Continuous Monitoring of Cerebrovascular Reactivity Using Pulse Waveform of Intracranial Pressure

Background

Guidelines for the management of traumatic brain injury (TBI) call for the development of accurate methods for assessment of the relationship between cerebral perfusion pressure (CPP) and cerebral autoregulation and to determine the influence of quantitative indices of pressure autoregulation on outcome. We investigated the relationship between slow fluctuations of arterial blood pressure (ABP) and intracranial pressure (ICP) pulse amplitude (an index called PAx) using a moving correlation technique to reflect the state of cerebral vasoreactivity and compared it to the index of pressure reactivity (PRx) as a moving correlation coefficient between averaged values of ABP and ICP.

Methods

A retrospective analysis of prospective 327 TBI patients (admitted on neurocritical care unit of a university hospital in the period 2003?C2009) with continuous ABP and ICP monitoring.

Results

PAx was worse in patients who died compared to those who survived (?0.04?±?0.15 vs. ?0.16?±?0.15, ??²?=?28, p?2?=?6, p?=?0.01).

Conclusions

PAx is a new modified index of cerebrovascular reactivity which performs equally well as established PRx in long-term monitoring in severe TBI patients, but importantly is potentially more robust at lower values of ICP. In view of establishing an autoregulation-oriented CPP therapy, continuous determination of PAx is feasible but its value has to be evaluated in a prospective controlled trail.     

Temporal changes in cerebral tissue oxygenation with cerebrovascular pressure reactivity in severe traumatic brain injury

Objective

To investigate the temporal relationship between cerebrovascular pressure reactivity and brain tissue oxygenation in patients with severe head injury.

Methods

In 40 patients, brain tissue oxygenation and intracranial pressure were monitored. Time‐averaged values for intracranial pressure (ICP), mean arterial pressure (MAP), cerebral perfusion pressure (CPP) and brain tissue oxygenation (PtiO₂) were computed. The pressure reactivity index (PRx) was calculated. The mean values of the variables were obtained at the 6‐h and 72‐h post‐injury time points, and the difference between the two time points for each of the variables was denoted as delta (δ).

Results

Of the 40 patients, 32 were survivors and 8 were non‐survivors. Statistically significant differences were present between these two groups with regard to δMAP (p = 0.013), ICP at 6 h (p = 0.027), CPP at 72 h (p = 0.018), δCPP (p = 0.033), PRx at 6 h (p = 0.029), PRx at 72 h (p = 0.002), PtiO₂ at 72 h (p<0.0005) and δPtiO₂ (p = 0.023) values, reflecting an improvement with time in survivors and a deterioration with time in non‐survivors. In non‐survivors, the magnitude of change in PtiO₂ and CPP with time correlated in a negative linear fashion (p = 0.042 and 0.029, respectively) with the change in PRx with time, whereas no such relationship was seen in survivors.

Conclusion

The severity of brain tissue oxygenation derangement correlates with increasing cerebrovascular dysautoregulation in patients succumbing to severe head injury, supporting the utility of PRx as a monitoring variable and the rationale for a target‐driven approach to head injury management.Cerebral ischaemia is a critical contributory factor to secondary brain injury after trauma. In the presence of an unstable cerebral perfusion pressure (CPP), the autoregulatory cerebrovascular reactivity attempts to maintain an adequate cerebral blood flow. Increasing CPP may result in raised or lowered intracranial pressure (ICP), depending on whether cerebral autoregulation is preserved. Rosner et al¹ have described how increases in CPP within the autoregulatory range lead to compensatory vasoconstriction to maintain a stable cerebral blood flow. In so doing, cerebral blood volume and thus ICP levels fall. However, outside of these autoregulatory limits, a pressure‐passive scenario exists where increases in CPP lead to vasodilatation and a rise in ICP. Investigators have defined an index comparing arterial blood pressure (ABP) and ICP to quantify this relationship between CPP and ICP, known as the pressure reactivity index (PRx).^2,3 If a rise in ABP (and hence CPP) leads to a parallel increase in ICP, a good correlation exists, and the PRx is positive. However, in the face of intact cerebral autoregulatory capacity, vasoconstriction in the face of rising CPP leads to a drop in ICP, and hence PRx approaches zero or takes a negative value. Measurement of PRx could thus form the basis for target‐driven management, as ABP can be manipulated.Clinical studies on patients with head injury have shown the feasibility of continuous monitoring of local brain tissue oxygenation (PtiO₂) as a variable for cerebral oxygenation.^4,5,6 Despite the limitations of such a local method of measurement, PtiO₂ indicates global cerebral oxygenation when the monitoring is carried out in a relatively uninjured part of the brain.⁶ The presence of autoregulation disturbance could conceivably lead to disturbance in oxygen tension in the tissue of interest by virtue of blood flow metabolism uncoupling as PtiO₂ reflects the net balance between oxygen supply and demand at the tissue level.⁷We hypothesised that a worsening PRx indicative of increasing dysautoregulation during the temporal course of monitoring is related to mortality, and this may arise from specific patterns of change in various physiological variables including PtiO₂.     

Monitoring cerebral autoregulation after head injury. Which component of transcranial Doppler flow velocity is optimal?

Background

Cerebral autoregulation assessed using transcranial Doppler (TCD) mean flow velocity (FV) in response to various physiological challenges is predictive of outcome after traumatic brain injury (TBI). Systolic and diastolic FV have been explored in other diseases. This study aims to evaluate the systolic, mean and diastolic FV for monitoring autoregulation and predicting outcome after TBI.

Methods

300 head-injured patients with blood pressure (ABP), intracranial pressure (ICP), cerebral perfusion pressure (CPP), and FV recordings were studied. Autoregulation was calculated as a correlation of slow changes in diastolic, mean and systolic components of FV with CPP (Dx, Mx, Sx, respectively) and ABP (Dxa, Mxa, Sxa, respectively) from 30 consecutive 10?s averaged values. The relationship with age, severity of injury, and dichotomized 6?months outcome was examined.

Results

Association with outcome was significant for Mx and Sx. For favorable/unfavorable and death/survival outcomes Sx showed the strongest association (F?=?20.11; P?=?0.00001 and F?=?13.10; P?=?0.0003, respectively). Similarly, indices derived from ABP demonstrated the highest discriminatory value when systolic FV was used (F?=?12.49; P?=?0.0005 and F?=?5.32; P?=?0.02, respectively). Indices derived from diastolic FV demonstrated significant differences (when calculated using CPP) only when comparing between fatal and non-fatal outcome.

Conclusions

Systolic flow indices (Sx and Sxa) demonstrated a stronger association with outcome than the mean flow indices (Mx and Mxa), irrespective of whether CPP or ABP was used for calculation.     

Association between intracranial, arterial pulse pressure amplitudes and cerebral autoregulation in head injury patients

OBJECTIVE: To explore whether intracranial pulse pressure amplitudes relate to arterial pulse pressure amplitudes and whether correlations between time-related changes in intracranial and arterial pulse pressure amplitudes associate with indices of cerebral autoregulation. METHODS: A total of 257 continuous and simultaneous intracranial pressure (ICP), arterial blood pressure (ABP) and middle cerebral artery (MCA) blood velocity recordings were obtained 1-14 days after ictus in 76 traumatic head injury patients and analysed retrospectively. Clinical outcome was assessed using the Glasgow outcome scale (GOS). Pulse pressure amplitudes of corresponding single ICP and ABP waves were correlated in consecutive 200 wave pairs. Mean ICP, mean ABP and mean ICP wave amplitudes, and mean and systolic MCA blood flow velocities, were computed in consecutive 6 second time windows. The indices of cerebral autoregulation PRx (moving correlation between mean ICP and mean ABP), and Mx and Sx (moving correlation between mean and systolic MCA blood velocity and cerebral perfusion pressure) were calculated over 4 minute periods and averaged over each recording. RESULTS: Intracranial pulse pressure amplitudes were not related to arterial pulse pressure amplitudes (mean of Pearson's correlations coefficients: 0.04). Outcome was related to mean ICP, PRx and Sx (p 相似文献   

Association between intracranial,arterial pulse pressure amplitudes and cerebral autoregulation in head injury patients

Abstract

Objective: To explore whether intracranial pulse pressure amplitudes relate to arterial pulse pressure amplitudes and whether correlations between time-related changes in intracranial and arterial pulse pressure amplitudes associate with indices of cerebral autoregulation.

Methods: A total of 257 continuous and simultaneous intracranial pressure (ICP), arterial blood pressure (ABP) and middle cerebral artery (MCA) blood velocity recordings were obtained 1–14 days after ictus in 76 traumatic head injury patients and analysed retrospectively. Clinical outcome was assessed using the Glasgow outcome scale (GOS). Pulse pressure amplitudes of corresponding single ICP and ABP waves were correlated in consecutive 200 wave pairs. Mean ICP, mean ABP and mean ICP wave amplitudes, and mean and systolic MCA blood flow velocities, were computed in consecutive 6 second time windows. The indices of cerebral autoregulation PRx (moving correlation between mean ICP and mean ABP), and Mx and Sx (moving correlation between mean and systolic MCA blood velocity and cerebral perfusion pressure) were calculated over 4 minute periods and averaged over each recording.

Results: Intracranial pulse pressure amplitudes were not related to arterial pulse pressure amplitudes (mean of Pearson's correlations coefficients: 0.04). Outcome was related to mean ICP, PRx and Sx (p ≤ 0.04, multiple regression analysis). Correlations between intracranial and arterial pulse pressure amplitudes were weakly related to PRx (Pearson's correlation coefficient: 0.16; p=0.01), but were not related to the indices of cerebral autoregulation Mx (Pearson's correlation coefficient: 0.07) and Sx (Pearson's correlation coefficient: 0.04).

Conclusions: In this cohort of pressure recordings, we found no evidence of a correlation between intracranial and arterial blood pressure amplitudes. The correlation appeared not to be related to the state of cerebral autoregulation, although a weak correlation was found with pressure reactivity index PRx.     

Critical Thresholds for Cerebrovascular Reactivity After Traumatic Brain Injury

Introduction

Pressure-reactivity index (PRx) is a useful tool in brain monitoring of trauma patients, but the question remains about its critical values. Using our TBI database, we identified the thresholds for PRx and other monitored parameters that maximize the statistical difference between death/survival and favorable/unfavorable outcomes. We also investigated how these thresholds depend on clinical factors such as age, gender and initial GCS.

Methods

A total of 459 patients from our database were eligible. Tables of 2?×?2 format were created grouping patients according to survival/death or favorable/unfavorable outcomes and varying thresholds for PRx, ICP and CPP. Pearson??s chi square was calculated, and the thresholds returning the highest score were assumed to have the best discriminative value. The same procedure was repeated after division according to clinical factors.

Results

In all patients, we found that PRx had different thresholds for survival (0.25) and for favorable outcome (0.05). Thresholds of 70?mmHg for CPP and 22?mmHg for ICP were identified for both survival and favorable outcomes. The ICP threshold for favorable outcome was lower (18?mmHg) in females and patients older than 55?years. In logistic regression models, independent variables associating with mortality and unfavorable outcome were age, GCS, ICP and PRx.

Conclusion

The prognostic role of PRx is confirmed but with a lower threshold of 0.05 for favorable outcome than for survival (0.25). Results for ICP are in line with current guidelines. However, the lower value in elderly and in females suggests increased vulnerability to intracranial hypertension in these groups.     

Relationship Between Brain Pulsatility and Cerebral Perfusion Pressure: Replicated Validation Using Different Drivers of CPP Change

Background

Determination of relationships between transcranial Doppler (TCD)-based spectral pulsatility index (sPI) and pulse amplitude (AMP) of intracranial pressure (ICP) in 2 groups of severe traumatic brain injury (TBI) patients (a) displaying plateau waves and (b) with unstable mean arterial pressure (MAP).

Methods

We retrospectively reviewed patients with severe TBI and continuous TCD monitoring displaying either plateau waves or unstable MAP from 1992 to 1998. We utilized linear and nonlinear regression techniques to describe both cohorts: cerebral perfusion pressure (CPP) versus AMP, CPP versus sPI, mean ICP versus ICP AMP, mean ICP versus sPI, and AMP versus sPI.

Results

Nonlinear regression techniques were employed to analyze the relationships with CPP. In plateau wave and unstable MAP patients, CPP versus sPI displayed an inverse nonlinear relationship (R ² = 0.820 vs. R ² = 0.610, respectively), with the CPP versus sPI relationship best modeled by the following function in both cases: PI = a + (b/CPP). Similarly, in both groups, CPP versus AMP displayed an inverse nonlinear relationship (R ² = 0.610 vs. R ² = 0.360, respectively). Positive linear correlations were displayed in both the plateau wave and unstable MAP cohorts between: ICP versus AMP, ICP versus sPI, AMP versus sPI.

Conclusions

There is an inverse relationship through nonlinear regression between CPP versus AMP and CPP versus sPI display. This provides evidence to support a previously-proposed model of TCD pulsatility index. ICP shows a positive linear correlation with AMP and sPI, which is also established between AMP and sPI.

     

Relationship of Vascular Wall Tension and Autoregulation Following Traumatic Brain Injury

Background

The vascular wall tension (WT) of small cerebral vessels can be quantitatively estimated through the concept of critical closing pressure (CrCP), which denotes the lower limit of arterial blood pressure (ABP), below which small cerebral arterial vessels collapse and blood flow ceases. WT can be expressed as the difference between CrCP and intracranial pressure (ICP) and represent active vasomotor tone. In this study, we investigated the association of WT and CrCP with autoregulation and outcome of a large group of patients after traumatic brain injury (TBI).

Methods

We retrospectively analysed recordings of ABP, ICP and transcranial Doppler (TCD) blood flow velocity from 280 TBI patients (median age: 29 years; interquartile range: 20–43). CrCP and WT were calculated using the cerebrovascular impedance methodology. Autoregulation was assessed based on TCD-based indices, Mx and ARI.

Results

Low values of WT were found to be associated with an impaired autoregulatory capacity, signified by its correlation to FV-based indices Mx (R = ?0.138; p = 0.021) and ARI (R = 0.118; p = 0.048). No relationship could be established between CrCP and any of the autoregulatory indices. Neither CrCP nor WT was found to correlate with outcome.

Conclusions

Impaired autoregulation was found to be associated with a lower WT supporting the role of vasoparalysis in the loss of autoregulatory capacity. In contrast, no links between CrCP and autoregulation could be identified.     

Further Controversies About Brain Tissue Oxygenation Pressure-Reactivity After Traumatic Brain Injury

Background

Continuous monitoring of cerebral autoregulation is considered clinically useful due to its ability to warn against brain ischemic insults, which may translate to a relationship with adverse outcome. It is typically performed using the pressure reactivity index (PRx) based on mean arterial pressure and intracranial pressure. A new ORx index based on brain tissue oxygenation and cerebral perfusion pressure (CPP) has been proposed that similarly allows for evaluation of cerebrovascular reactivity. Conflicting results exist concerning its clinical utility.

Methods

Retrospective analysis was performed in 85 patients with traumatic brain injury (TBI). ORx was calculated using three time windows of 5, 20, and 60 min. Correlation coefficients and individual “optimal CPP” (CPP_opt) were calculated using both PRx and ORx, and relation to patient outcome investigated.

Results

Correlation coefficients for all comparisons between PRx and ORx indicated poor association between these indices (range from ?0.04 to 0.07). PRx was significantly lower in patients with good outcome (p = 0.01), while none of the ORx indices proved to be significantly different in the two outcome groups. Higher mortality related to average CPP < CPP_opt was found regardless of which index was used to calculate CPP_opt.

Conclusion

In the TBI setting, ORx does not appear to correlate with vascular pressure reactivity as assessed with PRx. Its potential use for individualizing CPP thresholds remains unclear.

     

A Continuous Correlation Between Intracranial Pressure and Cerebral Blood Flow Velocity Reflects Cerebral Autoregulation Impairment During Intracranial Pressure Plateau Waves

Background

In the healthy brain, small oscillations in intracranial pressure (ICP) occur synchronously with those in cerebral blood volume (CBV), cerebrovascular resistance, and consequently cerebral blood flow velocity (CBFV). Previous work has shown that the usual synchrony between ICP and CBFV is lost during intracranial hypertension. Moreover, a continuously computed measure of the ICP/CBFV association (Fix index) was a more sensitive predictor of outcome after traumatic brain injury (TBI) than a measure of autoregulation (Mx index). In the current study we computed Fix during ICP plateau waves, to observe its behavior during a defined period of cerebrovascular vasodilatation.

Methods

Twenty-nine recordings of arterial blood pressure (ABP), ICP, and CBFV taken during ICP plateau waves were obtained from the Addenbrooke’s hospital TBI database. Raw data was filtered prior to computing Mx and Fix according to previously published methods. Analyzed data was segmented into three phases (pre, peak, and post), and a median value of each parameter was stored for analysis.

Results

ICP increased from a median of 22–44 mmHg before falling to 19 mmHg. Both Mx and Fix responded to the increase in ICP, with Mx trending toward +1, while Fix trended toward ?1. Mx and Fix correlated significantly (Spearman’s R = ?0.89, p < 0.000001), however, Fix spanned a greater range than Mx. A plot of Mx and Fix against CPP showed a plateau (Mx) or trough (Fix) consistent with a zone of “optimal CPP”.

Conclusions

The Fix index can identify complete loss of cerebral autoregulation as the point at which the normally positive CBF/CBV correlation is reversed. Both CBF and CBV can be monitored noninvasively using near-infrared spectroscopy (NIRS), suggesting that a noninvasive method of monitoring autoregulation using only NIRS may be possible.     

Should the Neurointensive Care Management of Traumatic Brain Injury Patients be Individualized According to Autoregulation Status and Injury Subtype?

Introduction

The status of autoregulation is an important prognostic factor in traumatic brain injury (TBI), and is important to consider in the management of TBI patients. Pressure reactivity index (PRx) is a measure of autoregulation that has been thoroughly studied, but little is known about its variation in different subtypes of TBI. In this study, we examined the impact of PRx and cerebral perfusion pressure (CPP) on outcome in different TBI subtypes.

Methods

107 patients were retrospectively studied. Data on PRx, CPP, and outcome were collected from our database. The first CT scan was classified according to the Marshall classification system. Patients were assigned to “diffuse” (Marshall class: diffuse-1, diffuse-2, and diffuse-3) or “focal” (Marshall class: diffuse-4, evacuated mass lesion, and non-evacuated mass lesion) groups. 2 × 2 tables were constructed calculating the proportions of favorable/unfavorable outcome at different combinations of PRx and CPP.

Results

Low PRx was significantly associated with favorable outcome in the combined group (p = 0.002) and the diffuse group (p = 0.04), but not in the focal group (p = 0.06). In the focal group higher CPP values were associated with worse outcome (p = 0.02). In diffuse injury patients with disturbed autoregulation (PRx >0.1), CPP >70 mmHg was associated with better outcome (p = 0.03).

Conclusion

TBI patients with diffuse injury may differ from those with mass lesions. In the latter higher levels of CPP may be harmful, possibly due to BBB disruption. In TBI patients with diffuse injury and disturbed autoregulation higher levels of CPP may be beneficial.     

The Values of Cerebrovascular Pressure Reactivity and Brain Tissue Oxygen Pressure Reactivity in Experimental Anhepatic Liver Failure

Background

We investigated in a porcine model of anhepatic acute liver failure (ALF), the value of two parameters describing cerebrovascular autoregulatory capacity, pressure reactivity index (PRx) and brain tissue oxygen pressure reactivity (ORx), regarding their power to predict the development of intracranial hypertension.

Methods

In six pigs, hepatectomy was performed. Only one animal was sham operated. All animals received neuromonitoring including arterial blood pressure, intracranial pressure (ICP), and brain tissue partial oxygen pressure (P_brO₂). The average time of neuromonitoring was 31.0 h. Cerebral perfusion pressures (CPP), cerebrovascular pressure reactivity index (PRx) and brain tissue oxygen reactivity index (ORx) were calculated.

Results

Perioperative disturbance of AR improved within 4 h after surgery. From 6 to 16 h post hepatectomy, ICP did slowly increase by 4 mmHg from baseline; CPP remained stable around 40 mmHg. PRx and ORx, however, indicated in this period a progressive loss of AR, reflected in a decrease of P_brO₂ despite unchanged CPP. Beyond 16 h, ICP rose quickly. At CPP levels below 35 mmHg, P_brO₂ fell to ischemic levels.

Conclusions

The loss of cerebrovascular autoregulatory capacity, indicated by a rise of PRx and ORx precedes the final crisis of uncontrollable intracranial hypertension in this animal model by hours. During this phase cerebral blood flow, as reflected in tissue oxygenation, deteriorates despite unchanged CPP. Monitoring of AR during ALF therefore seems to carry the power to identify a risk for development of critical CBF and intracranial hypertension.

     

Effect of Percutaneous Tracheostomy on Intracerebral Pressure and Perfusion Pressure in Patients with Acute Cerebral Dysfunction (TIP Trial): An Observational Study

Background

Bedside percutaneous tracheostomy (PT) is very commonly used for patients who require prolonged mechanical ventilation. The effect of tracheostomy on intracranial pressure (ICP) is currently a subject of controversy. The aim of our study is to clarify the relation between PT and its effect on ICP and cerebral perfusion pressure.

Methods

38 patients on our intensive care unit were included prospectively in an observational study. We examined mean values of HF, SpO₂, ICP, CPP, and MAP for changes over five different phases of the procedure using paired Mann?CWhitney U tests. A p value of <0.05 was considered significant. p values were Bonferroni corrected for multiple testing.

Results

PT was performed on 38 patients (f?=?19, m?=?19; mean?=?56?years). Median ICP before intervention was 9?mmHg. During positioning of the patient, ICP had risen to 14, during bronchoscopy to 16, and during tracheostomy to 18?mmHg, all being significantly higher than baseline level. Monitoring of MAP showed a significant increase to 101?mmHg only during tracheostomy. SpO₂ and HF did not show any significant changes. Mean duration of positioning, bronchoscopy and tracheostomy was 19, 10, and 17?min. 8 patients received osmotherapy due to a rise of ICP of more than 30?mmHg.

Conclusion

PT only leads to a significant rise of ICP during the procedure. Nevertheless, therapy of ICP is necessary in some patients. From our point of view, therefore, tracheostomy should only be performed under continuous monitoring of ICP and CPP in patients with severe cerebral dysfunctions and critically elevated ICP.     

The Effect of Positive End-Expiratory Pressure on Intracranial Pressure and Cerebral Hemodynamics

Background

Lung protective ventilation has not been evaluated in patients with brain injury. It is unclear whether applying positive end-expiratory pressure (PEEP) adversely affects intracranial pressure (ICP) and cerebral perfusion pressure (CPP). We aimed to evaluate the effect of PEEP on ICP and CPP in a large population of patients with acute brain injury and varying categories of acute lung injury, defined by PaO₂/FiO₂.

Method

Retrospective data were collected from 341 patients with severe acute brain injury admitted to the ICU between 2008 and 2015. These patients experienced a total of 28,644 paired PEEP and ICP observations. Demographic, hemodynamic, physiologic, and ventilator data at the time of the paired PEEP and ICP observations were recorded.

Results

In the adjusted analysis, a statistically significant relationship between PEEP and ICP and PEEP and CPP was found only among observations occurring during periods of severe lung injury. For every centimeter H₂O increase in PEEP, there was a 0.31 mmHg increase in ICP (p = 0.04; 95 % CI [0.07, 0.54]) and a 0.85 mmHg decrease in CPP (p = 0.02; 95 % CI [?1.48, ?0.22]).

Conclusion

Our results suggest that PEEP can be applied safely in patients with acute brain injury as it does not have a clinically significant effect on ICP or CPP. Further prospective studies are required to assess the safety of applying a lung protective ventilation strategy in brain-injured patients with lung injury.

     

Cerebrovascular Pressure Reactivity and Cerebral Oxygen Regulation After Severe Head Injury

Background

To investigate the relationship between cerebrovascular pressure reactivity and cerebral oxygen regulation after head injury.

Methods

Continuous monitoring of the partial pressure of brain tissue oxygen (P_brO₂), mean arterial blood pressure (MAP), and intracranial pressure (ICP) in 11 patients. The cerebrovascular pressure reactivity index (PRx) was calculated as the moving correlation coefficient between MAP and ICP. For assessment of the cerebral oxygen regulation system a brain tissue oxygen response (TOR) was calculated, where the response of P_brO₂ to an increase of the arterial oxygen through ventilation with 100 % oxygen for 15 min is tested. Arterial blood gas analysis was performed before and after changing ventilator settings.

Results

Arterial oxygen increased from 108 ± 6 mmHg to 494 ± 68 mmHg during ventilation with 100 % oxygen. P_brO₂ increased from 28 ± 7 mmHg to 78 ± 29 mmHg, resulting in a mean TOR of 0.48 ± 0.24. Mean PRx was 0.05 ± 0.22. The correlation between PRx and TOR was r = 0.69, P = 0.019. The correlation of PRx and TOR with the Glasgow outcome scale at 6 months was r = 0.47, P = 0.142; and r = ?0.33, P = 0.32, respectively.

Conclusions

The results suggest a strong link between cerebrovascular pressure reactivity and the brain’s ability to control for its extracellular oxygen content. Their simultaneous impairment indicates that their common actuating element for cerebral blood flow control, the cerebral resistance vessels, are equally impaired in their ability to regulate for MAP fluctuations and changes in brain oxygen.     

A National Trial on Differences in Cerebral Perfusion Pressure Values by Measurement Location

Background

Cerebral perfusion pressure (CPP) is a key parameter in management of brain injury with suspected impaired cerebral autoregulation. CPP is calculated by subtracting intracranial pressure (ICP) from mean arterial pressure (MAP). Despite consensus on importance of CPP monitoring, substantial variations exist on anatomical reference points used to measure arterial MAP when calculating CPP. This study aimed to identify differences in CPP values based on measurement location when using phlebostatic axis (PA) or tragus (Tg) as anatomical reference points. The secondary study aim was to determine impact of differences on patient outcomes at discharge.

Methods

This was a prospective, repeated measures, multi-site national trial. Adult ICU patients with neurological injury necessitating ICP and CPP monitoring were consecutively enrolled from seven sites. Daily MAP/ICP/CPP values were gathered with the arterial transducer at the PA, followed by the Tg as anatomical reference points.

Results

A total of 136 subjects were enrolled, resulting in 324 paired observations. There were significant differences for CPP when comparing values obtained at PA and Tg reference points (p < 0.000). Differences remained significant in repeated measures model when controlling for clinical factors (mean CPP-PA = 80.77, mean CPP-Tg = 70.61, p < 0.000). When categorizing CPP as binary endpoint, 18.8% of values were identified as adequate with PA values, yet inadequate with CPP values measured at the Tg.

Conclusion

Findings identify numerical differences for CPP based on anatomical reference location and highlight importance of a standard reference point for both clinical practice and future trials to limit practice variations and heterogeneity of findings.

     

Compensatory-Reserve-Weighted Intracranial Pressure and Its Association with Outcome After Traumatic Brain Injury

Objective

We introduced ‘compensatory-reserve-weighted intracranial pressure (ICP),’ named ‘weightedICP’ for brevity, as a variable that may better describe changes leading to mortality after traumatic brain injury (TBI) over the standard mean ICP.

Methods

ICP was monitored prospectively in over 1023 sedated and ventilated patients. The RAP coefficient (R—correlation, A—amplitude, and P—pressure) was calculated as the running correlation coefficient between slow changes in the pulse amplitude of ICP and the mean ICP. RAP has a value of 0 on the linear part of the pressure–volume curve and a value of + 1 on the ascending exponential part. Then, RAP decreases towards zero or even becomes negative when ICP increases further—a phenomenon thought to be related to the critical closing of cerebral vessels. In this study, we investigated a derived variable called weightedICP, calculated as ICP*(1 ? RAP).

Results

Mortality after TBI was associated with both elevated ICP and weightedICP. Analysis of variance showed higher values of test statistics for weightedICP (K = 93) than for ICP (K = 64) in outcome categorization. Additionally, receiver operator curve analysis indicated greater area under the curve for weightedICP (0.71) than for ICP (0.67) with respect to associated mortality; however, the difference was not statistically significant (p = 0.12). The best threshold (maximizing sensitivity and specificity) was 19.5 mm Hg for mean ICP, and 8 mm Hg for weightedICP. Mortality rate expressed as a function of mean ICP and weightedICP showed an ascending profile in both cases.

Conclusion

The proposed variable shows a significant association with mortality following head injury. It is sensitive to both the rising absolute ICP and to the critical deterioration of pressure–volume compensation.

     

Continuous Cerebral Blood Flow Autoregulation Monitoring in Patients Undergoing Liver Transplantation

Background

Clinical monitoring of cerebral blood flow (CBF) autoregulation in patients undergoing liver transplantation may provide a means for optimizing blood pressure to reduce the risk of brain injury. The purpose of this pilot project is to test the feasibility of autoregulation monitoring with transcranial Doppler (TCD) and near-infrared spectroscopy (NIRS) in patients undergoing liver transplantation and to assess changes that may occur perioperatively.

Methods

We performed a prospective observational study in 9 consecutive patients undergoing orthotopic liver transplantation. Patients were monitored with TCD and NIRS. A continuous Pearson??s correlation coefficient was calculated between mean arterial pressure (MAP) and CBF velocity and between MAP and NIRS data, rendering the variables mean velocity index (Mx) and cerebral oximetry index (COx), respectively. Both Mx and COx were averaged and compared during the dissection phase, anhepatic phase, first 30?min of reperfusion, and remaining reperfusion phase. Impaired autoregulation was defined as Mx????0.4.

Results

Autoregulation was impaired in one patient during all phases of surgery, in two patients during the anhepatic phase, and in one patient during reperfusion. Impaired autoregulation was associated with a MELD score?>15 (p?=?0.015) and postoperative seizures or stroke (p?p?=?0.0029). The relationship between COx and Mx remained when only patients with bilirubin?>1.2?mg/dL were evaluated (p?=?0.0419). There was no correlation between COx and baseline bilirubin (p?=?0.2562) but MELD score and COx were correlated (p?=?0.0458). Average COx was higher for patients with a MELD score?>15 (p?=?0.073) and for patients with a neurologic complication than for patients without neurologic complications (p?=?0.0245).

Conclusions

These results suggest that autoregulation is impaired in patients undergoing liver transplantation, even in the absence of acute, fulminant liver failure. Identification of patients at risk for neurologic complications after surgery may allow for prompt neuroprotective interventions, including directed pressure management.     

Effect of Early Physiotherapy on Intracranial Pressure and Cerebral Perfusion Pressure

Background

Physiotherapy plays an important role in the therapy of patients with acute cerebral diseases. Studies concerning the effects of physiotherapy on intracerebral pressure (ICP) and cerebral perfusion pressure (CPP) are, however, rare.

Methods

An observational study was performed on critically ill patients who were receiving ICP measurements and who were treated with passive range of motion (PROM) on our neuro-intensive care unit. ICP, CPP, mean arterial pressure (MAP) and heart rate were recorded continuously every minute, beginning 15 min before, during (26 min) and 15 min after treatment with PROM. Patients with mean ICP <15 mmHg (Group 1) and patients with mean ICP ≥15 mmHg (Group 2) before physiotherapy were analyzed separately.

Results

Overall there were 84 patients (f:m = 1:1) with 298 treatments units, 224 in Group 1 and 74 in Group 2, respectively. Mean ICP before treatment was 11.5 ± 5.1 mmHg, with a significant decrease of 1 mmHg during therapy (p = 2.0e–10). This was also true for Group 1 (baseline ICP 9.4 ± 3.7 mmHg, decrease of 0.7 mmHg, p = 3.8e–6) and Group 2 (baseline ICP 18.1 ± 2.7 mmHg, decrease of 2 mmHg, p = 3.7e–6). However, a persistent ICP reduction after therapy was seen only in Group 2. There were no significant differences between mean CPP and MAP comparing ICP before and after PROM in all groups. No adverse side effects of PROM were observed.

Conclusions

Physiotherapy with PROM can be used safely in patients with acute neurological diseases, even if ICP is elevated before therapy.