What is Neurogenic Shock?
Injury to the cervical or thoracic spinal cord can produce neurogenic shock.
Neurogenic shock results from the malfunction of the autonomic nervous system in regulating blood vessel tone and cardiac output. Classically, neurogenic shock in the injured patient results in hypotension (low blood pressure), with normal skin color and temperature and an inappropriately slow heart rale that contrasts with hypovolemic shock.
In the healthy patient, blood pressure is maintained by the controlled release of catecholamines (epinephrine and norepinephrine) from the adrenal glands. Sensors in the aortic and carotid arteries monitor the blood pressure. Catecholamines cause constriction of the blood vessels, increase the heart rate and the strength of heart contraction, and stimulate sweat glands.
The brain and spinal cord signal the adrenal glands to release catecholamines to keep the blood pressure in the normal range. In pure hemorrhagic shock, these sensors detect the hypovolemic state and compensate by constricting the blood vessels and speeding the heart rate. The high levels of catecholamines cause pale skin, tachycardia and sweating.
The mechanism of shock from spinal cord injury is just the opposite. There is no significant blood loss, but the injury to the spinal cord destroys the ability of the brain to regulate the release of catecholamines from the adrenals (the spinal cord cable is cut), so no catecholamines are released.
When the levels of catecholamines drop, the blood vessels dilate causing the blood to pool. This drop in blood returning to the heart causes the blood pressure to fall.
The brain cannot correct this because it cannot get the message to the adrenal glands due to the spinal cord damage.
The patient with neurogenic shock can not show the signs of pale skin, tachycardia, and sweating beca use the cord injury prevents the release of catecholamines.
The multiple-trauma patient may have both neurogenic shock and hemorrhagic shock. Neurogenic shock is a diagnosis of exclusion after all other potential causes of shock have been ruled out.