N-acetyl-L-cysteine protects against inhaled sulfur mustard poisoning in the large swine.

CONTEXT: Sulfur mustard is a blister agent that can cause death by pulmonary damage. There is currently no effective treatment. N-acetyl-L-cysteine (NAC) has mucolytic and antioxidant actions and is an important pre-cursor of cellular glutathione synthesis. These actions may have potential to reduce mustard-induced lung injury. OBJECTIVE: Evaluate the effect of nebulised NAC as a post-exposure treatment for inhaled sulfur mustard in a large animal model. MATERIALS AND METHODS: Fourteen anesthetized, surgically prepared pigs were exposed to sulfur mustard vapor (100 µg.kg⁻¹), 10 min) and monitored, spontaneously breathing, to 12 h. Control animals had no further intervention (n = 6). Animals in the treatment group were administered multiple inhaled doses of NAC (1 ml of 200 mg.ml⁻¹ Mucomyst™ at + 30 min, 2, 4, 6, 8, and 10 h post-exposure, n = 8). Cardiovascular and respiratory parameters were recorded. Arterial blood was collected for blood gas analysis while blood and bronchoalveolar lavage fluid were collected for hematology and inflammatory cell analysis. Urine was collected to detect a sulfur mustard breakdown product. Lung tissue samples were taken for histopathological and post-experimental analyses. RESULTS: Five of six sulfur mustard-exposed animals survived to 12 h. Arterial blood oxygenation (PaO2) and saturation levels were significantly decreased at 12 h. Arterial blood carbon dioxide (PaCO2) significantly increased, and arterial blood pH and bicarbonate (HCO3⁻) significantly decreased at 12 h. Shunt fraction was significantly increased at 12 h. In the NAC-treated group all animals survived to 12 h (n = 8). There was significantly improved arterial blood oxygen saturation, HCO3⁻ levels, and shunt fraction compared to those of the sulfur mustard controls. There were significantly fewer neutrophils and lower concentrations of protein in lavage compared to sulfur mustard controls. DISCUSSION: NAC's mucolytic and antioxidant properties may be responsible for the beneficial effects seen, improving clinically relevant physiological indices affected by sulfur mustard exposure. CONCLUSION: Beneficial effects of nebulized NAC were apparent following inhaled sulfur mustard exposure. Further therapeutic benefit may result from a combination therapy approach.

The injured lung: clinical issues and experimental models.

Exposure of military and civilian populations to inhaled toxic chemicals can take place as a result of deliberate release (warfare, terrorism) or following accidental releases from industrial concerns or transported chemicals. Exposure to inhaled toxic chemicals can result in an acute lung injury, and in severe cases acute respiratory distress syndrome, for which there is currently no specific medical therapy, treatment remaining largely supportive. This treatment often requires intensive care facilities that may become overwhelmed in mass casualty events and may be of limited benefit in severe cases. There remains, therefore, a need for evidence-based treatment to inform both military and civilian medical response teams on the most appropriate treatment for chemically induced lung injury. This article reviews data used to derive potential clinical management strategies for chemically induced lung injury.

Exposure-response effects of inhaled sulfur mustard in a large porcine model: a 6-h study.

CONTEXT: Inhalation of sulfur mustard (HD) vapor can cause life-threatening lung injury for which there is no specific treatment. A reproducible, characterized in vivo model is required to investigate novel therapies targeting HD-induced lung injury. MATERIALS AND METHODS: Anesthetized, spontaneously breathing large white pigs (~50 kg) were exposed directly to the lung to HD vapor at 60, 100, or 150 µg/kg, or to air, for ~10 min, and monitored for 6 h. Cardiovascular and respiratory parameters were recorded. Blood and bronchoalveolar lavage fluid (BALF) were collected to allow blood gas analysis, hematology, and to assay for lung inflammatory cells and mediators. Urine was collected and analyzed for HD metabolites. Histopathology samples were taken postmortem (PM). RESULTS: Air-exposed animals maintained normal lung physiology whilst lying supine and spontaneously breathing. There was a statistically significant increase in shunt fraction across all three HD-exposed groups when compared with air controls at 3-6 h post-exposure. Animals were increasingly hypoxemic with respiratory acidosis. The monosulfoxide ß-lyase metabolite of HD (1-methylsulfinyl-2-[2(methylthio)ethylsulfonyl)ethane], MSMTESE), was detected in urine from 2 h post-exposure. Pathological examination revealed necrosis and erosion of the tracheal epithelium in medium and high HD-exposed groups. CONCLUSION: These findings are consistent with those seen in the early stages of acute lung injury (ALI).

Delayed low-dose supplemental oxygen improves survival following phosgene-induced acute lung injury.

Phosgene is a chemical widely used in the plastics industry and has been used in warfare. It produces life-threatening pulmonary edema within hours of exposure; no antidote exists. This study examines pathophysiological changes seen following treatment with elevated inspired oxygen concentrations (Fi(O2)), in a model of phosgene-induced acute lung injury. Anesthetized pigs were exposed to phosgene (Ct 2500 mg min m(-3)) and ventilated (intermittent positive pressure ventilation, tidal volume 10 ml kg(-1), positive end-expiratory pressure 3 cm H(2)O, frequency 20 breaths min(-1)). The Fi(O2) was varied: group 1, Fi(O2) 0.30 (228 mm Hg) throughout; group 2, Fi(O2) 0.80 (608 mm Hg) immediately post exposure, to end; group 3, Fi(O2) 0.30 from 30 min post exposure, increased to 0.80 at 6 h post exposure; group 4, Fi(O2) 0.30 from 30 min post exposure, increased to 0.40 (304 mm Hg) at 6 h post exposure. Group 5, Fi(O2) 0.30 from 30 min post exposure, increased to 0.40 at 12 h post exposure. The current results demonstrate that oxygen is beneficial, with improved survival, arterial oxygen saturation, shunt fraction, and reduced lung wet weight to body weight ratio in all treatment groups, and improved arterial oxygen partial pressure in groups 2 and 3, compared to phosgene controls (group 1) animals. The authors recommend that treatment of phosgene-induced acute lung injury with inspired oxygen is delayed until signs or symptoms of hypoxia are present or arterial blood oxygenation falls. The lowest concentration of oxygen that maintains normal arterial oxygen saturation and absence of clinical signs of hypoxia is recommended.

Furosemide in the treatment of phosgene induced acute lung injury.

METHOD: Using previously validated methods, 16 anaesthetised large white pigs were exposed to phosgene (target inhaled dose 0.3 mg kg(-1)), established on mechanical ventilation and randomised to treatment with either nebulised furosemide (4 ml of 10 mg x ml(-1) solution) or saline control. Treatments were given at 1, 3, 5, 7, 9, 12, 16 and 20 hours post phosgene exposure; the animals were monitored to 24 hours following phosgene exposure. RESULTS: Furosemide treatment had no effect on survival, and had a deleterious effect on PaO2: FiO2 ratio between 19 and 24 hours. All other measures investigated were unaffected by treatment. CONCLUSION: Nebulised furosemide treatment following phosgene induced acute lung injury does not improve survival and worsens PaO2: FiO2 ratio. Nebulised furosemide should be avoided following phosgene exposure.

Early treatment with nebulised salbutamol worsens physiological measures and does not improve survival following phosgene induced acute lung injury.

OBJECTIVES: To examine the effectiveness of nebulised salbutamol in the treatment of phosgene induced acute lung injury. METHOD: Using previously validated methods, 12 anaesthetised large white pigs were exposed to phosgene (Ct 1978 +/- 8 mg min m(-3)), established on mechanical ventilation and randomised to treatment with either nebulised salbutamol (2.5 mg per dose) or saline control. Treatments were given 1, 5, 9, 13, 17 and 21 hours following phosgene exposure. The animals were followed to 24 hours following phosgene exposure. RESULTS: Salbutamol treatment had no effect on mortality and had a deleterious effect on arterial oxygenation, shunt fraction and heart rate. There was a reduction in the number of neutrophils from 24.0% +/- 4.4 to 12.17% +/- 2.1 (p < 0.05) in bronchoalveolar lavage, with some small decreases in inflammatory mediators in bronchoalveolar lavage but not in plasma. CONCLUSION: Nebulised salbutamol treatment following phosgene induced acute lung injury does not improve survival, and worsens various physiological parameters including arterial oxygen partial pressure and shunt fraction. Salbutamol treatment reduces neutrophil influx into the lung. Its sole use following phosgene exposure is not recommended.

Preliminary studies of sulphur mustard-induced lung injury in the terminally anesthetized pig: exposure system and methodology.

ABSTRACT Although normally regarded as a vesicant, inhalation of sulphur mustard (HD) vapor can cause life-threatening lung injury for which there is no specific treatment. Novel therapies for HD-induced lung injury are best investigated in an in vivo model that allows monitoring of a range of physiological variables. HD vapor was generated using two customized thermostatically controlled glass flasks in parallel. The vapor was passed into a carrier flow of air (81 L. min(-1)) and down a length of glass exposure tube (1.75 m). A pig was connected to the midpoint of the exposure tube via a polytetrafluoroethylene-lined endotracheal tube, Fleisch pneumotachograph, and sample port. HD vapor concentrations (40-122.8 mg. m(-3)) up-and downstream of the point of exposure were obtained by sampling onto Porapak absorption tubes with subsequent analysis by gas chromatography-flame photometric detection. Real-time estimates of vapor concentration were determined using a photo-ionization detector. Lung function indices (respiratory volumes, lung compliance, and airway resistance) were measured online throughout. Trial runs with methylsalicylate (MS) and animal exposures with HD demonstrated that the exposure system rapidly reached the desired concentration within 1 min and maintained stable output throughout exposure, and that the MS/HD concentration decayed rapidly to zero when switched off. A system is described that allows reproducible exposure of HD vapor to the lung of anesthetized white pigs. The system has proved to be robust and reliable and will be a valuable tool in assessing potential future therapies against HD-induced lung injury in the pig. Crown Copyright (c) 2007 Dstl.

Effects of inhaled nitric oxide on the anesthetized, mechanically ventilated, large white pig.

Inhalation of nitric oxide (NO) results in selective pulmonary vasodilation, which may be beneficial in the treatment of acute lung injury. However, NO has toxic effects, and it is important to monitor the effects and fate of inhaled NO. Under intravenous general anesthesia, large white female pigs were instrumented, ventilated with intermittent positive pressure ventilation (IPPV, FiO(2) 0.3; TV 10 ml kg(-1); RR 20 bpm; PEEP 3 cm H(2)O) and monitored for 24 h. Following a period of stabilization, groups were exposed to air (control), or to 10, 40, or 80 ppm NO, delivered via the endotracheal tube in each inspiratory breath. At regular intervals throughout the 24-h period, physiological measurements and arterial blood, plasma, and urine samples were collected. Inhalation of NO acted specifically on the pulmonary vasculature, as no alterations in systemic blood pressure were observed. Administration of NO at 80 ppm resulted in a decreased mean pulmonary artery pressure, decreased pulmonary wedge pressure, and increased methemoglobin and plasma/urine nitrate levels. At post mortem, congestion of the alveolar capillary network was noted in this group. In addition increases in plasma/urine nitrate levels were also observed in the 40 ppm group. In contrast, no significant alterations were observed in the 10 ppm group, compared to the control group. Therefore, 10 ppm inhaled NO is a dose that induced no pathological changes in normal healthy lungs and may be of use as a therapeutic adjunct in the management of acute lung injury.

Pathophysiological responses following phosgene exposure in the anaesthetized pig.

This study aimed to develop a reproducible model of phosgene-induced lung injury in the pig to facilitate the future development of therapeutic strategies. Ten female young adult large white pigs were used. Following induction of anaesthesia using a halothane/oxygen/nitrous oxide mixture, arterial and venous catheters were inserted together with a pulmonary artery thermodilution catheter, and a suprapubic urinary catheter by laparotomy. Anaesthesia was maintained throughout the experiment by intravenous infusion of ketamine, midazolam and alfentanil. On completion of surgery the animals were allowed to equilibrate for 1 h and then were divided into two groups. Group 1 (n = 5) was exposed to phosgene for 10 min (mean Ct = 2443 +/- 35 mg min m(-3)) while spontaneously breathing, whereas control animals (Group 2 n = 5) were exposed to air. At 30 min post-exposure, anaesthesia was deepened in order to allow the initiation of intermittent positive pressure ventilation and the animals were monitored for up to 24 h. Cardiovascular and respiratory parameters were monitored every 30 min and blood samples were taken for arterial and mixed venous blood gas analysis and clinical chemistry. A detailed post-mortem and histopathology was carried out on all animals following death or euthanasia at the end of the 24-h monitoring period. Control animals (Group 2) all survived until the end of the 24-h monitoring period with normal pathophysiological parameters. Histopathology showed only minimal passive congestion of the lung. Following exposure to phosgene (Group 1) there was one survivor to 24 h, with the remainder dying between 16.5 and 23 h (mean = 20 h). Histopathology from these animals showed areas of widespread pulmonary oedema, petechial haemorrhage and bronchial epithelial necrosis. There was also a significant increase in lung wet weight/body weight ratio (P < 0.001). During and immediately following exposure, a transient decrease in oxygen saturation and stroke volume index was observed. From 6 h there were significant decreases in arterial pH (P < 0.01), P(a)O(2) (P < 0.01) and lung compliance (P < 0.01), whereas oxygen delivery and consumption was reduced from 15 h onwards in phosgene-exposed animals. Mean pulmonary artery pressure of phosgene-exposed animals was increased from 15 h post-exposure, with periods of increased pulmonary vascular resistance index being recorded from 9 h onwards. We have developed a reproducible model of phosgene-induced lung injury in the anaesthetized pig. We have followed changes in cardiovascular and pulmonary dynamics for up to 24 h after exposure in order to demonstrate evidence of primary acute lung injury from 16 h post-exposure. Histopathology showed evidence of widespread damage to the lung and there was also a significant increase in lung wet weight/body weight ratio (P < 0.001).

The effect of hexafluorocyclobutene on rat bronchoalveolar lavage fluid surfactant phospholipids and alveolar type II cells.

Hexafluorocyclobutene (HFCB), a reactive organohalogen gas, causes overwhelming pulmonary oedema. We investigated its effect on the rat lung surfactant system, comparing its action on type II pneumocytes with air-exposed rats. The inflammatory cell population and protein content of bronchoalveolar lavage fluid was analysed following exposure to air or HFCB (LCt30). Six rat lung phospholipids were measured by high-performance liquid chromatography, following solid phase extraction (SPE) from lavage fluid. Transmission electron microscopy (TEM) was used to visualise effects on alveolar type II cell ultrastructure. HFCB caused changes in cell populations and increased lavage fluid protein compared to controls, suggesting a permeability oedema. Changes in the total amount and percentage composition (sustained decrease in phosphatidylglycerol and phosphatidylcholine) of surfactant phospholipids also occurred. TEM observations indicated no direct ultrastructural damage to the type II cells, but showed initial, rapid release of surfactant into the alveolar space. HFCB altered the surfactant system in a manner similar to that shown following another reactive organohalogen gas, perfluoroisobutene (PFIB), but differently to that after phosgene. These differences suggest different mechanisms of action even though pulmonary oedema is the final injury for all gases. Better knowledge of the mechanisms involved will improve prospects for prophylactic/therapeutic intervention.

The effect of perfluoroisobutene and phosgene on rat lavage fluid surfactant phospholipids.

1. This study investigated whether the reactive organohalogen gases perfluoroisobutene (PFIB) and phosgene, which cause death by overwhelming pulmonary oedema, affect the surfactant system or type II pneumocytes of rat lung. 2. The progression and type of pulmonary injury in Porton Wistar-derived rats was monitored over a 48 h period following exposure to either PFIB or phosgene (LCt30) by analyzing the inflammatory cells and protein in bronchoalveolar lavage fluid. Six rat lung phospholipids were measured by high-performance liquid chromatography, following solid phase extraction from lavage fluid. 3. Alterations in the cell population and lung permeability occurred following both gases, indicating that the injury was a permeability-type pulmonary oedema. Changes in the total amount of phospholipid and in the percentage composition of the surfactant were different for the two gases. PFIB produced increases in phosphatidylglycerol and phosphatidylcholine over the first hour, similar to that seen following air exposure, followed by substantial decreases in these phospholipids. Phosgene caused late increases in all phospholipids from 6 h post-exposure. 4. Differences in the response of the surfactant system to exposure to PFIB and phosgene suggest different mechanisms of action at the alveolar surface although the final injurious response is pulmonary oedema for both gases.