Regional flow during experimental hemorrhage and crystalloid resuscitation: persistence of low flow to the splanchnic organs

Rapid assessment of shock in a nonhuman primate model of uncontrolled hemorrhage: Association of traditional and nontraditional vital signs to mortality risk

BACKGROUND

Heart rate (HR), systolic blood pressure (SBP) and mean arterial pressure (MAP) are traditionally used to guide patient triage and resuscitation; however, they correlate poorly to shock severity. Therefore, improved acute diagnostic capabilities are needed. Here, we correlated acute alterations in tissue oxygen saturation (StO2) and end-tidal carbon dioxide (ETCO2) to mortality in a rhesus macaque model of uncontrolled hemorrhage.

METHODS

Uncontrolled hemorrhage was induced in anesthetized rhesus macaques by a laparoscopic 60% left-lobe hepatectomy (T = 0 minute). StO2, ETCO2, HR, as well as invasive SBP and MAP were continuously monitored through T = 480 minutes. At T = 120 minutes, bleeding was surgically controlled, and blood loss was quantified. Data analyses compared nonsurvivors (expired before T = 480 minutes, n = 5) with survivors (survived to T = 480 minutes, n = 11) using repeated-measures analysis of variance with Bonferroni correction. All p < 0.05 was considered statistically significant. Results were reported as mean ± SEM.

RESULTS

Baseline values were equivalent between groups for each parameter. In nonsurvivors versus survivors at T = 5 minutes, StO2 (55% ± 10% vs. 78% ± 3%, p = 0.02) and ETCO2 (15 ± 2 vs. 25 ± 2 mm Hg, p = 0.0005) were lower, while MAP (18 ± 1 vs. 23 ± 2 mm Hg, p = 0.2), SBP (26 ± 2 vs. 34 ± 3 mm Hg, p = 0.4), and HR (104 ± 13 vs. 105 ± 6 beats/min, p = 0.3) were similar. Association of values over T = 5-30 minutes to mortality demonstrated StO2 and ETCO2 equivalency with a significant group effect (p ≤ 0.009 for each parameter; R(2) = 0.92 and R(2) = 0.90, respectively). MAP and SBP associated with mortality later into the shock period (p < 0.04 for each parameter; R(2) = 0.91 and R(2) = 0.89, respectively), while HR yielded the lowest association (p = 0.8, R(2) = 0.83).

CONCLUSION

Acute alterations in StO2 and ETCO2 strongly associated with mortality and preceded those of traditional vital signs. The continuous, noninvasive aspects of Food and Drug Administration-approved StO2 and ETCO2 monitoring devices provide logistical benefits over other methodologies and thus warrant further investigation.

Damage Control and the Open Abdomen: Challenges for the Nonsurgical Intensivist

BACKGROUND

As strategies in acute care surgery focus on damage control to restore physiology, intensivists spanning all disciplines care for an increasing number of patients requiring massive transfusion, temporary abdominal closures, and their sequelae.

OBJECTIVE

To equip the nonsurgical intensivist with evidence-based management principles for patients with an open abdomen after damage control surgery.

DATA SOURCE

Search of PubMed database and manual review of bibliographies from selected articles.

DATA SYNTHESIS AND CONCLUSIONS

Temporary abdominal closure improves outcomes in patients with abdominal compartment syndrome, hemorrhagic shock, and intra-abdominal sepsis but creates new challenges with electrolyte derangement, hypovolemia, malnutrition, enteric fistulas, and loss of abdominal wall domain. Intensive care of such patients mandates attention to resuscitation, sepsis control, and expedient abdominal closure.

Strategies for modulating the inflammatory response after decompression from abdominal compartment syndrome

BACKGROUND

Management of the open abdomen is an increasingly common part of surgical practice. The purpose of this review is to examine the scientific background for the use of temporary abdominal closure (TAC) in the open abdomen as a way to modulate the local and systemic inflammatory response, with an emphasis on decompression after abdominal compartment syndrome (ACS).

METHODS

A review of the relevant English language literature was conducted. Priority was placed on articles published within the last 5 years.

RESULTS/CONCLUSION

Recent data from our group and others have begun to lay the foundation for the concept of TAC as a method to modulate the local and/or systemic inflammatory response in patients with an open abdomen resulting from ACS.

Total hepatic ischemia and reperfusion after state controlled hemorrhagic shock, with used of different solutions: effects of neutrophils sequestration in kidney of rats

PURPOSE: To evaluate and compare neutrophils sequestration in the renal cortex of rats, result of total hepatic ischemia and reperfusion after controlled hemorrhagic shock, with use of different electrolytic solutions. METHODS: Used 18 rats Wistar, males, adult, divided into three groups as the solution used to reanimation: Group PSS: physiologic saline solution; Group HSS: hypertonic saline hypertonic (7,5%) followed by lactated ringer's solution; Group LRS: lactated ringer's solution. All the animals were submitted to the bleeding controlled until mean arterial pressure (MAP) 40 mmHg, for 20 minutes. Performed volemic replacement until PAM=80 mmHg with the solution according the studied group, followed by laparotomy and Pringle's Maneuver for 15 minutes. The animals were accompanied until for two hours. To statistical comparisons between mean of neutrophils sequestration, in interstitium of the renal cortex, were made the tests One-way ANOVA and covariance analysis, adjusting itself for time of supervened. The hemodynamic parameters evaluated were: MAP, heat rate, cardiac index, vascular resistance system index. The analyzed metabolic variables were: pH, bicarbonate, base deficit and lactato, besides electrolytes. RESULTS: The mean values of supervened, in minutes, for group were: Group PSS 79,0±12,0; Group LRS 97,0±11,0; Group HSS 67,0±10. The mean values of neutrophils/field in the renal cortex were: Group PSS 0,55±0,68; Group LRS 1,68±0,53; Group HSS 1,33±0,43. When adjusted for time of supervened: Group PSS 0,55; Group LRS 1,62; Group HSS 1,39. There was statistically significant difference in neutrophils sequestration, between Group PSS regarding the others groups, using itself or not the adjustment by time of supervened (p=0,016 and p=0,0128). CONCLUSION: Both critical situations in this model, controlled hemorrhagic shock followed by Pringle's maneuver, promoted neutrophils sequestration in the interstitium renal of rat, and the physiologic saline solution demonstrated minor mean, differentiating statistically of the others solutions.

Heterogeneous Microcirculation in the Rat Small Intestine during Hemorrhagic Shock: Quantification of the Effects of Hypertonic-Hyperoncotic Resuscitation

PURPOSE

In the event of a spatial or temporal microvascular perfusion heterogeneity conventional methods are often inadequate to describe the microcirculatory changes. Our aim was to use a new formula to characterize and compare the microcirculatory reactions in the mucosa and longitudinal muscle of the rat small intestine in response to hypertonic/hyperoncotic and normotonic resuscitation strategies.

METHODS

Intravital videomicroscopy with an orthogonal polarization spectral (OPS) imaging technique was utilized. Microcirculatory variables were recorded during hemorrhagic shock (HS; 50 mm Hg mean arterial pressure for 60 min) and fluid replacement with 0.9% saline or with 7.2% saline containing 10% hydroxyethylstarch 200/0.5 (Osmohes; 4 ml/kg). Due to the temporal perfusion variability, microcirculatory changes were described using the calculation of the average red blood cell velocity (A-RBCV), while the spatial changes were calculated as a function of the size of the perfused capillary network.

RESULTS

During HS and the late phase of resuscitation, perfusion was characterized by capillary flow motion (i.e. variability in time) in the villi, and by spatial flow heterogeneity in the longitudinal muscle layer. The approximately 40% decrease in the calculated villus A-RBCV during HS was only partially affected by 0.9% saline, whereas Osmohes completely restored A-RBCV by increasing both the red blood cell velocity and the duration of high-flow periods at the onset of resuscitation in the villi. The approximately 60% reduction in A-RBCV in the muscle layer during HS was not followed by an appreciable recovery in either group, but Osmohes significantly increased A-RBCV in the late resuscitation phase.

CONCLUSIONS

The hypertonic/hyperoncotic solution induces a considerable microcirculatory improvement in two distinct layers of the small intestine after HS. This positive effect is related to the amelioration of the intestinal microcirculatory heterogeneity.

Salutary effects of androstenediol on cardiac function and splanchnic perfusion after trauma-hemorrhage

Recent studies have shown that dehydroepiandrosterone (DHEA) administration after trauma-hemorrhage (T-H) improves cardiovascular function and decreases cytokine production in male animals. Although androstenediol, one of the metabolites of DHEA, is reported to have estrogen-like activity, it remains unknown whether androstenediol per se has any salutary effects on cytokines and cardiovascular function after T-H. To examine this effect, male Sprague-Dawley rats underwent laparotomy and were bled to and maintained at a mean arterial blood pressure of 35–40 mmHg for ∼90 min. The animals were resuscitated with four times the volume of maximal bleedout volume in the form of Ringer lactate. Androstenediol (1 mg/kg body wt iv) or vehicle was administered at the end of resuscitation. Twenty-four hours after resuscitation, cardiac function and organ blood flow were measured by using 85Sr-microspheres. Circulating levels of nitrate/nitrite and IL-6 were also determined. Cardiovascular function and organ blood flow were significantly depressed after T-H. However, these parameters were restored by androstenediol treatment. The elevated plasma IL-6 levels after T-H were also lowered by androstenediol treatment. In contrast, plasma levels of nitrate/nitrite were the highest in the androstenediol-treated T-H animals. Because androstenediol administration after T-H decreases cytokine production and improves cardiovascular function, this agent appears to be a novel and useful adjunct for restoring the depressed cardiovascular function and for cytokine production in males after adverse circulatory conditions.

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.

Effect of estradiol administration on splanchnic perfusion after trauma-hemorrhage and sepsis

PURPOSE OF REVIEW

This review focuses on the latest mechanistic understanding of the effects of estradiol on the splanchnic circulation and the possibility of estradiol treatment as an adjunct for the treatment of trauma-hemorrhage and sepsis.

RECENT FINDINGS

Systemic hypotension induced by shock accompanies marked alterations in blood flow to various organs. Decreased splanchnic perfusion is frequently observed after insults, such as severe hemorrhage or sepsis, which leads to the destruction of the intestinal mucosal barrier and hepatic dysfunction. Studies suggest that estradiol acts as a facilitator of the intestinal blood flow via the increased production of nitric oxide, decreased production of vasoconstrictors, attenuated neutrophil adhesion, and decreased formation of oxygen free radicals.

SUMMARY

Trauma-hemorrhage results in decreased circulating blood volume. In contrast, sepsis is an inflammatory state mainly mediated by bacterial products. However, these divergent insults show similar pathophysiologic alterations in terms of the splanchnic circulation. Because estradiol effectively protects the organs from circulatory failure after various adverse circulatory conditions, many studies are being performed to clarify the molecular mechanism of estradiol action with regard to tissue circulation. Estradiol improves the macro- and microcirculation of the splanchnic organs by multiple mechanisms. Nonetheless, it remains unclear which mechanism plays the most important role in the treatment of trauma-hemorrhage and sepsis. Additional studies are required to elucidate the precise mechanism of estradiol action and to determine the usefulness of estradiol treatment for severe hemorrhage and sepsis in patients.

Near-infrared spectroscopy reflects changes in mesenteric and systemic perfusion during abdominal compartment syndrome

BACKGROUND

Continuous and minimally invasive near-infrared spectroscopy (NIRS)-derived gastric tissue oxygen saturation (GStO(2)) and muscle tissue oxygen saturation (MStO(2)) were evaluated in a clinically relevant porcine model of hemorrhagic shock and abdominal compartment syndrome (ACS).

METHODS

Phenobarbital-anesthetized swine underwent pulmonary artery catheter insertion for mixed venous oxygen saturation (SvO(2)) measurement and midline laparotomy to permit placement of a gastric NIRS probe, a jejunal (regional carbon dioxide [PrCO(2)]) tonometer, superior mesenteric artery (SMA) flow probe, and a portal vein oxygen saturation (SpvO(2)) catheter. A muscle NIRS probe was placed on the front limb. After randomization, Group 1 underwent hemorrhage and resuscitation. Group 2 had no hemorrhage or resuscitation. ACS was induced by peritoneal fluid infusion in both groups. A significant decrease in SMA flow, SpvO(2), GStO(2), SvO(2), and MStO(2) was observed after hemorrhage in Group 1 and with abdominal hypertension in both groups.

RESULTS

GStO(2) significantly correlated with SMA flow (Group 1: r(2) = 0.90; Group 2: r(2) = 0.83) and mesenteric oxygen delivery (mesenteric oxygen delivery, Group 1: r(2) = 0.73; Group 2: r(2) = 0.89). MStO(2) significantly correlated with SvO(2) (Group 1: r(2) = 0.99; Group 2: r(2) = 0.65) and systemic oxygen delivery (SDO2, Group 1: r(2) = 0.60; Group 2: r(2) = 0.88). Tonometer-derived PrCO(2) values did not change at any time point in either group.

CONCLUSIONS

NIRS measurement of GStO(2) and MStO(2) reflected changes in mesenteric and systemic perfusion respectively during hemorrhage and ACS.

Microvascular effects of oral interleukin-6 on ischemia/reperfusion in the murine small intestine

Oral administration of interleukin-6 (IL-6) has been shown to reduce hemorrhage-induced bacterial translocation from the gut in mice and rats. To examine the intestinal microvasculature, mice were given the electron-dense tracer horseradish peroxidase (HRP) after hemorrhage and IL-6 or vehicle administration. In normal mice and in those hemorrhaged and given IL-6, the electron-dense marker, administered intravenously, could be found in intestinal capillaries and between mucosal epithelial cells, suggesting that the microvasculature was patent. In mice given saline after shock, however, no marker was present in the gut, suggesting that the intestinal microvasculature was unable to deliver the marker to the epithelia. When mice were given HRP intralumenally (il) the tracer was able to penetrate between intestinal epithelial cells only in mice given vehicle after hemorrhage. This finding suggests that hemorrhaged mice were susceptible to sepsis and endotoxic shock from the leaky gut. In normal and IL-6-treated mice, the tracer was unable to pass from the lumen between mucosal epithelial cells, because the presence of an intact zonula occludens prevented passage. Functional studies supported the electron microscopy findings. Bacteria were cultured from the livers of mice fed vehicle after hemorrhage, but not from those fed IL-6. These data support the conclusions that parts of the intestinal microvasculature remain diminished after hemorrhage and resuscitation and that oral IL-6 restores this circulation.

Immune dysfunction in trauma

This article documents that all immunomodulation strategies for patients sustaining traumatic injury are still under intense investigation. Although we can speculate that combination strategies may be more beneficial than single-agent immunomodulation approaches, comprehensive clinical studies are required to determine efficacious immune therapy for trauma patients. The only strategy available to clinicians caring for trauma patients is immunonutrition, and this should be strongly considered as a rational approach to improve immune function and reduce septic complications in critically ill or injured patients.

Effect of hemorrhage on superior mesenteric artery flow during increased intra-abdominal pressures

BACKGROUND

Elevations in intra-abdominal pressure (IAP) adversely affect organ function. Prior hemorrhage and resuscitation exacerbates the cardiac and pulmonary effects of IAP. We have recently shown that superior mesenteric artery flow (SMAF) is reduced with increasing IAP. This study was designed to determine whether and how hemorrhage and resuscitation affects SMAF with increasing IAP.

METHODS

Ten pigs were divided into two groups after placement of a Doppler flow probe around the proximal SMA and insertion of a pulmonary artery (PA) catheter. Group 1 underwent intraperitoneal infusion of fluid to increase IAP to 10, 20, 30, and 40 mm Hg followed by a 20-minute equilibration period at each IAP. Group 2 was hemorrhaged 20% of circulating volume followed by standard resuscitation. After equilibration, this group had IAP increased in the same manner as group 1. Cardiac output (CO), PA pressures, and SMAF were recorded 1 hour after laparotomy and after equilibration at each IAP. Comparisons were made using repeated measures of analysis of variance, Student's t test, and linear regression analysis.

RESULTS

In group 2, a reduction in SMAF was noted at 30 and 40 mm Hg of IAP when compared with baseline (p = 0.009). This reduction was not seen in group 1. There was also a significant (p = 0.001) reduction in CO between baseline and all levels of increased IAP in group 2. This decrease was again not seen in group 1. The correlation between CO and SMAF in group 2 was r = 0.74, r2 = 0.55, p = 0.0001. There was no significant correlation between CO and SMAF in group 1.

CONCLUSION

SMAF and CO are reduced with increasing IAP to a greater degree when preceded by hemorrhage and resuscitation. Although there is a strong correlation between the reductions in CO and SMAF, the reduction in SMAF is greater than the reduction in CO. This finding suggests that optimizing cardiac function alone during periods of even moderate levels of increased IAP may be inadequate to normalize SMAF. This lends further support for early abdominal decompression in the treatment of trauma patients with increased IAP.

Diaspirin cross-linked hemoglobin is efficacious in gut resuscitation as measured by a GI tract optode

The objective of this study was to compare the efficacy of diaspirin cross-linked hemoglobin (DCLHb) with that of standard resuscitative fluids in restoring intestinal mucosal oxygenation and villous architecture after hemorrhage. Male rats were bled to a base deficit of 5 +/- 2 nmol/l under propofol anesthesia and monitored for 90 minutes postresuscitation with DCLHb, blood, lactated Ringer's solution, albumin, or nothing (DNR) for mucosal oxygen tension (Pmo2) and physiologic and laboratory parameters. Small intestinal histologic specimens were obtained and scored independently by two investigators blinded to therapy on a scale of 0 (normal) to 4 (worst). All treatments restored Pmo2; only DCLHb did so without exceeding baseline values. For untreated rats (DNR), Pmo2 was not restored. Normal mucosal architecture was maintained only in DCLHb-treated rats. As Pmo2 increased, mucosal score improved. In a rat model of controlled hemorrhage, Pmo2 changes measured by an optode correlated with gut histological abnormalities. By these criteria, DCLHb is superior to crystalloid, colloid, and blood in gut resuscitation.

Hemorrhagic shock

A great deal has been learned about the pathophysiologic condition of hemorrhagic shock. The response of the hormonal and inflammatory mediator systems in patients in hemorrhagic shock appears to represent a distinct set of responses different from those of other forms of shock. The classic neuroendocrine response to hemorrhage attempts to maintain perfusion to the heart and brain, often at the expense of other organ systems. This intense vasoconstriction occurs via central mechanisms. The response of the peripheral microcirculation is driven by local tissue hypoperfusion that results in vasodilation in the ischemic tissue bed. Activation of the systemic inflammatory response by hemorrhage and tissue injury is an important component of the pathophysiologic condition of hemorrhagic shock. Activators of this systemic inflammatory response include ischemia/reperfusion injury and neutrophil activation. Capillary "no-flow" with prolonged ischemia and "no-reflow" with reperfusion may initiate neutrophil activation in patients in hemorrhagic shock. The mechanisms that lead to decompensated and irreversible hemorrhagic shock include (1) "arteriolar hyposensitivity" as manifested by progressive arteriolar vasodilation and decreased responsiveness of the microcirculation to alpha-agonists, and (2) cellular injury and activation of both proinflammatory and counterinflammatory mechanisms. These changes represent a failure of the microcirculation. Redistribution of cardiac output and persistent gut ischemia after adequate resuscitation may also contribute to the development of irreversible hemorrhagic shock. Treatment of hemorrhagic shock includes rapid operative resuscitation to limit activation of the mediator systems and abort the microcirculatory changes that result from hemorrhagic shock. Volume resuscitation and control of hemorrhage, should occur simultaneously. The end point in volume resuscitation of hemorrhagic shock must be maintenance of organ system and cellular function. Whether we use adequate urine output, correction of lactic acidemia, optimization of oxygen delivery, or oxygen consumption as our specific goal, the general objective is to provide adequate crystalloid solution and packed red blood cells to achieve and maintain normal organ and cellular perfusion and function.

Redistribution of organ blood flow after hemorrhage and resuscitation in full-term piglets

Newborn piglets (aged 1 to 2 days and 7 to 14 days) were used to study (1) the redistribution of organ blood flow after a 25% acute blood loss and (2) the response to resuscitation with shed blood (20 mL/kg), crystalloid (normal saline [NS] or lactated Ringer's [LR]; 60 mL/kg), and colloid (Dextran-40, 20 mL/kg). Hemodynamic parameters showed little differences in the response to hemorrhage and resuscitation. The two age groups had no significant differences in parameters or blood flow (results combined). The animals maintained flow to the heart and central nervous system (CNS) and had significantly decreased flow to the kidneys and splanchnic organs. In the gastrointestinal tract, the small intestine was affected most severely, with a significant decrease in blood flow, especially to the mucosa. In all organ systems, Dextran 40 restored blood flow to levels significantly above the baseline. Shed blood and crystalloid restored flow to organs sustaining decreased flow, but crystalloid did not restore flow to the baseline level in the kidney and all segments of the gastrointestinal tract.