Influence of data resolution and interpolation method on assessment of secondary brain insults in neurocritical care

Pressure Time Dose as a Representation of Intracranial Pressure Burden and Its Dependency on Intracranial Pressure Waveform Morphology at Different Time Intervals

Intracranial pressure (ICP) burden or pressure time dose (PTD) is a valuable clinical indicator for pending intracranial hypertension, mostly based on threshold exceedance. Pulse frequency and waveform morphology (WFM) of the ICP signal contribute to PTD. The temporal resolution of the ICP signal has a great influence on PTD calculation but has not been systematically studied yet. Hence, the temporal resolution of the ICP signal on PTD calculation is investigated. We retrospectively analysed continuous 48 h ICP recordings with high temporal resolution obtained from 94 patients at the intensive care unit who underwent neurosurgery due to an intracranial haemorrhage and received an intracranial pressure probe (43 females, median age: 72 years, range: 23 to 88 years). The cumulative area under the curve above the threshold of 20 mmHg was compared for different temporal resolutions of the ICP signal (beat-to-beat, 1 s, 300 s, 1800 s, 3600 s). Events with prolonged ICP elevation were compared to those with few isolated threshold exceedances. PTD increased for lower temporal resolutions independent of WFM and frequency of threshold exceedance. PTDbeat-to-beat best reflected the impact of frequency of threshold exceedance and WFM. Events that could be distinguished in PTDbeat-to-beat became magnified more than 7-fold in PTD1s and more than 104 times in PTD1h, indicating an overestimation of PTD. PTD calculation should be standardised, and beat-by-beat PTD could serve as an easy-to-grasp indicator for the impact of frequency and WFM of ICP elevations on ICP burden.

Intracranial pressure for clinicians: it is not just a number

BACKGROUND

Invasive intracranial pressure (ICP) monitoring is a standard practice in severe brain injury cases, where it allows to derive cerebral perfusion pressure (CPP); ICP-tracing can also provide additional information about intracranial dynamics, forecast episodes of intracranial hypertension and set targets for a tailored therapy to prevent secondary brain injury. Nevertheless, controversies about the advantages of an ICP clinical management are still debated.

FINDINGS

This article reviews recent research on ICP to improve the understanding of the topic and uncover the hidden information in this signal that may be useful in clinical practice. Parameters derived from time-domain as well as frequency domain analysis include compensatory reserve, autoregulation estimation, pulse waveform analysis, and behavior of ICP in time. The possibility to predict the outcome and apply a tailored therapy using a personalised perfusion pressure target is also described.

CONCLUSIONS

ICP is a crucial signal to monitor in severely brain injured patients; a bedside computer can empower standard monitoring giving new metrics that may aid in clinical management, establish a personalized therapy, and help to predict the outcome. Continuous collaboration between engineers and clinicians and application of new technologies to healthcare, is vital to improve the accuracy of current metrics and progress towards better care with individualized dynamic targets.

Accuracy of Manual Intracranial Pressure Recording Compared to a Computerized High-Resolution System: A CENTER-TBI Analysis

BACKGROUND

Monitoring intracranial pressure (ICP) and cerebral perfusion pressure (CPP) is crucial in the management of the patient with severe traumatic brain injury (TBI). In several institutions ICP and CPP are summarized hourly and entered manually on bedside charts; these data have been used in large observational and interventional trials. However, ICP and CPP may change rapidly and frequently, so data recorded in medical charts might underestimate actual ICP and CPP shifts. The aim of this study was to evaluate the accuracy of manual data annotation for proper capturing of ICP and CPP. For this aim, we (1) compared end-hour ICP and CPP values manually recorded (MR) with values recorded continuously by computerized high-resolution (HR) systems and (2) analyzed whether MR ICP and MR CPP are reliable indicators of the burden of intracranial hypertension and low CPP.

METHODS

One hundred patients were included. First, we compared the MR data with the values stored in the computerized system during the first 7 days after admission. For this point-to-point analysis, we calculated the difference between end-hour MR and HR ICP and CPP. Then we analyzed the burden of high ICP (> 20 mm Hg) and low CPP (< 60 mm Hg) measured by the computerized system, in which continuous data were stored, compared with the pressure-time dose based on end-hour measurements.

RESULTS

The mean difference between MR and HR end-hour values was 0.02 mm Hg for ICP (SD 3.86 mm Hg) and 1.54 mm Hg for CPP (SD 8.81 mm Hg). ICP > 20 mm Hg and CPP < 60 mm Hg were not detected by MR in 1.6% and 5.8% of synchronized measurements, respectively. Analysis of the pathological ICP and CPP throughout the recording, however, indicated that calculations based on manual recording seriously underestimated the ICP and CPP burden (in 42% and 28% of patients, respectively).

CONCLUSIONS

Manual entries fairly represent end-hour HR ICP and CPP. However, compared with a computerized system, they may prove inadequate, with a serious risk of underestimation of the ICP and CPP burden.

Timing errors and temporal uncertainty in clinical databases-A narrative review

A firm concept of time is essential for establishing causality in a clinical setting. Review of critical incidents and generation of study hypotheses require a robust understanding of the sequence of events but conducting such work can be problematic when timestamps are recorded by independent and unsynchronized clocks. Most clinical models implicitly assume that timestamps have been measured accurately and precisely, but this custom will need to be re-evaluated if our algorithms and models are to make meaningful use of higher frequency physiological data sources. In this narrative review we explore factors that can result in timestamps being erroneously recorded in a clinical setting, with particular focus on systems that may be present in a critical care unit. We discuss how clocks, medical devices, data storage systems, algorithmic effects, human factors, and other external systems may affect the accuracy and precision of recorded timestamps. The concept of temporal uncertainty is introduced, and a holistic approach to timing accuracy, precision, and uncertainty is proposed. This quantitative approach to modeling temporal uncertainty provides a basis to achieve enhanced model generalizability and improved analytical outcomes.

Association of Refractory Pain in the Acute Phase After Subarachnoid Hemorrhage With Continued Outpatient Opioid Use

OBJECTIVE

Little is known about the prevalence of continued opioid use following aneurysmal subarachnoid hemorrhage (aSAH) despite guidelines recommending their use during the acute phase of disease. We sought to determine prevalence of opioid use following aSAH and test the hypothesis that acute pain and higher inpatient opioid dose increased outpatient opioid use.

METHODS

We reviewed consecutively admitted patients with aSAH from November 2015 through September 2019. We retrospectively collected pain scores and daily doses of analgesics. Pain burden was calculated as area under the pain-time curve. Univariate and multivariable regression models determined risk factors for continued opioid use at discharge and outpatient follow-up.

RESULTS

We identified 234 patients with aSAH with outpatient follow-up. Continued opioid use was common at discharge (55% of patients) and follow-up (47% of patients, median 63 [interquartile range 49-96] days from admission). Pain burden, craniotomy, and racial or ethnic minority status were associated with discharge opioid prescription in multivariable analysis. At outpatient follow-up, pain burden (odds ratio [OR] 1.88, 95% confidence interval [CI] 1.5-2.4), depression (OR 3.1, 95% CI 1.1-8.8), and racial or ethnic minority status (OR 2.1, 95% CI 1.1-4.0) were independently associated with continued opioid use; inpatient opioid dose was not.

CONCLUSION

Continued opioid use following aSAH is prevalent and related to refractory pain during acute illness, but not inpatient opioid dose. More efficacious analgesic strategies are needed to reduce continued opioid use in patients following aSAH.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that continued opioid use following aSAH is associated with refractory pain during acute illness but not hospital opioid exposure.

Impact of controlled normothermia following hypothermic targeted temperature management for post-rewarming fever and outcomes in post-cardiac arrest patients: A propensity score-matched analysis from a multicentre registry

AIM OF THE STUDY

We investigated whether controlled normothermia (CN) after the rewarming phase of targeted temperature management (TTM) is associated with preventing post-rewarming fever and outcomes 6 months after out-of-hospital cardiac arrest (OHCA).

METHODS

This was an analysis of a prospective registry comprising OHCA patients treated with TTM at 22 academic hospitals between October 2015 and December 2018. We calculated the incremental area under the curve (iAUC) for body temperature greater than or equal to 37.5 °C for each patient during the first 24 h after the end of rewarming. The relationships among CN and iAUC, 6-month survival and good neurological outcome were analysed. To minimize differences in the baseline characteristics of the patients, we used propensity score-matched analysis.

RESULTS

In total, 1144 patients were enrolled. After propensity score matching, 646 patients (comprising 323 pairs) were obtained. In the unmatched cohort, post-rewarming CN was significantly associated with a lower iAUC (0.34 [1.38] vs. 1.19 [2.27]; p < 0.001) but not 6-month survival (adjusted odds ratio (OR): 1.121; 95% confidence interval (CI): 0.836-1.504; p = 0.446) and good neurological outcome (adjusted OR: 1.030; 95% CI: 0.734-1.446; p = 0.863). The results were similar in the propensity score-matched cohort (0.38 [1.56] vs. 1.03 [2.21], p < 0.001, OR: 1.347, 95% CI: 0.989-1.835, p = 0.059 and OR: 1.280, 95% CI 0.925-1.772, p = 0.137, respectively).

CONCLUSION

Post-rewarming CN prevents high fever in the normothermia phase of TTM. However, our data suggest the lack of association between CN and the patient's 6-month survival and good neurological outcome.

Neonatal NIRS monitoring: recommendations for data capture and review of analytics

Brain injury is one of the most consequential problems facing neonates, with many preterm and term infants at risk for cerebral hypoxia and ischemia. To develop effective neuroprotective strategies, the mechanistic basis for brain injury must be understood. The fragile state of neonates presents unique research challenges; invasive measures of cerebral blood flow and oxygenation assessment exceed tolerable risk profiles. Near-infrared spectroscopy (NIRS) can safely and non-invasively estimate cerebral oxygenation, a correlate of cerebral perfusion, offering insight into brain injury-related mechanisms. Unfortunately, lack of standardization in device application, recording methods, and error/artifact correction have left the field fractured. In this article, we provide a framework for neonatal NIRS research. Our goal is to provide a rational basis for NIRS data capture and processing that may result in better comparability between studies. It is also intended to serve as a primer for new NIRS researchers and assist with investigation initiation.

Impact of duration and magnitude of raised intracranial pressure on outcome after severe traumatic brain injury: A CENTER-TBI high-resolution group study

Magnitude of intracranial pressure (ICP) elevations and their duration have been associated with worse outcomes in patients with traumatic brain injuries (TBI), however published thresholds for injury vary and uncertainty about these levels has received relatively little attention. In this study, we have analyzed high-resolution ICP monitoring data in 227 adult patients in the CENTER-TBI dataset. Our aim was to identify thresholds of ICP intensity and duration associated with worse outcome, and to evaluate the uncertainty in any such thresholds. We present ICP intensity and duration plots to visualize the relationship between ICP events and outcome. We also introduced a novel bootstrap technique to evaluate uncertainty of the equipoise line. We found that an intensity threshold of 18 ± 4 mmHg (2 standard deviations) was associated with worse outcomes in this cohort. In contrast, the uncertainty in what duration is associated with harm was larger, and safe durations were found to be population dependent. The pressure and time dose (PTD) was also calculated as area under the curve above thresholds of ICP. A relationship between PTD and mortality could be established, as well as for unfavourable outcome. This relationship remained valid for mortality but not unfavourable outcome after adjusting for IMPACT core variables and maximum therapy intensity level. Importantly, during periods of impaired autoregulation (defined as pressure reactivity index (PRx)>0.3) ICP events were associated with worse outcomes for nearly all durations and ICP levels in this cohort and there was a stronger relationship between outcome and PTD. Whilst caution should be exercised in ascribing causation in observational analyses, these results suggest intracranial hypertension is poorly tolerated in the presence of impaired autoregulation. ICP level guidelines may need to be revised in the future taking into account cerebrovascular autoregulation status considered jointly with ICP levels.

Fentanyl and Midazolam Are Ineffective in Reducing Episodic Intracranial Hypertension in Severe Pediatric Traumatic Brain Injury

OBJECTIVE

To evaluate the clinical effectiveness of bolus-dose fentanyl and midazolam to treat episodic intracranial hypertension in children with severe traumatic brain injury.

DESIGN

Retrospective cohort.

SETTING

PICU in a university-affiliated children's hospital level I trauma center.

PATIENTS

Thirty-one children 0-18 years of age with severe traumatic brain injury (Glasgow Coma Scale score of ≤ 8) who received bolus doses of fentanyl and/or midazolam for treatment of episodic intracranial hypertension.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The area under the curve from high-resolution intracranial pressure-time plots was calculated to represent cumulative intracranial hypertension exposure: area under the curve for intracranial pressure above 20 mm Hg (area under the curve-intracranial hypertension) was calculated in 15-minute epochs before and after administration of fentanyl and/or midazolam for the treatment of episodic intracranial hypertension. Our primary outcome measure, the difference between predrug and postdrug administration epochs (Δarea under the curve-intracranial hypertension), was calculated for all occurrences. We examined potential covariates including age, injury severity, mechanism, and time after injury; time after injury correlated with Δarea under the curve-intracranial hypertension. In a mixed-effects model, with patient as a random effect, drug/dose combination as a fixed effect, and time after injury as a covariate, intracranial hypertension increased after administration of fentanyl and/or midazolam (overall aggregate mean Δarea under the curve-intracranial hypertension = +17 mm Hg × min, 95% CI, 0-34 mm Hg × min; p = 0.04). The mean Δarea under the curve-intracranial hypertension increased significantly after administration of high-dose fentanyl (p = 0.02), low-dose midazolam (p = 0.006), and high-dose fentanyl plus low-dose midazolam (0.007). Secondary analysis using age-dependent thresholds showed no significant impact on cerebral perfusion pressure deficit (mean Δarea under the curve-cerebral perfusion pressure).

CONCLUSIONS

Bolus dosing of fentanyl and midazolam fails to reduce the intracranial hypertension burden when administered for episodic intracranial hypertension. Paradoxically, we observed an overall increase in intracranial hypertension burden following drug administration, even after accounting for within-subject effects and time after injury. Future work is needed to confirm these findings in a prospective study design.

Data collection and interpretation

Patient monitoring is routinely performed in all patients who receive neurocritical care. The combined use of monitors, including the neurologic examination, laboratory analysis, imaging studies, and physiological parameters, is common in a platform called multi-modality monitoring (MMM). However, the full potential of MMM is only beginning to be realized since for the most part, decision making historically has focused on individual aspects of physiology in a largely threshold-based manner. The use of MMM now is being facilitated by the evolution of bio-informatics in critical care including developing techniques to acquire, store, retrieve, and display integrated data and new analytic techniques for optimal clinical decision making. In this review, we will discuss the crucial initial steps toward data and information management, which in this emerging era of data-intensive science is already shifting concepts of care for acute brain injury and has the potential to both reshape how we do research and enhance cost-effective clinical care.

Patient-Specific Thresholds and Doses of Intracranial Hypertension in Severe Traumatic Brain Injury

Based on continuous monitoring of the pressure reactivity index (PRx), we defined individualized intracranial pressure (ICP) thresholds by graphing the relationship between ICP and PRx. We hypothesized that an "ICP dose" based on individually assessed ICP thresholds might correlate more closely with 6-month outcome compared with ICP doses derived from the recommended universal thresholds of 20 and 25 mmHg. Data from 327 patients with severe traumatic brain injury (TBI) were analyzed. ICP doses were computed as the cumulative area under the curve above the defined thresholds in graphing ICP versus time. The term Dose 20 (D20) was used to refer to an ICP threshold of 20 mm Hg. The markers D25 and DPRx were calculated similarly. The discriminative ability of each dose with regard to mortality was assessed by receiver operating characteristics analysis using fivefold cross-validation (CV). DPRx was found to be the best discriminator of mortality, despite the fact that D20 was twice as large as DPRx. Individualized doses of intracranial hypertension were stronger predictors of mortality than doses derived from the universal thresholds of 20 and 25 mm Hg. The PRx could offer a method of individualizing the ICP threshold.

Patient-specific thresholds of intracranial pressure in severe traumatic brain injury

Object

Based on continuous monitoring of the pressure reactivity index (PRx), the authors defined individualized intracranial pressure (ICP) thresholds by graphing the relationship between ICP and PRx. These investigators hypothesized that an “ICP dose” based on individually assessed ICP thresholds would correlate more closely with the 6-month outcome when compared with ICP doses derived by the recommended universal thresholds of 20 and 25 mm Hg.

Methods

This study was a retrospective analysis of prospectively collected data from 327 patients with severe traumatic brain injury.

Results

Individualized thresholds were visually identified from graphs of PRx versus ICP; PRx > 0.2 was the cutoff. Intracranial pressure doses were then computed as the cumulative area under the curve above the defined thresholds in graphing ICP versus time. The term “Dose 20” (D20) was used to refer to an ICP threshold of 20 mm Hg; the markers D25 and DPRx were calculated similarly. Separate logistic regression models were fit with death as the outcome and each dose as the predictor, both alone and adjusted for covariates. The discriminative ability of each dose for mortality was assessed by receiver operating characteristic AUC analysis in which 5-fold cross-validation was used. A clearly identifiable PRx-based threshold was possible in 224 patients (68%). The DPRx (AUC 0.81, 95% CI 0.74–0.87) was found to have the highest area under the curve (AUC) over both D20 (0.75, 95% CI 0.68–0.81) and D25 (0.77, 95% CI 0.70–0.83); in the cross-validation model, DPRx remained the best discriminator of mortality (DPRx: AUC 0.77 [95% CI 0.68–0.89]; D20: 0.72 [95% CI 0.66–0.81]; and D25: 0.65 [95% CI 0.56–0.73]).

Conclusions

The authors explored the importance of different ICP thresholds for outcome by calculating patient-specific ICP doses based on the continuous monitoring of cerebrovascular pressure reactivity. They found that these individualized doses of intracranial hypertension were stronger predictors of death than doses derived from the universal thresholds of 20 and 25 mm Hg. The PRx could offer a method that can be directed toward individualizing the ICP threshold.

Altering physiological networks using drugs: steps towards personalized physiology

Background

The rise of personalized medicine has reminded us that each patient must be treated as an individual. One factor in making treatment decisions is the physiological state of each patient, but definitions of relevant states and methods to visualize state-related physiologic changes are scarce. We constructed correlation networks from physiologic data to demonstrate changes associated with pressor use in the intensive care unit.

Methods

We collected 29 physiological variables at one-minute intervals from nineteen trauma patients in the intensive care unit of an academic hospital and grouped each minute of data as receiving or not receiving pressors. For each group we constructed Spearman correlation networks of pairs of physiologic variables. To visualize drug-associated changes we split the networks into three components: an unchanging network, a network of connections with changing correlation sign, and a network of connections only present in one group.

Results

Out of a possible 406 connections between the 29 physiological measures, 64, 39, and 48 were present in each of the three component networks. The static network confirms expected physiological relationships while the network of associations with changed correlation sign suggests putative changes due to the drugs. The network of associations present only with pressors suggests new relationships that could be worthy of study.

Conclusions

We demonstrated that visualizing physiological relationships using correlation networks provides insight into underlying physiologic states while also showing that many of these relationships change when the state is defined by the presence of drugs. This method applied to targeted experiments could change the way critical care patients are monitored and treated.

Guidelines for the early management of patients with acute ischemic stroke: a guideline for healthcare professionals from the American Heart Association/American Stroke Association

BACKGROUND AND PURPOSE

The authors present an overview of the current evidence and management recommendations for evaluation and treatment of adults with acute ischemic stroke. The intended audiences are prehospital care providers, physicians, allied health professionals, and hospital administrators responsible for the care of acute ischemic stroke patients within the first 48 hours from stroke onset. These guidelines supersede the prior 2007 guidelines and 2009 updates.

METHODS

Members of the writing committee were appointed by the American Stroke Association Stroke Council's Scientific Statement Oversight Committee, representing various areas of medical expertise. Strict adherence to the American Heart Association conflict of interest policy was maintained throughout the consensus process. Panel members were assigned topics relevant to their areas of expertise, reviewed the stroke literature with emphasis on publications since the prior guidelines, and drafted recommendations in accordance with the American Heart Association Stroke Council's Level of Evidence grading algorithm.

RESULTS

The goal of these guidelines is to limit the morbidity and mortality associated with stroke. The guidelines support the overarching concept of stroke systems of care and detail aspects of stroke care from patient recognition; emergency medical services activation, transport, and triage; through the initial hours in the emergency department and stroke unit. The guideline discusses early stroke evaluation and general medical care, as well as ischemic stroke, specific interventions such as reperfusion strategies, and general physiological optimization for cerebral resuscitation.

CONCLUSIONS

Because many of the recommendations are based on limited data, additional research on treatment of acute ischemic stroke remains urgently needed.

Brain hypoxia is associated with short-term outcome after severe traumatic brain injury independently of intracranial hypertension and low cerebral perfusion pressure

BACKGROUND

Brain hypoxia (BH) can aggravate outcome after severe traumatic brain injury (TBI). Whether BH or reduced brain oxygen (Pbto(2)) is an independent outcome predictor or a marker of disease severity is not fully elucidated.

OBJECTIVE

To analyze the relationship between Pbto(2), intracranial pressure (ICP), and cerebral perfusion pressure (CPP) and to examine whether BH correlates with worse outcome independently of ICP and CPP.

METHODS

We studied 103 patients monitored with ICP and Pbto(2) for > 24 hours. Durations of BH (Pbto(2) < 15 mm Hg), ICP > 20 mm Hg, and CPP < 60 mm Hg were calculated with linear interpolation, and their associations with outcome within 30 days were analyzed.

RESULTS

Duration of BH was longer in patients with unfavorable (Glasgow Outcome Scale score, 1-3) than in those with favorable (Glasgow Outcome Scale, 4-5) outcome (8.3 ± 15.9 vs 1.7 ± 3.7 hours; P < .01). In patients with intracranial hypertension, those with BH had fewer favorable outcomes (46%) than those without (81%; P < .01); similarly, patients with low CPP and BH were less likely to have favorable outcome than those with low CPP but normal Pbto(2) (39% vs 83%; P < .01). After ICP, CPP, age, Glasgow Coma Scale score, Marshall computed tomography grade, and Acute Physiology and Chronic Health Evaluation II score were controlled for, BH was independently associated with poor prognosis (adjusted odds ratio for favorable outcome, 0.89 per hour of BH; 95% confidence interval, 0.79-0.99; P = .04).

CONCLUSION

Brain hypoxia is associated with poor short-term outcome after severe traumatic brain injury independently of elevated ICP, low CPP, and injury severity. Pbto(2) may be an important therapeutic target after severe traumatic brain injury.

Blood-based diagnostics of traumatic brain injuries

Traumatic brain injury is a major health and socioeconomic problem that affects all societies. However, traditional approaches to the classification of clinical severity are the subject of debate and are being supplemented with structural and functional neuroimaging, as the need for biomarkers that reflect elements of the pathogenetic process is widely recognized. Basic science research and developments in the field of proteomics have greatly advanced our knowledge of the mechanisms involved in damage and have led to the discovery and rapid detection of new biomarkers that were not available previously. However, translating this research for patients' benefits remains a challenge. In this article, we summarize new developments, current knowledge and controversies, focusing on the potential role of these biomarkers as diagnostic, prognostic and monitoring tools of brain-injured patients.

Automated measurement of "pressure times time dose" of intracranial hypertension best predicts outcome after severe traumatic brain injury

BACKGROUND

Earlier, more accurate assessment of secondary brain injury is essential in management of patients with traumatic brain injury (TBI). We assessed the accuracy and utility of high-resolution automated intracranial pressure (ICP) and cerebral perfusion pressure (CPP) recording and their analysis in patients with severe TBI.

METHODS

ICP and CPP data for 30 severe TBI patients were collected automatically at 6-second intervals. The degree and duration of ICP and CPP above and below treatment thresholds were calculated as "pressure times time dose" (PTD; mm Hg . h) using automated recordings (PTDa) or manual recordings (PTDm) for early stage (trauma resuscitation unit [TRU]) and total monitoring time (TRU and intensive care unit).

RESULTS

Bland-Altman plots showed lack of agreement between PTDa and PTDm. For ICP >20 mm Hg and CPP <60 mm Hg, PTDa, but not PTDm, was significantly higher in patients with unfavorable outcome (Extended Glasgow Outcome Scale score <or=4) than in patients with favorable outcome (Extended Glasgow Outcome Scale score >4). Total PTDa for ICP >20 mm Hg and CPP <60 mm Hg had high predictive power for functional outcome (area under the receiver operating characteristics curve: 0.92 +/- 0.05 and 0.82 +/- 0.08, respectively) and inhospital mortality (0.76 +/- 0.15 and 0.79 +/- 0.14, respectively) and were strongly correlated with length of intensive care unit stay (p = 0.009 and 0.007), length of hospital stay (p = 0.009 and 0.005), and discharge Glasgow Coma Scale scores (p = 0.008 and p = 0.038). PTDa of CPP >100 mm Hg during TRU monitoring and during the first 24 hours showed highest predictive power for mortality (area under the receiver operating characteristics curve: 0.72 +/- 0.18 and 0.85 +/- 0.13, respectively). PTDa was better than PTDm and the duration of episodes alone in predicting outcome.

CONCLUSIONS

PTD calculation of high resolution ICP and CPP recording is a reliable and feasible way of monitoring severe TBI patients.

Identification of complex metabolic states in critically injured patients using bioinformatic cluster analysis

Introduction

Advances in technology have made extensive monitoring of patient physiology the standard of care in intensive care units (ICUs). While many systems exist to compile these data, there has been no systematic multivariate analysis and categorization across patient physiological data. The sheer volume and complexity of these data make pattern recognition or identification of patient state difficult. Hierarchical cluster analysis allows visualization of high dimensional data and enables pattern recognition and identification of physiologic patient states. We hypothesized that processing of multivariate data using hierarchical clustering techniques would allow identification of otherwise hidden patient physiologic patterns that would be predictive of outcome.

Methods

Multivariate physiologic and ventilator data were collected continuously using a multimodal bioinformatics system in the surgical ICU at San Francisco General Hospital. These data were incorporated with non-continuous data and stored on a server in the ICU. A hierarchical clustering algorithm grouped each minute of data into 1 of 10 clusters. Clusters were correlated with outcome measures including incidence of infection, multiple organ failure (MOF), and mortality.

Results

We identified 10 clusters, which we defined as distinct patient states. While patients transitioned between states, they spent significant amounts of time in each. Clusters were enriched for our outcome measures: 2 of the 10 states were enriched for infection, 6 of 10 were enriched for MOF, and 3 of 10 were enriched for death. Further analysis of correlations between pairs of variables within each cluster reveals significant differences in physiology between clusters.

Conclusions

Here we show for the first time the feasibility of clustering physiological measurements to identify clinically relevant patient states after trauma. These results demonstrate that hierarchical clustering techniques can be useful for visualizing complex multivariate data and may provide new insights for the care of critically injured patients.

Relationship of “dose” of intracranial hypertension to outcome in severe traumatic brain injury

Object

It has recently been suggested that the degree of intracranial pressure (ICP) above the treatment goal can be estimated by the area under the curve (AUC) of ICP versus time in patients with severe traumatic brain injury (TBI). The objective of this study was to determine whether the calculated “ICP dose”—the ICP AUC—is related to mortality rate, outcome, and Marshall CT classification.

Methods

Of 135 patients (age range 1–82 years) with severe TBI treated during a 5-year period at the authors' institution, 113 patients underwent ICP monitoring (84%). Ninety-three patients with a monitoring time > 24 hours were included for analysis of ICP AUC calculated using the trapezoidal method. Computed tomography scans were assessed according to the Marshall TBI classification. Patients with Glasgow Outcome Scale scores at 6 months and > 3 years were separated into 2 groups based on outcome.

Results

Sixty patients (65%) had ICP values > 20 mm Hg, and 12 (13%) developed severe intracranial hypertension and died secondary to herniation. A multiple regression analysis adjusting for Glasgow Coma Scale score, age, pupillary abnormalities and Injury Severity Scale score demonstrated that the ICP AUC was a significant predictor of poor outcome at 6 months (p = 0.034) and of death (p = 0.035). However, it did not predict long-term outcome (p = 0.157). The ICP AUC was significantly higher in patients with Marshall head injury Categories 3 and 4 (24 patients) than in those with Category 2 (23 patients, p = 0.025) and Category 5 (46 patients, p = 0.021) TBIs using the worst CT scan obtained.

Conclusions

The authors found a significant relationship between the dose of ICP, the worst Marshall CT score, and patient outcome, suggesting that the AUC method may be useful in refining and improving the treatment of ICP in patients with TBI.

Cumulative dose of hypertension predicts outcome in intracranial hemorrhage better than American Heart Association guidelines

BACKGROUND

Hypertension is common after intracranial hemorrhage (ICH) and may be associated with higher mortality and adverse neurologic outcome. The American Heart Association recommends that blood pressure be maintained at a mean arterial pressure (MAP) less than 130 mm Hg to prevent secondary brain injury.

OBJECTIVES

To prospectively evaluate whether a new method of assessing hypertension in ICH more accurately identifies patients at risk for adverse outcomes.

METHODS

The authors prospectively studied all patients presenting to two University of California, San Francisco hospitals with acute ICH from June 1, 2001, to May 31, 2004. Factors related to acute hospitalization were recorded in a database, including all charted vital signs for the first 15 days. Patients were followed up for one year, with their modified Rankin Scale (mRS) score at 12 months as primary outcome. Hypertension dose was determined as the area under the curve between patient MAP and a cut point of 110 mm Hg while in the emergency department (ED). The dose was adjusted for time spent in the ED (dose/time(ed) [d/t(ed)]). Hypertension dose was divided into four categories (none, and progressive tertiles). Multivariate logistic regression was used to calculate the odds ratio for adverse mRS by tertiles of d/t(ed).

RESULTS

A total of 237 subjects with an ED average (+/-SD) length of stay of 3.42 (+/-3.7) hours were enrolled. In a multivariate logistic regression model controlling for the effects of age, volume of hemorrhage, presence of intraventricular hemorrhage, race, and preexisting hypertension, there was a 4.7- and 6.1-fold greater likelihood of an adverse neurologic outcome (by mRS) at one and 12 months, respectively, in the highest d/t(ed) tertile relative to the referent group without hypertension.

CONCLUSIONS

Hypertension after acute ICH is associated with adverse neurologic outcome. The dose of hypertension may more accurately identify patients at risk for adverse outcomes than the American Heart Association guidelines and may lead to better outcomes if treated when identified in this manner.

Intracranial pressure monitoring in intensive care: clinical advantages of a computerized system over manual recording

Introduction

The presence of intracranial hypertension (HICP) after traumatic brain injury (TBI) affects patient outcome. Intracranial pressure (ICP) data from electronic monitoring equipment are usually calculated and recorded hourly in the clinical chart by trained nurses. Little is known, however, about how precisely this method reflects the real patterns of ICP after severe TBI. In this study, we compared hourly manual recording with a validated and continuous computerized reference standard.

Methods

Thirty randomly selected patients with severe TBI and HICP admitted to the neuroscience intensive care unit (Policlinico University Hospital, Milan, Italy) were retrospectively studied. A 24-hour interval with ICP monitoring was randomly selected for each patient. The manually recorded data available for analysis covered 672 hours corresponding to 36,492 digital data points. The two methods were evaluated using the correlation coefficient and the Bland and Altman method. We used the proportion test to analyze differences in the number of episodes of HICP (ICP > 20 mm Hg) detected with the two methods and the paired t test to analyze differences in the percentage of time of HICP.

Results

There was good agreement between the digitally collected ICP and the manual recordings of the end-hour values. Bland and Altman analysis confirmed a mean difference between the two methods of 0.05 mm Hg (standard deviation 3.66); 96% of data were within the limits of agreement (+7.37 and -7.28). The average percentages of time of ICP greater than 20 mm Hg were 39% calculated from the digital measurements and 34% from the manual observations. From the continuous digital recording, we identified 351 episodes of ICP greater than 20 mm Hg lasting at least five minutes and 287 similar episodes lasting at least ten minutes. Conversely, end-hour ICP of greater than 20 mm Hg was observed in only 204 cases using manual recording methods.

Conclusion

Although manually recorded end-hour ICP accurately reflected the computerized end-hour and mean hour values, the important omission of a number of episodes of high ICP, some of long duration, results in a clinical picture that is not accurate or informative of the true pattern of unstable ICP in patients with TBI.

Novel neuroproteomic approaches to studying traumatic brain injury

Neuroproteomics entails wide-scope study of the nervous system proteome in both its content and dynamics. The field employs high-end analytical mass spectrometry and novel high-throughput antibody approaches to characterize as many proteins as possible. The most common application has been differential analysis to identify a limited set of highly dynamic proteins associated with injury, disease, or other altered states of the nervous system. Traumatic brain injury (TBI) is an important neurological condition where neuroproteomics has revolutionized the characterization of protein dynamics, leading to a greater understanding of post-injury biochemistry. Further, proteins of altered abundance or post-translational modifications identified by neuroproteomic studies are candidate biochemical markers of TBI. This chapter explores the use of neuroproteomics in the study of TBI and the validation of identified putative biomarkers for subsequent clinical translation into novel injury diagnostics.