Best Of AAST #5: MAP Goals For Spinal Cord Injury

The use of mean arterial pressure (MAP) goals in the management of spinal cord injury is commonplace. But hit the literature some time and try to find out what the ideal MAP is, or if they even make a difference. It’s very difficult to come up with really solid data.

The group at Dignity Health St. Joseph’s Hospital in Phoenix reviewed their own trauma registry over a 6 year period. They chose a specific MAP goal (85 torr) and sifted through all of their electronic health record data to see how consistently they achieved it, the pressor dose needed to do so, and an objective measure of neurologic improvement while in the hospital (ASIA impairment scale).

Here are the factoids:

  • There were 136 patients studied, with an average ISS of 24 and average length of stay (LOS) of 10 days
  • Each patient had an average of 157 MAP determinations, and MAP > 85 (MAP85) was achieved in about 72% of those readings
  • About 80% of patients required a pressor to maintain MAP85, with an average dose equivalent to 26mg of norepinephrine during their stay
  • Patients with an ASIA improvement of at least one level were at MAP85 79% of the time vs 68% for those that did not improve
  • Multivariate regression showed that MAP85 was the main factor associated with the higher ASIA scores

The authors concluded that MAP85 was an important predictor of neurologic improvement, and that increased vigilance in maintaining it would help optimize neurologic recovery.

Here are my comments: The ASIA Impairment Score is a detailed description of the degree of neurologic injury in patients with spinal cord injury. The worksheet used to document consists of two pages and requires an in-depth sensory and motor exam. This is then translated into a alphabetical grade from A (no sensory or motor function even in the sacral segments) to E (normal exam).

This is a very interesting study, but I always worry about the test instrument. In order to use this scoring system and have good inter-rater reliability, the people that administer the test must be specifically trained. Otherwise the results become muddled.

The last thing that I always think about in association studies like this is, how do you know you included all of the relevant factors? Are there potentially significant variables that you wish you had that just weren’t in your trauma registry?

Here are my comments and questions for the authors:

  • Tell us about the personnel who administered the ASIA assessment. Did every one of them have specific training to do it? This is important to ensure that the major conclusion in the study is valid.
  • It is hard to follow the change in ASIA score based on the patient’s initial exam. Please show us how many A’s became B (or higher), etc.
  • Was the amount of time that MAP goals were not met clinically significant? Using the length of stay and MAP determination numbers given, and assuming that the first three days were the most significant for recovery, each patient would have had their MAP measured every half hour during those three days. The patients who did not have an improved ASIA score had 50 measurements, on average, where MAP was < 85. But the patients who did improve still had 33 measurements below  goal. Does this 17 measurement difference really matter?

I’m hoping to firm up my appreciation for MAP85 while listening to your presentation!

Reference: Mean arterial pressure maintenance following spinal cord injury: does meeting the target matter? AAST 2020 Oral Abstract #8.

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