Characterization of cerebrovascular reactivity after craniectomy for acute brain injury

Critical thresholds of long-pressure reactivity index and impact of intracranial pressure monitoring methods in traumatic brain injury

BACKGROUND

Moderate-to-severe traumatic brain injury (TBI) has a global mortality rate of about 30%, resulting in acquired life-long disabilities in many survivors. To potentially improve outcomes in this TBI population, the management of secondary injuries, particularly the failure of cerebrovascular reactivity (assessed via the pressure reactivity index; PRx, a correlation between intracranial pressure (ICP) and mean arterial blood pressure (MAP)), has gained interest in the field. However, derivation of PRx requires high-resolution data and expensive technological solutions, as calculations use a short time-window, which has resulted in it being used in only a handful of centers worldwide. As a solution to this, low resolution (longer time-windows) PRx has been suggested, known as Long-PRx or LPRx. Though LPRx has been proposed little is known about the best methodology to derive this measure, with different thresholds and time-windows proposed. Furthermore, the impact of ICP monitoring on cerebrovascular reactivity measures is poorly understood. Hence, this observational study establishes critical thresholds of LPRx associated with long-term functional outcome, comparing different time-windows for calculating LPRx as well as evaluating LPRx determined through external ventricular drains (EVD) vs intraparenchymal pressure device (IPD) ICP monitoring.

METHODS

The study included a total of n = 435 TBI patients from the Karolinska University Hospital. Patients were dichotomized into alive vs. dead and favorable vs. unfavorable outcomes based on 1-year Glasgow Outcome Scale (GOS). Pearson's chi-square values were computed for incrementally increasing LPRx or ICP thresholds against outcome. The thresholds that generated the greatest chi-squared value for each LPRx or ICP parameter had the highest outcome discriminatory capacity. This methodology was also completed for the segmentation of the population based on EVD, IPD, and time of data recorded in hospital stay.

RESULTS

LPRx calculated with 10-120-min windows behaved similarly, with maximal chi-square values ranging at around a LPRx of 0.25-0.35, for both survival and favorable outcome. When investigating the temporal relations of LPRx derived thresholds, the first 4 days appeared to be the most associated with outcomes. The segmentation of the data based on intracranial monitoring found limited differences between EVD and IPD, with similar LPRx values around 0.3.

CONCLUSION

Our work suggests that the underlying prognostic factors causing impairment in cerebrovascular reactivity can, to some degree, be detected using lower resolution PRx metrics (similar found thresholding values) with LPRx found clinically using as low as 10 min-by-minute samples of MAP and ICP. Furthermore, EVD derived LPRx with intermittent cerebrospinal fluid draining, seems to present similar outcome capacity as IPD. This low-resolution low sample LPRx method appears to be an adequate substitute for the clinical prognostic value of PRx and may be implemented independent of ICP monitoring method when PRx is not feasible, though further research is warranted.

Critical Care Experience With Clinical Cerebral Autoregulation Testing in Adults With Traumatic Brain Injury

BACKGROUND

To describe the setting, feasibility, and safety of static cerebral autoregulation testing in critically injured adults with traumatic brain injury (TBI).  Methods: We reviewed static autoregulation testing using transcranial Doppler (TCD) ultrasound in patients > 18 years with TBI ICD codes between January 1, 2014, and December 31, 2021. Adverse events during testing were defined as systemic hypertension (systolic blood pressure (SBP>180 mmHg), bradycardia (HR<40 bpm), and high ICP (>30 mmHg). Impaired and absent cerebral autoregulation was defined as an autoregulatory index (ARI) <0.4 and ARI 0, respectively. We characterized prescribed changes in intracranial pressure (ICP) and cerebral perfusion pressure (CPP) targets by autoregulation testing results.  Results: A total of 135 patients, median age 31 (interquartile range (IQR) 24, 43) years, 71.9% male, admission Glasgow coma scale (GCS) score 3 (IQR 3, 5.5), and 70.9% with subdural hematoma from severe (GCS 3-8; 133 (98.5%)) and moderate (GCS 9-12; 2 (1.5%)) TBI, underwent 309 attempted testing. All patients were mechanically ventilated and had ICP monitoring; 246 (80%) had brain tissue oxygen monitoring, and 68 (22%) had an external ventricular drain. The median number of autoregulation tests was two (range 1-3) tests/patient, and the median admission to the first test time was two days (IQR 1, 3). Of 55 (17.8%) tests not completed, systemic hypertension (32, 10.4%), intracranial hypertension (10, 3.2%), and bradycardia (3, 0.9%) were transient. Fifty-three (51%) of the first (n=104) autoregulation tests showed impaired/absent cerebral autoregulation. Impaired/absent autoregulation results at the first test were associated with repeat cerebral autoregulation testing (RR 2.25, 95% CI [1.40-3.60], p=0.0007) than intact cerebral autoregulation results. Pre-testing cerebral hemodynamic targets were maintained (n=131; 86.8%) when cerebral autoregulation was impaired (n=151; RR 1.49, 95% CI [1.25-1.77], p<0.0001). However, 15 (9.9%) test results led to higher ICP targets (from 20 mmHg to 25 mmHg), 5 (3.3%) results led to an increase in CPP target (from 60 mmHg to 70 mmHg), and five out of 131 (3.8%) patients underwent decompressive craniectomy and placement of an external ventricular drain. Intact cerebral autoregulation results (n=43/103, 41.7%) were associated with a change in ICP targets from 20 mmHg to 25 mmHg (RR 3.15, 95% CI [1.97-5.03], p<0.0001).  Conclusions: Static cerebral autoregulation testing was feasible, safe, and useful in individualizing the care of patients with moderate-severe TBI receiving multimodal neuromonitoring. Testing results guided future testing, cerebral hemodynamic targets, and procedural decisions. Impaired cerebral autoregulation was very common.

Evaluation and application of ultra-low-frequency pressure reactivity index in pediatric traumatic brain injury patients

PURPOSE

While clinical practice suggests that knowing the cerebral autoregulation (CA) status of traumatic brain injury (TBI) patients is crucial in assessing the best treatment, evidence in pediatric TBI (pTBI) is limited. The pressure reactivity index (PRx) is a surrogate method for the continuous estimation of CA in adults; however, calculations require continuous, high-resolution monitoring data. We evaluate an ultra-low-frequency pressure reactivity index (UL-PRx), based on data sampled at ∼5-min periods, and test its association with 6-month mortality and unfavorable outcome in a cohort of pTBI patients.

METHODS

Data derived from pTBI patients (0-18 years) requiring intracranial pressure (ICP) monitoring were retrospectively collected and processed in MATLAB using an in-house algorithm.

RESULTS

Data on 47 pTBI patients were included. UL-PRx mean values, ICP, cerebral perfusion pressure (CPP), and derived indices showed significant association with 6-month mortality and unfavorable outcome. A value of UL-PRx of 0.30 was identified as the threshold to better discriminate both surviving vs deceased patients (AUC: 0.90), and favorable vs unfavorable outcomes (AUC: 0.70) at 6 months. At multivariate analysis, mean UL-PRx and % time with ICP > 20 mmHg, remained significantly associated with 6-month mortality and unfavorable outcome, even when adjusted for International Mission for Prognosis and Analysis of Clinical Trials in TBI (IMPACT)-Core variables. In six patients undergoing secondary decompressive craniectomy, no significant changes in UL-PRx were found after surgery.

CONCLUSIONS

UL-PRx is associated with a 6-month outcome even if adjusted for IMPACT-Core. Its application in pediatric intensive care unit could be useful to evaluate CA and offer possible prognostic and therapeutic implications in pTBI patients.

CLINICALTRIALS

GOV: NCT05043545, September 14, 2021, retrospectively registered.

Ketamine Boluses Are Associated with a Reduction in Intracranial Pressure and an Increase in Cerebral Perfusion Pressure: A Retrospective Observational Study of Patients with Severe Traumatic Brain Injury

Background

Increased intracranial pressure (ICP) and hypotension have long been shown to lead to worse outcomes in the severe traumatic brain injury (TBI) population. Adequate sedation is a fundamental principle in TBI care, and ketamine is an attractive option for sedation since it does not commonly cause systemic hypotension, whereas most other sedative medications do. We evaluated the effects of ketamine boluses on both ICP and cerebral perfusion pressure (CPP) in patients with severe TBI and refractory ICP.

Methods

We conducted a retrospective review of all patients admitted to the neurointensive care unit at a single tertiary referral center who had a severe traumatic brain injury with indwelling intracranial pressure monitors. We identified those patients with refractory intracranial pressure who received boluses of ketamine. We defined refractory as any sustained ICP greater than 20 mmHg after the patient was adequately sedated, serum Na was at goal, and CO₂ was maintained between 35 and 40 mmHg. The primary outcome was a reduction in ICP with a subsequent increase in CPP.

Results

The patient cohort consisted of 44 patients with a median age of 30 years and a median presenting Glasgow Coma Scale (GCS) of 5. The median reduction in ICP after administration of a ketamine bolus was −3.5 mmHg (IQR −9 to +1), and the postketamine ICP was significantly different from baseline (p < 0.001). Ketamine boluses led to an increase in CPP by 2 mmHg (IQR −5 to +12), which was also significantly different from baseline (p < 0.001).

Conclusion

In this single-institution study of patients with severe traumatic brain injury, ketamine boluses were associated with a reduction in ICP and an increase in CPP. This was a retrospective review of 43 patients and is therefore limited in nature, but further randomized controlled trials should be performed to confirm the findings.

Complications Following Decompressive Craniectomy

BACKGROUND

 Decompressive craniectomy (DC) has become the definitive surgical procedure to manage a medically intractable rise in intracranial pressure. DC is a life-saving procedure resulting in lower mortality but also higher rates of severe disability. Although technically straightforward, DC is accompanied by many complications. It has been reported that complications are associated with worse outcome. We reviewed a series of patients who underwent DC at our department to establish the incidence and types of complications.

METHODS

 We retrospectively evaluated the incidence of complications after DC performed in 135 patients during the time period from January 2013 to December 2018. Postoperative complications were evaluated using clinical status and CT during 6 months of follow-up. In addition, the impact of potential risk factors on the incidence of complications and the impact of complications on outcome were assessed.

RESULTS

 DC was performed in 135 patients, 93 of these for trauma, 22 for subarachnoid hemorrhage, 13 for malignant middle cerebral artery infarction, and 7 for intracerebral hemorrhage. Primary DC was performed in 120 patients and secondary DC in 15 patients. At least 1 complication occurred in each of 100 patients (74%), of which 22 patients (22%) were treated surgically. The following complications were found: edema or hematoma of the temporal muscle (34 times), extracerebral hematoma (33 times), extra-axial fluid collection (31 times), hemorrhagic progression of contusions (19 times), hydrocephalus (12 times), intraoperative malignant brain edema (10 times), temporal muscle atrophy (7 times), significant intraoperative blood loss (6 times), epileptic seizures (5 times), and skin necrosis (4 times). Trauma (p = 0.0006), coagulopathy (p = 0.0099), and primary DC (p = 0.0252) were identified as risk factors for complications. There was no significant impact of complications on outcome.

CONCLUSIONS

 The incidence of complications following DC is high. However, we did not confirm a significant impact of complications on outcome. We emphasize that some phenomena are so frequent that they can be considered a consequence of primary injury or natural sequelae of the DC rather than its direct complication.

B waves: a systematic review of terminology, characteristics, and analysis methods

Background

Although B waves were introduced as a concept in the analysis of intracranial pressure (ICP) recordings nearly 60 years ago, there is still a lack consensus on precise definitions, terminology, amplitude, frequency or origin. Several competing terms exist, addressing either their probable physiological origin or their physical characteristics. To better understand B wave characteristics and ease their detection, a literature review was carried out.

Methods

A systematic review protocol including search strategy and eligibility criteria was prepared in advance. A literature search was carried out using PubMed/MEDLINE, with the following search terms: B waves + review filter, slow waves + review filter, ICP B waves, slow ICP waves, slow vasogenic waves, Lundberg B waves, MOCAIP.

Results

In total, 19 different terms were found, B waves being the most common. These terminologies appear to be interchangeable and seem to be used indiscriminately, with some papers using more than five different terms. Definitions and etiologies are still unclear, which makes systematic and standardized detection difficult.

Conclusions

Two future lines of action are available for automating macro-pattern identification in ICP signals: achieving strict agreement on morphological characteristics of “traditional” B waveforms, or starting a new with a fresh computerized approach for recognition of new clinically relevant patterns.

Early and late clinical outcomes after decompressive craniectomy for traumatic refractory intracranial hypertension: a systematic review and meta-analysis of current evidence

INTRODUCTION

Decompressive craniectomy (DC) to control refractory intracranial hypertension in patients with traumatic brain injury (TBI), has been listed as possible but controversial therapeutic approach in the latest version of TBI management guidelines. This study aimed to perform a systematic review and meta-analysis on efficacy and safety of DC compared to standard care in TBI patients.

EVIDENCE ACQUISITION

A database search from 2011 to 2017 was conducted to identify studies pertinent to DC compared to standard care after TBI. The primary outcomes were mortality and functional outcome upon hospital discharge and at 6 and 12 months after intervention, whereas secondary outcomes were intracranial pressure (ICP) control, hospitalization data and occurrence of adverse events.

EVIDENCE SYNTHESIS

Three randomized controlled trials and two observational studies enrolling 3451 patients were selected for qualitative analysis, among which four were included in the meta-analysis. DC-treated patients showed a significant reduction of overall mortality (RR, 0.57; 95% CI: 0.5-0.66; P<0.001; I2=17%) with no profound beneficial effect on functional outcome (RR, 0.89; 95% CI: 0.78-1.02; P=0.09; I2=58%) compared to those receiving standard care. A more efficient ICP reduction and a tendency towards shorter duration of hospitalization were recorded in DC versus standard care group. Adverse events are more common in DC-treated patients.

CONCLUSIONS

It seems that, in TBI patients with intracranial hypertension, the use of DC is associated with survival benefit when compared to medical therapy alone, but with no clear improvement of functional outcome. Yet no definite conclusion can be drawn due to limited quantity and considerable heterogeneity of available data.

Changes in Posttraumatic Brain Edema in Craniectomy-Selective Brain Hypothermia Model Are Associated With Modulation of Aquaporin-4 Level

Both hypothermia and decompressive craniectomy have been considered as a treatment for traumatic brain injury. In previous experiments we established a murine model of decompressive craniectomy and we presented attenuated edema formation due to focal brain cooling. Since edema development is regulated via function of water channel proteins, our hypothesis was that the effects of decompressive craniectomy and of hypothermia are associated with a change in aquaporin-4 (AQP4) concentration. Male CD-1 mice were assigned into following groups (n = 5): sham, decompressive craniectomy, trauma, trauma followed by decompressive craniectomy and trauma + decompressive craniectomy followed by focal hypothermia. After 24 h, magnetic resonance imaging with volumetric evaluation of edema and contusion were performed, followed by ELISA analysis of AQP4 concentration in brain homogenates. Additional histopathological analysis of AQP4 immunoreactivity has been performed at more remote time point of 28d. Correlation analysis revealed a relationship between AQP4 level and both volume of edema (r² = 0.45, p < 0.01, ^**) and contusion (r² = 0.41, p < 0.01, ^**) 24 h after injury. Aggregated analysis of AQP4 level (mean ± SEM) presented increased AQP4 concentration in animals subjected to trauma and decompressive craniectomy (52.1 ± 5.2 pg/mL, p = 0.01; ^*), but not to trauma, decompressive craniectomy and hypothermia (45.3 ± 3.6 pg/mL, p > 0.05; ns) as compared with animals subjected to decompressive craniectomy only (32.8 ± 2.4 pg/mL). However, semiquantitative histopathological analysis at remote time point revealed no significant difference in AQP4 immunoreactivity across the experimental groups. This suggests that AQP4 is involved in early stages of brain edema formation after surgical decompression. The protective effect of selective brain cooling may be related to change in AQP4 response after decompressive craniectomy. The therapeutic potential of this interaction should be further explored.

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.

Massive Brain Swelling and Death After Cranioplasty: A Systematic Review

BACKGROUND

Although cranioplasty is a common procedure, it may cause a variety of complications. Massive brain swelling after cranioplasty (MBSC) is an unusual complication that has been reported more frequently in recent years. Most of the existing information about this condition is speculative and the cause remains unclear.

METHODS

A PubMed and Scopus search adhering to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines was performed to include studies reporting patients with MBSC. Different information was analyzed in these cases to describe the characteristics and identify risk factors for MBSC.

RESULTS

The search yielded 19 articles with a total of 26 patients. All studies were case reports and small case series. In most patients, preoperative intracranial hypotension and a considerable degree of sinking of skin flap were identified; this was the only constant finding observed in these cases. In addition, we propose a grading system to estimate the degree of preoperative sinking of skin flap and an algorithm with recommendations to decrease the incidence of MBSC.

CONCLUSIONS

MBSC is an unusual, highly lethal, and probably underreported condition. The information gathered in this review indicates that MBSC occurs secondary to a cascade of pathologic events triggered by the bone flap implantation. This evidence suggests that the primary pathologic change is a sudden increase in the intracranial pressure acting on a brain chronically exposed to intracranial hypotension.

Detection of Impaired Cerebral Autoregulation Using Selected Correlation Analysis: A Validation Study

Multimodal brain monitoring has been utilized to optimize treatment of patients with critical neurological diseases. However, the amount of data requires an integrative tool set to unmask pathological events in a timely fashion. Recently we have introduced a mathematical model allowing the simulation of pathophysiological conditions such as reduced intracranial compliance and impaired autoregulation. Utilizing a mathematical tool set called selected correlation analysis (sca), correlation patterns, which indicate impaired autoregulation, can be detected in patient data sets (scp). In this study we compared the results of the sca with the pressure reactivity index (PRx), an established marker for impaired autoregulation. Mean PRx values were significantly higher in time segments identified as scp compared to segments showing no selected correlations (nsc). The sca based approach predicted cerebral autoregulation failure with a sensitivity of 78.8% and a specificity of 62.6%. Autoregulation failure, as detected by the results of both analysis methods, was significantly correlated with poor outcome. Sca of brain monitoring data detects impaired autoregulation with high sensitivity and sufficient specificity. Since the sca approach allows the simultaneous detection of both major pathological conditions, disturbed autoregulation and reduced compliance, it may become a useful analysis tool for brain multimodal monitoring data.

Autoregulation monitoring and outcome prediction in neurocritical care patients: Does one index fit all?

Indexes PRx and Mx have been formerly introduced to assess cerebral autoregulation and have been shown to be associated with 3-month clinical outcome. In a mixed cohort of neurocritical care patients, we retrospectively investigated the impact of selected clinical characteristics on this association. Forty-one patients (18-77 years) with severe traumatic (TBI, N = 20) and non-traumatic (N = 21) brain injuries were studied. Cerebral blood flow velocity, arterial blood pressure and intracranial pressure were repeatedly recorded during 1-h periods. Calculated PRx and Mx were correlated with 3-month clinical outcome score of modified Rankin Scale (mRS) in different subgroups with specific clinical characteristics. Both PRx and Mx correlated significantly with outcome (PRx: r = 0.38, p < 0.05; AUC = 0.64, n.s./Mx: r = 0.48, p < 0.005; AUC = 0.80, p < 0.005) in the overall group, and in patients with hemicraniectomy (N = 17; PRx: r = 0.73, p < 0.001; AUC = 0.89, p < 0.01/Mx: r = 0.69, p < 0.005; AUC = 0.87, p < 0.05). Mx, not PRx, correlated significantly with mRS in patients with heart failure (N = 17; r = 0.69, p < 0.005; AUC = 0.92, p < 0.005), and in non-traumatic patients (r = 0.49, p < 0.05; AUC = 0.79, p < 0.05). PRx, not Mx, correlated significantly with mRS in TBI patients (r = 0.63, p < 0.01; AUC = 0.89, p < 0.01). Both indexes did not correlate with mRS in diabetes patients (N = 15), PRx failed in hypocapnic patients (N = 26). Both PRx and Mx were significantly associated with 3-month clinical outcome, even in patients with hemicraniectomy. PRx was more appropriate for TBI patients, while Mx was better suited for non-traumatic patients and patients with heart failure. Prognostic values of indexes were affected by diabetes (both Mx and PRx) and hypocapnia (PRx only).

Decompressive Craniectomy Increases Brain Lesion Volume and Exacerbates Functional Impairment in Closed Head Injury in Mice

Decompressive craniectomy has been widely used in patients with head trauma. The randomized clinical trial on an early decompression (DECRA) demonstrated that craniectomy did not improve the neurological outcome, in contrast to previous animal experiments. The goal of our study was to analyze the effect of decompressive craniectomy in a murine model of head injury. Male mice were assigned into the following groups: sham, decompressive craniectomy, closed head injury (CHI), and CHI followed by craniectomy. At 24 h post-trauma, animals underwent the Neurological Severity Score test (NSS) and Beam Balance Score test (BBS). At the same time point, magnetic resonance imaging was performed, and volume of edema and contusion was assessed, followed by histopathological analysis. According to NSS, animals undergoing both trauma and craniectomy presented the most severe neurological impairment. Also, balancing time was reduced in this group compared with sham animals. Both edema and contusion volume were increased in the trauma and craniectomy group compared with sham animals. Histopathological analysis showed that all animals that underwent trauma presented substantial neuronal loss. In animals treated with craniectomy after trauma, a massive increase of edema with hemorrhagic transformation of contusion was documented. Decompressive craniectomy applied after closed head injury in mice leads to additional structural and functional impairment. The surgical decompression via craniectomy promotes brain edema formation and contusional blossoming in our model. This additive effect of combined mechanical and surgical trauma may explain the results of the DECRA trial and should be explored further in experiments.

Posttraumatic refractory intracranial hypertension and brain herniation syndrome: cerebral hemodynamic assessment before decompressive craniectomy

Background. The pathophysiology of traumatic brain swelling remains little understood. An improved understanding of intracranial circulatory process related to brain herniation may have treatment implications. Objective. To investigate the cerebral hemodynamic changes associated with brain herniation syndrome due to traumatic brain swelling. Methods. Nineteen head-injured patients with evidence of refractory intracranial hypertension and transtentorial herniation were prospectively studied. Cerebral hemodynamic assessment by transcranial Doppler (TCD) ultrasonography was performed prior to decompressive craniectomy. Patients and their cerebral hemispheres were classified according to TCD-hemodynamic patterns, and the data correlated with neurological status, midline shift on CT scan, and Glasgow outcome scale scores at 6 months after injury. Results. A wide variety of cerebral hemodynamic findings were observed. Ten patients (52.7%) presented with cerebral oligoemia, 3 patients (15.8%) with cerebral hyperemia, and 6 patients with nonspecific circulatory pattern. Circulatory disturbances were more frequently found in the side of maximal cerebral swelling than in the opposite side. Pulsatility index (PI) values suggested that ICP varied from acceptable to considerably high; patients with increased PI, indicating higher microvascular resistance. No correlation was found between cerebral hemodynamic findings and outcome. Conclusions. There is a marked heterogeneity of cerebral hemodynamic disturbances among patients with brain herniation syndrome.

Decompressive craniectomy and head injury: brain morphometry, ICP, cerebral hemodynamics, cerebral microvascular reactivity, and neurochemistry

There has been renewed interest in decompressive craniectomy as a surgical treatment for elevated intracranial pressure (ICP), although evidence-based clinical data are still lacking and some experimental results are conflicting. Ongoing clinical trials on the use of this operation after traumatic brain injury (TBI) may clarify the clinical application of this technique, however, some pathophysiological issues, such as the timing of this operation, its effect on brain edema formation, and its role for secondary brain damage, are still controversial. This review addresses recent clinical data on the influence of decompressive craniectomy on the brain pathophysiology in TBI. Decompressive craniectomy with dural augmentation enlarges intracranial space so that the swollen cerebral hemisphere could expand out of normal cranial limits, avoiding progression of brain herniation. The gain in intracranial volume results in both the improvement of cerebral compliance and a decrease in ICP; the latter favors a rise in both cerebral blood flow and cerebral microvascular perfusion, which can be accompanied by elevation in brain tissue oxygen tension (PbtO2) as well as the return of abnormal metabolic parameters to normal values in cases of cerebral ischemia. Enhancement of edema formation, impairment of cerebrovascular pressure reactivity, and non-restoration of brain aerobic metabolism due to metabolic crisis may occur after craniectomy and require further investigations. This review suggests that decompressive craniectomy as the sole treatment is likely to be insufficient; efforts must be made to maintain adequate brain hemodynamics, preferably coupled with brain metabolism, in addition to treating brain metabolic abnormalities, during postoperative stages.

Cerebral blood flow, brain tissue oxygen, and metabolic effects of decompressive craniectomy

Decompressive craniectomy (DC) is used for patients with traumatic brain injury (TBI), malignant edema from middle cerebral artery infarction, aneurysmal subarachnoid hemorrhage, and non-traumatic intracerebral or cerebellar hemorrhage. The objective of the procedure is to relieve intractable intracranial hypertension and/or to prevent or reverse cerebral herniation. Decompressive craniectomy has been shown to decrease mortality in selected patients with large hemispheric infarction and to control intracranial pressure in addition to improving pressure-volume compensatory reserve after TBI. The clinical effectiveness of DC in patients with TBI is under evaluation in ongoing randomized clinical trials. There are several unresolved controversies regarding optimal candidate selection, timing, technique, and post-operative management and complications. The nature and temporal progression of alterations in cerebral blood flow, brain tissue oxygen, and microdialysis markers have only recently been researched. Elucidating the pathophysiology of pressure-flow and cerebral hemodynamic consequences of DC could assist in optimizing clinical decision making and further defining the role of decompressive craniectomy.

The relationship between cerebral blood flow autoregulation and cerebrovascular pressure reactivity after traumatic brain injury

BACKGROUND

Cerebrovascular pressure reactivity is the principal mechanism of cerebral autoregulation. Assessment of cerebral autoregulation can be performed by using the mean flow index (Mx) based on transcranial Doppler ultrasonography. Cerebrovascular pressure reactivity can be monitored by using the pressure reactivity index (PRx), which is based on intracranial pressure monitoring. From a practical point of view, PRx can be monitored continuously, whereas Mx can only be monitored in short periods when transcranial Doppler probes can be applied.

OBJECTIVE

To assess to what degree impairment in pressure reactivity (PRx) is associated with impairment in cerebral autoregulation (Mx).

METHODS

A database of 345 patients with traumatic brain injury was screened for data availability including simultaneous Mx and PRx monitoring. Absolute differences, temporal changes, and association with outcome of the 2 indices were analyzed.

RESULTS

A total of 486 recording sessions obtained from 201 patients were available for analysis. Overall a moderate correlation between Mx and PRx was found (r = 0.58; P < .001). The area under the receiver operator characteristic curve designed to detect the ability of PRx to predict impaired cerebral autoregulation was 0.700 (95% confidence interval: 0.607-0.880). Discrepancies between Mx and PRx were most pronounced at an intracranial pressure of 30 mm Hg and they were significantly larger for patients who died (P = .026). Both Mx and PRx were significantly lower at day 1 postadmission in patients who survived than in those who died (P < .01).

CONCLUSION

There is moderate agreement between Mx and PRx. Discrepancies between Mx and PRx are particularly significant in patients with sustained intracranial hypertension. However, for clinical purposes, there is only limited interchangeability between indices.

'Long' pressure reactivity index (L-PRx) as a measure of autoregulation correlates with outcome in traumatic brain injury patients

BACKGROUND

Cerebral autoregulation and, consequently, cerebrovascular pressure reactivity, can be disturbed after traumatic brain injury (TBI). Continuous monitoring of autoregulation has shown its clinical importance as an independent predictor of neurological outcome. The cerebral pressure reactivity index (PRx) reflects that changes in seconds of cerebrovascular reactivity have prognostic significance. Using an alternative algorithm similar to PRx, we investigate whether the utilization of lower-frequency changes of the order of minutes of mean arterial blood pressure (MAP) and intracranial pressure (ICP) could have a prognostic value in TBI patients.

MATERIALS AND METHODS

Head-injured patients requiring continued advanced multimodal monitoring, including hemodynamic, ICP and microdialysis (MD) monitoring, were analyzed retrospectively. A low-frequency sample pressure reactivity index (L-PRx) was calculated, using 20-min averages of MAP and ICP data as a linear Pearson's correlation. The mean values per patient were correlated to outcome at 6 months after injury. Differences of monitoring parameters between non-survivors and survivors were compared.

RESULTS

A total of 29 patients (mean age 37.2 years, 26 males) suffering from TBI were monitored for a mean of 109.6 h (16-236 h, SD ± 60.4). Mean L-PRx was found to be of 0.1 (-0.2 to 0.6, SD ± 0.20), six patients presented impaired (>0.2) values. The averaged L-PRx correlated significantly with ICP (r = 0.467, p = 0.011) and 6-month outcome (r = -0.556, p = 0.002). Significant statistical differences were found in L-PRx, cerebral perfusion pressure (CPP), lactate, and lactate-pyruvate ratio when comparing patients who died (n = 5) and patients who survived.

CONCLUSIONS

L-PRx correlates with the 6-month outcome in TBI patients. Very slow changes of MAP and ICP may contain important autoregulation information. L-PRx may be an alternative algorithm for the estimation of cerebral autoregulation and clinical prognosis.

Decompressive craniectomy: a meta-analysis of influences on intracranial pressure and cerebral perfusion pressure in the treatment of traumatic brain injury

OBJECT

In recent years, the role of decompressive craniectomy for the treatment of traumatic brain injury (TBI) in patients with refractory intracranial hypertension has been the subject of several studies. The purpose of this review was to evaluate the contribution of decompressive craniectomy in reducing intracranial pressure (ICP) and increasing cerebral perfusion pressure (CPP) in these patients.

METHODS

Comprehensive literature searches were performed for articles related to the effects of decompressive craniectomy on ICP and CPP in patients with TBI. Inclusion criteria were as follows: 1) published manuscripts, 2) original articles of any study design except case reports, 3) patients with refractory elevated ICP due to traumatic brain swelling, 4) decompressive craniectomy as a type of intervention, and 5) availability of pre- and postoperative ICP and/or CPP data. Primary outcomes were ICP decrease and/or CPP increase for assessing the efficacy of decompressive craniectomy. The secondary outcome was the persistence of reduced ICP 24 and 48 hours after the operation.

RESULTS

Postoperative ICP values were significantly lower than preoperative values immediately after decompressive craniectomy (weighted mean difference [WMD] -17.59 mm Hg, 95% CI -23.45 to -11.73, p < 0.00001), 24 hours after (WMD -14.27 mm Hg, 95% CI -24.13 to -4.41, p < 0.00001), and 48 hours after (WMD -12.69 mm Hg, 95% CI -22.99 to -2.39, p < 0.0001). Postoperative CPP was significantly higher than preoperative values (WMD 7.37 mm Hg, 95% CI 2.32 to 12.42, p < 0.0001).

CONCLUSIONS

Decompressive craniectomy can effectively decrease ICP and increase CPP in patients with TBI and refractory elevated ICP. Further studies are necessary to define the group of patients that can benefit most from this procedure.

Decompressive craniectomy and cerebral blood flow regulation in head injured patients: a case studied by perfusion CT

Previous studies have reported increased cerebral blood flow (CBF) velocity after decompressive craniectomy in traumatic brain injury (TBI) patients. A 27-year-old man presented with clinical and tomographic signs of cerebral herniation secondary to TBI. Prior to decompressive craniectomy, hemodynamic study by perfusion computed tomography (CT) indicated diffuse cerebral hyperperfusion. Following surgical decompression, the patient recovered neurologically and perfusion CT disclosed a decrease in the intensity of cerebral perfusion. The patient's blood pressure levels were similar at both pre- and postoperative perfusion CT examinations. This finding provides indirect evidence that decompressive craniectomy may improve mechanisms of CBF regulation in TBI, providing pathophysiological insights in the cerebral hemodynamics of TBI patients. This is the first report analyzing the hemodynamic changes through perfusion CT (PCT) in a patient with decompressive craniotomy due to TBI.

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.

Decompressive craniectomy - operative technique and perioperative care

With improvements in neurocritical care advanced measures of treating raised intracranial pressure (ICP) are more frequently utilised. Decompressive craniectomy is an effective ICP-lowering procedure; however its benefits are maximised with optimal surgical technique and perioperative care, as well as by paying attention to possible complications. This article focuses on the current indications and rationale for decompressive craniectomy, and the surgical technique of bifrontal and unilateral decompression. The key surgical points include a large craniectomy window and opening of the dura, leaving it unsutured or performing a wide non-constricting duroplasty. Perioperative care and possible complications are also discussed.

Favorable Outcome in Traumatic Brain Injury Patients With Impaired Cerebral Pressure Autoregulation When Treated at Low Cerebral Perfusion Pressure Levels

BACKGROUND:

Cerebral pressure autoregulation (CPA) is defined as the ability of the brain vasculature to maintain a constant blood flow over a range of different systemic blood pressures by means of contraction and dilatation.

OBJECTIVE:

To study CPA in relation to physiological parameters, treatment, and outcome in a series of traumatic brain injury patients.

METHODS:

In this prospective observational study, 44 male and 14 female patients (age, 15–72 years; mean, 38.7 years; Glasgow Coma Scale score, 4-13; median, 7) were analyzed. Patients were divided into groups on the basis of status of CPA (more pressure active vs more pressure passive) and level of cerebral perfusion pressure (CPP; low vs high CPP). The proportions of favorable outcome in the groups were assessed. Differences in physiological variables in the different groups were analyzed.

RESULTS:

Patients with more impaired CPA treated at CPP levels below median had a significantly higher proportion of favorable outcome compared with patients with more impaired CPA treated at CPP levels above median. No significant difference in outcome was seen between patients with more intact CPA when divided by level of CPP. In patients with more impaired CPA, CPP &lt; 50 mm Hg and CPP &lt; 60 mm Hg were associated with favorable outcome, whereas CPP &gt; 70 mm Hg and CPP &gt; 80 mm Hg were associated with unfavorable outcome. In patients with more intact CPA, no difference in physiological variables was seen between patients with favorable and unfavorable outcomes.

CONCLUSION:

Our results support that in traumatic brain injury patients with impaired CPA, CPP should not be elevated.

Prediction of outcome utilizing both physiological and biochemical parameters in severe head injury

Traumatic brain injury is a major socioeconomic burden, and the use of statistical models to predict outcomes after head injury can help to allocate limited health resources. Earlier prediction models analyzing admission data have been used to achieve prediction accuracies of up to 80%. Our aim was to design statistical models utilizing a combination of both physiological and biochemical variables obtained from multimodal monitoring in the neurocritical care setting as a complement to earlier models. We used decision tree and logistic regression analysis on variables including intracranial pressure (ICP), mean arterial pressure (MAP), cerebral perfusion pressure (CPP), and pressure reactivity index (PRx), as well as multimodal monitoring parameters to assess brain tissue oxygenation (PbtO(2)), and microdialysis parameters to predict outcomes based on a dichotomized Glasgow Outcome Score. Further analysis was carried out on various subgroup combinations of physiological and biochemical parameters. The reliability of the head injury models was assessed using a 10-fold cross-validation technique. In addition, the confusion matrix was also used to assess the sensitivity, specificity, and the F-ratio. In all, 2,413 time series records were extracted from 26 patients treated at our neurocritical care unit over a 1-year period. Decision tree analysis was found to be superior to logistic regression analysis in predictive accuracy of outcome. The combined use of microdialysis variables and PbtO(2), in addition to ICP, MAP, and CPP was found have the best predictive accuracy. The use of physiological and biochemical variables based on a decision tree analysis model has shown to provide an improvement in predictive accuracy compared with other previous models. The potential application is for outcome prediction in the multivariate setting of advanced multimodality monitoring, and validates the use of multimodal monitoring in the neurocritical care setting to have a potential benefit in predicting outcomes of patients with severe head injury.

LONG-TERM OUTCOME OF SUBCUTANEOUSLY PRESERVED AUTOLOGOUS CRANIOPLASTY

OBJECTIVE

Decompressive craniectomy for intracranial hypertension mandates later cranioplasty. Autologous cranioplasties can be preserved either by freezing or placement in a subcutaneous pocket. There are few data on the long-term follow-up of patients treated in such a fashion.

METHODS

A retrospective study was conducted on 100 consecutive patients who underwent decompressive craniectomy and placement of the bone flap in a subcutaneous pocket in the abdominal wall between 2000 and 2005. Initial diagnosis, Glasgow Coma Scale score on admission, complications, and Glasgow Outcome Score were recorded.

RESULTS

Of the 100 patients who underwent autocranioplasty, the primary diagnosis was traumatic brain injury (76%), subarachnoid hemorrhage (17%), primary intracerebral hemorrhage (3%), and tumor (4%). The mean age of the sample was 39 years (age range, 10–72 years). The mean follow-up duration was 25 months. The average Glasgow Coma Scale score on admission was 7. Eight patients died before replacement of the bone flap. The average time between craniectomy and replacement of bone flap was 42 days. The mean Glasgow Outcome Score was 4 at the time of the 1-year follow-up evaluation. Seven of the 79 patients (9%) for whom 1-year review data were available had a cosmetic result that was unacceptable and required removal of the flap (bone flap infections in 5 patients, unacceptable bone flap resorption in 2 patients)

CONCLUSION

Our study indicates that storage of a cranioplasty flap in a subcutaneous pouch in the abdominal wall has a favorable long-term outcome.

Comparative study of decompressive craniectomy after mass lesion evacuation in severe head injury

OBJECTIVE

This study was conducted to evaluate outcome after decompressive craniectomy (DC) in the setting of mass evacuation with or without intracranial pressure (ICP) monitoring.

METHODS

Over a 48-month period (March 2000 to March 2004), 54 of 967 consecutive head injury patients underwent DC for evacuation of a mass lesion. DC was performed without ICP monitoring in 27 patients who required urgent decompression (group A) and in 27 patients who did not require urgent surgery and who had their ICP monitored for 1 to 14 days before surgery (group B).

RESULTS

In group A, the mean Glasgow Coma Scale score was 6.0; 80% had computed tomographic evidence of a shift greater than 5 mm; and 25 patients underwent DC immediately after resuscitation. In group B, the mean Glasgow Coma Scale score was 7.3; 40% had computed tomographic evidence of shift; and 75% underwent DC 24 hours or longer after presentation. Overall, 22 patients died (12 in group A and 10 in group B), 11 remained vegetative or severely disabled (3 in group A and 8 in group B), and 19 had good recovery (11 in group A and 8 in group B). Two patients were lost to follow-up. In 18 group B patients with ICP greater than 20 mm Hg before mass evacuation, ICP dropped an average of 13 mm Hg (P < 0.001). A mass lesion greater than 50 mL (odds ratio [OR], 2.86; 95% confidence interval [CI], 1.04-7.89) and evidence of low attenuation on computed tomography before (OR, 3.3; 95% CI, 1.1-10.3) or after (OR, 2.92; 95% CI, 1.02-8.34) DC were predictors of death. A good outcome occurred in 42% of patients with and in 63% of patients without delayed traumatic injury (OR, 0.3; 95% CI, 0.1-1.1). Outcome was favorable in 78.6% of patients who had no ICP monitoring before DC versus 47.1% of patients with ICP monitoring (OR, 0.2; 95% CI, 0.1-1.2).

CONCLUSION

In this study, mortality after DC for mass lesion was greater than expected, and outcome did not differ between patients with or without ICP monitoring.

Complications of decompressive craniectomy for traumatic brain injury

Decompressive craniectomy is widely used to treat intracranial hypertension following traumatic brain injury (TBI). Two randomized trials are currently underway to further evaluate the effectiveness of decompressive craniectomy for TBI. Complications of this procedure have major ramifications on the risk-benefit balance in decision-making during evaluation of potential surgical candidates. To further evaluate the complications of decompressive craniectomy, a review of the literature was performed following a detailed search of PubMed between 1980 and 2009. The author restricted her study to literature pertaining to decompressive craniectomy for patients with TBI. An understanding of the pathophysiological events that accompany removal of a large piece of skull bone provides a foundation for understanding many of the complications associated with decompressive craniectomy. The author determined that decompressive craniectomy is not a simple, straightforward operation without adverse effects. Rather, numerous complications may arise, and they do so in a sequential fashion at specific time points following surgical decompression. Expansion of contusions, new subdural and epidural hematomas contralateral to the decompressed hemisphere, and external cerebral herniation typify the early perioperative complications of decompressive craniectomy for TBI. Within the 1st week following decompression, CSF circulation derangements manifest commonly as subdural hygromas. Paradoxical herniation following lumbar puncture in the setting of a large skull defect is a rare, potentially fatal complication that can be prevented and treated if recognized early. During the later phases of recovery, patients may develop a new cognitive, neurological, or psychological deficit termed syndrome of the trephined. In the longer term, a persistent vegetative state is the most devastating of outcomes of decompressive craniectomy. The risk of complications following decompressive craniectomy is weighed against the life-threatening circumstances under which this surgery is performed. Ongoing trials will define whether this balance supports surgical decompression as a first-line treatment for TBI.

Perioperative uses of transcranial perfusion monitoring

Transcranial perfusion monitoring provides early warning of impending brain ischemia and may be used to guide management of cerebral perfusion and oxygenation. The monitoring options include measurement of intracranial and cerebral perfusion pressures, assessment of cerebral blood flow, and assessment of the adequacy of perfusion by measurement of cerebral oxygenation and brain tissue biochemistry. Some monitoring techniques are well established, whereas others are relatively new to the clinical arena and their indications are still being evaluated. Currently available monitoring techniques are reviewed and their appropriateness and application to the perioperative period is discussed.

Continuous monitoring of cerebrovascular pressure reactivity in patients with head injury

Object

Cerebrovascular pressure reactivity is the ability of cerebral vessels to respond to changes in transmural pressure. A cerebrovascular pressure reactivity index (PRx) can be determined as the moving correlation coefficient between mean intracranial pressure (ICP) and mean arterial blood pressure.

Methods

The authors analyzed a database consisting of 398 patients with head injuries who underwent continuous monitoring of cerebrovascular pressure reactivity. In 298 patients, the PRx was compared with a transcranial Doppler ultrasonography assessment of cerebrovascular autoregulation (the mean index [Mx]), in 17 patients with the PET–assessed static rate of autoregulation, and in 22 patients with the cerebral metabolic rate for O2. Patient outcome was assessed 6 months after injury.

Results

There was a positive and significant association between the PRx and Mx (R2 = 0.36, p < 0.001) and with the static rate of autoregulation (R2 = 0.31, p = 0.02). A PRx > 0.35 was associated with a high mortality rate (> 50%). The PRx showed significant deterioration in refractory intracranial hypertension, was correlated with outcome, and was able to differentiate patients with good outcome, moderate disability, severe disability, and death. The graph of PRx compared with cerebral perfusion pressure (CPP) indicated a U–shaped curve, suggesting that too low and too high CPP was associated with a disturbance in pressure reactivity. Such an optimal CPP was confirmed in individual cases and a greater difference between current and optimal CPP was associated with worse outcome (for patients who, on average, were treated below optimal CPP [R2 = 0.53, p < 0.001] and for patients whose mean CPP was above optimal CPP [R2 = −0.40, p < 0.05]). Following decompressive craniectomy, pressure reactivity initially worsened (median −0.03 [interquartile range −0.13 to 0.06] to 0.14 [interquartile range 0.12–0.22]; p < 0.01) and improved in the later postoperative course. After therapeutic hypothermia, in 17 (70.8%) of 24 patients in whom rewarming exceeded the brain temperature threshold of 37°C, ICP remained stable, but the average PRx increased to 0.32 (p < 0.0001), indicating significant derangement in cerebrovascular reactivity.

Conclusions

The PRx is a secondary index derived from changes in ICP and arterial blood pressure and can be used as a surrogate marker of cerebrovascular impairment. In view of an autoregulation–guided CPP therapy, a continuous determination of a PRx is feasible, but its value has to be evaluated in a prospective controlled trial.

Cerebral oxygenation, vascular reactivity, and neurochemistry following decompressive craniectomy for severe traumatic brain injury

OBJECT

This study addresses the changes in brain oxygenation, cerebrovascular reactivity, and cerebral neurochemistry in patients following decompressive craniectomy for the control of elevated intracranial pressure (ICP) after severe traumatic brain injury (TBI).

METHODS

Sixteen consecutive patients with isolated TBI and elevated ICP, who were refractory to maximal medical therapy, underwent decompressive craniectomy over a 1-year period. Thirteen patients were male and 3 were female. The mean age of the patients was 38 years and the median Glasgow Coma Scale score on admission was 5. RESULTS Six months following TBI, 11 patients had a poor outcome (Group 1, Glasgow Outcome Scale [GOS] Score 1-3), whereas the remaining 5 patients had a favorable outcome (Group 2, GOS Score 4 or 5). Decompressive craniectomy resulted in a significant reduction (p < 0.001) in the mean ICP and cerebrovascular pressure reactivity index to autoregulatory values (< 0.3) in both groups of patients. There was a significant improvement in brain tissue oxygenation (PbtO(2)) in Group 2 patients from 3 to 17 mm Hg and an 85% reduction in episodes of cerebral ischemia. In addition, the durations of abnormal PbtO(2) and biochemical indices were significantly reduced in Group 2 patients after decompressive craniectomy, but there was no improvement in the biochemical indices in Group 1 patients despite surgery.

CONCLUSIONS

Decompressive craniectomy, when used appropriately in protocol-driven intensive care regimens for the treatment of recalcitrant elevated ICP, is associated with a return of abnormal metabolic parameters to normal values in patients with eventually favorable outcomes.

Effect of decompressive craniectomy on intracranial pressure and cerebrospinal compensation following traumatic brain injury

Object

Decompressive craniectomy is an advanced treatment option for intracranial pressure (ICP) control in patients with traumatic brain injury. The purpose of this study was to evaluate the effect of decompressive craniectomy on ICP and cerebrospinal compensation both within and beyond the first 24 hours of craniectomy.

Methods

This study was a retrospective analysis of the physiological parameters from 27 moderately to severely head-injured patients who underwent decompressive craniectomy for progressive brain edema. Of these, 17 patients had undergone prospective digital recording of ICP with estimation of ICP waveform–derived indices. The pressure-volume compensatory reserve (RAP) index and the cerebrovascular pressure reactivity index (PRx) were used to assess those parameters. The values of parameters prior to and during the 72 hours after decompressive craniectomy were included in the analysis.

Results

Decompressive craniectomy led to a sustained reduction in median (interquartile range) ICP values (21.2 mm Hg [18.7; 24.2 mm Hg] preoperatively compared with 15.7 mm Hg [12.3; 19.2 mm Hg] postoperatively; p = 0.01). A similar improvement was observed in RAP. A significantly lower mean arterial pressure (MAP) was needed after decompressive craniectomy to maintain optimum cerebral perfusion pressure (CPP) levels, compared with the preoperative period (99.5 mm Hg [96.2; 102.9 mm Hg] compared with 94.2 mm Hg [87.9; 98.9 mm Hg], respectively; p = 0.017). Following decompressive craniectomy, the PRx had positive values in all patients, suggesting acquired derangement in pressure reactivity.

Conclusions

In this study, decompressive craniectomy led to a sustained reduction in ICP and improvement in cerebral compliance. Lower MAP levels after decompressive craniectomy are likely to indicate a reduced intensity of treatment. Derangement in cerebrovascular pressure reactivity requires further studies to evaluate its significance and influence on outcome.

Changes in brain biochemistry and oxygenation in the zone surrounding primary intracerebral hemorrhage

BACKGROUND

While the management of primary intracerebral hemorrhage (ICH) remains controversial, there remains a subset of patients that undergo clot evacuation. This study aims to characterize brain physiology and biochemistry after surgery for this condition.

METHODS

Thirty-six consecutive patients requiring ventilation for primary ICH had intracranial pressure (ICP), tissue oxygenation (PbO2) and cerebral microdialysis (CMD) monitoring. 28 patients with a Glasgow Outcome Score (GOS) of 1-3 formed group 1 while 5 patients with a GOS of 4-5 formed group 2. The control group consisted of 3 patients managed conservatively without surgery.

FINDINGS

The mean PbO2 (24.5 +/- 20.8 mmHg) was higher in the patients in group 1 (poor outcome) compared with those in the control group (13.6 +/- 9.0 mmHg) (p < 0.001). Compared to patients in group 2, the patients in group 1 also had a higher PbO2 (p = 0.02) together with worse levels of lactate/pyruvate (L/P) ratio and glycerol (p < 0.001). In all 3 groups, ICP reduction to < 20 mmHg was achieved together with a return to of pressure reactivity (PRx) to < 0.3.

CONCLUSIONS

In spontaneous ICH, derangements in the perilesional tissue demonstrated by local techniques of PbO2 monitoring and CMD are not seen in global indices such as the PRx.

Perioperative uses of transcranial perfusion monitoring

Transcranial perfusion monitoring provides early warning of impending brain ischemia and may be used to guide management of cerebral perfusion and oxygenation. The monitoring options include measurement of intracranial and cerebral perfusion pressures, assessment of cerebral blood flow, and assessment of the adequacy of perfusion by measurement of cerebral oxygenation and brain tissue biochemistry. Some monitoring techniques are well established, whereas others are relatively new to the clinical arena and their indications are still being evaluated. Currently available monitoring techniques are reviewed and their appropriateness and application to the perioperative period is discussed.

Intracranial Pressure: More Than a Number

✓Many doctors involved in the critical care of head-injured patients understand intracranial pressure (ICP) as a number, characterizing the state of the brain pressure–volume relationships. However, the dynamics of ICP, its waveform, and secondarily derived indices portray useful information about brain homeostasis. There is circumstantial evidence that this information can be used to modify and optimize patients' treatment. Secondary variables, such as pulse amplitude and the magnitude of slow waves, index of compensatory reserve, and pressure–reactivity index (PRx), look promising in clinical practice. The optimal cerebral perfusion pressure (CPP) derived using the PRx is a new concept that may help to avoid excessive use of vasopressors in CPP-oriented therapy. However, the use of secondary ICP indices remains to be confirmed in clinical trials.