Hypoxia aggravates lipopolysaccharide-induced lung injury

Association of Serum Mannose With Acute Respiratory Distress Syndrome Risk and Survival

IMPORTANCE

Acute respiratory distress syndrome (ARDS) confers high mortality risk among critically ill patients. Identification of biomarkers associated with ARDS risk may guide clinical diagnosis and prognosis.

OBJECTIVE

To systematically evaluate the association of blood metabolites with ARDS risk and survival.

DESIGN, SETTING, AND PARTICIPANTS

In this cohort study, data from the Molecular Epidemiology of ARDS (MEARDS) study, a prospective cohort of 403 patients with ARDS and 1227 non-ARDS controls, were analyzed. Patients were recruited in intensive care units (ICUs) at Massachusetts General Hospital and Beth Israel Deaconess Medical Center, both in Boston, Massachusetts, from January 1, 1998, to December 31, 2014. Data analysis was performed from December 9, 2018, to January 4, 2019.

MAIN OUTCOMES AND MEASURES

Participants were followed up daily for ARDS development defined by Berlin criteria, requiring fulfillment of chest radiograph and oxygenation criteria on the same calendar day during invasive ventilatory assistance. A 2-stage study design was used to explore novel metabolites associated with ARDS risk and survival.

RESULTS

Of the 1630 participants from MEARDS who were admitted to the ICU , 403 (24.7%) were diagnosed with ARDS (mean [SD] age, 63.0 [17.0] years; 251 [62.3%] male) and 1227 (75.3%) were at-risk but did not have ARDS (mean [SD] age, 62.3 [16.9] years; 753 [61.4%] male). Mendelian randomization suggested that genetically regulated serum mannose was associated with ARDS risk (odds ratio [OR], 0.64; 95% CI, 0.53-0.78; P = 7.46 × 10-6) in the discovery stage. In the functional validation stage incorporating 83 participants with ARDS and matched at-risk participants in the control group from the ICU, the protective association of mannose with ARDS risk was validated (OR, 0.67; 95% CI, 0.46-0.97; P = .03). Furthermore, serum mannose was associated with 28-day (OR, 0.25; 95% CI, 0.11-0.56; P = 6.95 × 10-4) and 60-day (OR, 0.36; 95% CI, 0.19-0.71; P = 3.12 × 10-3) mortality and 28-day (hazard ratio, 0.49; 95% CI, 0.32-0.74; P = 6.41 × 10-4) and 60-day (hazard ratio, 0.55; 95% CI, 0.37-0.80; P = 2.11 × 10-3) survival.

CONCLUSIONS AND RELEVANCE

In this study, genetically regulated serum mannose appeared to be associated with ARDS risk and outcome, and increased serum mannose at admission was associated with reduced ARDS risk and better survival. These findings could inform prevention and clinical intervention in ARDS cases, which have increased with the expansion of the coronavirus disease 2019 pandemic.

Effects of chronic intermittent hypoxia caused by obstructive sleep apnea on lipopolysaccharide-induced acute lung injury

AIM OF THE STUDY

Obstructive sleep apnea (OSA) is a common disease associated with significant morbidity and mortality. Sleep quality is an important issue; some patients with acute lung injury (ALI) have underlying OSA. However, the potential influences of OSA on ALI have not been reported until now. In this study, we evaluated the impact of preceding intermittent hypoxia (IH), a typical characteristic of OSA, on lipopolysaccharide (LPS)-induced ALI in a mouse model.

METHODS

C57BL/6J mice were randomly divided into four groups: room air-control (RA-CTL), intermittent hypoxia-control (IH-CTL), room air-lipopolysaccharide (RA-LPS), and intermittent hypoxia-lipopolysaccharide (IH-LPS) groups. The mice were exposed to RA or IH (20 cycles/h, FiO₂ nadir 7 ± 0.5%, 8 h/day) for 30 days. The LPS groups received intratracheal LPS on day 28.

RESULTS

The IH-LPS group tended to exhibit more severe inflammation, fibrosis, and oxidative stress compared to the other groups, including the RA-LPS group. Total cell, neutrophil, and eosinophil counts in bronchoalveolar lavage fluid increased significantly in the IH-LPS group compared to the RA-LPS group. Compared to the RA-LPS group, the hydroxyproline level increased significantly in the IH-LPS group. In addition, the IH-LPS group exhibited significantly more terminal deoxynucleotidyl transferase dUTP nick end labeled-positive cells compared to the RA-LPS group.

CONCLUSIONS

We found that prior IH may negatively impact LPS-induced ALI in a mouse model. This result suggests that ALI in patients with OSA may be more of a concern. Further research into the mechanisms underlying the effects of IH on ALI is needed.

Invited review: Compartmentalization of the inflammatory response in sepsis and SIRS

Sepsis and systemic inflammatory response syndrome (SIRS) are associated with an exacerbated production of both pro- and anti-inflammatory mediators that are mainly produced within tissues. Although a systemic process, the pathophysiological events differ from organ to organ, and from organ to peripheral blood, leading to the concept of compartmentalization. The nature of the insult ( e.g. burn, hemorrhage, trauma, peritonitis), the cellular composition of each compartment ( e.g . nature of phagocytes, nature of endothelial cells), and its micro-environment ( e.g. local presence of granulocyte-macrophage colony stimulating factor [GM-CSF] in the lungs, low levels of arginine in the liver, release of endotoxin from the gut), and leukocyte recruitment, have a great influence on local inflammation and on tissue injury. High levels of pro-inflammatory mediators ( e.g. interleukin-1 [IL-1], tumor necrosis factor [TNF], gamma interferon [IFN-γ], high mobility group protein-1 [HMGB1], macrophage migration inhibitory factor [MIF]) produced locally and released into the blood stream initiate remote organ injury as a consequence of an organ cross-talk. The inflammatory response within the tissues is greatly influenced by the local delivery of neuromediators by the cholinergic and sympathetic neurons. Acetylcholine and epinephrine contribute with IL-10 and other mediators to the anti-inflammatory compensatory response initiated to dampen the inflammatory process. Unfortunately, this regulatory response leads to an altered immune status of leukocytes that can increase the susceptibility to further infection. Again, the nature of the insult, the nature of the leukocytes, the presence of circulating microbial components, and the nature of the triggering agent employed to trigger cells, greatly influence the immune status of the leukocytes that may differ from one compartment to another. While anti-inflammatory mediators predominate within the blood stream to avoid igniting new inflammatory foci, their presence within tissues may not always be sufficient to prevent the initiation of a deleterious inflammatory response in the different compartments.

Blunt Chest Trauma in Mice after Cigarette Smoke-Exposure: Effects of Mechanical Ventilation with 100% O2

Cigarette smoking (CS) aggravates post-traumatic acute lung injury and increases ventilator-induced lung injury due to more severe tissue inflammation and apoptosis. Hyper-inflammation after chest trauma is due to the physical damage, the drop in alveolar PO₂, and the consecutive hypoxemia and tissue hypoxia. Therefore, we tested the hypotheses that 1) CS exposure prior to blunt chest trauma causes more severe post-traumatic inflammation and thereby aggravates lung injury, and that 2) hyperoxia may attenuate this effect. Immediately after blast wave-induced blunt chest trauma, mice (n=32) with or without 3-4 weeks of CS exposure underwent 4 hours of pressure-controlled, thoraco-pulmonary compliance-titrated, lung-protective mechanical ventilation with air or 100 % O₂. Hemodynamics, lung mechanics, gas exchange, and acid-base status were measured together with blood and tissue cytokine and chemokine concentrations, heme oxygenase-1 (HO-1), activated caspase-3, and hypoxia-inducible factor 1-α (HIF-1α) expression, nuclear factor-κB (NF-κB) activation, nitrotyrosine formation, purinergic receptor 2X₄ (P2XR₄) and 2X₇ (P2XR₇) expression, and histological scoring. CS exposure prior to chest trauma lead to higher pulmonary compliance and lower PaO₂ and Horovitz-index, associated with increased tissue IL-18 and blood MCP-1 concentrations, a 2-4-fold higher inflammatory cell infiltration, and more pronounced alveolar membrane thickening. This effect coincided with increased activated caspase-3, nitrotyrosine, P2XR₄, and P2XR₇ expression, NF-κB activation, and reduced HIF-1α expression. Hyperoxia did not further affect lung mechanics, gas exchange, pulmonary and systemic cytokine and chemokine concentrations, or histological scoring, except for some patchy alveolar edema in CS exposed mice. However, hyperoxia attenuated tissue HIF-1α, nitrotyrosine, P2XR₇, and P2XR₄ expression, while it increased HO-1 formation in CS exposed mice. Overall, CS exposure aggravated post-traumatic inflammation, nitrosative stress and thereby organ dysfunction and injury; short-term, lung-protective, hyperoxic mechanical ventilation have no major beneficial effect despite attenuation of nitrosative stress, possibly due to compensation of by regional alveolar hypoxia and/or consecutive hypoxemia, resulting in down-regulation of HIF-1α expression.

Growth of human bronchial epithelial cells at an air-liquid interface alters the response to particle exposure

Background

We tested the hypothesis that normal human bronchial epithelial (NHBE) cells 1) grown submerged in media and 2) allowed to differentiate at air-liquid interface (ALI) demonstrate disparities in the response to particle exposure.

Results

Following exposure of submerged NHBE cells to ambient air pollution particle collected in Chapel Hill, NC, RNA for IL-8, IL-6, heme oxygenase 1 (HOX1) and cyclooxygenase 2 (COX2) increased. The same cells allowed to differentiate over 3, 10, and 21 days at ALI demonstrated no such changes following particle exposure. Similarly, BEAS-2B cells grown submerged in media demonstrated a significant increase in IL-8 and HOX1 RNA after exposure to NIST 1648 particle relative to the same cells exposed after growth at ALI. Subsequently, it was not possible to attribute the observed decreases in the response of NHBE cells to differentiation alone since BEAS-2B cells, which do not differentiate, showed similar changes when grown at ALI. With no exposure to particles, differentiation of NHBE cells at ALI over 3 to 21 days demonstrated significant decrements in baseline levels of RNA for the same proteins (i.e. IL-8, IL-6, HOX1, and COX2). With no exposure to particles, BEAS-2B cells grown at ALI showed comparable changes in RNA for IL-8 and HOX1. After the same particle exposure, NHBE cells grown at ALI on a transwell in 95% N₂-5% CO₂ and exposed to NIST 1648 particle demonstrated significantly greater changes in IL-8 and HOX1 relative to cells grown in 95% air-5% CO₂.

Conclusions

We conclude that growth of NHBE cells at ALI is associated with a diminished biological effect following particle exposure relative to cells submerged in media. This decreased response showed an association with increased oxygen availability.

Respiratory epithelial cell lines exposed to anoxia produced inflammatory mediator

Human epithelial cell lines were utilized to examine the effects of anoxia on cellular growth and metabolism. Three normal human epithelial cells lines (A549, NHBE, and BEAS-2B) as well as a cystic fibrosis cell line (IB3-1) and its mutation corrected cell line (C38) were grown in the presence and absence of oxygen for varying periods of time. Interleukin-8 (IL-8) levels were measured by enzyme-linked immunosorbent assay technique. Cellular metabolism and proliferation were assayed by determining mitochondrial oxidative burst activity by tetrazolium compound reduction. The viability of cells was indirectly measured by lactate dehydrogenase release. A549, NHBE, and BEAS-2B cells cultured in the absence of oxygen showed a progressive decrease in metabolic activity and cell proliferation after one to three days. There was a concomitant increase in IL-8 production. Cell lines from cystic fibrosis (CF) patients did not show a similar detrimental effect of anoxia. However, the IL-8 level was significantly increased only in IB3-1 cells exposed to anoxia after two days. Anoxia appears to affect certain airway epithelial cell lines uniquely with decreased cellular proliferation and a concomitant increased production of a cytokine with neutrophilic chemotactic activity. The increased ability of the CF cell line to respond to anoxia with increased secretion of inflammatory cytokines may contribute to the inflammatory damage seen in CF bronchial airway. This study indicates the need to use different cell lines in in vitro studies investigating the role of epithelial cells in airway inflammation and the effects of environmental influences.

Acute hypoxia decreases E. coli LPS-induced cytokine production and NF-kappaB activation in alveolar macrophages

Reductions in alveolar oxygenation during lung hypoxia/reoxygenation (H/R) injury are common after gram-negative endotoxemia. However, the effects of H/R on endotoxin-stimulated cytokine production by alveolar macrophages are unclear and may depend upon thresholds for hypoxic oxyradical generation in situ. Here TNF-alpha and IL-1beta production were determined in rat alveolar macrophages stimulated with Escherichia coli lipopolysaccharide (LPS, serotype O55:B5) while exposed to either normoxia for up to 24h, to brief normocarbic hypoxia (1.5h at an atmospheric PO(2)=10+/-2mm Hg), or to combined H/R. LPS-induced TNF-alpha and IL-1beta were reduced at the peak of hypoxia and by reoxygenation in LPS+H/R cells (P<0.01) compared with normoxic controls despite no changes in reduced glutathione (GSH) or in PGE2 production. Both TNF-alpha mRNA and NF-kappaB activation were reduced by hypoxia that suppressed superoxide anion generation. Thus, dynamic reductions in the ambient PO(2) of alveolar macrophages that do not deplete GSH suppress LPS-induced TNF-alpha expression, IL-1beta production, and NF-kappaB activation even as oxyradical production is decreased.

Nonventilatory strategies for patients with life-threatening 2009 H1N1 influenza and severe respiratory failure

Severe respiratory failure (including acute lung injury and acute respiratory distress syndrome) caused by 2009 H1N1 influenza infection has been reported worldwide. Refractory hypoxemia is a common finding in these patients and can be challenging to manage. This review focuses on nonventilatory strategies in the advanced treatment of severe respiratory failure and refractory hypoxemia such as that seen in patients with severe acute respiratory distress syndrome attributable to 2009 H1N1 influenza. Specific modalities covered include conservative fluid management, prone positioning, inhaled nitric oxide, inhaled vasodilatory prostaglandins, and extracorporeal membrane oxygenation and life support. Pharmacologic strategies (including steroids) investigated for the treatment of severe respiratory failure are also reviewed.

Pulmonary contusion primes systemic innate immunity responses

INTRODUCTION

Traumatic injury may result in an exaggerated response to subsequent immune stimuli such as nosocomial infection. This "second hit" phenomenon and molecular mechanism(s) of immune priming by traumatic lung injury, specifically, pulmonary contusion, remain unknown. We used an animal model of pulmonary contusion to determine whether the injury resulted in priming of the innate immune response and to test the hypothesis that resuscitation fluids could attenuate the primed response to a second hit.

METHODS

Male, 8 to 9 weeks, C57/BL6 mice with a pulmonary contusion were challenged by a second hit of intratracheal administration of the Toll-like receptor 4 agonist, lipopolysaccharide (LPS, 50 microg) 24 hours after injury (injury + LPS). Other experimental groups were injury + vehicle or LPS alone. A separate group was injured and resuscitated by 4 cc/kg of hypertonic saline (HTS) or Lactated Ringer's (LR) resuscitation before LPS challenge. Mice were killed 4 hours after LPS challenge and blood, bronchoalveolar lavage, and tissue were isolated and analyzed. Data were analyzed using one-way analysis of variance with Bonferroni multiple comparison posttest for significant differences (*p < or = 0.05).

RESULTS

Injury + LPS showed immune priming observed by lung injury histology and increased bronchoalveolar lavage neutrophilia, lung myeloperoxidase and serum IL-6, CXCL1, and MIP-2 levels when compared with injury + vehicle or LPS alone. After injury, resuscitation with HTS, but not Lactated Ringer's was more effective in attenuating the primed response to a second hit.

CONCLUSION

Pulmonary contusion primes innate immunity for an exaggerated response to a second hit with the Toll-like receptor 4 agonist, LPS. We observed synergistic increases in inflammatory mediator expression in the blood and a more severe lung injury in injured animals challenged with LPS. This priming effect was reduced when HTS was used to resuscitate the animal after lung contusion.

Alveolar hypoxia, alveolar macrophages, and systemic inflammation

Diseases featuring abnormally low alveolar PO₂ are frequently accompanied by systemic effects. The common presence of an underlying inflammatory component suggests that inflammation may contribute to the pathogenesis of the systemic effects of alveolar hypoxia. While the role of alveolar macrophages in the immune and defense functions of the lung has been long known, recent evidence indicates that activation of alveolar macrophages causes inflammatory disturbances in the systemic microcirculation. The purpose of this review is to describe observations in experimental animals showing that alveolar macrophages initiate a systemic inflammatory response to alveolar hypoxia. Evidence obtained in intact animals and in primary cell cultures indicate that alveolar macrophages activated by hypoxia release a mediator(s) into the circulation. This mediator activates perivascular mast cells and initiates a widespread systemic inflammation. The inflammatory cascade includes activation of the local renin-angiotensin system and results in increased leukocyte-endothelial interactions in post-capillary venules, increased microvascular levels of reactive O₂ species; and extravasation of albumin. Given the known extrapulmonary responses elicited by activation of alveolar macrophages, this novel phenomenon could contribute to some of the systemic effects of conditions featuring low alveolar PO₂.

The systemic inflammation of alveolar hypoxia is initiated by alveolar macrophage-borne mediator(s)

Alveolar hypoxia produces widespread systemic inflammation in rats. The inflammation appears to be triggered by activation of mast cells by a mediator released from alveolar macrophages, not by the reduced systemic partial pressure of oxygen (PO2). If this is correct, the following should apply: (1) neither mast cells nor tissue macrophages should be directly activated by hypoxia; and (2) mast cells should be activated when in contact with hypoxic alveolar macrophages, but not with hypoxic tissue macrophages. We sought here to determine whether hypoxia activates isolated alveolar macrophages, peritoneal macrophages, and peritoneal mast cells, and to study the response of the microcirculation to supernatants of these cultures. Rat mesenteric microcirculation intravital microscopy was combined with primary cultures of alveolar macrophages, peritoneal macrophages, and peritoneal mast cells. Supernatant of hypoxic alveolar macrophages, but not of hypoxic peritoneal macrophages, produced inflammation in mesentery. Hypoxia induced a respiratory burst in alveolar, but not peritoneal macrophages. Cultured peritoneal mast cells did not degranulate with hypoxia. Immersion of mast cells in supernatant of hypoxic alveolar macrophages, but not in supernatant of hypoxic peritoneal macrophages, induced mast cell degranulation. Hypoxia induced release of monocyte chemoattractant protein-1, a mast cell secretagogue, from alveolar, but not peritoneal macrophages or mast cells. We conclude that a mediator released by hypoxic alveolar macrophages activates mast cells and triggers systemic inflammation. Reduced systemic PO2 and activation of tissue macrophages do not play a role in this phenomenon. The inflammation could contribute to systemic effects of diseases featuring alveolar hypoxia.

Gene regulation in the adaptive process to hypoxia in lung epithelial cells

Lung alveolar epithelial cells are normally very well oxygenated but may be exposed to hypoxia in many pathological conditions such as pulmonary edema, acute respiratory distress syndrome, chronic obstructive pulmonary diseases, or in some environmental conditions such ascent to high altitude. The ability of alveolar epithelial cells to cope with low oxygen tensions is crucial to maintain the structural and functional integrity of the alveolar epithelium. Alveolar epithelial cells appear to be remarkably tolerant to oxygen deprivation as they are able to maintain adequate cellular ATP content during prolonged hypoxic exposure when mitochondrial oxidative phosphorylation is limited. This property mostly relies on the ability of the cells to rapidly modify their gene expression program, stimulating the expression of genes involved in anaerobic energy supply and repressing expression of genes involved in some ATP-consuming cellular processes. This adaptive strategy of the cells is mostly, but not entirely, dependent on the expression of hypoxia-inducible factors (HIFs), known to be responsible for orchestrating a large number of hypoxia-sensitive genes. This review focuses on the role of HIF isoforms expressed in alveolar epithelial cells exposed to hypoxia and on the specific hypoxic gene regulation that takes place in alveolar epithelial cells either through HIF-dependent or -independent pathways.

Aspiration syndromes: 10 clinical pearls every physician should know

Aspiration syndromes are clinically and pathologically classified into three sets of disorders: (i) large airway mechanical obstruction caused by foreign bodies; (ii) aspiration pneumonitis; and (iii) aspiration pneumonia. In this article, we discuss the common clinical presentations, risk factors, radiographic features and methods of management of these disorders. We highlight recent recommendations and controversies surrounding the prevention of aspiration pneumonia in the critically ill patient. Finally, we review ethical dilemmas surrounding feeding and aspiration risk concerns in debilitated and demented patients.

HIF-1alpha expression in response to lipopolysaccaride mediates induction of hepatic inflammatory cytokine TNFalpha

HIF-1alpha is a transcription factor that acts as a master regulator of gene expression induced by hypoxia. Recent studies have demonstrated that the potent inflammatory factor, lipopolysaccharide (LPS), can also activate HIF-1alpha in myeloid cells. However, the molecular mechanisms at the transcriptional level of HIF-1alpha induction by LPS remained undefined. Here, we investigated the regulatory mechanism of HIF-1alpha expression by LPS in hepatocytes and identified that LPS-induced HIF-1alpha mediate gene transcription of a typical inflammatory mediator, tumor-necrosis factor alpha (TNFalpha). Increased HIF-1alpha gene expression by LPS was defined in a series of hepatic cell lines by RT-PCR, Western blotting and promoter transactivation assay. The JNK signaling and c-Jun activation were required to induce the HIF-1alpha gene transcription by LPS. The finding that a cascade transcriptional activation of distinct set of transcription factors, c-Jun and HIF-1alpha, in response to LPS stimulation associates with induction of TNFalpha gene transcription lends new insights into the functional mechanisms by which complex patterns of gene regulation on LPS-derived HIF activation are achieved.

Thromboxane hypersensitivity in hypoxic pulmonary artery myocytes: altered TP receptor localization and kinetics

Hypoxia-induced neonatal persistent pulmonary hypertension (PPHN) is characterized by sustained vasospasm and increased thromboxane (TxA2)-to-prostacyclin ratio. We previously demonstrated that moderate hypoxia induces myocyte TxA2 hypersensitivity. Here, we examined TxA2 prostanoid receptor (TP-R) localization and kinetics following hypoxia to determine the mechanism of hypoxia-induced TxA2 hypersensitivity. Primary cultured neonatal pulmonary artery myocytes were exposed to 10% O2 (hypoxic myocytes; HM) or 21% O2 (normoxic myocytes; NM) for 3 days. PPHN was induced in neonatal piglets by in vivo exposure to 10% FiO2 for 3 days. TP-R was studied in whole lung sections from pigs with hypoxic PPHN- and age-matched controls; intracellular localization was studied by immunocytochemistry. TP-R affinity was studied in cultured myocytes by saturation binding kinetics using 3H-SQ-29548 and competitive binding kinetics by coincubation with U-46619. Phosphorylation and coupling were examined in immunoprecipitated TP-R. We report distal propagation of TP-R expression in PPHN, extending to pulmonary arteries <50 microm. In HM, intracellular TP-R moves towards the perinuclear region, mirroring a change in endoplasmic reticulum (ER) morphology. TP-R kinetics also alter in HM membranes, with decreased Kd and Bmax (maximal binding sites). Additionally, in hypoxia, 3H-SQ-29548 is displaced at lower concentration of U-46619 than in normoxia, suggesting increased agonist affinity. Phosphorylation of serine residues on HM TP-R was significantly decreased compared with NM; this difference correlated with increased Galphaq coupling in hypoxia and was ablated by incubation with PKA. We conclude that the TP-R is normally desensitized in the neonatal pulmonary circuit by PKA-mediated regulatory phosphorylation, decreasing ligand affinity and coupling to Galphaq; this protection is lost following hypoxic exposure. Also, the appearance of TP-R in resistance arteries after development of hypoxic PPHN may contribute to increased pulmonary arterial pressure.

Severe respiratory failure: advanced treatment options

BACKGROUND

Severe respiratory failure (including acute lung injury and acute respiratory distress syndrome) continues to be associated with significant mortality and morbidity in patients of all ages.

OBJECTIVE

To review the laboratory and clinical data in support of and future directions for the advanced treatment of severe respiratory failure.

DATA SOURCES

MEDLINE/PubMed search of all relevant primary and review articles.

DATA SYNTHESIS

Our understanding of lung pathophysiology and the role of ventilator-induced lung injury through basic science investigation has led to advances in lung protective strategies for the mechanical ventilation support of patients with severe respiratory failure. Specific modalities reviewed include low-tidal volume ventilation, permissive hypercapnia, the open lung approach, recruitment maneuvers, airway pressure release ventilation, high-frequency oscillatory ventilation, prone positioning, and extracorporeal life support. The pharmacologic strategies (including corticosteroids, surfactant, and nitric oxide) investigated for the treatment of severe respiratory failure are also reviewed.

CONCLUSION

In patients with severe respiratory failure, an incremental approach to the management of severe hypoxemia requires implementation of the strategies reviewed, with knowledge of the evidence base to support these strategies.

Intestinal anastomosis surgery with no septic shock primes for a dysregulatory response to a second stimulus

BACKGROUND

Major surgery is believed to contribute to immune dysregulation and high susceptibility to microbes. Recently, the inflammatory "two-hit" model has been accepted to elucidate development of multiple organ failure in surgical patients. Our purpose was to examine whether intestinal surgery, which causes a minor insult with no septic shock, may modify the immune response to exogenous LPS as a second stimulus.

MATERIALS AND METHODS

Using a rat intestinal transection and anastomosis surgery model, we sequentially examined blood cell counts, body temperatures, and plasma cytokines. Rats were administered with LPS intravenously or intratracheally various days after surgery. Phagocytic activity and TNFalpha production in bronchoalveolar lavage (BAL) cells, plasma cytokines, and survival rates were evaluated.

RESULTS

The surgery itself caused no severe shock or circulating cytokine elevation, whereas the number of granulocytes in the blood was significantly elevated after surgery. LPS-induced elevation of circulating IFNgamma attenuated 3 days after surgery. In contrast, IL-10 was enhanced 3-10 days after surgery. Hyporesponsiveness of BAL cells to LPS was observed 3 days after surgery but not the next day after surgery. However, rats intratracheally exposed to LPS 10-13 days after surgery exhibited higher mortality.

CONCLUSIONS

Although our surgical procedure was not supposed to be a severe insult, it sufficiently primed rats for an altered response to a second stimulus (endotoxin), which included enhanced mortality. This study provided an improved understanding of pathophysiological changes following surgery and described a useful model for developing preventive and therapeutic strategies for complications after surgery.