Research Reports - 'Long' pressure reactivity index (L-PRx) as a measure of autoregulation correlates with outcome in traumatic brain injury patients

Acta Neurochir (Wien). 2012 Sep;154(9):1575-81

Sánchez-Porras R, Santos E, Czosnyka M, Zheng Z, Unterberg AW, Sakowitz OW

BACKGROUND: Cerebral autoregulation and, consequently, cerebrovascular pressure
reactivity, can be disturbed after traumatic brain injury (TBI). Continuous
monitoring of autoregulation has shown its clinical importance as an independent
predictor of neurological outcome. The cerebral pressure reactivity index (PRx)
reflects that changes in seconds of cerebrovascular reactivity have prognostic
significance. Using an alternative algorithm similar to PRx, we investigate
whether the utilization of lower-frequency changes of the order of minutes of
mean arterial blood pressure (MAP) and intracranial pressure (ICP) could have a
prognostic value in TBI patients.
MATERIALS AND METHODS: Head-injured patients requiring continued advanced
multimodal monitoring, including hemodynamic, ICP and microdialysis (MD)
monitoring, were analyzed retrospectively. A low-frequency sample pressure
reactivity index (L-PRx) was calculated, using 20-min averages of MAP and ICP
data as a linear Pearson's correlation. The mean values per patient were
correlated to outcome at 6 months after injury. Differences of monitoring
parameters between non-survivors and survivors were compared.
RESULTS: A total of 29 patients (mean age 37.2 years, 26 males) suffering from
TBI were monitored for a mean of 109.6 h (16-236 h, SD ± 60.4). Mean L-PRx was
found to be of 0.1 (-0.2 to 0.6, SD ± 0.20), six patients presented impaired
(>0.2) values. The averaged L-PRx correlated significantly with ICP (r = 0.467,
p = 0.011) and 6-month outcome (r = -0.556, p = 0.002). Significant statistical
differences were found in L-PRx, cerebral perfusion pressure (CPP), lactate, and
lactate-pyruvate ratio when comparing patients who died (n = 5) and patients who
survived.
CONCLUSIONS: L-PRx correlates with the 6-month outcome in TBI patients. Very slow
changes of MAP and ICP may contain important autoregulation information. L-PRx
may be an alternative algorithm for the estimation of cerebral autoregulation and
clinical prognosis.

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