Pressure-controlled Hemorrhagic Shock Research Articles

The pulse pressure/heart rate ratio as a marker of stroke volume changes during hemorrhagic shock and resuscitation in anesthetized swine

Emergency physicians and anesthesiologists need accurate estimates of stroke volume when massive unexpected hemorrhage occurs. Using an animal model of hemorrhagic shock under general anesthesia, we hypothesized that the pulse pressure-heart rate ratio (PP/HR) would be an accurate marker of stroke volume changes during hemorrhage and resuscitation. In 16 swine under bispectral index-controlled, intravenous propofol-remifentanil anesthesia, pressure-controlled hemorrhagic shock was induced to achieve 30 mm Hg of mean arterial pressure, after which treatment was randomized to fluid (HES, n = 4), norepinephrine (NE, n = 4), both (HES + NE, n = 4), or neither (control, n = 4). Pulmonary artery thermodilution continuous cardiac output, stroke volume, and central arterial pressures were recorded at baseline (T0), after 30 minutes (T30) and 60 (T60) minutes of hemorrhage, during treatment (T90 and T120) and after blood retransfusion (T180). At T60, blood withdrawal was 995 (301) mL (38 [8] mL/kg), resulting in a 70% decrease in stroke volume and a 3.3-fold decrease in PP/HR (each p < 0.01). When stroke volume data pointed at T0, T30 and T60 were plotted against the various hemodynamic variables under study, the PP/HR ratio exhibited the strongest relationship to stroke volume (r = 0.72). The area under the receiver operating characteristic curve set to detect a 15% stroke volume decrease was larger for PP/HR (0.95 [0.94-0.97]) than for mean arterial pressure (0.91 [0.89-0.93]) (p < 0.013). During resuscitation in the HES and NE groups, correlation coefficients were significantly higher between stroke volume and PP/HR (0.75 [0.63-0.84] and 0.79 [0.67-0.86]) than between stroke volume and mean arterial pressure (0.52 [0.32-0.67], p = 0.042, and 0.49 [0.28-0.65], p = 0.0018, respectively). The PP/HR ratio was strongly related to stroke volume during hemorrhagic shock and resuscitation in anesthetized swine.

The effect of hydrogen on hemorrhagic shock induced acute lung injury in rats

To investigate the effect of hydrogen inhalation on acute lung injury after hemorrhagic shock in rats. Twenty-four adult male Sprague-Dawley (SD) rats were equally randomized into three groups: sham operation group, model group and hydrogen-treatment group. Pressure-controlled hemorrhagic shock and resuscitation model was reproduced by blood-letting for 1 hour followed by fluid replacement for 2 hours. The rats in model group received a mixture of 50% oxygen-50% nitrogen during the process. The rats in hydrogen-treatment group received inhalation of a mixture of 2% hydrogen-48% nitrogen-50% oxygen 10 minutes before fluid replacement till the end of resuscitation. The arterial blood samples were collected for the measurement of arterial partial pressure of oxygen (PaO₂) before exsanguination, 1 hour after shock, 1 hour and 2 hours after fluid replacement. Blood and lung tissues were collected at the end of experiment, and tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) levels in plasma, lung wet/dry weight ratio (W/D), malondialdehyde (MDA) content, superoxide dismutase (SOD) and myeloperoxidase (MPO) activity in the lung tissue were determined. The lung tissue was subjected to pathological examination. At the end of fluid replacement, compared with model group, hydrogen could significantly reduce pulmonary edema (lung W/D ratio: 4.72 ± 0.12 vs. 4.94 ± 0.14, P<0.05), inhibit oxidative stress (MDA: 0.55 ± 0.09 nmol/mg vs. 0.72 ± 0.08 nmol/mg, P<0.05), enhance antioxidant activity (SOD activity: 79.53 ± 14.33 U/mg vs. 59.55 ± 9.07 U/mg, P<0.05), reduce the release of pro-inflammatory cytokines (TNF-α: 55.58 ± 10.06 ng/L vs. 66.58 ± 5.17 ng/L; IL-6: 23.00 ± 2.77 ng/L vs. 27.09 ± 2.46 ng/L, both P<0.05) and inhibit neutrophil infiltration (MPO: 1.05 ± 0.18 U/g vs. 1.40 ± 0.14 U/g, P<0.05). It alleviated the damage to lung tissue, and then improved the lung function (PaO₂: 146.3 ± 22.1 mm Hg vs. 123.6 ± 16.0 mm Hg, P<0.05). Hydrogen treatment can alleviate acute lung injury as a result of hemorrhagic shock and resuscitation.

Effect of Hyperoxia on Resuscitation of Experimental Combined Traumatic Brain Injury and Hemorrhagic Shock in Mice

Hypotension and hypoxemia worsen traumatic brain injury outcomes. Hyperoxic resuscitation is controversial. The authors proposed that hyperoxia would improve hemodynamics and neuronal survival by augmenting oxygen delivery despite increased oxidative stress and neuroinflammation in experimental combined controlled cortical impact plus hemorrhagic shock in mice. Adult C57BL6 mice received controlled cortical impact followed by 35 min of hemorrhagic shock (mean arterial pressure, 25-27 mmHg). The resuscitation phase consisted of lactated Ringer's boluses titrated to mean arterial pressure greater than 70 mmHg. Definitive care included returning shed blood. Either oxygen or room air was administered during the resuscitation phases. Brain tissue levels of oxidative stress and inflammatory markers were measured at 24 h and hippocampal neuronal survival was quantified at 7 days. Hyperoxia markedly increased brain tissue oxygen tension approximately four- to fivefold (n = 8) and reduced resuscitation fluid requirements approximately 15% (n = 53; both P < 0.05). Systemic and cerebral physiologic variables were not significantly affected by hyperoxia. Hippocampal neuron survival was approximately 40% greater with oxygen versus room air (n = 18, P = 0.03). However, ascorbate depletion doubled with oxygen versus room air (n = 11, P < 0.05). Brain tissue cytokines and chemokines were increased approximately 2- to 20-fold (n = 10) after combined controlled cortical impact injury plus hemorrhagic shock, whereas hyperoxia shifted cytokines toward a proinflammatory profile. Hyperoxic resuscitation of cortical impact plus hemorrhagic shock reduced fluid requirements and increased brain tissue oxygen tension and hippocampal neuronal survival but exacerbated ascorbate depletion and neuroinflammation. The benefits of enhanced oxygen delivery during resuscitation of traumatic brain injury may outweigh detrimental increases in oxidative stress and neuroinflammation.

MALP-2 pre-treatment modulates systemic inflammation in hemorrhagic shock

BackgroundTLR-2 is expressed on the surface of leucocytes, lung and liver tissue and initiates the activation of immune response after interaction with components of the bacterial cell wall. In this experiment we investigated whether immunostimulation with TLR-2 agonists under conditions of sterile inflammation (hemorrhagic shock (HS)) may affect the immune response and remote organ inflammation.MethodsMale C57/BL6 mice were subjected to standardized pressure-controlled HS (MAP of 35 mmHg for 90 minutes). The TLR-2 agonist macrophage-activated lipopeptide-2 (MALP-2) was administered (i.p.) either 12 hours prior to the induction of HS (Group MALP PT) or after the hypotensive period (90 minutes) (Group MALP T). After six hours, plasma cytokine levels (IL-6, KC, IL-10, and MCP-1) and lung and liver MPO activity were assessed.ResultsPre-treatment with MALP-2 resulted in a significant attenuation of the systemic pro-inflammatory (IL-6) response (MALP PT: 0.83±0.2 ng/ml vs. MALP T: 1.7±0.09 ng/ml) (p<0.05). In comparison to the liver MPO activity, lung MPO levels in in group MALP PT did not show differences to levels measured in MALP T mice (1.200±200 ng/mg vs. 1.800±200 ng/mg).ConclusionsAfter initial inflammation, MALP-2 pre-treatment was associated with attenuated systemic immune response after sterile stimulus. The TLR-2 agonist appears to affect sterile inflammation pathways. The exact mechanisms should be studied further to better understand these affects.

A Combined Trauma Model of Chest and Abdominal Trauma With Hemorrhagic Shock—Description of a New Porcine Model

Despite the high incidence and prognostic relevance of hemorrhagic shock and abdominal and blunt chest trauma in multiply injured patients, there are no animal models combining these injuries. Therefore, we established a new porcine multiple trauma model consisting of blunt chest trauma, penetrating abdominal trauma (two incisions in the right upper liver lobe using a four-edged scalpel and subsequent liver packing), and pressure-controlled hemorrhagic shock with a mean arterial pressure of 30 ± 5 mmHg (a maximum of 45% of the total blood volume). The combined traumatic insult led to severe signs of hemorrhagic shock and impaired pulmonary function. In conclusion, a consistent, reproducible, and clinically relevant porcine model of multisystem injury with controlled (pressure-controlled blood withdrawal) and uncontrolled components of hemorrhage (liver laceration) with the potential for rebleeding was established.

Modeling Traumatic-Hemorrhagic Shock—Nothing Is Simple and Easy

Modeling Traumatic-Hemorrhagic Shock—Nothing Is Simple and Easy

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Introduction: Hemorrhagic shock causes global ischemia-reperfusion injury and contributes morbidity and mortality. Hypothesis: The inhibition of mitochondrial permeability transition pore (mPTP) opening during ischemia-reperfusion can ameliorate injuries in the specific organs. We investigated the effects of cyclosporine A on hemodynamics and survival in hemorrhagic shock. Methods: Male Sprague-Dawley rats were subjected to pressure-controlled hemorrhagic shock (mean arterial pressure = 38 ± 1mmHg) for 90minutes. After hemorrhagic shock period, rats were randomly allocated to one of three groups (control group, n=7; CsA10 group, n=7; CsA50 group, n=5). Cyclosporine A (10 mg/kg for CsA10 group; 50 mg/kg for CsA50 group) or vehicle (normal saline) were administered via tail vein for 10 minutes and shed blood were transfused for 15 minutes. Survival time and blood pressure were observed until death and compared among groups. Results: Survival times were significantly longer in CsA groups than in control group (Median survival time was 283.5 minutes in control group, 365 minutes in CsA10 group, and 720 minutes in CsA50 group; log-rank test p=0.0121 for control vs. CsA10, p=0.0011 for CsA10 vs. CsA50). MAP during the reperfusion and observation period was significantly higher in CsA groups than in normal saline group. Conclusions: Cyclosporine A increased MAP dose-dependently during resuscitation period and consequently increased survival time.

Models of hemorrhagic shock: Differences in the physiological and inflammatory response

IntroductionThe hemorrhagic shock (HS) model is commonly used to initiate a systemic post-traumatic inflammatory response. Numerous experimental protocols exist and it is unclear how differences in these models affect the immune response making it difficult to compare results between studies. The aim of this study was to compare the inflammatory response of different established protocols for volume-controlled shock in a murine model. MethodsMale C57/BL6 mice 6–10weeks and weighing 20–25g were subjected to volume-controlled or pressure-controlled hemorrhagic shock. In the volume-controlled group 300μl, 500μl, or 700μl blood was collected over 15min and mean arterial pressure was continuously monitored during the period of shock. In the pressure-controlled hemorrhagic shock group, blood volume was depleted with a goal mean arterial pressure of 35mmHg for 90min. Following hemorrhage, mice from all groups were resuscitated with the extracted blood and an equal volume of lactated ringer solution. Six hours from the initiation of hemorrhagic shock, serum IL-6, KC, MCP-1 and MPO activity within the lung and liver tissue were assessed. ResultsIn the volume-controlled group, the mice were able to compensate the initial blood loss within 30min. Approximately 800μl of blood volume was removed to achieve a MAP of 35mmHg (p<0.001). No difference in the pro-inflammatory cytokine (IL-6 and KC) profile was measured between the volume-controlled groups (300μl, 500μl, or 700μl). The pressure-controlled group demonstrated significantly higher cytokine levels (IL-6 and KC) than all volume-controlled groups. Pulmonary MPO activity increased with the severity of the HS (p<0.05). This relationship could not be observed in the liver. ConclusionVolume-controlled hemorrhagic shock performed following current literature recommendations may be insufficient to produce a profound post-traumatic inflammatory response. A decrease in the MAP following blood withdrawal (300μl, 500μl or 700μl) was usually compensated within 30min. Pressure-controlled hemorrhagic shock is a more reliable for induction of a systemic inflammatory response.

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.

Hypothermia reduces resuscitation fluid volumes required to maintain blood pressure in a rat hemorrhagic shock model

To examine the hypothesis that resuscitative hypothermia would (1) reduce fluid requirements and reactive oxygen species production during a period of resuscitation and (2) improve survival after hemorrhagic shock (HS) in rats. Sixteen rats underwent an HS phase (phase I: 0-75 minutes), with pressure-controlled HS at a mean arterial pressure of 30 mm Hg ± 5 mm Hg; a resuscitation phase (phase II: 75-150 minutes), with fluid resuscitation to maintain mean arterial pressure ≥75 mm Hg; and an observation phase (phase III: from 150 minutes to 72 hours). During phase II, eight rats were randomized into a normothermia group (group 1: 38°C) or a hypothermia group (group 2: 34°C). Fluid requirements during phase II and survival at 72 hours were compared between groups. Plasma levels of Vitamin E and %coenzyme Q9 (%CoQ9) were also assessed. The fluid requirement during resuscitation in phase II was 8.2 ± 1.4 mL/100 g in group 1 versus 2.1 mL/100 g ± 0.7 mL/100 g in group 2 (p < 0.01). Vitamin E level decreased to 10.8 μmol/L ± 1.8 μmol/L during HS in all rats. After resuscitation, it was restored to a baseline level of 15.9 μmol/L ± 3.1 μmol/L in group 2 but remained at 10.2 μmol/L ± 0.8 μmol/L in group 1 (p < 0.05). %CoQ9 did not differ significantly between the groups. At 72 hours, six of eight rats in group 1, and all rats in group 2 survived (NS). In a rat HS model, hypothermia during resuscitation from HS reduces resuscitation fluid volume required to maintain blood pressure and restores Vitamin E to the baseline level, and appears to have no adverse impact on long survival after HS.

Inhalative IL-10 Attenuates Pulmonary Inflammation following Hemorrhagic Shock without Major Alterations of the Systemic Inflammatory Response

Several studies report immunomodulatory effects of endogenous IL-10 after trauma. The present study investigates the effect of inhalative IL-10 administration on systemic and pulmonary inflammation in hemorrhagic shock. Male C57/BL6 mice (8 animals per group) were subjected to pressure-controlled hemorrhagic shock for 1.5 hrs followed by resuscitation and inhalative administration of either 50 μL PBS (Shock group) or 50 μg/kg recombinant mouse IL-10 dissolved in 50 μL PBS (Shock + IL-10 group). Animals were sacrificed after 4.5 hrs of recovery and serum IL-6, IL-10, KC, and MCP-1 concentrations were measured with ELISA kits. Acute pulmonary inflammation was assessed by pulmonary myeloperoxidase (MPO) activity and pulmonary H&E histopathology. Inhalative IL-10 administration decreased pulmonary inflammation without altering the systemic concentrations of IL-6, IL-10, and KC. Serum MCP-1 levels were significantly reduced following inhalative IL-10 administration. These findings suggest that inhalative IL-10 administration may modulate the pulmonary microenvironment without major alterations of the systemic inflammatory response, thus minimizing the potential susceptibility to infection and sepsis.

Pressure-controlled hemorrhagic shock in mice: a new model of acute kidney injury

At the present time, mice models have failed to reproduce human acute kidney injury (AKI) and new relevant models of AKI are required [1]. In this study we developed a model of AKI in mice based on pressure-controlled hemorrhagic shock that closely reproduces hypotension involved in most of human ischemic AKI.

Indução anestésica após o tratamento do choque hemorrágico: estudo experimental comparando a cetamina e o etomidato

Bleeding causing hemorrhagic shock usually requires surgical treatment under general anesthesia. Anesthetic drugs may further compromise hemodynamics. The objective was to compare the hemodynamic effects of ketamine and etomidate during anesthetic induction in dogs submitted to an experimental model of hemorrhagic shock and resuscitation.Thirty-two mongrel dogs were submitted to a pressure-controlled hemorrhagic shock, resuscitation and anesthetic induction model. After achieving the target pressure of 40 mmHg, they were randomly assigned in two groups according to the resuscitation fluid to be used: NaCl 0.9% (32 mL.kg-1) and NaCl 7.5% (4 mL.kg-1). After volume infusion, these groups were reassigned according to anesthetic drug used: GI) NaCl 0.9% and ketamine; GII) NaCl 7.5% and ketamine; GIII) NaCl 0.9% and etomidate; and GIV) NaCl 7.5% and etomidate. Hemodynamic measurements were obtained at five moments: (M0) baseline; (M1) after bleeding to shock; (M2) after volume expansion; (M3) 5 minutes after anesthetic induction; (M4) 15 minutes after anesthetic induction. Statistical analysis was performed using Student t test and two way ANOVA. Value of p lower than 0.05, was considered significant.After shock, both solutions restored hemodynamics to baseline values. Independently of anesthetic agent or expansion solution used, mean arterial pressure remained unaltered for all groups after induction. Central venous pressure, heart rate, pulmonary capillary wedge pressure and pulmonary vascular resistance index increased significantly after ketamine infusion. Cardiac index, systemic vascular resistance index and oxygen transport variables remained stable in all groups.Etomidate or ketamine were able to maintain hemodynamic stability in dogs undergoing severe hemorrhagic shock treated with NaCl 0.9% or NaCl 7.5%.

Titrated hypertonic/hyperoncotic solution for hypotensive fluid resuscitation during uncontrolled hemorrhagic shock in rats

Background: In volume- or pressure-controlled hemorrhagic shock (HS) a bolus intravenous infusion of hypertonic/hyperoncotic solution (HHS) proved beneficial compared to isotonic crystalloid solutions. During uncontrolled HS in animals, however, HHS by bolus increased blood pressure unpredictably, and increased blood loss and mortality. We hypothesized that a titrated i.v. infusion of HHS, compared to titrated lactated Ringer's solution (LR), for hypotensive fluid resuscitation during uncontrolled HS reduces fluid requirement, does not increase blood loss, and improves survival. Methods: We used our three-phased uncontrolled HS outcome model in rats. HS phase I began with blood withdrawal of 3 ml/100 g over 15 min, followed by tail amputation. Then, hydroxyethyl starch 10% in NaCl 7.2% was given i.v. to the HHS group ( n = 10) and LR to the control group ( n = 10), both titrated to prevent mean arterial pressure (MAP) from falling below 40 mmHg during HS time 20–90 min. At HS 90 min, resuscitation phase II of 180 min began with hemostasis, return of all the blood initially shed, plus fluids i.v. as needed to maintain normotension (MAP ≥ 70 mmHg). Liver dysoxia was monitored as increase in liver surface pCO 2 during phases I and II. Observation phase III was to 72 h. Results: During HS, preventing a decrease in MAP below 40 mmHg required HHS 4.9 ± 0.6 ml/kg (all data mean ± S.E.M.), compared to LR 62.2 ± 16.6 ml/kg ( P < 0.001), with no group difference in MAP. Uncontrolled blood loss during HS from the tail stump was 13.3 ± 1.9 ml/kg with HHS infusion, versus 12.6 ± 2.5 ml/kg with LR infusion ( P = 0.73). Serum sodium concentrations were moderately elevated at the end of HS in the HHS group (149 ± 3 mmol/l) versus the LR group (139 ± 1 mmol/l) ( P = 0.001), and remained elevated throughout. Liver pCO 2 increased during HS in both groups equally ( P < 0.001 versus baseline), and tended to return to baseline levels at the end of HS. Blood gas and lactate values throughout did not differ between groups. During HS, 2 of 10 rats in the HHS group versus 0 of 10 in the LR group died ( P = 0.47). There was no difference between HHS and LR groups in survival rates to 72 h (3 of 10 in the HHS group versus 2 of 10 in the LR group) ( P = 1.0). Survival times, by life table analysis, were not different ( P = 0.75). Conclusion: In prolonged uncontrolled HS, a titrated i.v. infusion of HHS can maintain controlled hypotension with only one-tenth of the volume of LR required, without increasing blood loss. This titrated HHS strategy may not increase the chance of long-term survival.

Regional heterogeneity of cerebral blood flow response to graded pressure-controlled hemorrhage.

Little is known about the regional distribution of cerebral blood flow (CBF) in nonanesthetized animals during periods of lowered blood pressure. The present investigation addresses the specific reaction patterns of local cerebral blood flow (LCBF) in comparison with mean CBF during graded pressure-controlled hemorrhagic shock in conscious rats. Conscious rats were subjected to graded pressure-controlled hemorrhage (to 85, 70, 55, or 40 mm Hg) by arterial blood withdrawal. After a period of 30 minutes, blood pressure was stabilized by withdrawal or reinfusion of blood. LCBF was determined autoradiographically by the iodo(14C)antipyrine method in 34 brain structures, and mean CBF was calculated and compared with the values of nonhemorrhaged control animals. Mean CBF remained unchanged except for the group with the lowest blood pressure of 40 mm Hg (decrease in CBF of 28%). Otherwise, LCBF was increased in some brain structures at an unchanged mean CBF. Congruently, at 40 mm Hg, the decrease in mean CBF did not show up in all brain structures, the local pattern of CBF varying between an unchanged and a profoundly decreased CBF. The mean coefficient of variation of CBF was increased with the severity of hemorrhagic shock, which indicates an enhanced heterogeneity of CBF. Because of the substantial heterogeneity in the responses of LCBF to pressure-controlled hemorrhage, autoregulation of CBF during pressure-controlled hemorrhagic shock has to be reconsidered on a regional basis.

Endogenous central histamine-induced reversal of critical hemorrhagic hypotension in rats: studies with L-histidine.

Activation of the histaminergic system is characteristic of response to the action of adverse or potentially dangerous stimuli that disturb circulatory homeostasis, such as dehydration and changes in blood pressure. Previous study demonstrates that inhibition of histamine N-methyltransferase, which catabolizes histamine released from neurons, leads to the increase in endogenous central histamine concentrations and to the reversal of critical hemorrhagic hypotension. In the present study, the influence of intraperitoneal loading with histamine precursor L-histidine on central cardiovascular regulation was studied in a model of irreversible pressure-controlled hemorrhagic shock. Experiments were carried out in male Wistar rats anesthetized with ketamine/xylazine subjected to critical hemorrhagic hypotension of 20 to 25 mmHg, which resulted in the death of all control saline-treated animals within 30 min. L-histidine administered in 5 min of critical hypotension produced dose-dependent increases in mean arterial pressure and heart rate (100-500 mg/kg), and a 100% survival rate of 2 h (500 mg/kg), whereas in normotensive animals, it did not influence cardiovascular parameters. The resuscitating effect of L-histidine (500 mg/kg) was associated with increases in histamine concentrations in the cerebral cortex (0.97 +/- 0.11 nmol/g of wet tissue vs. 0.67 +/- 0.22 nmol/g of wet tissue; P<0.05), hypothalamus (4.78 +/- 0.58 nmol/g of wet tissue vs. 4.08 +/- 0.43 nmol/g of wet tissue; P<0.01), and medulla oblongata (0.55 +/- 0.18 nmol/g of wet tissue vs. 0.34 +/- 0.09 nmol/g of wet tissue; P<0.05), as well as with no changes in plasma histamine concentrations in comparison with the saline-treated group 20 min after injection. Pretreatment with (S)-alpha-fluoromethylhistidine (alpha-FMH, 0.5 mg intracerebroventricularly), an irreversible inhibitor of L-histidine decarboxylase, produced a decrease in central histamine concentrations and diminished volumes of blood required to achieve critical hypotension. Moreover, alpha-FMH inhibited L-histidine-induced increases in central histamine concentrations and its resuscitating effect. In conclusion, the increase in central histamine concentrations after loading with L-histidine in rats subjected to critical hemorrhagic hypovolemia leads to the reversal of hypotension and the improvement in the survival rate of 2 h. On the other hand, inhibition of L-histidine decarboxylase activity, and thus histamine synthesis, produces a decrease in hemodynamic stability in hypotension, which suggests the histaminergic system-induced activation of compensatory mechanisms in hemorrhagic shock.

Differential fluid regulation during and after soft tissue trauma and hemorrhagic shock in males and proestrus females.

Gender differences in immune and organ functions have been described in different rodent models of trauma- and pressure-controlled hemorrhagic shock. We hypothesized that gender influences the regulation of plasma and tissue fluids in rats under such conditions. To study this we used male and weight matched proestrus female Sprague-Dawley rats, which were assigned to three groups (n = 7/group): sham, maximal bleedout (trauma and 45 min of blood pressure at 35 mmHg without resuscitation), or 5 h after completion of trauma-hemorrhage and resuscitation. Trauma-hemorrhage involved midline laparotomy and approx. 90 min of hemorrhagic shock (35 mmHg), followed by fluid resuscitation (4x the shed blood volume with Ringers lactate). (51)Cr-EDTA, (125)I-albumin distribution, and wet weight/dry weight were used to calculate plasma volume and extracellular fluid volume and cellular water content. Proestrus female rats showed significantly higher plasma volumes compared with weight-matched males. The volume of blood withdrawn in the first 15 min of hemorrhagic shock was significantly less in proestrus females compared with males; however, there was no significant difference in the total shed blood volume. Moreover, proestrus females showed less interstitial edema formation compared with male rats at 5 h after resuscitation. We conclude that differences in the regulation of plasma and tissue volumes exist between males and proestrus females during and after trauma-hemorrhage. The increased circulating blood volume could contribute the improved immune and organ functions in proestrus females under those conditions.

Mild hypothermia increases survival from severe pressure-controlled hemorrhagic shock in rats.

In previous studies, mild hypothermia (34 degrees C) during uncontrolled hemorrhagic shock (HS) increased survival. Hypothermia also increased mean arterial pressure (MAP), which may have contributed to its beneficial effect. We hypothesized that hypothermia would improve survival in a pressure-controlled HS model and that prolonged hypothermia would further improve survival. Thirty rats were prepared under light nitrous oxide/halothane anesthesia with spontaneous breathing. The rats underwent HS with an initial blood withdrawal of 2 mL/100 g over 10 minutes and pressure-controlled HS at a MAP of 40 mm Hg over 90 minutes (without anticoagulation), followed by return of shed blood and additional lactated Ringer's solution to achieve normotension. Hemodynamic monitoring and anesthesia were continued to 1 hour, temperature control to 12 hours, and observation without anesthesia to 72 hours. After HS of 15 minutes, 10 rats each were randomized to group 1, with normothermia (38 degrees C) throughout; group 2, with brief mild hypothermia (34 degrees C during HS 15-90 minutes plus 30 minutes after reperfusion); and group 3, with prolonged mild hypothermia (same as group 2, then 35 degrees C [possible without shivering] from 30 minutes after reperfusion to 12 hours). MAP during HS and initial resuscitation was the same in all three groups, but was higher in the hypothermia groups 2 and 3, compared with the normothermia group 1, at 45 and 60 minutes after reperfusion. Group 1 required less blood withdrawal to maintain MAP 40 mm Hg during HS and more lactated Ringer's solution for resuscitation. At end of HS, lactate levels were higher in group 1 than in groups 2 and 3 (p < 0.02). Temperatures were according to protocol. Survival to 72 hours was achieved in group 1 by 3 of 10 rats, in group 2 by 7 of 10 rats (p = 0.18 vs. group 1), and in group 3 by 9 of 10 rats (p = 0.02 vs. group 1, p = 0.58 vs. group 2). Survival time was longer in group 2 (p = 0.09) and group 3 (p = 0.007) compared with group 1. Brief hypothermia had physiologic benefit and a trend toward improved survival. Prolonged mild hypothermia significantly increased survival after severe HS even with controlled MAP. Extending the duration of hypothermia beyond the acute phases of shock and resuscitation may be needed to ensure improved outcome after prolonged HS.

Effect of mesenteric ischemia and reperfusion or hemorrhagic shock on intestinal mucosal permeability and ATP content in rats.

In a reductionist in vitro system, intestinal epithelial permeability appears to be dependent on cellular ATP content. In order to extend these prior observations, we used rat models of mesenteric ischemia/reperfusion (I/R) and pressure-controlled hemorrhagic shock to test the hypothesis that intestinal barrier function is directly proportional to tissue ATP content. I/R was induced by clamping the mesenteric vessels for 60 min followed by 60 min of reperfusion. Normal, ischemic, and reperfused ileal segments were prepared from each rat (n = 12). Hemorrhagic shock was induced by bleeding rats (n = 9) to a mean arterial pressure of 30 mmHg and maintaining this pressure for 4 h by infusing Ringer's lactate solution as necessary. Ileal segments were harvested before induction of hemorrhage and at 1 h intervals thereafter. Everted gut sacs were prepared to measure the mucosal-to-serosal passage of fluorescein-conjugated dextran (FD4; M.W. = 4 kDa). Tissue ATP levels were determined using a luciferase assay. FD4 clearance rates were plotted as a function of tissue ATP content. Linear regression analyses showed a strong inverse relationship between intestinal permeability and tissue ATP level in rats subjected to I/R (r2 = 0.78; P < 0.001) or hemorrhage (r2 = 0.82; P < 0.001). These data support the idea that ATP content is a determinant of intestinal epithelial barrier function in vivo.