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

Abstract

Current guidelines for the care of patients with acute spinal cord injuries (SCIs) recommend maintaining mean arterial pressure (MAP) values of 85-90 mm 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 q1 min 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 120 mm Hg to 40 mm Hg in 1 mm 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 994,875 q1 min arterial line blood pressure measurements were recorded for the included patients amid 1,688,194 min of recorded intensive care observations. A large proportion of measures were below 85 mm 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 85 mm 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 >85 mm Hg may be appropriate after acute SCI.

Higher Mean Arterial Pressure Values Correlate with Neurologic Improvement in Patients with Initially Complete Spinal Cord Injuries

“…Our group recently validated this recommendation with a large dataset of high-frequency MAP measurements obtained from 100 SCI patients. We found that maintenance of MAP values above 85 mmHg correlated with improved neurological recovery 3,6 and that the benefit associated with MAP augmentation decreased over time. Importantly, we also found that the proportion of values <85 mmHg correlated more strongly with outcome than mean values suggesting that efforts to prevent even brief drops below threshold are important.…”

“…Despite what we have learned about secondary injury, we are as yet without a safe and effective therapeutic which attenuates these processes 3–5 . Physicians have been more successful treating secondary insults which occur at the level of the organism and include hypoxia, and hypotension 6–13 . Indeed, supportive care aimed at preventing or reducing these insults is the mainstay of modern medical care, and is credited with the improved mortality and morbidity seen following SCI in recent decades 14 .…”

Associations Between Anesthetic Variables and Functional Outcome in Dogs With Thoracolumbar Intervertebral Disk Extrusion Undergoing Decompressive Hemilaminectomy

“…A recent study also suggested that acute spikes of systemic hypertension at the time of experimental SCI are associated with poorer outcome in rodent models, suggesting that both extremes of blood pressure might in fact have harmful consequences, and hypertension would have been missed with the current study design 45. The effect of systemic hypotension on outcome in acute SCI has been extensively evaluated in experimental studies and human medicine 21, 26. As a consequence of the loss of autoregulation that occurs during acute secondary SCI, spinal cord blood flow becomes directly vulnerable to fluctuations in MABP and intrathecal pressure 17, 46.…”

“…Although the oscillometric monitor used in this study1 has previously been evaluated for validity with encouraging results,53 this method does reduce the accuracy of measurements when compared to direct arterial measurement and the results should be considered in light of this. Future studies could therefore better evaluate associations between hemodynamic anesthetic variables and long‐term outcome by utilizing more consistent techniques for prospectively monitoring intraoperative systemic perfusion parameters, such as continuously recorded direct arterial blood pressure recordings,26 as well as defined anesthetic medication protocols and using recently described methods for directly monitoring local indicators of tissue perfusion such as spinal cord blood flow and intraspinal pressure 19, 22, 23, 48. A prospective design in future studies could also utilize recordings of other downstream indicators of tissue perfusion such as plasma l ‐lactate concentration.…”

“…Spinal cord perfusion is dependent on the relationship between systemic blood pressure and intrathecal pressure, in the same way that cerebral perfusion pressure is defined by mean arterial blood pressure (MABP) and intracranial pressure 17, 19, 24. Systemic hypotension might have serious consequences for the injured spinal cord, and alongside the avoidance of systemic hypoxia, management of blood pressure remains the mainstay of neuroprotective treatment in veterinary and human acute SCI 7, 19, 21, 25, 26…”