Building a Better Fluid for Emergency Resuscitation of Traumatic Brain Injury

Traumatic Brain Injury-A Review of Intravenous Fluid Therapy

This manuscript will review intravenous fluid therapy in traumatic brain injury. Both human and animal literature will be included. Basic treatment recommendations will also be discussed.

Physiology of Human Hemorrhage and Compensation

Hemorrhage is a leading cause of death following traumatic injuries in the United States. Much of the previous work in assessing the physiology and pathophysiology underlying blood loss has focused on descriptive measures of hemodynamic responses such as blood pressure, cardiac output, stroke volume, heart rate, and vascular resistance as indicators of changes in organ perfusion. More recent work has shifted the focus toward understanding mechanisms of compensation for reduced systemic delivery and cellular utilization of oxygen as a more comprehensive approach to understanding the complex physiologic changes that occur following and during blood loss. In this article, we begin with applying dimensional analysis for comparison of animal models, and progress to descriptions of various physiological consequences of hemorrhage. We then introduce the complementary side of compensation by detailing the complexity and integration of various compensatory mechanisms that are activated from the initiation of hemorrhage and serve to maintain adequate vital organ perfusion and hemodynamic stability in the scenario of reduced systemic delivery of oxygen until the onset of hemodynamic decompensation. New data are introduced that challenge legacy concepts related to mechanisms that underlie baroreflex functions and provide novel insights into the measurement of the integrated response of compensation to central hypovolemia known as the compensatory reserve. The impact of demographic and environmental factors on tolerance to hemorrhage is also reviewed. Finally, we describe how understanding the physiology of compensation can be translated to applications for early assessment of the clinical status and accurate triage of hypovolemic and hypotensive patients. © 2021 American Physiological Society. Compr Physiol 11:1531-1574, 2021.

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.

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.

Hemorrhagic shock-induced cerebral bioenergetic imbalance is corrected by pharmacologic treatment with EF24 in a rat model

Maintenance of cerebral viability and function is an important goal of critical care in victims of injury due to ischemia and hypovolemia. As part of the multiple organ dysfunction syndrome, the brain function after trauma is influenced by the systemic inflammatory response. We investigated the effect of EF24, an anti-inflammatory bis-chalcone, on cerebral bioenergetics in a rat model of 45% hemorrhagic shock. The rats were treated with EF24 (0.4 mg/kg) or EF24 with an artificial oxygen carrier liposome-encapsulated hemoglobin (LEH). The volume of LEH administered was equal to the shed blood. The brain was collected after 6 h of shock for biochemical assays. EF24 treatment showed significant recovery of ATP, phosphocreatine, and NAD/NADH ratio. It also increased citrate synthase activity and cytochrome c oxidase subunit IV expression which were reduced in shock brain. Furthermore, it reduced the shock-induced accumulation of pyruvate and pyruvate dehydrogenase kinase-1 expression, suggesting that EF24 treatment improves cerebral energetics by restoring perturbed pyruvate metabolism in the mitochondria. These effects of EF24 were associated with reduced poly(ADP-ribose) polymerase cleavage and a significant improvement in the levels of nerve growth factor and brain-derived neurotrophic factor in shock brain. Co-administration of LEH with EF24 was only marginally more effective as compared to the treatment with EF24 alone. These results show that EF24 treatment sets up a pro-survival phenotype in shock by resurrecting cerebral bioenergetics. Since EF24 was effective in the absence of accompanying fluid resuscitation, it has potential utility as a pre-hospital pharmacotherapy in shock due to accidental blood loss.

Early treatment with lyophilized plasma protects the brain in a large animal model of combined traumatic brain injury and hemorrhagic shock

BACKGROUND

Combination of traumatic brain injury (TBI) and hemorrhagic shock (HS) can result in significant morbidity and mortality. We have previously shown that early administration of fresh frozen plasma (FFP) in a large animal model of TBI and HS reduces the size of the brain lesion as well as the associated edema. However, FFP is a perishable product that is not well suited for use in the austere prehospital settings. In this study, we tested whether a shelf-stable, low-volume, lyophilized plasma (LSP) product was as effective as FFP.

METHODS

Yorkshire swine (42-50 kg) were instrumented to measure hemodynamic parameters, intracranial pressure, and brain tissue oxygenation. A prototype, computerized, cortical impact device was used to create 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 induced (40-45% total blood volume) concurrent with the TBI. After 2 hours of shock, animals were treated with (1) normal saline (NS, n = 5), (2) FFP (n = 5), and (3) LSP (n = 5). The volume of FFP and LSP matched the shed blood volume, whereas NS was 3 times the volume. Six hours after resuscitation, brains were sectioned and stained with TTC (2, 3, 5-Triphenyltetrazolium chloride), and lesion size (mm) and swelling (percent change in volume compared with the contralateral, uninjured side) were measured.

RESULTS

This protocol resulted in a highly reproducible brain injury, with clinically relevant changes in blood pressure, cardiac output, tissue hypoperfusion, intracranial pressure, and brain tissue oxygenation. Compared with NS, treatment with LSP significantly (p < 0.05) decreased brain lesion size and swelling (51% and 54%, respectively).

CONCLUSION

In a clinically realistic combined TBI + HS model, early administration of plasma products decreases brain lesion size and edema. LSP is as effective as FFP, while offering many logistic advantages.

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.

Adenocaine and Mg(2+) reduce fluid requirement to maintain hypotensive resuscitation and improve cardiac and renal function in a porcine model of severe hemorrhagic shock*

OBJECTIVES

Hypotensive resuscitation is gaining clinical acceptance in the treatment of hemorrhagic shock. Our aims were to investigate: 1) the effect of 7.5% NaCl with adenocaine (adenosine and lidocaine, AL) and AL with Mg (ALM) on fluid requirement to maintain a minimum mean arterial pressure of 50 mm Hg, and 2) the effect of a second bolus of 0.9% NaCl with AL during return of shed blood on cardiac and renal function in a porcine model of hemorrhagic shock.

DESIGN

Pigs were randomized to: Sham (n = 5), Sham + ALM/AL (n = 5), hemorrhage control (n = 11), or hemorrhage + ALM/AL (n = 9). Hemorrhage animals were bled to a mean arterial pressure of 35 mm Hg. After 90 mins, pigs were fluid resuscitated with Ringers acetate and 20 mL 7.5% NaCl with ALM to maintain a target mean arterial pressure of minimum 50 mm Hg. Shed blood and 0.9% NaCl with AL were infused 30 mins later. Hemorrhage control group was subjected to the same protocol but without ALM/AL. Hemodynamics, cardiodynamics (pressure-volume analysis), oxygen consumption, and kidney function were measured for 6 hrs.

SETTING

University hospital laboratory.

SUBJECTS

Female farm-bred pigs.

RESULTS

Fluid volume infused during hypotensive resuscitation was 40% less in the 7.5% NaCl-/ALM-treated pigs than controls (25 vs. 41 mL/kg, p < .05). ALM was associated with a significant increase in dp/dtmax, end-systolic blood pressure, and systemic vascular resistance. Return of shed blood and 0.9% NaCl/AL reduced whole body oxygen consumption by 27% (p < .05), and significantly improved the end-systolic pressure-volume relationship and preload recruitable stroke work compared to controls. Glomerular filtration rate in the ALM/AL group returned to 83% of baseline compared to 54% in controls (p = .01).

CONCLUSION

Resuscitation with 7.5% NaCl ALM increases cardiac function and reduces fluid requirements during hypotensive resuscitation, whereas a second AL infusion during blood resuscitation transiently reduces whole body oxygen consumption and improves cardiac and renal function.

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.

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.

Low-Volume Resuscitation for Severe Intraoperative Hemorrhage: A Step in the Right Direction

The impact on outcomes resulting from crystalloids used with hemostatic close ratio resuscitation (HCRR) in intraoperative hemorrhage (IOH) has not been analyzed. We hypothesize a survival advantage in patients with IOH managed with a low-volume resuscitation (LVR) protocol during HCRR. A 4-year case-control study was conducted to determine the impact on mortality of LVR versus conventional resuscitation efforts (CRE) during HCRR. A total of 45 patients managed with a HCRR + LVR protocol (combination Hextend® and 3% hypertonic saline) and 55 historical cohorts managed with HCRR + CRE (lactated Ringer's) were included. Patient demographics, number of intraoperative units of packed red blood cells (PRBCs) and fresh-frozen plasma (FFP) received, and FFP:PRBC ratio were similar between groups. The mean intraoperative fluid volume was 0.76 L in the HCRR + LVR group versus 4.7 L in the HCRR + CRE group ( P = 0.003). In a linear regression model HCRR + LVR versus HCRR + CRE, mean trauma intensive care unit length of stay was ± versus 11 days ( P = 0.009); 30-day overall mortality was 11.1 versus 32.7 per cent ( P = 0.009); perioperative mortality was 2.2 to 10.9 per cent ( P = 0.13); and intensive care unit mortality 8.8 to 21.8 per cent ( P = 0.07). LVR protocol conveyed a survival benefit to patients undergoing HCRR (odds ratio for mortality, 0.07 [95% confidence interval 0.07–0.54]). This is the first civilian study to analyze the impact of LVR in patients managed with HCRR during IOH. Patients with IOH managed with HCRR and a predefined LVR protocol with Hextend® and 3 per cent hypertonic saline had an overall survival advantage and shorter trauma intensive care unit length of stay. LVR can be an effective alternative to CRE when used in combination with HCRR in patients with IOH.

A high-throughput screening assay of ascorbate in brain samples

Ascorbate is a vital reductant/free radical scavenger in the CNS, whose content defines - to a large extent - the redox status and the antioxidant reserves. Quick, reliable and specific methods for its measurement in brain samples are highly desirable. We have developed a new high-throughput screening assay for measurements of ascorbate using a fluorescence plate-reader. This assay is based on a direct reaction of ascorbate with a nitroxide radical conjugated with a fluorogenic acridine moiety, 4-((9-acridinecarbonyl)-amino)-2,2,6,6-tetramethylpiperidine-1-oxyl radical (AC-TEMPO), yielding fluorescent hydroxylamine product (AC-TEMPO-H). The reaction was monitored over time using fluorescence and electron spin resonance techniques. The appearance of fluorescent AC-TEMPO-H was linear within the range of 3.75-75μM AscH(-) in the sample (0.5-10μM AscH(-) in the well). Assay was validated with high performance liquid chromatography method. The concentration of ascorbate in murine tissue samples, including brain samples after traumatic brain injury and hemorrhagic shock, was measured.

Nucleoside transport inhibitor, dipyridamole, induced myocardial protection following hemorrhagic shock in ex vivo perfused rat hearts

INTRODUCTION

Successful protection against post-resuscitation myocardial injury is not available for trauma patients. Whereas intensive improvement in resuscitation strategies reduce myocardial injury, death among trauma patients are among the highest in the world due to myocardial dysfunction and multiple organ failure. Dipyridamole is a nucleoside transport inhibitor. Recent studies have shown that elevation of serum adenosine caused by dipyridamole improve cardiac function. The purpose of the present study was to examine the myocardial protective effects of dipyridamole therapy following 1 h of hemorrhagic shock.

METHODS

Sprague-Dawley rats were used. The study consisted of three phases: Phase I to examine the direct effects of dipyridamole on myocardial function by perfusion of the isolated hearts with Krebs Henseleit buffer (KHB) + dipyridamole on the Langendorff apparatus. Phase II examined the protective effects of dipyridamole following 60 min of hemorrhagic shock (HS) by ex vivo treatment with dipyridimole 20 μg/L for 5 min followed by resuscitation with KHB for 55 min. Phase III: 60 min HS followed by in vivo treatment by injecting 1 ml of (20 μg/L) dipyridamole intra-arterially, and resuscitation for 30 min. Myocardial protection was assessed by measuring left ventricular generated pressure (LVGP) and end diastolic pressures (LVEDP).

RESULTS

During ex vivo resuscitation, hearts from dipyridamole treated animals had significantly higher LVGP, and significantly lower LVEDP versus controls.

CONCLUSION

Dipyridamole therapy produces protection against post-resuscitation myocardial injury in rats.

First report on safety and efficacy of hetastarch solution for initial fluid resuscitation at a level 1 trauma center

BACKGROUND

For logistics, the US Army recommends Hextend (Hospira; 6% hetastarch in buffered electrolyte, HET) for battlefield resuscitation. To support this practice, there are laboratory data, but none in humans. To test the hypothesis that HET is safe and effective in trauma, we reviewed our first 6 months of use at a civilian level 1 trauma center.

STUDY DESIGN

From June 2008 to December 2008, trauma patients received standard of care (SOC) +/- 500 to 1,000 mL of HET within 2 hours of admission at surgeon discretion. Each case was reviewed, with waiver of consent.

RESULTS

There were 1,714 admissions; 805 received HET and 909 did not. With HET versus SOC, overall mortality was 5.2% versus 8.9% (p = 0.0035) by univariate analysis. Results were similar after penetrating injury only (p = 0.0016) and in those with severe injury, defined by Glasgow Coma Scale <9 (p = 0.0013) or Injury Severity Score >26 (p = 0.0142). After HET, more patients required ICU admission (40.9% vs. 34.5%; p = 0.0334) and transfusions of blood (34.4% vs. 20.2%; p = 0.0014) or plasma (20.7% vs. 12.2%; p = 0.0251), but there were no treatment-related differences in prothrombin time or partial thromboplastin time. The 24-hour urine outputs and requirements for blood, plasma, and other fluids were similar. However, increased early deaths with SOC implicate possible selection bias. If that factor was controlled for with multivariate analysis, the same trends were present, but the apparent treatment effects of HET were no longer statistically significant.

CONCLUSIONS

In the first trial to date in hemodynamically unstable trauma patients, and the largest trial to date in any population of surgical patients, initial resuscitation with HET was associated with reduced mortality and no obvious coagulopathy. A randomized blinded trial is necessary before these results can be accepted with confidence.

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.

Animal models for trauma research: what are the options?

Even if trauma patients initially avoid death after trauma (due to massive blood volume loss, primary severe brain injury), they are still at risk for multiple organ failure. Thus, it is crucial to elucidate the underlying pathophysiological mechanisms of trauma/hemorrhagic shock and the immune response involved. As of now, many hemorrhagic shock/trauma studies have used various types of animal models. Despite a large number of results from these efforts, some authors have argued that animal model results are difficult to translate directly into the clinical scenario. This review summarizes the advantages and the disadvantages of using animal models in trauma/hemorrhagic shock studies and discusses the relevance of various animal studies to the clinical scenario.

Dissolving microneedles for transdermal drug delivery

Microfabrication technology has been adapted to produce micron-scale needles as a safer and painless alternative to hypodermic needle injection, especially for protein biotherapeutics and vaccines. This study presents a design that encapsulates molecules within microneedles that dissolve within the skin for bolus or sustained delivery and leave behind no biohazardous sharp medical waste. A fabrication process was developed based on casting a viscous aqueous solution during centrifugation to fill a micro-fabricated mold with biocompatible carboxymethylcellulose or amylopectin formulations. This process encapsulated sulforhodamine B, bovine serum albumin, and lysozyme; lysozyme was shown to retain full enzymatic activity after encapsulation and to remain 96% active after storage for 2 months at room temperature. Microneedles were also shown to be strong enough to insert into cadaver skin and then to dissolve within minutes. Bolus delivery was achieved by encapsulating molecules just within microneedle shafts. For the first time, sustained delivery over hours to days was achieved by encapsulating molecules within the microneedle backing, which served as a controlled release reservoir that delivered molecules by a combination of swelling the backing with interstitial fluid drawn out of the skin and molecule diffusion into the skin via channels formed by dissolved microneedles. We conclude that dissolving microneedles can be designed to gently encapsulate molecules, insert into skin, and enable bolus or sustained release delivery.

Cerebrovascular resuscitation after polytrauma and fluid restriction

BACKGROUND

There are few reproducible models of blast injury, so it is difficult to evaluate new or existing therapies. We developed a clinically relevant polytrauma model to test the hypothesis that cerebrovascular resuscitation is optimized when intravenous fluid is restricted.

STUDY DESIGN

Anesthetized swine (42+/-5 kg, n=35) received blasts to the head and bilateral chests with captive bolt guns, followed by hypoventilation (4 breaths/min; FiO(2)=0.21). After 30 minutes, resuscitation was divided into phases to simulate typical prehospital, emergency room, and ICU care. For 30 to 45 minutes, group 1, the control group (n=5), received 1L of normal saline (NS). For 45 to 120 minutes, additional NS was titrated to mean arterial pressure (MAP) > 60 mmHg. After 120 minutes, mannitol (1g/kg) and phenylephrine were administered to manage cerebral perfusion pressure (CPP) > 70 mmHg, plus additional NS was given to maintain central venous pressure (CVP) > 12 mmHg. In group 2 (n=5), MAP and CPP targets were the same, but the CVP target was>8 mmHg. Group 3 (n=5) received 1 L of NS followed only by CPP management. Group 4 (n=5) received Hextend (Abbott Laboratories), instead of NS, to the same MAP and CPP targets as group 2.

RESULTS

Polytrauma caused 13 deaths in the 35 animals. In survivors, at 30 minutes, MAP was 60 to 65 mmHg, heart rate was >100 beats/min, PaO(2) was < 50 mmHg, and lactate was>5 mmol/L. In two experiments, no fluid or pressor was administered; the tachycardia and hypotension persisted. The first liter of intravenous fluid partially corrected these variables, and also partially corrected mixed venous O(2), gastric and portal venous O(2), cardiac output, renal blood flow, and urine output. Additional NS (total of 36+/-1 mL/kg/h and 17+/-6 mL/kg/h, in groups 1 and 2, respectively) correlated with increased intracranial pressure to 38+/-4 mmHg (group 1) and 26+/-4 mmHg (group 2) versus 22+/-4 mmHg in group 3 (who received 5+/-1 mL/kg/h). CPP was maintained only after mannitol and phenylephrine. By 5 hours, brain tissue PO(2) was>20 mmHg in groups 1 and 2, but only 6+/-1 mmHg in group 3. In contrast, minimal Hextend (6+/-3 mL/kg/h) was needed; the corrections in MAP and CPP were immediate and sustained, intracranial pressure was lower (14+/-2 mmHg), and brain tissue PO(2) was> 20 mmHg. Neuropathologic changes were consistent with traumatic brain injury, but there were no statistically significant differences between groups.

CONCLUSIONS

After polytrauma and resuscitation to standard MAP and CPP targets with mannitol and pressor therapy, we concluded that intracranial hypertension was attenuated and brain oxygenation was maintained with intravenous fluid restriction; cerebrovascular resuscitation was optimized with Hextend versus NS; and longer term studies are needed to determine neuropathologic consequences.

Effects of arginine vasopressin during resuscitation from hemorrhagic hypotension after traumatic brain injury

OBJECTIVE

Two series of experiments were designed to evaluate whether early arginine vasopressin improves acute outcome following resuscitation from traumatic brain injury and severe hemorrhagic hypotension.

DESIGN

Prospective randomized, blinded animal study.

SETTING

University laboratory.

SUBJECTS

Thirty-three swine.

INTERVENTIONS

In series 1 (n = 19), after traumatic brain injury with hemorrhage and 12 mins of shock (mean arterial pressure approximately 20 mm Hg), survivors (n = 16) were initially resuscitated with 10 mL/kg crystalloid. After 30 mins, crystalloid and blood with either 0.1 unit x kg(-1) x hr(-1) arginine vasopressin or placebo was titrated to a mean arterial pressure target >or=60 mm Hg. After 90 mins, all received mannitol and the target was cerebral perfusion pressure >or=60 mm Hg. To test cerebrovascular function, 7.5% inhaled CO2 was administered periodically. In series 2 (n = 14), the identical protocol was followed except the shock period was 20 mins and survivors (n = 10) received a bolus of either arginine vasopressin (0.2 units/kg) or placebo during the initial fluid resuscitation.

MEASUREMENTS AND MAIN RESULTS

In series 1, by 300 mins after traumatic brain injury with arginine vasopressin (n = 8) vs. placebo (n = 8), the fluid and transfusion requirements were reduced (both p < .01), intracranial pressure was improved (11 +/- 1 vs. 23 +/- 2 mmHg; p < .0001), and the CO2-evoked intracranial pressure elevation was reduced (7 +/- 2 vs. 26 +/- 3 mm Hg, p < .001), suggesting improved compliance. In series 2, with arginine vasopressin vs. placebo, cerebral perfusion pressure was more rapidly corrected (p < .05). With arginine vasopressin, five of five animals survived 300 mins, whereas three of five placebo animals died. The survival time with placebo was 54 +/- 4 mins (p < .05 vs. arginine vasopressin).

CONCLUSIONS

Early supplemental arginine vasopressin rapidly corrected cerebral perfusion pressure, improved cerebrovascular compliance, and prevented circulatory collapse during fluid resuscitation of hemorrhagic shock after traumatic brain injury.

Changes in intracranial pressure, coagulation, and neurologic outcome after resuscitation from experimental traumatic brain injury with hetastarch

BACKGROUND

In a model of traumatic brain injury (TBI), 2 protocols compared changes in intracranial pressure (ICP), coagulation, and neurologic outcome after intravenous fluid (IVF) resuscitation with either Hextend (HEX, 6% hetastarch in lactated electrolyte injection) or standard of care, crystalloid plus mannitol (MAN).

METHODS

In the nonsurvivor protocol, swine (n = 28) received a fluid percussion TBI and hemorrhage (27 +/- 3 mL/kg). At 30 minutes, resuscitation began with lactated Ringer's (LR) or HEX. After 60 minutes, MAN (1 g/kg) or placebo was given plus supplemental IVF to maintain cerebral perfusion pressure (CPP) > or = 70 mm Hg for 240 minutes. Swine in the survivor group (n = 15) also underwent TBI and hemorrhage, and resuscitation with HEX was compared to that of normal saline (NS)+MAN. Neurologic outcome and coagulation were evaluated for 72 hours.

RESULTS

In the nonsurvivor protocol, HEX, LR+MAN, and HEX+MAN attenuated the time-related rise of ICP and prevented ICP >20 mm Hg versus LR alone (P < .05). HEX alone maintained CPP (relative to baseline) and decreased total IVF by 50% versus LR +/- MAN (P < .05). MAN had no additive effect with HEX. Coagulation, measured by thromboelastograph reaction time (R), was 11 +/- 1 and 9 +/- 1 minutes at baseline and after TBI (before randomization). At 240 minutes after HEX or LR+MAN, R was 6 +/- 1 or 7 +/- 2 minutes, which indicates a hypercoagulable state, but there was no difference between treatments. In the survivor protocol, ICP and CPP were similar with NS+MAN versus HEX, but IVF requirement was 161 +/- 20 versus 28 +/- 3 mL/kg (P < .05). Motor scores were higher on days 2 and 3 with HEX (P < .05). At 72 hours, R was 28 +/- 14 versus 26 +/- 6 minutes with NS+MAN versus HEX, which indicates a hypocoagulable state, but there was no difference between treatments.

CONCLUSIONS

Hextend as the sole resuscitation fluid after severe TBI reduces fluid requirement, obviates the need for mannitol, improves neurologic outcome, and has no adverse effect on the coagulation profile relative to the crystalloid plus mannitol standard of care.