The fallibility of the
T6
neurological level of injury for determining autonomic dysreflexia risk
Ryan Solinsky, Kimberly Hareland, Sungchul Huh, Brittany Snider, Daniel Veith Abstract
Background
The T6 neurological level of spinal cord injury (SCI) is classically taught as differentiating who is and is not at risk for autonomic dysreflexia (AD); yet the reliability of this metric has rarely been tested.
Objectives
To determine how often individuals with SCI above and below the T6 neurological level of injury (NLI) experience symptomatic AD, quantify AD in the autonomic physiology laboratory, and describe underlying mechanisms that clinically manifest.
Design
Cross‐sectional.
Setting
Academic medical center.
Participants
138 individuals with/without SCI.
Interventions
Not applicable.
Main Outcome Measures
Symptoms of AD were quantified using the validated Autonomic Dysfunction Following SCI‐AD survey. Deep autonomic physiology characterization was further completed ( n = 34 uninjured controls, n = 28 individuals with SCI) to identify underlying AD mechanisms. Continuous blood pressure, heart rate, regional vascular resistance in the arm/leg, and pre/posttest catecholamines were recorded. Vascular responsiveness and baroreflex sensitivity were assessed with intravenous phenylephrine boluses. Foot cold pressor and bladder pressor tests served as below level mild noxious stimuli to elicit controlled AD.
Results
AD symptoms were, as expected, significantly higher after SCI compared to uninjured controls ( p < .001). Symptomatic AD was identified in 77% of individuals with SCI at/above T6, compared to 38% with injuries below T6. McNemar's statistic indicated the T6 neurological level poorly differentiated who developed symptomatic AD ( p = .039). During laboratory testing, 57% of those with SCI at/above T6 experienced AD, as did 57% of those with injuries below T6 ( p = .33). Physiologically, AD in individuals with SCI below T6 can be due to heightened vascular responsiveness and poor baroreflex sensitivity, leading to minimal compensatory bradycardia.
Conclusions
Symptomatic and objective AD occurs in those with SCI above and below the T6 NLI threshold. As such, targeted autonomic testing must translate to the bedside to accurately quantify AD risk. In the interim, though the T6 threshold has become cannon in many patient and resident education materials regarding AD risk, evidence suggests clinical care should avoid using this strict cutoff.