Empirical targets for acute hemodynamic management of individuals with spinal cord injury

Author: Squair, Jordan PhD et al

Title: Empirical targets for acute hemodynamic management of individuals with spinal cord injury

Background:

Ideal clinically significant BP goals and/or spinal cord perfusion pressure goals are not well defined

Guidelines suggest MAP 85-90mmHg x7 days after injury

Trial Design:

prospective observational

n=92

Intrathecal lumbar catheter placed L2-3 or L3-4 to measure CSFP (cerebrospinal fluid pressure)

MAP (mean arterial pressure) measured with arterial line

Manual hourly recording of MAP and CSFP

SCPP (spinal cord perfusion pressure) calculated as MAP-CSFP

MAP target 80-85mmHg for 120 hours after enrollment (=5 days)

Volume resuscitation = first line MAP augmentation (crystalloid, colloid, PRBC)

Second line MAP augmentation = norepinephrine, phenylephrine, dopamine, or combination

CSFP not manipulated

Each hemodynamic parameter grouped into 5 target ranges (time spent within each group determined by data points at or above the target range with a 5% error)

Fisher exact test used to compare individuals in target range vs not in target range if AIS improved at least 1 grade or not

Duration: The recruitment period or description of manner in which participants recruited was not discussed in this paper. This paper represents analysis of patient data obtained from a prior publication (https://n.neurology.org/content/89/16/1660.long).

Based on prior publication:

Patient recruitment from single institution from March 2006 expanded to multicenter in September 2012

Objectives: “determine the hemodynamic conditions associated with optimal neurologic improvement in individuals with acute traumatic spinal cord injury”

Inclusion criteria (https://n.neurology.org/content/89/16/1660.long):

AIS grade A, B, or C

Bony spinal injury between C0 and L1

Placement of lumbar catheter within 48 hours of injury

Ability to be assessed clinically for reliable neurologic exam

Exclusion criteria (https://n.neurology.org/content/89/16/1660.long):

Concomitant head injury

Major trauma to chest, pelvis, or extremities requiring invasive intervention (internal or external fixation)

Sedation or intoxication that prevented valid neurologic exam

Primary endpoint:

AIS conversion defined as change in AIS of at least 1 grade

Hypothesis: The percent of time an individual spends within ideal hemodynamic target is linearly related to motor improvement

Statistical analysis:

Relative risk iterations to determine the MAP, CSFP, and SCPP at which relative risk of motors score improvement was 1

Linear relationship between MAP and motor score improvement, CSFP and motor score improvement, SCPP and motor score improvement

Transition point = likelihood of improving neurologically and remaining unchanged were equal

Definitions/reminders

Relative risk = ratio of probability of an event occurring in the exposed group versus probability of event occurring in non exposed group

Sensitivity Analysis:

The manner in which RR of 1 was determined is a kind of sensitivity analysis in that multiple different cutoffs for hemodynamic parameters show different RR

Results:

Cervical injuries n=55

Thoracic injuries n = 28

Lumbar injuries n=9

CSFP of 26mmHg correlated with RR=1 for improvement of AIS grade by at least 1

MAP of 74mmHg correlated with RR=1 for improvement of AIS grade by at least 1

SCPP of 50mmHg correlated with RR=1 for improvement of AIS grade by at least 1

Limitations:

Study is a correlation as opposed to association

Conclusions:

“Our results provide a framework to guide the development of widespread institutional management guidelines for acute traumatic SCI”

Strengths:

Data available upon request for further data analysis if desired

Attempt at providing a starting point for further studies

Weaknesses:

“To determine the optimal hemodynamic conditions (MAP, CSFP SCPP) associated with neurologic improvement, we statistically iterated through a range of physicologically possible hemodynamic cutoffs and found the point at which neurologic recover (defined as improvement in American Spinal Injury Association Impairment Scale [AIS] grade or motor score) started to become evident.” Does this mean they analyzed data with different cutoffs until statistically significant benefits identified? Seems like a built in bias to find relevance.

No mention of spinal surgical intervention or timing to spinal surgical intervention (Surgical decompression may be associated with increased concordance between MAP and SCPP eliminating need for intrathecal monitoring to guide management whether that further increasing MAP or draining CSF from lumbar drain to target SCPP)

No mention of timing of first official exam (for instance if patient still in spinal shock then there may be a bias toward improvement)

Were patients kept flat (presumably for spinal precautions), and if not where was the lumbar drain leveled at since the tip of the catheter could be tunneled higher or lower within intrathecal space affecting pressure reading (flat restrictions may have been lifted if surgical decompression/stabilization occurred prior to 5 day monitoring expiration)

Application:

Patients may frequently automap therefore intervention would be remove CSF however with RR of 1 being at 74mmHg, is there benefit is decreasing CSFP given MAP-CSFP likely >55mmHg if MAP starting high already

MAP>85mmHg already associated with RR>10 of improved AIS grade

Change to practice: I do not plan on placing lumbar drain to measure pressure or drain CSF since MAP>85 associated with RR>10 for improvement with no further intervention (in terms of draining CSF)