Pulsatile intracranial pressure and cerebral autoregulation after traumatic brain injury.

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.

ICM+, a flexible platform for investigations of cerebrospinal dynamics in clinical practice.

BACKGROUND: ICM+ software encapsulates 20 years of our experience in brain monitoring gained in multiple neurosurgical and intensive care centres. It collects data from a variety of bedside monitors and produces on-line time trends of parameters defined using configurable signal processing formulas. The resulting data can be displayed in a variety of ways including time trends, histograms, cross histograms, correlations, etc. For technically minded researchers there is a plug-in mechanism facilitating registration of third party libraries of functions and analysis tools. METHODS: The latest version of the ICM+ software has been used in 162 severely head injured patients in the Neurosciences Critical Care Unit of the Addenbrooke's Cambridge University Hospital. Intracranial pressure (ICP) and invasive arterial blood pressure (ABP) were monitored routinely. Mean values of ICP, ABP, cerebral perfusion pressure (CPP) and various indices describing pressure reactivity (PRx), pressure-volume compensation (RAP) and vascular waveforms of ICP were calculated. Error-bar chart showing reactivity index PRx versus CPP ('Optimal CPP' chart) was calculated continuously. FINDINGS: PRx showed a significant relationship with CPP (ANOVA: p < 0.021) indicating loss of cerebral pressure-reactivity for low CPP (CPP < 55 mmHg) and for high CPPs (CPP > 95 mmHg). Examining PRx-CPP curves in individual patients revealed that CPP(OPT) not only varied between subjects but tended to fluctuate as the patient's state changed during the stay in the ICU. Calculation window of 6-8 h provided enough data to capture the CPP(OPT) curve. CONCLUSIONS: ICM+ software proved to be useful both academically and clinically. The complexity of data analysis is hidden inside loadable profiles thus allowing clinically minded investigators to take full advantage of signal processing engine in their research into cerebral blood and fluid dynamics.

Pulse amplitude of intracranial pressure waveform in hydrocephalus.

BACKGROUND: There is increasing interest in evaluation of the pulse amplitude of intracranial pressure (AMP) in explaining dynamic aspects of hydrocephalus. We reviewed a large number of ICP recordings in a group of hydrocephalic patients to assess utility of AMP. MATERIALS AND METHODS: From a database including approximately 2,100 cases of infusion studies (either lumbar or intraventricular) and overnight ICP monitoring in patients suffering from hydrocephalus of various types (both communicating and non-communicating), etiology and stage of management (non-shunted or shunted) pressure recordings were evaluated. For subgroup analysis we selected 60 patients with idiopathic NPH with full follow-up after shunting. In 29 patients we compared pulse amplitude during an infusion study performed before and after shunting with a properly functioning shunt. Amplitude was calculated from ICP waveforms using spectral analysis methodology. FINDINGS: A large amplitude was associated with good outcome after shunting (positive predictive value of clinical improvement for AMP above 2.5 mmHg was 95%). However, low amplitude did not predict poor outcome (for AMP below 2.5 mmHg 52% of patients improved). Correlations of AMP with ICP and Rcsf were positive and statistically significant (N = 131 with idiopathic NPH; R = 0.21 for correlation with mean ICP and 0.22 with Rcsf; p< 0.01). Correlation with the brain elastance coefficient (or PVI) was not significant. There was also no significant correlation between pulse amplitude and width of the ventricles. The pulse amplitude decreased (p < 0.005) after shunting. CONCLUSIONS: Interpretation of the ICP pulse waveform may be clinically useful in patients suffering from hydrocephalus. Elevated amplitude seems to be a positive predictor for clinical improvement after shunting. A properly functioning shunt reduces the pulse amplitude.