Cervical Spinal Cord Injury and Hypotension
High cervical spinal cord transection (above C5-C6) causes hypotension through disruption of descending sympathetic pathways, not through a specific "cervical nerve" per se, but rather through interruption of sympathetic outflow from the brain to the spinal sympathetic neurons. 1
Mechanism of Hypotension in Cervical Cord Injury
The pathophysiology involves loss of supraspinal control over sympathetic nervous system activity when the cervical spinal cord is transected or injured at high levels:
Tetraplegic patients with high cervical cord transection develop sympathetic impairment and postural hypotension due to interruption of descending sympathetic pathways from the brain to spinal sympathetic neurons 1
The rostroventral lateral medulla (RVLM) normally interacts with cervical spinal cord neurons to regulate sympathetic activity, including renal sympathetic activity and blood pressure control 2
When this connection is severed by high cervical injury, patients lose the ability to mount appropriate sympathetic responses to maintain blood pressure during positional changes, exercise, and food ingestion 1
Clinical Manifestations
Cervical spinal cord injury above the sympathetic outflow (T1-L2) produces:
Postural hypotension that is less severe than in chronic autonomic failure because compensatory hormonal mechanisms partially compensate 1
Paradoxical paroxysmal hypertension due to increased spinal sympathetic reflex activity below the lesion, occurring because descending inhibitory pathways from the brain are severed 1
Loss of blood pressure regulation during head-up tilt, exercise, and food ingestion - stimuli that normally activate sympathetic efferent nerves 1
Blood Pressure Management in Acute Cervical Spinal Cord Injury
For acute cervical spinal cord injury, maintain mean arterial pressure (MAP) >85 mmHg continuously during the acute phase to optimize neurological outcomes and reduce mortality 3
Use continuous arterial catheter monitoring because MAP falls below target approximately 25% of the time without close monitoring 3
The correlation between MAP and neurological improvement is strongest in the first 2-3 days after admission 3
Fluid administration is first-line treatment for acute hypotension before initiating vasopressors in patients without contraindications 3
Important Distinction
There is no single "cervical nerve" that causes low blood pressure. Rather, high cervical spinal cord injury disrupts the descending sympathetic control pathways that travel through the cervical cord to reach sympathetic preganglionic neurons in the thoracolumbar spinal cord (T1-L2), which then project to peripheral sympathetic ganglia including the superior cervical ganglion 1, 4