Neurogenic Shock

Neurogenic shock results from acute loss of sympathetic nervous system outflow, most commonly from traumatic spinal cord injury above the T6 level. The sympathetic nervous system exits the spinal cord from T1 through L2 (thoracolumbar outflow). When the cord is injured above this level, sympathetic signals to blood vessels and the heart are disrupted below the injury. This produces two hallmark features: (1) Massive vasodilation below the injury level due to unopposed parasympathetic tone, causing blood to pool in peripheral vasculature and reducing venous return (preload); (2) Bradycardia from loss of sympathetic cardiac accelerator fibers (T1-T4) leaving the vagus nerve (parasympathetic) unopposed on the heart. The combination of bradycardia + hypotension + warm dry skin is UNIQUE to neurogenic shock and distinguishes it from all other shock types (which present with tachycardia and cool clammy skin). Additional features include poikilothermia (inability to thermoregulate below the injury because sympathetic control of sweat glands and cutaneous blood flow is lost), priapism, and loss of motor/sensory function below the injury. Neurogenic shock must be differentiated from spinal shock, which is a neurological phenomenon...