Background: Strong correlation between mean intracranial pressure (ICP) and its pulse wave amplitude (AMP) has been demonstrated in different clinical scenarios. We investigated the relationship between invasive mean arterial blood pressure (ABP) and AMP to explore its potential role as a descriptor of cerebrovascular pressure reactivity after traumatic brain injury (TBI).
Methods: We retrospectively analyzed data of patients suffering from TBI with brain monitoring. Transcranial Doppler blood flow velocity, ABP, ICP were recorded digitally. Cerebral perfusion pressure (CPP) and AMP were derived. A new index-pressure-amplitude index (PAx)-was calculated as the Pearson correlation between (averaged over 10 s intervals) ABP and AMP with a 5 min long moving average window. The previously introduced transcranial Doppler-based autoregulation index Mx was evaluated in a similar way, as the moving correlation between blood flow velocity and CPP. The clinical outcome was assessed after 6 months using the Glasgow outcome score.
Results: 293 patients were studied. The mean PAx was -0.09 (standard deviation 0.21). This negative value indicates that, on average, an increase in ABP causes a decrease in AMP and vice versa. PAx correlated strong with Mx (R (2) = 0.46, P < 0.0002). PAx also correlated with age (R (2) = 0.18, P < 0.05). PAx was found to have as good predictive outcome value (area under curve 0.71, P < 0.001) as Mx (area under curve 0.69, P < 0.001).
Conclusions: We demonstrated significant correlation between the known cerebral autoregulation index Mx and PAx. This new index of cerebrovascular pressure reactivity using ICP pulse wave information showed to have a strong association with outcome in TBI patients.