A novel physiologic model for the study of abdominal compartment syndrome (ACS)

Enteral resuscitation with oral rehydration solution to reduce acute kidney injury in burn victims: Evidence from a porcine model

Intravenous (IV) resuscitation of burn patients has greatly improved outcomes and become a cornerstone of modern burn care. However, the heavy fluids and vascular access required may not be feasible in austere environments, mass casualty, or delayed transport scenarios. Enteral resuscitation has been proposed for these situations; we sought to examine the effectiveness of this strategy on improving burn-induced kidney injury. Anesthetized Yorkshire swine sustaining 40% TBSA full-thickness contact burns were randomized to three groups (n = 6/group): fluid deprivation, ad libitum water access, or 70 mL/kg/d Oral Rehydration Salt solution (ORS). Urine and blood were collected at baseline (BL), 6, 12, 24, 32, and 48h post-burn, at which point tissue was harvested and CT angiography performed. Although fluid consumption by ad libitum and ORS groups were matched (132±54mL/kg versus 120±24mL/kg, respectively), ORS intake increased urine output compared with water and no water (47.3±9.0 mL/kg versus 16.1±2.5 mL/kg, and 24.5±1.7 mL/kg respectively). Plasma creatinine peaked 6h following burn (1.67±0.07mg/dL) in all animals, but at 48h was comparable to BL in animals receiving water (1.23±0.06mg/dL) and ORS (1.30±0.09mg/dL), but not fluid deprived animals (1.56±0.05mg/dL) (P<0.05). Circulating levels of blood urea nitrogen steadily increased, but also decreased by 48h in animals receiving enteral fluids (P<0.05). Water deprivation reduced renal artery diameter (-1.4±0.17mm), whereas resuscitation with water (-0.44±0.14 mm) or ORS maintained it (-0.63±0.20 mm;P< 0.02). Circulating cytokines IL-1β, IL-6, IFNγ, and GM-CSF were moderately elevated in the fluid-deprived group. Taken together, the data suggest that enteral resuscitation with ORS rescues kidney function following burn injury. Incorporating enteral fluids may improve outcomes in resource-poor environments and possibly reduce IV fluid requirements to prevent co-morbidities associated with over-resuscitation. Studies into different volumes/types of enteral fluids are warranted. While ORS has saved many lives in cholera-associated dehydration, it should be investigated further for use in burn patients.

Effect of intra-abdominal volume increment on kidneys in minipigs with intra-abdominal hypertension after hemorrhagic shock and resuscitation

BACKGROUND

To investigate the effect of intra-abdominal volume increment (IAVI) on intra-abdominal hypertension (IAH) in the kidneys.

METHODS

Eight minipigs were successfully established as IAH models and were randomly divided into two groups: the IAVI group and the sham-operated group. The intravesicular pressure, inferior vena cava pressure and urine volume were measured before shock, 2 h after IAH, and 22 h after surgery, respectively. The following indices were measured: serum creatinine, urea nitrogen, renal cortical thickness, ratio of abdominal anteroposterior diameter/transverse diameter, renal thickness, diameter of the renal sinus and the wet/dry ratio of renal tissues.

RESULTS

The intravesicular pressure (IVP) of the 8 minipig IAH models was calculated to be 21.16 ± 4.63 mmHg. There was a significant increase in the abdominal anteroposterior diameter/transverse diameter ratio. The minipigs in the IAVI group survived during the observational period, whereas 2 minipigs died at 18 h and 20 h in the sham-operated group. Twenty-two hours after surgery, the animals in the IAVI group displayed increased urinary volume (UV) and decreased Cr and Ur and remarkable decreases of VP and IVCP. After IAH, the renal cortical thickness and the renal thickness increased significantly. The renal wet/dry ratio in the sham-operated group was higher than that in the IAVI group.

CONCLUSION

IAVI helps to control renal dysfunction after IAH, which may be related to lowering the intra-abdominal pressure, thus alleviating renal edema and blood stasis.

Influence of two different levels of intra-abdominal hypertension on bacterial translocation in a porcine model

BACKGROUND

The purpose of the present study was to quantify bacterial translocation to mesenteric lymph nodes due to different levels of intra-abdominal hypertension (IAH; 15 vs. 30 mmHg) lasting for 24 h in a porcine model.

METHODS

We examined 18 anesthetized and intubated pigs (52.3 ± 4.7 kg) which were randomly allocated to three experimental groups (each n = 6) and studied over a period of 24 h. After preparation and establishing a steady state, the intra-abdominal pressure (IAP) was increased stepwise to 30 mmHg in six animals using a carbon dioxide (CO2) insufflator (IAP-30 group). In the second group, IAP was increased to 15 mmHg (IAP-15 group), while IAP remained unchanged in another six pigs (control group). Using a pulse contour cardiac output (PiCCO®) monitoring system, hemodynamic parameters as well as blood gases were recorded periodically. Moreover, peripheral and portal vein blood samples were taken for microbiological examinations. Lymph nodes from the ileocecal junction were sampled during an intra-vital laparotomy at the end of the observational period. After sacrificing the animals, bowel tissue samples and corresponding mesenteric lymph nodes (MLN) were extracted for histopathological and microbiological analyses.

RESULTS

Cardiac output decreased in all groups. In IAP-30 animals, volumetric preload indices significantly decreased, while those of IAP-15 pigs did not differ from those of controls. Under IAH, the mean arterial pressure (MAP) in the IAP-30 group declined, while MAP in the IAP-15 group was significantly elevated (controls unchanged). PO2 and PCO2 remained unchanged. The grade of ischemic damage of the intestines (histopathologically quantified using the Park score) increased significantly with different IAH levels. Accordingly, the amount of translocated bacteria in intestinal wall specimens as well as in MLN significantly increased with the level of IAH. Lymph node cultures confirmed the relation between bacterial translocation (BT) and IAP. The most often cultivated species were Escherichia coli, Staphylococcus, Clostridium, Pasteurella, and Streptococcus. Bacteremia was detected only occasionally in all three groups (not significantly different) showing gut-derived bacteria such as Proteus, Klebsiella, and E. coli spp.

CONCLUSION

In this porcine model, a higher level of ischemic damage and more BT were observed in animals subjected to an IAP of 30 mmHg when compared to animals subjected to an IAP of 15 mmHg or controls.

Evaluating the effects of immediate application of negative pressure therapy after decompression from abdominal compartment syndrome in an experimental porcine model

PURPOSE

The purpose of this large-animal study was to assess the safety and effects of negative pressure therapy (NPT) when used as temporary abdominal closure in the immediate post-decompression period after abdominal compartment syndrome (ACS).

METHODS

Using a hemorrhagic shock/resuscitation and mesenteric venous pressure elevation model, ACS was physiologically induced in 12 female Yorkshire swine. At decompression, animals were allocated to either NPT (n = 6) or Bogota bag (n = 6) as temporary abdominal closure and studied for a period of 48 h or until death. Outcomes measured included morbidity and mortality, as well as hemodynamic parameters, ventilator-related measurements, blood gases, coagulation factors, and organ (liver, kidney, lung, and intestinal) edema and histology at the time of death/sacrifice.

RESULTS

All animals developed ACS. Early application of NPT was associated with decreases in mesenteric venous and central venous pressure, and significantly increased drainage of peritoneal fluid. In addition, there was no increase in the incidence of mortality, recurrent intra-abdominal hypertension/ACS, or any deleterious effects on markers of organ injury.

CONCLUSIONS

Early application of NPT in this porcine ACS model is safe and does not appear to be associated with an increased risk of recurrent intra-abdominal hypertension. The results of this animal study suggest that the application of NPT following decompression from ACS results in greater peritoneal fluid removal and may translate into augmented intestinal edema resolution secondary to more favorable fluid flux profiles.

A clinically applicable porcine model of septic and ischemia/reperfusion-induced shock and multiple organ injury

BACKGROUND

Although many sepsis treatments have shown efficacy in acute animal models, at present only activated protein C is effective in humans. The likely reason for this discrepancy is that most of the animal models used for preclinical testing do not accurately replicate the complex pathogenesis of human sepsis. Our objective in this study was to develop a clinically applicable model of severe sepsis and gut ischemia/reperfusion (I/R) that would cause multiple organ injury over a period of 48 h.

MATERIALS AND METHODS

Anesthetized, instrumented, and ventilated pigs were subjected to a "two-hit" injury by placement of a fecal clot through a laparotomy and by clamping the superior mesenteric artery (SMA) for 30 min. The animals were monitored for 48 h. Wide spectrum antibiotics and intravenous fluids were given to maintain hemodynamic status. FiO(2) was increased in response to oxygen desaturation. Twelve hours following injury, a drain was placed in the laparotomy wound. Extensive hemodynamic, lung, kidney, liver, and renal function measurements and serial measurements of arterial and mixed venous blood gases were made. Bladder pressure was measured as a surrogate for intra-peritoneal pressure to identify the development of the abdominal compartment syndrome (ACS). Plasma and peritoneal ascites cytokine concentration were measured at regular intervals. Tissues were harvested and fixed at necropsy for detailed morphometric analysis.

RESULTS

Polymicrobial sepsis developed in all animals. There was a progressive deterioration of organ function over the 48 h. The lung, kidney, liver, and intestine all demonstrated clinical and histopathologic injury. Acute lung injury (ALI) and ACS developed by consensus definitions. Increases in multiple cytokines in serum and peritoneal fluid paralleled the dysfunction found in major organs.

CONCLUSION

This animal model of Sepsis+I/R replicates the systemic inflammation and dysfunction of the major organ systems that is typically seen in human sepsis and trauma patients. The model should be useful in deciphering the complex pathophysiology of septic shock as it transitions to end-organ injury thus allowing sophisticated preclinical studies on potential treatments.

A murine model for the study of edema induced intestinal contractile dysfunction

BACKGROUND

We have published extensively regarding the effects of edema on intestinal contractile function. However, we have found the need to expand our model to mice to take advantage of the much larger arsenal of research support, especially in terms of transgenic mouse availability and development. To that end, we have developed and validated a hydrostatic intestinal edema model in mice.

METHODS

Male C57 Black 6 mice were subjected to a combination of high volume crystalloid resuscitation and mesenteric venous hypertension in an effort to induce hydrostatic intestinal edema. Wet to dry ratios, myeloperoxidase activity, mucosal injury scoring, STAT-3 nuclear activation, phosphorylated STAT-3 levels, NF-κB nuclear activation, myosin light chain phosphorylation, intestinal contractile activity, and intestinal transit were measured to evaluate the effects of the model.

KEY RESULTS

High volume crystalloid resuscitation and mesenteric venous hypertension resulted in the development of significant intestinal edema without an increase in myeloperoxidase activity or mucosal injury. Edema development was associated with increases in STAT-3 and NF-κB nuclear activation as well as phosphorylated STAT-3. There was a decrease in myosin light chain phosphorylation, basal and maximally stimulated intestinal contractile activity, and intestinal transit.

CONCLUSION & INFERENCES

Hydrostatic edema in mice results in activation of a signal transduction profile that culminates in intestinal contractile dysfunction. This novel model allows for advanced studies into the pathogenesis of hydrostatic edema induced intestinal contractile dysfunction.

A novel mechanism for neutrophil priming in trauma: potential role of peritoneal fluid

BACKGROUND

We sought to determine the effect of peritoneal fluid from a novel animal model of abdominal compartment syndrome (ACS) on the proinflammatory status of polymorphonuclear leukocytes (PMNs) and monocytes. We hypothesize that peritoneal fluid is a potential priming and/or activating agent for PMNs/monocytes.

METHODS

ACS was induced in female Yorkshire swine, and peritoneal fluid was collected at the time of decompressive laparotomy. Naïve PMNs/monocytes were primed and/or activated with peritoneal fluid, phosphatidylcholine (PAF) plus peritoneal fluid, peritoneal fluid plus n-formyl-met-leu-phe (fMLP), and peritoneal fluid plus phorbol 12-myristate 13-acetate (PMA). Activation was determined by surface marker expression of integrins (CD11b an CD18) and selectins (CD62L). Additionally, proinflammatory cytokines in peritoneal fluid were analyzed.

RESULTS

Peritoneal fluid did not activate PMNs but increased CD11b expression on monocytes. When used as a primer for fMLP- or PMA-induced activation, peritoneal fluid significantly increased CD11b and CD18 expression on PMNs and monocytes. Peritoneal fluid collected at 6 and 12 h post decompressive laparotomy had similar effects. Interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) levels were increased in peritoneal fluid.

CONCLUSION

Peritoneal fluid represents a primer for PMNs/monocytes and seems to act through receptor-dependent and receptor-independent pathways. Strategies to reduce the amount of peritoneal fluid may decrease the locoregional and systemic inflammatory response by reducing priming and activation of neutrophils/monocytes.