Smoke inhalation is a multilevel insult to the pulmonary system

Inflammatory role of AMP-activated protein kinase signaling in an experimental model of toxic smoke inhalation injury

OBJECTIVE

The molecular mechanisms underlying lung inflammation in toxic smoke inhalation injury are unknown. We investigated the signaling pathway responsible for the induction of interleukin 8 by wood smoke extract in lung epithelial cells and lung inflammation induced by wood smoke exposure in mice.

DESIGN

A randomized, controlled study.

SETTING

A research laboratory.

INTERVENTIONS AND MAIN RESULTS

Exposure of primary human bronchial epithelial cells to wood smoke extract sequentially activated NADPH oxidase and increased intracellular reactive oxygen species level; activated AMP-activated protein kinase, extracellular signal-regulated kinase and Jun N-terminal kinase (two mitogen-activated protein kinases), and nuclear factor-κB and signal transducer and activator of transcription protein 3 (two transcription factors); and induced interleukin-8. Inhibition of NADPH oxidase activation with apocynin or siRNA targeting p47(phox ) (a subunit of NADPH oxidase) attenuated the increased intracellular reactive oxygen species level, AMP-activated protein kinase activation, and interleukin-8 induction. Removal of intracellular reactive oxygen species by N-acetyl-cysteine reduced the activation of AMP-activated protein kinase, extracellular signal-regulated kinase and Jun N-terminal kinase, and interleukin-8 induction. Prevention of AMP-activated protein kinase activation by Compound C or AMP-activated protein kinase siRNA lessened the activation of Jun N-terminal kinase, extracellular signal-regulated kinase, nuclear factor-κB, signal transducer and activator of transcription protein 3 and interleukin-8 induction. Inhibition of Jun N-terminal kinase and extracellular signal-regulated kinase activation by inhibitors reduced the activation of nuclear factor-κB and signal transducer and activator of transcription protein 3 and interleukin-8 induction. Abrogation of nuclear factor-κB and signal transducer and activator of transcription protein 3 activation by inhibitors attenuated the interleukin-8 induction. Additionally, acute exposure of mice to wood smoke promoted AMP-activated protein kinase phosphorylation and expression of macrophage inflammatory protein 2 (an interleukin-8 homolog) in lung epithelial cells and lungs and lung inflammation, all of which were reduced by Compound C treatment.

CONCLUSIONS

Interleukin-8 induction by wood smoke extract in lung epithelial cells is mediated by novel NADPH oxidase-dependent, reactive oxygen species-sensitive AMP-activated protein kinase signaling with Jun N-terminal kinase and extracellular signal-regulated kinase as the downstream kinases and nuclear factor-κB and signal transducer and activator of transcription protein 3 as the downstream transcription factors. This AMP-activated protein kinase signaling is likely important for inducing lung inflammation with toxic smoke exposure in mice.

Gas distribution in a two-compartment model ventilated in high-frequency percussive and pressure-controlled modes

PURPOSE

To demonstrate in a two-compartment heterogeneous mechanical model of the lung how different loads applied to one compartment, while the other is kept constant, would modify gas distribution between the two pathways under high-frequency percussive ventilation (HFPV). Additionally, these results were compared with those generated in the same model by pressure-controlled ventilation (PCV).

METHODS

Analysis was based on a Siemens lung simulator, representing a fixed branch of the system with an elastance equal to 45 cmH(2)O/L and a resistance of 20 cmH(2)O/L/s, and a single-compartment lung simulator, representing a variable pathway of the model, presenting three elastic loads varying between 35 and 85 cmH(2)O/L and three resistive loads varying between 5 and 50 cmH(2)O/L/s. Each simulator represented one compartment of the model connected to a central airway that was ventilated with either a volumetric diffusive respirator (VDR-4; Percussionaire Corporation, Sandpoint, ID, USA) or a Siemens Servo 900c ventilator. Flow and pressures were measured in each branch of the model under nine conditions representing the combinations of three elastic and three resistive loads (variable branch) while the loads in the other pathway were kept constant.

RESULTS

HFPV was able to avoid hyperinflation and reduce tidal volume in a bicompartmental heterogeneous lung model. Under HFPV, gas distribution between the two compartments was not constrained by their time constants. PCV yielded gas distribution as determined by the time constant of each compartment.

CONCLUSIONS

HFPV accommodated volume distribution without overinflating compartments with low time constants, thus possibly presenting a potential protective behavior in mechanically heterogeneous lungs.

Inhalation burn injury in children

With advances in burn care, many children are surviving severe burn injuries. Inhalation injury remains a predictor of morbidity and mortality in burn injury. Inhalation of smoke and toxic gases leads to pulmonary complications, including airway obstruction from bronchial casts, pulmonary edema, decreased pulmonary compliance, and ventilation-perfusion mismatch, as well as systemic toxicity from carbon monoxide poisoning and cyanide toxicity. The diagnosis of inhalation injury is suggested by the history and physical exam and can be confirmed by bronchoscopy. Management consists of supportive measures, pulmonary toilet, treatment of pulmonary infection and ventilatory support as needed. This review details the pathophysiology, diagnosis, and management options for inhalation injury.

High-frequency percussive ventilation improves perioperatively clinical evolution in pulmonary resection

OBJECTIVE

During thoracotomy, positive end-expiratory pressure is applied to the dependent lung and continuous positive airway pressure (CPAP) inflates the nondependent lung to avoid hypoxemia. These methods do not allow the removal of produced secretions. We hypothesized that high-frequency percussive ventilation(HFPV) can improve both conditions and reduce hospital length of stay in these patients.

DESIGN

Randomized prospective study.

SETTING

University Hospital.

PATIENTS

Fifty-three consecutive patients undergoing elective pulmonary partial resection were enrolled. Nine were excluded because of surgical reasons.

INTERVENTIONS

The nondependent lung was ventilated with HFPV in 22 patients and other 22 received CPAP. In both groups,the dependent lung was ventilated with continuous mechanical ventilation.

MEASUREMENT AND MAIN RESULTS

Cardiocirculatory variables and blood gas analysis were measured during surgery. Postoperatively,all patients underwent chest physiotherapy, and SpO2,body temperature, the amount of sputum produced, and chest radiography were recorded. Before nondependent lung re-expansion,HFPV patients presented higher PaO2 than CPAP group (p = 0.020). The amount of secretions was higher in chronic obstructive pulmonary disease patients treated with HFPV than in those who received CPAP (199 and 64 mL, respectively, p = 0.028). HFPV increased by 5.28 times the chance of sputum production by chronic obstructive pulmonary disease patients (chi(2) = 46.66, p < 0.0001; odds ratio = 5.28). A patient treated with HFPV had a 3.14-fold larger chance of being discharged earlier than a CPAP-treated subject (likelihood ratio = 11.5, p = 0.0007).

CONCLUSIONS

Under the present settings, HFPV improved oxygenation in one-lung ventilation during pulmonary resection. Postoperatively, it decreased the length of stay and increased the removal of secretions in comparison with CPAP.

Pneumonia After Inhalation Injury

We sought to evaluate the incidence, morbidity, and mortality of pneumonia among inhalation injury patients requiring admission to our burn unit. We undertook a retrospective study of 228 consecutive patients with inhalation injury who were admitted to the burn unit of a level one trauma center between 2001 and 2004. Of the remaining 117 patients with inhalation injury and requiring hospitalization for at least 48 hours, 32 (27%) developed pneumonia. The average patient with inhalation injury and pneumonia developed their infiltrate on day 6 +/- 5 days and required 3 +/- 4 burn operations. There was no difference seen in age, sex, or carboxyhemoglobin level between inhalation injury patients with and without pneumonia (P > .05). The inhalation injury patients that had an associated TBSA burn of at least 20% had a 60% (12/20) pneumonia rate, which was significantly higher then the 21% (20/97) pneumonia rate observed in patients with an association burn less then 20%. The overall mortality of patients with inhalation injury and pneumonia was 19% (6/32), double the mortality rate of 9% (8/85) found in patients with inhalation injury and no pneumonia. The average length of stay of inhalation injury patients with pneumonia was significantly longer (47 +/- 44 days) then inhalation injury patients without pneumonia (26 +/- 54 days; P < .05). The presence of pneumonia among inhalation injury patients significantly increased length of stay and doubled mortality rates. Admission carboxyhemoglobin levels, age, and sex had no relationship to the development of pneumonia. An increase in TBSA burn was associated with a higher pneumonia rate.

Wood smoke extract induces oxidative stress-mediated caspase-independent apoptosis in human lung endothelial cells: role of AIF and EndoG

Although a link between toxic smoke and oxidant lung vascular injury has been indicated, the cellular mechanisms of smoke-induced injury to lung endothelial cells are unknown. We investigated oxidative stress and apoptosis induced by wood smoke extract (SE) in human pulmonary artery endothelial cells (HPAECs) and delineated their relationship. We found that SE increased intracellular reactive oxygen species (ROS), depleted intracellular glutathione, and upregulated Cu/Zn superoxide dismutase and heme oxygenase-1 (2 antioxidant enzymes), but it failed to alter the expression of catalase and glutathione peroxidase. In addition, SE promoted apoptosis as indicated by the external exposure of membrane phosphatidylserine, the loss of mitochondrial membrane potential, an increase in the level of Bax (a proapoptotic protein), and enhanced DNA fragmentation. This apoptosis was associated with mitochondrial-to-nuclear translocation of apoptosis-inducing factor (AIF) and endonuclease G (EndoG) (2 apoptogenic proteins) but was independent of caspase cascade activation. Whereas N-acetylcysteine (an antioxidant) effectively reversed the SE-induced increase in ROS and depletion of glutathione, it also suppressed SE-induced nuclear translocation of either AIF or EndoG and prevented the enhanced DNA fragmentation that would have resulted from this. We conclude that 1) although SE upregulates Cu/Zn superoxide dismutase and heme oxygenase-1, it nevertheless increases intracellular oxidative stress in HPAECs, and 2) SE promotes oxidative stress-mediated caspase-independent HPAEC apoptosis that involves mitochondrial-to-nuclear translocation of AIF and EndoG. Thus modulations of the expression of antioxidant enzymes and the caspase-independent apoptotic pathway are possible target choices for potential therapeutic regimes to treat smoke-induced lung injury.

High frequency percussive ventilation and conventional ventilation after smoke inhalation: a randomised study

Inhalation injury and bacterial pneumonia represent some of the most important causes of mortality in burn patients. Thirty-five severely burned patients were randomised on admission for conventional ventilation (CV; control group) versus high frequency percussive ventilation (HFPV; study group). HFPV is a ventilatory mode, introduced 10 years ago which combines the advantages of CV with some of those of high frequency ventilation. Arterial blood gases, ventilatory and hemodynamic variables were recorded for 5 days at 2h intervals. Incident complications were classically managed. A statistical analysis (Student's t-test and Wilcoxon signed rank test) demonstrated a significant higher PaO(2)/FiO(2) from days 0 to 3 in the HFPV group. No significant differences were observed for the other parameters. Our findings suggest that HFPV can improve blood oxygenation during the acute phase following inhalation injury allowing reduction of FiO(2). No significant differences were observed between groups for mortality nor incidence of infectious complications in this study.

A murine model of smoke inhalation

The United States has one of the world's largest per capita fire death rates. House fires alone kill >9,000 Americans annually, and smoke inhalation is the leading cause of mortality from structural fires. Animal models are needed to develop therapies to combat this problem. We have developed a murine model of smoke inhalation through the design, construction, and use of a controlled-environment smoke chamber. There is a direct relationship between the quantity of wood combusted and mortality in mice. As with human victims, the primary cause of death from smoke inhalation is an elevated blood carboxyhemoglobin level. Lethal (78%) and sublethal (50%) carboxyhemoglobin levels were obtained in mice subjected to varying amounts of smoke. Mice exposed to wood smoke demonstrated more dramatic pathology than mice exposed to cotton or polyurethane smoke. A CD-1 model of wood smoke exposure was developed, demonstrating type II cell hypertrophy, cytoplasmic blebbing, cytoplasmic vacuolization, sloughing, hemorrhage, edema, macrophage infiltration, and lymphocyte infiltration. The bronchoalveolar lavage fluid of smoke-exposed mice demonstrated a significant increase in total cell counts compared with those in control mice. These findings are comparable to the lung tissue response observed in human victims of smoke inhalation.

Recovery from blast lung injury: one-year follow-up

BACKGROUND

Blast injury to the lung is one of the devastating threats facing victims of an explosion. Although the pathogenesis of blast injury has been studied, little is known about the long-term effects on lung function in survivors.

OBJECTIVE

To examine the pulmonary function of survivors 1 year after sustaining a blast injury.

DESIGN

Prospective study.

SETTING

Pulmonary function test laboratory at Hadassah Medical Center, Jerusalem.

PARTICIPANTS

Eleven surviving victims of a blast injury sustained during a bus terrorist explosion.

MEASUREMENTS

Twelve months after the injury, physical examinations, lung function tests, and progressive cardiopulmonary exercise examinations were conducted, and chest radiographs were obtained.

RESULTS

The average age was 28 +/- 9.8 years. Most of the victims had multiple injuries in addition to the lung injury. Ten patients received mechanical ventilation, and 6 patients required chest drainage. All patients were treated in the ICU, with an average stay of 11.8 +/- 9 days. The patients were discharged to their homes or to a rehabilitation center 32.4 +/- 27. 3 days after the explosion. One year later, none had any pulmonary-related complaints. Physical examination of the lungs was normal. Most of the patients demonstrated normal lung function tests and complete resolution of the chest radiograph findings.

CONCLUSION

Most patients who survive lung blast injury will regain good lung function within a year.