Noninvasive Assessment of ICP: Evaluation of New TBI Data.

BACKGROUND: In a previously introduced mathematical model, intracranial pressure (ICP) was noninvasively assessed using cerebral blood flow velocity (CBFV) and arterial blood pressure (ABP). In this study this method is evaluated using new data from patients with traumatic brain injury (TBI). MATERIALS AND METHODS: Three hundred fifteen data recordings of 137 patients (114 men; age 14-78 years, mean age 37 ± 17 years) with severe TBI were studied. CBFV, ABP, and invasively assessed ICP were simultaneously recorded for 1 h. Noninvasive ICP (nICP) was calculated and compared with ICP. RESULTS: On 315 recordings, average deviation between ICP and nICP (± standard deviation) was 4.9 ± 3.3 mmHg. The standard deviation of differences (ICP - nICP) was 5.6 mmHg. The 95 % confidence interval of ICP prediction ranged from -9.6 to 12.3 mmHg. Mean ICP was 16.7 mmHg and mean nICP was 18.0 mmHg. When nICP was adjusted by their difference 1.3 mmHg (nICPadj = nICP - 1.3), the 95 % confidence limits of ICP prediction became ±11.0 mmHg. In recordings with highly dynamic ICP signals (n = 27), ICP and nICP correlated on average with R = 0.51 ± 0.47. CONCLUSIONS: nICP assessment showed reasonable accuracy and may be used in clinical studies of patients without any indication for ICP probe implantation.

Is Impaired Autoregulation Associated with Mortality in Patients with Severe Cerebral Diseases?

BACKGROUND: Cerebral autoregulation (CA) is a mechanism that compensates for variations in cerebral perfusion pressure (CPP) by changes in cerebral blood flow resistance to keep the cerebral blood flow constant. In this study, the relationship between lethal outcome during hospitalisation and the autoregulation-related indices PRx and Mx was investigated. MATERIALS AND METHODS: Thirty patients (aged 18-77 years, mean 53 ± 16 years) with severe cerebral diseases were studied. Cerebral blood flow velocity (CBFV), arterial blood pressure (ABP) and intracranial pressure (ICP) were repeatedly recorded. CA indices were calculated as the averaged correlation between CBFV and CPP (Mx) and between ABP and ICP (PRx). Positive index values indicated impairment of CA. RESULTS: Six patients died in hospital. In this group both PRx and Mx were significantly higher than in the group of survivors (PRx: 0.41 ± 0.33 vs 0.09 ± 0.25; Mx: 0.28 ± 0.40 vs 0.03 ± 0.21; p = 0.01 and 0.04, respectively). PRx and Mx correlated significantly with Glasgow Outcome Scale (GOS) score (PRx: R = -0.40, p < 0.05; Mx: R = -0.54, p < 0.005). PRx was the only significant risk factor for mortality (p < 0.05, logistic regression). CONCLUSION: Increased PRx and Mx were associated with risk of death in patients with severe cerebral diseases. The relationship with mortality was more pronounced in PRx, whereas Mx showed a better correlation with GOS score.

Non-invasively estimated ICP pulse amplitude strongly correlates with outcome after TBI.

INTRODUCTION: An existing monitoring database of brain signal recordings in patients with head injury has been re-evaluated with regard to the accuracy of estimation of non-invasive ICP (nICP) and its components, with a particular interest in the implications for outcome after head injury. METHODS: Middle cerebral artery blood flow velocity (FV), ICP and arterial blood pressure (ABP) were recorded. Non-invasive ICP (nICP) was calculated using a mathematical model. Other signals analysed included components of ICP (n" indicates non-invasive): ICP pulse amplitude (Amp, nAmp), amplitude of the respiratory component (Resp, nResp), amplitude of slow vasogenic waves of ICP (Slow, nSlow) and index of compensatory reserve (RAP, nRAP). Mean values of analysed signals were compared against each other and between patients who died and survived. RESULTS: The correlation between ICP and nICP was moderately strong, R = 0.51 (95% prediction interval [PI] 17 mm Hg). The components of nICP and ICP were also moderately correlated with each other: the strongest correlation was observed for Resp vs. nResp (r = 0.66), while weaker for Amp vs. nAmp (r = 0.41). Non-invasive pulse amplitude of ICP showed the strongest association with outcome, with the -difference between those who survived and those who died reaching a significance level of p < 0.000001. DISCUSSION: When compared between patients who died and who survived mean nAmp showed the greatest difference, suggesting its potential to predict mortality after TBI.