Heparin Nebulization Attenuates Acute Lung Injury in Sepsis ... : Shock (original) (raw)
INTRODUCTION
Acute lung injury (ALI) after inhalation of cotton smoke is characterized by copious exudate production resulting in the formation of casts. A previous investigation (1) from our laboratory revealed that, in ALI after inhalation of cotton smoke, the airway epithelium is shed, leaving the basal membrane vulnerable. Loss of this fluid barrier results in excessive exudate formation (2,3). The exudative material is rich in plasma proteins and fibrinogen, which combines with the abundant mucus secretions and sloughed epithelial cells to form airway casts. The casts occlude the airways causing atelectasis in the occluded lung and hypoxia and barotrauma to the ventilated areas.
It could be speculated that local impairment of the coagulation system could prevent cast formation in the airways. In the coagulation cascade, the transformation of fibrinogen to fibrin is dependent on the presence of activated thrombin. We have previously reported that nebulization of heparin in combination with the free radical scavenger dimethylsulfoxide into the airway reduces the pathophysiological changes associated with smoke inhalation in sheep (4). These results have been confirmed after smoke inhalation lung injury in pediatric patients using aerosolized inhaled heparin in combination with methylcystein instead of dimethylsulfoxide (5).
Normally, intravascular coagulation is prevented by a balance between thrombin and its counterpart, antithrombin, which is produced in the liver. Heparin catalyzes the reaction between thrombin and antithrombin by forming into complexes, thereby inhibiting the generation of fibrin. Clot formation can also be impaired by increasing the antithrombin concentration (6,7).
ALI frequently arises after smoke inhalation complicated by pneumonia induced by Pseudomonas aeruginosa (8,9). We have recently modeled ALI by instilling P. aeruginosa into the airways of sheep after smoke inhalation. The purpose of the present study was to test the hypothesis that inhaled nebulized heparin would reduce the pathophysiological changes associated with pneumonia after smoke inhalation lung injury.
MATERIALS AND METHODS
Animal preparation
The Animal Care and Use Committee of The University of Texas Medical Branch approved the experiments reported in this manuscript. All animals were handled within the guidelines established by the American Physiological Society. The experiments were performed in adherence to the National Institutes of Health Guidelines on the Use of Laboratory Animals. Fourteen female sheep (body weight of 37.0 ± 0.9 kg) were surgically prepared as previously described (10). After the measurement of baseline data, 15 animals received a smoke and bacterial challenge, and four animals received a sham injury. The technique for the induction of inhalation injury was described previously (11). After smoke inhalation, animals were mechanically ventilated with 100% O2 throughout the 24-h study. Thirty minutes after the smoke inhalation, an experimental bacterial solution was instilled into the lung lobes using a bronchoscope. Live P. aeruginosa (2–5 × 1011 cfu) was suspended in 30 mL of saline and instilled into the right lower and middle lobes (10 mL each), as well as the left lower lobe (10 mL). Ringer's lactate (5–7 mL kg−1 h−1) was infused intravenously to prevent hemoconcentration. After 24 h, lung samples were taken to evaluate the lung injury. Sham injury group (n = 4) received tracheostomy and 48 breaths of sham smoke (room air) while under a halothane anesthesia. After the sham smoke, animals were mechanically ventilated with 100% O2 in the same way as the injured group. The concentration of nitrite (NOx; total amount of NO metabolites) in plasma was measured using an NO chemiluminescent detector (model 7020; Antek Instruments, Houston, TX) (12).
To nebulize heparin or saline, a nebulizer (Airlife Misty-Neb; Baxter, CA) was connected to the tracheobronchial tree (4). Heparin (n = 5; 1000 U/mL from beef lung; Pharmacia & Upjohn, Kalamazoo, MI) or saline (n = 5) was given at 4-h intervals for 24 h by a nebulizer. An additional five animals received continuous infusion of heparin (300 U/kg/23 h). The pH of the heparin we used was 5.0–7.5, and the osmolality was approximately 400 mOsm. These treatments were begun 1 h after the administration of smoke and bacterial challenge. The experimental protocol is shown in Figure 1. Activated clotting time was monitored during the experiment (Hemochron, model 801; International Technidyne, Edson, NJ). Plasma level of fibrin degradation products (FDP) was measured at baseline (0 h) and 24 h with a latex agglutination assay kit (FDP Plasma kit; Diagnostica Stago, Parsippany, NJ).
Experimental protocol. The time when bacteria was installed was called time 0. The treatment of either heparin nebulization (n = 5), saline nebulization (n = 5), or heparin infusion (n = 5) was started 1 h after the injury (time = 1 h). Sham injury group received a sham smoke and were mechanically ventilated in a same fashion.
Lung histology
After the animals were sacrificed, the right lower lobe in each animal was excised and inflated with 10% formalin. Fixed samples were embedded in paraffin, sectioned into 6-μm pieces, and stained with hematoxylin-eosin. A pathologist who was unaware of the group assignment analyzed the samples. We established a scoring system to evaluate the histology. Twenty-four areas of lung parenchyma were graded on a scale of 0–4 (0, absent and appears normal; 1, light; 2, moderate; 3, strong; 4, intense) for congestion, edema, inflammation, and hemorrhage. A mean score for each of the parameters was then calculated.
Airway obstruction by cast formation was also evaluated. Fifteen bronchi and 30 bronchioles were investigated, and the percentage of area obstructed by the cast was estimated (0%–100%). All the histological samples were re-reviewed by a second pathologist in order to assign a consensus score.
Bacterial viability test
To test the effect of heparin on bacterial growth, we mixed the solution of P. aeruginosa with various concentrations of heparin sodium (Pharmacia & Upjohn). After 30 min of coincubation with heparin, bacterial solution was pipetted into Tryptic Soy Agar (Difco, Sparks, MD) pour plates and was incubated at 37°C for 24 h. The number of colonies observed per plate was counted.
Statistical analysis
Data are expressed as means ± SE. Analysis of variance (ANOVA) for multiple comparisons (two-way ANOVA) and Scheffe's post hoc test were used to compare data within the groups. In the changes in hemokinetics and blood gases at certain time points, a Student t test was used to compare between the groups. For the histological study, a nonparametric Kruskal-Wallis test was performed. A P < 0.05 was considered statistically significant.
RESULTS
Lung wet/dry (W/D) weight ratio
The peak levels of carboxyhemoglobin in the saline-nebulization, heparin-nebulization, and heparin infusion groups were 74.7% ± 7.1%, 75.8% ± 10.9%, and 86.6% ± 6.6%, respectively (not significant differences). Thus, all the groups received almost the same amount of smoke using our procedure. The carboxyhemoglobin level after 48 breaths of sham smoke was 4.7% ± 0.2%.
In saline-nebulized animals, the lung W/D weight ratio increased significantly 24 h after smoke inhalation followed by bronchial instillation of bacteria. This increase was significantly attenuated heparin-nebulization, but not by intravenous heparin (Fig. 2).
Changes in lung W/D weight ratio. Lung W/D weight ratio is shown in noninjured (Sham; n = 4), saline-nebulization (saline; n = 5), heparin-nebulization (Neb-hep; n = 5), and intravenous heparin (Iv-hep, n = 5) 24 h after the insult. †denotes a significant difference vs. sham animals (P < 0.05). An asterisk denotes a difference vs. saline-nebulized animals (P < 0.05).
Changes in pulmonary gas exchange
The PaO2/FiO2 ratio (P/F) dropped markedly in the saline-treated group (Fig. 3A). In the heparin-nebulized group, the drop was significantly attenuated after 12 h. The pulmonary shunt fraction (Qs/Qt) increased in the saline-treated group, reaching 50%–60% at 24 h, but was significantly lower in the heparin-nebulized group (Fig. 3B). Intravenous heparin did not attenuate either P/F ratio and shunt fraction (data not shown).
Changes in P/F ratio and pulmonary shunt fraction. P/F ratio (A) and pulmonary shunt fraction (Qs/Qt; B) were calculated. Data are expressed as the means ± SE. ○ represent saline-nebulized (n = 5) animals, ● represent heparin-nebulized (n = 5) animals, and □ represent sham (n = 4). An asterisk denotes a difference vs. saline-nebulized animals (P < 0.05).
Hemodynamic changes
In sheep exposed to inhalation of nebulized saline, the mean arterial pressure (MAP) decreased to a significantly lower level. In contrast, heparin-nebulized animals maintained baseline MAP, although it was lower than in the sham-injured group (Fig. 4A). PAP and the LAP rose significantly in both heparin-and saline-nebulized groups (Fig. 4, B and C). The latter variables tended to be higher in the heparin-nebulized group than in the saline-nebulized group, but no significant statistical differences were found. CI increased significantly in the saline-treated group, but did not reach significance in the heparin-nebulized group. The sham group showed a drop in CI after mechanical ventilation was started with 100% oxygen (Fig. 4D). Although systemic vascular resistance index (SVRI) dropped markedly in both saline-and heparin-nebulized groups, the decrease after 18 h was significantly less in the heparin-nebulized group (Fig. 5A). The left ventricular stroke work index dropped in the saline-treated group, but the fall in the heparin-treated group was significantly less (Fig. 5B).
Changes in hemokinetic parameters. MAP (A), pulmonary arterial pressure (PAP; B), left atrial pressure (LAP; C), and cardiac index (CI; D) were monitored during the study. Data are expressed as the means ± SE. ○ represent saline nebulized animals (n = 5), ● represent heparin-nebulized (n = 5), and □ represent sham animals (n = 4). An asterisk denotes a difference vs. the saline-nebulized group (P < 0.05).
Changes in SVRI (A) and left ventricular stroke work index (LVSWI; B). Data are expressed as the means ± SE. ○ represent saline-nebulized animals (n = 5), ● represent heparin-nebulized animals (n = 5), and □ represent sham (n = 4). An asterisk denotes a difference vs. saline-nebulized group (P < 0.05).
Changes in plasma nitrate/nitrite (NOx) levels
The plasma NOx levels increased significantly after the insult, and no difference was demonstrated between the saline-and heparin-nebulized groups (Fig. 6).
Changes in plasma nitrate and nitrite levels. Plasma levels of nitrate and nitrite (NOx) were measured. Data are expressed as the mean ± SE. ○ represent saline-nebulized animals (n = 5), ● represent heparin-nebulized (n = 5), and □ represent sham (n = 4). †denotes a significant difference vs. baseline levels (P < 0.05).
Activated clotting time and FDP
In the heparin-nebulized group, the activated clotting time at baseline (0 h) and 24 h after exposure to smoke and bacteria was 141 ± 20 s and 139 ± 13 s, respectively (not significant). Plasma FDP was determined semiquantitatively by means of a commercially available assay (positive, >20 μg/mL; negative, <5 μg/mL; ±, 5–20 μg/mL). All determinations were negative at baseline. In the saline-treated group, three animals tested positive and two tested negative at 24 h for FDP. The heparin-treated group displayed the same result: three animals tested positive and two tested negative, suggesting that inhalation of nebulized heparin did not attenuate the coagulation/fibrinolytic abnormalities associated with sepsis.
Histology
Twenty-four hours after the smoke and bacterial challenge, there was a marked inflammatory reaction in the lungs characterized by cellular infiltrates in the interstitium and the air spaces of the lung. The infiltrates were predominantly composed of neutrophils. Interstitial edema, vascular congestion, and hemorrhage were also observed. The latter changes were markedly attenuated in the heparin-treated group. The histology scores, as based on the number of areas with congestion, edema, inflammation, and hemorrhage, were all significantly higher after exposure to smoke and bacteria (Fig. 7). All of the scores were lower in the heparin-nebulized group, although no significant difference could be found except in the hemorrhage category (Fig. 7). The total histology score was significantly attenuated by heparin nebulization (Fig. 8).
Changes in lung histology score. Histological changes were evaluated as congestion, edema, inflammation, and hemorrhage 24 h after the smoke and bacterial challenge. White bars represent noninjured sham animals (n = 4), black bars represent animals nebulized with saline and receiving smoke/bacteria (n = 5), and slashed bars represent animals nebulized with heparin and receiving smoke/bacteria (n = 5). Data are expressed as the means ± SE. †denotes significant difference vs. noninjured sham (P < 0.05). An asterisk denotes a difference vs. saline-nebulized animals (P < 0.05).
Effect of heparin nebulization on the total histology score. The sum of histology scores of the four parameters were calculated. Data are expressed as the means ± SE. The open bar represents noninjured sham control animals (n = 4), the closed bar represents smoke/bacteria with saline-nebulization (Neb-Saline; n = 5), and the slashed bar represents heparin-nebulized animals (Neb-Hep; n = 5). †denotes a significant difference vs. noninjured sham (P < 0.05). An asterisk denotes a difference vs. saline-nebulized animals (P < 0.05).
We also found that many bronchi and/or bronchioles were obstructed by infiltrates of neutrophils, shed bronchial epithelial cells, mucus, and fibrin. Airway obstruction was found in more than 30% of both bronchi and bronchioles (Fig. 9). Heparin nebulization reduced the cast formation in both areas, and the percentage of obstructed airways was significantly lower in animals exposed to nebulized inhaled heparin (Fig. 9).
Microscopic evaluation of airway obstruction. Percentage of airway obstruction by the cast was estimated by two individual pathologists who were blinded to the animal groupings as described in the “Materials and Methods” section. Fifteen bronchi and 30 bronchioles were investigated. Data are expressed as the means ± SE. White bars represent noninjured sham (n = 4) animals, black bars represent animals nebulized with saline and receiving smoke/bacteria (n = 5), and slashed bars represent animals nebulized with heparin and receiving smoke/bacteria (n = 5). †denotes a significant difference vs. sham animals (P <0.05). An asterisk denotes a difference vs. saline-nebulized animals (P < 0.05).
Bacterial viability test
According to the label information, the heparin sodium that we used contained 0.495 mg/mL benzyl alcohol, however, 10–1000 U/mL heparin sodium did not affect the P. aeruginosa viability (Table 1).
Effect of heparin on bacterial viability. Various concentration of heparin were coincubated with Pseudomonas aeruginosa solution and plated. Data are expressed as the mean (CFUs/dish) ± SE of triplicate studies
DISCUSSION
In several respects, the present animal model mimics the hyperdynamic sepsis seen after ALI in humans. Characteristically, the animals displayed a fall in systemic arterial pressure due to a decrease in SVRI (Figs. 4 and 5) that was paralleled by raised plasma levels of NOx (Fig. 6).
There are some experimental studies demonstrating the efficacy of intravenously administered heparin after smoke inhalation injury or sepsis. Cox et al. (13) reported that heparin reduces smoke inhalation lung injury in sheep, and Griffin et al. (14) have demonstrated that heparin improves the survival of sepsis in swine. Previous investigations from our laboratory using sheep have demonstrated favorable effects on smoke inhalation lung injury of a combination of nebulized heparin and dimethylsulfoxide (4,5,15). In the present study, the systemic hypotension and the deterioration of gas exchange were antagonized by inhalation of nebulized heparin alone, but not by intravenous heparin. As shown in Figure 9, inhalation of aerosolized heparin significantly prevented the cast formation.
Abnormalities in the production and transport of airway secretions play an important role in the pathophysiology of smoke inhalation lung injury. The synthesis of mucous becomes disorganized. Other components of airway contents, including neutrophils and shed bronchial epithelial cells, contribute to the abnormal secretions. In addition, ciliary function may be inhibited or damaged by smoke inhalation (16). The consequences of these derangements are the widespread plugging of small bronchi and bronchioles. During the experiments, we tried to remove the casts by bagging and suctioning the airway. Large casts (thick pseudomembranes) were occasionally observed in saline-treated animals after 12 h, but rarely in heparin-treated animals. We nebulized a double dose (20 cc/each every 4 h; n = 3) of saline into three sheep with smoke and bacterial injury, and the results were the same as those seen with lower doses of saline, as reported in the present study (data not shown). Saline nebulization at these latter levels resulted in a similar changes in W/D ratio and P/F ratio as animals not nebulized with saline and injured with smoke and bacteria.
Alveolar fibrin formation is a common hallmark of acute and chronic lung inflammatory processes, including severe pneumonia and acute respiratory distress syndrome (ARDS) (17). Activation of the tissue factor-induced coagulation pathway in the alveolar compartment, accompanied by inhibition of the regional fibrinolytic system that promotes deposition of fibrin in alveoli, may well contribute to the functional impairment of the lung. Recently, investigators noticed that tissue factor is expressed on alveolar epithelial cells (18) and alveolar macrophages (19). Drake et al. (20) demonstrated that in baboons suffering from Escherichia coli sepsis, the tissue factor expression was strongly positive in alveolar epithelial cells. Since the exudation of plasma is enhanced in sepsis, factor VIIa binds to the expressed tissue factor in the alveoli, thus activating the extrinsic coagulation pathway. A defect in fibrinolysis can also potentiate fibrin deposition in inflammatory foci (21). Although levels of plasminogen activator antigen are increased, its activity is almost completely inhibited by plasminogen activator inhibitor-1 during sepsis (22). In patients with ARDS, enhanced coagulation and depressed fibrinolysis have been found (23). The latter imbalance may be an important factor in the pathogenesis of ARDS, which is a major complication of sepsis (23). Fibrin has also been shown to act as a potent inhibitor of lung surfactant through the incorporation of hydrophobic surfactant components (24). These changes result in alveolar collapse and increased fraction of intrapulmonary shunt, both of which are characteristic features of the gas exchange abnormalities encountered in acute pneumonia and ARDS. FDP may rise following intravascular fibrin formation. In the present study, FDP showed no difference between the groups. Although inhalation of nebulized heparin inhibited cast formation in the airways, it does not inhibit the disseminated intravascular coagulation in sepsis.
Cast formation results in parts of the lung becoming hypoinflated and other parts becoming hyperinflated. Hyperinflation is known to cause induction of cytokines such as TNF-α, IL-1, and/or IL-6 (25). Furthermore, Pugin et al. (26) found that mechanical ventilation activates nuclear factor-κB in lung macrophages. Narimanbekov et al. (27) noted a higher number of neutrophils in lung lavage and a higher histological injury score in hyperventilated as compared with normoventilated rabbit lungs. In the present study, aerosolized heparin improved not only the gas exchange, but also the water balance (W/D weight ratio) of the lung, suggesting that inhibition of cast formation will attenuate the pulmonary vascular fluid flux, which is also consistent with the observations in the histology scores. We think that inhibition of airway obstruction will contribute to the attenuation of lung inflammation and pulmonary vascular injury.
Recent studies have shown that exhaled NO was increased in murine and porcine sepsis (28,29) and is considered an early marker of lung injury. Since cast formation may inhibit the exhalation of NO, NO produced in the lung epithelial cells may diffuse into the pulmonary arterioles, causing their dilation and increasing the shunt flow. Thus, the cast formation may expand the effect of NO, thereby increasing the shunt fraction with an associated drop in the P/F ratio. The effects of NO are diversified. It is well known that NO inhibits the NO synthase (NOS) activity by a negative feedback mechanism (30). Consequently, NOS within the nonventilated alveoli may be inhibited due to cast formation, whereas NOS within the ventilated alveoli is not inhibited. This may be a reason why we could not find the difference in plasma NOx between the groups. Further investigations of the mRNA for lung iNOS are warranted.
Heparin is also known to bind various chemokines such as IL-8 (31). Recently, it was shown that heparin-chemokine complexes were unable to bind to the receptor, resulting in a block of the biological activity (31). Therefore, nebulized heparin may act like an anti-IL-8 agent, thus inhibiting the neutrophil recruitment to the alveolar space. The anti-inflammatory effect of heparin is complex. Presently, we do not know whether heparin works through its anticoagulant or anti-inflammatory mechanisms. However, heparin preparations that lack anticoagulant properties are now available (32). Using this compound, we may be able to investigate the further mechanism of action. Specific thrombin inhibitors such as hirudin or argatoroban are considered as investigative tools in our sepsis model because they are not reported to have an anti-inflammatory effect.
In conclusion, the inhibition of clot formation in the blood vessels by heparin is common knowledge, but the inhibition of cast formation in the airway by heparin nebulization is a novel idea that is both unique and useful. Clinical studies have already reported favorable effects of heparin nebulization in patients suffering from smoke inhalation injury (5). We suggest that this strategy be considered for a prospective multicenter, placebo-controlled, clinical trial.
ACKNOWLEDGMENTS
We thank Nettie Biondo, John Salsbury, Steve Lee, and Jeff Nelson for their excellent technical assistance.
REFERENCES
1. Abdi S, Evans MJ, Cox RA, Lubbesmeyer H, Herndon DN, Traber DL: Inhalation injury to tracheal epithelium in an ovine model of cotton smoke exposure: early phase (30 minutes). Am Rev Respir Dis 142:1436–1439, 1990.
2. Herndon DN, Traber LD, Linares H, Flynn JT, Niehaus G, Kramer G, Traber DL: Etiology of the pulmonary pathophysiology associated with inhalation injury. Resuscitation 14:43–59, 1986.
3. Herndon DN, Traber DL, Niehaus GD, Linares HA, Traber LD: The pathophysiology of smoke inhalation injury in a sheep model. J Trauma 24:1044–1051, 1984.
4. Kimura R, Mlcak R, Richardson J, Desai M, Herndon D, Traber LD, Traber DL: Treatment of smoke-induced pulmonary injury with nebulized dimethylsulfoxide. Circ Shock 25:333–341, 1988.
5. Desai MH, Brown M, Mlcak R, Richardson J, Traber LD, Herndon DN, Traber DL: Reduction of smoke induced lung injury with dimethylsulfoxide (DMSO) and heparin treatment. Surg Forum 36:103–104, 1985.
6. Mammen EF: Antithrombin: its physiological importance and role in DIC. Semin Thromb Hemost 24:19–25, 1998.
7. Balk R, Emerson T, Fourrier F, Kruse JA, Mammen EF, Schuster HP, Vinazzer H: Therapeutic use of antithrombin concentrate in sepsis. Semin Thromb Hemost 24:183–194, 1998.
8. Rue LW, Cioffi WG, Mason Jr, AD McManus WF, Pruitt Jr: BA The risk of pneumonia in thermally injured patients requiring ventilatory support. J Burn Care Rehabil 16:262–268, 1995.
9. Linares HA: A report of 115 consecutive autopsies in burned children: 1966–1980. Burns Incl Therm Inj 8:263–270, 1982.
10. Herndon DN, Adams Jr, T Traber LD, Traber DL: Inhalation injury and positive pressure ventilation in a sheep model. Circ Shock 12:107–113, 1984.
11. Kimura R, Traber LD, Herndon DN, Linares HA, Lübbesmeyer HJ, Traber DL: Increasing duration of smoke exposure induces more severe lung injury in sheep. J Appl Physiol 64:1107–1113, 1988.
12. Soejima K, Traber LD, Schmalstieg FC, Hawkins H, Jodoin JM, Szabo C, Szabo E, Varig L, Salzman A, Traber DL: Role of nitric oxide in vascular permeability after combined burns and smoke inhalation injury. Am J Respir Crit Care Med 163:745–752, 2001.
13. Cox CS, Zwischenberger JB, Traber DL, Traber LD, Haque AK, Herndon DN: Heparin improves oxygenation and minimizes barotrauma after severe smoke inhalation in an ovine model. Surg Gynecol Obstet 176:339–349, 1993.
14. Griffin MP, Gore DC, Zwischenberger JB, Lobe TE, Hall M, Traber DL, Herndon DN: Does heparin improve survival in experimental porcine gram-negative septic shock? Circ Shock 31:343–349, 1990.
15. Brown M, Desai M, Traber LD, Herndon DN, Traber DL: Dimethylsulfoxide with heparin in the treatment of smoke inhalation injury. J Burn Care Rehabil 9:22–25, 1988.
16. Hubbard GB, Langlinais PC, Shimazu T, Okerberg CV, Mason Jr, AD Pruitt Jr: BA The morphology of smoke inhalation injury in sheep. J Trauma 31:1477–1486, 1991.
17. Gunther A, Mosavi P, Heinemann S, Ruppert C, Muth H, Markart P, Grimminger F, Walmrath D, Temmesfeld-Wollbruck B, Seeger W: Alveolar fibrin formation caused by enhanced procoagulant and depressed fibrinolytic capacities in severe pneumonia: comparison with the acute respiratory distress syndrome. Am J Respir Crit Care Med 161:454–462, 2000.
18. Gross TJ, Simon RH, Sitrin RG. Tissue factor procoagulant expression by rat alveolar epithelial cells. Am J Respir Cell Mol Biol 6:397–403, 1992.
19. Sitrin RG, Brubaker PG, Shellito JE, Kaltreider HB: The distribution of procoagulant and plasminogen activator activities among density fractions of normal rabbit alveolar macrophages. Am Rev Respir Dis 133:468–472, 1986.
20. Drake TA, Cheng J, Chang A, Taylor Jr: FB Expression of tissue factor, thrombomodulin, and E-selectin in baboons with lethal Escherichia coli sepsis [published erratum appears in Am J Pathol 1993 Aug;143(2):649]. Am J Pathol 142:1458–1470, 1993.
21. Bertozzi P, Astedt B, Zenzius L, Lynch K, LeMaire F, Zapol W, Chapman Jr: HA Depressed bronchoalveolar urokinase activity in patients with adult respiratory distress syndrome. N Engl J Med 322:890–897, 1990.
22. Garcia-Fernandez N, Montes R, Purroy A, Rocha E: Hemostatic disturbances in patients with systemic inflammatory response syndrome (SIRS) and associated acute renal failure (ARF). Thromb Res 100:19–25, 2001.
23. Vervloet MG, Thijs LG, Hack CE: Derangements of coagulation and fibrinolysis in critically ill patients with sepsis and septic shock. Semin Thromb Hemost 24:33–44, 1998.
24. Seeger W, Elssner A, Gunther A, Kramer HJ, Kalinowski HO: Lung surfactant phospholipids associate with polymerizing fibrin: loss of surface activity [published erratum appears in Am J Respir Cell Mol Biol 1993 Oct;9(4):462]. Am J Respir Cell Mol Biol 9:213–220, 1993.
25. von Bethmann AN, Brasch F, Nusing R, Vogt K, Volk HD, Muller KM, Wendel A, Uhlig S: Hyperventilation induces release of cytokines from perfused mouse lung. Am J Respir Crit Care Med 157:263–272, 1998.
26. Pugin J, Dunn I, Jolliet P, Tassaux D, Magnenat JL, Nicod LP, Chevrolet JC: Activation of human macrophages by mechanical ventilation in vitro. Am J Physiol 275:L1040–L1050, 1998.
27. Narimanbekov IO, Rozycki HJ: Effect of IL-1 blockade on inflammatory manifestations of acute ventilator-induced lung injury in a rabbit model. Exp Lung Res 21:239–254, 1995.
28. Stewart TE, Valenza F, Ribeiro SP, Wener AD, Volgyesi G, Mullen JB, Slutsky AS: Increased nitric oxide in exhaled gas as an early marker of lung inflammation in a model of sepsis. Am J Respir Crit Care Med 151:713–718, 1995.
29. Fujii Y, Goldberg P, Hussain SN: Intrathoracic and extrathoracic sources of exhaled nitric oxide in porcine endotoxemic shock. Chest 114:569–576, 1998.
30. Assreuy J, Cunha FQ, Liew FY, Moncada S: Feedback inhibition of nitric oxide synthase activity by nitric oxide. Br J Pharmacol 108:833–837, 1993.
31. Kuschert GS, Coulin F, Power CA, Proudfoot AE, Hubbard RE, Hoogewerf AJ, Wells TN: Glycosaminoglycans interact selectively with chemokines and modulate receptor binding and cellular responses. Biochemistry (Mosc) 38:12959–12968, 1999.
32. Xie X, Rivier AS, Zakrzewicz A, Bernimoulin M, Zeng XL, Wessel HP, Schapira M, Spertini O: Inhibition of selectin-mediated cell adhesion and prevention of acute inflammation by nonanticoagulant sulfated saccharides. J Biol Chem 275:34818–34825, 2000.
Keywords:
Airway cast; pneumonia; shunt; histology score; sepsis; acute respiratory distress syndrome
© 2002 Lippincott Williams & Wilkins, Inc.