Changes in intracranial pressure and cerebral autoregulation in patients with severe traumatic brain injury

Escalating Mean Arterial Pressure in Severe Traumatic Brain Injury: A Prospective, Observational Study

To investigate cerebral autoregulatory status in patients with severe traumatic brain injury (TBI), guidelines now suggest active manipulation of mean arterial pressure (MAP). There is a paucity of data, however, describing the effect on intracranial pressure (ICP) when MAP is raised. Consecutive patients with TBI requiring ICP monitoring were enrolled from November 2019 to April 2020. The MAP and ICP were recorded continuously, and clinical annotations were made whenever intravenous vasopressors were commenced or adjusted to defend cerebral perfusion pressure (CPP) targets. A significant change in MAP burden was defined as MAP >100min.mm Hg over 15 min. The primary outcome was the change in ICP burden over the same 15-min period. Bedside and clinical parameters were then compared between these groups. Twenty-eight patients were enrolled, providing 212 clinical events, of which 60 were deemed significant. Over the first 15 min, 65% were associated with a net negative ICP burden. A greater reduction in ICP burden was observed with events occurring in patients without a history of hypotension at scene (p = 0.016), after three days post-injury (p = 0.0018), and where the pressure-reactivity index (PRx) was <0.25 (p = 0.0005) or the ICP amplitude to CPP correlation coefficient (RAC) was <-0.10 (p = 0.0036) at the initiation of vasopressor changes. The ICP burden in the first 15 min was highly correlated with the next 15-min period. In patients with severe TBI requiring ICP monitoring, increasing MAP to pursue a CPP target was followed by a net negative ICP burden in approximately two-thirds of events. These data suggest a MAP challenge may be a useful adjunct in managing intracranial hypertension.

Cerebrovascular Autoregulation Monitoring in the Management of Adult Severe Traumatic Brain Injury: A Delphi Consensus of Clinicians

BACKGROUND

Several methods have been proposed to measure cerebrovascular autoregulation (CA) in traumatic brain injury (TBI), but the lack of a gold standard and the absence of prospective clinical data on risks, impact on care and outcomes of implementation of CA-guided management lead to uncertainty.

AIM

To formulate statements using a Delphi consensus approach employing a group of expert clinicians, that reflect current knowledge of CA, aspects that can be implemented in TBI management and CA research priorities.

METHODS

A group of 25 international academic experts with clinical expertise in the management of adult severe TBI patients participated in this consensus process. Seventy-seven statements and multiple-choice questions were submitted to the group in two online surveys, followed by a face-to-face meeting and a third online survey. Participants received feedback on average scores and the rationale for resubmission or rephrasing of statements. Consensus on a statement was defined as agreement of more than 75% of participants.

RESULTS

Consensus amongst participants was achieved on the importance of CA status in adult severe TBI pathophysiology, the dynamic non-binary nature of CA impairment, its association with outcome and the inadvisability of employing universal and absolute cerebral perfusion pressure targets. Consensus could not be reached on the accuracy, reliability and validation of any current CA assessment method. There was also no consensus on how to implement CA information in clinical management protocols, reflecting insufficient clinical evidence.

CONCLUSION

The Delphi process resulted in 25 consensus statements addressing the pathophysiology of impaired CA, and its impact on cerebral perfusion pressure targets and outcome. A research agenda was proposed emphasizing the need for better validated CA assessment methods as well as the focused investigation of the application of CA-guided management in clinical care using prospective safety, feasibility and efficacy studies.

Secondary Cerebral Ischemia at Traumatic Brain Injury Is More Closely Related to Cerebrovascular Reactivity Impairment than to Intracranial Hypertension

The purpose of this study was to investigate the relationship between the development of secondary cerebral ischemia (SCI), intracranial pressure (ICP) and cerebrovascular reactivity (CVR) after traumatic brain injury (TBI).

METHODS

89 patients with severe TBI with ICP monitoring were studied retrospectively. The mean age was 36.3 ± 4.8 years, 53 men, 36 women. The median Glasgow Coma Score (GCS) was 6.2 ± 0.7. The median Injury Severity Score was 38.2 ± 12.5. To specify the degree of impact of changes in ICP and CVR on the SCI progression in TBI patients, logistic regression was performed. Significant p-values were <0.05.

RESULTS

The deterioration of CVR in combination with the severity of ICP has a significant impact on the increase in the prevalence rate of SCI. A logistic regression analysis for a model of SCI dependence on intracranial hypertension and CVR was performed. The results of the analysis showed that CVR was the most significant factor affecting SCI development in TBI.

CONCLUSIONS

The development of SCI in severe TBI depends largely on CVR impairment and to a lesser extent on ICP level. Treatment for severe TBI patients with SCI progression should not be aimed solely at intracranial hypertension correction but also at CVR recovery.

Predictable Values of Decompressive Craniectomy in Patients with Acute Subdural Hematoma: Comparison between Decompressive Craniectomy after Craniotomy Group and Craniotomy Only Group

Objective

Patients with traumatic acute subdural hematoma (ASDH) often require surgical treatment. Among patients who primarily underwent craniotomy for the removal of hematoma, some consequently developed aggressive intracranial hypertension and brain edema, and required secondary decompressive craniectomy (DC). To avoid reoperation, we investigated factors which predict the requirement of DC by comparing groups of ASDH patients who did and did not require DC after craniotomy.

Methods

The 129 patients with ASDH who underwent craniotomy from September 2007 to September 2017 were reviewed. Among these patients, 19 patients who needed additional DC (group A) and 105 patients who underwent primary craniotomy only without reoperation (group B) were evaluated. A total of 17 preoperative and intraoperative factors were analyzed and compared statistically. Univariate and multivariate analyses were used to compare these factors.

Results

Five factors showed significant differences between the two groups. They were the length of midline shifting to maximal subdural hematoma thickness ratio (magnetization transfer [MT] ratio) greater than 1 (p<0.001), coexistence of intraventricular hemorrhage (IVH) (p<0.001), traumatic intracerebral hemorrhage (TICH) (p=0.001), intraoperative findings showing intracranial hypertension combined with brain edema (p<0.001), and bleeding tendency (p=0.02). An average value of 2.74±1.52 was obtained for these factors for group A, which was significantly different from that for group B (p<0.001).

Conclusion

An MT ratio >1, IVH, and TICH on preoperative brain computed tomography images, intraoperative signs of intracranial hypertension, brain edema, and bleeding tendency were identified as factors indicating that DC would be required. The necessity for preemptive DC must be carefully considered in patients with such risk factors.

Intracranial Hypertension and Cerebral Autoregulation: A Systematic Review and Meta-Analysis

OBJECTIVE

To present a systematic review and meta-analysis to establish the relation between cerebral autoregulation (CA) and intracranial hypertension.

METHODS

An electronic search using the term "Cerebral autoregulation and intracranial hypertension" was designed to identify studies that analyzed cerebral blood flow autoregulation in patients undergoing intracranial pressure (ICP) monitoring. The data were used in meta-analyses and sensitivity analyses.

RESULTS

A static CA technique was applied in 10 studies (26.3%), a dynamic technique was applied in 25 studies (65.8%), and both techniques were used in 3 studies (7.9%). Static CA studies using the cerebral blood flow technique revealed impaired CA in patients with an ICP ≥20 (standardized mean difference [SMD] 5.44%, 95% confidence interval [CI] 0.25-10.65, P = 0.04); static CA studies with transcranial Doppler revealed a tendency toward impaired CA in patients with ICP ≥20 (SMD -7.83%, 95% CI -17.52 to 1.85, P = 0.11). Moving correlation studies reported impaired CA in patients with ICP ≥20 (SMD 0.06, 95% CI 0.07-0.14, P < 0.00001). A comparison of CA values and mean ICP revealed a correlation between greater ICP and impaired CA (SMD 5.47, 95% CI 1.39-10.1, P = 0.01). Patients with ICP ≥20 had an elevated risk of impaired CA (OR 2.27, 95% CI 1.20-4.31, P = 0.01).

CONCLUSIONS

A clear tendency toward CA impairment was observed in patients with increased ICP.

The value of intraoperative intracranial pressure monitoring for predicting re-operation using salvage decompressive craniectomy after craniotomy in patients with traumatic mass lesions

BACKGROUND

The risk factors of predicting the need for postoperative decompressive craniectomy due to intracranial hypertension after primary craniotomy remain unclear. This study aimed to investigate the value of intraoperative intracranial pressure (ICP) monitoring in predicting re-operation using salvage decompressive craniectomy (SDC).

METHODS

From January 2008 to October 2014, we retrospectively reviewed 284 patients with severe traumatic brain injury (STBI) who underwent craniotomy for mass lesion evacuation without intraoperative brain swelling. Intraoperative ICP was documented at the time of initial craniotomy and then again after the dura was sutured. SDC was used when postoperative ICP was continually higher than 25 mmHg for 1 h without a downward trend. Univariate and multivariate analyses were applied to both initial demographic and radiographic features to identify risk factors of SDC requirement.

RESULTS

Of 284, 41 (14.4%) patients who underwent SDC had a higher Initial ICP than those who didn't (38.1 ± 9.2 vs. 29.3 ± 8.1 mmHg, P < 0.001), but there was no difference in ICP after the dura was sutured. The factors which have significant effects on SDC are higher initial ICP [odds ratio (OR): 1.100, 95% confidence interval (CI): 1.052-1.151, P < 0.001], older age (OR: 1.039, 95% CI: 1.002-1.077, P = 0.039), combined lesions (OR: 3.329, 95% CI: 1.199-9.244, P = 0.021) and early hypotension (OR: 2.524, 95% CI: 1.107-5.756, P = 0.028). The area under the curve of multivariate regression model was 0.771.

CONCLUSIONS

The incidence of re-operation using SDC after craniotomy was 14.4%. The independent risk factors of SDC requirement are initial ICP, age, early hypotension and combined lesions.

Carotid artery blood flow decreases after rapid head rotation in piglets

Modification of cerebral perfusion pressure and cerebral blood flow (CBF) are crucial components of the therapies designed to reduce secondary damage after traumatic brain injury (TBI). Previously we documented a robust decrease in CBF after rapid sagittal head rotation in our well-validated animal model of diffuse TBI. Mechanisms responsible for this immediate (<10 min) and sustained (∼24 h) reduction in CBF have not been explored. Because the carotid arteries are a major source of CBF, we hypothesized that blood flow through the carotid arteries (Q) and vessel diameter (D) would decrease after rapid nonimpact head rotation without cervical spine injury. Four-week-old (toddler) female piglets underwent rapid (<20 msec) sagittal head rotation without impact, previously shown to produce diffuse TBI with reductions in CBF. Ultrasonographic images of the bilateral carotid arteries were recorded at baseline (pre-injury), as well as immediately after head rotation and 15, 30, 45, and 60 min after injury. Diameter (D) and waveform velocity (V) were used to calculate blood flow (Q) through the carotid arteries using the equation Q=(0.25)πD(2)V. D, V, and Q were normalized to the pre-injury baseline values to obtain a relative change after injury in right and left carotid arteries. Three-way analysis of variance and post-hoc Tukey-Kramer analyses were used to assess statistical significance of injury, time, and side. The relative change in carotid artery diameter and flow was significantly decreased in injured animals in comparison with uninjured sham controls (p<0.0001 and p=0.0093, respectively) and did not vary with side (p>0.39). The average carotid blood velocity did not differ between sham and injured animals (p=0.91). These data suggest that a reduction in global CBF after rapid sagittal head rotation may be partially mediated by a reduction in carotid artery flow, via vasoconstriction.

Higher optic nerve sheath diameters are associated with lower ocular blood flow velocities in glaucoma patients

PURPOSE

To investigate the relationship between optic nerve sheath diameter (ONSD) and retrobulbar blood flow velocities, as measured by color Doppler imaging (CDI) in glaucoma patients.

METHODS

We performed a prospective, randomized, observer-masked study involving a total of 197 subjects. Once enrolled, they were divided by three groups: healthy controls (n = 51), normal-tension glaucoma patients (NTG, n = 58), and primary, open-angle glaucoma patients (POAG, n = 88). All subjects underwent a general ophthalmological examination, an ultrasound-based assessment of the ONSD, and a hemodynamic study of the retrobulbar vascularization using CDI. Non-parametric tests, chi-square contingency tables, and the Deming correlations were used to explore differences and correlations between variables in the diagnostic groups.

RESULTS

ONSD was not different between experimental groups (p = 0.28). ONSD correlated positively with the pulsatility index of the ophthalmic artery in healthy individuals (p = 0.007), but not in glaucoma patients (NTG: p = 0.41; POAG: p = 0.22). In NTG patients, higher ONSD values were associated with lower end-diastolic and mean flow velocities in the short ciliary arteries (p = 0.005 in both correlations). No such correlation was found in healthy nor POAG groups (p range between 0.15 to 0.96). ONSD was not associated with any CDI-related variable of the central retinal artery in any cohort. Venous outflow velocities were not associated with ONSD in any of the three groups.

CONCLUSIONS

ONSD is negatively correlated with retrobulbar blood flow velocities in glaucoma patients, but not in healthy controls.

Transcranial Doppler can predict intracranial hypertension in children with severe traumatic brain injuries

PURPOSE

The purpose of this study is to evaluate the accuracy of emergency Transcranial Doppler (TCD) to predict intracranial hypertension and abnormal cerebral perfusion pressure in children with severe traumatic brain injury (TBI).

PATIENTS AND METHODS

A descriptive and retrospective cross-sectional study was designed through data collected from medical records of children with severe TBI (Glasgow coma scale ≤ 8), admitted to a level I pediatric trauma center, between January 2000 and December 2005. Early TCD examination was performed upon admission, and TCD profiles were considered as altered using previously validated threshold values for diastolic velocity (<25 cm/s) and pulsatility index (>1.31) or when no-flow/backflow was detected. Invasive intracranial pressure (ICP) and cerebral perfusion pressure (CPP) monitoring were considered as the gold standard to measure intracranial hypertension (ICH). Statistical analyses compared TCD profiles to increased ICP (≥ 20 mmHg) and abnormal cerebral perfusion pressure (<50 mmHg) at admission.

RESULTS

Non-invasive TCD and ICP monitoring were performed in 117 severe head-injured children. Mean age was 7.6 ± 4.4 years, with a male prevalence (71%). Median initial Glasgow coma scale was 6. TCD had 94% of sensitivity to identify ICH at admission and a negative predict value of 95% to identify normal ICP at admission. Its sensitivity to predict abnormal cerebral perfusion pressure was 80%.

CONCLUSIONS

The high sensitivity of admission TCD to predict ICH and abnormal CPP after trauma demonstrates that TCD is an excellent first-line examination to determine those children who need urgent aggressive treatment and continuous invasive ICP monitoring.

Blood Pressure Management in Acute Head Injury

Head injury remains a major cause of preventable death and serious morbidity in young adults. Based on the available evidence, it appears that a cerebral perfusion pressure of 50 to 70 mm Hg is generally adequate to ensure cerebral oxygen delivery and prevent ischemia. However, evidence suggests that perfusion requirements may not only vary across the injured brain but also differ depending on the time since injury. Such heterogeneity, both within and between subjects, suggests that individualized therapy may be an appropriate treatment strategy. Future studies should aim to assess which groups of patients, and what regional pathophysiological derangements, may benefit with improvements in functional outcome from therapeutic increases or decreases in cerebral perfusion pressure beyond these proposed limits. Such functional improvements may be of immense importance to patients and require formal neurocognitive assessments to discriminate improvements.

One-minute dynamic cerebral autoregulation in severe head injury patients and its comparison with static autoregulation. A transcranial Doppler study

OBJECTIVE

To compare dynamic and static responses of cerebral blood flow to sudden or slow changes in arterial pressure in severe traumatic brain injury (TBI) patients.

DESIGN

Prospective study.

PATIENTS AND METHODS

We studied 12 severe TBI patients, age 16-63 years, and median GCS 6. We determined the dynamic cerebral autoregulation: response of cerebral blood flow velocity to a step blood pressure drop, and the static cerebral autoregulation: change in cerebral blood flow velocity after a slow hypertensive challenge.

RESULTS

During the dynamic response, the median drop in arterial pressure was 21 mm Hg. Dynamic response was graded between 9 (best) and 0 (worst). The median value was 5; four patients showed high values, (8-9), five patients showed intermediate values (4-6). In three patients (value = 0), the CBFV drop was greater than the cerebral perfusion pressure drop, and maintained through 60 s. The static cerebral autoregulation was preserved in 6/11 patients. The comparison between the two showed four different combinations. The five patients with impaired static cerebral autoregulation showed unfavorable outcome.

CONCLUSIONS

A sharp dynamic vasodilator response could not be sustained, and a slow or absent reaction to a sudden hypotensive challenge could show an acceptable cerebral autoregulation in the steady state. We found that patients with impaired static cerebral autoregulation had a poor outcome, whereas those with preserved static cerebral autoregulation experience favorable outcomes.

Design and validation of a critical pathway for hospital management of patients with severe traumatic brain injury

BACKGROUND

Critical pathways for the management of patients with severe traumatic brain injury (STBI) may contribute to reducing the incidence of hospital complications, length of hospitalization stay, and cost of care. Such pathways have previously been developed for departments with significant resource availability. In Mexico, STBI is the most important cause of complications and length of stay in neurotrauma services at public hospitals. Although current treatment is designed basically in accordance with the Brain Trauma Foundation guidelines, shortfalls in the availability of local resources make it difficult to comply with these standards, and no critical pathway is available that accords with the resources of public hospitals. The purpose of the present study was to design and to validate a critical pathway for managing STBI patients that would be suitable for implementation in neurotrauma departments of middle-income level countries.

METHODS

The study comprised two phases: design (through literature review and design plan) and validation (content, construct, and appearance) of the critical pathway.

RESULTS

The validated critical pathway for managing STBI patients entails four sequential subprocesses summarizing the hospital's care procedures, and includes three components: (1) nodes and criteria (in some cases, indicators are also included); (2) health team members in charge of the patient; (3) maximum estimated time for compliance with recommendations.

CONCLUSIONS

This validated critical pathway is based on the current scientific evidence and accords with the availability of resources of middle-income countries.

CURRENT CONTROVERSIES IN THE MANAGEMENT OF PATIENTS WITH SEVERE TRAUMATIC BRAIN INJURY

BACKGROUND

Traumatic brain injury is a major cause of mortality and morbidity, particularly among young men. The efficacy and safety of most of the interventions used in the management of patients with traumatic brain injury remain unproven. Examples include the 'cerebral perfusion pressure-targeted' and 'volume-targeted' management strategies for optimizing cerebrovascular haemodynamics and specific interventions, such as hyperventilation, osmotherapy, cerebrospinal fluid drainage, barbiturates, decompressive craniectomy, therapeutic hypothermia, normobaric hyperoxia and hyperbaric oxygen therapy.

METHODS

A review of the literature was performed to examine the evidence base behind each intervention.

RESULTS

There is no class I evidence to support the routine use of any of the therapies examined.

CONCLUSION

Well-designed, large, randomized controlled trials are needed to determine therapies that are safe and effective from those that are ineffective or harmful.

Association between dynamic cerebral autoregulation and mortality in severe head injury

The objective of the study was to test the hypothesis that dynamic cerebral pressure-autoregulation is associated with the outcome of patients with severe head injury and to derive optimal criteria for future studies on the predictive value of autoregulation indices. Repeated measurements were performed on 32 patients with severe head injury. Arterial blood pressure (ABP) was measured continuously with an intravascular catheter, intracranial pressure (ICP) was recorded with a subdural semiconductor transducer and cerebral blood flow velocity (CBFV) was measured with Doppler ultrasound in the middle cerebral artery. Transfer function analysis was performed on mean beat-to-beat values, using ABP or CBFV as input variables and CBFV or ICP as the output variables. A dynamic index of autoregulation (ARI) ranging between 0 and 9 was extracted from the CBFV step response for a change in ABP. No significant differences between survivors and non-survivors were found due to mean values of ICP, ABP, CPP, CBFV, pCO2, GCS, age or heart rate. The transfer functions between ABP-ICP and CBFV-ICP did not show any significant differences either. The median [lower, upper quartiles] ARI was significantly lower for non-survivors compared with survivors [4.8 (0.0, 5.9) v. 6.9 (5.9, 7.4), p= 0.004]. The correlation between ARI and GOS was also significant (r=0.464, p=0.011). Cohen's coefficient was optimal for a threshold of ARI= 5.86 (kappa 0.51, p=0.0036), leading to a sensitivity for death of 75%, specificity=76.5%, odds ratio =9.75 and overall precision = 75.8%. The difference in ARI values between survivors and non-survivors persisted when results were adjusted for GCS (p = 0.028). A similar analysis for the Marshall CT scale did not reach significance (p = 0.072). A logistic regression analysis confirmed that apart from the ARI, no other variables had a significant contribution to predict outcome. In this group of patients, death following severe head injury could not be explained by traditional indices of risk, but was strongly correlated to indices of dynamic cerebral pressure-autoregulation extracted by means of transfer function analysis. Future studies using a prospective design are needed to validate the predictive value of the ARI index, as estimated by transfer function analysis, in relation to death and other unfavourable outcomes.

Cerebral hemodynamic responses to blood pressure manipulation in severely head-injured patients in the presence or absence of intracranial hypertension

The management of cerebral perfusion pressure (CPP) remains a controversial issue in the critical care of severely head-injured patients. Recently, it has been proposed that the state of cerebrovascular autoregulation should determine individual CPP targets. To find optimal perfusion pressure, we pharmacologically manipulated CPP in a range of 51 mm Hg (median; 25th-75th percentile, 48-53 mm Hg) to 108 mm Hg (102-112 mm Hg) on Days 0, 1, and 2 after severe head injury in 13 patients and studied the effects on intracranial pressure (ICP), autoregulation capacity, and brain tissue partial pressure of oxygen. Autoregulation was expressed as a static rate of regulation for 5-mm Hg CPP intervals based on middle cerebral artery flow velocity. When ICP was normal (26 occasions), there were no major changes in the measured variables when CPP was altered from a baseline level of 78 mm Hg (74-83 mm Hg), indicating that the brain was within autoregulation limits. Conversely, when intracranial hypertension was present (11 occasions), CPP reduction to less than 77 mm Hg (73-82 mm Hg) further increased ICP, decreased the static rate of regulation, and decreased brain tissue partial pressure of oxygen, whereas a CPP increase improved these variables, indicating that the brain was operating at the lower limit of autoregulation. We conclude that daily trial manipulation of arterial blood pressure over a wide range can provide information that may be used to optimize CPP management.

Therapeutic hypertension: principles and methods

The aspects of cardiovascular physiology important for the safe and effective implementation and titration of hypertensive therapy among neurosurgical patients with neurological or neurosurgical illness/injury are reviewed. Therapeutic hypertension may be an appropriate treatment for some neurological or neurosurgical conditions, e.g., vasospasm or support of cerebral perfusion pressure. Initiation and maintenance of hypertension should be done safely to avoid complications and/or undesired side effects. Accurate measurement of the arterial and central vascular pressures, the limitations of those methods, and alternative estimates of intravascular volume are reviewed. Hypertensive therapy is accomplished by modifying cardiac output and systemic vascular resistance, the principal physiological determinants of blood pressure. The goals of hypertensive therapy can be achieved by proper evaluation and manipulation of the four components of cardiac output, preload, afterload, heart rate and contractility. Measurement or calculation of estimates of these parameters is important in the selection of proper medications or supplemental fluid administration.

Traumatic brain injury

PURPOSE OF REVIEW

Management of the patient with traumatic brain injury is a rapidly advancing field, characterized in recent years by an improved understanding of intracranial pathophysiology and ways in which outcomes can be improved. Many traditional therapies, such as fluid restriction and hyperventilation, have been called into question and are no longer recommended. Other proposed therapies, such as deliberate hypothermia, remain controversial. This detailed review of the recent literature helps the reader come to an understanding of current scientific and evidence-based practices in this area, with emphasis on those therapies most likely to be of use to the practicing intensivist.

RECENT FINDINGS

High-quality care of the traumatic brain injury patient demands the integrated activities of a number of different medical and nursing specialties. The best outcomes today are achieved by those systems that are able to focus as a team on the collective goal of minimizing secondary brain injury, and the respiratory therapist adjusting the patient's mechanical ventilation may be just as important to this effort as the attending neurosurgeon. Although the search for new diagnostic, prognostic, and therapeutic modalities continues (many of the more promising of which are reviewed in this article), it is clear that there exists no "silver bullet" therapy that will help all patients. Instead, it is the systematic integration and application of many small advances that will ultimately lead to better outcomes.

SUMMARY

Some issues in traumatic brain injury have now been resolved, and specific recommendations can be made. Fluid therapy directed toward a euvolemic state is now universally recommended, for example, as is the role of intracranial pressure monitoring. Other areas, such as the use of hypertonic saline, remain controversial. In both cases the authors have made an effort to cite the most recent literature, so that readers can draw their own conclusions from the original source material.

Monitoring of cerebral perfusion pressure during intracranial hypertension: a sufficient parameter of adequate cerebral perfusion and oxygenation?

OBJECTIVE

A cerebral perfusion pressure (CPP) oriented treatment is a widely accepted standard for patients with intracranial hypertension. In an animal model of controlled intracranial hypertension we investigated whether CPP is a reliable parameter of sufficient cerebral perfusion and oxygenation. Using near-infrared reflexion spectroscopy the effect of decreasing CPP due to increasing intracranial pressure (ICP) on cerebral tissue oxygenation was studied.

METHODS

Ten rabbits were subjected to artificially elevated ICP using the cisterna-magna infusion technique. Regional cerebral O(2) saturation of hemoglobin (tiSO(2)), regional tissue concentration of hemoglobin (tiHb), and CPP were recorded continuously. CPP was investigated with respect to tiSO(2). Electrocortical activity was simultaneously recorded by two-channel EEG to determine the onset of ischemia.

RESULTS

Reduced CPP due to increased ICP led to a continuous decrease in tiSO(2.) There was progressive suppression of EEG frequency and amplitude with decreasing CPP in all animals. Onset of EEG-silence due to elevated ICP was observed in a wide range of CPP-values between 9 and 42 mmHg. At the same time tiSO(2) varied merely between 0 and 5%.

CONCLUSIONS

Regarding the EEG effects due to increased ICP (EEG silence), CPP values showed a wide interindividual variability, in contrast to tiSO(2). In our animal model the sole calculation of CPP did not reflect adequate cerebral perfusion.