Effects of fluid resuscitation on mesenteric microvascular blood flow and lymphatic activity after severe hemorrhagic shock in rats

Ringer's lactate solution enhances the inflammatory response during fluid resuscitation of experimentally induced haemorrhagic shock in rats

INTRODUCTION

Hemorrhagic shock leads to systemic oxygen deficit (hypoxaemia) that results in systemic inflammatory response syndrome (SIRS), a recognised cause of late mortality in this case. The aim of this study was to analyse the impact of fluid resuscitation, using two Ringer solutions, on the microcirculation changes that take place during experimentally induced haemorrhagic shock.

MATERIAL AND METHODS

A model of the rat cremaster muscle was used to assess microcirculation in vivo. The experimental groups (n = 10 each) included: control (CTRL); shock (HSG); Ringer's acetate (RAG); and Ringer's lactate (RLG). Microhaemodynamic parameters were measured during the experiment.

RESULTS

A statistically significantly higher level of leukocytes, both those attached to the endothelium and those located in the extravascular space (p < 0.05), was reported in the lactate Ringer (LR) group compared with the AR group. There were significant differences in the activity of A3 arterioles compared with A1 and A2 arterioles. Ringer's lactate solution seemed to the inflammation response during fluid resuscitation from haemorrhagic shock. A3 arterioles are likely to play a role as a pre-capillary sphincter in the skeletal muscle.

CONCLUSIONS

The present study revealed that fluid resuscitation with Ringer's lactate solution exacerbates inflammation in the skeletal muscle. It is worth noting that Ringer's acetate solution reduces local inflammation and could therefore be recommended as the "first line" crystalloid of the fluid resuscitation during haemorrhagic shock.

Hemorrhagic Shock and the Microvasculature

The microvasculature plays a central role in the pathophysiology of hemorrhagic shock and is also involved in arguably all therapeutic attempts to reverse or minimize the adverse consequences of shock. Microvascular studies specific to hemorrhagic shock were reviewed and broadly grouped depending on whether data were obtained on animal or human subjects. Dedicated sections were assigned to microcirculatory changes in specific organs, and major categories of pathophysiological alterations and mechanisms such as oxygen distribution, ischemia, inflammation, glycocalyx changes, vasomotion, endothelial dysfunction, and coagulopathy as well as biomarkers and some therapeutic strategies. Innovative experimental methods were also reviewed for quantitative microcirculatory assessment as it pertains to changes during hemorrhagic shock. The text and figures include representative quantitative microvascular data obtained in various organs and tissues such as skin, muscle, lung, liver, brain, heart, kidney, pancreas, intestines, and mesentery from various species including mice, rats, hamsters, sheep, swine, bats, and humans. Based on reviewed findings, a new integrative conceptual model is presented that includes about 100 systemic and local factors linked to microvessels in hemorrhagic shock. The combination of systemic measures with the understanding of these processes at the microvascular level is fundamental to further develop targeted and personalized interventions that will reduce tissue injury, organ dysfunction, and ultimately mortality due to hemorrhagic shock. Published 2018. Compr Physiol 8:61-101, 2018.

The effect of pPolyHb on hemodynamic stability and mesenteric microcirculation in a rat model of hemorrhagic shock

The effects of polymerized porcine hemoglobin (pPolyHb) on hemodynamic stability and maintenance of mesenteric microvascular function were explored in a rat model of hemorrhagic shock (HS). Following controlled hemorrhage, rats were infused with equal volumes of either pPolyHb, hetastarch (HES), or red blood cell (RBC). The results showed that pPolyHb was superior to HES and RBC in restoring hemodynamic stability and reversing anaerobic metabolism. We observed a reduction in the diameter of mesenteric microvasculature after HS. Resuscitation with pPolyHb and RBC was able to restore the diameters of the venules and arterioles, whereas HES failed to restore the diameters during the observation period.

Microcirculatory perfusion shows wide inter-individual variation and is important in determining shock reversal during resuscitation in a porcine experimental model of complex traumatic hemorrhagic shock

Background

Traumatic hemorrhagic shock (THS) is a leading cause of preventable death following severe traumatic injury. Resuscitation of THS is typically targeted at blood pressure, but the effects of such a strategy on systemic and microcirculatory flow remains unclear. Failure to restore microcirculatory perfusion has been shown to lead to poor outcomes in experimental and clinical studies. Systemic and microcirculatory variables were examined in a porcine model of complex THS, in order to investigate inter-individual variations in flow and the effect of microcirculatory perfusion on reversal of the shock state.

Methods

Baseline standard microcirculatory variables were obtained for 22 large white pigs using sublingual incident dark field (IDF) video-microscopy. All animals were subjected to a standardised hind-limb injury followed by a controlled haemorrhage of approximately 35 % of blood volume (shock phase). This was followed by 60 min of fluid resuscitation with either 0.9 % saline or component blood products and a target SBP of 80 mmHg (early resuscitation phase). All animals were then given blood products to a target SBP of 110 mmHg for 120 min (mid-resuscitation phase), and a further 100 min (late resuscitation phase). IDF readings were obtained at the midpoint of each of these phases. Cardiac output was measured using a pulmonary artery catheter. Animals were divided into above average (A) and below average (B) perfused vessel density (PVD) groups based on the lowest recorded PVD measurement taken during the shock and early resuscitation phases.

Results

There was minimal inter-individual variation in blood pressure but wide variation of both systemic and microcirculatory flow variables during resuscitation. During shock and early resuscitation, group A (n = 10) had a mean PVD of 10.5 (SD ± 2.5) mm/mm² and group B (n = 12) 5.5 (SD ± 4.1) mm/mm². During the later resuscitation phases, group A maintained a significantly higher PVD than group B. Group A initially had a higher cardiac output, but the difference between the groups narrowed as resuscitation progressed. At the end of resuscitation, group A had significantly lower plasma lactate, higher lactate clearance, lower standard base deficit and smaller mixed venous-arterial CO₂ gradient. There was no significant difference in blood pressure between the two groups at any stage.

Conclusion

There was a wide variation in both macro- and microcirculatory flow variables in this pressure-targeted experimental model of THS resuscitation. Early changes in microvascular perfusion appear to be key determinants in the reversal of the shock state during resuscitation. Microcirculatory flow parameters may be more reliable markers of physiological insult than pressure-based parameters and are potential targets for goal-directed resuscitation.

Electronic supplementary material

The online version of this article (doi:10.1186/s40635-016-0088-z) contains supplementary material, which is available to authorized users.

Comparison of 3% and 7.5% Hypertonic Saline in Resuscitation After Traumatic Hypovolemic Shock

Hypertonic saline solutions (HSSs) (7.5%) are useful in the resuscitation of patients with hypovolemic shock because they provide immediate intravascular volume expansion via the delivery of a small volume of fluid, improving cardiac function. However, the effects of using 3% HSS in hypovolemic shock resuscitation are not well known. This study was designed to compare the effects of and complications associated with 3% HSS, 7.5% HSS, and standard fluid in resuscitation. In total, 294 severe trauma patients were enrolled from December 2008 to February 2012 and subjected to a double-blind randomized clinical trial. Individual patients were treated with 3% HSS (250 mL), 7.5% HSS (250 mL), or lactated Ringer's solution (LRS) (250 mL). Mean arterial pressure, blood pressure, and heart rate were monitored and recorded before fluid infusion and at 10, 30, 45, and 60 min after infusion, and the incidence of complications and survival rate were analyzed. The results indicate that 3% and 7.5% HSSs rapidly restored mean arterial pressure and led to the requirement of an approximately 50% lower total fluid volume compared with the LRS group (P < 0.001). However, a single bolus of 7.5% HSS resulted in an increase in heart rate (mean of 127 beats/min) at 10 min after the start of resuscitation. Higher rates of arrhythmia and hypernatremia were noted in the 7.5% HSS group, whereas higher risks of renal failure (P< 0.001), coagulopathy (P < 0.001), and pulmonary edema (P < 0.001) were observed in the LRS group. Neither severe electrolyte disturbance nor anaphylaxis was observed in the HSS groups. It is notable that 3% HSS had similar effects on resuscitation because both the 7.5% HSS and LRS groups but resulted in a lower occurrence of complications. This study demonstrates the efficacy and safety of 3% HSS in the resuscitation of patients with hypovolemic shock.

Plasma colloid osmotic pressure is an early indicator of injury and hemorrhagic shock

OBJECTIVE

Hemorrhagic shock is the leading cause of traumatic deaths; many could be potentially prevented with appropriate resuscitation. However, to initiate resuscitation, one must identify patients with hemorrhagic shock early. In this article, we determined the associations between plasma colloid osmotic pressure (COP) and clinical outcomes in severely injured trauma patients.

METHODS

Plasma samples were collected from 104 trauma patients upon admission to the emergency department and 10 healthy volunteers to serve as control subjects. Plasma osmolality, COP, and serum protein were measured and correlated to clinical data. Thrombelastography and impedance aggregometry were performed to assess coagulopathy. Commercial enzyme-linked immunosorbent assays were used to quantify syndecan 1.

RESULTS

Plasma COP was significantly reduced in trauma patients compared to control subjects 17.7 ± 2.6 vs. 20.7 ± 2.1 mmHg (P < 0.05) and strongly correlated to serum protein values (R = 0.7). We divided our cohort into low (COP ≤16.5 mmHg) and normal (COP >16.5 mmHg) subgroups, illustrating significantly higher Injury Severity Score scores in patients with low COP (21 vs. 10, P = 0.007), despite no differences in vital signs. Patients with low COP received more red blood cells, plasma, and platelets (4 vs. 0 total units, P = 0.0005) within 24 h of admission. Syndecan 1 levels were significantly higher (184 vs. 52 ng/mL, P = 0.027) in patients with low COP.

CONCLUSIONS

Reduced plasma COP and serum protein in trauma patients are indicative of injury severity. In the absence of significant alterations in vital signs, plasma COP levels were associated with increased requirements for blood products and increased syndecan 1 shedding. We believe that plasma COP provides new insight in guiding resuscitation.

Systematic review of randomized clinical trials on the use of hydroxyethyl starch for fluid management in sepsis

Background

Patients with sepsis typically require large resuscitation volumes, but the optimal type of fluid remains unclear. The aim of this systematic review was to evaluate current evidence on the effectiveness and safety of hydroxyethyl starch for fluid management in sepsis.

Methods

Computer searches of MEDLINE, EMBASE and the Cochrane Library were performed using search terms that included hydroxyethyl starch; hetastarch; shock, septic; sepsis; randomized controlled trials; and random allocation. Additional methods were examination of reference lists and hand searching. Randomized clinical trials comparing hydroxyethyl starch with other fluids in patients with sepsis were selected. Data were extracted on numbers of patients randomized, specific indication, fluid regimen, follow-up, endpoints, hydroxyethyl starch volume infused and duration of administration, and major study findings.

Results

Twelve randomized trials involving a total of 1062 patients were included. Ten trials (83%) were acute studies with observation periods of 5 days or less, most frequently assessing cardiorespiratory and hemodynamic variables. Two trials were designed as outcome studies with follow-up for 34 and 90 days, respectively. Hydroxyethyl starch increased the incidence of acute renal failure compared both with gelatin (odds ratio, 2.57; 95% confidence interval, 1.13–5.83) and crystalloid (odds ratio, 1.81; 95% confidence interval, 1.22–2.71). In the largest and most recent trial a trend was observed toward increased overall mortality among hydroxyethyl starch recipients (odds ratio, 1.35; 95% confidence interval, 0.94–1.95), and mortality was higher (p < 0.001) in patients receiving > 22 mL·kg^-1 hydroxyethyl starch per day than lower doses.

Conclusion

Hydroxyethyl starch increases the risk of acute renal failure among patients with sepsis and may also reduce the probability of survival. While the evidence reviewed cannot necessarily be applied to other clinical indications, hydroxyethyl starch should be avoided in sepsis.

Osmolality- and Na+-dependent effects of hyperosmotic NaCl solution on contractile activity and Ca2+ cycling in rat ventricular myocytes

Hypertonic NaCl solutions have been used for small-volume resuscitation from hypovolemic shock. We sought to identify osmolality- and Na(+)-dependent components of the effects of the hyperosmotic NaCl solution (85 mOsm/kg increment) on contraction and cytosolic Ca(2+) concentration ([Ca(2+)](i)) in isolated rat ventricular myocytes. The biphasic change in contraction and Ca(2+) transient amplitude (decrease followed by recovery) was accompanied by qualitatively similar changes in sarcoplasmic reticulum (SR) Ca(2+) content and fractional release and was mimicked by isosmotic, equimolar increase in extracellular [Na(+)] ([Na(+)](o)). Raising osmolality with sucrose, however, augmented systolic [Ca(2+)](i) monotonically without change in SR parameters and markedly decreased contraction amplitude and diastolic cell length. Functional SR inhibition with thapsigargin abolished hyperosmolality effects on [Ca(2+)](i). After 15-min perfusion, both hyperosmotic solutions slowed mechanical relaxation during twitches and [Ca(2+)](i) decline during caffeine-evoked transients, raised diastolic and systolic [Ca(2+)](i), and depressed systolic contractile activity. These effects were greater with sucrose solution, and were not observed after isosmotic [Na(+)](o) increase. We conclude that under the present experimental conditions, transmembrane Na(+) redistribution apparently plays an important role in determining changes in SR Ca(2+) mobilization, which markedly affect contractile response to hyperosmotic NaCl solutions and attenuate the osmotically induced depression of contractile activity.

Pleural liquid during hemorrhagic hypotension

The effect of approximately 25% or 35% blood loss (b.l.) on volume, pressure, and protein concentration of pleural liquid has been determined in anesthetized rabbits in lateral or supine posture. Volume and pressure of pleural liquid did not change with 25% b.l. 30 and 60 min after beginning of hemorrhage, and with 35% b.l. at 30 min (bleeding time approximately 10 and 12 min, respectively). With 35% b.l. protein concentration of pleural liquid was 85% greater (P<0.01) than control; moreover, percent albumin was smaller (P<0.05), and percent globulin greater (P<0.05) than control. Decrease in arterial plasma protein concentration, hematocrit, and pH after hemorrhage fit literature data. Ventilation at 15 and 30 min increased (P<0.01) by 16% and 23%, respectively, with 25% b.l., but it did not change with 35% b.l., a condition borderline to survival in anesthetized rabbits without ad hoc treatment. Pleural liquid seems protected against derangements from hemorrhage up to 25% b.l. for periods shorter than 1 h.

Can albumin administration relieve lung injury in trauma/hemorrhagic shock?

AIM: To study the effect of albumin administration on lung injury in trauma/hemorrhagic shock (T/HS).

METHODS: Sixty experimental animals were randomly divided into three groups: rats undergoing laparotomy without shock (T/SS); rats with T/HS and resuscitation with blood plus twice the volume of shed blood as Ringer’s lactate (RL), and rats with T/HS and resuscitation with blood plus additional 3 mL of 50 g/L human albumin. Expression of polymorphonuclear neutrophil (PMN) CD11b/CD18, intercellular adhesion molecule-1 (ICAM-1) of jugular vein blood and the severity of lung injuries [determined mainly by measuring activity of lung tissue myeloperoxidase (MPO) and lung injury score (LIS)] were measured after a 3-h recovery period.

RESULTS: All three groups showed a significant difference in the expressions of CD11b/CD18, ICAM-1, and severity of lung injury. The expressions of CD11b/CD18 in T/SS group, T/HS + RL group, T/HS + albumin group were 17.76% ± 2.11%, 31.25% ± 3.48%, 20.36% ± 3.21%, respectively (F = 6.25, P < 0.05). The expressions of ICAM-1 (U/mL) in T/SS group, T/HS + RL group, T/HS + albumin group were 258.76 ± 98.23, 356.23 ± 65.6, 301.01 ± 63.21, respectively (F = 5.86, P < 0.05). The expressions of MPO (U/g) in T/SS group, T/HS + RL group, T/HS + albumin group were 2.53 ± 0.11, 4.63 ± 1.31, 4.26 ± 1.12, respectively (F = 6.26, P < 0.05). Moreover, LIS in T/HS + RL group, T/HS + albumin group was 2.62 ± 0.23, 1.25 ± 0.24, respectively. The expressions of CD11b/CD18, ICAM-1 and MPO in T/HS + RL group were significantly increased compared to T/SS group (P = 0.025, P = 0.036, P = 0.028, respectively). However, administration of 3 mL of 50 g/L albumin significantly down-regulated the expressions of CD11b/CD18, ICAM-1 and lung injury index (MPO and LIS) when compared with the T/HS + RL rats (P = 0.035, P = 0.046, P = 0.038, P = 0.012, respectively).

CONCLUSION: The infusion of albumin during resuscitation period can protect lung from injury and decrease the expressions of CD11b/CD18, ICAM-1 in T/HS rats.

CEREBROVASCULAR DYSFUNCTION IS AN ATTRACTIVE TARGET FOR THERAPY IN HEAT STROKE¶

1. The aim of the present review is to summarize clinical observations and results of animal models that advance the knowledge of the attenuation of cerebrovascular dysfunction in the setting of heat stroke. It is a narrative review of selected published literature from Medline over the period 1959-2005. 2. All heat-stressed rodents, even under general anaesthesia, have hyperthermia, systemic inflammation, hypercoagulable state, arterial hypotension and tissue ischaemia and injury in multiple organs. These findings demonstrate that rodent heat stroke models can nearly mirror the full spectrum of human heat stroke. Experimental heat stroke fulfills the empirical triad used for the diagnosis of classical human heat stroke, namely hyperthermia, central nervous system alterations and a history of heat stress. 3. These physiological dysfunctions and survival during heat stroke can be improved by whole-body or brain cooling therapy adopted immediately after the onset of heat stroke. 4. However, in the absence of body or brain cooling, these heat stroke reactions can still be reduced by the following measures: (i) fluid replacement with 3% NaCl solution, 10% human albumin or hydroxyethyl starch; (ii) intravenous delivery of anti-inflammatory drugs, free radical scavengers or interleukin-1 receptor antagonists; (iii) hyperbaric oxygen therapy; or (iv) transplantation of human umbilical cord blood cells. 5. In addition, before initiation of heat stress, prior manipulations with one of the following measures was found to be able to protect against heat stroke reactions: (i) systemic delivery of alpha-tocopherol, mannitol, inducible nitric oxide synthase inhibitors, mu-opioid receptor antagonists, endothelin ETA receptor antagonists, serotoninergic nerve depletors or receptor antagonists, or glutamate receptor antagonists; or (ii) heat shock protein 72 preconditioning. 6. There is compelling evidence that cerebrovascular dysfunction is an attractive target for therapy in heat stroke.

Profiling biochemical and hemodynamic markers using chronically instrumented, conscious and unrestrained rats undergoing severe, acute controlled hemorrhagic hypovolemic shock as an integrated in-vivo model system to assess new blood substitutes

The aim of the present study was to assess several biochemical and physiological endpoint parameters alongside controlled hemorrhagic and recovery phases of chronically instrumented, conscious and unrestrained healthy rats. Male Sprague-Dawley rats (12-14 weeks; 430+/-20 g; n=22-18) were instrumented with a saline-perfused femoral arterial catheter and placed individually in a metabolic cage for up to 20 days, allowing instant assessments of the hemodynamic profile and blood and urine sampling for hematological profile and biochemical measurements to assess hepatic, renal and metabolic functions. In addition, body weight, food and water intake, and diuresis were monitored daily. After a 7-day stabilization period, the rats underwent severe and acute hemorrhagic shock (HS) (removal of 50% of total circulating blood volume), kept in hypovolemic shock for an ischemic period of 50 min and then resuscitated over 10 min. Gr. 1 was re-infused with autologous shed blood (AB; n=10) whereas Gr. 2 was infused 1:1 with a solution of sterile saline-albumin (SA; 7% w/v) (n=8-12). Ischemic rats recovered much more rapidly following AB re-infusion than those receiving SA. Normal hemodynamic and biochemical profiles were re-established after 24 h. Depressed blood pressure lasted 4-5 days in SA rats. The hematological profile in the SA resuscitated rats was even more drastically affected. Circulating plasma concentrations of hemoglobin (-40%), hematocrit (-50%), RBC (-40%) and platelets (-41%) counts were still severely decreased 24 h after the acute ischemic event whereas WBC counts increased 2.2-fold by day 4. It took 5-9 days for these profiles to normalize after ischemia-reperfusion with SA. Diuresis increased in both groups (by 45+/-7% on day 1) but presented distinct electrolytic profiles. Hepatic and renal functions were normal in AB rats whereas altered in SA rats. The present set of experiments enabled us to validate a model of HS in conscious rats and the use of an integrated in vivo platform as a valuable tool to characterize HS-induced stress and to test new classes of blood substitutes in real time, post-event, over days.

How monitoring of the microcirculation may help us at the bedside

PURPOSE OF REVIEW

Recent technologic developments have allowed the direct visualization of the microcirculation at the bedside. The present review explores how the monitoring of microcirculation can help in clinical practice.

RECENT FINDINGS

Using orthogonal polarization spectral (OPS) imaging techniques, various investigators have reported microcirculatory alterations in critically ill patients and especially in patients with severe sepsis and septic shock. These alterations include a decrease in vessel density and an increased proportion of nonperfused or intermittently perfused capillaries. The persistence of these alterations is associated with the development of organ failure and death. Several therapeutic interventions, including vasoactive agents, fluid resuscitation, and activated protein C, can affect the microcirculation. Vasoactive agents have variable effects but vasodilatory agents seem very promising. Unfortunately, although many animal studies have investigated the effects of many of these interventions, human data are limited.

SUMMARY

Microcirculation plays an important role in the pathogenesis of shock and organ dysfunction, especially in sepsis. Monitoring microcirculation at the bedside may be used to assess severity of the disease and to predict outcome, but in the absence of sufficient data regarding the effects of therapeutic interventions it cannot yet be used to guide therapy, even though this approach is promising.

EFFECTS OF COLLOID RESUSCITATION ON PERIPHERAL MICROCIRCULATION, HEMODYNAMICS, AND COLLOIDAL OSMOTIC PRESSURE DURING ACUTE SEVERE HEMORRHAGE IN RABBITS

We examined the effects of hydroxyethyl starch (HES) on the microcirculation, hemodynamics, and colloidal osmotic pressure in a rabbit model of hemorrhagic shock. A total of 40 rabbits was anesthetized with pentobarbital and isoflurane, and they were mechanically ventilated. An ear chamber was prepared to examine blood vessels by intravital microscopy. Shock was induced by removing nearly half of the circulating blood volume. Twenty rabbits received 20 mL of HES by intravenous infusion immediately after blood letting. Additional HES was then administered intravenously to a total volume of 100 mL. The other 20 rabbits (control) were intravenously given 40 mL of lactated Ringer's solution (LR), followed by additional LR to a total volume of 200 mL, administered under the same conditions as HES. After blood letting, arteriolar diameter decreased similarly in the the HES and LR groups (HES, 40.5% +/- 14.8% of the baseline value versus LR, 43.3% +/- 13.1%). After the completion of infusion, arteriolar diameter significantly recovered to 90.8% +/- 10.2% of the baseline value in the HES group as compared with only 62.6% +/- 10.7% in the LR group (P < 0.005). Recovery of arterial blood flow velocity and blood flow rate was also significantly better in the HES group than in the LR group (P < 0.005). Mean arteriolar pressure, central venous pressure, and plasma colloid osmotic pressure after the completion of infusion were significantly greater in the HES group than in the LR group (P < 0.005). We conclude that intravenous infusion of HES effectively maintains the microcirculation, hemodynamics, and colloidal osmotic pressure in a rabbit model of acute severe hemorrhage.

RESUSCITATION FROM HEMORRHAGIC SHOCK WITH MalPEG-ALBUMIN: COMPARISON WITH MalPEG-HEMOGLOBIN

Our aim was to determine the efficacy of polyethylene glycol-conjugated human albumin (MalPEG-Alb) in restoring circulatory volume after 1 h of hemorrhagic shock. Experiments were performed in the awake condition in the hamster skin fold preparation. Microhemodynamic parameters and tissue Po2 were assessed with intravital microscopy and the use of the phosphorescence quenching technique. One hour after shock induction by withdrawal of 50% of the blood volume, animals were resuscitated with MalPEG-Alb (n = 6). Systemic and microhemodynamic parameters following resuscitation were identical to those obtained with the same protocol using MalPEG-Hb (1). However, parameters related to microvascular oxygen distribution were significantly lower in the MalPEG-Alb group compared with the previous data from the MalPEG-Hb group in that tissue oxygen partial pressure was 5 +/- 2 mmHg (vs. 8 +/- 3 mmHg, P < 0.05), oxygen delivery was reduced to 60 +/- 27% (P < 0.05), and oxygen consumption was reduced to 69 +/- 28% (P < 0.05). Both molecules were matched in composition (4.2 g/dL) and surface chemistry. MalPEG-Alb colloid osmotic pressure was 37 mmHg (vs. 49 mmHg for MalPEG-Hb), and viscosity was 2.7 cP (vs. 2.5 cP for MalPEG-Hb). The present results show that both solutions are efficacious plasma expanders and that the hemoglobin-based solution provides improved oxygen distribution and tissue Po2 in the hamster chamber model.

HYDROXYETHYL STARCH PRODUCES ATTENUATION OF CIRCULATORY SHOCK AND CEREBRAL ISCHEMIA DURING HEATSTROKE

We hypothesized that hydroxyethyl starch (HES), which maintains colloid osmotic pressure and potentially "seals" capillary leaks, would ameliorate circulatory shock and cerebral ischemia during heatstroke in a rat model. Animals under urethane anesthesia were exposed to high ambient temperature (Ta) of 42 degrees C until mean arterial pressure and local cerebral blood flow in the striatum began to decrease from peak level, which was arbitrarily defined as the onset of heatstroke. Control rats were exposed to 24 degrees C. In rats treated with 1 mL/kg, 11 mL/kg, or 22 mL/kg of normal saline (NS) immediately after the onset of heatstroke, the values for survival time (interval between the initiation of heatstroke and animal death) were found to be 21 +/- 2, 36 +/- 9, or 92 +/- 7 min, respectively. Intravenous administration of 11 mL/kg of HES (about 5 times the volume-expanding effect of 11 mL/kg of NS), but not 2 mL/kg of HES (about the same volume-expanding effect as 11 mL/kg NS), significantly increased the survival time from the control values of 36 +/- 9 min to new values of 181 +/- 13 min. In NS (11 mL/kg)-treated or HES (2 mL/kg)-treated rats after heatstroke onset, the values for mean arterial pressure, stroke volume, total peripheral resistance, cerebral blood flow, blood pH, Paco2, Pao2, and brain Po2 were significantly lower than those of rats kept at Ta 24 degrees C. In contrast, the values for colonic temperature and the extracellular concentrations of glutamate, glycerol, and lactate/pyruvate ratio obtained in striatum were significantly higher than those of controls. The heatstroke-induced arterial hypotension, decreased stroke volume and total peripheral resistance, decreased blood pH and Pao2, decreased brain Po2, and increased levels of striatal glutamate, glycerol, and lactate/pyruvate ratio in NS-treated rats were all attenuated significantly by increasing the volume expansion with 11 mL/kg of HES administered immediately at the onset of heatstroke. Our data suggest that HES therapy seems superior to NS treatment during heatstroke. The benefit of HES therapy during heatstroke might have something to do with volume expansion rather than capillary permeability.

HYPEROXIC VENTILATION REDUCES SIX-HOUR MORTALITY AFTER PARTIAL FLUID RESUSCITATION FROM HEMORRHAGIC SHOCK

Ventilation with 100% oxygen (Fio(2) 1.0; hyperoxic ventilation; HV) as an alternative to red blood cell transfusion enables survival in otherwise lethal normovolemic anemia. The aim of the present study was to investigate whether HV as a supplement to fluid infusion therapy could also restore adequate tissue oxygenation and prevent death in otherwise lethal hemorrhagic shock. In 14 anesthetized pigs ventilated on room air (Fio(2) 0.21), hemorrhagic shock was induced by controlled withdrawal of blood (target mean arterial pressure 35-40 mmHg) and maintained for 1 h. Subsequently, the animals were partially fluid-resuscitated (i.e., replacement of lost plasma volume) either with hydroxyethyl starch (6% HES, 200/0.5) alone (G 0.21) or with HES supplemented by HV (G 1.0). After completion of partial fluid resuscitation, all animals were followed up for the next 6 h. Five of seven animals of G 0.21 died within the 6-h observation period (i.e., 6-h mortality 71%). Death was preceded by a continuous increase of the serum concentrations of arterial lactate and persistent tissue hypoxia. In contrast to that, all animals of G 1.0 survived the 6-h observation period without lactic acidosis and with improved tissue oxygenation (i.e., 6-h mortality 0%; G 0.21 versus G 1.0 P < 0.05). In anesthetized pigs submitted to lethal hemorrhagic shock, the supplementation of partial fluid resuscitation with HV improved tissue oxygenation and enabled survival for 6 h.

Abdominal compartment syndrome: the cause or effect of postinjury multiple organ failure

Abdominal compartment syndrome (ACS) has emerged to be a significant problem in patients who develop postinjury multiple organ failure (MOF). Current laboratory research suggests that ACS could be a second hit for the development of MOF. Recent studies demonstrate that ACS is an independent predictor of MOF and that the prevention of ACS decreases the incidence of MOF. The Trauma Research Centers at the University of Colorado and the University of Texas-Houston Medical School are focused on defining the role of the gut in postinjury MOF. Because ACS is a plausible modifiable risk factor, our interest has been to 1) describe the epidemiology of ACS, 2) build prediction models, 3) provide strategies for prevention and treatment of ACS, and 4) develop relevant laboratory models. This review summarizes our findings.

Improving Microcirculation is More Effective Than Substitution of Red Blood Cells to Correct Metabolic Disorder in Experimental Hemorrhagic Shock

Microcirculatory perfusion deficits and impaired tissue oxygenation in nonvital organs frequently occur after hemorrhage and they contribute to potentially lethal complications. The aim of this study was to test the influence of colloid osmotic pressure, viscosity, and red blood cell (RBC) content of the resuscitative fluid on metabolic disorder, perfusion, and oxygenation in peripheral tissues. Awake hamsters were subjected to hemorrhage of 50% and were resuscitated with 25% of blood volume with solutions containing 6% pegylated bovine albumin only (PEG-BSA 0) and 6% PEG-BSA mixed with autologous RBCs to reach 4 g/dL (PEG-BSA 4) and 8 g/dL (PEG-BSA 8) of hemoglobin. PEG-BSA had a viscosity of 4.2 cP and a COP of 116 mmHg. Microhemodynamics and tissue pO2 were assessed in the hamster chamber window preparation with intravital microscopy. Arterial base excess tended to be lower than baseline for PEG-BSA 0 and PEG-BSA 4 (ns), whereas base deficit remained significantly decreased for PEG-BSA 8 (P<0.05 vs. baseline). Oxygen extraction was 91% +/- 2% of the oxygen delivery for PEG-BSA 0 compared with 85% +/- 2% for PEG-BSA 8 (P<0.05). Functional capillary density was 61%, 47%, and 45% for PEG-BSA 0 (P<0.05 vs. other groups), PEG-BSA 4 and PEG-BSA 8, respectively. We conclude that arterial base excess and oxygen extraction ratio in the tissue was better restored if a higher fraction of PEG-BSA and less RBCs were infused. This was attributed to a more homogeneous distribution of oxygen, as reflected by functional capillary density. Our results suggest that the transfusion trigger in hemorrhagic shock may be shifted toward lower hemoglobin concentrations if highly viscous and oncotic solutions are used.

Organ-Specific Extravasation of Albumin-Bound Evans Blue During Nonresuscitated Hemorrhagic Shock in Rats

Shock-induced enhanced capillary permeability is associated with alterations in the interstitial matrix composition and contributes to organ damage. This study was designed to evaluate albumin extravasation in various organ tissues during severe, hemorrhagic shock without fluid resuscitation and reperfusion. Target value of hemorrhagic shock was a reduction of cardiac output (CO) by 50% induced by removal of blood. Twelve anesthetized Sprague-Dawley rats (260-325 g) kept under continuous hemodynamic monitoring were randomly assigned to a group of hemorrhagic shock (n = 6) and a control group of normovolemic animals (n = 6). After 30 min of shock 50 mg/kg b.w. Evans blue (EB) was injected intravenously followed by an incubation period of 20 min. Exsanguination and wash out of the intravascular space was performed by a pressure-controlled perfusion with heparinized saline before harvesting organs to quantify albumin-bound EB extravasation. We found that withdrawal of 4.7 +/- 0.4 mL (mean, +/-SEM) blood, which accounts for 21.1% of the calculated total blood volume, resulted in a reduction of CO from 36.1 +/- 3.1 to 19.4 +/- 2.7 mL/min. Simultaneously, MAP decreased from 98 +/- 6 to 40 +/- 1 mmHg. In hemorrhaged rats, the interstitial concentration of EB in lung and kidney was significantly higher than observed in intact animals, whereas heart, spleen, liver, ileum, skeletal muscle, and skin showed no significant microvascular damage. We conclude that despite the absence of fluid resuscitation and reperfusion, microvascular damage in lung and kidney is evident within the first thirty minutes of hemorrhagic shock.