Effect of cerebral perfusion pressure augmentation with dopamine and norepinephrine on global and focal brain oxygenation after traumatic brain injury

The Impact of Inotropes and Vasopressors on Cerebral Oxygenation in Patients with Traumatic Brain Injury and Subarachnoid Hemorrhage: A Narrative Review

Traumatic brain injury (TBI) and subarachnoid hemorrhage (SAH) are critical neurological conditions that necessitate specialized care in the Intensive Care Unit (ICU). Managing cerebral perfusion pressure (CPP) and mean arterial pressure (MAP) is of primary importance in these patients. To maintain targeted MAP and CPP, vasopressors and/or inotropes are commonly used. However, their effects on cerebral oxygenation are not fully understood. The aim of this review is to provide an up-to date review regarding the current uses and pathophysiological issues related to the use of vasopressors and inotropes in TBI and SAH patients. According to our findings, despite achieving similar hemodynamic parameters and CPP, the effects of various vasopressors and inotropes on cerebral oxygenation, local CBF and metabolism are heterogeneous. Therefore, a more accurate understanding of the cerebral activity of these medications is crucial for optimizing patient management in the ICU setting.

Effects of Reversal of Hypotension on Cerebral Microcirculation and Metabolism in Experimental Sepsis

The effects of reversal of hypotension on the cerebral microcirculation, oxygenation, and metabolism in septic shock remain unclear. In 12 sheep, peritonitis was induced by injection of feces into the abdominal cavity. At the onset of septic shock (mean arterial pressure (MAP) < 65 mmHg, unresponsive to fluid challenge), a norepinephrine infusion was titrated in eight sheep to restore a MAP ≥ 75 mmHg; the other four sheep were kept hypotensive. The microcirculation of the cerebral cortex was evaluated using side-stream dark-field video-microscopy. Brain partial pressure of oxygen (PbtO2) was measured, and cerebral metabolism was assessed using microdialysis. All animals developed septic shock after a median of 15 (14−19) h. When MAP was raised using norepinephrine, the PbtO2 increased significantly (from 41 ± 4 to 55 ± 5 mmHg), and the cerebral lactate/pyruvate ratio decreased (from 47 ± 13 to 28 ± 4) compared with values at shock onset. Changes in the microcirculation were unchanged with restoration of MAP and the glutamate increased further (from 17 ± 11 to 23 ± 16 μM), as it did in the untreated animals. In septic shock, the correction of hypotension with vasopressors may improve cerebral oxygenation but does not reverse the alterations in brain microcirculation or cerebral metabolism.

Optimal Out-of-Hospital Blood Pressure in Major Traumatic Brain Injury: A Challenge to the Current Understanding of Hypotension

STUDY OBJECTIVE

Little is known about the out-of-hospital blood pressure ranges associated with optimal outcomes in traumatic brain injuries (TBI). Our objective was to evaluate the associations between out-of-hospital systolic blood pressure (SBP) and multiple hospital outcomes without assuming any predefined thresholds for hypotension, normotension, or hypertension.

METHODS

This was a preplanned secondary analysis from the Excellence in Prehospital Injury Care (EPIC) TBI study. Among patients (age ≥10 years) with major TBIs (Barell Matrix type 1 and/or Abbreviated Injury Scale-head severity ≥3) and lowest out-of-hospital SBPs of 40 to 299 mmHg, we utilized generalized additive models to summarize the distributions of various outcomes as smoothed functions of SBP, adjusting for important and significant confounders. The subjects who were enrolled in the study phase after the out-of-hospital TBI guideline implementation were used to validate the models developed from the preimplementation cohort.

RESULTS

Among 12,169 included cases, the mortality model revealed 3 distinct ranges: (1) a monotonically decreasing relationship between SBP and the adjusted probability of death from 40 to 130 mmHg, (2) lowest adjusted mortality from 130 to 180 mmHg, and (3) rapidly increasing mortality above 180 mmHg. A subanalysis of the cohorts with isolated TBIs and multisystem injuries with TBIs revealed SBP mortality patterns that were similar to each other and to that of the main analysis. While the specific SBP ranges varied somewhat for the nonmortality outcomes (hospital length of stay, ICU length of stay, discharge to skilled nursing/inpatient rehabilitation, and hospital charges), the patterns were very similar to that of mortality. In each model, validation was confirmed utilizing the postimplementation cohort.

CONCLUSION

Optimal adjusted mortality was associated with a surprisingly high SBP range (130 to 180 mmHg). Below this level, there was no point or range of inflection that would indicate a physiologically meaningful threshold for defining hypotension. Nonmortality outcomes showed very similar patterns. These findings highlight how sensitive the injured brain is to compromised perfusion at SBP levels that, heretofore, have been considered adequate or even normal. While the study design does did not allow us to conclude that the currently recommended treatment threshold (<90 mmHg) should be increased, the findings imply that the definition of hypotension in the setting of TBI is too low. Randomized trials evaluating treatment levels significantly higher than 90 mmHg are needed.

Early Effects of Passive Leg-Raising Test, Fluid Challenge, and Norepinephrine on Cerebral Autoregulation and Oxygenation in COVID-19 Critically Ill Patients

Background: Coronavirus disease 2019 (COVID-19) patients are at high risk of neurological complications consequent to several factors including persistent hypotension. There is a paucity of data on the effects of therapeutic interventions designed to optimize systemic hemodynamics on cerebral autoregulation (CA) in this group of patients. Methods: Single-center, observational prospective study conducted at San Martino Policlinico Hospital, Genoa, Italy, from October 1 to December 15, 2020. Mechanically ventilated COVID-19 patients, who had at least one episode of hypotension and received a passive leg raising (PLR) test, were included. They were then treated with fluid challenge (FC) and/or norepinephrine (NE), according to patients' clinical conditions, at different moments. The primary outcome was to assess the early effects of PLR test and of FC and NE [when clinically indicated to maintain adequate mean arterial pressure (MAP)] on CA (CA index) measured by transcranial Doppler (TCD). Secondary outcomes were to evaluate the effects of PLR test, FC, and NE on systemic hemodynamic variables, cerebral oxygenation (rSo₂), and non-invasive intracranial pressure (nICP). Results: Twenty-three patients were included and underwent PLR test. Of these, 22 patients received FC and 14 were treated with NE. The median age was 62 years (interquartile range = 57-68.5 years), and 78% were male. PLR test led to a low CA index [58% (44-76.3%)]. FC and NE administration resulted in a CA index of 90.8% (74.2-100%) and 100% (100-100%), respectively. After PLR test, nICP based on pulsatility index and nICP based on flow velocity diastolic formula was increased [18.6 (17.7-19.6) vs. 19.3 (18.2-19.8) mm Hg, p = 0.009, and 12.9 (8.5-18) vs. 15 (10.5-19.7) mm Hg, p = 0.001, respectively]. PLR test, FC, and NE resulted in a significant increase in MAP and rSo₂. Conclusions: In mechanically ventilated severe COVID-19 patients, PLR test adversely affects CA. An individualized strategy aimed at assessing both the hemodynamic and cerebral needs is warranted in patients at high risk of neurological complications.

How much oxygen for the injured brain - can invasive parenchymal catheters help?

PURPOSE OF REVIEW

Each year in the United States there are over 2.5 million visits to emergency departments for traumatic brain injury (TBI), 300,000 hospitalizations, and 50,000 deaths. TBI initiates a complex cascade of events which can lead to significant secondary brain damage. Great interest exists in directly measuring cerebral oxygen delivery and demand after TBI to prevent this secondary injury. Several invasive, catheter-based devices are now available which directly monitor the partial pressure of oxygen in brain tissue (PbtO2), yet significant equipoise exists regarding their clinical use in severe TBI.

RECENT FINDINGS

There are currently three ongoing multicenter randomized controlled trials studying the use of PbtO2 monitoring in severe TBI: BOOST-3, OXY-TC, and BONANZA. All three have similar inclusion/exclusion criteria, treatment protocols, and outcome measures. Despite mixed existing evidence, use of PbtO2 is already making its way into new TBI guidelines such as the recent Seattle International Brain Injury Consensus Conference. Analysis of high-fidelity data from multimodal monitoring, however, suggests that PbtO2 may only be one piece of the puzzle in severe TBI.

SUMMARY

While current evidence regarding the use of PbtO2 remains mixed, three ongoing clinical trials are expected to definitively answer the question of what role PbtO2 monitoring plays in severe TBI.

Fifteen-minute consultation: Severe traumatic brain injury in paediatrics

Paediatric traumatic brain injury (TBI) is a non-degenerative, acquired brain insult. Following a blow or penetrating trauma to the head, normal brain function is disrupted. If it occurs during the early stages of development, deficits may not immediately become apparent but unfold and evolve over time. We address the difficulties that arise when treating a child with severe TBI.

The cerebrovascular response to norepinephrine: A scoping systematic review of the animal and human literature

Intravenous norepinephrine (NE) is utilized commonly in critical care for cardiovascular support. NE's impact on cerebrovasculature is unclear and may carry important implications during states of critical neurological illness. The aim of the study was to perform a scoping review of the literature on the cerebrovascular/cerebral blood flow (CBF) effects of NE. A search of MEDLINE, BIOSIS, EMBASE, Global Health, SCOPUS, and Cochrane Library from inception to December 2019 was performed. All manuscripts pertaining to the administration of NE, in which the impact on CBF/cerebral vasculature was recorded, were included. We identified 62 animal studies and 26 human studies. Overall, there was a trend to a direct vasoconstriction effect of NE on the cerebral vasculature, with conflicting studies having demonstrated both increases and decreases in regional CBF (rCBF) or global CBF. Healthy animals and those undergoing cardiopulmonary resuscitation demonstrated a dose-dependent increase in CBF with NE administration. However, animal models and human patients with acquired brain injury had varied responses in CBF to NE administration. The animal models indicate an increase in cerebral vasoconstriction with NE administration through the alpha receptors in vessels. Global and rCBF during the injection of NE displays a wide variation depending on treatment and model/patient.

In adult patients with severe traumatic brain injury, does the use of norepinephrine for augmenting cerebral perfusion pressure improve neurological outcome? A systematic review

BACKGROUND AND OBJECTIVE

Despite multiple interventions, mortality due to severe traumatic brain injury (sTBI) within mature Trauma Systems has remained unchanged over the last decade. During this time, the use of vasoactive infusions (commonly norepinephrine) to achieve a target blood pressure and cerebral perfusion pressure (CPP) has been a mainstay of sTBI management. However, evidence suggests that norepinephrine, whilst raising blood pressure, may reduce cerebral oxygenation. This study aimed to review the available evidence that links norepinephrine augmented CPP to clinical outcomes for these patients.

METHODS

A systematic review examining the evidence for norepinephrine augmented CPP in TBI patients was undertaken. Strict inclusion and exclusion criteria were developed for a dedicated literature search of multiple scientific databases. Two dedicated reviewers screened articles, whilst a third dedicated reviewer resolved conflicts.

RESULTS

The systematic review yielded 4,809 articles, of which 1,197 duplicate articles were removed. After abstract/title screening, 45 articles underwent full text review, resulting in the identification of two articles that investigated the effect of norepinephrine administration on clinical outcomes in patients following TBI when compared to other vasopressors. Neither study found a difference in neurological outcome between the vasopressor groups. No articles measured the effect of norepinephrine compared to no vasopressor use on the clinical outcome of patients with sTBI.

CONCLUSIONS

Despite being a mainstay of pharmacological management for hypotension in patients following sTBI, there is minimal clinical evidence supporting the use of norepinephrine in targeting a CPP for either improving neurological outcomes or reducing mortality. Outcomes-based clinical trials exploring the role of brain tissue perfusion and oxygenation monitoring are required to validate any benefit.

Anesthetic considerations for extracranial injuries in patients with associated brain trauma

Patients with severe traumatic brain injury often presents with extracranial injuries, which may contribute to fatal outcome. Anesthetic management of such polytrauma patients is extremely challenging that includes prioritizing the organ system to be dealt first, reducing on-going injury, and preventing secondary injuries. Neuroprotective and neurorescue measures should be instituted simultaneously during extracranial surgeries. Selection of anesthetic drugs that minimally interferes with cerebral dynamics, maintenance of hemodynamics and cerebral perfusion pressure, optimal utilization of multimodal monitoring techniques, and aggressive rehabilitation approach are the key factors for improving overall patient outcome.

Intensive Care in Traumatic Brain Injury Including Multi-Modal Monitoring and Neuroprotection

Moderate to severe traumatic brain injuries (TBI) require treatment in an intensive care unit (ICU) in close collaboration of a multidisciplinary team consisting of different medical specialists such as intensivists, neurosurgeons, neurologists, as well as ICU nurses, physiotherapists, and ergo-/logotherapists. Major goals include all measurements to prevent secondary brain injury due to secondary brain insults and to optimize frame conditions for recovery and early rehabilitation. The distinction between moderate and severe is frequently done based on the Glascow Coma Scale and therefore often is just a snapshot at the early time of assessment. Due to its pathophysiological pathways, an initially as moderate classified TBI may need the same sophisticated surveillance, monitoring, and treatment as a severe form or might even progress to a severe and difficult to treat affection. As traumatic brain injury is rather a syndrome comprising a range of different affections to the brain and as, e.g., age-related comorbidities and treatments additionally may have a great impact, individual and tailored treatment approaches based on monitoring and findings in imaging and respecting pre-injury comorbidities and their therapies are warranted.

A randomized controlled study comparing high-dose insulin to vasopressors or combination therapy in a porcine model of refractory propranolol-induced cardiogenic shock

Context: Although cerebral perfusion (CP) is preserved across a wide range of mean arterial pressures (MAP) through cerebral-vascular autoregulation, the relationship between MAP and CP in refractory poison-induced cardiogenic shock (PICS) has never been studied. We compared the effects of therapies used in PICS: high-dose insulin (HDI), HDI plus norepinephrine (NE), and vasopressors alone (NE plus epinephrine (Epi)) on cerebral tissue oxygenation (P_tO₂). Methods: Fifteen swine were randomized to either HDI, HDI + NE, or NE + Epi. All animals received a propranolol infusion using an established model of toxicity. At primary toxicity (P₁), defined as a 25% reduction in heart rate (HR) multiplied by MAP, the HDI and HDI + NE groups received HDI and the NE + Epi group received NE. Once a sustained MAP < 55 mmHg was reached (P₂), the HDI group received saline (NS), the HDI + NE group received NE and the NE + Epi group received Epi until death or censoring. P_tO₂ and hemodynamic parameters including MAP, cardiac output (CO) and central venous pressure (CVP) were measured every 10 minutes. Glucose and potassium were measured at predetermined intervals. Results: Animals treated with HDI + NE maintained P_tO₂ over time more than the HDI-alone group. Due to rapid hemodynamic collapse, we were unable to analyze P_tO₂ data in the vasopressor only animals. Mean survival time was 1.9, 2.9 and 0.1 hours for the HDI, HDI + NE and NE + Epi groups, respectively. Survival time from P₂ (sustained MAP <55 mmHg) to death or censoring was not different between HDI and HDI + NE groups. Conclusions: HDI + NE treatment was superior to HDI-alone at preserving P_tO₂ when MAP < 55 mmHg. We were unable to compare the P_tO₂ between the NE + Epi to the HDI or HDI + NE due to rapid decline in CO and death. If MAP is sustained at < 55 mmHg after maximizing HDI, adjunctive treatment with NE should be considered to preserve P_tO₂.

Transfusion practices in traumatic brain injury

Purpose of review

The aim of this review is to summarize the recent studies looking at the effects of anemia and red blood cell transfusion in critically-ill patients with traumatic brain injury (TBI), describe the transfusion practice variations observed worldwide, and outline the ongoing trials evaluating restrictive versus liberal transfusion strategies for TBI.

Recent findings

Anemia is common among critically-ill patients with TBI, it is also thought to exacerbate secondary brain injury, and is associated with an increased risk of poor outcome. Conversely, allogenic red blood cell transfusion carries its own risks and complications, and has been associated with worse outcomes. Globally, there are large reported differences in the hemoglobin threshold used for transfusion after TBI. Observational studies have shown differential results for improvements in cerebral oxygenation and metabolism after red blood cell transfusion in TBI.

Summary

Currently, there is insufficient evidence to make strong recommendations regarding which hemoglobin threshold to use as a transfusion trigger in critically-ill patients with TBI. There is also uncertainty whether the restrictive transfusion strategy used in general critical care can be extrapolated to acutely brain injured patients. Ultimately, the consequences of anemia-induced cerebral injury need to be weighed up against the risks and complications associated with red blood cell transfusion.

A Direct Comparison between Norepinephrine and Phenylephrine for Augmenting Spinal Cord Perfusion in a Porcine Model of Spinal Cord Injury

Current clinical guidelines recommend elevating the mean arterial blood pressure (MAP) to increase spinal cord perfusion in patients with acute spinal cord injury (SCI). This is typically achieved with vasopressors such as norepinephrine (NE) and phenylephrine (PE). These drugs differ in their pharmacological properties and potentially have different effects on spinal cord blood flow (SCBF), oxygenation (PO₂), and downstream metabolism after injury. Using a porcine model of thoracic SCI, we evaluated how these vasopressors influenced intraparenchymal SCBF, PO₂, hydrostatic pressure, and metabolism within the spinal cord adjacent to the injury site. Yorkshire pigs underwent a contusion/compression SCI at T10 and were randomized to receive either NE or PE for MAP elevation of 20 mm Hg, or no MAP augmentation. Prior to injury, a combined SCBF/PO₂ sensor, a pressure sensor, and a microdialysis probe were inserted into the spinal cord adjacent to T10 at two locations: a "proximal" site and a "distal" site, 2 mm and 22 mm from the SCI, respectively. At the proximal site, NE and PE resulted in little improvement in SCBF during cord compression. Following decompression, NE resulted in increased SCBF and PO₂, whereas decreased levels were observed for PE. However, both NE and PE were associated with a gradual decrease in the lactate to pyruvate (L/P) ratio after decompression. PE was associated with greater hemorrhage through the injury site than that in control animals. Combined, our results suggest that NE promotes better restoration of blood flow and oxygenation than PE in the traumatically injured spinal cord, thus providing a physiological rationale for selecting NE over PE in the hemodynamic management of acute SCI.

Pathophysiological central nervous system changes in a porcine model of acetaminophen-induced acute liver failure

BACKGROUND

Critical care management of patients suffering from acute liver failure (ALF) continues to be challenging. Animal models studying the pathophysiological central nervous system alterations during the course of ALF provide an opportunity to improve diagnostic and therapeutic strategies. The aim of this study was to analyse the course of cerebral oxygenation in addition to conventional neuromonitoring during the course of acetaminophen-induced ALF.

METHODS

ALF was induced by intrajejunal acetaminophen administration in 20 German landrace pigs. All animals underwent invasive hemodynamic and neuromonitoring and were maintained under standardized intensive care support. Neuromonitoring consisted of continuous intraparenchymatous recording of intracranial pressure and brain partial oxygen pressure. Hemodynamic and ventilation parameters were continuously recorded; laboratory parameters were analysed every eight hours. Mean values were compared using the Wilcoxon test.

RESULTS

Acute liver failure occurred in all intoxicated animals after 23±2h, resulting in death due to ALF after further 15±2h. Continuous neuromonitoring was performed in all animals during the whole experiment without observing signs of intracranial haemorrhage. Two hours after manifestation of ALF an increase in brain tissue oxygen (PtiO2) was observed. Brain oxygenation stayed stable until nine hours before death. Intracranial pressure (ICP) remained basically at a plateau level until manifestation of ALF. In the following ten hours a linear and slow increase was observed until five hours before death, followed by a fast and continuous rise in ICP to a final level of 35±1mmHg. Cerebral perfusion pressure (CPP) began to decrease 25h prior to exitus, further decreasing to 18±2mmHg at the end of the experiment. A strong negative linear correlation was found between PtiO2 and ICP (R=0.97). Arterial partial pressure of oxygen (PaO2) below 100mmHg was associated with lower PtiO2 levels. Changes in arterial partial pressure of carbon dioxide (PaC02) did not influence PtiO2 values. Hemoglobin values below 7g/dl were associated with lower PtiO2 values.

CONCLUSIONS

The results of our experiments demonstrate that ICP and PtiO2 measurements indicate impending damage well before serious complications occur and their use should be considered in order to protect endangered brain function in the presence of acetaminophen-induced ALF.

Consensus statement from the 2014 International Microdialysis Forum

Microdialysis enables the chemistry of the extracellular interstitial space to be monitored. Use of this technique in patients with acute brain injury has increased our understanding of the pathophysiology of several acute neurological disorders. In 2004, a consensus document on the clinical application of cerebral microdialysis was published. Since then, there have been significant advances in the clinical use of microdialysis in neurocritical care. The objective of this review is to report on the International Microdialysis Forum held in Cambridge, UK, in April 2014 and to produce a revised and updated consensus statement about its clinical use including technique, data interpretation, relationship with outcome, role in guiding therapy in neurocritical care and research applications.

The differential effects of norepinephrine and dopamine on cerebrospinal fluid pressure and spinal cord perfusion pressure after acute human spinal cord injury

STUDY DESIGN

Prospective vasopressor cross-over interventional studyObjectives:To examine how two vasopressors used in acute traumatic spinal cord injury (SCI) affect intrathecal cerebrospinal fluid pressure and the corresponding spinal cord perfusion pressure (SCPP).

SETTING

Vancouver, British Columbia, Canada.

METHODS

Acute SCI patients over the age of 17 with cervical or thoracic ASIA Impairment Scale (AIS). A, B or C injuries were enrolled in this study. Two vasopressors, norepinephrine and dopamine, were evaluated in a 'crossover procedure' to directly compare their effect on the intrathecal pressure (ITP). The vasopressor cross-over procedures were performed in the intensive care unit where ITP, mean arterial pressure (MAP) and heart rate were being continuously measured. The SCPP was calculated as the difference between MAP and ITP.

RESULTS

A total of 11 patients were enrolled and included in our analysis. There were 6 patients with AIS A, 3 with AIS B and 2 with AIS C injuries at baseline. We performed 24 cross-over interventions in these 11 patients. There was no difference in MAP with the use of norepinephrine versus dopamine (84±1 mm Hg for both; P=0.33). Conversely, ITP was significantly lower with the use of norepinephrine than with dopamine (17±1 mm Hg vs 20±1 mm Hg, respectively, P<0.001). This decrease in ITP with norepinephrine resulted in an increased SCPP during the norepinephrine infusion when compared with dopamine (67±1 mm Hg vs 65±1 mm Hg respectively, P=0.0049).

CONCLUSION

Norepinephrine was able to maintain MAP with a lower ITP and a correspondingly higher SCPP as compared with dopamine in this study. These results suggest that norepinephrine may be preferable to dopamine if vasopressor support is required post SCI to maintain elevated MAPs in accordance with published guidelines.

Monitoring of brain and systemic oxygenation in neurocritical care patients

Maintenance of adequate oxygenation is a mainstay of intensive care, however, recommendations on the safety, accuracy, and the potential clinical utility of invasive and non-invasive tools to monitor brain and systemic oxygenation in neurocritical care are lacking. A literature search was conducted for English language articles describing bedside brain and systemic oxygen monitoring in neurocritical care patients from 1980 to August 2013. Imaging techniques e.g., PET are not considered. A total of 281 studies were included, the majority described patients with traumatic brain injury (TBI). All tools for oxygen monitoring are safe. Parenchymal brain oxygen (PbtO2) monitoring is accurate to detect brain hypoxia, and it is recommended to titrate individual targets of cerebral perfusion pressure (CPP), ventilator parameters (PaCO2, PaO2), and transfusion, and to manage intracranial hypertension, in combination with ICP monitoring. SjvO2 is less accurate than PbtO2. Given limited data, NIRS is not recommended at present for adult patients who require neurocritical care. Systemic monitoring of oxygen (PaO2, SaO2, SpO2) and CO2 (PaCO2, end-tidal CO2) is recommended in patients who require neurocritical care.

Brain tissue oxygenation, lactate-pyruvate ratio, and cerebrovascular pressure reactivity monitoring in severe traumatic brain injury: systematic review and viewpoint

BACKGROUND

Prevention and detection of secondary brain insults via multimodality neuromonitoring is a major goal in patients with severe traumatic brain injury (TBI).

OBJECTIVE

Explore the underlying pathophysiology and clinical outcome correlates as it pertains to combined monitoring of ≥2 from the following variables: partial brain tissue oxygen tension (PbtO(2)), pressure reactivity index (PRx), and lactate pyruvate ratio (LPR).

METHODS

Data sources included Medline, EMBASE, and evidence-based databases (Cochrane DSR, ACP Journal Club, DARE, and the Cochrane Controlled Trials Register). The PRISMA recommendations were followed. Two authors independently selected articles meeting inclusion criteria. Studies enrolled adults who required critical care and monitoring in the setting of TBI. Included studies reported on correlations between the monitored variables and/or reported on correlations of the variables with clinical outcomes.

RESULTS

Thirty-four reports were included (32 observational studies and 2 randomized controlled trials) with a mean sample size of 34 patients (range 6-223), and a total of 1,161 patient-observations. Overall methodological quality was moderate. Due to inter-study heterogeneity in outcomes of interest, study design, and in both number and type of covariates included in multivariable analyses, quantitative synthesis of study results was not undertaken.

CONCLUSION

Several literature limitations were identified including small number of subjects, lack of clinical outcome correlations, inconsistent probe location, and overall moderate quality among the included studies. These limitations preclude any firm conclusions; nevertheless we suggest that the status of cerebrovascular reactivity is not only important for cerebral perfusion pressure optimization but should also inform interpretation and interventions targeted on PbtO(2) and LPR. Assessment of reactivity can be the first step in approaching the relations among cerebral blood flow, oxygen delivery, demand, and cellular metabolism.

Pathophysiology and clinical management of moderate and severe traumatic brain injury in the ICU

Moderate and severe traumatic brain injury (TBI) is the leading cause of morbidity and mortality among young individuals in high-income countries. Its pathophysiology is divided into two major phases: the initial neuronal injury (or primary injury) followed by secondary insults (secondary injury). Multimodality monitoring now offers neurointensivists the ability to monitor multiple physiologic parameters that act as surrogates of brain ischemia and hypoxia, the major driving forces behind secondary brain injury. The heterogeneity of the pathophysiology of TBI makes it necessary to take into consideration these interacting physiologic factors when recommending for or against any therapies; it may also account for the failure of all the neuroprotective therapies studied so far. In this review, the authors focus on neuroclinicians and neurointensivists, and discuss the developments in therapeutic strategies aimed at optimizing intracranial pressure and cerebral perfusion pressure, and minimizing cerebral hypoxia. The management of moderate to severe TBI in the intensive care unit is moving away from a pure "threshold-based" treatment approach toward consideration of patient-specific characteristics, including the state of cerebral autoregulation. The authors also include a concise discussion on the management of medical and neurologic complications peculiar to TBI as well as an overview of prognostication.

Differing effects when using phenylephrine and norepinephrine to augment cerebral blood flow after traumatic brain injury in the immature brain

Low cerebral blood flow (CBF) states have been demonstrated in children early after traumatic brain injury (TBI), and have been correlated with poorer outcomes. Cerebral perfusion pressure (CPP) support following severe TBI is commonly implemented to correct cerebral hypoperfusion, but the efficacy of various vasopressors has not been determined. Sixteen 4-week-old female swine underwent nonimpact inertial brain injury in the sagittal plane. Intraparenchymal monitors were placed to measure intracranial pressure (ICP), CBF, brain tissue oxygen tension (PbtO2), and cerebral microdialysis 30 min to 6 h post-injury. One hour after injury, animals were randomized to receive either phenylephrine (PE) or norepinephrine (NE) infusions titrated to a CPP>70 mm Hg for 5 h. Animals were euthanized 6 h post-TBI, and brains were fixed and stained to assess regions of cell and axonal injury. After initiation of CPP augmentation with NE or PE infusions, there were no differences in ICP between the groups or over time. Animals receiving NE had higher PbtO2 than those receiving PE (29.6±10.2 vs. 19.6±6.4 torr at 6 h post-injury, p<0.05). CBF increased similarly in both the NE and PE groups. CPP support with PE resulted in a greater reduction in metabolic crisis than with NE (lactate/pyruvate ratio 16.7±2.4 vs. 42.7±10.2 at 6 h post-injury, p<0.05). Augmentation of CPP to 70 mm Hg with PE resulted in significantly smaller cell injury volumes at 6 h post-injury than CPP support with NE (0.4% vs. 1.4%, p<0.05). Despite similar increases in CBF, CPP support with NE resulted in greater brain tissue oxygenation and hypoxic-ischemic injury than CPP support with PE. Future clinical studies comparing the effectiveness of various vasopressors for CPP support are warranted.

Current concepts of optimal cerebral perfusion pressure in traumatic brain injury

Traumatic brain injury (TBI) consists of varied pathophysiological consequences and alteration of intracranial dynamics, reduction of the cerebral blood flow and oxygenation. In the past decade more emphasis has been directed towards optimizing cerebral perfusion pressure (CPP) in patients who have suffered TBI. Injured brain may show signs of ischemia if CPP remains below 50 mmHg and raising the CPP above 60 mmHg may avoid cerebral oxygen desaturation. Though CPP above 70 mmHg is influential in achieving an improved patient outcome, maintenance of CPP higher than 70 mmHg was associated with greater risk of acute respiratory distress syndrome (ARDS). The target CPP has been laid within 50-70 mmHg. Cerebral blood flow and metabolism are heterogeneous after TBI and with regional temporal differences in the requirement for CPP. Brain monitoring techniques such as jugular venous oximetry, monitoring of brain tissue oxygen tension (PbrO₂), and cerebral microdialysis provide complementary and specific information that permits the selection of the optimal CPP. This review highlights the rationale for use CPP directed therapies and neuromonitoring to identify optimal CPP of head injured patients. The article also reviews the evidence provided by various clinical trials regarding optimal CPP and their application in the management of head injured patients.

Brain Tissue Oxygen Monitoring in Neurocritical Care

Brain injury results from ischemia, tissue hypoxia, and a cascade of secondary events. The cornerstone of neurocritical care management is optimization and maintenance of cerebral blood flow (CBF) and oxygen and substrate delivery to prevent or attenuate this secondary damage. New techniques for monitoring brain tissue oxygen tension (PtiO2) are now available. Brain PtiO2 reflects both oxygen delivery and consumption. Brain hypoxia (low brain PtiO2) has been associated with poor outcomes in patients with brain injury. Strategies to improve brain PtiO2 have focused mainly on increasing oxygen delivery either by increasing CBF or by increasing arterial oxygen content. The results of nonrandomized studies comparing brain PtiO2-guided therapy with intracranial pressure/cerebral perfusion pressure-guided therapy, while promising, have been mixed. More studies are needed including prospective, randomized controlled trials to assess the true value of this approach. The following is a review of the physiology of brain tissue oxygenation, the effect of brain hypoxia on outcome, strategies to increase oxygen delivery, and outcome studies of brain PtiO2-guided therapy in neurocritical care.

Perioperative management of traumatic brain injury

Traumatic brain injury (TBI) is a major public health problem and the leading cause of death and disability worldwide. Despite the modern diagnosis and treatment, the prognosis for patients with TBI remains poor. While severity of primary injury is the major factor determining the outcomes, the secondary injury caused by physiological insults such as hypotension, hypoxemia, hypercarbia, hypocarbia, hyperglycemia and hypoglycemia, etc. that develop over time after the onset of the initial injury, causes further damage to brain tissue, worsening the outcome in TBI. Perioperative period may be particularly important in the course of TBI management. While surgery and anesthesia may predispose the patients to new onset secondary injuries which may contribute adversely to outcomes, the perioperative period is also an opportunity to detect and correct the undiagnosed pre-existing secondary insults, to prevent against new secondary insults and is a potential window to initiate interventions that may improve outcome of TBI. For this review, extensive Pubmed and Medline search on various aspects of perioperative management of TBI was performed, followed by review of research focusing on intraoperative and perioperative period. While the research focusing specifically on the intraoperative and immediate perioperative TBI management is limited, clinical management continues to be based largely on physiological optimization and recommendations of Brain Trauma Foundation guidelines. This review is focused on the perioperative management of TBI, with particular emphasis on recent developments.

Parenchymal brain oxygen monitoring in the neurocritical care unit

Patients admitted to the neurocritical care unit (NCCU) often have serious conditions that can be associated with high morbidity and mortality. Pharmacologic agents or neuroprotectants have disappointed in the clinical environment. Current NCCU management therefore is directed toward identification, prevention, and treatment of secondary cerebral insults that evolve over time and are known to aggravate outcome. This strategy is based on a variety of monitoring techniques including use of intraparenchymal monitors. This article reviews parenchymal brain oxygen monitors, including the available technologies, practical aspects of use, the physiologic rationale behind their use, and patient management based on brain oxygen.

Dopamine prevents impairment of autoregulation after traumatic brain injury in the newborn pig through inhibition of Up-regulation of endothelin-1 and extracellular signal-regulated kinase mitogen-activated protein kinase

OBJECTIVE

Traumatic brain injury contributes to morbidity in children and boys are disproportionately represented. Autoregulation is impaired more in male compared with female piglets after traumatic brain injury through sex-dependent up-regulation of the spasmogen endothelin-1 and extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase (MAPK), a family of three kinases: ERK, p38, and JNK). Elevation of mean arterial pressure leading to increased cerebral perfusion pressure via phenylephrine improves impairment of autoregulation after traumatic brain injury in female but not male piglets through modulation of endothelin-1 and ERK MAPK up-regulation, blocked in females, but aggravated in males. We hypothesized that pressor choice to elevate cerebral perfusion pressure is important in improving cerebral hemodynamics after traumatic brain injury and that dopamine will prevent impairment of autoregulation in both male and female piglets through blockade of endothelin-1 and ERK MAPK.

DESIGN

Prospective, randomized animal study.

SETTING

University laboratory.

SUBJECTS

Newborn (1-5 days old) pigs.

INTERVENTIONS

Cerebral perfusion pressure and pial artery diameter were determined before and after lateral fluid percussion brain injury was produced in piglets equipped with a closed cranial window. Dopamine (15 µg/kg/min IV) was administered 30 mins post fluid percussion injury. Cerebrospinal fluid ERK MAPK was determined by enzyme-linked immunosorbent assay.

MEASUREMENTS AND MAIN RESULTS

Dopamine increased cerebral perfusion pressure equivalently in both sexes and prevented sex-dependent reductions in pial artery diameter after fluid percussion injury. Loss of pial artery dilation during hypotension was greater in male than in female piglets after fluid percussion injury, but dopamine prevented such impairment equivalently in both sexes post injury. endothelin-1 and ERK MAPK release was greater in male compared to female piglets after fluid percussion injury, but dopamine also blocked their up-regulation equivalently in male and female piglets after fluid percussion injury.

CONCLUSIONS

These data indicate that dopamine is protective of autoregulation after fluid percussion injury in both sexes. These observations advocate for the consideration of development of sex based therapies for treatment of hemodynamic sequalae of pediatric traumatic brain injury.

Severe traumatic brain injury

PURPOSE OF REVIEW

Although adherence to traumatic brain injury (TBI) guidelines has been associated with improved patient outcomes, guideline adherence remains suboptimal in practice. With neurologists becoming increasingly involved in specialized neurointensive care units and in the care of patients with severe TBI, familiarization with these guidelines is essential.

RECENT FINDINGS

Intracranial monitoring of different physiologic variables has increased in the past few years. Intracranial pressure (ICP)-driven therapy has been replaced by ICP-cerebral perfusion pressure (CPP)-driven therapy. More recently, the importance of brain oxygen optimization in addition to ICP-CPP has been recognized, and clinical trials are underway to study the effect of this approach. Surgical management of patients with TBI is also evolving rapidly with further studies on decompressive craniectomy. These are significant advances to improve TBI outcomes.

SUMMARY

This article summarizes the routine monitoring of patients with severe TBI and offers insight into some novel physiologic monitoring devices available. The guidelines for management of patients with severe TBI are summarized along with outcome measures.

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.

Perioperative management of the pediatric patient with traumatic brain injury

TBI and its sequelae remain a major healthcare issue throughout the world. With an improved understanding of the pathophysiology of TBI, refinements of monitoring technology, and ongoing research to determine optimal care, the prognosis of TBI continues to improve. In 2003, the Society of Critical Care Medicine published guidelines for the acute management of severe TBI in infants, children, and adolescents. As pediatric anesthesiologists are frequently involved in the perioperative management of such patients including their stabilization in the emergency department, familiarity with these guidelines is necessary to limit preventable secondary damage related to physiologic disturbances. This manuscript reviews the current evidence-based medicine regarding the care of pediatric patients with TBI as it relates to the perioperative care of such patients. The issues reviewed include those related to initial stabilization, airway management, intra-operative mechanical ventilation, hemodynamic support, administration of blood and blood products, positioning, and choice of anesthetic technique. The literature is reviewed regarding fluid management, glucose control, hyperosmolar therapy, therapeutic hypothermia, and corticosteroids. Whenever possible, management recommendations are provided.

Perioperative management of adult traumatic brain injury

This article presents an overview of the management of traumatic brain injury (TBI) as relevant to the practicing anesthesiologist. Key concepts surrounding the pathophysiology and anesthetic principles are used to describe potential ways to reduce secondary insults and improve outcomes after TBI.

Reviewing the reliability, effectiveness and applications of Licox in traumatic brain injury

AIMS AND OBJECTIVES

To review the pathophysiology, accuracy, effectiveness and use of Licox for brain tissue oxygen monitoring in traumatic brain injury (TBI).

BACKGROUND

The Licox monitoring system allows continuous monitoring of partial pressure of brain tissue oxygen (PbO(2)), brain tissue temperature and intracranial pressure (ICP). The application and effectiveness of the use of Licox in TBI is not clearly explored within the literature.

INCLUSION CRITERIA

A date limit of 1995-2009, English language, all animal and human studies and the following terms were searched: Licox, brain tissue oxygenation, cerebral oxygenation and TBI. MEDLINE database was the primary data source.

EXCLUSION CRITERIA

All paediatric papers were excluded from the search. Studies not related to pathophysiology and management of TBI and brain tissue oximetry in adults were excluded. Data relevant to the subject under consideration were extracted by three independent clinicians to form a narrative report. Studies were critically evaluated using the NHS Public Health Resource Unit's checklist for each study analysed.

CONCLUSIONS

Licox offers new insights into cerebral pathology and physiology. The continuous bedside monitoring provides real-time data that can be used to improve patient management and prognosis in specialist units by trained and experienced staff. More research is required to understand the limitations of this technology and why it is not in widespread use. RELEVENCE TO CLINICAL PRACTICE: A clinical tool that could be utilized more often in the right setting to improve care to patients suffering from TBI by disseminating more information on this unique tool.

Medical management of compromised brain oxygen in patients with severe traumatic brain injury

BACKGROUND

Brain tissue oxygen (PbtO(2)) monitoring is used in severe traumatic brain injury (TBI) patients. How brain reduced PbtO(2) should be treated and its response to treatment is not clearly defined. We examined which medical therapies restore normal PbtO(2) in TBI patients.

METHODS

Forty-nine (mean age 40 ± 19 years) patients with severe TBI (Glasgow Coma Scale [GCS] ≤ 8) admitted to a University-affiliated, Level I trauma center who had at least one episode of compromised brain oxygen (PbtO(2) <25 mmHg for >10 min), were retrospectively identified from a prospective observational cohort study. Intracranial pressure (ICP), cerebral perfusion pressure (CPP), and PbtO(2) were monitored continuously. Episodes of compromised PbtO(2) and brain hypoxia (PbtO(2) <15 mmHg for >10 min) and the medical interventions that improved PbtO(2) were identified.

RESULTS

Five hundred and sixty-four episodes of compromised PbtO2 were identified from 260 days of PbtO2 monitoring. Medical management used in a "cause-directed" manner successfully reversed 72% of the episodes of compromised PbtO(2), defined as restoration of a "normal" PbtO(2) (i.e. ≥ 25 mmHg). Ventilator manipulation, CPP augmentation, and sedation were the most frequent interventions. Increasing FiO(2) restored PbtO(2) 80% of the time. CPP augmentation and sedation were effective in 73 and 66% of episodes of compromised brain oxygen, respectively. ICP reduction using mannitol was effective in 73% of treated episodes, though was used only when PbtO(2) was compromised in the setting of elevated ICP. Successful medical treatment of brain hypoxia was associated with decreased mortality. Survivors (n = 38) had a 71% rate of response to treatment and non-survivors (n = 11) had a 44% rate of response (P = 0.01).

CONCLUSION

Reduced PbtO(2) may occur in TBI patients despite efforts to maintain CPP. Medical interventions other than those to treat ICP and CPP can improve PbtO(2). This may increase the number of therapies for severe TBI in the ICU.

Vasopressor use and effect on blood pressure after severe adult traumatic brain injury

BACKGROUND

We describe institutional vasopressor usage, and examine the effect of vasopressors on hemodynamics: heart rate (HR), mean arterial blood pressure (MAP), intracranial pressure (ICP), cerebral perfusion pressure (CPP), brain tissue oxygenation (PbtO(2)), and jugular venous oximetry (SjVO(2)) in adults with severe traumatic brain injury (TBI).

METHODS

We performed a retrospective analysis of 114 severely head injured patients who were admitted to the neurocritical care unit of Level 1 trauma center and who received vasopressors (phenylephrine, norepinephrine, dopamine, vasopressin or epinephrine) to increase blood pressure

RESULTS

Phenylephrine was the most commonly used vasopressor (43%), followed by norepinephrine (30%), dopamine (22%), and vasopressin (5%). Adjusted for age, gender, injury severity score, vasopressor dose, baseline blood pressure, fluid administration, propofol sedation, and hypertonic saline infusion, phenylephrine use was associated with 8 mmHg higher mean arterial pressure (MAP) than dopamine (P = 0.03), and 12 mmHg higher cerebral perfusion pressure (CPP) than norepinephrine (P = 0.02) during the 3 h after vasopressor start. There was no difference in ICP between the drug groups, either at baseline or after vasopressor treatment.

CONCLUSIONS

Most severe TBI patients received phenylephrine. Patients who received phenylephrine had higher MAP and CPP than patients who received dopamine and norepinephrine, respectively.

Use and effect of vasopressors after pediatric traumatic brain injury

BACKGROUND

Vasopressors are commonly used to increase mean arterial blood pressure (MAP) and cerebral perfusion pressure (CPP) after traumatic brain injury (TBI), but there are few data comparing vasopressor effectiveness after pediatric TBI.

OBJECTIVE

To determine which vasopressor is most effective at increasing MAP and CPP in children with moderate-to-severe TBI.

METHODS

After institutional review board approval, we performed a retrospective cohort study of children 0-17 years old admitted to a level 1 trauma center (Harborview Medical Center, Seattle, Wash., USA) between 2002 and 2007 with moderate-to-severe TBI who received a vasopressor to increase blood pressure. Baseline demographic and physiologic characteristics and hourly physiologic monitoring for 3 h after having started a vasopressor were abstracted. We evaluated differences in MAP and CPP at 3 h after initiation of therapy between phenylephrine, dopamine and norepinephrine among patients who did not require a second vasopressor during this time. Multivariate linear regression was used to adjust for age, gender, injury severity score and baseline MAP or CPP and to cluster by subject.

RESULTS

Eighty-two patients contributed data to the entire dataset. The most common initial medication was phenylephrine for 47 (57%). Patients receiving phenylephrine and norepinephrine tended to be older than those receiving dopamine and epinephrine. Thirteen (16%) of the patients received a second vasopressor during the first 3 h of treatment and were thus not included in the regression analyses; these patients received more fluid resuscitation and exhibited higher in-hospital mortality (77 vs. 32%; p = 0.004) compared to patients receiving a single vasopressor. The norepinephrine group exhibited a 5 mm Hg higher MAP (95% CI: -4 to 13; p = 0.31) and a 12 mm Hg higher CPP (95% CI: -2 to 26; p = 0.10) than the phenylephrine group, and a 5 mm Hg higher MAP (95% CI: -4 to 15; p = 0.27) and a 10 mm Hg higher CPP (95% CI: -5 to 25; p = 0.18) than the dopamine group. However, in post hoc analysis, after adjusting for time to start of vasopressor, hypertonic saline and pentobarbital, the effect on MAP was lost, but the CPP was 8 mm Hg higher (95% CI: -10 to 25; p = 0.39) than in the phenylephrine group, and 5 mm Hg higher (95% CI: -14 to 24; p = 0.59) than in the dopamine group.

CONCLUSIONS

Vasopressor use varied by age. While there was no statistically significant difference in MAP or CPP between vasopressor groups, norepinephrine was associated with a clinically relevant higher CPP and lower intracranial pressure at 3 h after start of vasopressor therapy compared to the other vasopressors examined.

Radial oxygen gradients over rat cortex arterioles

PURPOSE

We present the results of the visualisation of radial oxygen gradients in rats' cortices and their potential use in neurocritical management.

METHODS

PO₂ maps of the cortex of ten sedated, intubated and controlled ventilated Wistar rats were obtained with a camera (SensiMOD, PCO, Kelheim, Germany). Those pictures were analysed and edited by a custom-made software. A virtual matrix, designed to evaluate the cortical O₂ partial pressure, was placed vertically to the artery under investigation, and afterwards multiple regions of interest were measured (width 10 pixels, length 15-50 pixels). The results showed a map of the cerebral oxygenation, which allowed us to calculate radial oxygen gradients over arterioles. Three groups were defined according to the level of the arterial pO₂: PaO₂ < 80, PaO₂ 80-120 and PaO₂ > 120. Gradients were analysed from the middle of the vessel to its border (1), from the border into the parenchyma next to the vessel (2) and a combination of both (3).

RESULTS

Gradient 1 showed significantly different cortical pO₂ values between the three different groups. The mean pO₂ values were 2.62, 5.29 and 5.82 mmHg/mm. Gradient 2 measured 0.56, 0.90 and 1.02 mmHg/mm respectively. Gradient 3 showed significant results between the groups with values of 3.18, 6.19 and 6.84 mmHg/mm.

CONCLUSION

Using these gradients, it is possible to describe and compare the distribution of oxygen to the brain parenchyma. With the presented technique, it is possible to detect pO₂ changes in the oxygen supply of the brain cortex.

Brain tissue oxygen tension monitoring in pediatric severe traumatic brain injury. Part 1: Relationship with outcome

INTRODUCTION

Intracranial pressure (ICP) monitoring and cerebral perfusion pressure (CPP) management are the current standards to guide care of severe traumatic brain injury (TBI). However, brain hypoxia and secondary brain injury can occur despite optimal ICP and CPP. In this study, we used brain tissue oxygen tension (PbtO(2)) monitoring to examine the association between multiple patient factors, including PbtO(2), and outcome in pediatric severe TBI.

MATERIALS AND METHODS

In this prospective observational study, 52 children (less than 15 years) with severe TBI were managed with continuous PbtO(2) and ICP monitoring. The relationships between outcome [Glasgow Outcome Score (GOS) and Pediatric Cerebral Performance Category Scale] and clinical, radiologic, treatment, and physiological variables, including PbtO(2), were examined using multiple logistic regression analysis.

RESULTS

Outcome was favorable in 40 patients (77%) and unfavorable (mortality, 9.6%; n = 5) in 12 (23%). In univariate analysis, the following variables had a significant association with unfavorable outcome: initial GCS, computed tomography classification, ICP(peak), mICP(24), mICP, CPP(low), CPP(<40), pupil reactivity, PbtO(2)(low), PbtO(2) < 5 mmHg, PbtO(2) < 10 mmHg, mPbtO(2)(24), and time-severity product. PbtO(2) parameters had the strongest independent association with poor outcome in multiple regression analysis. In particular, when PbtO(2) was <5 mmHg for >1 h, the adjusted OR for poor outcome was 27.4 (95% confidence interval, 1.9-391). No variables apart from PbtO(2) were independently associated with mortality when controlled for PbtO(2).

CONCLUSION

Reduced PbtO(2) is shown to be an independent factor associated with poor outcome in pediatric severe TBI in the largest study to date. It appears to have a stronger association with outcome than conventionally evaluated measures.

Brain tissue oxygen tension monitoring in pediatric severe traumatic brain injury. Part 2: Relationship with clinical, physiological, and treatment factors

INTRODUCTION

Brain tissue oxygen tension (PbtO(2)) monitoring is used increasingly in adult severe traumatic brain injury (TBI) management. Several factors are known to influence PbtO(2) in adults, but the variables that affect PbtO(2) in pediatric TBI are not well described. This study examines the relationships between PbtO(2) and (1) physiological markers of potential secondary insults commonly used in pediatric TBI, in particular intracranial pressure (ICP), cerebral perfusion pressure (CPP), and systemic hypoxia, and (2) other clinical factors and treatment received that may influence PbtO(2).

MATERIALS AND METHODS

In this prospective observational study, 52 children (mean age, 6.5 +/- 3.4 years; range, 9 months to 14 years old) with severe TBI and a median post-resuscitation Glasgow Coma Score (GCS) of 5 were managed with continuous PbtO(2) monitoring. The relationships between PbtO(2) parameters (Pbt)(2)(low), PbtO(2) < 5, PbtO(2) < 10, and mPbtAO(2)(24)) and clinical, physiological, and treatment factors were explored using time-linked data and Spearman's correlation coefficients.

RESULTS

No clinical, physiological, or treatment variable was significantly associated with all PbtO(2) parameters, but individual associations were found with initial GCS (PbtO(2) < 5, p = 0.0113), admission Pediatric Trauma Score (PbtO(2) < 10, 0.0175), mICP > 20 (mPbtO(2)(24), p = 0.0377), CPP(low) (PbtO(2)(low), p = 0.0065), CPP < 40 (PbtO(2)(low), p = 0.0269; PbtO(2) < 5, p = 0.0212), P(a)O(2) < 60 (mPbtO(2)(24), p = 0.0037), S(a)O(2) < 90 (PbtO(2)(low), p = 0.0438), and use of inotropes during ICU care (PbtO(2)(low), p = 0.0276; PbtO(2) < 10, p = 0.0277; p = mPbtO(2)(24)).

CONCLUSION

Delivery of oxygen to the brain is important to limit secondary neuronal injury after severe TBI. Our data show that PbtO(2) is poorly predicted by clinical and physiological factors commonly measured in the pediatric ICU. Multimodality monitoring may be needed to detect all secondary cerebral insults in pediatric TBI.

RESUSCITATION AND CRITICAL CARE OF POOR-GRADE SUBARACHNOID HEMORRHAGE

AS OUTCOMES HAVE improved for patients with aneurysmal subarachnoid hemorrhage, most mortality and morbidity that occur today are the result of severe diffuse brain injury in poor-grade patients. The premise of this review is that aggressive emergency cardiopulmonary and neurological resuscitation, coupled with early aneurysm repair and advanced multimodality monitoring in a specialized neurocritical care unit, offers the best approach for achieving further improvements in subarachnoid hemorrhage outcomes. Emergency care should focus on control of elevated intracranial pressure, optimization of cerebral perfusion and oxygenation, and medical and surgical therapy to prevent rebleeding. In the postoperative period, advanced monitoring techniques such as continuous electroencephalography, brain tissue oxygen monitoring, and microdialysis can detect harmful secondary insults, and may eventually be used as end points for goal-directed therapy, with the aim of creating an optimal physiological environment for the comatose injured brain. As part of this paradigm shift, it is essential that aggressive surgical and medical support be linked to compassionate end-of-life care. As neurosurgeons become confident that comfort care can be implemented in a straightforward fashion after a failed trial of early maximal intervention, the usual justification for withholding treatment (survival with neurological devastation) becomes less relevant, and lives may be saved as more patients recover beyond expectations.

Blood Pressure Management in Acute Head Injury

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