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Continuous Assessment of “Optimal” Cerebral Perfusion Pressure in Traumatic Brain Injury: A Cohort Study of Feasibility, Reliability, and Relation to Outcome

By Currents Editor posted 02-11-2019 13:55

  

By Andreas H. Kramer, Philippe L. Couillard, David A. Zygun, Marcel J. Aries, Clare N. Gallagher

Background

Guidelines recommend maintaining cerebral perfusion pressure (CPP) between 60 and 70 mmHg in patients with severe traumatic brain injury (TBI), but acknowledge that optimal CPP may vary depending on cerebral blood flow autoregulation. Previous retrospective studies suggest that targeting CPP where the pressure reactivity index (PRx) is optimized (CPPopt) may be associated with improved recovery.

Methods

We performed a retrospective cohort study involving TBI patients who underwent PRx monitoring to assess issues of feasibility relevant to future interventional studies: (1) the proportion of time that CPPopt could be detected; (2) inter-observer variability in CPPoptdetermination; and (3) agreement between manual and automated CPPopt estimates. CPPoptwas determined for consecutive 6-h epochs during the first week following TBI. Sixty PRx-CPP tracings were randomly selected and independently reviewed by six critical care professionals. We also assessed whether greater deviation between actual CPP and CPPopt (ΔCPP) was associated with poor outcomes using multivariable models.

Results

In 71 patients, CPPopt could be manually determined in 985 of 1173 (84%) epochs. Inter-observer agreement for detectability was moderate (kappa 0.46, 0.23–0.68). In cases where there was consensus that it could be determined, agreement for the specific CPPopt value was excellent (weighted kappa 0.96, 0.91–1.00). Automated CPPopt was within 5 mmHg of manually determined CPPopt in 93% of epochs. Lower PRx was predictive of better recovery, but there was no association between ΔCPP and outcome. Percentage time spent below CPPoptincreased over time among patients with poor outcomes (p = 0.03). This effect was magnified in patients with impaired autoregulation (defined as PRx > 0.2; p = 0.003).

Conclusion

Prospective interventional clinical trials with regular determination of CPPopt and corresponding adjustment of CPP goals are feasible, but measures to maximize consistency in CPPopt determination are necessary. Although we could not confirm a clear association between ΔCPP and outcome, time spent below CPPopt may be particularly harmful, especially when autoregulation is impaired.

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