What Is Spinal Shock? How Do I Know When It Is Over?
Spinal shock is a combination of areflexia/hyporeflexia and autonomic dysfunction that accompanies spinal cord injury. The initial hyporeflexia presents as a loss of both cutaneous and deep tendon reflexes below the level of injury accompanied by loss of sympathetic outflow, resulting in hypotension and bradycardia. Reflexes generally return in a specific pattern, with cutaneous reflexes generally returning before deep tendon reflexes.
Ko et al1 have described a specific pattern of reflex return with the delayed plantar reflex (DPR) returning first, followed by the bulbocavernosis (BC) and cremasteric (CR) reflexes, and finally the ankle and knee jerk reflexes (AJ, KJ). As mentioned previously, the first reflex to return is an abnormal delayed plantar reflex (DPR). The second reflex that returns is the bulbocavernosous reflex (BCR). This reflex is checked to determine the ending of spinal shock. A BCR is elicited by squeezing the penile glans or the clitoris and feeling for an involuntary contraction of the anus. Tugging on a foley catheter can also elicit this reflex. It generally returns 1 to 3 days after the injury.
Autonomic dysfunction is worse with higher levels of injury. In cervical spinal cord injuries, the sympathetic outflow is diminished with a persistent parasympathetic output by the vagus nerve, resulting in bradycardia and hypotension. This autonomic dysfunction generally persists for months, and there is evidence to suggest that there is always some level of abnormality. Sympathetic activity can still be present and mediated by the spinal cord distal to the level of injury. Because of this sympathetic/parasympathetic imbalance, patients with complete spinal cord injury can have hypertensive crisis resulting from an overdistended bladder or colon.2
Because of this continuum of events after a spinal cord injury, the definition of spinal shock itself and the end point are variable. A recent article by Ditunno et al3 describes spinal shock and the stages of reflexic recovery. This progression includes initial hyporeflexia (0 to 1 days), reflex return (1 to 3 days), early hyperreflexia (1 to 4 weeks), and late hypereflexia (1 to 12 months).3 In our institution, as in other level 1 trauma centers, we believe that spinal shock is at an end when the bulbocavernosus reflex returns.
1. Ko HY, Ditunno JF, Jr., Graziani V, et al. The pattern of reflex recovery during spinal shock. Spinal Cord. 1999;37:402-409.
2. Silver JR. Early autonomic dysreflexia. Spinal Cord. 2000;38:229-233.
3. Ditunno JF, Little JW, Tessler A, et al. Spinal shock revisited: a four-phase model. Spinal Cord. 2004;42:383-395.