Mesenteric and renal oxygen transport during hemorrhage and reperfusion: evaluation of optimal goals for resuscitation

The study of n-3PUFAs protecting the intestinal barrier in rat HS/R model

BACKGROUND

N-3 PUFAs have been demonstrated in vitro it could prevent the intestinal tight junctions (TJs) from the ischemia/re-perfusion injury and the inflammatory reaction injury. The purpose of this study was to evaluate the protection of n-3 PUFAs on the intestinal TJs in the rat model of hemorrhagic shock followed by resuscitation.

METHODS

Male SD rats (n = 72; 250 ~ 300 g) were randomly divided into 6 groups: SHAM, hemorrhagic shock (HS), hemorrhagic shock/resuscitation (HS/R), ω-6 group, ω-3 group and ω-3 treatment group. Shock was induced, and a mean arterial pressure was maintained at 35 to 40 mmHg for 60 minutes. Resuscitation was carried out by returning half of the shed blood and Ringer's lactate solution. In ω-6 and ω-3 group, Intralipid or fish oil (0.2 g/Kg), respectively, was infused 30 minutes after shock. And fish oil was infused with resuscitation in ω-3 treatment group. Half of each group was killed at 30 minutes and 4 hours after resuscitation, respectively. The serum samples and the intestinal sample was collected for further examination.

RESULT

There is no difference between ω-3, ω-3 treatment and sham group in Chiu's score, but the other three groups have higher scores than they did. Compared with HS, HSR and ω-6 group, ω-3 and ω-3 treatment group showed most intact in intestinal mucoscal villi and TJs through HE, SEM and LSCM. The levels of IL-6 and TNF-α of bowel tissue in ω-3 and ω-3 treatment group were significantly lower than HS and HSR groups'. At the time point of 30 min, the levels of serum endotoxin were dramatically higher in HS、 HSR and ω-6 groups when compared with ω-3, ω-3 treatment and sham group. However, it in ω-3 group was greater than sham and HS group until 4 hours.

CONCLUSION

Fish oil pretreatment before resuscitation showed a beneficial effect to the intestinal TJs and atteunated inflammation after H/R in HS/R rat model and is better than ω-6 PUFAs did.

Heparin-binding EGF-like growth factor (HB-EGF) therapy for intestinal injury: Application and future prospects

Throughout the past 20 years, we have been investigating the potential therapeutic roles of heparin-binding EGF-like growth factor (HB-EGF), a member of the epidermal growth factor family, in various models of intestinal injury including necrotizing enterocolitis (NEC), intestinal ischemia/reperfusion (I/R) injury, and hemorrhagic shock and resuscitation (HS/R). Our studies have demonstrated that HB-EGF acts as an effective mitogen, a restitution-inducing reagent, a cellular trophic factor, an anti-apoptotic protein and a vasodilator, via its effects on various cell types in the intestine. In the current paper, we have reviewed the application and therapeutic effects of HB-EGF in three classic animal models of intestinal injury, with particular emphasis on its protection of the intestines from NEC. Additionally, we have summarized the protective functions of HB-EGF on various target cells in the intestine. Lastly, we have provided a brief discussion focusing on the future development of HB-EGF clinical applications for the treatment of various forms of intestinal injury including NEC.

Recombinant human erythropoietin improves gut barrier function in a hemorrhagic shock and resuscitation rat model

BACKGROUND

Gut injury and bacterial translocation develop and persist after limited periods of hemorrhagic shock. Erythropoietin (EPO) can exert hemodynamic, anti-inflammatory, and tissue protective effects. We tested the hypothesis that EPO given at the time of resuscitation with saline will reduce functional ileal injury 24 hours after shock.

METHODS

Sprague-Dawley rats (n = 6 per group) were randomized to sham surgery or hemorrhagic shock maintained at mean arterial pressure 40 mm Hg for 60 minutes and then treated with either saline resuscitation (three times the volume of shed blood) or saline + recombinant human EPO (rHuEPO) resuscitation. Intravenous rHuEPO (1,000 U/kg) was given at the start of saline resuscitation, and at 24 hours ileal function was evaluated using quantitative cultures of mesenteric lymph nodes to assess for bacterial translocation (colony-forming units per gram of tissue [CFU/g]), determination of portal vein plasma endotoxin levels and histopathological evaluation using semi-thin plastic sections of the distal ileum. In a second series of animals, fluorescein isothiocyanate-dextran 4000 (FD-4) was used to assess mucosal permeability of the distal ileum to macromolecules.

RESULTS

At 24 hours, the saline group had morphologic evidence of intestinal injury when compared with the sham group, and the degree of mucosal injury was less in the saline + rHuEPO when compared with the saline group, which demonstrated significantly reduced bacterial translocation to the mesenteric lymph nodes (383 CFU/g ± 111 CFU/g vs. 1130 CFU/g ± 297 CFU/g; p < 0.05) and decreased terminal ileum permeability to FD-4 (3.08 μg/mL ± 0.31 μg/mL vs. 5.14 μg/mL ± 0.88 μg/mL; p < 0.05). No significant difference was found in the portal vein endotoxin levels between the two groups. Histopathological evaluation demonstrated a trend for decreased enterocyte disarray or disruption and vacuolization in the saline + rHuEPO versus saline group.

CONCLUSION

Using rHuEPO at time of saline resuscitation resulted in decreased bacterial translocation and permeability to macromolecules 24 hours after shock. These observations suggest that rHuEPO can mediate a protective effect on intestinal mucosal barrier function during ischemic injury.

The temporal evolution of acute respiratory distress syndrome following shock

BACKGROUND AND OBJECTIVE

The objective of this review is to provide an comprehensive overview of the evolution of acute respiratory distress syndrome (ARDS) in cellular, animal and human models with specific reference to sepsis and haemorrhage. Within this work we have attempted to describe the temporal evolution of the disease process.ARDS is a complication of pulmonary and systemic disease and it can follow sepsis or haemorrhage. The definition of this condition states an acute onset and this review seeks to clarify the time course of that onset following sepsis and haemorrhage. The underlying pathophysiological mechanisms include activation of the immune response, neutrophil activation and sequestration of these into the alveolus with subsequent tissue damage and hypoxia.

RESULTS

The biological evolution of these processes from sepsis or haemorrhage has been well described and the earliest measurable changes in the process occur within 15 min with the clinical manifestations of the syndrome occurring within 12 h. The rapid development of this condition should be considered during the treatment of haemorrhagic or septic shock.

The effect of erythropoietin on microcirculation perfusion and tissue bioenergetics of the small intestine in a hemorrhagic shock and resuscitation rat model

BACKGROUND

Erythropoietin (EPO) can exert acute hemodynamic and anti-inflammatory effects in addition to erythropoiesis. We tested the hypothesis that EPO given at resuscitation with saline will improve capillary perfusion and tissue oxygenation in the gut using a hemorrhagic shock model.

METHODS

Sprague-Dawley rats were bled 30 mL/kg to maintain a mean arterial blood pressure of 40 mm Hg for 50 minutes and then randomized to one of four resuscitation groups (n = 6 per group): blood, blood + recombinant human EPO (rHuEPO), saline, and saline + rHuEPO. Intravenous rHuEPO (1,000 U/kg) was given at the start of resuscitation. Intravital microscopy was used to measure perfused capillary density, flow motion of red blood cell (RBC), and tissue NADH fluorescence 60 minutes after resuscitation. Venous oxygenation saturation (Svo2) was also measured in a second experiment.

RESULTS

In the blood +/- rHuEPO resuscitation group, the perfused capillary density, RBC flow motion scores, and NADH fluorescence returned to near normal values. The saline + rHuEPO group compared with the saline group demonstrated an increased RBC flow motion score (2.32 vs. 1.60; p < 0.01); however, the perfused capillary density was not significantly increased (23.03 Cap/mm vs. 21.61 Cap/mm; p = 0.40). The saline + rHuEPO group also demonstrated statistically significant lower NADH fluorescence than the saline group after shock following resuscitation (110% +/- 3.64% vs. 122% +/- 4.26%; p < 0.05) suggesting decreased tissue dysoxia. The Svo2 in the saline + rHuEPO group was higher when compared with the saline group (45% vs. 38% by continuous oximetry; 38% vs. 29% by co-oximetry; p < 0.05).

CONCLUSION

Our results suggest that the addition of rHuEPO at the time of saline resuscitation may have beneficial effects in hemorrhagic shock by improving tissue perfusion and decreasing dysoxia in the gut.

Sustained Gastric Mucosal Acidosis After Hemorrhage in Spite of Rapid Hemodynamic Restoration With Blood or Hypertonic/Hyperoncotic Solution

Splanchnic hypoperfusion has been implicated as the motor of multiple organ dysfunction. Hypertonic saline has shown to benefit microcirculatory blood flow. In hemorrhaged animals, we tested the hypothesis that small-volume 3% NaCl/10% dextran 40 (3%HSD) promotes global and regional improvements, including gastric mucosal acidosis reversal. Seventeen dogs (18.8 +/- 1.2 kg) were bled (20 mL/min) to a mean arterial pressure of 40-45 mm Hg, which was maintained at these levels for 15 min. They were randomly assigned to two groups: Blood (n = 9), total shed blood retransfused at 40 mL/min; or a 4-min bolus injection of 3%HSD (n = 8), in a volume equivalent to 25% of total shed blood. All animals were followed for 30 min thereafter. Gastric mucosal PCO2 (gas tonometry), portal vein PCO2, superior mesenteric artery blood flow (SMA, ultrasonic flowprobes), and systemic and regional O2-derived variables were evaluated throughout the protocol. Hemorrhage induced significant reductions of arterial pressure, cardiac output, and SMA blood flow, while portal-arterial and gastric-arterial PCO2 gradients increased. Total shed blood transfusion, as well as 3%HSD bolus injection, promptly restored all parameters, except for the increased gastric-arterial PCO2 gradient. We conclude that persistent gastric mucosal acidosis cannot be adequately predicted by global and splanchnic O2 derived variables in following hemorrhage and resuscitation with total shed blood transfusion or small-volume hypertonic-hyperoncotic solution.

Heparin-binding epidermal growth factor-like growth factor gene disruption is associated with delayed intestinal restitution, impaired angiogenesis, and poor survival after intestinal ischemia in mice

PURPOSE

We have demonstrated that administration of heparin-binding epidermal growth factor-like growth factor (HB-EGF) protects the intestines from injury. The aim of the current study was to evaluate the effect of HB-EGF gene disruption on intestinal restitution, angiogenesis, and long-term survival after intestinal ischemia/reperfusion (I/R) injury.

METHODS

HB-EGF (-/-) and wild-type HB-EGF (+/+) littermate mice were subjected to 45 minutes of superior mesenteric artery occlusion followed by reperfusion. Functional recovery of the gut permeability barrier was evaluated with Ussing chamber studies, and microvessel density was evaluated immunohistochemically. Animal survival was evaluated using the Kaplan-Meier method.

RESULTS

Histologic damage after ischemia was significantly higher in HB-EGF (-/-) mice compared with HB-EGF (+/+) mice, associated with a significantly higher number of incompetent (nonhealed, nonresurfaced) villi indicative of delayed structural healing by restitution. HB-EGF (-/-) mice had increased intestinal permeability after intestinal I/R. HB-EGF (-/-) mice had significantly lower microvessel density at 3 and 7 days after I/R, indicating that HB-EGF gene deletion resulted in delayed onset of angiogenesis. Two-week mortality rates were significantly higher in HB-EGF (-/-) mice.

CONCLUSIONS

Endogenous HB-EGF significantly enhances healing by restitution, prolongs survival, and enhances angiogenesis in mice subjected to intestinal I/R injury. These findings support our hypothesis that HB-EGF administration may improve outcome in patients with intestinal I/R injury, including necrotizing enterocolitis.

Acute pancreatitis severity is exacerbated by intestinal ischemia-reperfusion conditioned mesenteric lymph

OBJECTIVE

To determine the effect of intestinal ischemia-reperfusion (IIR) on acute pancreatitis (AP) and the role of mesenteric lymph.

SUMMARY BACKGROUND DATA

Intestinal ischemia is an early feature of AP and is related to the severity of disease. It is not known whether this contributes to the severity of AP or is a consequence.

METHODS

Two experiments are reported here using intravital microscopy and a rodent model of mild acute pancreatitis (intraductal 2.5% sodium taurocholate). In the first, rats had an episode of IIR during AP that was produced by temporary occlusion of the superior mesenteric artery (30 min or 3 x 10 min) followed by 2h reperfusion. In a second study rats with AP had an intravenous infusion of mesenteric lymph collected from donor rats that had been subjected to IIR. In both experiments the pancreatic erythrocyte velocity (EV), functional capillary density (FCD), leukocyte adherence (LA), histology and edema index were measured.

RESULTS

The addition of IIR to AP caused a decline in the pancreatic microcirculation greater than that of AP alone (EV 42% of baseline vs. 73% of baseline AP alone, FCD 43% vs 72%, LA 7 fold increase vs 4 fold increase). This caused an increased severity of AP as evidenced by 1.4-1.8 fold increase of pancreatic edema index and histologic injury respectively. A very similar exacerbation of microvascular failure and increased pancreatitis severity was then demonstrated by the intravenous infusion of IIR conditioned mesenteric lymph from donor animals.

CONCLUSIONS

Unidentified factors released into the mesenteric lymph following IIR injury are capable of exacerbating AP. This highlights an important role for the intestine in the pathophysiology of AP pathogenesis and identifies mesenteric lymph as a potential therapeutic target.

Heparin-binding EGF-like growth factor preserves mesenteric microcirculatory blood flow and protects against intestinal injury in rats subjected to hemorrhagic shock and resuscitation

BACKGROUND

The gut is highly susceptible to injury after hemorrhagic shock and resuscitation (HS/R) because of progressive mesenteric hypoperfusion. The aim of the current study was to evaluate the effect of heparin-binding EGF-like growth factor (HB-EGF) on mesenteric microcirculatory blood flow and intestinal injury in rats subjected to HS/R.

METHODS

HS/R was induced in adult rats, with some rats receiving HB-EGF (600 mug/kg) IV at the onset of resuscitation (HS/R+HB-EGF) and others receiving vehicle only (HS/R). FITC-dextran was administered intra-arterially to evaluate mesenteric microcirculation, and intestinal damage and restitution were evaluated histologically. Data were expressed as mean +/- SE, with P < .05 considered statistically significant.

RESULTS

Microcirculatory blood flow was significantly reduced 1 hour after HS/R. HS/R+HB-EGF rats had significantly increased microcirculatory flow compared with HS/R rats at 1 hour (4.5 +/- 0.43 vs 2.64 +/- 0.46, P < .05) and 3 hours (8.04 +/- 1.58 vs 2.89 +/- 0.63, P < .05) after HS/R. HS/R+HB-EGF rats had significantly less intestinal damage compared with HS/R rats 3 hours after resuscitation (2.04 +/- 0.5 vs 3.08 +/- 0.5, P < .05), along with significantly fewer incompetent (nonresurfaced, nonhealed) villi, which is indicative of improved restitution.

CONCLUSIONS

HB-EGF significantly improved postresuscitation microcirculatory blood flow in rats subjected to HS/R, associated with significantly decreased intestinal damage and increased restitution. These results suggest that HB-EGF may be a useful therapeutic agent that improves intestinal blood flow in patients with intestinal injury secondary to hemorrhagic shock.

Sublingual Capnometry for Rapid Determination of the Severity of Hemorrhagic Shock

BACKGROUND

Sublingual capnometry (SLCO2) is a rapid, minimally invasive bedside test of focal tissue perfusion. We hypothesized that SLCO2 could diagnose hemorrhagic shock and monitor adequacy of resuscitation. We compared the ability of SLCO2, serum lactate (LAC), and base deficit (BD) to predict outcome in hypotensive trauma patients.

METHODS

Prospective, observational trial at two Level I trauma centers was performed. Inclusion criteria were blunt or penetrating trauma patients, age > or =16 years, with hypotension (systolic blood pressure < or =90 mm Hg). SLCO2, LAC, and BD were measured in each patient at admission, at the end of active hemorrhage, and at 6, 24, and 48 hours. Data are reported as means (+/-SD).

RESULTS

A total of 86 patients were enrolled: mean age 35 (+/-17) years, 80% male, 51% blunt trauma, Injury Severity Score score 20 (+/-14). Twenty patients died. SLCO2 at admission was 52.4 (+/-13.3) in survivors versus 87.9 (+/-35.6) in nonsurvivors (p < 0.001). Receiver operating characteristic (ROC) curves showed that SLCO2, LAC, and BD were all good predictors of mortality. The area under each ROC curve was as follows: SLCO2 (0.82; 95% CI 0.70-0.96; p < 0.001), LAC (0.80; 95% CI 0.69-0.91; p < 0.001), BD (0.87; 95% CI 0.77-0.98; p < 0.001). There was no significant difference (p > 0.05) in the areas under the three curves.

CONCLUSIONS

SLCO2 predicted survival in hypotensive trauma patients. It had equivalent diagnostic ability to LAC and BD. This rapid test may supplement standard, more invasive measures of hemorrhagic shock.

Different patterns of pulse spectrum between survivors and non-survivors during progressive hemorrhage in rats

Previous work from our laboratory has demonstrated that the percentage differences of 2nd (C2) and 3rd (C3) pulse harmonics related to Kidney and Spleen were both increased toward another steady state in rats after acute hemorrhage. Therefore, it is suggested that changes in pulse spectra might represent the ability of animals to survive a model of progressive hemorrhage. In this study, the difference of the pulse spectra patterns between survivors and non-survivors after progressive hemorrhage (by loss of 5%, 10% or 20% of the estimated blood volume) in anesthetized rats is determined. Seven rats, dead within 2 hours after a loss of 20% of the estimated blood volume hemorrhage, were defined as 'non-survivors'. The other eleven rats, more than 2 hours after hemorrhage, were defined as 'survivors'. Pulse waves of arterial blood pressure before and after the hemorrhage were measured in parallel to the pulse spectrum analysis. Data among different phases were analyzed using one-way analysis of variance (ANOVA) with Duncan's test for pairwise comparisons. Differences between survivor and non-survivor groups at each phase were analyzed using Student's t-test. A mixed-effects linear regression model was applied to evaluate the relationship in harmonics, which significantly differed between the two groups. The study results showed that in rats, during progressive hemorrhage, the percentage differences of 2nd harmonic proportion increased significantly; however, the result failed to show any significant difference between survivors and non-survivors. After the third blood withdrawal process, the percentage differences of 3rd harmonic proportion increased more significantly in the survivors. In addition, the percentage differences of 1st harmonic proportion related to the Liver for the survivor group was significantly lower than that of the non-survivors. After analysis with the mixed linear regression model, C3 and C1 demonstrated a linear regression relationship, and there existed significant differences between survivors and non-survivors. These results suggest that C3 might play an important role in physiology regarding surviving capability after progressive hemorrhage.

Resonance Raman spectroscopy: a new technology for tissue oxygenation monitoring

OBJECTIVE

To evaluate resonance Raman spectroscopy for the detection of changes in sublingual mucosal hemoglobin oxygen saturation (Smo2) in response to hemorrhage and resuscitation, and to compare Smo2 with other indicators of tissue oxygenation including central venous oxygen saturation (Scvo2), lactate, base excess, and shed blood volume.

DESIGN

Prospective single group pilot study.

SETTING

University laboratory.

SUBJECTS

Five Sprague-Dawley rats.

INTERVENTIONS

Animals were anesthetized and instrumented for measurement of arterial and central venous blood gases. Raman spectroscopy was performed using a krypton ion laser providing excitation at 406.7 nm (5 mW). A 1-mm2 region of the sublingual tongue surface was chosen for investigation. Animals were subjected to stepwise hemorrhage until approximately 50% of the blood volume was removed. At each hemorrhage and resuscitation interval, Raman spectroscopy was performed and corresponding arterial and central venous blood gas and lactate measurements were made. Smo2 was calculated as the ratio of the oxygenated heme spectral peak height to the sum of the oxy- and deoxyhemoglobin spectral peak heights. Raman spectroscopy-derived Smo2 measurements were compared with Scvo2 as well as with other indicators of oxygenation.

MEASUREMENTS AND MAIN RESULTS

The mean difference between Smo2 and Scvo2 for all paired measurements was 5.8+/-11.7 absolute saturation points. Smo2 was significantly (p<.0001) correlated with Scvo2 (r=.80), lactate (r=-.78), base excess (r=.80), and shed blood volume (r=-.75). Smo2 and Scvo2 showed similar levels of precision for predicting elevated lactate and base deficit.

CONCLUSIONS

These studies demonstrate the ability of Raman spectroscopy to noninvasively track microvascular hemoglobin oxygenation in tissue and favorably correlate with other important indicators of tissue oxygenation such as Scvo2, lactate, base deficit, and shed blood volume. The technique shows promise as a method to noninvasively monitor tissue oxygenation.

Methods of monitoring shock

Intensive monitoring is a crucial component of the management of shock. However, there is little consensus about optimal strategies for monitoring. Although the pulmonary artery catheter has been widely used, conflicting data exist about the utility of this device. A variety of other techniques have been developed in hopes of providing clinically useful information about myocardial function, intravascular volume, and indices of organ function. In addition, there is evolving evidence that targeting and monitoring certain physiological goals may be most important early in the course of shock. In this chapter, we examine many of the available monitoring techniques and the evidence supporting their use.

Diagnostic Utility of Sublingual Pco2 for Detecting Hemorrhage in Penetrating Trauma Patients

BACKGROUND

Hemorrhage results in early compromise of splanchnic circulation. Studies have shown that sublingual Pco2 (SLCO2) correlates with gut perfusion. We tested SLCO2's ability to detect hemorrhage. We compared SLCO2 with arterial base deficit (BD) and lactate (LAC).

METHODS

This was a prospective study of patients with penetrating torso trauma. SLCO2 was measured at triage. Blood loss was defined as none (group 1), minimal to moderate (<1,500 mL) (group 2), or severe (>/=1,500 mL) (group 3). Data were reported as mean (95% confidence interval) and compared by analysis of variance. Receiver operating characteristic curves compared diagnostic performance between SLCO2, BD, and LAC.

RESULTS

One hundred eight patients were enrolled. There was a significant difference (p < 0.001) in SLCO2 between all blood loss groups: group 1, 46.9 mm Hg (44.9-49.0 mm Hg); group 2, 53.5 mm Hg (50.8-56.2 mm Hg); and group 3, 66.0 mm Hg (53.1-78.9 mm Hg). There were no significant (p > 0.05) differences for receiver operating characteristic curves between SLCO2, BD, or LAC.

CONCLUSION

SLCO2 differentiated blood loss groups. SLCO2 may be useful in triage of penetrating trauma patients.

Trends in burn resuscitation: shifting the focus from fluids to adequate endpoint monitoring, edema control, and adjuvant therapies

Bum shock is a complex process involving a series of intertwined physiologic responses to injury that require more rigorous intervention than simply a change in fluid tonicity, fluid composition, or fluid resuscitation volume. Controversy ensues over monitoring techniques and resuscitation goals, in part because the identification of true markers of perfusion is clouded by intradependence of endpoints on other metabolic processes. The persistence of cellular hypoperfusion in patients who have been deemed adequately resuscitated by global indices supports the growing realization that failure of conventional endpoint-monitoring strategies to detect compensated bum shock can lead to significant organ injury from SIRS or MODS. Current endpoints should be interpreted in the aggregate, because none have yet been demonstrated to reflect tissue perfusion status independently and accurately. Numerous technologically advanced endpoints to predict patient outcome, which may be useful in determining futility of treatment or end-of-life decisions, are now available. Still lack-ing, however, is a reliable tool proven to improve outcome that can guide bum shock resuscitation therapies successfully. Exciting new research in tissue oxygenation and perfusion has revealed that damaging mediator cascades and irreversible microvascular changes may preclude complete resolution of bum shock solely through restoration of oxygen delivery. Because bum patients now frequently survive the early resuscitation phase. the focus should be on controlling derangements in oxygen use and correcting occult hypoperfusion to reduce later adverse patient outcomes from SIRS, sepsis, and MODS. Bum-specific research on resuscitation endpoints and monitoring strategies lags behind research in other patient populations. Present standards and monitoring guidelines for bum shock resuscitation should be critically evaluated and based on true, scientifically validated data rather than on observational studies or personal beliefs. Thus the continuing challenge for clinicians and researchers:burn centers must collaborate to perform large, multi-center studies to evaluate critically and to prove resuscitation endpoints and therapies. Future technologies targeted at microcirculatory perfusion and cellular oxygenation offer an exciting promise for less invasive, easily accessible, more accurate endpoints and treatments for bum shock resuscitation.

Injury (nociceptive afferent nerve stimulation) modifies the hemodynamic and metabolic responses to hemorrhage in immature swine

OBJECTIVE

To determine the effects of reinfusion of shed blood on the regional blood flow changes induced by hemorrhage and hemorrhage plus nociceptive nerve stimulation (injury) with special reference to the gut.

DESIGN

Randomized controlled laboratory study.

SETTING

Medical Research Council laboratory, university medical school.

SUBJECTS

Four groups of anesthetized immature female Large-White pigs (15-27 kg): 30% hemorrhage, 30% hemorrhage plus afferent nerve stimulation, nerve stimulation alone, surgical controls.

INTERVENTIONS

In addition to standard invasive hemodynamic monitoring, electromagnetic flow probes were placed around a branch of the superior mesenteric artery and the right femoral artery. Stimulating electrodes were placed on brachial nerves in both axillae. Animals underwent 30% hemorrhage over 30 mins. After a 30-min shock period, the shed blood was reinfused at 2 mL/kg/min.

MEASUREMENTS AND MAIN RESULTS

Measurements/calculations of standard global hemodynamics, gut and femoral blood flows/vascular resistance, metabolism, arterial plasma lactate, portal venous endotoxin, interleukin-6, and tumor necrosis factor-alpha were made before and after hemorrhage, before and after reinfusion, and at 30-min intervals for 3 hrs. Blood and tissue samples were taken for the presence of translocated coliforms. Hemorrhage elicited the expected changes in global hemodynamics, metabolism, and gut and femoral blood flows. There was a partial hemodynamic recovery during the shock period. Nearly all hemodynamic and metabolic variables were rapidly restored by reinfusion. The response to hemorrhage was modified by nerve stimulation: Reductions in systemic hemodynamics and gut flow were greater, and there was no recovery during the shock phase. Cytokine and endotoxin concentrations increased significantly in all groups. There was no bacterial translocation.

CONCLUSIONS

When hemorrhage occurs in the presence of nerve stimulation (injury), the relative protection of the gut circulation is attenuated and this effect persists after the end of hemorrhage and reinfusion. However, there was no evidence that injury increased the hemorrhage/surgery-induced cytokine and endotoxin responses.

Effects of sustained post-traumatic shock and initial fluid resuscitation on extravascular lung water content and pulmonary vascular pressures in a porcine model of shock

BACKGROUND

The temporal evolution of lung injury following post-traumatic shock is poorly understood. In the present study we have tested the hypothesis that manifestations of pulmonary vascular dysfunction may be demonstrable within the first hour after the onset of shock.

METHODS

Twenty-nine anaesthetized pigs (mean weight 27.4 kg; (SD) 3.2) were randomly allocated to three groups: control (C, n=9), shock resuscitated with either NaCl 0.9% (S, n=10), or 4% gelatine (G, n=10). Shock was maintained for 1 h followed by fluid resuscitation with either normal saline or 4% gelatine solution. Cardiac output (CO), mean arterial pressure (MAP), mixed venous saturation (Sv(O(2))), blood lactate concentration, mean pulmonary artery pressure (MPAP), MPAP/MAP, pulmonary vascular resistance (PVR), extravascular lung water index (EVLWi), Pa(O(2))/FI(O(2)), venous admixture (Q(.)(S)/Q(.)(T)), and dynamic lung compliance (C(dyn)) were measured at baseline, beginning of shock phase, end of shock phase, and post-resuscitation.

RESULTS

At the end of volume resuscitation CO was restored to control values in both shock groups. MAP remained significantly below control values (95% CI: C=70-95, S=28-52, G=45-69 mm Hg) in both shock groups. MPAP/MAP was significantly greater in both shock groups at the end of the shock phase (95% CI; C=0.15-0.24, S=0.28-0.38, G=0.32-0.42) and at the post-resuscitation phase (95% CI: C=0.12-0.30, S=0.43-0.61, G=0.32-0.49) indicating the presence of relative pulmonary hypertension. This was associated with a significant increase in PVR in Group S (F=3.9; P<0.05). There were no significant changes in Pa(O(2))/FI(O(2)), Q(.)(S)/Q(.)(T), EVLWi, or C(dyn). In a small cohort of animals a measurable increase in EVLWi (>30%) and reduction in C(dyn) (>10%) were observed.

CONCLUSIONS

Pulmonary vascular injury manifesting as relative pulmonary hypertension and increased PVR may occur within the first hour after the onset of shock. These changes may not be accompanied by overt changes in oxygenation, compliance, or EVLWi. Br J Anaesth 2003; 91: 224-32

Resuscitation from hemorrhagic shock: experimental model comparing normal saline, dextran, and hypertonic saline solutions

OBJECTIVE

To compare the effectiveness of normal saline, dextran, hypertonic, and hypertonic-hyperoncotic solutions in hemorrhagic shock.

DESIGN

Laboratory investigation.

SETTING

University hospital, Emergency Surgery and Intensive Care staff.

SUBJECTS

Thirty-two large white female pigs.

INTERVENTIONS

Routine care included: anesthesia and sedation (ketamine 10 mg/kg, droperidol 0.25 mg/kg, diazepam 0.7 mg/kg, fentanyl 0.006 mg/kg, 2% enflurane, 20% nitrous oxide, pancuronium bromide 0.13 mg/kg); volume-controlled ventilation (Paco(2) 35-40 torr; 4.7-5.4 kPa); cannulation of right carotid artery and pulmonary artery. Three flow probes (subdiaphragmatic aorta, superior mesenteric artery, right renal artery) and regional venous catheters (superior mesenteric vein, right renal vein) were positioned. Animals were bled to 45 mm Hg for 1 hr and resuscitated with four different fluids and blood to normal aortic blood flow and hemoglobin.

MEASUREMENTS AND MAIN RESULTS

Mean arterial pressure and blood flow through abdominal aorta ([OV0312](aor)), mesenteric artery ([OV0312](mes)), and renal artery ([OV0312](ren)) were continuously monitored. Cardiac output, systemic and regional oxygen delivery ([U1E0A]o(2), [U1E0A]o(2mes), [U1E0A]o(2ren)), and consumption ([OV0312]o(2), [OV0312]o(2mes), [OV0312]o(2ren)) were recorded every 30 mins. Baseline [OV0312](aor) was restored with different amounts of fluids in the four groups: normal saline (91.35 +/- 22.18 mL/kg); dextran (16.24 +/- 4.42 mL/kg); hypertonic (13.70 +/- 1.44 mL/kg); and hypertonic-hyperoncotic (9.11 +/- 1.20 mL/kg). The amount of sodium load was less using dextran and hypertonic-hyperoncotic and sodium levels were only transiently increased after hypertonic infusion. Mean arterial pressure and cardiac output were normalized in all groups. Animals resuscitated with normal saline and dextran showed increased pulmonary artery pressures. [U1E0A]o(2) was significantly higher after hypertonic-hyperoncotic infusion, because of reduced hemodilution. Hypertonic and hypertonic-hyperoncotic normalized [OV0312](mes), [U1E0A]o(2mes), [OV0312]o(2mes), [OV0312](ren), and [U1E0A]o(2ren), whereas normal saline and dextran did not achieve this result. At the end of the experiment, hypertonic-hyperoncotic maintained mean arterial pressure, cardiac output, and [U1E0A]o(2) until the end of observation in contrast to normal saline, dextran, and hypertonic.

CONCLUSIONS

Resuscitation with a small volume of hypertonic-hyperoncotic solution allows systemic and splanchnic hemodynamic and oxygen transport recovery, without an increase in pulmonary artery pressure. It only transiently increased sodium concentration.

Sublingual capnometry: an alternative to gastric tonometry for the management of shock resuscitation

Normal vital signs do not reflect the physiologic aberrations after blood loss. Recognition of hypoperfusion during resuscitation can avoid the development of multiple organ failure. Advances in technology enable the clinician to monitor changes, potentially identifying tissue hypoxia much earlier than previously was possible. Gastric tonometry can be quite helpful in the intensive care unit in identifying gastric hypoperfusion, but has considerable drawbacks. The ability to monitor P(SI)CO(2) via sublingual capnometers overcomes some limitations of gastric tonometry and may be a valuable aid in the prehospital phase, the emergency department, and the intensive care unit in identifying end points of resuscitation.

Mesenteric hemodynamic response to circulatory shock

PURPOSE OF REVIEW

The mesenteric hemodynamic response to circulatory shock is substantial and asymmetrical; the vasoconstrictive response disproportionately affects the mesenteric organs. The cardiac output is sustained partially, at no cost in nutrient flow to the mesenteric organs, by vasoconstriction of the mesenteric veins, resulting in the "autotransfusion" of up to 30% of the circulating blood volume into the systemic circulation.

RECENT FINDINGS

Hemorrhagic or cardiogenic shock also results in decreased perfusion pressure, prompting selective vasoconstriction of the mesenteric arterioles to maintain perfusion pressure of the vital organs, here at the selective expense of the mesenteric organs. Septic shock may be associated with increased or decreased mesenteric blood flow but is characterized by increased oxygen consumption, exceeding the capability of mesenteric oxygen delivery.

SUMMARY

The response to any of these conditions can, variably and unpredictably, cause hemorrhagic gastric stress erosions, nonocclusive mesenteric ischemia of the small bowel, ischemic colitis, ischemic hepatitis, acalculous cholecystitis, and/or ischemic pancreatitis. Injury to the mesenteric organs can also initiate the systemic inflammatory response syndrome and, consequently, multiple organ failure.

The role of the intestine in the pathophysiology and management of severe acute pancreatitis

BACKGROUND

The outcome of severe acute pancreatitis has scarcely improved in 10 years. Further impact will require new paradigms in pathophysiology and treatment. There is accumulating evidence to support the concept that the intestine has a key role in the pathophysiology of severe acute pancreatitis which goes beyond the notion of secondary pancreatic infection. Intestinal ischaemia and reperfusion and barrier failure are implicated in the development of multiple organ failure.

DISCUSSION

Conventional management of severe acute pancreatitis has tended to ignore the intestine. More recent attempts to rectify this problem have included 1) resuscitation aimed at restoring intestinal blood flow through the use of appropriate fluids and splanchnic-sparing vasoconstrictors or inotropes; 2) enteral nutrition to help maintain the integrity of the intestinal barrier; 3) selective gut decontamination and prophylactic antibiotics to reduce bacterial translocation and secondary infection. Novel therapies are being developed to limit intestinal injury, and these include antioxidants and anti-cytokine agents. This paper focuses on the role of the intestine in the pathogenesis of severe acute pancreatitis and reviews the implications for management.