Delayed hemorrhagic hypotension exacerbates the hemodynamic and histopathologic consequences of traumatic brain injury in rats

Head Kinematics, Blood Biomarkers, and Histology in Large Animal Models of Traumatic Brain Injury and Hemorrhagic Shock

Traumatic brain injury (TBI) and severe blood loss resulting in hemorrhagic shock (HS) are each leading causes of mortality and morbidity worldwide, and present additional treatment considerations when they are comorbid (TBI+HS) as a result of competing pathophysiological responses. The current study rigorously quantified injury biomechanics with high precision sensors and examined whether blood-based surrogate markers were altered in general trauma as well as post-neurotrauma. Eighty-nine sexually mature male and female Yucatan swine were subjected to a closed-head TBI+HS (40% of circulating blood volume; n = 68), HS only (n = 9), or sham trauma (n = 12). Markers of systemic (e.g., glucose, lactate) and neural functioning were obtained at baseline, and at 35 and 295 min post-trauma. Opposite and approximately twofold differences existed for both magnitude (device > head) and duration (head > device) of quantified injury biomechanics. Circulating levels of neurofilament light chain (NfL), glial fibrillary acidic protein (GFAP), and ubiquitin C-terminal hydrolase L1 (UCH-L1) demonstrated differential sensitivity for both general trauma (HS) and neurotrauma (TBI+HS) relative to shams in a temporally dynamic fashion. GFAP and NfL were both strongly associated with changes in systemic markers during general trauma and exhibited consistent time-dependent changes in individual sham animals. Finally, circulating GFAP was associated with histopathological markers of diffuse axonal injury and blood-brain barrier breach, as well as variations in device kinematics following TBI+HS. Current findings therefore highlight the need to directly quantify injury biomechanics with head mounted sensors and suggest that GFAP, NfL, and UCH-L1 are sensitive to multiple forms of trauma rather than having a single pathological indication (e.g., GFAP = astrogliosis).

Immunopathological Alterations after Blast Injury and Hemorrhage in a Swine Model of Prolonged Damage Control Resuscitation

Trauma-related hemorrhagic shock (HS) remains a leading cause of death among military and civilian trauma patients. We have previously shown that administration of complement and HMGB1 inhibitors attenuate morbidity and mortality 24 h after injury in a rat model of blast injury (BI) and HS. To further validate these results, this study aimed to develop a swine model and evaluate BI+HS-induced pathophysiology. Anesthetized Yucatan minipigs underwent combined BI and volume-controlled hemorrhage. After 30 min of shock, animals received an intravenous bolus of PlasmaLyte A and a continuous PlasmaLyte A infusion. The survival rate was 80% (4/5), and the non-survivor expired 72 min post-BI. Circulating organ-functional biomarkers, inflammatory biomarkers, histopathological evaluation, and CT scans indicated evidence of multiple-organ damage, systemic innate immunological activation, and local tissue inflammation in the injured animals. Interestingly, a rapid and dramatic increase in plasma levels of HMGB1 and C3a and markedly early myocarditis and encephalitis were associated with early death post-BI+HS. This study suggests that this model reflects the immunopathological alterations of polytrauma in humans during shock and prolonged damage control resuscitation. This experimental protocol could be helpful in the assessment of immunological damage control resuscitation approaches during the prolonged care of warfighters.

17α-Ethinyl estradiol-3-sulfate increases survival and hemodynamic functioning in a large animal model of combined traumatic brain injury and hemorrhagic shock: a randomized control trial

Background

Traumatic brain injury (TBI) and severe blood loss resulting in hemorrhagic shock (HS) represent leading causes of trauma-induced mortality, especially when co-occurring in pre-hospital settings where standard therapies are not readily available. The primary objective of this study was to determine if 17α-ethinyl estradiol-3-sulfate (EE-3-SO4) increases survival, promotes more rapid cardiovascular recovery, or confers neuroprotection relative to Placebo following TBI + HS.

Methods

All methods were approved by required regulatory agencies prior to study initiation. In this fully randomized, blinded preclinical study, eighty (50% females) sexually mature (190.64 ± 21.04 days old; 28.18 ± 2.72 kg) Yucatan swine were used. Sixty-eight animals received a closed-head, accelerative TBI followed by removal of approximately 40% of circulating blood volume. Animals were then intravenously administered EE-3-SO4 formulated in the vehicle at 5.0 mg/mL (dosed at 0.2 mL/kg) or Placebo (0.45% sodium chloride solution) via a continuous pump (0.2 mL/kg over 5 min). Twelve swine were included as uninjured Shams to further characterize model pathology and replicate previous findings. All animals were monitored for up to 5 h in the absence of any other life-saving measures (e.g., mechanical ventilation, fluid resuscitation).

Results

A comparison of Placebo-treated relative to Sham animals indicated evidence of acidosis, decreased arterial pressure, increased heart rate, diffuse axonal injury and blood–brain barrier breach. The percentage of animals surviving to 295 min post-injury was significantly higher for the EE-3-SO4 (28/31; 90.3%) relative to Placebo (24/33; 72.7%) cohort. EE-3-SO4 also restored pulse pressure more rapidly post-drug administration, but did not confer any benefits in terms of shock index. Primary blood-based measurements of neuroinflammation and blood brain breach were also null, whereas secondary measurements of diffuse axonal injury suggested a more rapid return to baseline for the EE-3-SO4 group. Survival status was associated with biological sex (female > male), as well as evidence of increased acidosis and neurotrauma independent of EE-3-SO4 or Placebo administration.

Conclusions

EE-3-SO4 is efficacious in promoting survival and more rapidly restoring cardiovascular homeostasis following polytraumatic injuries in pre-hospital environments (rural and military) in the absence of standard therapies. Poly-therapeutic approaches targeting additional mechanisms (increased hemostasis, oxygen-carrying capacity, etc.) should be considered in future studies.

Survival Rates and Biomarkers in a Large Animal Model of Traumatic Brain Injury Combined With Two Different Levels of Blood Loss

INTRODUCTION

The pathology resulting from concurrent traumatic brain injury (TBI) and hemorrhagic shock (HS; TBI+HS) are leading causes of mortality and morbidity worldwide following trauma. However, the majority of large animal models of TBI+HS have utilized focal/contusional injuries rather than incorporating the types of brain trauma (closed-head injury caused by dynamic acceleration) that typify human injury.

OBJECTIVE

To examine survival rates and effects on biomarkers from rotational TBI with two levels of HS.

METHODS

Twenty-two sexually mature Yucatan swine (30.39 ± 2.25 kg; 11 females) therefore underwent either Sham trauma procedures (n = 6) or a dynamic acceleration TBI combined with either 55% (n = 8) or 40% (n = 8) blood loss in this serial study.

RESULTS

Survival rates were significantly higher for the TBI+40% (87.5%) relative to TBI+55% (12.5%) cohort, with the majority of TBI+55% animals expiring within 2 h post-trauma from apnea. Blood-based neural biomarkers and immunohistochemistry indicated evidence of diffuse axonal injury (increased NFL/Aβ42), blood-brain barrier breach (increased immunoglobulin G) and inflammation (increased glial fibrillary acidic protein/ionized calcium-binding adaptor molecule 1) in the injured cohorts relative to Shams. Invasive hemodynamic measurements indicated increased shock index and decreased pulse pressure in both injury cohorts, with evidence of partial recovery for invasive hemodynamic measurements in the TBI+40% cohort. Similarly, although both injury groups demonstrated ionic and blood gas abnormalities immediately postinjury, metabolic acidosis continued to increase in the TBI+55% group ∼85 min postinjury. Somewhat surprisingly, both neural and physiological biomarkers showed significant changes within the Sham cohort across the multi-hour experimental procedure, most likely associated with prolonged anesthesia.

CONCLUSION

Current results suggest the TBI+55% model may be more appropriate for severe trauma requiring immediate medical attention/standard fluid resuscitation protocols whereas the TBI+40% model may be useful for studies of prolonged field care.

A systematic review of large animal models of combined traumatic brain injury and hemorrhagic shock

Traumatic brain injury (TBI) and severe blood loss (SBL) frequently co-occur in human trauma, resulting in high levels of mortality and morbidity. Importantly, each of the individual post-injury cascades is characterized by complex and potentially opposing pathophysiological responses, complicating optimal resuscitation and therapeutic approaches. Large animal models of poly-neurotrauma closely mimic human physiology, but a systematic literature review of published models has been lacking. The current review suggests a relative paucity of large animal poly-neurotrauma studies (N = 52), with meta-statistics revealing trends for animal species (exclusively swine), characteristics (use of single biological sex, use of juveniles) and TBI models. Although most studies have targeted blood loss volumes of 35-45%, the associated mortality rates are much lower relative to Class III/IV human trauma. This discrepancy may result from potentially mitigating experimental factors (e.g., mechanical ventilation prior to or during injury, pausing/resuming blood loss based on physiological parameters, administration of small volume fluid resuscitation) that are rarely associated with human trauma, highlighting the need for additional work in this area.

Treatment of combined traumatic brain injury and hemorrhagic shock with fractionated blood products versus fresh whole blood in a rat model

INTRODUCTION

Treatment of combined traumatic brain injury and hemorrhagic shock, poses a particular challenge due to the possible conflicting consequences. While restoring diminished volume is the treatment goal for hypovolemia, maintaining adequate cerebral perfusion pressure and avoidance of secondary damage remains a treatment goal for the injured brain. Various treatment modalities have been proposed, but the optimal resuscitation fluid and goals have not yet been clearly defined. A growing body of evidence suggests that in hypovolemic shock, resuscitation with fresh whole blood (FWB) may be superior to component therapy without platelets (which are likely to be unavailable in the pre-hospital setting). Nevertheless, the effects of this approach have not been studied in the combined injury. Previously, in a rat model of combined injury we have found that mild resuscitation to MABP of 80 mmHg with FWB is superior to fluid resuscitation or aggressive resuscitation with FWB. In this study, we investigate the physiological and neurological outcomes in a rat model of combined traumatic brain injury (TBI) and hypovolemic shock, submitted to treatment with varying amounts of FWB, compared to similar resuscitation goals with fractionated blood products-red blood cells (RBCs) and plasma in a 1:1 ratio regimen.

MATERIALS AND METHODS

40 male Lewis rats were divided into control and treatment groups. TBI was inflicted by a free-falling rod on the exposed cranium. Hypovolemia was induced by controlled hemorrhage of 30% blood volume. Treatment groups were treated either with fresh whole blood or with RBC + plasma in a 1:1 ratio, achieving a resuscitation goal of a mean arterial blood pressure (MAP) of 80 mmHg at 15 min. MAP was assessed at 60 min, and neurological outcomes and mortality in the subsequent 24 h.

RESULTS

At 60 min, hemodynamic parameters were improved compared to controls, but not significantly different between treatment groups. Survival rates at 48 h were 100% for both of the mildly resuscitated groups (MABP 80 mmHg) with FWB and RBC + plasma. The best neurological outcomes were found in the group mildly resuscitated with FWB and were better when compared to resuscitation with RBC + plasma to the same MABP goal (FWB: Neurological Severity Score (NSS) 6 ± 2, RBC + plasma: NSS 10 ± 2, p = 0.02).

CONCLUSIONS

In this study, we find that mild resuscitation with goals of restoring MAP to 80 mmHg (which is lower than baseline) with FWB, provided better hemodynamic stability and survival. However, the best neurological outcomes were found in the group resuscitated with FWB. Thus, we suggest that resuscitation with FWB is a feasible modality in the combined TBI + hypovolemic shock scenario, and may result in improved outcomes compared to platelet-free component blood products.

Erythropoietin in patients with traumatic brain injury and extracranial injury-A post hoc analysis of the erythropoietin traumatic brain injury trial

BACKGROUND

Erythropoietin (EPO) may reduce mortality after traumatic brain injury (TBI). Secondary brain injury is exacerbated by multiple trauma, and possibly modifiable by EPO. We hypothesized that EPO decreases mortality more in TBI patients with multiple trauma, than in patients with TBI alone.

METHODS

A post hoc analysis of the EPO-TBI randomized controlled trial conducted in 2009 to 2014. To evaluate the impact of injuries outside the brain, we calculated an extracranial Injury Severity Score (ISS) that included the same components of the ISS, excluding head and face components. We defined multiple trauma as two injured body regions with an Abbreviated Injury Scale (AIS) score of 3 or higher. Cox regression analyses, allowing for potential differential responses per the presence or absence of extracranial injury defined by these injury scores, were used to assess the effect of EPO on time to mortality.

RESULTS

Of 603 included patients, the median extracranial ISS was 6 (interquartile range, 1-13) and 258 (43%) had an AIS score of 3 or higher in at least two body regions. On Cox regression, EPO was associated with decreased mortality in patients with greater extracranial ISS (interaction p = 0.048) and weakly associated with differential mortality with multiple trauma (AIS score > 3 or in two regions, interaction p = 0.17). At 6 months in patients with extracranial ISS higher than 6, 10 (6.8%) of 147 EPO-treated patients compared with 26 (17%) of 154 placebo-treated patients died (risk reduction, 10%; 95% confidence interval, 2.9-17%; p = 0.007).

CONCLUSION

In this post hoc analysis, EPO administration was associated with a potential differential improvement in 6-month mortality in TBI patients with more severe extracranial injury. These findings need confirmation in future clinical and experimental studies.

LEVEL OF EVIDENCE

Therapeutic study, level III.

Traumatic Brain Injury and Polytrauma in Theaters of Combat: The Case for Neurotrauma Resuscitation?

Polytrauma associated with traumatic brain injury (TBI) is defined as a concurrent injury to the brain and one or more body areas or organ systems that results in physical, cognitive, and psychosocial impairments. Consequently, polytrauma accompanied by TBI presents a unique challenge for emergency medicine, in particular, to those associated with the austere environments encountered in military theaters of operation and the logistics of en-route care. Here, we attempt to put needed focus on this medical emergency, specifically addressing the problem of an exsanguinating polytrauma requiring fluid resuscitation complicated by TBI. Critical questions to consider are the following: (1) What is the optimal resuscitation fluid for these patients? (2) In defining the resuscitation fluid, what considerations must be given with regard to the very specific logistics of military operations? and (3) Can treatment of the brain injury be initiated in parallel with resuscitation practices. Recognizing the immense clinical and experimental complexity of this problem, our goal was to encourage research that embraces with high-fidelity 'combined' animal models of polytrauma and TBI with an objective toward elucidating safe and effective neurotherapeutic resuscitation protocols.

Combined hypoxemic and hypotensive insults altered physiological responses and neurofunction in a severity-dependent manner following penetrating ballistic-like brain injury in rats

BACKGROUND

Traumatic brain injury often occurs with concomitant hypoxemia (HX) and hemorrhagic shock (HS), leading to poor outcomes. This study characterized the acute physiology and subacute behavioral consequences of these additional insults in a model of penetrating ballistic-like brain injury (PBBI).

METHODS

Rats were randomly assigned into sham control, HX + HS (HH), 5% PBBI alone, 5% PBBI + HH, 10% PBBI alone, and 10% PBBI + HH groups. Mean arterial pressure, heart rate, and breathing rate were monitored continuously. In the combined injury groups, animals were subjected to 30-minute HX (Pao2, 30-40 mm Hg) and then 30-min HS (mean arterial pressure, 40 mm Hg) followed by fluid resuscitation with lactated Ringer's solution after PBBI or sham PBBI. Motor function was assessed using the rotarod task at 7 days and 14 days after injury. Cognitive function was assessed in the Morris water maze task from 13 days to 17 days after injury.

RESULTS

Combined HH caused acute bradycardia that was reversed by fluid resuscitation. During HX phase, tachypnea was observed in all HH groups. Persistent bradypnea was detected in 10% PBBI + HH group during the resuscitation phase. PBBI produced significant decrements in motor performance (vs. sham and HH groups). Additional insults significantly worsened motor deficits following 5% PBBI but not 10% PBBI. Both 5% PBBI and 10% PBBI produced significant cognitive deficits in the Morris water maze task with worsened deficits evident following the more severe injury (i.e., 10% PBBI). Alternatively, rats subjected to 5% PBBI + HH exhibited cognitive impairment that was significantly worse compared with 5% PBBI alone, whereas this worsening effect was not detected in the 10% PBBI groups.

CONCLUSION

This study characterized the physiological responses and neurobehavioral profiles following combined PBBI and HH. Ten percent PBBI produces motor and cognitive deficits, which may exceed a sensitivity threshold capacity. In contrast, 5% PBBI produces a lower, albeit significant, magnitude of deficits and thus provides a more sensitive screen for evaluating the cumulative effects of additional insults, which were indeed demonstrated to significantly worsen outcome.

Combined Neurotrauma Models: Experimental Models Combining Traumatic Brain Injury and Secondary Insults

Patients with severe traumatic brain injury (TBI) frequently present with concomitant injuries that may cause secondary brain injury and impact outcomes. Animal models have been developed that combine contemporary models of TBI with a secondary neurologic insult such as hypoxia, shock, long bone fracture, and radiation exposure. Combined injury models may be particularly useful when modeling treatment strategies and in efforts to map basic research to a heterogeneous patient population. Here, we review these models and their collective contribution to the literature on TBI. In addition, we provide protocols and notes for two well-characterized models of TBI plus hemorrhagic shock.

Identification of ideal resuscitation pressure with concurrent traumatic brain injury in a rat model of hemorrhagic shock

BACKGROUND

Traumatic brain injury (TBI) is often associated with uncontrolled hemorrhagic shock (UHS), which contributes significantly to the mortality of severe trauma. Studies have demonstrated that permissive hypotension resuscitation improves the survival for uncontrolled hemorrhage. What the ideal target mean arterial pressure (MAP) is for TBI with UHS remains unclear.

METHODS

With the rat model of TBI in combination with UHS, we investigated the effects of a series of target resuscitation pressures (MAP from 50-90 mm Hg) on animal survival, brain perfusion, and organ function before hemorrhage controlled.

RESULTS

Rats in 50-, 60-, and 70-mm Hg target MAP groups had less blood loss and less fluid requirement, a better vital organ including mitochondrial function and better cerebral blood flow, and animal survival (8, 6, and 7 of 10, respectively) than 80- and 90-mm Hg groups. The 70-mm Hg group had a better cerebral blood flow and cerebral mitochondrial function than in 50- and 60-mm Hg groups. In contrast, 80- and 90-mm Hg groups resulted in an excessive hemodilution, a decreased blood flow, an increased brain water content, and more severe cerebral edema.

CONCLUSIONS

A 50-mm Hg target MAP is not suitable for the resuscitation of TBI combined with UHS. A 70 mm Hg of MAP is the ideal target resuscitation pressure for this trauma, which can keep sufficient perfusion to the brain and keep good organ function including cerebral mitochondrial function.

Polynitroxylated-pegylated hemoglobin attenuates fluid requirements and brain edema in combined traumatic brain injury plus hemorrhagic shock in mice

Polynitroxylated-pegylated hemoglobin (PNPH), a bovine hemoglobin decorated with nitroxide and polyethylene glycol moieties, showed neuroprotection vs. lactated Ringer's (LR) in experimental traumatic brain injury plus hemorrhagic shock (TBI+HS).

HYPOTHESIS

Resuscitation with PNPH will reduce intracranial pressure (ICP) and brain edema and improve cerebral perfusion pressure (CPP) vs. LR in experimental TBI+HS. C57/BL6 mice (n=20) underwent controlled cortical impact followed by severe HS to mean arterial pressure (MAP) of 25 to 27 mm Hg for 35 minutes. Mice (n=10/group) were then resuscitated with a 20 mL/kg bolus of 4% PNPH or LR followed by 10 mL/kg boluses targeting MAP>70 mm Hg for 90 minutes. Shed blood was then reinfused. Intracranial pressure was monitored. Mice were killed and %brain water (%BW) was measured (wet/dry weight). Mice resuscitated with PNPH vs. LR required less fluid (26.0±0.0 vs. 167.0±10.7 mL/kg, P<0.001) and had a higher MAP (79.4±0.40 vs. 59.7±0.83 mm Hg, P<0.001). The PNPH-treated mice required only 20 mL/kg while LR-resuscitated mice required multiple boluses. The PNPH-treated mice had a lower peak ICP (14.5±0.97 vs. 19.7±1.12 mm Hg, P=0.002), higher CPP during resuscitation (69.2±0.46 vs. 45.5±0.68 mm Hg, P<0.001), and lower %BW vs. LR (80.3±0.12 vs. 80.9±0.12%, P=0.003). After TBI+HS, resuscitation with PNPH lowers fluid requirements, improves ICP and CPP, and reduces brain edema vs. LR, supporting its development.

Pharmacologic resuscitation for hemorrhagic shock combined with traumatic brain injury

BACKGROUND

We have previously demonstrated that valproic acid (VPA), a histone deacetylase inhibitor, can improve survival after hemorrhagic shock (HS), protect neurons from hypoxia-induced apoptosis, and attenuate the inflammatory response. We have also shown that administration of 6% hetastarch (Hextend [Hex]) after traumatic brain injury (TBI) decreases brain swelling, without affecting size of the lesion. This study was performed to determine whether addition of VPA to Hex would decrease the lesion size in a clinically relevant large animal model of TBI + HS.

METHODS

Yorkshire swine (42-50 kg) were instrumented to measure hemodynamic parameters, intracranial pressure, and brain tissue oxygenation. A custom-designed, computer-controlled cortical impact device was used to create a TBI through a 20-mm craniotomy: 15-mm cylindrical tip impactor at 4-m/s velocity, 100-millisecond dwell time, and 12-mm penetration depth. Volume-controlled hemorrhage was started (40% blood volume) concurrent with the TBI. After 2 hours of shock, animals were randomized to one of three resuscitation groups (n = 7 per group) as follows: (1) isotonic sodium chloride solution; (2) 6% hetastarch, Hex; and (3) Hex and VPA 300 mg/kg (Hex + VPA). Volumes of Hex matched the shed blood, whereas that of the isotonic sodium chloride solution was three times the volume. VPA treatment was started after an hour of shock. After 6 hours of postresuscitation monitoring, brains were sectioned into 5-mm slices and stained with 2, 3, 5-Triphenyltetrazolium chloride to quantify the lesion size (mm) and brain swelling (percent change compared with uninjured side). Levels of acetylated histone H3 were determined to quantify acetylation, and myeloperoxidase and interleukine-1β (IL-1β) levels were measured as markers of brain inflammation.

RESULTS

Combination of 40% blood loss with cortical impact and a period of shock (2 hours) and resuscitation resulted in a highly reproducible brain injury. Lesion size and brain swelling in the Hex + VPA group (1,989 [156.8] mm, and 19% [1.6%], respectively) were significantly smaller than the isotonic sodium chloride solution group (3,335 [287.9] mm and 36% [2.2%], respectively). Hex alone treatment significantly decreased the swelling (27% [1.6%]) without reducing the lesion size. The number of CD11b-positive cells as well as myeloperoxidase and IL-1 levels in the brains were significantly reduced by the VPA treatment.

CONCLUSION

In a combined HS and TBI model, treatment with artificial colloid (Hex) improves hemodynamic parameters and reduces swelling, without affecting the actual size of the brain lesion. Addition of VPA effectively reduces both the size of brain lesion and associated swelling by attenuating the inflammatory response.

The acute effects of hemorrhagic shock on cerebral blood flow, brain tissue oxygen tension, and spreading depolarization following penetrating ballistic-like brain injury

Traumatic brain injury (TBI) often occurs in conjunction with additional trauma, resulting in secondary complications, such as hypotension as a result of blood loss. This study investigated the combined effects of penetrating ballistic-like brain injury (PBBI) and hemorrhagic shock (HS) on physiological parameters, including acute changes in regional cerebral blood flow (rCBF), brain tissue oxygen tension (P(bt)O₂), and cortical spreading depolarizations (CSDs). All recordings were initiated before injury (PBBI/HS/both) and maintained for 2.5 h. Results showed that PBBI alone and combined PBBI and HS produced a sustained impairment of ipsilateral rCBF that decreased by 70% from baseline (p<0.05). Significant and sustained reductions in P(bt)O₂ (50% baseline; p<0.05) were also observed in the injured hemisphere of the animals subjected to both PBBI and HS (PBBI+HS). In contrast, PBBI alone produced smaller, more transient reductions in P(bt)O₂ levels. The lower limit of cerebral autoregulation was significantly higher in the PBBI+HS group (p<0.05, compared to HS alone). Critically, combined injury resulted in twice the number of spontaneous CSDs as in PBBI alone (p<0.05). It also lowered the propagation speed of CSD and the threshold of CSD occurrence [induced CSD at higher mean arterial pressure (MAP)]. However, rCBF and P(bt)O₂ were not responsive to the depolarizations. Our data suggest that PBBI together with HS causes persistent impairment of CBF and brain tissue oxygen tension, increasing the probability of CSDs that likely contribute to secondary neuropathology and compromise neurological recovery.

Severe traumatic brain injury and controlled hemorrhage in rats: quest for the optimal mean arterial blood pressure after whole fresh donor blood resuscitation

Treatment of combined traumatic brain injury and hypovolemic shock poses a particular challenge due to the possible conflicting consequences. While restoring diminished volume is the treatment goal for hypovolemia, maintaining and adequate cerebral perfusion pressure and avoidance of secondary damage remain a treatment goal for the injured brain. Various treatment modalities have been proposed, but the optimal resuscitation fluid and goals have not yet been clearly defined. In this study, we investigate the physiological and neurological outcomes in a rat model of combined traumatic brain injury and hypovolemic shock, submitted to treatment with varying amounts of fresh blood. Forty-eight male Lewis rats were divided into control and treatment groups. Traumatic brain injury was inflicted by a free-falling rod on the exposed cranium. Hypovolemia was induced by controlled hemorrhage of 30% blood volume. Treatment groups were treated by fresh whole blood with varying volumes, reaching resuscitation goals of a mean arterial blood pressure (MAP) of 80, 100, and 120 mmHg at 15 min. Mean arterial blood pressure was assessed at 60 min and neurological outcomes and mortality in the subsequent 48 h. At 60 min, MAP was highest for the group resuscitated most aggressively. Neurological outcomes and mortality inversely correlated with the aggressiveness of resuscitation. In this study, we find that mild resuscitation with goals of restoring MAP to 80 mmHg (which is lower than baseline) provided best results when considering hemodynamic stability, survival, and neurological outcomes. An aggressive resuscitation may be detrimental, inducing processes that eventually cause a significant decrease in survival.

Animal models of traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of mortality and morbidity both in civilian life and on the battlefield worldwide. Survivors of TBI frequently experience long-term disabling changes in cognition, sensorimotor function and personality. Over the past three decades, animal models have been developed to replicate the various aspects of human TBI, to better understand the underlying pathophysiology and to explore potential treatments. Nevertheless, promising neuroprotective drugs that were identified as being effective in animal TBI models have all failed in Phase II or Phase III clinical trials. This failure in clinical translation of preclinical studies highlights a compelling need to revisit the current status of animal models of TBI and therapeutic strategies.

Edaravone increases regional cerebral blood flow after traumatic brain injury in mice

Traumatic brain injury (TBI) is a major cause of preventable death and serious morbidity, with subsequent low cerebral blood flow (CBF) considered to be associated with poor prognosis. In the present study, we demonstrated the effect of the free radical scavenger edaravone on regional CBF (rCBF) after TBI. Male mice (C57/BL6) were subjected to TBI using a controlled cortical impactor device. Immediately after TBI, the animals were intravenously administered 3.0 mg/kg of edaravone or a vehicle saline solution. Two-dimensional rCBF images were acquired before and 24 h post-TBI, and were quantified in the ipsilateral and contralateral hemispheres (n = 5 animals per group). CBF in the vehicle-treated animals decreased broadly over the ipsilateral hemisphere, with the region of low rCBF spreading from the frontal cortex to the occipital lobe. The zone of lowest rCBF matched that of the contusion area. The mean rCBF at 24 h for a defined elliptical region between the bregma and lambda was 73.7 ± 5.8 %. In comparison, the reduction of rCBF in edaravone-treated animals was significantly attenuated (93.4 ± 5.7 %, p < 0.05). The edaravone-treated animals also exhibited higher rCBF in the contralateral hemisphere compared with that seen in -vehicle-treated animals. It is suggested that edaravone reduces neuronal damage by scavenging reactive oxygen species (ROS) and by maintaining intact the autoregulation of the cerebral vasculature.

MRI assessment of cerebral blood flow after experimental traumatic brain injury combined with hemorrhagic shock in mice

Secondary insults such as hypotension or hemorrhagic shock (HS) can greatly worsen outcome after traumatic brain injury (TBI). We recently developed a mouse combined injury model of TBI and HS using a controlled cortical impact (CCI) model and showed that 90 minutes of HS can exacerbate neuronal death in hippocampus beneath the contusion. This combined injury model has three clinically relevant phases, a shock, pre hospital, and definitive care phases. Mice were randomly assigned to four groups, shams as well as a CCI only, an HS only, and a CCI+HS groups. The CCI and HS reduced cerebral blood flow (CBF) in multiple regions of interest (ROIs) in the hemisphere ipsilateral and contralateral to injury. Hemorrhagic shock to a level of ∼30 mm Hg exacerbated the CCI-induced CBF reductions in multiple ROIs ipsilateral to injury (hemisphere and thalamus) and in the hemisphere contralateral to injury (hemisphere, thalamus, hippocampus, and cortex, all P<0.05 versus CCI only, HS only or both). An important effect of HS duration was also seen after CCI with maximal CBF reduction seen at 90 minutes (P<0.0001 group-time effect in ipsilateral hippocampus). Given that neuronal death in hippocampus is exacerbated by 90 minutes of HS in this model, our data suggest an important role for exacerbation of posttraumatic ischemia in mediating the secondary injury in CCI plus HS. In conclusion, the serial, non invasive assessment of CBF using ASL-MRI (magnetic resonance imaging with arterial spin labeling) is feasible in mice even in the complex setting of combined CCI+HS. The impact of resuscitation therapies and various mutant mouse strains on CBF and other outcomes merits investigation in this model.

Effects of trauma, hemorrhage and resuscitation in aged rats

Traumatic brain injury (TBI) is a leading cause of death in the elderly and the incidence of mortality and morbidity increases with age. This study tested the hypothesis that, after TBI followed by hemorrhagic hypotension (HH) and resuscitation, cerebral blood flow (CBF) would decrease more in aged compared with young rats. Young adult (4-6 months) and aged (20-24 months) male Sprague-Dawley rats were anesthetized with isoflurane, prepared for parasagittal fluid percussion injury (FPI) and randomly assigned to receive either moderate FPI (2.0 atm) only, moderate FPI+severe HH (40 mm Hg for 45 min) followed by return of shed blood, or sham FPI. Intracranial pressure (ICP), CBF, and mean arterial pressure (MAP) were measured and, after twenty-four hours survival, the rats were euthanized and their brains were sectioned and stained with Fluoro-Jade (FJ), a dye that stains injured neurons. After moderate FPI, severe HH and reinfusion of shed blood, MAP and CBF were significantly reduced in the aged group, compared to the young group. Both FPI and FPI+HH groups significantly increased the numbers of FJ-positive neurons in hippocampal cell layers CA1, CA2 and CA3 (p<0.05 vs Sham) in young and aged rats. Despite differences in post-resuscitation MAP and CBF, there were no differences in the numbers of FJ-positive neurons in aged compared to young rats after FPI, HH and blood resuscitation. Although cerebral hypoperfusion in the aged rats was not associated with increased hippocampal cell injury, the trauma-induced reductions in CBF and post-resuscitation blood pressure may have resulted in damage to brain regions that were not examined or neurological or behavioral impairments that were not assessed in this study. Therefore, the maintenance of normal blood pressure and cerebral perfusion would be advisable in the treatment of elderly patients after TBI.

Severe brief pressure-controlled hemorrhagic shock after traumatic brain injury exacerbates functional deficits and long-term neuropathological damage in mice

Hypotension after traumatic brain injury (TBI) worsens outcome. We published the first report of TBI plus hemorrhagic shock (HS) in mice using a volume-controlled approach and noted increased neuronal death. To rigorously control blood pressure during HS, a pressure-controlled HS model is required. Our hypothesis was that a brief, severe period of pressure-controlled HS after TBI in mice will exacerbate functional deficits and neuropathology versus TBI or HS alone. C57BL6 male mice were randomized into four groups (n=10/group): sham, HS, controlled cortical impact (CCI), and CCI+HS. We used a pressure-controlled shock phase (mean arterial pressure [MAP]=25-27 mm Hg for 35 min) and its treatment after mild to moderate CCI including, a 90 min pre-hospital phase, during which lactated Ringer's solution was given to maintain MAP >70 mm Hg, and a hospital phase, when the shed blood was re-infused. On days 14-20, the mice were evaluated in the Morris water maze (MWM, hidden platform paradigm). On day 21, the lesion and hemispheric volumes were quantified. Neuropathology and hippocampal neuron counts (hematoxylin and eosin [H&E], Fluoro-Jade B, and NeuN) were evaluated in the mice (n=60) at 24 h, 7 days, or 21 days (n=5/group/time point). HS reduced MAP during the shock phase in the HS and CCI+HS groups (p<0.05). Fluid requirements during the pre-hospital phase were greatest in the CCI+HS group (p<0.05), and were increased in HS versus sham and CCI animals (p<0.05). MWM latency was increased on days 14 and 15 after CCI+HS (p<0.05). Swim speed and visible platform latency were impaired in the CCI+HS group (p<0.05). CCI+HS animals had increased contusion volume versus the CCI group (p<0.05). Hemispheric volume loss was increased 33.3% in the CCI+HS versus CCI group (p<0.05). CA1 cell loss was seen in CCI+HS and CCI animals at 24 h and 7 days (p<0.05). CA3 cell loss was seen after CCI+HS (p<0.05 at 24 h and 7 days). CA1 cell loss at 21 days was seen only in CCI+HS animals (p<0.05). Brief, severe, pressure-controlled HS after CCI produces robust functional deficits and exacerbates neuropathology versus CCI or HS alone.

Traumatic brain injury and hemorrhagic shock: evaluation of different resuscitation strategies in a large animal model of combined insults

Traumatic brain injury (TBI) and hemorrhagic shock (HS) are the leading causes of trauma-related mortality and morbidity. Combination of TBI and HS (TBI + HS) is highly lethal, and the optimal resuscitation strategy for this combined insult remains unclear. A critical limitation is the lack of suitable large animal models to test different treatment strategies. We have developed a clinically relevant large animal model of TBI + HS, which was used to evaluate the impact of different treatments on brain lesion size and associated edema. Yorkshire swine (42-50 kg) were instrumented to measure hemodynamic parameters and intracranial pressure. A computer-controlled cortical impact device was used to create a TBI through a 20-mm craniotomy: 15-mm cylindrical tip impactor at 4 m/s velocity, 100-ms dwell time, and 12-mm penetration depth. Volume-controlled hemorrhage was started (40% blood volume) concurrent with the TBI. After 2 h of shock, animals were randomized to one of three resuscitation groups (n = 5/group): (a) normal saline (NS); (b) 6% hetastarch, Hextend (Hex); and (c) fresh frozen plasma (FFP). Volumes of Hex and FFP matched the shed blood, whereas NS was three times the volume. After 6 h of postresuscitation monitoring, brains were sectioned into 5-mm slices and stained with TTC (2,3,5-triphenyltetrazolium chloride) to quantify the lesion size and brain swelling. Combination of 40% blood loss with cortical impact and a period of shock (2 h) resulted in a highly reproducible brain injury. Total fluid requirements were lower in the Hex and FFP groups. Lesion size and brain swelling in the FFP group (2,160 ± 202.63 mm and 22% ± 1.0%, respectively) were significantly smaller than those in the NS group (3,285 ± 130.8 mm3 and 37% ± 1.6%, respectively) (P < 0.05). Hex treatment decreased the swelling (29% ± 1.6%) without reducing the lesion size. Early administration of FFP reduces the size of brain lesion and associated swelling in a large animal model of TBI + HS. In contrast, artificial colloid (Hex) decreases swelling without reducing the actual size of the brain lesion.

Red Blood Cell Transfusion and Transfusion Alternatives in Traumatic Brain Injury

OPINION STATEMENT: Anemia develops in about 50% of patients hospitalized with traumatic brain injury (TBI) and is recognized as a cause of secondary brain injury. This review examines the effects of anemia and transfusion on TBI patients through a literature search to identify original research on anemia and transfusion in TBI, the effects of transfusion on brain physiology, and the role of erythropoietin or hemoglobin-based blood substitutes (HBBSs). However, the amount of high-quality, prospective data available to help make decisions about when TBI patients should be transfused is very small. Randomized transfusion trials have involved far too few TBI patients to reach definitive conclusions. Thus, it is hardly surprising that there is widespread practice variation. In our opinion, a hemoglobin transfusion threshold of 7 g/dL cannot yet be considered safe for TBI patients admitted to hospital, and in particular to the ICU, as it is for other critically ill patients. Red blood cell transfusions often have immediate, seemingly beneficial effects on cerebral physiology, but the magnitude of this effect may depend in part upon how long the cells have been stored before administration. In light of existing physiological data, we generally aim to keep hemoglobin concentrations greater than 9 g/dL during the first several days after TBI. In part, the decision is based on the patient's risk of or development of secondary ischemia or brain injury. An increasing number of centers use multimodal neurologic monitoring, which may help to individualize transfusion goals based on the degree of cerebral hypoxia or metabolic distress. When available, brain tissue oxygen tension values less than 15-20 mm Hg or a lactate:pyruvate ratio greater than 30-40 would influence us to use more aggressive hemoglobin correction (e.g., a transfusion threshold of 10 g/dL). Clinicians can attempt to reduce transfusion requirements by limiting phlebotomy, minimizing hemodilution, and providing appropriate prophylaxis against gastrointestinal hemorrhage. Administration of exogenous erythropoietin may have a small impact in further reducing the need for transfusion, but it also may increase complications, most notably deep venous thrombosis. Erythropoietin is currently of great interest as a potential neuroprotective agent, but until it is adequately evaluated in randomized controlled trials, it should not be used routinely for this purpose. HBBSs are also of interest, but existing preparations have not been shown to be beneficial-or even safe-in the context of TBI.

Histopathological and behavioral effects of immediate and delayed hemorrhagic shock after mild traumatic brain injury in rats

The purpose of this study was to investigate the increased susceptibility of the brain, after a controlled mild cortical impact injury, to a secondary ischemic insult. The effects of the duration and the timing of the secondary insult after the initial cortical injury were studied. Rats anesthetized with isoflurane underwent a 3 m/sec, 2.5-mm deformation cortical impact injury followed by hypotension to 40 mm Hg induced by withdrawing blood from a femoral vein. The duration of hypotension was varied from 40 to 60 min. The timing of 60 min of hypotension was varied from immediately post-injury to 7 days after the injury. Outcome was assessed by behavioral tasks and histological examination at 2 weeks post-injury. A separate group of animals underwent measurement of the acute physiology including mean blood pressure (MAP), intracranial pressure (ICP), and cerebral blood flow (CBF) using a laser Doppler technique. Increasing durations of hypotension resulted in marked expansion of the contusion, from 6.5±1.8 mm³ with sham hypotension to 27.1±3.9 mm³ with 60 min of hypotension. This worsening of the contusion was found only when then hypotension occurred immediately after injury or at 1 h after injury. CA3 neuron loss followed a similar pattern, but the injury group differences were not significant. Motor tasks, including beam balance and beam walking, were significantly worse following 50 and 60 min of hypotension. Performance on the Morris water maze task was also significantly related to the injury group. Studies of the acute cerebral hemodynamics demonstrated that CBF was significantly more impaired during hypotension in the animals that underwent the mild TBI compared to those that underwent sham TBI. The perfusion deficit was worst at the impact site, but also significant in the pericontusional brain. With 50 and 60 min of hypotension, CBF did not recover following resuscitation at the impact site, and recovered only transiently in the pericontusional brain. These results demonstrate that mild TBI, like more severe levels of TBI, can impair the brain's ability to maintain CBF during a period of hypotension, and result in a worse outcome.

Animal modelling of traumatic brain injury in preclinical drug development: where do we go from here?

Traumatic brain injury (TBI) is the leading cause of death and disability in young adults. Survivors of TBI frequently suffer from long-term personality changes and deficits in cognitive and motor performance, urgently calling for novel pharmacological treatment options. To date, all clinical trials evaluating neuroprotective compounds have failed in demonstrating clinical efficacy in cohorts of severely injured TBI patients. The purpose of the present review is to describe the utility of animal models of TBI for preclinical evaluation of pharmacological compounds. No single animal model can adequately mimic all aspects of human TBI owing to the heterogeneity of clinical TBI. To successfully develop compounds for clinical TBI, a thorough evaluation in several TBI models and injury severities is crucial. Additionally, brain pharmacokinetics and the time window must be carefully evaluated. Although the search for a single-compound, 'silver bullet' therapy is ongoing, a combination of drugs targeting various aspects of neuroprotection, neuroinflammation and regeneration may be needed. In summary, finding drugs and prove clinical efficacy in TBI is a major challenge ahead for the research community and the drug industry. For a successful translation of basic science knowledge to the clinic to occur we believe that a further refinement of animal models and functional outcome methods is important. In the clinical setting, improved patient classification, more homogenous patient cohorts in clinical trials, standardized treatment strategies, improved central nervous system drug delivery systems and monitoring of target drug levels and drug effects is warranted.

Neuroprotection with an erythropoietin mimetic peptide (pHBSP) in a model of mild traumatic brain injury complicated by hemorrhagic shock

Pyroglutamate helix B surface peptide (pHBSP) is an 11 amino acid peptide, designed to interact with a novel cell surface receptor, composed of the classical erythropoietin (EPO) receptor disulfide linked to the beta common receptor. pHBSP has the cytoprotective effects of EPO without stimulating erythropoiesis. Effects on early cerebral hemodynamics and neurological outcome at 2 weeks post-injury were compared in a rat model of mild cortical impact injury (3m/sec, 2.5 mm deformation) followed by 50 min of hemorrhagic hypotension (MAP 40 mm Hg for 50 min). Rats were randomly assigned to receive 5000 U/kg of EPO, 30 μg/kg of pHBSP, or an inactive substance every 12 h for 3 days, starting at the end of resuscitation from the hemorrhagic hypotension, which was 110 min post-injury. Both treatments reduced contusion volume at 2 weeks post-injury, from 20.8±2.8 mm(3) in the control groups to 7.7±2.0 mm(3) in the EPO-treated group and 5.9±1.5 mm(3) in the pHBSP-treated group (p=0.001). Both agents improved recovery of cerebral blood flow in the injured brain following resuscitation, and resulted in more rapid recovery of performance on beam balancing and beam walking tests. These studies suggest that pHBSP has neuroprotective effects similar to EPO in this model of combined brain injury and hypotension. pHBSP may be more useful in the clinical situation because there is less risk of thrombotic adverse effects.

Metabolic effects of a late hypotensive insult combined with reduced intracranial compliance following traumatic brain injury in the rat

INTRODUCTION

Traumatic brain injury makes the brain vulnerable to secondary insults. Post-traumatic alterations in intracranial dynamics, such as reduced intracranial compliance (IC), are thought to further potentiate the effects of secondary insults. Reduced IC combined with intracranial volume insults leads to metabolic disturbances in a rat model. The aim of the present study was to discern whether a post-traumatic hypotensive insult in combination with reduced IC caused more pronounced secondary metabolic disturbances in the injured rat brain.

MATERIALS AND METHODS

Rats were randomly assigned to four groups (n = 8/group): 1) trauma with hypotension; 2) trauma and reduced IC with hypotension; 3) sham injury with hypotension; and 4) sham injury and reduced IC with hypotension. A weight drop model of cortical contusion trauma was used. IC was reduced by gluing rubber film layers on the inside of bilateral bone flaps before replacement. Microdialysis probes were placed in the perimeter of the trauma zone. Hypotension was induced 2 h after trauma. Extracellular (EC) levels of lactate, pyruvate, hypoxanthine, and glycerol were analyzed.

RESULTS

The trauma resulted in a significant increase in EC dialysate levels of lactate, lactate/pyruvate ratio, hypoxanthine, and glycerol. A slight secondary increase in lactate was noted for all groups but group 2 during hypotension, otherwise no late effects were seen. There were no effects of reduced IC.

DISCUSSION

In conclusion, reduced IC did not increase the metabolic disturbances caused by the post-traumatic hypotensive insult. The results suggest that a mild to moderate hypotensive insult after initial post-traumatic resuscitation may be tolerated better than an early insult before resuscitation.

Resuscitation of traumatic brain injury and hemorrhagic shock with polynitroxylated albumin, hextend, hypertonic saline, and lactated Ringer's: Effects on acute hemodynamics, survival, and neuronal death in mice

Outcome after traumatic brain injury (TBI) is worsened by hemorrhagic shock (HS), but the optimal resuscitation approach is unclear. In particular, treatment of TBI patients with colloids remains controversial. We hypothesized that resuscitation with the colloids polynitroxylated albumin (PNA) or Hextend (HEX) is equal or superior to resuscitation with the crystalloids hypertonic (3%) saline (HTS) or lactated Ringer's solution (LR) after TBI plus HS in mice. C57/BL6 mice (n = 30) underwent controlled cortical impact (CCI) and 90 min of volume-controlled HS (2 mL/100 g). The mice were randomized to resuscitation with LR, HEX, HTS, or PNA, followed by 30 min of test fluid administration targeting a mean arterial pressure (MAP) of >50 mm Hg. Shed blood was re-infused to target a MAP >70 mm Hg. At 7 days post-insult, hippocampal neuron counts were assessed in hematoxylin and eosin-stained sections to quantify neuronal damage. Prehospital MAP was higher, and prehospital and total fluid requirements were lower in the PNA and HEX groups (p < 0.05 versus HTS or LR). Also, 7-day survival was highest in the PNA group, but was not significantly different than the other groups. Ipsilateral hippocampal CA1 and CA3 neuron loss did not differ between groups. We conclude that the colloids PNA and HEX exhibited more favorable effects on acute resuscitation parameters than HTS or LR, and did not increase hippocampal neuronal death in this model.

Blast-induced brain injury and posttraumatic hypotension and hypoxemia

Explosive munitions account for more than 50% of all wounds sustained in military combat, and the proportion of civilian casualties due to explosives is increasing as well. But there has been only limited research on the pathophysiology of blast-induced brain injury, and the contributions of alterations in cerebral blood flow (CBF) or cerebral vascular reactivity to blast-induced brain injury have not been investigated. Although secondary hypotension and hypoxemia are associated with increased mortality and morbidity after closed head injury, the effects of secondary insults on outcome after blast injury are unknown. Hemorrhage accounted for approximately 50% of combat deaths, and the lungs are one of the primary organs damaged by blast overpressure. Thus, it is likely that blast-induced lung injury and/or hemorrhage leads to hypotensive and hypoxemic secondary injury in a significant number of combatants exposed to blast overpressure injury. Although the effects of blast injury on CBF and cerebral vascular reactivity are unknown, blast injury may be associated with impaired cerebral vascular function. Reactive oxygen species (ROS) such as the superoxide anion radical and other ROS, likely major contributors to traumatic cerebral vascular injury, are produced by traumatic brain injury (TBI). Superoxide radicals combine with nitric oxide (NO), another ROS produced by blast injury as well as other types of TBI, to form peroxynitrite, a powerful oxidant that impairs cerebral vascular responses to reduced intravascular pressure and other cerebral vascular responses. While current research suggests that blast injury impairs cerebral vascular compensatory responses, thereby leaving the brain vulnerable to secondary insults, the effects of blast injury on the cerebral vascular reactivity have not been investigated. It is clear that further research is necessary to address these critical concerns.

Hemorrhagic shock after experimental traumatic brain injury in mice: effect on neuronal death

Traumatic brain injury (TBI) from blast injury is often complicated by hemorrhagic shock (HS) in victims of terrorist attacks. Most studies of HS after experimental TBI have focused on intracranial pressure; few have explored the effect of HS on neuronal death after TBI, and none have been done in mice. We hypothesized that neuronal death in CA1 hippocampus would be exacerbated by HS after experimental TBI. C57BL6J male mice were anesthetized with isoflurane, mean arterial blood pressure (MAP) was monitored, and controlled cortical impact (CCI) delivered to the left parietal cortex followed by continued anesthesia (CCI-only), or either 60 or 90 min of volume-controlled HS. Parallel 60- or 90-min HS-only groups were also studied. After HS (+/-CCI), 6% hetastarch was used targeting MAP of > or =50 mm Hg during a 30-min Pre-Hospital resuscitation phase. Then, shed blood was re-infused, and hetastarch was given targeting MAP of > or =60 mm Hg during a 30-min Definitive Care phase. Neurological injury was evaluated at 24 h (fluorojade C) or 7 days (CA1 and CA3 hippocampal neuron counts). HS reduced MAP to 30-40 mm Hg in all groups, p < 0.05 versus CCI-only. Ipsilateral CA1 neuron counts in the 90-min CCI+HS group were reduced at 16.5 +/- 14.1 versus 30.8 +/- 6.8, 32.3 +/- 7.6, 30.6 +/- 2.2, 28.1 +/- 2.2 neurons/100 mum in CCI-only, 60-min HS-only, 90-min HS-only, and 60-min CCI+HS, respectively, all p < 0.05. CA3 neuron counts did not differ between groups. Fluorojade C staining confirmed neurodegeneration in CA1 in the 90-min CCI+HS group. Our data suggest a critical time window for exacerbation of neuronal death by HS after CCI and may have implications for blast injury victims in austere environments where definitive management is delayed.

Duration of ATP reduction affects extent of CA1 cell death in rat models of fluid percussion injury combined with secondary ischemia

Secondary ischemia (SI) following traumatic brain injury (TBI) increases damage to the brain in both animals and humans. The current study determined if SI after TBI alters the extent or duration of reduced energy production within the first 24 h post-injury and hippocampal cell loss at one week post-injury. Adult male rats were subjected to sham injury, lateral (LFPI) or central fluid percussion injury (CFPI) only, or to combined LFPI or CFPI with SI. The SI was 8 min of bilateral forebrain ischemia combined with hemorrhagic hypotension, applied at 1 h following FPI. After LFPI alone adenosine triphosphate (ATP) levels within the ipsilateral CA1 were reduced at 2 h (p < 0.05) and subsequently recovered. After LFPI+SI the ATP reductions in CA1 ipsilateral to FPI persisted for 24 h (p < 0.01). ATP levels in the contralateral CA1 were not affected by LFPI alone or LFPI+SI. After CFPI alone CA1 ATP levels were depressed bilaterally only at 2 h (p < 0.05). Similar to the LFPI paradigm, CFPI+SI reduced ATP levels for 24 h (p < 0.01), with bilateral ATP reductions seen after CFPI+SI. Cell counts in the CA1 region at 7 days post-injury revealed no significant neuronal cell loss after LFPI or CFPI alone. Significant neuronal cell loss was present only within the ipsilateral (p < 0.001) CA1 after LFPI+SI, but cell loss was bilateral (p < 0.001) after CFPI+SI. Thus, SI prolongs ATP reductions induced by LFPI and CFPI within the CA1 region and this SI-induced energy reduction appears to adversely affect regional neuronal viability.

Increased risk of death associated with hypotension is not altered by the presence of brain injury in pediatric trauma patients

BACKGROUND

Hypotension is a well-known predictor of mortality in pediatric trauma patients. However, it is unknown whether the mortality rate is higher in patients with traumatic brain injury (TBI) than in those without TBI. We hypothesized that systemic hypotension increases mortality in pediatric patients with TBI more than it does in pediatric patients with extracranial injuries only.

METHODS

Multivariate logistic regression was used to determine the relationship between hypotension and the risk of death. Patients were then divided into 2 groups: TBI and No-TBI and the model was applied separately to each group.

RESULTS

Overall mortality was 2%. After adjusting for confounding variables, hypotension remained a strong independent predictor of mortality. However, the increased risk of death was similar in patients with and without TBI.

CONCLUSION

Hypotension is an important predictor of death in pediatric trauma patients. The increased risk of death associated with hypotension is similar with or without traumatic brain injury.

Traumatic brain injury in older adults: epidemiology, outcomes, and future implications

Traumatic brain injury (TBI) is a significant problem in older adults. In persons aged 65 and older, TBI is responsible for more than 80,000 emergency department visits each year; three-quarters of these visits result in hospitalization as a result of the injury. Adults aged 75 and older have the highest rates of TBI-related hospitalization and death. Falls are the leading cause of TBI for older adults (51%), and motor vehicle traffic crashes are second (9%). Older age is known to negatively influence outcome after TBI. Although geriatric and neurotrauma investigators have identified the prognostic significance of preadmission functional ability, comorbidities, sex, and other factors such as cerebral perfusion pressure on recovery after illness or injury, these variables remain understudied in older adults with TBI. In the absence of good clinical data, predicting outcomes and providing care in the older adult population with TBI remains problematic. To address this significant public health issue, a refocusing of research efforts on this population is justified to prevent TBI in the older adult and to discern unique care requirements to facilitate best patient outcomes.

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.

Arterial hypotension triggers perifocal depolarizations and aggravates secondary damage in focal brain injury

Perifocal depolarizations (PFD) have been observed after traumatic brain injury, are known to disturb cerebrovascular reactivity and thus may contribute to the morphological consequences of brain injury. In this investigation, the role of PFD was studied in focal brain lesions with/without induction of delayed hypotension. Cerebral freeze lesions were induced in anesthetized normotensive rats that underwent perfusion fixation of brains 5 min, 4 h or 24 h after lesioning, respectively, to obtain quantitative histopathology. In additional groups, a 45-min period of moderate hypobaric hypotension was applied 15 min post-trauma and brains were perfusion fixed after 4 h or 24 h. In a second series, the direct current (DC) potential and cortical laser-Doppler flow (LDF) were measured adjacent to lesions under normotensive or hypotensive conditions. Sham procedures were carried out in rats that underwent hypotension alone. Lesioning resulted in a significant LDF decrease to 50% of baseline, further decreased during hypotension to less than 40% of control (P < 0.05). Sham animals had LDF values between 60 and 70% of control when subjected to hypotension. Focal brain injury always induced a negative DC shift shortly after lesioning. In 6 of 8 rats that underwent cold lesion plus hypotension, a second PFD was observed approximately 2.5 min after onset of hypotension accompanied by a relative LDF increase by 25 +/- 12%. Lesion expansion was significantly worsened by hypotension (8.19 +/- 0.56 mm(3) at 24 h) compared with normotensive rats (7.01 +/- 0.3 mm(3) at 24 h, P < 0.01). We conclude that hypotension triggers depolarizations by an ischemic mechanism that contributes to final tissue damage.

Hypotension Does Not Increase Mortality in Brain-Injured Patients More Than it Does in Non-Brain-Injured Patients

OBJECTIVES

Hypotension increases mortality after all types of injuries. Prior studies comparing mortality of hypotensive traumatic brain injury (TBI) patients to normotensive TBI patients have implied that hypotension is particularly detrimental after TBI. It is unknown whether hypotension affects TBI patients more severely than it affects other types of patients. We hypothesized that hypotension does not increase mortality in TBI patients more than it does in non-TBI patients.

METHODS

National Trauma Data Bank (1994-2002) patients aged 18 to 45 years with blunt mechanisms of injury treated at Level I and Level II centers were included. Deaths occurring before 24 hours were excluded. Logistic regression was used to measure the association between hypotension (< or =90 mm Hg) and death after adjusting for confounding variables of age, gender, comorbidities, complications, Glasgow Coma Scale score, and severity of associated injuries. Odds ratios (95% confidence interval) indicate the risk of death in hypotensive patients in each group compared with normotensive patients in the same group.

RESULTS

The study population consisted of 79,478 patients (TBI, 30,742; no TBI, 48,736). Hypotension independently quadrupled the risk of death after adjusting for confounding variables (odds ratio [OR], 4.8; 95% confidence interval [CI], 4.1-5.6). However, increase in this risk associated with hypotension was the same in TBI (OR, 4.1; 95% CI, 3.5-4.9) and non-TBI patients (OR, 4.6; 95% CI, 3.4-6.0). Furthermore, the relationship between hypotension and TBI did not change with increasing head Abbreviated Injury Scale score severity.

CONCLUSION

Hypotension is an independent risk factor for mortality. However, it does not increase mortality in TBI patients more than it does for non-TBI patients.

Experience-dependent behavioral plasticity is disturbed following traumatic injury to the immature brain

Traumatic brain injury (TBI) is most prevalent in children and young adults. The long-term effects of pediatric TBI include cognitive and behavioral impairments; however, over time, it is difficult to distinguish individual variability in intellect and behavior from sequelae of early injury. Postnatal day (PND) 19 rats underwent lateral fluid percussion (FP) injury, followed by rearing in either standard (STD) or enriched environment (EE) conditions. The hypothesis was that the traditional enhancement of cognitive functioning following EE rearing would be attenuated when this rearing is preceded by TBI at PND19. Thirty days after injury, Morris water maze (MWM) acquisition and subsequent probe trial retention were used to assess the behavioral effects of injury on experience-dependent plasticity induced by housing in EE at two different time windows. MWM acquisition demonstrated improvements following early EE rearing in both sham and injured animals; however, the degree of improvement was greater for uninjured animals. When EE rearing was delayed for 2 weeks after injury, the injury effect was absent and the effect of rearing even stronger. Memory testing in the early EE groups using a delayed probe trial showed an effect of injury and housing, with the sham EE animals benefiting the most. After the delayed EE, sham EE animals again showed more probe target hits, while FPEE animals did not, demonstrating an enduring memory deficit. These data confirm that early TBI has effects on experience-dependent plasticity resulting in long-term neurobehavioral deficits. In addition, the ability to benefit from environmental stimulation following TBI is dependent upon time after injury.

Lateral fluid percussion brain injury: a 15-year review and evaluation

This article comprehensively reviews the lateral fluid percussion (LFP) model of traumatic brain injury (TBI) in small animal species with particular emphasis on its validity, clinical relevance and reliability. The LFP model, initially described in 1989, has become the most extensively utilized animal model of TBI (to date, 232 PubMed citations), producing both focal and diffuse (mixed) brain injury. Despite subtle variations in injury parameters between laboratories, universal findings are evident across studies, including histological, physiological, metabolic, and behavioral changes that serve to increase the reliability of the model. Moreover, demonstrable histological damage and severity-dependent behavioral deficits, which partially recover over time, validate LFP as a clinically-relevant model of human TBI. The LFP model, also has been used extensively to evaluate potential therapeutic interventions, including resuscitation, pharmacologic therapies, transplantation, and other neuroprotective and neuroregenerative strategies. Although a number of positive studies have identified promising therapies for moderate TBI, the predictive validity of the model may be compromised when findings are translated to severely injured patients. Recently, the clinical relevance of LFP has been enhanced by combining the injury with secondary insults, as well as broadening studies to incorporate issues of gender and age to better approximate the range of human TBI within study design. We conclude that the LFP brain injury model is an appropriate tool to study the cellular and mechanistic aspects of human TBI that cannot be addressed in the clinical setting, as well as for the development and characterization of novel therapeutic interventions. Continued translation of pre-clinical findings to human TBI will enhance the predictive validity of the LFP model, and allow novel neuroprotective and neuroregenerative treatment strategies developed in the laboratory to reach the appropriate TBI patients.

Traumatic brain injury elevates glycogen and induces tolerance to ischemia in rat brain

Previous studies have demonstrated that traumatic brain injury (TBI) increases the vulnerability of the brain to an acute episode of hypoxia-ischemia. The objective of the present study was to determine whether TBI alters the vulnerability of the brain to a delayed episode of ischemia and, if so, to identify contributing mechanisms. Sprague-Dawley rats were subjected to lateral fluid-percussion (FP) brain injury (n = 14) of moderate severity (2.3-2.5 atm), or sham-injury (n = 12). After recovery for 24 h, all animals underwent an 8-min episode of forebrain ischemia, followed by survival for 6 days. Ischemic damage in the hippocampus and cerebral cortex of the FP-injured hemisphere was compared to that in the contralateral hemisphere and to that in sham-injured animals. Remarkably, the number of surviving CA(1) neurons in the middle and lateral segments of the hippocampus in the FP-injured hemisphere was significantly greater than that in the contralateral hemisphere and sham-injured animals (p < 0.05). Likewise, in the cerebral cortex the number of damaged neurons tended to be lower in the FP-injured hemisphere than in the contralateral hemisphere. These results suggest that TBI decreased the vulnerability of the brain to a delayed episode of ischemia. To determine whether TBI triggers protective metabolic alterations, glycogen levels were measured in cerebral cortex and hippocampus in additional animals 24 h after FP-injury (n = 13) or sham-injury (n = 7). Cortical glycogen levels in the ipsilateral hemisphere increased to 12.9 +/- 6.4 mmol/kg (mean +/- SD), compared to 6.4 +/- 1.8 mmol/kg in the opposite hemisphere and 5.7 +/- 1.3 mmol/kg in sham-injured animals (p < 0.001). Similarly, in the hippocampus glycogen levels in the FP-injured hemisphere increased to 13.4 +/- 4.9 mmol/kg, compared to 8.1 +/- 2.4 mmol/kg in the contralateral hemisphere (p < 0.004) and 6.2 +/- 1.5 mmol/kg in sham-injured animals (p < 0.001). These results demonstrate that TBI triggers a marked accumulation of glycogen that may protect the brain during ischemia by serving as an endogenous source of metabolic energy.

Metabolic, neurochemical, and histologic responses to vibrissa motor cortex stimulation after traumatic brain injury

During the prolonged metabolic depression after traumatic brain injury (TBI), neurons are less able to respond metabolically to peripheral stimulation. Because this decreased responsiveness has been attributed to circuit dysfunction, the present study examined the metabolic, neurochemical, and histologic responses to direct cortical stimulation after lateral fluid percussion injury (LFPI). This study addressed three specific hypotheses: that neurons, if activated after LFPI, will increase their utilization of glucose even during a period of posttraumatic metabolic depression; that this secondary activation results in an increase in the production of lactate and a depletion of extracellular glucose; and that because cells are known to be in a state of energy crisis after traumatic brain injury, additional energy demands resulting from activation can result in their death. The results indicate that stimulating to levels eliciting a vibrissa twitch resulted in an increase in the cerebral metabolic rate for glucose (CMR(glc); micromol.100 g(-1).min(-1)) of 34% to 61% in the sham-operated, 1-hour LFPI, and 7-day LFPI groups. However, in the 1-day LFPI group, stimulation induced a 161% increase in CMR(glc) and a 35% decrease in metabolic activation volume. Extracellular lactate concentrations during stimulation significantly increased from 23% in the sham-injured group to 55% to 63% in the 1-day and 7-day LFPI groups. Extracellular glucose concentrations during stimulation remained unchanged in the sham-injured and 7-day LFPI groups, but decreased 17% in the 1-day LFPI group. The extent of cortical degeneration around the stimulating electrode in the 1-day LFPI group nearly doubled when compared with controls. These results indicate that at 1 day after LFPI, the cortex can respond to stimulation with an increase in anaerobic glycolysis; however, this metabolic response to levels eliciting a vibrissa response via direct cortical stimulation appears to constitute a secondary injury in the TBI brain.

Low-dose prostacyclin improves cortical perfusion following experimental brain injury in the rat

It was recently shown that prostacyclin at a low dose reduces cortical cell death following brain trauma in the rat. Conceivably, prostacyclin with its vasodilatory, anti-aggregatory, anti-adhesive and permeability-reducing properties improved a compromised perfusion caused by post-traumatic vasoconstriction, microthrombosis and increased microvascular permeability. The objective of the present study was therefore to investigate the hemodynamic effects of low-dose prostacyclin in the traumatized rat cortex. Following a fluid percussion brain injury or a sham procedure, animals were treated with a continuous intravenous infusion of prostacyclin of 1 or 2 ng x kg(-1) x min(-1), or vehicle. Blood flow ([(14)C]-iodoantipyrine), the permeability-surface area product (PS) for [(51)Cr]-EDTA, and brain water content were measured after 3 or 48 h of treatment. Blood flow values in the injured cortex were transiently reduced to 0.42 +/- 0.2 mL x min(-1) in the vehicle group 3 h following trauma from a corresponding value of about 1.6 mL x min(-1) in the sham group, with recovery of blood flow after 48 h. Prostacyclin treatment caused a dose-dependent increase in blood flow which reached statistical significance 48 h following trauma. Brain water content and PS increased in the injured cortex post trauma and the higher dose of prostacyclin increased these parameters further at 48 h compared to the vehicle group (p < 0.05). The latter effects of prostacyclin cannot be attributed to an increase in permeability, as prostacyclin did not influence PS or brain water content following sham trauma. In fact prostacyclin has been shown to have permeability-decreasing properties. We conclude that prostacyclin improves cortical perfusion following brain trauma. The simultaneous aggravation of brain edema can be explained by an increased surface area, perhaps in combination with increased capillary hydrostatic pressure.