Influence of norepinephrine and dopamine on cortical perfusion, EEG activity, extracellular glutamate, and brain edema in rats after controlled cortical impact 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.

A Novel Nomogram for Predicting Malignant Cerebral Edema After Endovascular Thrombectomy in Acute Ischemic Stroke: A Retrospective Cohort Study

BACKGROUND

Malignant cerebral edema (MCE) is a common and feared complication after endovascular thrombectomy (EVT) in acute ischemic stroke (AIS). This study aimed to establish a nomogram to predict MCE in anterior circulation large vessel occlusion stroke (LVOS) patients receiving EVT in order to guide the postoperative medical care in the acute phase.

METHODS

In this retrospective cohort study, 381 patients with anterior circulation LVOS receiving EVT were screened from 636 hospitalized patients with LVOS at 2 stroke medical centers. Clinical baseline data and imaging data were collected within 2-5 days of admission to the hospital. The patients were divided into 2 groups based on whether MCE occurred after EVT. Multivariate logistic regression analysis was used to evaluate the independent risk factors for MCE and to establish a nomogram.

RESULTS

Sixty-six patients out of 381 (17.32%) developed MCE. The independent risk factors for MCE included admission National Institutes of Health Stroke Scale (NIHSS) ≥16 (odds ratio [OR] 1.851; 95% CI 1.029-3.329; P = 0.038), ASPECT score (OR 0.621; 95% CI 0.519-0.744; P < 0.001), right hemisphere (OR 1.636; 95% CI 0.941-2.843; P = 0.079), collateral circulation (OR 0.155; 95% CI 0.074-0.324; P < 0.001), recanalization (OR 0.223; 95% CI 0.109-0.457; P < 0.001), hematocrit (OR, 0.937; 95% CI: 0.892-0.985; P =0.010), and glucose (OR 1.118; 95% CI 1.023-1.223; P = 0.036), which were adopted as parameters of the nomogram. The receiver operating characteristic curve analysis showed that the area under the curve of the nomogram in predicting MCE was 0.901(95% CI 0.848-0.940; P < 0.001). The Hosmer-Lemeshow test results were not significant (P = 0.685), demonstrating a good calibration of the nomogram.

CONCLUSIONS

The novel nomogram composed of admission NIHSS, ASPECT scores, right hemisphere, collateral circulation, recanalization, hematocrit, and serum glucose provide a potential predictor for MCE in patients with AIS after EVT.

Stroke Lateralization in Large Hemisphere Infarctions: Characteristics, Stroke-Related Complications, and Outcomes

Objectives: To assess the hemispheric differences in characteristics, stroke-related complications, and outcomes of patients with large hemisphere infarctions (LHI).

Methods: We enrolled consecutive patients admitted within 24 h after the diagnosis of LHI (defined as an ischemic stroke involving more than 50% of the territory of the middle cerebral artery in computed tomography and/or magnetic resonance imaging). Univariate and multivariate analysis were performed to explore the association between lateralization and stroke-related complications and clinical outcomes.

Results: A total of 314 patients with LHI were enrolled, with 171 (54.5%) having right hemispheric involvement. Right-sided patients with LHI had lower baseline National Institutes of Health Stroke Scale (NIHSS) score (18 vs. 22, p < 0.001), higher frequency of atrial fibrillation (69.0 vs. 52.4%, p = 0.003), and higher proportion of cardio-embolism (73.1 vs. 56.6%, p = 0.013) than the left. Right-sided LHI had higher incidence rates of malignant brain edema (MBE) (48.5 vs. 30.8%, p = 0.001) and a composite of cardiovascular events (29.8 vs. 17.5%, p = 0.011) during hospitalization. The incidence rate of 1-month mortality (34.5 vs. 23.8%, p = 0.036) was higher in right-sided patients with LHI, but there were no hemispheric differences in the incidence rates of 3-month mortality and unfavorable outcome (both p > 0.05). Multivariate analyses suggested right hemisphere involvement was independently associated with increased risk of MBE (adjusted OR 2.37, 95% CI 1.26–4.43, p = 0.007) and composite of cardiovascular events (adjusted OR 2.04, 95% CI 1.12–3.72, p = 0.020). However, it was not independently associated with 1-month death, 3-month mortality, and 3-month unfavorable outcome (all p > 0.05).

Conclusions: Right-sided patients with LHI had higher frequency of atrial fibrillation and cardio-embolism than the left-sided patients. Right hemisphere involvement was independently associated with increased risk of MBE and composite of cardiovascular events during hospitalization, whereas stroke lateralization was not an independent predictor of mortality and unfavorable outcome in patients with LHI.

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.

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.

Cerebral hemorrhage increases plasma concentrations of noradrenalin and creatine kinase MB fraction with induction of cardiomyocyte damage in rats

The incidence of cardiac damage is high during acute cerebral hemorrhage. The animal data on the relationship between cerebral apoplexy and cardiac damage are lacking. Thus, the aim of the study was to evaluate the effects of cerebral hemorrhage on plasma concentrations of monoamine transmitter noradrenalin (NA), creatine kinase muscle and brain (CK-MB) isoenzyme fraction, and cardiomyocyte changes in the rat model. In this study, 140 Wistar rats were randomly and equally divided into experimental and control groups, and collagenase was injected into the right caudate nucleus to induce cerebral hemorrhage in the experimental group. Plasma NA was analyzed using high-performance liquid chromatography with electrochemical detection and serum CK-MB was measured by enzyme reaction rate method. We found that both NA and CK-MB were elevated (p < 0.05) at 6 h after cerebral hematoma formation; the levels were 2.46 ± 0.05 μg/L and 3.51 ± 0.23 μkat/L, respectively. NA and CK-MB concentrations reached peak levels at 24 h which were found to be 3.52 ± 0.06 μg/L and 5.47 ± 0.49 μkat/L, respectively. Thereafter, NA and CK-MB concentrations decreased gradually. Plasma NA declined to the preoperative level (1.66 ± 0.03 μg/L) at 72 h, while CK-MB level (2.71 ± 0.17 μkat/L) was found to be still higher than its preoperative level. It was, therefore, concluded that plasma NA might be involved in the induction and development of cardiomyocytes damage during cerebral hemorrhage.

Hemispheric differences in malignant middle cerebral artery stroke

BACKGROUND

We recently reported that left versus right hemisphere cerebral infarctions patients more frequently have worse outcomes. However our clinical experience led us to suspect that the incidence of malignant middle cerebral artery infarctions (MMCA) was higher in the right compared to the left hemispheric strokes.

OBJECTIVE

To determine whether laterality in MMCA stroke is an important determinant of stroke sequelae.

METHODS

A systematic search was performed for publications in PubMed using "malignant middle cerebral artery and infarction". A total of 73 relevant studies were abstracted.

RESULTS

MMCA laterality data were available for 2673 patients, with 1687 (63%) right hemispheric involvement, thus right being more commonly associated with MMCA (binomial test, p<0.05). While mortality rates were similar, right hemispheric MMCA (n=271) had mortality of 31% (n=85) whereas left hemispheric MMCA (n=144) had mortality of 36% (n=53), morbidity rates were worse on the right.

CONCLUSION

MMCA stroke appears to be more common on the right, and this laterality is also associated with significantly higher morbidity. Further prospective studies are needed to more completely understand the nature of this laterality as well as test possible new treatments to reduce mortality and morbidity associated with MMCA.

Phase synchronization in electroencephalographic recordings prognosticates outcome in paediatric coma

Brain injury from trauma, cardiac arrest or stroke is the most important cause of death and acquired disability in the paediatric population. Due to the lifetime impact of brain injury, there is a need for methods to stratify patient risk and ultimately predict outcome. Early prognosis is fundamental to the implementation of interventions to improve recovery, but no clinical model as yet exists. Healthy physiology is associated with a relative high variability of physiologic signals in organ systems. This was first evaluated in heart rate variability research. Brain variability can be quantified through electroencephalographic (EEG) phase synchrony. We hypothesised that variability in brain signals from EEG recordings would correlate with patient outcome after brain injury. Lower variability in EEG phase synchronization, would be associated with poor patient prognosis. A retrospective study, spanning 10 years (2000-2010) analysed the scalp EEGs of children aged 1 month to 17 years in coma (Glasgow Coma Scale, GCS, <8) admitted to the paediatric critical care unit (PCCU) following brain injury from TBI, cardiac arrest or stroke. Phase synchrony of the EEGs was evaluated using the Hilbert transform and the variability of the phase synchrony calculated. Outcome was evaluated using the 6 point Paediatric Performance Category Score (PCPC) based on chart review at the time of hospital discharge. Outcome was dichotomized to good outcome (PCPC score 1 to 3) and poor outcome (PCPC score 4 to 6). Children who had a poor outcome following brain injury secondary to cardiac arrest, TBI or stroke, had a higher magnitude of synchrony (R index), a lower spatial complexity of the synchrony patterns and a lower temporal variability of the synchrony index values at 15 Hz when compared to those patients with a good outcome.

High-capacity peptide-centric platform to decode the proteomic response to brain injury

Traumatic brain injury (TBI) is a progressive disease process underlain by dynamic and interactive biochemical mechanisms; thus, large-scale and unbiased assessments are needed to fully understand its highly complex pathobiology. Here, we report on a new high-capacity label-free proteomic platform to evaluate the post-TBI neuroproteome. Six orthogonal separation stages and data-independent MS were employed, affording reproducible quantitative assessment on 18 651 peptides across biological replicates. From these data 3587 peptides were statistically responsive to TBI of which 18% were post-translationally modified. Results revealed as many as 484 proteins in the post-TBI neuroproteome, which was fully nine times the number determined from our prior study of focal cortical injury. Yet, these data were generated using 25 times less brain tissue per animal relative to former methodology, permitting greater anatomical specificity and proper biological replication for increased statistical power. Exemplified by these data, we discuss benefits of peptide-centric differential analysis to more accurately infer novel biological findings testable in future hypothesis-driven research. The high-capacity label-free proteomic platform is designed for multi-factor studies aimed at expanding our knowledge on the molecular underpinnings of TBI and to develop better diagnostics and therapeutics.

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.

Effects of lisuride hydrogen maleate on pericontusional tissue metabolism, brain edema formation, and contusion volume development after experimental traumatic brain injury in rats

After traumatic brain injury (TBI), the primary insult is followed by a cascade of secondary events which lead to enlargement of the primary lesion and are potentially amenable to therapeutic intervention. Lisuride is a dopaminergic agonist with additional serotoninergic, adrenergic, and glutamate antagonistic properties. In lack of previous data on lisuride in TBI, and based on well documented changes of dopamine metabolism after TBI, we speculated that lisuride could provide neuroprotection in the acute and post-acute stage of controlled cortical impact (CCI) injury in rats. The effect of varying dosages of lisuride on physiological parameter was investigated. Cerebral microdialysis (CMD) was employed to provide a temporal profile of lactate, pyruvate, glucose and glutamate in the pericontusional brain tissue. Additionally, brain edema formation and the development of contusion volume were assessed. In this study, no effect of treatment was seen on physiological parameters or microdialysis profiling of tissue metabolites. Whereas posttraumatic increase in brain water content and an increase in contusion volume could be observed, there was no significant effect of treatment. Taken together, our results suggest that lisuride does not provide neuroprotection in the CCI model at the acute and subacute stages. Based on the available literature, however, it might be possible that dopamine agonists such as lisuride, respectively, improve outcome in terms of cognitive function in a chronic setting.

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.

Contemporary pharmacologic issues in the management of traumatic brain injury

Traumatic brain injury (TBI) is a major cause of death and disability in the United States. While there are no pharmacotherapeutic options currently available for attenuating the neurologic injury cascade after TBI, numerous pharmacologic issues are encountered in these critically ill patients. Adequate fluid resuscitation, reversal of coagulopathy, maintenance of cerebral perfusion, and treatment of intracranial hypertension are common interventions early in the treatment of TBI. Other deleterious complications such as venous thromboembolism, extremes in glucose concentrations, and stress-related mucosal disease should be anticipated and avoided. Early provision of nutrition and prevention of drug or alcohol withdrawal are also cornerstones of routine care in TBI patients. Prevention of infections and seizures may also be helpful. Clinicians caring for TBI patients should be familiar with the pharmacologic issues typical of this vulnerable population in order to develop optimal strategies of care to anticipate and prevent common complications.

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.

Heterogeneous regional and temporal energetic impairment following controlled cortical impact injury in rats

OBJECTIVES

Following traumatic brain injury metabolic stability is impaired. Duration and reversibility of these changes might be important to guide specific interventions.

METHODS

To characterize temporal and regional changes in cerebral metabolism, 68 male Sprague-Dawley rats were subjected to a focal cortical contusion. Lesion progression and mitochondrial impairment were determined by magnetic resonance imaging (MRI) and triphenyl tetrazolium chloride (TTC) staining, respectively. Metabolic alterations were determined at hours 6 and 24 and day 7 by measuring extracellular glucose, lactate and hypoxanthine levels with microdialysis catheters placed adjacent and distant to the contusion and by quantifying changes in tissue ATP, lactate and glucose using bioluminescence imaging.

RESULTS

The cortical lesion reached its maximal extent at hour 24 and remained confined to the ipsilateral hemisphere. In microdialysate, at hour 6, extracellular hypoxanthine and lactate reached maximal values, thereafter hypoxanthine normalized while lactate remained increased. Extracellular glucose reached the highest values at hour 24 and remained elevated. Bioluminescence imaging revealed heterogeneous changes in areas distant to the contusion. No significant changes were found in ATP content. Slightly elevated tissue glucose until 24 hours in the ipsilateral hemisphere was observed. Following a continuous increase, lactate levels were the highest by 6 hours in the ipsilateral cortex and hippocampus.

DISCUSSION

CCI is associated with disturbances in energetic metabolism. Metabolic perturbation is not restricted to the early phase and the contusional region following focal cortical contusion, but also involves hippocampus and primarily uninjured parts of the hemisphere.

Acute, transient hemorrhagic hypotension does not aggravate structural damage or neurologic motor deficits but delays the long-term cognitive recovery following mild to moderate traumatic brain injury

OBJECTIVES

Posttraumatic hypotension is believed to increase morbidity and mortality in traumatically brain-injured patients. Using a clinically relevant model of combined traumatic brain injury with superimposed hemorrhagic hypotension in rats, the present study evaluated whether a reduction in mean arterial blood pressure aggravates regional brain edema formation, regional cell death, and neurologic motor/cognitive deficits associated with traumatic brain injury.

DESIGN

Experimental prospective, randomized study in rodents.

SETTING

Experimental laboratory at a university hospital.

SUBJECTS

One hundred nineteen male Sprague-Dawley rats weighing 350-385 g.

INTERVENTIONS

Experimental traumatic brain injury of mild to moderate severity was induced using the lateral fluid percussion brain injury model in anesthetized rats (n = 89). Following traumatic brain injury, in surviving animals one group of animals was subjected to pressure-controlled hemorrhagic hypotension, maintaining the mean arterial blood pressure at 50-60 mm Hg for 30 mins (n = 47). The animals were subsequently either resuscitated with lactated Ringer's solution (three times shed blood volume, n = 18) or left uncompensated (n = 29). Other groups of animals included those with isolated traumatic brain injury (n = 34), those with isolated hemorrhagic hypotension (n = 8), and sham-injured control animals receiving anesthesia and surgery alone (n = 22).

MEASUREMENTS AND MAIN RESULTS

The withdrawal of 6-7 mL of arterial blood significantly reduced mean arterial blood pressure by 50% without decreasing arterial oxygen saturation or Pao2. Brain injury induced significant cerebral edema (p < .001) in vulnerable brain regions and cortical tissue loss (p < .01) compared with sham-injured animals. Neither regional brain edema formation at 24 hrs postinjury nor the extent of cortical tissue loss assessed at 7 days postinjury was significantly aggravated by superimposed hemorrhagic hypotension. Brain injury-induced neurologic deficits persisted up to 20 wks after injury and were also not aggravated by the hemorrhagic hypotension. Cognitive dysfunction persisted for up to 16 wks postinjury. The superimposition of hemorrhagic hypotension significantly delayed the time course of cognitive recovery.

CONCLUSIONS

A single, acute hypotensive event lasting 30 mins did not aggravate the short- and long-term structural and motor deficits but delayed the speed of recovery of cognitive function associated with experimental traumatic brain injury.

Characterization of the effects of adenosine receptor agonists on cerebral blood flow in uninjured and traumatically injured rat brain using continuous arterial spin-labeled magnetic resonance imaging

Hypoperfusion after traumatic brain injury may exacerbate damage. Adenosine, a vasodilator, regulates cerebral blood flow (CBF). Treatment with adenosine receptor agonists has shown benefit in experimental CNS trauma; however, their effects on CBF after injury remain undefined. We used magnetic resonance imaging to assess CBF in uninjured rats both early and at 24 h after intrahippocampal administration of either the nonselective adenosine receptor agonist 2-chloroadenosine (2-CA, 12 nmol) or the A(2A)-receptor agonist 2-p-(2-carboxyethyl)-phenethylamino-5'-N-ethylcarbox-amidoadenosine (CGS 21680, 6 nmol). We also assessed the effects of these agents on cerebral metabolic rate for glucose (CMRglu). We then assessed the effect of 2-CA on CBF at 3.5 to 5 h after controlled cortical impact (CCI). Injection of 2-CA into uninjured rat brain produced marked increases in CBF in ipsilateral hippocampus and cortex versus vehicle (P<0.05); CBF increases persisted even at 24 h. Measurement of hippocampal levels of 2-CA showed persistent increases to 24 h. CGS 21680 produced even more marked global increases in CBF than seen with 2-CA (2-6-fold versus vehicle, P<0.05 in 10/12 regions of interest (ROIs)). Neither agonist altered CMRglu versus vehicle. After CCI, 2-CA increased CBF in ipsilateral hippocampal and hemispheric ROIs (P<0.05 versus vehicle), but the response was attenuated at severe injury levels. We report marked increases in CBF after injection of adenosine receptor agonists into uninjured rat brain despite unaltered CMRglu. 2-Chloroadenosine produced enduring increases in CBF in uninjured brain and attenuated posttraumatic hypoperfusion. Future studies of adenosine-related therapies in CNS injury should address the role of CBF.

Small volume resuscitation with HyperHaes improves pericontusional perfusion and reduces lesion volume following controlled cortical impact injury in rats

The hyperosmolar and hyperoncotic properties of HyperHaes (HHES) might improve impaired posttraumatic cerebral perfusion. Possible beneficial effects on pericontusional perfusion, brain edema, and contusion volume were investigated in rats subjected to controlled cortical impact (CCI). Male Sprague-Dawley rats (n = 60) anesthetized with isoflurane were subjected to a left temporoparietal CCI. Thereafter, rats were randomized to receive HHES (10% hydroxyethylstarch, 7.5% NaCl) or physiological saline solution (4 mL/kg body weight) intravenously. Mean arterial blood pressure (MABP) and intracranial pressure (ICP) were determined before and following CCI, after drug administration and 24 h later. Regional pericontusional cortical perfusion was determined by scanning laser Doppler flowmetry before CCI, and 30 min, 4 and 24 h after injury. At 24 h brain swelling and water content were measured gravimetrically. At 7 days, cortical contusion volume was determined planimetrically. MABP was not influenced by HHES. ICP was significantly decreased immediately after HHES infusion (5.7 +/- 0.4 vs. 7.1 +/- 1.0 mm Hg; p < 0.05). Pericontusional cortical perfusion was significantly decreased by 44% compared to pre-injury levels (p < 0.05). HHES significantly improved cortical perfusion at 4 h after CCI, approaching baseline values (85 +/- 12%). While increased posttraumatic brain edema was not reduced by HHES at 24 h, cortical contusion volume was significantly decreased in the HHES-treated rats at 7 days after CCI (23.4 +/- 3.5 vs. 39.6 +/- 6.2 mm3; p < 0.05). Intravaneous administration of HHES within 15 min after CCI has a neuroprotective potential, as it significantly attenuated impaired pericontusional perfusion and markedly reduced the extent of induced structural damage.

Does induced hypertension reduce cerebral ischaemia within the traumatized human brain?

Recent changes in published guidelines for the management of patients with severe head injury are based on data showing that aggressive maintenance of cerebral perfusion pressure (CPP) can worsen outcome due to extracranial complications of therapy. However, it remains unclear whether CPP augmentation could reduce cerebral ischaemia, a finding which might prompt the search for CPP augmentation protocols that avoid these extracranial complications. We studied 10 healthy volunteers and 20 patients within 6 days of closed head injury. All subjects underwent imaging of cerebral blood flow (CBF), blood volume (CBV), oxygen metabolism (CMRO2) and oxygen extraction fraction (OEF) using 15O PET. In addition, for patients, the EEG power ratio index (PRI), burst suppression ratio and somatosensory evoked potentials (SEP) were obtained and CPP was increased from 68 +/- 4 to 90 +/- 4 mmHg using an infusion of norepinephrine and measurements were repeated. Following elevation of CPP, CBF and CBV were increased and CMRO2 and OEF were reduced (P < 0.001 for all comparisons). Regions with a reduction in CMRO2 were associated with the greatest reduction in OEF (r2 = 0.3; P < 0.0001). Although CPP elevation produced a significant fall in the ischaemic brain volume (IBV) (from 15 +/- 16 to 5 +/- 4 ml; P < 0.01) and improved flow metabolism coupling, the IBV was small and clinically insignificant in the majority of these patients. However, the reduction in IBV was directly related to the baseline IBV (r2 = 0.97; P < 0.001) and patients with large baseline IBV showed substantial and clinically significant reductions. CPP augmentation increased the EEG PRI (5.0 +/- 1.5 versus 4.3 +/- 1.4, P < 0.01), implying an overall decrease in neural activity, but these changes did not correlate with the reduction in CMRO2 and there was no change in SEP cortical amplitude (N20-P27). These data provide support for recent changes in recommended CPP levels for head injury management across populations of patients with significant head injury. However, they do not provide guidance on whether the intervention may be more appropriate at earlier stages after injury, or in patients selected because of high baseline IBV. It also remains unclear whether CPP values below 65 mmHg can be safely used in this population. Clarification of the significance of a reduction in CMRO2 and neuronal electrical function will require further study.

Direct comparison of cerebrovascular effects of norepinephrine and dopamine in head-injured patients

OBJECTIVE

To directly compare the cerebrovascular effects of norepinephrine and dopamine in patients with acute traumatic brain injury.

DESIGN

Prospective randomized crossover trial.

SETTING

Neurosciences critical care unit of a university hospital.

PATIENTS

Ten acutely head-injured patients requiring vasoactive drugs to maintain a cerebral perfusion pressure of 65 mm Hg.

INTERVENTIONS

Patients were randomized to start the protocol with either norepinephrine or dopamine. Using an infusion of the allocated drug, cerebral perfusion pressure was adjusted to 65 mm Hg. After 20 mins of data collection, cerebral perfusion pressure was increased to 75 mm Hg by increasing the infusion rate of the vasoactive agent. After 20 mins of data collection, cerebral perfusion pressure was increased to 85 mm Hg and again data were collected for 20 mins. Subsequently, the infusion rate of the vasoactive drug was reduced until a cerebral perfusion pressure of 65 mm Hg was reached and the drug was exchanged against the other agent. The protocol was then repeated.

MEASUREMENTS AND MAIN RESULTS

Mean arterial pressure and intracranial pressure were monitored and cerebral blood flow was estimated with transcranial Doppler. Norepinephrine led to predictable and significant increases in flow velocity for each step increase in cerebral perfusion pressure (57.5+/-19.9 cm x sec, 61.3+/-22.3 cm x sec, and 68.4+/-24.8 cm x sec at 65, 75, and 85 mm Hg, respectively; p <.05 for all three comparisons), but changes with dopamine were variable and inconsistent. There were no differences between absolute values of flow velocity or intracranial pressure between the two drugs at any cerebral perfusion pressure level.

CONCLUSIONS

Norepinephrine may be more predictable and efficient to augment cerebral perfusion in patients with traumatic brain injury.

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

OBJECTIVE

To compare the effects of a cerebral perfusion pressure (CPP) intervention achieved with dopamine and norepinephrine after severe head injury.

DESIGN

Prospective, controlled, trial.

SETTING

Neurosciences critical care unit.

PATIENTS

Eleven patients with a head injury, requiring dopamine or norepinephrine infusions to support CPP.

INTERVENTION

Cerebral tissue gas measurements were recorded using a multimodal sensor, and regional chemistry was assessed using microdialysis. Patients received in, randomised order, either dopamine or norepinephrine to achieve and maintain a CPP of 65 mmHg, and then, following a 30-min period of stable haemodynamics, a CPP of 85 mmHg. Data were then acquired using the second agent. Haemodynamic measurements and measurements of cerebral physiology were made during each period.

MEASUREMENTS AND RESULTS

The CPP augmentation with norepinephrine, but not with dopamine, resulted in a significant reduction in arterial-venous oxygen difference (37+/-11 vs 33+/-12 ml/l) and a significant increase in brain tissue oxygen (2.6+/-1.1 vs 3.0+/-1.1 kPa). The CPP intervention did not significantly affect intracranial pressure. There were no significant differences between norepinephrine and dopamine on cerebral oxygenation or metabolism either at baseline or following a CPP intervention; however, the response to a CPP intervention with dopamine seemed to be more variable than the response achieved with norepinephrine.

CONCLUSIONS

If CPP is to be raised to a level higher than 65-70 mmHg, then it is important to recognise that the response to the intervention may be unpredictable and that the vasoactive agent used may be of importance.

Edema and brain trauma

Brain edema leading to an expansion of brain volume has a crucial impact on morbidity and mortality following traumatic brain injury (TBI) as it increases intracranial pressure, impairs cerebral perfusion and oxygenation, and contributes to additional ischemic injuries. Classically, two major types of traumatic brain edema exist: "vasogenic" due to blood-brain barrier (BBB) disruption resulting in extracellular water accumulation and "cytotoxic/cellular" due to sustained intracellular water collection. A third type, "osmotic" brain edema is caused by osmotic imbalances between blood and tissue. Rarely after TBI do we encounter a "hydrocephalic edema/interstitial" brain edema related to an obstruction of cerebrospinal fluid outflow. Following TBI, various mediators are released which enhance vasogenic and/or cytotoxic brain edema. These include glutamate, lactate, H(+), K(+), Ca(2+), nitric oxide, arachidonic acid and its metabolites, free oxygen radicals, histamine, and kinins. Thus, avoiding cerebral anaerobic metabolism and acidosis is beneficial to control lactate and H(+), but no compound inhibiting mediators/mediator channels showed beneficial results in conducted clinical trials, despite successful experimental studies. Hence, anti-edematous therapy in TBI patients is still symptomatic and rather non-specific (e.g. mannitol infusion, controlled hyperventilation). For many years, vasogenic brain edema was accepted as the prevalent edema type following TBI. The development of mechanical TBI models ("weight drop," "fluid percussion injury," and "controlled cortical impact injury") and the use of magnetic resonance imaging, however, revealed that "cytotoxic" edema is of decisive pathophysiological importance following TBI as it develops early and persists while BBB integrity is gradually restored. These findings suggest that cytotoxic and vasogenic brain edema are two entities which can be targeted simultaneously or according to their temporal prevalence.

Differential Concentration-Dependent Effects of Prolonged Norepinephrine Infusion on Intraparenchymal Hemorrhage and Cortical Contusion in Brain-Injured Rats

Under clinical conditions catecholamines are infused to elevate cerebral perfusion pressure and improve impaired posttraumatic cerebral microcirculation. This, however, is associated with the risk of additional hemorrhage in the acute phase following traumatic brain injury. In the present study we investigated the dose-dependent effects of prolonged norepinephrine infusion on arterial blood pressure, blood glucose, and structural damage in brain-injured rats. At 4 h following induction of a focal cortical contusion (CCI), 40 rats were randomized to receive low (0.15), medium (0.3), or high dose (1 microg/kg/min) norepinephrine. Control rats were given equal volume of NaCl. Norepinephrine and NaCl were infused intravenously via Alzet osmotic pumps for 44 h. Mean arterial blood pressure (MABP), blood gases and blood glucose were determined before, at 4, 24, 48 h after CCI in repeatedly anesthetized rats (n = 28). Systolic arterial blood pressure (SABP) was measured using the tail cuff method in awake, restrained rats (n = 12). Cortical contusion and intraparenchymal hemorrhage volume were quantified at 48 h in all rats. MABP determined in anesthetized rats was only marginally increased. SABP was significantly elevated during infusion of medium and high dose norepinephrine in awake rats, exceeding 140 mm Hg. Medium and high dose norepinephrine significantly increased cortical hemorrhage by 157% and 142%, without increasing the cortical contusion volume. Low dose norepinephrine significantly reduced the cortical contusion by 44%. Norepinephrine aggravates the underlying brain damage during the acute posttraumatic phase. Future studies are needed to determine the least deleterious norepinephrine concentration.

Effects of early and late intravenous norepinephrine infusion on cerebral perfusion, microcirculation, brain-tissue oxygenation, and edema formation in brain-injured rats

OBJECTIVES

Reduction of cerebral perfusion during the early phase after traumatic brain injury is followed by a later phase of normal to increased perfusion. Thus, pharmacologically elevating mean arterial blood pressure with the aim of improving cerebral perfusion may exert different time-dependent effects on cortical perfusion, microcirculation, tissue oxygenation and brain edema formation after traumatic brain injury.

DESIGN

Randomized, placebo-controlled trial.

SETTING

Experimental laboratory at a university hospital.

SUBJECTS

A total of 37 male Sprague-Dawley rats subjected to a focal cortical contusion.

INTERVENTIONS

At 4 or 24 hrs after focal traumatic brain injury, mean arterial blood pressure was increased to 120 mm Hg for 90 mins by infusing norepinephrine. In rats receiving physiologic saline, mean arterial blood pressure remained unchanged. In the first series, pericontusional cortical perfusion was measured using the laser Doppler flowmetry scanning technique before injury and before, during, and after the infusion period. In a second series, intracranial and cerebral perfusion pressure and intraparenchymal perfusion and tissue oxygen measured within the contused and pericontusional cortex were recorded continuously before, during, and after norepinephrine infusion. Changes in cortical microcirculation were investigated by orthogonal polarization spectral imaging. At the end of each experiment, hemispheric swelling and water content were determined gravimetrically.

MEASUREMENTS AND MAIN RESULTS

At 4 and 24 hrs after traumatic brain injury, intravenous norepinephrine significantly increased pericontusional cortical perfusion, which was also reflected by an increase in diameters and flow velocities of pericontusional arterioles and venules. Cerebral perfusion pressure and intraparenchymal perfusion and tissue oxygen were significantly increased during norepinephrine infusion at 4 and 24 hrs. Hemispheric swelling and water content showed no difference between the groups.

CONCLUSIONS

After cortical impact injury, early and late intravenous norepinephrine infusion pressure-dependently increased cerebral perfusion and tissue oxygenation without aggravating or reducing brain edema formation. Future studies are warranted to determine long-term changes of short and prolonged norepinephrine-induced increases in mean arterial blood pressure and cerebral perfusion pressure.