Mean Arterial Blood Pressure Correlates with Neurological Recovery after Human Spinal Cord Injury: Analysis of High Frequency Physiologic Data

Current guidelines for the care of patients with acute spinal cord injuries (SCIs) recommend maintaining mean arterial pressure (MAP) values of 85-90mm Hg for 7 days after an acute SCI however, little evidence supports this recommendation. We sought to better inform the relationship between MAP values and neurological recovery. A computer system automatically collected and stored q1min physiological data from intensive care unit monitors on patients with SCI over a 6-year period. Data for 100 patients with acute SCI were collected. 74 of these patients had American Spinal Injury Association Impairment Scale (AIS) grades determined by physical examination on admission and at time of hospital discharge. Average MAP values as well as the proportion of MAP values below thresholds were explored for values from 120mm Hg to 40mm Hg in 1mm Hg increments; the relationship between these measures and outcome was explored at various time points up to 30 days from the time of injury. A total of 994,875q1min arterial line blood pressure measurements were recorded for the included patients amid 1,688,194min of recorded intensive care observations. A large proportion of measures were below 85mm Hg despite generally acceptable average MAP values. Higher average MAP values correlated with improved recovery in the first 2-3 days after SCI while the proportion of MAP values below the accepted threshold of 85mm Hg seemed a stronger correlate, decreasing in strength over the first 5-7 days after injury. This study provides strong evidence supporting a correlation between MAP values and neurological recovery. It does not, however, provide evidence of a causal relationship. Duration of hypotension may be more important than average MAP. It provides support for the notion of MAP thresholds in SCI recovery, and the highest MAP values correlated with the greatest degree of neurological recovery. The results are concordant with current guidelines in suggesting that MAP thresholds >85mm Hg may be appropriate after acute SCI.