it is a relatively uncommon form of shock overall (Guly, 2008). Patients with injuries at T4 or higher are most likely to be affected by neurogenic shock (Wing, 2008). It is caused by the loss of sympathetic tone to the nervous system, ultimately leading to an unopposed vagal tone (Stein, 2012). Many times the terms “spinal shock” and “neurogenic shock” are used interchangeably, although they are two separate entities. Spinal shock consists of the loss of sensation and motor function immediately following a spinal cord injury (Nacimiento, 1999). During this period of spinal shock, reflexes are depressed or absent distal to the site of the injury. Spinal shock may last for several hours to several weeks post injury (Nacimiento, 1999).
Symptoms of neurogenic shock consist of bradycardia and hypotension (Grigorean, 2009). Bradycardia is typically not present in other forms of shock, and may provide a clue to clinicians that a patient has sustained a spinal cord injury. However, emergency physicians should recognize that hemorrhagic shock needs to be first ruled out, even in patients with bradycardia, many patients with hemorrhagic shock are not tachycardic (Stein, 2012). Cardiac dysfunction is another feature of neurogenic shock, and patients may present with dysrhythmias following injury to the spinal cord (Grigorean, 2009).
The American Spinal Injury Association (ASIA) has classified injuries based on motor and sensory findings at the time of injury. ASIA A and B injuries are the worst; with A being a complete motor and sensory loss with no preserved function in the sacral segments S4-S5. ASIA B includes patients who have sacral sparing, meaning that they have function of S4 and S5 (Marino, 2003). Neurogenic shock is rarely encountered in the emergency department, however, it is important to recognize that almost 100% of patients who sustain complete motor cervical ASIA A or ASIA B injuries develop bradycardia. Thirty five percent of these patients ultimately require vasopressors, so management of neurogenic shock is imperative for emergency physicians (McKinley, 2006). There is no conclusive data regarding the optimal time to start vasopressors, however, it is important to maintain appropriate hemodynamic goals in patients with spinal cord injuries.
Hemodynamic goals in patients with spinal cord injuries are unique. A systolic blood pressure <90 mmHg must be corrected immediately (Muzevich, 2009). The American Association of Neurological Surgeons and the Congress of Neurological Surgeons Guidelines for the Acute Management of Spinal Cord Injuries both recommend a MAP at 85 to 90 mm Hg for the first seven days following a spinal cord injury based on observational descriptions of the hemodynamics in spinal cord injured patients (Levi, 1993; Licina, 2005).
Patients who are suspected of being in neurogenic shock should receive adequate fluid resuscitation prior to initiating vasopressors (Wing, 2008). However, there are no current recommendations regarding the first line vasopressor for neurogenic shock (Stein, 2012). Depending on a patient’s hemodynamics, this vasopressor will likely be norepinephrine, phenylephrine, or dopamine.
Norepinephrine is an excellent first line vasopressor in neurogenic shock due to its alpha and some beta activity, thus leading to its ability to improve blood pressure and heart rate (Stein, 2012). Phenylephrine is another common choice because it is easy to titrate and can be given through a peripheral line. A disadvantage of phenylephrine is the fact that it can lead to reflex bradycardia due to its lack of beta agonism. This drug may be most appropriate in patients who are not bradycardic (Wing, 2008). Dopamine is another option, however, it may lead to diuresis and ultimately worsened hypovolemia (Stein, 2012). It does have beta agonism, and in bradycardic patients may be favored over phenylephrine (Muzevich, 2009). Dopamine is unlikely to be tolerated in patients who are experiencing dysrhythmias.