Hypothermia and hemostasis in severe trauma: A new crossroads workshop report

Induced Moderate Hypothermia in Aortic Rupture With Retroperitoneal Bleeding: A Randomized Porcine Study

OBJECTIVE

Induced hypothermia improves outcome in aortic arch surgery, neonatal neurointensive care, and transplant surgery for example. In contrast, spontaneous hypothermia has been associated with worse outcomes in patients suffering from hemorrhagic shock, mostly explained by its adverse effects on the coagulation system. We investigated if induced hypothermia would impair short-term survival in experimental aortic rupture with retroperitoneal bleeding.

METHODS

Anesthetized pigs were randomized into 2 groups: hypothermia by peritoneal lavage of ice-cold Ringer's acetate and external cooling (n = 10) and normothermia (n = 10). Aortic rupture with retroperitoneal bleeding was induced by endovascular means creating a 6 mm hole in the retroperitoneal portion of abdominal aorta. Survival (primary outcome), hemodynamics, and arterial blood gases including lactate were collected and analyzed up to 180 min after aortic rupture.

RESULTS

The body temperature (mean ± standard deviation) in the hypothermic group was 31.5 ± 1.0 °C and 38.7 ± 0.4 °C in the normothermic group at the time for aortic rupture. Survival up to 180 min after the retroperitoneal bleeding was significantly higher in the hypothermic compared with the normothermic group (P = 0.023).

CONCLUSIONS

Induced hypothermia did not impair survival in this experimental retroperitoneal aortic bleeding model in anesthetized pigs. This finding may indicate a minor role for the coagulation system in this type of bleeding.

Microcirculatory effects of rewarming in experimental hemorrhagic shock

BACKGROUND

Rewarming is a recommended therapy during the resuscitation of hypothermic patients with hemorrhagic shock. In experimental models, however, it increases inflammatory response and mortality. Although microcirculation is potential target of inflammation, the microvascular effects of rewarming during the resuscitation of hemorrhagic shock have not been studied. Our goal was to assess the systemic and microcirculatory effects of an increase in core temperature (T°) during the retransfusion of hemorrhagic shock in sheep. Our hypothesis was that rewarming could hamper microcirculation.

METHODS

In anesthetized and mechanically ventilated sheep, we measured systemic, intestinal, and renal hemodynamics and oxygen transport. O₂ consumption (VO₂) and respiratory quotient were measured by indirect calorimetry. Cortical renal, intestinal villi and sublingual microcirculation were assessed by IDF-videomicroscopy. After basal measurements, hemorrhagic shock was induced and T° was reduced to ~33 °C. After 1 h of shock and hypothermia, blood was retransfused and Ringer lactate solution was administered to prevent arterial hypotension. In the control group (n = 12), T° was not modified, while in the intervention (rewarming) group, it was elevated ~3 °C. Measurements were repeated after 1 h.

RESULTS

During shock, both groups showed similar systemic and microvascular derangements. After retransfusion, VO₂ remained decreased compared to baseline in both groups, but was lower in the control compared to the rewarming group. Perfused vascular density has a similar behavior in both groups. Compared to baseline, it remained reduced in peritubular (control vs. rewarming group, 13.8 [8.7-17.5] vs. 15.7 [10.1-17.9] mm/mm², PNS) and villi capillaries (14.7 [13.6-16.8] vs. 16.3 [14.2-16.9] mm/mm², PNS), and normalized in sublingual mucosa (19.1 [16.0-20.3] vs. 16.6 [14.7-17.2] mm/mm², PNS).

CONCLUSIONS

This is the first experimental study assessing the effect of rewarming on systemic, regional, and microcirculatory perfusion in hypothermic hemorrhagic shock. We found that a 3 °C increase in T° neither improved nor impaired the microvascular alterations that persisted after retransfusion. In addition, sublingual mucosa was less susceptible to reperfusion injury than villi and renal microcirculation.

Implantable biomedical materials for treatment of bone infection

The treatment of bone infections has always been difficult. The emergence of drug-resistant bacteria has led to a steady decline in the effectiveness of antibiotics. It is also especially important to fight bacterial infections while repairing bone defects and cleaning up dead bacteria to prevent biofilm formation. The development of biomedical materials has provided us with a research direction to address this issue. We aimed to review the current literature, and have summarized multifunctional antimicrobial materials that have long-lasting antimicrobial capabilities that promote angiogenesis, bone production, or "killing and releasing." This review provides a comprehensive summary of the use of biomedical materials in the treatment of bone infections and a reference thereof, as well as encouragement to perform further research in this field.

Effects of Systemic Hypothermia on Microcirculation in Conditions of Hemodynamic Stability and in Hemorrhagic Shock

INTRODUCTION

Although hypothermia is independently associated with an increased mortality in trauma patients, it might be an effective therapeutic approach for otherwise lethal hemorrhage. The effect of hypothermia on microcirculation, however, has been poorly studied in this setting. Our goal was to characterize the effects of hypothermia on microcirculation in normal conditions and in severe hemorrhagic shock.

METHODS

In anesthetized and mechanically ventilated sheep, we measured cardiac output (CO), renal blood flow (RBF), and systemic and renal O2 consumption (VO2). Cortical renal, intestinal villi, and sublingual microcirculation was assessed by IDF-videomicroscopy. After basal measurements, sheep were assigned to hypothermia (n = 12) and normothermia (n = 12) groups. Central temperature was reduced to ∼34°C and maintained at baseline in each group, respectively. Measurements were repeated after 1 h of hemodynamic stable conditions and 1 h of severe hemorrhagic shock.

RESULTS

In conditions of hemodynamic stability, the hypothermia group showed lower CO, RBF, and systemic and renal VO2 than the normothermia group. Red blood cell velocity was also lower in renal, villi, and sublingual microvascular beds (836 ± 195 vs. 1,066 ± 162, 916 ± 105 vs. 1051 ± 41, and 970 ± 182 vs. 1,102 ± 49 μm/s, respectively; P < 0.0001 for all). In hemorrhagic shock, most of the microvascular variables were similarly compromised in both the groups. In hypo- and normothermia groups, the percentage of reduction in perfused vascular density was higher in renal than in intestinal and sublingual microcirculation (66 ± 31 vs. 31 ± 23 and 15 ± 15%, and 78 ± 26 vs. 32 ± 37 and 18 ± 21%, P < 0.01 for both).

CONCLUSIONS

This is the first experimental study assessing the effect of systemic hypothermia on microcirculation in severe hemorrhagic shock. The main finding was that hypothermia did not hamper additionally the microcirculatory derangements induced by hemorrhagic shock. In addition, renal microcirculation was more susceptible to hemorrhagic shock than villi and sublingual microcirculation.

The impact of hypothermia on outcomes in massively transfused patients

BACKGROUND

Hypothermia is associated with poor outcomes after injury. The relationship between hypothermia during contemporary large volume resuscitation and blood product consumption is unknown. We evaluated this association, and the predictive value of hypothermia on mortality.

METHODS

Patients predicted to receive massive transfusion at 12 level 1 trauma centers were randomized in the Pragmatic Randomized Optimal Platelet and Plasma Ratios (PROPPR) trial and were grouped into those who were hypothermic (<36°C) or normothermic (36-38.5°C) within the first 6 hours of emergency department arrival. The impact of hypothermia or normothermia on the volume of blood product required during the first 24 hours was determined via negative binomial regression, adjusting for treatment arm, injury severity score, mechanism, demographics, pre-emergency department fluid volume, blood administered before becoming hypothermic, pulse and systolic blood pressure on arrival, and the time exposed to hypothermic or normothermic temperatures.

RESULTS

Of 680 patients, 590 had a temperature measured during the first 6 hours in hospital, and 399 experienced hypothermia. The mean number of red blood cell (RBC) units given to all patients in the first 24 hours of admission was 8.8 (95% confidence interval [CI], 7.9-9.6). In multivariable analysis, every 1°C decrease in temperature below 36.0°C was associated with a 10% increase (incidence rate ratio, 0.90; 95% CI, 0.89-0.92; p < 0.00) in consumption of RBCs during the first 24 hours of admission. There was no association between RBC administration and a temperature above 36°C. Hypothermia on arrival was an independent predictor of mortality, with an adjusted odds ratio of 2.7 (95% CI, 1.7-4.5; p < 0.00) for 24-hour mortality and 1.8 (95% CI, 1.3-2.4; p < 0.00) for 30-day mortality.

CONCLUSION

Hypothermia is associated with increase in blood product consumption and mortality. These findings support the maintenance of normothermia in trauma patients and suggest that further investigation on the impact of cooling or rewarming during massive transfusion is warranted.

LEVEL OF EVIDENCE

Prognostic, level III.

Infusion of Cold Saline into the Carotid Artery Does Not Affect Outcome After Intrastriatal Hemorrhage

Localized brain hypothermia (HYPO) can be achieved by infusing cold saline into the carotid artery of animals and patients. Studies suggest that HYPO improves behavioral and histological outcomes in focal ischemia models. Given that ischemic stroke and intracerebral hemorrhage (ICH) share pathophysiological overlap, we tested whether cold saline infusion is safe and neuroprotective when given during collagenase-induced ICH. Eighty-five adult male Sprague-Dawley rats were used. Experiment 1 investigated brain and body temperature changes associated with a cold saline infusion paradigm that was scaled from patients according to brain weight and blood volume (3 mL/20-minute infusion). Experiment 2 determined whether HYPO aggravated bleeding volume. Experiment 3 investigated if cerebral edema or elemental concentrations were altered by HYPO. We also collected core body temperature and activity data through telemetry. Experiment 4 investigated whether behavioral outcomes (e.g., skilled reaching) and tissue loss were influenced by HYPO. Our HYPO protocol decreased the ipsilateral striatal temperature by ∼0.20°C (p < 0.001), with no other effects. HYPO did not affect hematoma volume (p = 0.64), cerebral edema (p = 0.34), or elemental concentrations (p = 0.49) at 24 hours post-ICH. Although ICH caused persistent behavioral impairments, HYPO did not improve behavioral outcomes (measured by a neurological deficit scale, cylinder, and the staircase test; p > 0.05 for all). Brain tissue loss was not different between groups on day 28 post-ICH (p = 0.90). Although cold saline infusion appears to be safe in the acute post-ICH period, there was no evidence that this therapy improved outcome. However, our treatment protocol was relatively mild and additional interventions might help improve efficacy. Finally, our findings may also speak to the safety of this cooling approach in focal ischemia where hemorrhagic transformation is a risk; future studies on this issue are needed.

Trauma care: Finding a better way

In a Perspective, Hasan Alam discusses emerging treatment approaches in trauma care.

Deep and profound hypothermia in haemorrhagic shock, friend or foe? A systematic review

INTRODUCTION

Survival in exsanguinating cardiac arrest patients is poor, as is neurological outcome in survivors. Hypothermia has traditionally been seen as harmful to trauma patients and associated with increased mortality; however, there has been speculation that cooling to very low temperatures (≤20°C) could be used to treat haemorrhagic trauma patients by the induction of a suspended animation period through extreme cooling, which improves survival and preserves neurological function. This has been termed emergency preservation and resuscitation (EPR).

METHODS

A systematic review of the literature was used to examine the evidence base behind the use of deep and profound hypothermia in haemorrhagic shock (HS). It included original research articles (human or animal) with cooling to ≤20°C after HS or an experimental model replicating it. Normovolaemic cardiac arrest, central nervous system injury and non-HS models were excluded.

RESULTS

Twenty articles using 456 animal subjects were included, in which 327 were cooled to ≤20°C. All studies describing good survival rates were possible using EPR and 19/20 demonstrated that EPR can preserve neurological function after prolonged periods of circulatory arrest or minimal circulatory flow. This additional period can be used for surgical intervention to arrest haemorrhage in HS that would otherwise be lethal.

CONCLUSIONS

The outcomes of this review have significant implications for application to human patients and the ongoing human clinical trial (EPR for Cardiac Arrest from Trauma). Current evidence suggests that hypothermia ≤20°C used in the form of EPR could be beneficial to the HS patient.

FAST ultrasound examination as a predictor of outcomes after resuscitative thoracotomy: a prospective evaluation

OBJECTIVE

The objective of this study was to examine the ability of Focused Assessment Using Sonography for Trauma (FAST) to discriminate between survivors and nonsurvivors undergoing resuscitative thoracotomy (RT).

BACKGROUND

RT is a high-risk, low-salvage procedure performed in arresting trauma patients with poorly defined indications.

METHODS

Patients undergoing RT from 10/2010 to 05/2014 were prospectively enrolled. A FAST examination including parasternal/subxiphoid cardiac views was performed before or concurrent with RT. The result was captured as adequate or inadequate with presence or absence of pericardial fluid and/or cardiac motion. A sensitivity analysis utilizing the primary outcome measure of survival to discharge or organ donation was performed.

RESULTS

Overall, 187 patients arrived in traumatic arrest and underwent FAST. Median age 31 (1-84), 84.5% male, 51.3% penetrating. Loss of vital signs occurred at the scene in 48.1%, en-route in 23.5%, and in the ED in 28.3%. Emergent left thoracotomy was performed in 77.5% and clamshell thoracotomy in 22.5%. Sustained cardiac activity was regained in 48.1%. However, overall survival was only 3.2%. An additional 1.6% progressed to organ donation. FAST was inadequate in 3.7%, 28.9% demonstrated cardiac motion and 8.6% pericardial fluid. Cardiac motion on FAST was 100% sensitive and 73.7% specific for the identification of survivors and organ donors.

CONCLUSIONS

With a high degree of sensitivity for the detection of potential survivors after traumatic arrest, FAST represents an effective method of separating those that do not warrant the risk and resource burden of RT from those who may survive. The likelihood of survival if pericardial fluid and cardiac motion were both absent was zero.

Induced hypothermia during resuscitation from hemorrhagic shock attenuates microvascular inflammation in the rat mesenteric microcirculation

Microvascular inflammation occurs during resuscitation following hemorrhagic shock, causing multiple organ dysfunction and mortality. Preclinical evidence suggests that hypothermia may have some benefit in selected patients by decreasing this inflammation, but this effect has not been extensively studied. Intravital microscopy was used to visualize mesenteric venules of anesthetized rats in real time to evaluate leukocyte adherence and mast cell degranulation. Animals were randomly allocated to normotensive or hypotensive groups and further subdivided into hypothermic and normothermic resuscitation (n = 6 per group). Animals in the shock groups underwent mean arterial blood pressure reduction to 40 to 45 mmHg for 1 h via blood withdrawal. During the first 2 h following resuscitation by infusion of shed blood plus double that volume of normal saline, rectal temperature of the hypothermic groups was maintained at 32°C to 34°C, whereas the normothermic groups were maintained between 36°C to 38°C. The hypothermic group was then rewarmed for the final 2 h of resuscitation. Leukocyte adherence was significantly lower after 2 h of hypothermic resuscitation compared with normothermic resuscitation: (2.8 ± 0.8 vs. 8.3 ± 1.3 adherent leukocytes, P = 0.004). Following rewarming, leukocyte adherence remained significantly different between hypothermic and normothermic shock groups: (4.7 ± 1.2 vs. 9.5 ± 1.6 adherent leukocytes, P = 0.038). Mast cell degranulation index (MDI) was significantly decreased in the hypothermic (1.02 ± 0.04 MDI) versus normothermic (1.22 ± 0.07 MDI) shock groups (P = 0.038) after the experiment. Induced hypothermia during resuscitation following hemorrhagic shock attenuates microvascular inflammation in rat mesentery. Furthermore, this decrease in inflammation is carried over after rewarming takes place.

Hypothermia and valproic acid activate prosurvival pathways after hemorrhage

BACKGROUND

Therapeutic hypothermia (hypo) and valproic acid (VPA, a histone deacetylase inhibitor) have independently been shown to be protective in models of trauma and hemorrhagic shock but require logistically challenging doses to be effective. Theoretically, combined treatment may further enhance effectiveness, allowing us to use lower doses of each modality. The aim of this study was to determine whether a combination of mild hypo and VPA treatments would offer better cytoprotection compared with that of individual treatments in a hemorrhage model.

MATERIALS AND METHODS

Male Sprague-Dawley rats were subjected to 40% volume-controlled hemorrhage, kept in shock for 30 min, and assigned to one of the following treatment groups: normothermia (36°C-37°C), hypo (30 ± 2°C), normothermia + VPA (300 mg/kg), and hypo + VPA (n = 5 per group). After 3 h of observation, the animals were sacrificed, liver tissue was harvested and subjected to whole cell lysis, and levels of key proteins in the prosurvival Akt pathway were measured using Western blot.

RESULTS

Activation of the proapoptotic protein cleaved caspase-3 was significantly lower in the combined treatment group relative to normothermia (P < 0.05). Levels of the prosurvival Bcl-2 was significantly higher in the combined treatment group relative to sham, normothermia, and normothermia + VPA groups (P < 0.005). The downstream prosurvival protein phospho-GSK-3β was significantly higher in the sham, hypo, and combined treatment groups compared with that in normothermia groups with or without VPA (P < 0.05). Levels of the prosurvival β-catenin were significantly higher in the combined treatment group relative to normothermia (P < 0.01).

CONCLUSIONS

This is the first in vivo study to demonstrate that combined treatment with VPA and hypo offers better cytoprotection than these treatments given independently.

Development of a novel neuroprotective strategy: combined treatment with hypothermia and valproic acid improves survival in hypoxic hippocampal cells

BACKGROUND

Therapeutic hypothermia and histone deacetylase inhibitors, such as valproic acid (VPA), independently have been shown to have neuroprotective properties in models of cerebral ischemic and traumatic brain injury. However, the depth of hypothermia and the dose of VPA needed to achieve the desired result are logistically challenging. It remains unknown whether these two promising strategies can be combined to yield synergistic results. We designed an experiment to answer this question by subjecting hippocampal-derived HT22 cells to severe hypoxia in vitro.

METHODS

Mouse hippocampal HT22 cells were exposed to 200 μM cobalt chloride (CoCl(2)), which created hypoxic conditions in vitro. Cells were incubated for 6 or 30 hours under the following conditions: (1) Dulbecco's Modified Eagle Medium; (2) 200 μM CoCl(2); (3) 200 μM CoCl(2) plus 1 mmol/L VPA; (4) 200 μM CoCl(2) plus 32°C hypothermia; and (5) 200 μM CoCl(2) plus both 1 mmol/L VPA and 32°C hypothermia. Cellular viability was evaluated by (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) and lactate dehydrogenase release assays at 30 hours after treatment. Levels of acetylated histone H3, hypoxia-inducible factor-1α, phospho-GSK-3β, β-catenin, and high-mobility group box-1 were measured by Western blotting.

RESULTS

High levels of acetylated histone H3 were detected in the VPA-treated cells. The release of lactate dehydrogenase was greatly suppressed after the combined hypothermia + VPA treatment (0.269 ± 0.003) versus VPA (0.836 ± 0.026) or hypothermia (0.451 ± 0.005) treatments alone (n = 3, P = .0001). (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) assay showed that the number of viable cells was increased by 17.6 % when VPA and hypothermia were used in combination (n = 5, P = .0001). Hypoxia-inducible factor-1α and phospho-GSK-3β expression were synergistically affected by the combination treatment, whereas high-mobility group box-1 was increased by VPA treatment, and inhibited by the hypothermia.

CONCLUSION

This is the first study to demonstrate that the neuroprotective effects of VPA and hypothermia are synergistic. This novel approach can be used to develop more effective therapies for the prevention of neuronal death.

Thrombin generation and fibrin clot formation under hypothermic conditions: an in vitro evaluation of tissue factor initiated whole blood coagulation

BACKGROUND

Despite trauma-induced hypothermic coagulopathy being familiar in the clinical setting, empirical experimentation concerning this phenomenon is lacking. In this study, we investigated the effects of hypothermia on thrombin generation, clot formation, and global hemostatic functions in an in vitro environment using a whole blood model and thromboelastography, which can recapitulate hypothermia.

METHODS

Blood was collected from healthy individuals through venipuncture and treated with corn trypsin inhibitor, to block the contact pathway. Coagulation was initiated with 5pM tissue factor at temperatures 37°C, 32°C, and 27°C. Reactions were quenched over time, with soluble and insoluble components analyzed for thrombin generation, fibrinogen consumption, factor (f)XIII activation, and fibrin deposition. Global coagulation potential was evaluated through thromboelastography.

RESULTS

Data showed that thrombin generation in samples at 37°C and 32°C had comparable rates, whereas 27°C had a much lower rate (39.2 ± 1.1 and 43 ± 2.4 nM/min vs 28.6 ± 4.4 nM/min, respectively). Fibrinogen consumption and fXIII activation were highest at 37°C, followed by 32°C and 27°C. Fibrin formation as seen through clot weights also followed this trend. Thromboelastography data showed that clot formation was fastest in samples at 37°C and lowest at 27°C. Maximum clot strength was similar for each temperature. Also, percent lysis of clots was highest at 37°C followed by 32°C and then 27°C.

CONCLUSIONS

Induced hypothermic conditions directly affect the rate of thrombin generation and clot formation, whereas global clot stability remains intact.

Minimising blood loss in early trauma resuscitation

Worldwide, trauma is responsible for more than 10,000 deaths each day with hundreds of thousands seriously injured. Current trauma resuscitation strategies are based on supporting haemostasis, maintaining circulating volume and rapidly identifying sites of blood loss. Approaches include hypotensive/hypovolaemic resuscitation, avoidance of colloids and crystalloids, early blood product based resuscitation, early imaging to identify sites of blood loss and damage control surgery. In this paper, we focus on ways to minimise blood loss and preserve the circulating volume. These include minimal movement of the patient, splinting fractures, use of tourniquets, application of local haemostatic dressings/agents, keeping the patient warm and giving tranexamic acid to improve clot strength. The recent CRASH-2 trial provided unequivocal evidence that tranexamic acid reduces mortality in bleeding trauma patients. This will be discussed in detail. When employed as part of a package of care in a well-rehearsed trauma system, these interventions to preserve the remaining circulating volume have the potential to save lives and allow patients to survive until timely definitive haemostasis can occur.

Potential role of therapeutic hypothermia in the salvage of traumatic hemorrhagic shock

Although therapeutic hypothermia could serve as a potential therapeutic strategy for treatment of traumatic hemorrhagic shock, significant controversy exists regarding its safety and feasibility. The current resuscitation strategy in traumatic hemorrhagic shock may also require updating. In this article, we have carried out an extensive literature search in this field and propose an initial algorithm for use of therapeutic hypothermia in traumatic hemorrhagic shock. This work lays essential groundwork for future investigations in this field.

Damage control resuscitation from major haemorrhage in polytrauma

Trauma is a global disease that affects patients across the socio-economic spectrum. Uncontrolled major haemorrhage occurs from both blunt and penetrating trauma which may lead to hypovolaemic shock and ultimately death. In polytrauma patients that require urgent resuscitation secondary to major haemorrhage, high volume fluid infusions followed by definitive surgical care have been superseded by damage control resuscitation. DCR is a systematic approach to major trauma that integrates the principles of haemostatic resuscitation, permissive hypotension and damage control surgery (DCS). The aim of DCR is to aggressively minimise hypovolaemic shock and limit the development of coagulopathy, hypothermia and acidosis known as the lethal triad. Besides increased volumes of scientific knowledge to underpin modern trauma resuscitation techniques upon, patient survival is also dependent upon effective teamwork and leadership. In conclusion, successful resuscitation from major haemorrhage depends upon a variety of factors distilled into a trauma team with effective leadership, excellent technical and non-technical team skills as well as the early initiation of DCR.