A new model for the study of the abdominal compartment syndrome in rats

Acute Compartment Syndrome Modeling with Sequential Infusion Shows the Deep Posterior Compartment Is Not Functionally Discrete

BACKGROUND

Clinical case series have indicated that 1 or 2-compartment decompression of the anterior or lateral leg may be sufficient for release, but, currently, no cadaveric model has verified that approach. The objective of this study was to investigate the functional relationship between compartments by alternating sequences of infusion and fasciotomy release.

METHODS

This study utilized multicompartment sequential pressurization with simultaneous monitoring by continuous pressure sensors to model compartment syndrome in a human cadaver leg. Subsequent sequential release of compartments and continuous streaming of pressure readings permitted unique insights.

RESULTS

A leg model allowed the examination of pressure changes in all 4 compartments as treated with sequential fasciotomies. The successful modeling of lower-leg pressures consistent with compartment syndrome showed that discrepancies relative to accepted concepts were seen when the deep posterior compartment was pressurized in isolation. Also, release of 1 of the 2 of either the anterior or lateral compartments seems to be sufficient for decompression to acceptable pressure levels.

CONCLUSIONS

The deep posterior compartment does not appear to be completely discrete and instead follows the pressurization curve of the posterior muscle group. This indicates that release of the deep posterior compartment may not be needed in all acute compartment syndrome scenarios.

CLINICAL RELEVANCE

Surgical techniques can be modified for treatment of acute compartment syndrome to avoid large scar lengths, deep dissection, and multiple exposures that could improve patient outcomes.

Percutaneous Forefoot Decompression in a Foot Compartment Syndrome Model

Acute compartment syndrome of the foot is a controversial topic. Release of the foot has been seen as complicated because of large incisions and postoperative morbidity, and there has been debate over whether this procedure is actually effective for releasing all areas of increased pressure. New sensor technology affords the opportunity to advance our understanding of acute compartment syndrome of the foot and its treatment. The purpose of the present study was to determine whether percutaneous decompression could be performed for the treatment of compartment syndrome in a forefoot model.

Effect of intra-abdominal hypertension on plasma exogenous creatinine clearance in conscious and anesthetized dogs

OBJECTIVE

To evaluate the effect of intra-abdominal pressure (IAP) on plasma exogenous creatinine clearance in both conscious and anesthetized dog models using a balloon technique to generate intra-abdominal hypertension.

DESIGN

Prospective, cross-over, experimental study.

SETTING

University-based small animal research facility.

ANIMALS

Six healthy male Beagle dogs.

INTERVENTIONS

A balloon device comprising a Foley urinary catheter and latex balloon was placed in the intra-abdominal cavity. Plasma exogenous creatinine clearance was compared after intravenous administration of exogenous creatinine solution at 80 mg/kg under 4 different treatment conditions as follows: control and IAP levels of 25 mm Hg in conscious dogs and control and IAP levels of 25 mm Hg in anesthetized dogs (CC, C25, AC, and A25, respectively). Samples were obtained before (T0) and 10, 20, 30, 60, 90, 120, 240, 360, 480, and 600 min after administration of creatinine in all treatment groups.

MEASUREMENTS AND MAIN RESULTS

There were no significant differences in plasma creatinine concentration for CC, AC, and C25 during the treatment period. However, in the A25 treatment condition, the plasma creatinine concentration increased significantly at 10, 20, 30, 60, 90, and 120 min after administration of creatinine (P < 0.05). Plasma creatinine clearances were 5.0 ± 0.5, 4.7 ± 1.2, 5.5 ± 0.9, and 2.5 ± 0.5 mL/kg/min for 600 min (CC, AC, C25, and A25, respectively). In the A25 treatment condition, the plasma exogenous creatinine clearance decreased significantly to 50%, 47%, and 55% of that under control conditions (CC, AC, and C25, respectively). After decompression of the abdomen, plasma creatinine concentrations declined rapidly and returned to basal concentrations.

CONCLUSIONS

Intra-abdominal hypertension under general anesthesia could cause renal hypoperfusion. Timely decompression may improve the outcome of acutely increased IAP when surgery and/or general anesthesia is required in canine patients.

A novel balloon technique to induce intra-abdominal hypertension and its effects on cardiovascular parameters in a conscious dog model

OBJECTIVE

To evaluate a new balloon technique to induce intra-abdominal hypertension (IAH) and abdominal compartment syndrome in a conscious dog model, and to evaluate the effect of intra-abdominal pressure (IAP) on cardiovascular, respiratory, and arterial blood gas values in conscious dogs with IAH.

DESIGN

Prospective, experimental study.

SETTING

University-based small animal research facility.

ANIMALS

Six healthy Beagle dogs, 4 males, and 2 females.

INTERVENTIONS

A new balloon device designed for this study using a Foley urethral catheter and latex balloon was placed in the abdominal cavity. Consecutive measurements of IAP were made by measuring the intravesicular pressure. The abdomen was inflated with air to IAPs of 10, 15, 20, and 25 mm Hg. Heart rate, respiratory rate, systolic arterial blood pressure, and arterial blood gases were evaluated at baseline and at 15, 30, 45, 60, 120, 240, and 300 minutes after IAP increase.

MEASUREMENTS AND MAIN RESULTS

The air insufflated into the intra-abdominal balloon device significantly increased the IAP and led to sustained IAH. The respiratory rate increased significantly (P < 0.05) when IAP was increased to 15, 20, and 25 mm Hg. Although heart rate, systolic arterial blood pressure, PaO₂ , and PaCO₂ did not show statistically significant differences between baseline and posttreatment values over time, the dogs with increased IAP showed a distended abdomen and apparent discomfort, and 4/6 (67%) vomited. After measurement of IAP, air was removed. There were no adverse effects noted after removal of the balloon device.

CONCLUSION

The balloon device was successfully insufflated and led to sustained IAH in conscious dogs. This balloon technique does not require general anesthesia for instillation or removal of gas after installment. An acute IAP increase in normal conscious dogs induced discomfort, vomiting, and increased respiratory effort.

Hypoxic renal injury in newborns with abdominal compartment syndrome (clinical and experimental study)

BackgroundSurgical treatment for gastroschisis and congenital diaphragmatic hernia (CDH) commonly leads to abdominal compartment syndrome (ACS) associated with hypoxic renal injury. We hypothesized that measurement of urinary and serum concentrations of vascular endothelial growth factor (VEGF), π-glutathione S-transferase (π-GST), and monocyte chemoattractant protein-1 (MCP-1) may serve for noninvasive detection of hypoxic renal injury in such patients.MethodsIntra-abdominal pressure (IAP), renal excretory function, and the biomarker levels were analyzed before, 4, and 10 days after surgery. Association between the biomarker levels and renal histology was investigated using an original model of ACS in newborn rats.ResultsFour days after surgery, IAP increased, renal excretory function decreased, and the levels of VEGF, π-GST, and MCP-1 increased, indicating renal injury. Ten days after surgery, IAP partially decreased, renal excretory function completely restored, but the biomarker levels remained elevated, suggesting the ongoing kidney injury. In the model of ACS, increase in the biomarker levels was associated with progressing kidney morphological alteration.ConclusionSurgical treatment for gastroschisis and CDH is associated with prolonged hypoxic kidney injury despite complete restoration of renal excretory function. Follow-up measurement of VEGF, π-GST, and MCP-1 levels may provide a better tool for noninvasive assessment of renal parenchyma in newborns with ACS.

Comparison of Melatonin, Hypertonic Saline, and Hydroxyethyl Starch for Resuscitation of Secondary Intra-Abdominal Hypertension in an Animal Model

A variety of agents may have a beneficial effect in reducing injury-induced intestinal edema of fluid, but studies confirming the efficacy and mechanisms of these agents in secondary intra-abdominal hypertension (IAH) are lacking. This study was to compare the effectiveness of melatonin, 7.5% hypertonic saline (HS), and hydroxyethyl starch 130/0.4 (HES) on the resuscitation of secondary IAH in a rat model. Female SD rats were divided into: sham group, shock group, lactated Ringer solution (LR) group, melatonin group, HS group, and HES group. Except for the sham group, all rats underwent a combination of inducing portal hypertension, hemorrhaging to a MAP of 40 mmHg for 2 hr, and using an abdominal restraint device. The collected blood was reinfused and the rats were treated with LR (30ml/h), melatonin (50 mg/kg) + LR, HS (6 ml/kg) + LR, and HES (30 ml/kg) + LR, respectively. The shock group received no fluids. LR was continuously infused for 6hr. The intestinal permeability, immunofluorescence of tight junction proteins, transmission electron microscopy, level of inflammatory mediators (TNF-a, IL-1β, IL-6) and of biochemical markers of oxidative stress (malondialdehyde, myeloperoxidase activity, and glutathione peroxidase) were assessed. Expressions of the protein kinase B (Akt) and of tight junction proteins were detected by Western blot. Compared with LR, HS, and HES, melatonin was associated with less inflammatory and oxidative injury, less intestinal permeability and injury, and lower incidence of secondary IAH in this model. The salutary effect of melatonin in this model was associated with the upregulation of intestinal Akt phosphorylation.

Melatonin prevents secondary intra-abdominal hypertension in rats possibly through inhibition of the p38 MAPK pathway

Exogenous administration of melatonin has been demonstrated to down-regulate inflammatory responses and attenuate organ damage in various models. However, the salutary effect of melatonin against secondary intra-abdominal hypertension (IAH) remains unclear. This study sought to test the influence of melatonin on secondary IAH in a pathophysiological rat model and the underlying mechanisms involved. Before resuscitation, male rats underwent a combination of induced portal hypertension, applying an abdominal restraint device, and hemorrhaging to mean arterial pressure (MAP) of 40mmHg for 2h. After blood reinfusion, the rats were treated with lactated Ringer solution (LR) (30mL/h), melatonin (50mg/kg) +LR, and SB-203580 (10μmol/kg)+LR. LR was continuously infused for 6h. MAP, the inferior vena cava pressure and urine output were monitored. Histopathological examination, immunofluorescence of tight junction proteins, and transmission electron microscopy were administered. Intestinal permeability, myeloperoxidase activity, malondialdehyde, glutathione peroxidase, and levels of TNF-a, IL-2, and IL-6, were assessed. The expression of extracellular signal-regulated kinase, p38, c-Jun NH2-terminal kinase, translocation of nuclear factor kappa B subunit, signal transducers and activators of transcription and tight junction proteins were detected by Western blot. We found that melatonin inhibited the inflammatory responses, decreased expression of p38 MAPK, attenuated intestinal injury, and prevented secondary IAH. Moreover, administration of SB203580 abolished the increase in p38 MAPK and also attenuated intestinal injury. These data indicate that melatonin exerts a protective effect in intestine in secondary IAH primarily by attenuating the inflammatory responses which are in part attributable to p38 MAPK inhibition.

Abnormal Expression of Urea Transporter Protein in a Rat Model of Hepatorenal Syndrome Induced by Succinylated Gelatin

BACKGROUND

Hepatorenal syndrome (HRS) is a serious complication of advanced chronic liver disease. Abdominal compartment syndrome (ACS) occurs with dysfunction of multiple organs when abdominal pressure increases. Here, we report on a novel model of ACS with ascites and a model of HRS in rats to observe the urea transporter protein (UT) expression in the 2 models.

MATERIAL AND METHODS

A liver cirrhosis model was induced by CCl4. After changes of liver histopathology were observed, rats were injected intraperitoneally with succinylated gelatin to establish a model of ACS and HRS. Then, changes in BUN, Cr, and renal histopathology were detected. Moreover, the UT in ACS and HRS were also quantified.

RESULTS

The surfaces of liver in the cirrhotic group became coarse, with visible small nodules and became yellow and greasy. The normal structure of the hepatic lobules were destroyed, and hyperplasia of fibrotic tissue and pseudo-lobe was observed. The levels of BUN and Cr were significantly increased in rats suffering from ACS and HRS, respectively, compared to their control groups. In addition, the mRNA levels of UT-A2 and UT-A3 decreased in rats with HRS compared to cirrhotic rats. However, there was no significant difference between the mRNA levels of UT-A2, UT-A3, and UT-B in rats with ACS vs. normal rats.

CONCLUSIONS

It is feasible to model ACS in rats by injecting succinylated gelatin into the abdominal cavity. Increasing the intra-abdominal pressure by succinylated gelatin is also a novel approach for modeling HRS in cirrhotic rats. Compared with control rats, there is an abnormal mRNA expression of UT in ACS rats and HRS rats.

The role of intestinal mucosa injury induced by intra-abdominal hypertension in the development of abdominal compartment syndrome and multiple organ dysfunction syndrome

Introduction

Abdominal distension is common in critical illness. There is a growing recognition that intra-abdominal hypertension (IAH) may complicate nonsurgical critical illness as well as after abdominal surgery. However, the pathophysiological basis of the injury to the intestinal mucosal barrier and its influence on the onset of abdominal compartment syndrome (ACS) and multiorgan dysfunction syndrome (MODS) remain unclear. We measured intestinal microcirculatory blood flow (MBF) during periods of raised intra-abdominal pressure (IAP) and examined how this influenced intestinal permeability, systemic endotoxin release, and histopathological changes.

Methods

To test different grades of IAH to the injury of intestinal mucosa, 96 New Zealand white rabbits aged 5 to 6 months were exposed to increased IAP under nitrogen pneumoperitoneum of 15 mmHg or 25 mmHg for 2, 4 or 6 hours. MBF was measured using a laser Doppler probe placed against the jejunal mucosa through a small laparotomy. Fluorescein isothiocyanate (FITC)-conjugated dextran was administered by gavage. Intestinal injury and permeability were measured using assays for serum FITC-dextran and endotoxin, respectively, after each increase in IAP. Structural injury to the intestinal mucosa at different levels of IAH was confirmed by light and transmission electron microscopy.

Results

MBF reduced from baseline by 40% when IAP was 15 mmHg for 2 hours. This doubled to 81% when IAP was 25 mmHg for 6 hours. Each indicator of intestinal injury increased significantly, proportionately with IAP elevation and exposure time. Baseline serum FITC-dextran was 9.30 (± SD 6.00) μg/ml, rising to 46.89 (±13.43) μg/ml after 15 mmHg IAP for 4 hours (P <0.01), and 284.59 (± 45.18) μg/ml after 25 mmHg IAP for 6 hours (P <0.01). Endotoxin levels showed the same pattern. After prolonged exposure to increased IAP, microscopy showed erosion and necrosis of jejunal villi, mitochondria swelling and discontinuous intracellular tight junctions.

Conclusions

Intra-abdominal hypertension can significantly reduce MBF in the intestinal mucosa, increase intestinal permeability, result in endotoxemia, and lead to irreversible damage to the mitochondria and necrosis of the gut mucosa. The dysfunction of the intestinal mucosal barrier may be one of the important initial factors responsible for the onset of ACS and MODS.

A new model for the study of secondary intra-abdominal hypertension in rats

BACKGROUND

To build a new and appropriate model of secondary intra-abdominal hypertension (IAH) in rats.

METHODS

A total of 32 female Sprague-Dawley rats were randomized into four groups. Group I: the rats were hemorrhaged to a mean arterial pressure (MAP) of 40 mm Hg for 1 h and portal hypertension was induced by partial ligation of the portal vein 1 h later; Group II: after inducing portal hypertension, hemorrhagic shock of MAP of 40 mm Hg was induced and maintained for 1 h; Group III: after inducing portal hypertension, hemorrhagic shock of MAP of 40 mm Hg was induced and maintained for 2 h; Group IV: after inducing portal hypertension, hemorrhagic shock of MAP of 40 mm Hg was induced and maintained for 2 h, and a specially designed abdominal restraint device was used. After these procedures, respectively, the collected blood was reinfused and lactated Ringer solution was continuously infused until the secondary IAH model was established.

RESULTS

No models were built in Groups I, II, and III. One rat died in Group IV after portal vein ligation, and all the remaining rats successfully developed IAH; the success rate was 87.5%. During the resuscitation period, the average time was 5.26 ± 0.59 h and the average total infusion volume was 665.5 ± 86.04 mL/kg.

CONCLUSION

A rat model of secondary IAH was successfully established by resuscitation after a combination of inducing portal hypertension, hemorrhaging to a MAP of 40 mm Hg for 2 h, and using an abdominal restraint device. All these criteria mimic key etiological factors for the development of secondary IAH.

Evaluation of the relationship between pelvic fracture and abdominal compartment syndrome in traumatic patients

INTRODUCTION

An increase in abdominal pressure can lead to so-called intra-abdominal compartment syndrome (ACS). Multiple factors such as an increase in retroperitoneal volume due to pancreatitis, bleeding and edema as a result of pelvic fracture can lead to compartment syndrome. Prevention is better than cure in compartment syndrome. By measuring the intra-abdominal pressure (IAP) through the bladder, a quick and accurate assessment of abdominal pressure is achieved. Therefore, this study aimed to evaluate the relationship between pelvic fracture and ACS in traumatic patients.

MATERIALS AND METHODS

This research was a descriptive-analytical study conducted on 100 patients referring to the Shiraz Nemazee Hospital in 2010. IAP was monitored every 4 h in patients suspected to be at high risk for ACS, e.g., those undergoing severe abdominal trauma and pelvic fracture. The IAP was measured via the urinary bladder using the procedure described by Kron et al. Data collected were analyzed using SPSS software.

RESULTS

The findings showed that ACS occurred in 28 of 100 patients. With regard to the associated injuries with abdominal trauma, 19% of all patients and 46/42% of the patients with ACS had pelvic fracture. Chi-square test revealed a significant relationship between pelvic fracture and incidence rate of ACS (P < 0.001).

CONCLUSIONS

According to the collected data, pelvic fracture due to a trauma can be one of the important causes of an increase in IAP and ACS. In this lethal condition, prevention is better than cure. Therefore, serial measurement of IAP through the bladder in high-risk patients (those with pelvic fracture by trauma) is recommended to the nurses to diagnose this condition and to decrease the incidence of mortality.

The importance of timing of decompression in severe acute pancreatitis combined with abdominal compartment syndrome

BACKGROUND

Surgical decompression is widely considered as an important treatment in patients with severe acute pancreatitis (SAP) and abdominal compartment syndrome (ACS). Until now, the indication and optimal time of decompression remain unknown, and no experimental data exist, although extremely high mortality has been repeatedly reported in these patients. The aim of this study was to evaluate the effects of three different time points for decompression in a 24-hour lasting porcine model.

METHODS

Following baseline registrations, 32 animals were divided into four groups (8 animals each group) as follows: one SAP-alone group and three SAP + ACS groups, which received decompression at 6, 9, and 12 hours. We used a N2 pneumoperitoneum to increase the intra-abdominal pressure to 25 mm Hg and retrograde intra-ductal infusion of sodium taurocholate to induce SAP. Global hemodynamic profiles, urine output, systemic oxygenation, and serum biochemical parameters of the animals were studied. At the end of the experiment, histologic examination of the intestine and lung was performed.

RESULTS

The survival time of the 12-hour group was significantly shortened (p = 0.037 vs. 9 hours and p = 0.008 vs. 6 hours). In SAP + ACS animals, decompression at 6 hours restored systemic hemodynamics, oxygen-derived parameters, organ function, and inflammatory intensity to a level comparable with that of the SAP-alone group. In contrast, animals in the 9 hours and 12 hours developed more severe hemodynamic and organ dysfunction. The histopathologic analyses also revealed higher grade injury of the intestine and lung in animals receiving delayed decompression.

CONCLUSION

Well-timed decompression in a porcine model of SAP incorporating 25-mm Hg intra-abdominal hypertension/ACS was associated with significantly reduced mortality, improved systemic hemodynamics and organ function, as well as alleviated histologic injury and inflammatory intensity. According to our results and previous reports, both too early and too late decompression should be avoided owing to significant morbidity for the former and unfavorable outcomes for the latter.

Developing a new experimental model of abdominal compartment syndrome

OBJECTIVE

To describe an experimental, unprecedented model that mimics the abdominal compartment syndrome (ACS).

METHODS

twenty rats were randomly divided into four groups. To simulate ACS intra-abdominal hypertension (IAH) was induced by inserting cotton surgical dressing (Zobec ®), 15x15cm (intra-abdominal pressure constant and equal to 12 mmHg) associated with hypovolemia induced by withdrawing blood, keeping mean arterial pressure (MAP) around 60 mmHg (HYPO). To dissociate the effects of those IAH-induced hypovolemia per se, two other groups were analyzed: one with only with IAH and another with only hypovolemia. The simulation group (sham) underwent the same surgical procedure performed earlier, however, the levels of intra-abdominal pressure and MAP were kept in 3 mmHg and 90 mmHg, respectively.

RESULTS

By analyzing the impact of IAH on the small intestine, we observed necrosis of the villi, congestion, and neutrophilic infiltration. Hypovolemia induced only inflammation and edema of the villi. However, the association of IAH and HYPO led to hemorrhagic infarction, besides worsening of the aforementioned parameters.

CONCLUSION

This model was effective in inducing ACS expressed by the effects found in the small intestine.

Kidney safety during surgical pneumoperitoneum: an experimental study in rats

BACKGROUND

Elevations of intraabdominal pressure during laparoscopic procedures may lead to oliguria or anuria in mammals. Despite this, previous research has not been able to confirm an associated kidney injury. This study aimed to investigate the occurrence of an early kidney lesion secondary to surgical pneumoperitoneum in a rat model using the expression of neutrophil gelatinase-associated lipocalin (N-GAL) as a biomarker for early kidney injury.

METHODS

In this study, 20 male Sprague-Dawley rats under general anesthesia and mechanically ventilated were allocated to one of five experimental time-dependent groups: group 1 (1-h control), group 2 (1-h pneumoperitoneum), group 3 (2-h control), group 4 (2-h pneumoperitoneum), and group 5 (positive kidney injury group induced by intravenous administration of cisplatin 7.5 mg/kg). To evaluate the renal expression of N-GAL 24 h after the procedure, all the rats underwent a 2-h urine output evaluation as well as laparotomy and bilateral nephrectomy performed sequentially to investigate the presence of renal injury using immunofluorescence qualification and western blotting.

RESULTS

Urine output was reduced and N-GAL expression was increased in the animals from the cisplatin group. The animals undergoing 1- or 2-h pneumoperitoneum displayed urine output and N-GAL expression similar to that of the animals from the matching control groups.

CONCLUSIONS

Under the experimental conditions of this study, the animals with normal preoperative renal function did not show any type of acute kidney injury associated with the presence of a stabilized surgical pneumoperitoneum.

Evaluation of a simple valve mechanism used to stabilize intraabdominal pressure during surgically induced pneumoperitoneum in small animals

BACKGROUND

Preventing sudden changes in intraabdominal pressure (IAP) during surgical pneumoperitoneum may reduce adverse events. This study aimed to describe a valve system that stabilizes intraabdominal pressure, minimizing complications of erratic fluctuations in IAP.

METHODS

Five male Sprague-Dowley rats were submitted to pneumoperitoneum, with the insufflator set sequentially at 5, 10, and 15 mmHg for each rat. Measures of IAP were taken initially without the valve and then using the same insufflator levels with the valve system regulated to three different pressures (5, 10, and 15 mmHg). The mean of the three highest registered pressures during a 15-min observation was used as the maximal pressure, and the mean of the three lowest registered pressures was used as the minimal pressure for each experimental setting.

RESULTS

Without the valve system, the pressure level set by the insufflator correlated poorly with the actual IAP. When the valve system was used, the IAP pressure was limited by the valve settings regardless of the insufflator settings. Also, the variability of IAP was significantly higher when no valve was used than in all situations that had implementation of the system.

CONCLUSIONS

The valve system was very effective in stabilizing IAP, allowing a reproducible and reliable estimate of IAP and greatly reducing the variability resulting from the cycling mechanism of the insufflator. Due to the small dimensions of intracorporeal cavities in the newborn, this mechanism may help to improve safety when neonatal video-assisted surgery is performed.

A modified model of the abdominal compartment syndrome

BACKGROUND

To develop an animal model in rats and to investigate whether an intra-abdominal pressure (IAP) of 20 mm Hg will lead to a condition comparable with the abdominal compartment syndrome in humans.

METHODS

Forty Sprague-Dawley rats were used. In the study group, IAP was increased to 20 mm Hg using a nitrogen gas pneumoperitoneum for 4 hours. We also observed the next reperfusion period for another 4 hours. In the controls, IAP remained unchanged. Hemodynamic readings, peak inspiratory pressure, renal function parameters, and blood gas were obtained. Additionally, histopathologic examinations were performed.

RESULTS

In the presence of intra-abdominal hypertension (IAH), mean arterial pressure was reduced, whereas central venous pressure was increased significantly. Peak inspiratory pressure remained >35 mbar in the 4 hours of IAH and recovered after decompression. Arterial Po(2) decreased substantially while Pco(2) increased soon after IAH. IAH caused a metabolic acidosis, which was further complicated by the respiratory acidosis. Decompression resulted in normocapnia but the metabolic acidosis persisted. Renal blood flow and urine output decreased obviously, whereas little change was found in blood urea nitrogen and creatinine. The histopathologic study revealed parenchymal injury in lung and intestine.

CONCLUSIONS

This animal model was simple and easily reproducible. An IAP of 20 mm Hg can lead to a condition comparable with the abdominal compartment syndrome in humans.

Commonly applied positive end-expiratory pressures do not prevent functional residual capacity decline in the setting of intra-abdominal hypertension: a pig model

INTRODUCTION

Intra-abdominal hypertension is common in critically ill patients and is associated with increased morbidity and mortality. The optimal ventilation strategy remains unclear in these patients. We examined the effect of positive end-expiratory pressures (PEEP) on functional residual capacity (FRC) and oxygen delivery in a pig model of intra-abdominal hypertension.

METHODS

Thirteen adult pigs received standardised anaesthesia and ventilation. We randomised three levels of intra-abdominal pressure (3 mmHg (baseline), 18 mmHg, and 26 mmHg) and four commonly applied levels of PEEP (5, 8, 12 and 15 cmH2O). Intra-abdominal pressures were generated by inflating an intra-abdominal balloon. We measured intra-abdominal (bladder) pressure, functional residual capacity, cardiac output, haemoglobin and oxygen saturation, and calculated oxygen delivery.

RESULTS

Raised intra-abdominal pressure decreased FRC but did not change cardiac output. PEEP increased FRC at baseline intra-abdominal pressure. The decline in FRC with raised intra-abdominal pressure was partly reversed by PEEP at 18 mmHg intra-abdominal pressure and not at all at 26 mmHg intra-abdominal pressure. PEEP significantly decreased cardiac output and oxygen delivery at baseline and at 26 mmHg intra-abdominal pressure but not at 18 mmHg intra-abdominal pressure.

CONCLUSIONS

In a pig model of intra-abdominal hypertension, PEEP up to 15 cmH2O did not prevent the FRC decline caused by intra-abdominal hypertension and was associated with reduced oxygen delivery as a consequence of reduced cardiac output. This implies that PEEP levels inferior to the corresponding intra-abdominal pressures cannot be recommended to prevent FRC decline in the setting of intra-abdominal hypertension.

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

BACKGROUND

: Current abdominal compartment syndrome (ACS) models rely on intraperitoneal instillation of fluid, air, and other space-occupying substances. Although this allows for the study of the effects of increased abdominal pressure, it poorly mimics its pathogenesis. We have developed the first reported large animal model of ACS incorporating hemorrhagic shock/resuscitation.

METHODS

: Hemorrhagic shock was induced and maintained (1 hour) in 12 Yorkshire swine by bleeding to a mean arterial pressure (MAP) of 50 mm Hg. The collected blood plus two additional volumes of crystalloid was then reinfused. Mesenteric venous hypertension was induced by tightening a previously placed portal vein snare in a nonocclusive manner to mimic the effects of abdominal packing. Crystalloids were infused to maintain MAP. Hemodynamic measurements, abdominal pressure, peak inspiratory pressures, urine output, and blood chemistries were measured sequentially. Animals were studied for 36 hours after decompression.

RESULTS

: ACS (intra-abdominal pressure of > or =20 mm Hg with new organ dysfunction) developed in all animals. There were significant increases in peak inspiratory pressure, central venous pressure, and pulmonary artery pressure and decreases in MAP upon development of ACS. Urine output was significantly decreased before decompression. Mean blood lactate decreased and base excess increased significantly after decompression.

CONCLUSIONS

: We have created the first reported physiologic animal ACS model incorporating hemorrhagic shock/resuscitation and the effects of damage control surgery.

Microscopic and ultrastructural changes of the intestine in abdominal compartment syndrome

BACKGROUND

The purpose of the study was to examine the microscopic changes of intestine villus and ultrastructural changes of tight junction in the presence of intra-abdominal hypertension (IAH) of 20 mmHg.

MATERIALS AND METHODS

Forty Sprague-Daley rats (250 +/- 25 g) divided into four groups (n = 10) were studied. In 30 animals, the intra-abdominal pressure was increased to 20 mmHg for 1 hr, 2 hr, and 4 hr, respectively. The others served as controls. The specimens of the intestines were submitted to histopathology using hematoxylin and eosin staining, and to ultrastructural analysis using a scanning electron microscope.

RESULTS

The histopathological study revealed different degrees of changes ranging from swelling and degeneration of villous epithelial cells to extensive denudation and collapse of the villus. Ultrastructural analysis revealed dilatation of the tight junctions and paracellular spaces in the presence of IAH. The severity of the damage was related to the time of IAH.

CONCLUSIONS

Increased IAH caused a significant damage to the intestinal epithelium and a marked dilatation of intestinal tight junction, leading to the increased mucosal barrier permeability. It may explain why IAH was often associated with bacterial translocation and sepsis.

Microdialysis of the rectus abdominis muscle for early detection of impending abdominal compartment syndrome

OBJECTIVE

To investigate whether microdialysis is capable of assessing metabolic derangements during intra-abdominal hypertension (IAH), and whether monitoring of the rectus abdominis muscle (RAM) by microdialysis represents a reliable approach in the early detection of organ dysfunctions in abdominal compartment syndrome (ACS).

DESIGN

Prospective, randomized, controlled animal study.

SETTING

University animal research facility.

SUBJECTS

Fifteen isoflurane-anesthetized and mechanically ventilated Sprague-Dawley rats.

INTERVENTIONS

IAH of 20 mmHg was induced for 3 h and followed by decompression and reperfusion for another 3-h period (n = 10). Five sham-operated animals served as controls. Microdialysis was performed in the anterior gastric wall, liver, kidney, and RAM. The anterior cervical muscles served as distant reference. Glucose, lactate, pyruvate, and glycerol was analyzed throughout the 6-h experiment.

MEASUREMENTS AND MAIN RESULTS

Prolonged IAH induced significant cardiopulmonary dysfunction and persistent abdominal organ injury. Microdialysis revealed a significant increase of lactate/pyruvate and glycerol in kidney, intestine and liver, indicating ischemia, energy failure, and cell membrane damage. In addition, at 3 h IAH glucose was significantly decreased in all organs studied. The distant reference did not show any alteration of lactate/pyruvate, glycerol, and glucose over the entire 6-h observation period. In contrast to the other organs, microdialysis of the RAM showed an early and more pronounced increase of lactate, lactate/pyruvate and glycerol already at 1 h IAH. It is noteworthy that lactate, glycerol, and glucose did not completely recover upon decompression of IAH.

CONCLUSIONS

Our data suggest that continuous microdialysis in the RAM may represent a promising tool for early detecting IAH-induced metabolic derangements.