Epidurals, Ethics, and Expectations: Talking Risks and Benefits in Obstetric Anesthesia

A spinal cord injury at or above T7 (T5-T8, depending on reference) predisposes a patient to autonomic hyperreflexia. Autonomic hyperreflexia is typically first seen within four to six months of spinal cord injury and can continue to occur for years. With a stimulus below the level of the spinal cord injury lesion, intact lower motor neurons send an impulse up the spinal cord. However, this impulse is interrupted at the site of the spinal cord injury and unable to reach the cerebral cortex. This leads to an impaired feedback loop. However, the ascending signal reaches the thoracic sympathetic splanchnic nerves resulting in hypertension. This hypertension is recognized by the carotid sinus and aortic arch baroreceptors leading to a parasympathetic reflexive bradycardic response via the vagus nerve. No autonomic nervous system changes occur below the level of spinal cord injury since these signal pathways are also interrupted.