Effects of prone and supine posture on cardiopulmonary function after experimental chlorine gas lung injury

Effect of TRPV4 Antagonist GSK2798745 on Chlorine Gas-Induced Acute Lung Injury in a Swine Model

As a regulator of alveolo-capillary barrier integrity, Transient Receptor Potential Vanilloid 4 (TRPV4) antagonism represents a promising strategy for reducing pulmonary edema secondary to chemical inhalation. In an experimental model of acute lung injury induced by exposure of anesthetized swine to chlorine gas by mechanical ventilation, the dose-dependent effects of TRPV4 inhibitor GSK2798745 were evaluated. Pulmonary function and oxygenation were measured hourly; airway responsiveness, wet-to-dry lung weight ratios, airway inflammation, and histopathology were assessed 24 h post-exposure. Exposure to 240 parts per million (ppm) chlorine gas for ≥50 min resulted in acute lung injury characterized by sustained changes in the ratio of partial pressure of oxygen in arterial blood to the fraction of inspiratory oxygen concentration (PaO2/FiO2), oxygenation index, peak inspiratory pressure, dynamic lung compliance, and respiratory system resistance over 24 h. Chlorine exposure also heightened airway response to methacholine and increased wet-to-dry lung weight ratios at 24 h. Following 55-min chlorine gas exposure, GSK2798745 marginally improved PaO2/FiO2, but did not impact lung function, airway responsiveness, wet-to-dry lung weight ratios, airway inflammation, or histopathology. In summary, in this swine model of chlorine gas-induced acute lung injury, GSK2798745 did not demonstrate a clinically relevant improvement of key disease endpoints.

Recapitulation of human pathophysiology and identification of forensic biomarkers in a translational model of chlorine inhalation injury

Chlorine gas (Cl2) has been repeatedly used as a chemical weapon, first in World War I and most recently in Syria. Life-threatening Cl2 exposures frequently occur in domestic and occupational environments, and in transportation accidents. Modeling the human etiology of Cl2-induced acute lung injury (ALI), forensic biomarkers, and targeted countermeasures development have been hampered by inadequate large animal models. The objective of this study was to develop a translational model of Cl2-induced ALI in swine to understand toxico-pathophysiology and evaluate whether it is suitable for screening potential medical countermeasures and to identify biomarkers useful for forensic analysis. Specific pathogen-free Yorkshire swine (30-40 kg) of either sex were exposed to Cl2 (≤240 ppm for 1 h) or filtered air under anesthesia and controlled mechanical ventilation. Exposure to Cl2 resulted in severe hypoxia and hypoxemia, increased airway resistance and peak inspiratory pressure, and decreased dynamic lung compliance. Cl2 exposure resulted in increased total leucocyte and neutrophil counts in bronchoalveolar lavage fluid, vascular leakage, and pulmonary edema compared with the air-exposed group. The model recapitulated all three key histopathological features of human ALI, such as neutrophilic alveolitis, deposition of hyaline membranes, and formation of microthrombi. Free and lipid-bound 2-chlorofatty acids and chlorotyrosine-modified proteins (3-chloro-l-tyrosine and 3,5-dichloro-l-tyrosine) were detected in plasma and lung tissue after Cl2 exposure. In this study, we developed a translational swine model that recapitulates key features of human Cl2 inhalation injury and is suitable for testing medical countermeasures, and validated chlorinated fatty acids and protein adducts as biomarkers of Cl2 inhalation.NEW & NOTEWORTHY We established a swine model of chlorine gas-induced acute lung injury that exhibits several features of human acute lung injury and is suitable for screening potential medical countermeasures. We validated chlorinated fatty acids and protein adducts in plasma and lung samples as forensic biomarkers of chlorine inhalation.

Toxic effects of chlorine gas and potential treatments: a literature review

Chlorine gas is one of the highly produced chemicals in the USA and around the world. Chlorine gas has several uses in water purification, sanitation, and industrial applications; however, it is a toxic inhalation hazard agent. Inhalation of chlorine gas, based on the concentration and duration of the exposure, causes a spectrum of symptoms, including but not limited to lacrimation, rhinorrhea, bronchospasm, cough, dyspnea, acute lung injury, death, and survivors develop signs of pulmonary fibrosis and reactive airway disease. Despite the use of chlorine gas as a chemical warfare agent since World War I and its known potential as an industrial hazard, there is no specific antidote. The resurgence of the use of chlorine gas as a chemical warfare agent in recent years has brought speculation of its use as weapons of mass destruction. Therefore, developing antidotes for chlorine gas-induced lung injuries remains the need of the hour. While some of the pre-clinical studies have made substantial progress in the understanding of chlorine gas-induced pulmonary pathophysiology and identifying potential medical countermeasure(s), yet none of the drug candidates are approved by the U.S. Food and Drug Administration (FDA). In this review, we summarized pathophysiology of chlorine gas-induced pulmonary injuries, pre-clinical animal models, development of a pipeline of potential medical countermeasures under FDA animal rule, and future directions for the development of antidotes for chlorine gas-induced lung injuries.

Inhalation Injury and Toxic Industrial Chemical Exposure

Toxic industrial chemicals include chlorine, phosgene, hydrogen sulfide, and ammonia have variable effects on the respiratory tract, and maybe seen alone or in combination, secondary to inhalation injury. Other considerations include the effects of cyanide, carbon monoxide, and fire suppressants. This Clinical Practice Guideline (CPG) will provide the reader with a brief overview of these important topics and general management strategies for each as well as for inhalation injury. Chlorine, phosgene, hydrogen sulfide, and ammonia are either of intermediate or high water solubility leading to immediate reactions with mucous membranes of the face, throat, and lungs and rapid symptoms onset after exposure. The exception to rapid symptom onset is phosgene which may take up to a day to develop severe acute respiratory distress syndrome. Management of these patients includes early airway management, lung-protective ventilator strategies, aggressive pulmonary toilet, and avoidance of volume overload.

Sarcoendoplasmic reticulum Ca(2+) ATPase. A critical target in chlorine inhalation-induced cardiotoxicity

Autopsy specimens from human victims or experimental animals that die due to acute chlorine gas exposure present features of cardiovascular pathology. We demonstrate acute chlorine inhalation-induced reduction in heart rate and oxygen saturation in rats. Chlorine inhalation elevated chlorine reactants, such as chlorotyrosine and chloramine, in blood plasma. Using heart tissue and primary cardiomyocytes, we demonstrated that acute high-concentration chlorine exposure in vivo (500 ppm for 30 min) caused decreased total ATP content and loss of sarcoendoplasmic reticulum calcium ATPase (SERCA) activity. Loss of SERCA activity was attributed to chlorination of tyrosine residues and oxidation of an important cysteine residue, cysteine-674, in SERCA, as demonstrated by immunoblots and mass spectrometry. Using cardiomyocytes, we found that chlorine-induced cell death and damage to SERCA could be decreased by thiocyanate, an important biological antioxidant, and by genetic SERCA2 overexpression. We also investigated a U.S. Food and Drug Administration-approved drug, ranolazine, used in treatment of cardiac diseases, and previously shown to stabilize SERCA in animal models of ischemia-reperfusion. Pretreatment with ranolazine or istaroxime, another SERCA activator, prevented chlorine-induced cardiomyocyte death. Further investigation of responsible mechanisms showed that ranolazine- and istaroxime-treated cells preserved mitochondrial membrane potential and ATP after chlorine exposure. Thus, these studies demonstrate a novel critical target for chlorine in the heart and identify potentially useful therapies to mitigate toxicity of acute chlorine exposure.

Inhaled matters of the heart

Inhalations of atmospheric pollutants, especially particulate matters, are known to cause severe cardiac effects and to exacerbate preexisting heart disease. Heart failure is an important sequellae of gaseous inhalation such as that of carbon monoxide. Similarly, other gases such as sulphur dioxide are known to cause detrimental cardiovascular events. However, mechanisms of these cardiac toxicities are so far unknown. Increased susceptibility of the heart to oxidative stress may play a role. Low levels of antioxidants in the heart as compared to other organs and high levels of reactive oxygen species produced due to the high energetic demand and metabolic rate in cardiac muscle are important in rendering this susceptibility. Acute inhalation of high concentrations of halogen gases is often fatal. Severe respiratory injury and distress occurs upon inhalation of halogens gases, such as chlorine and bromine; however, studies on their cardiac effects are scant. We have demonstrated that inhalation of high concentrations of halogen gases cause significant cardiac injury, dysfunction, and failure that can be critical in causing mortalities following exposures. Our studies also demonstrated that cardiac dysfunction occurs as a result of a direct insult independent of coexisting hypoxia, since it is not fully reversed by oxygen supplementation. Therefore, studies on offsite organ effects of inhaled toxic gases can impact development of treatment strategies upon accidental or deliberate exposures to these agents. Here we summarize the knowledge of cardiovascular effects of common inhaled toxic gases with the intent to highlight the importance of consideration of cardiac symptoms while treating the victims.

Chlorine inhalation-induced myocardial depression and failure

Victims of chlorine (Cl2) inhalation that die demonstrate significant cardiac pathology. However, a gap exists in the understanding of Cl2-induced cardiac dysfunction. This study was performed to characterize cardiac dysfunction occurring after Cl2 exposure in rats at concentrations mimicking accidental human exposures (in the range of 500 or 600 ppm for 30 min). Inhalation of 500 ppm Cl2 for 30 min resulted in increased lactate in the coronary sinus of the rats suggesting an increase in anaerobic metabolism by the heart. There was also an attenuation of myocardial contractile force in an ex vivo (Langendorff technique) retrograde perfused heart preparation. After 20 h of return to room air, Cl2 exposure at 500 ppm was associated with a reduction in systolic and diastolic blood pressure as well echocardiographic/Doppler evidence of significant left ventricular systolic and diastolic dysfunction. Cl2 exposure at 600 ppm (30 min) was associated with biventricular failure (observed at 2 h after exposure) and death. Cardiac mechanical dysfunction persisted despite increasing the inspired oxygen fraction concentration in Cl2-exposed rats (500 ppm) to ameliorate hypoxia that occurs after Cl2 inhalation. Similarly ex vivo cardiac mechanical dysfunction was reproduced by sole exposure to chloramine (a potential circulating Cl2 reactant product). These results suggest an independent and distinctive role of Cl2 (and its reactants) in inducing cardiac toxicity and potentially contributing to mortality.

Multiple small bowel ligation compared to conventional primary repair after abdominal gunshot wound with haemorrhagic shock

AIMS

The aim of this study was to evaluate the effects of early rapid control of multiple bowel perforations on cardiovascular function in combined abdominal missile trauma and haemorrhagic shock compared with conventional surgery.

METHODS

Eighteen anesthetised pigs were injured with a standardised abdominal missile trauma. The animals were bled to a mean arterial pressure of 50 mm Hg for 30 minutes, after which they were resuscitated and had laparotomy. They were divided into conventional surgery group (n=9) with primary resection and anastomosis of bowel -injuries and early rapid multiple bowel ligation group (n?=?9). Repeated measurement analysis of variance was used for analysis.

RESULTS

There was profound hypotension, reduced cardiac output, increased vascular resistance and lactic acidaemia in both groups. Lactic acidaemia persisted longer in the early rapid multiple bowel ligation group. There were no significant differences in mean arterial pressure, cardiac output , stroke volume or systemic vascular resistance between the groups. The mean operation time was significantly shorter in the early rapid multiple bowel ligation group (13.3 (1.5) (SEM) minutes, compared with 116.4 (1.74) (SEM) minutes in the conventional surgery group, p =0.001).

CONCLUSIONS

Damage control principles have shortened the operating time in our model but did not improve the cardiovascular function and caused more lactic acidaemia than conventional repair.

Oxygenation and cerebral perfusion pressure improved in the prone position

BACKGROUND

Treatment of patients in the prone position is a well-established method to improve oxygenation in general intensive care unit (ICU) practice. This method is rarely used in a neurosurgical ICU, considering the risk of intracranial hypertension. The aim of this study was to analyse the effect of prone position on intracranial pressure (ICP), cerebral perfusion pressure (CPP) and systemic oxygenation in patients with reduced intracranial compliance. We hypothesize that the beneficial effects of prone position can outweigh the hazardous effects on the intracranial pressure.

METHODS

Eight patients with traumatic brain injury or subarachnoid hemorrhage (SAH) were studied in the supine and prone posture. Hemodynamics, arterial oxygenation, respiratory mechanics, ICP and CPP were continuously measured.

RESULTS

A significant improvement in PaO(2) was observed in the prone position, from 12.6 +/- 1.4 kPa to 15.7 +/- 3.2 kPa (P= 0.02). Both intracranial pressure and mean arterial pressure increased in the prone position, from 12 +/- 6 to 15 +/- 4 mmHg (P= 0.03) and from 78 +/- 8 to 88 +/- 8 mmHg (P= 0.005), respectively. Arterial pressure increased to a greater extent than ICP, resulting in improved CPP, from 66 +/- 7 to 73 +/- 8 mmHg (P= 0.03) in the prone position.

CONCLUSIONS

The prone position can be used to improve the oxygenation as well as CPP in patients with traumatic brain injury or SAH. However, this method results in raised ICP, and should be used cautiously in patients with reduced intracranial compliance.

The effects of early rapid control of multiple bowel perforations after high-energy trauma to the abdomen: implications for damage control surgery

BACKGROUND

This study evaluates the effects of early rapid control of multiple bowel perforations on cardiovascular and pulmonary function in high-energy traumatic shock compared with conventional small bowel resection anastomosis.

METHODS

Fifteen anesthetized pigs, 10 to 12 weeks old, were exposed to a reproducible high-energy trauma and were divided into two groups. In the first group, the resection anastomosis group (RA, n = 8), small-bowel injuries were treated with resection and anastomosis; in the second group, the multiple bowel ligation group (BL, n = 7), small-bowel injuries were treated by resection and ligation. Repeated measurement analysis of variance was used to study the within group change overtime, the between group difference, and the interaction between them. Mean outcome measures were intravascular pressures, cardiac output, vascular resistance, lactic acid, and blood gases.

RESULTS

The high-energy injuries caused traumatic shock in both groups with reduced cardiac output (p < 0.001) and lactic acidemia (p < 0.001). The BL group had a trend for higher cardiac output (p = 0.06). The rise in systemic and pulmonary vascular resistance was significantly reduced in the BL group compared with the RA group (p < 0.05). The BL group had a strong trend for higher oxygen extraction ratio (p = 0.06). There was a trend for less oxygen consumption in the BL group (p = 0.07). There was no difference in the lactic acidemia between the two groups.

CONCLUSIONS

Early rapid control of multiple bowel perforations after high-energy trauma resulted in less impairment of cardiovascular function than conventional resection anastomosis of the bowel.

Inhaled and intravenous corticosteroids both attenuate chlorine gas-induced lung injury in pigs

BACKGROUND

The accidental release of chlorine gas is a constant threat in urban areas. The purpose of this randomized, blinded, controlled experiment was to examine the effects of post-injury administration of inhaled or intravenous corticosteroid in chlorine gas-injured pigs followed for 23 h.

METHODS

Anaesthetized, ventilated pigs (n = 24) in the prone position were exposed to chlorine gas (400 parts per million in air) (1160 mg/m3) for 15 min, then randomly allocated to receive inhaled budesonide (BUD) and intravenous placebo, intravenous betamethasone (BETA) and inhaled placebo or inhaled and intravenous placebo. Haemodynamics, gas exchange and lung mechanics were evaluated for 23 h after exposure to chlorine gas.

RESULTS

Airway and pulmonary artery pressures increased and arterial oxygenation fell sharply (from 13.5 +/- 0.8 to 6.7 +/- 0.9 kPa, P < 0.001) after chlorine gas exposure. These immediate changes were followed by a gradual improvement over 5-7 h to a stable level of dysfunction for the rest of the experiment in placebo animals. Arterial oxygen tension, pulmonary vascular resistance and airway pressure recovered faster and more completely in the budesonide and betamethasone groups than in the placebo group (P < 0.01). Lung wet weight to dry weight ratios were greater in the placebo group than in the budesonide and betamethasone groups (6.34 +/- 0.59 vs. 5.56 +/- 0.38 and 5.53 +/- 0.54, respectively, P < 0.05). There was a trend towards lower histological injury scores compared with placebo in animals that received budesonide (P = 0.05) or betamethasone (P = 0.07).

CONCLUSION

Treatment of chlorine gas lung injury with nebulized budesonide or intravenous betamethasone had similar positive effects on recovery of lung function.

Administration of Aerosolized Terbutaline and Budesonide Reduces Chlorine Gas–Induced Acute Lung Injury

BACKGROUND

The pathophysiology and treatment of chlorine gas-induced acute lung injury is poorly characterized and based on anecdotal data. This study aimed to assess the effects of aerosolized beta-2 adrenergic agonist and corticosteroid therapy on chlorine gas-induced lung injury.

METHODS

Anesthetized, ventilated pigs were exposed to chlorine gas (400 parts per million for 20 minutes), then assigned randomly 30 minutes later to receive aerosolized terbutaline, budesonide, terbutaline followed by budesonide or placebo (6 pigs in each group). Hemodynamics, gas exchange, and lung mechanics were evaluated for another 5 hours.

RESULTS

All the animals demonstrated an immediate increase in airway and pulmonary artery pressure as well as sharp drops in arterial oxygen tension (PaO2) and lung compliance (CL). Recovery of PaO2 and CL was greatest in the terbutaline plus budesonide group, but therapy with terbutaline and budesonide alone also was associated with significant improvement in PaO2 and CL, as compared with placebo.

CONCLUSIONS

Treatment of acute chlorine gas lung injury with aerosolized terbutaline followed by aerosolized budesonide improved lung function. Combined treatment was more effective than treatment with either drug alone.