Cellular edema regulates tissue capillary perfusion after hemorrhage resuscitation

Direct Peritoneal Resuscitation: A Novel Adjunct to Damage Control Laparotomy

Direct peritoneal resuscitation is a validated resuscitation strategy for patients undergoing damage control surgery for hemorrhage, sepsis, or abdominal compartment syndrome with open abdomen and planned reexploration after a period of resuscitation in the intensive care unit. Direct peritoneal resuscitation can decrease visceral edema, normalize body water ratios, accelerate primary abdominal wall closure after damage control surgery, and prevent complications associated with open abdomen. This review article describes the physiological benefits of direct peritoneal resuscitation, how this technique fits within management priorities for the patient in shock, and procedural components in the care of open abdomen surgical patients receiving direct peritoneal resuscitation. Strategies for successful implementation of a novel multidisciplinary intervention in critical care practice are explored.

Superior Survival Outcomes of a Polyethylene Glycol-20k Based Resuscitation Solution in a Preclinical Porcine Model of Lethal Hemorrhagic Shock

OBJECTIVE

To compare early outcomes and 24-hour survival after LVR with the novel polyethylene glycol-20k-based crystalloid (PEG-20k), WB, or hextend in a preclinical model of lethal HS.

BACKGROUND

Posttraumatic HS is a major cause of preventable death. Current resuscitation strategies focus on restoring oxygen-carrying capacity (OCC) and coagulation with blood products. Our lab shows that PEG-20k is an effective non-sanguineous, LVR solution in acute models of HS through mechanisms targeting cell swelling-induced microcirculatory failure.

METHODS

Male pigs underwent splenectomy followed by controlled hemorrhage until lactate reached 7.5-8.5 mmol/L. They were randomized to receive LVR with PEG-20k, WB, or Hextend. Surviving animals were recovered 4 hours post-LVR. Outcomes included 24-hour survival rates, mean arterial pressure, lactate, hemoglobin, and estimated intravascular volume changes.

RESULTS

Twenty-four-hour survival rates were 100%, 16.7%, and 0% in the PEG-20k, WB, and Hextend groups, respectively (P = 0.001). PEG-20k significantly restored mean arterial press, intravascular volume, and capillary perfusion to baseline, compared to other groups. This caused complete lactate clearance despite decreased OCC. Neurological function was normal after next-day recovery in PEG-20k resuscitated pigs.

CONCLUSION

Superior early and 24-hour outcomes were observed with PEG-20k LVR compared to WB and Hextend in a preclinical porcine model of lethal HS, despite decreased OCC from substantial volume-expansion. These findings demonstrate the importance of enhancing microcirculatory perfusion in early resuscitation strategies.

Where's the Leak in Vascular Barriers? A Review

Edema is typically presented as a secondary effect from injury, illness, disease, or medication, and its impact on patient wellness is nested within the underlying etiology. Therefore, it is often thought of more as an amplifier to current preexisting conditions. Edema, however, can be an independent risk factor for patient deterioration. Improper management of edema is costly not only to the patient, but also to treatment and care facilities, as mismanagement of edema results in increased lengths of hospital stay. Direct tissue trauma, disease, or inappropriate resuscitation and/or ventilation strategies result in edema formation through physical disruption and chemical messenger-based structural modifications of the microvascular barrier. Derangements in microvascular barrier function limit tissue oxygenation, nutrient flow, and cellular waste removal. Recent studies have sought to elucidate cellular signaling and structural alterations that result in vascular hyperpermeability in a variety of critical care conditions to include hemorrhage, burn trauma, and sepsis. These studies and many others have highlighted how multiple mechanisms alter paracellular and/or transcellular pathways promoting hyperpermeability. Roles for endothelial glycocalyx, extracellular matrix and basement membrane, vesiculo-vacuolar organelles, cellular junction and cytoskeletal proteins, and vascular pericytes have been described, demonstrating the complexity of microvascular barrier regulation. Understanding these basic mechanisms inside and out of microvessels aid in developing better treatment strategies to mitigate the harmful effects of excessive edema formation.

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.

Supra-plasma expanders: the future of treating blood loss and anemia without red cell transfusions?

Oxygen delivery capacity during profoundly anemic conditions depends on blood's oxygen-carrying capacity and cardiac output. Oxygen-carrying blood substitutes and blood transfusion augment oxygen-carrying capacity, but both have given rise to safety concerns, and their efficacy remains unresolved. Anemia decreases oxygen-carrying capacity and blood viscosity. Present studies show that correcting the decrease of blood viscosity by increasing plasma viscosity with newly developed plasma expanders significantly improves tissue perfusion. These new plasma expanders promote tissue perfusion, increasing oxygen delivery capacity without increasing blood oxygen-carrying capacity, thus treating the effects of anemia while avoiding the transfusion of blood.

[Pathophysiology of hemorragic shock]

This review addresses the pathophysiology of hemorrhagic shock, a condition produced by rapid and significant loss of intravascular volume, which may lead to hemodynamic instability, decreases in oxygen delivery, decreased tissue perfusion, cellular hypoxia, organ damage, and death. The initial neuroendocrine response is mainly a sympathetic activation. Haemorrhagic shock is associated altered microcirculatory permeability and visceral injury. It is also responsible for a complex inflammatory response associated with hemostasis alteration.

Cell Impermeant-based Low-volume Resuscitation in Hemorrhagic Shock: A Biological Basis for Injury Involving Cell Swelling

OBJECTIVE

To determine the role of cell swelling in severe hemorrhagic shock and resuscitation injury.

BACKGROUND

Circulatory shock induces the loss of energy-dependent volume control mechanisms. As water enters ischemic cells, they swell, die, and compress nearby vascular structures, which further aggravates ischemia by reducing local microcirculatory flow and oxygenation. Loading the interstitial space with cell impermeant molecules prevents water movement into the cell by passive biophysical osmotic effects, which prevents swelling injury and no-reflow.

METHODS

Adult rats were hemorrhaged to a pressure of 30 to 35  mm Hg, held there until the plasma lactate reached 10  mM, and given a low-volume resuscitation (LVR) (10%-20% blood volume) with saline or various cell impermeants (sorbitol, raffinose, trehalose, gluconate, and polyethylene glycol-20k (PEG-20k). When lactate again reached 10  mM after LVR, full resuscitation was started with crystalloid and red cells. One hour after full resuscitation, the rats were euthanized. Capillary blood flow was measured by the colored microsphere technique.

RESULTS

Impermeants prevented ischemia-induced cell swelling in liver tissue and dramatically improved LVR outcomes in shocked rats. Small cell impermeants and PEG-20k in LVR solutions increased tolerance to the low flow state by two and fivefold, respectively, normalized arterial pressure during LVR, and lowered plasma lactate after full resuscitation, relative to saline. This was accompanied by higher capillary blood flow with cell impermeants.

CONCLUSIONS

Ischemia-induced lethal cell swelling during hemorrhagic shock is a key mediator of resuscitation injury, which can be prevented by cell impermeants in low-volume resuscitation solutions.

Fluid resuscitation and vasopressors in severe trauma patients

PURPOSE OF REVIEW

To discuss the fluid resuscitation and the vasopressor support in severe trauma patients.

RECENT FINDINGS

A critical point is to prevent a potential increase in bleeding by an overly aggressive resuscitative strategy. Indeed, large-volume fluid replacement may promote coagulopathy by diluting coagulation factors. Moreover, an excessive level of mean arterial pressure may induce bleeding by preventing clot formation.

SUMMARY

Fluid resuscitation is the first-line therapy to restore intravascular volume and to prevent cardiac arrest. Thus, fluid resuscitation before bleeding control must be limited to the bare minimum to maintain arterial pressure to minimize dilution of coagulation factors and complications of over fluid resuscitation. However, a strategy of low fluid resuscitation needs to be handled in a flexible way and to be balanced considering the severity of the hemorrhage and the transport time. A target systolic arterial pressure of 80-90 mmHg is recommended until the control of hemorrhage in trauma patients without brain injury. In addition to fluid resuscitation, early vasopressor support may be required to restore arterial pressure and prevent excessive fluid resuscitation. It is crucial to find the best alchemy between fluid resuscitation and vasopressors, to consider hemodynamic monitoring and to establish trauma resuscitative protocols.

Intestinal Microcirculatory Flow Alterations in Necrotizing Enterocolitis are Improved by Direct Peritoneal Resuscitation

Vasoconstriction of the neonatal intestinal microvasculature is a central mechanistic event in development of necrotizing enterocolitis. We hypothesized that topical treatment of the intestine with dialysate fluid would ameliorate the vasoconstriction in necrotizing enterocolitis (NEC). NEC was induced in experimental groups. Control animals were delivered vaginally and dam-fed (control group). Neonatal pups underwent laser Doppler flow study of the terminal ileum to determine real-time blood flow in the intestinal microvasculature. After baseline flow was determined, dialysis solution was added to the peritoneal cavity and alterations in microcirculation were recorded. Baseline ileal blood flow in the control group was significantly higher than in NEC rat pups at 48 hours post delivery ( P < 0.05), but not at 24 hours ( P = NS). Ileal blood flow increased in all groups after adding dialysate ( P < 0.05), improving ileal blood flow in the 48-hour NEC group and reaching the baseline level of the 48-hour control group ( P < 0.05). Our data shows blood flow to be higher in 48-hour controls as compared with 24-hour controls suggesting a time-dependency in the development of intestinal vasoregulatory processes. All groups had an increase in blood flow with dialysate treatment. This may represent a novel initial therapy to improve intestinal ischemia in human necrotizing enterocolitis.

Toward computational identification of multiscale "tipping points" in acute inflammation and multiple organ failure

Sepsis accounts annually for nearly 10% of total U.S. deaths, costing nearly $17 billion/year. Sepsis is a manifestation of disordered systemic inflammation. Properly regulated inflammation allows for timely recognition and effective reaction to injury or infection, but inadequate or overly robust inflammation can lead to Multiple Organ Dysfunction Syndrome (MODS). There is an incongruity between the systemic nature of disordered inflammation (as the target of inflammation-modulating therapies), and the regional manifestation of organ-specific failure (as the subject of organ support), that presents a therapeutic dilemma: systemic interventions can interfere with an individual organ system's appropriate response, yet organ-specific interventions may not help the overall system reorient itself. Based on a decade of systems and computational approaches to deciphering acute inflammation, along with translationally-motivated experimental studies in both small and large animals, we propose that MODS evolves due to the feed-forward cycle of inflammation → damage → inflammation. We hypothesize that inflammation proceeds at a given, "nested" level or scale until positive feedback exceeds a "tipping point." Below this tipping point, inflammation is contained and manageable; when this threshold is crossed, inflammation becomes disordered, and dysfunction propagates to a higher biological scale (e.g., progressing from cellular, to tissue/organ, to multiple organs, to the organism). Finally, we suggest that a combination of computational biology approaches involving data-driven and mechanistic mathematical modeling, in close association with studies in clinically relevant paradigms of sepsis/MODS, are necessary in order to define scale-specific "tipping points" and to suggest novel therapies for sepsis.

Preliminary resuscitation for perforated necrotizing enterocolitis: 2 cases treated with initial direct peritoneal resuscitation

We used peritoneal infusions of 2.5% dextrose solution as an adjunct to resuscitation of 2 very low-birth-weight infants having perforated necrotizing enterocolitis. This was repeated every 12 hours for 7 days before and 1 day after extensive bowel resection. The designation of this research method has been termed direct peritoneal resuscitation. We discuss our observations and the evolution of this technique from studies in the animal laboratory to a recent trial in patients with abdominal trauma. We propose that the early response benefit of this preoperative resuscitation seen in our 2 cases be investigated by others. Prospective controlled trials could then be considered for those high-risk patients having diffuse disease and shock.

Direct peritoneal resuscitation accelerates primary abdominal wall closure after damage control surgery

BACKGROUND

Damage control surgery is a staged approach to the trauma patient in extremis that improves survival, but leads to open abdominal wounds that are difficult to manage. We evaluated whether directed peritoneal resuscitation (DPR) when used as a resuscitation strategy in severely injured trauma patients with hemorrhagic shock requiring damage control surgery would affect the amount of and timing of resuscitation and/or show benefits in time to abdominal closure and reduction of intra-abdominal complications.

STUDY DESIGN

A retrospective case-matched study of patients undergoing damage control surgery for hemorrhagic shock secondary to trauma between January 2005 and December 2008 was performed. Twenty patients undergoing standardized wound closure and adjunctive DPR were identified and matched to 40 controls by Injury Severity Score, age, gender, and mechanism of injury. A single early death was excluded because of inability to control ongoing hemorrhage.

RESULTS

There were no differences in age, gender, or mechanism of injury between the groups. Injury Severity Score (35.07 +/- 17.1 versus DPR 34.95 +/- 16.95; p = 0.82) and packed red blood cell administration in 24 hours (23.8 +/- 14.35 U versus DPR 26.9 +/- 14.1 U; p = 0.43) were similar between the groups. Presenting pH was similar between the study group and the DPR group (7.24 +/- 0.13 d versus DPR 7.26 +/- 0.11; p = 0.8). Time to definitive abdominal closure was significantly less in the DPR group compared with controls (DPR: 4.35 +/- 1.6 d versus 7.05 +/- 3.31; p < 0.003). DPR also allowed for a higher rate of primary fascial closure, lower intra-abdominal complication rate, and lower rate of ventral hernia formation at 6 months. Adjunctive DPR afforded a definitive wound closure advantage compared with Wittmann patch closure techniques (DPR 4.35 +/- 1.6 versus Wittmann patch 6.375 +/- 1.3; p = 0.004).

CONCLUSIONS

The addition of adjunctive DPR to the damage control strategy shortens the interval to definitive fascial closure without affecting overall resuscitation volumes. As a result, this mitigates intra-abdominal complications associated with open abdomen and damage control surgery and affords better patient outcomes.

Resuscitation-induced intestinal edema and related dysfunction: state of the science

High volume resuscitation and damage control surgical methods, while responsible for significantly decreasing morbidity and mortality from traumatic injuries, are associated with pathophysiologic derangements that lead to subsequent end organ edema and dysfunction. Alterations in hydrostatic and oncotic pressures frequently result in intestinal edema and subsequent dysfunction. The purpose of this review is to examine the principles involved in the development of intestinal edema, current and historical models for the study of edema, effects of edema on intestinal function (particularly ileus), molecular mediators governing edema-induced dysfunction, potential role of mechanotransduction , and therapeutic effects of hypertonic saline. We review the current state of the science as it relates to resuscitation induced intestinal edema and resultant dysfunction.

Hemorrhage-induced hepatic injury and hypoperfusion can be prevented by direct peritoneal resuscitation

BACKGROUND

Crystalloid fluid resuscitation after hemorrhagic shock (HS) that restores/maintains central hemodynamics often culminates in multi-system organ failure and death due to persistent/progressive splanchnic hypoperfusion and end-organ damage. Adjunctive direct peritoneal resuscitation (DPR) using peritoneal dialysis solution reverses HS-induced splanchnic hypoperfusion and improves survival. We examined HS-mediated hepatic perfusion (galactose clearance), tissue injury (histopathology), and dysfunction (liver enzymes).

METHODS

Anesthetized rats were randomly assigned (n = 8/group): (1) sham (no HS); (2) HS (40% mean arterial pressure for 60 min) plus conventional i.v. fluid resuscitation (CR; shed blood + 2 volumes saline); (3) HS + CR + 30 mL intraperitoneal (IP) DPR; or (4) HS + CR + 30 mL IP saline. Hemodynamics and hepatic blood flow were measured for 2 h after CR completion. In duplicate animals, liver and splanchnic tissues were harvested for histopathology (blinded, graded), hepatocellular function (liver enzymes), and tissue edema (wet-dry ratio).

RESULTS

Group 2 decreased liver blood flow, caused liver injuries (focal to submassive necrosis, zones 2 and 3) and tissue edema, and elevated liver enzymes (alanine aminotransferase (ALT), 149 +/- 28 microg/mL and aspartate aminotransferase (AST), 234 +/- 24 microg/mL; p < 0.05) compared to group 1 (73 +/- 9 and 119 +/- 10 microg/mL, respectively). Minimal/no injuries were observed in group 3; enzymes were normalized (ALT 89 +/- 9 microg/mL and AST 150 +/- 17 microg/mL), and tissue edema was similar to sham.

CONCLUSIONS

CR from HS restored and maintained central hemodynamics but did not restore or maintain liver perfusion and was associated with significant hepatocellular injury and dysfunction. DPR added to conventional resuscitation (blood and crystalloid) restored and maintained liver perfusion, prevented hepatocellular injury and edema, and preserved liver function.

Hemorrhagic shock and resuscitation-mediated tissue water distribution is normalized by adjunctive peritoneal resuscitation

BACKGROUND

Adjunctive direct peritoneal resuscitation (DPR) from hemorrhagic shock (HS) improves intestinal blood flow and abrogates postresuscitation edema. HS causes water shifts as a result of sodium redistribution and changes in transcapillary Starling forces. Conventional resuscitation (CR) with crystalloid aggravates water sequestration. We examined the compartment pattern of organ tissue water after HS and CR, and modulation of tissue edema by adjunctive DPR.

STUDY DESIGN

Rats were hemorrhaged (40% mean arterial pressure for 60 minutes) and assigned to four groups (n = 7): sham, no HS; HS no resuscitation; HS+CR (shed blood plus 2 volumes Ringer's lactate); and HS+CR+DPR (20 mL clinical intraperitoneal (IP) dialysis fluid). Isotopic markers determined equilibrium distribution volumes [V(D)] in gut, liver, lung, and muscle by quantitative autoradiography (2-hour postresuscitation). Total tissue water (TTW) was determined by wet-dry weights. Extracellular water was measured from (14)C-mannitol V(D), and intravascular volume (IVV) from (131)I-labeled IgG V(D). Cellular and interstitial water volumes were calculated.

RESULTS

HS alone decreased IVV in all tissues and TTW in gut, lung, and muscle, but not liver, compared with shams. IVV remained decreased with all resuscitations despite restoration of central hemodynamics. CR caused interstitial edema in gut, liver, and muscle, and cellular edema in lung. DPR reduced (liver, muscle) or prevented (gut, lung) these volume shifts.

CONCLUSIONS

HS decreases IVV. HS-induced water shifts are organ-specific and prominent in gut, lung, and muscle. CR restores central hemodynamics, does not restore IVV, and alters organ-specific TTW distribution. Adjunctive DPR with IP dialysis fluid normalizes TTW and water compartment distribution and prevents edema. Combined effect of DPR and intravascular fluid replacement appears to prevent global tissue edema and improve outcomes from HS.