The effect of smoke inhalation on pulmonary surfactant

Inhalation Injury, Respiratory Failure, and Ventilator Support in Acute Burn Care

Sustaining an inhalation injury increases the risk of severe complications and mortality. Current evidential support to guide treatment of the injury or subsequent complications is lacking, as studies either exclude inhalation injury or design limit inferences that can be made. Conventional ventilator modes are most commonly used, but there is no consensus on optimal strategies. Settings should be customized to patient tolerance and response. Data for pharmacotherapy adjunctive treatments are limited.

Exercise in bushfire smoke for high performance athletes: A Position Statement from the Australian Institute of SportEndorsed by Australasian College of Sport and Exercise Physicians (ACSEP) and Sport Medicine Australia (SMA)

OBJECTIVES

The frequency of bushfires in Australia is increasing and it is expected bushfire smoke will become a more prevalent phenomenon impacting air quality. The objective of this position statement is to provide guidance to the sport sector regarding exercise in air affected by bushfire smoke.

DESIGN

This is position statement from the Australian Institute of Sport, based on a narrative review of the literature regarding bushfire smoke and its effects on health and exercise performance.

METHODS

A narrative review of scientific publications regarding the effects of bushfire smoke on health and exercise performance.

RESULTS

Bushfire smoke has negative impacts on health and performance. Athletes exercising at high intensity over a prolonged duration will increase their exposure to air pollutants. Athletes with a history of elevated airway responsiveness are likely to be at increased risk of an adverse response to bushfire smoke exposure.

CONCLUSIONS

Athletes, coaches, support staff and sport organisations should monitor air quality (PM2.5 concentration) and make appropriate adjustments to training duration and intensity.

Current concepts in the pathophysiology and treatment of inhalation injury

The opinions or assertions contained herein are the private views of the author, and are not to be construed as official or as reflecting the official views of the Department of the Army or Department of Defense. Smoke inhalation injury occurs in about 10% of patients admitted to burn centres, and increases the mortality of burn patients by up to 20% over predictions based on age and burn size alone. The primary lesion in smoke inhalation injury is localized to the small airways, with alveolar injury and pulmonary oedema exercising a less prominent role during the initial phases. Injury incites a cascade of events that include ventilation-perfusion mismatch, secondary lung injury, systemic inflammation, impaired immune function, and pneumonia. The most important recent developments in the treatment of inhalation injury have included improved methods of pulmonary care targeted at the pathophysiology of the injury, such as high-frequency percussive ventilation and gentle mechanical ventilation.

Respiratory Effects of Short-Term, High-Intensity Toxic Inhalations: Smoke, Gases, and Fumes

Respiratory insufficiency resulting from inhalation of hot air, smoke, or toxic gas is a common cause of death in fire victims. Toxic gas inhalation in settings other than fires is a less common but still important cause of death and disability. Pulmonary inhalation injury and systemic intoxication from exposure to a variety of agents are discussed with regard to their pathogenesis, pathophysi ology, diagnosis, and treatment. Upper airway obstruc tion and noncardiogenic pulmonary edema are the life- threatening respiratory complications in the immediate postinhalation period. Carbon monoxide and hydrogen cyanide intoxication are frequently associated with in halation injury in fire victims. Early recognition and treatment of inhalation injury and systemic intoxication in victims of fires and industrial and environmental acci dents could well result in improved survival.

Face and/or neck burns: a risk factor for respiratory infection?

Infections are a common cause of morbidity and mortality in burn patients, and almost 50% of infection-related deaths in burn patients are caused by pneumonia. The proportion of facial and/or neck burns (FNB) in burn centre admissions is high, and these patients have a well known respiratory risk. However, it is not well established in the literature if the occurrence of a FNB is a risk factor for respiratory infection during hospitalization. A retrospective, single-centre trial at the burn unit of the Prelada Hospital was conducted, including patients admitted between January 2011 and December 2014. The primary objective was to investigate the existence of a relation between face and/or neck burns and occurrence of respiratory infection. A total of 229 patients were included in the study, 126 with FNB and 103 without FNB. Higher total body surface area (TBSA) burned, inhalation injury and early endotracheal intubation were statistically more frequent in the FNB group. These variables were also more prevalent in the group that developed respiratory infection during the burn unit stay. Concerning FNB patients, the most frequent microbiological strains isolated in respiratory secretion cultures were Staphylococcus aureus, Pseudomonas aeruginosa and Streptococcus pneumonia, while in nFNB patients it was Klebsiella pneumoniae. In our population, only early ETI, inhalation injury and higher TBSA appear to be independent risk factors for respiratory infection in FNB patients, although age, male sex and co-morbidities are also known risk factors for respiratory infection in burn patients.

Acute Lung Injury Causes Asynchronous Alveolar Ventilation That Can Be Corrected by Individual Sighs

RATIONALE

Improved ventilation strategies have been the mainstay for reducing mortality in acute respiratory distress syndrome. Their unique clinical effectiveness is, however, unmatched by our understanding of the underlying mechanobiology, and their impact on alveolar dynamics and gas exchange remains largely speculative.

OBJECTIVES

To assess changes in alveolar dynamics and associated effects on local gas exchange in experimental models of acute lung injury (ALI) and their responsiveness to sighs.

METHODS

Alveolar dynamics and local gas exchange were studied in vivo by darkfield microscopy and multispectral oximetry in experimental murine models of ALI induced by hydrochloric acid, Tween instillation, or in antibody-mediated transfusion-related ALI.

MEASUREMENTS AND MAIN RESULTS

Independent of injury mode, ALI resulted in asynchronous alveolar ventilation characteristic of alveolar pendelluft, which either spontaneously resolved or progressed to a complete cessation or even inversion of alveolar ventilation. The functional relevance of the latter phenomena was evident as impaired blood oxygenation in juxtaposed lung capillaries. Individual sighs (2 × 10 s at inspiratory plateau pressure of 30 cm H2O) largely restored normal alveolar dynamics and gas exchange in acid-induced ALI, yet not in Tween-induced surfactant depletion.

CONCLUSIONS

We describe for the first time in detail the different forms and temporal sequence of impaired alveolar dynamics in the acutely injured lung and report the first direct visualization of alveolar pendelluft. Moreover, we identify individual sighs as an effective strategy to restore intact alveolar ventilation by a mechanism independent of alveolar collapse and reopening.

Diagnosis and management of inhalation injury: an updated review

In this article we review recent advances made in the pathophysiology, diagnosis, and treatment of inhalation injury. Historically, the diagnosis of inhalation injury has relied on nonspecific clinical exam findings and bronchoscopic evidence. The development of a grading system and the use of modalities such as chest computed tomography may allow for a more nuanced evaluation of inhalation injury and enhanced ability to prognosticate. Supportive respiratory care remains essential in managing inhalation injury. Adjuncts still lacking definitive evidence of efficacy include bronchodilators, mucolytic agents, inhaled anticoagulants, nonconventional ventilator modes, prone positioning, and extracorporeal membrane oxygenation. Recent research focusing on molecular mechanisms involved in inhalation injury has increased the number of potential therapies.

Assessing inhalation injury in the emergency room

Respiratory tract injuries caused by inhalation of smoke or chemical products are related to significant morbidity and mortality. While many strategies have been built up to manage cutaneous burn injuries, few logical diagnostic strategies for patients with inhalation injuries exist and almost all treatment is supportive. The goals of initial management are to ensure that the airway allows adequate oxygenation and ventilation and to avoid ventilator-induced lung injury and substances that may complicate subsequent care. Intubation should be considered if any of the following signs exist: respiratory distress, stridor, hypoventilation, use of accessory respiratory muscles, blistering or edema of the oropharynx, or deep burns to the face or neck. Any patients suspected to have inhalation injuries should receive a high concentration of supplemental oxygen to quickly reverse hypoxia and to displace carbon monoxide from protein binding sites. Management of carbon monoxide and cyanide exposure in smoke inhalation patients remains controversial. Absolute indications for hyperbaric oxygen therapy do not exist because there is a low correlation between carboxyhemoglobin levels and the severity of the clinical state. A cyanide antidote should be administered when cyanide poisoning is clinically suspected. Although an ideal approach for respiratory support of patients with inhalation injuries do not exist, it is important that they are supported using techniques that do not further exacerbate respiratory failure. A well-organized strategy for patients with inhalation injury is critical to reduce morbidity and mortality.

Indoor fuel exposure and the lung in both developing and developed countries: an update

Almost 3 billion people worldwide burn solid fuels indoors. Despite the large population at risk worldwide, the effect of exposure to indoor solid fuel smoke has not been adequately studied. Indoor air pollution from solid fuel use is strongly associated with chronic obstructive pulmonary disease, acute respiratory tract infections, and lung cancer, and weakly associated with asthma, tuberculosis, and interstitial lung disease. Tobacco use further potentiates the development of respiratory disease among subjects exposed to solid fuel smoke. There is a need to perform additional interventional studies in this field.

Update on the critical care management of severe burns

Care of the severely injured patient with burn requires correct diagnosis, appropriately tailored resuscitation, and definitive surgical management to reduce morbidity and mortality. Currently, mortality rates related to severe burn injuries continue to steadily decline due to the standardization of a multidisciplinary approach instituted at tertiary health care centers. Prompt and accurate diagnoses of burn wounds utilizing Lund-Browder diagrams allow for appropriate operative and nonoperative management. Coupled with diagnostic improvements, advances in resuscitation strategies involving rates, volumes, and fluid types have yielded demonstrable benefits related to all aspects of burn care. More recently, identification of comorbid conditions such as inhalation injury and malnutrition have produced appropriate protocols that aid the healing process in severely injured patients with burn. As more patients survive larger burn injuries, the early diagnosis and successful treatment of secondary and tertiary complications are becoming commonplace. While advances in this area are exciting, much work to elucidate immune pathways, diagnostic tests, and effective treatment regimens still remain. This review will provide an update on the critical care management of severe burns, touching on accurate diagnosis, resuscitation, and acute management of this difficult patient population.

Comparison of airway pressure release ventilation to conventional mechanical ventilation in the early management of smoke inhalation injury in swine

OBJECTIVE

The role of airway pressure release ventilation in the management of early smoke inhalation injury has not been studied. We compared the effects of airway pressure release ventilation and conventional mechanical ventilation on oxygenation in a porcine model of acute respiratory distress syndrome induced by wood smoke inhalation.

DESIGN

Prospective animal study.

SETTING

Government laboratory animal intensive care unit.

PATIENTS

Thirty-three Yorkshire pigs.

INTERVENTIONS

Smoke inhalation injury.

MEASUREMENTS AND MAIN RESULTS

Anesthetized female Yorkshire pigs (n = 33) inhaled room-temperature pine-bark smoke. Before injury, the pigs were randomized to receive conventional mechanical ventilation (n = 15) or airway pressure release ventilation (n = 12) for 48 hrs after smoke inhalation. As acute respiratory distress syndrome developed (PaO2/Fio2 ratio <200), plateau pressures were limited to <35 cm H2O. Six uninjured pigs received conventional mechanical ventilation for 48 hrs and served as time controls. Changes in PaO2/Fio2 ratio, tidal volume, respiratory rate, mean airway pressure, plateau pressure, and hemodynamic variables were recorded. Survival was assessed using Kaplan-Meier analysis. PaO2/Fio2 ratio was lower in airway pressure release ventilation vs. conventional mechanical ventilation pigs at 12, 18, and 24 hrs (p < .05) but not at 48 hrs. Tidal volumes were lower in conventional mechanical ventilation animals between 30 and 48 hrs post injury (p < .05). Respiratory rates were lower in airway pressure release ventilation at 24, 42, and 48 hrs (p < .05). Mean airway pressures were higher in airway pressure release ventilation animals between 6 and 48 hrs (p < .05). There was no difference in plateau pressures, hemodynamic variables, or survival between conventional mechanical ventilation and airway pressure release ventilation pigs.

CONCLUSIONS

In this model of acute respiratory distress syndrome caused by severe smoke inhalation in swine, airway pressure release ventilation-treated animals developed acute respiratory distress syndrome faster than conventional mechanical ventilation-treated animals, showing a lower PaO2/Fio2 ratio at 12, 18, and 24 hrs after injury. At other time points, PaO2/Fio2 ratio was not different between conventional mechanical ventilation and airway pressure release ventilation.

Biomass smoke exposures: toxicology and animal study design

The International Biomass Smoke Health Effects (IBSHE) conference was convened in Missoula, MT, to define our current knowledge of smoke exposure and the potential health effects. In an effort to ascertain the relative health effects of an exposure to biomass smoke, numerous studies have utilized either animal or in vitro systems. A wide variety of systems that have been employed ranged from more mainstream animal models (i.e., rodents) and transformed cell lines to less common animal (piglets and dogs) and explant models. The Toxicology and Animal Study Design Workgroup at IBSHE was tasked with an analysis of the use of animal models in the assessment of the health effects of biomass smoke exposure. The present article contains a mini-review of models utilized historically, in addition to the adverse health effects assessed, and an overview of the discussion within the breakout session. The most common question that arose in discussions at the IBSHE conference was from local and federal health departments: What level of smoke is unhealthy? The present workgroup determined categories of exposure, common health concerns, and the availability of animal models to answer key health questions.

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.

Anesthetic considerations for major burn injury in pediatric patients

Major burn injury remains a significant cause of morbidity and mortality in pediatric patients. With advances in burn care and with the development of experienced multi-disciplinary teams at regionalized burn centers, many children are surviving severe burn injury. As members of the multi-disciplinary care team, anesthesia providers are called upon to care for these critically ill children. These children provide several anesthetic challenges, such as difficult airways, difficult vascular access, fluid and electrolyte imbalances, altered temperature regulation, sepsis, cardiovascular instability, and increased requirements of muscle relaxants and opioids. The anesthesia provider must understand the physiologic derangements that occur with severe burn injury as well as the subsequent anesthetic implications.

Smoke inhalation lung injury: an update

OBJECTIVES

The purpose of this study is to present a multifaceted, definitive review of the past and current status of smoke inhalation injury. History along with current understanding of anatomical, physiology, and biologic components will be discussed.

METHODS

The literature has been reviewed from the early onset of the concept of smoke inhalation in the 1920s to our current understanding as of 2007.

RESULTS

The results indicate that the current pathophysiologic concept is of a disease process that leads to immediate and delayed pulmonary injury best managed by aggressive physiologic support. Management approaches for the biochemical changes have not kept up with current knowledge. The lung injury process is activated by toxins in the smoke's gas and particle components and perpetuated by a resulting lung inflammation. This inflammatory process becomes self-perpetuating through the activation of a large number of inflammatory cascades. In addition, smoke injury leads to significant systemic abnormalities injuring other organs and accentuating the burn injury process and subsequently leading to mediator-induced cellular injury leading potentially to multisystem organ failure.

CONCLUSIONS

Smoke inhalation injury results in the anatomic finding of denuded and sometimes sloughed airways mucosa. Physiologic findings include small airways containing fibrin casts of mucosa and neutrophils. Airway hyper-reactivity results as well, leading to further decreased collapse, causing obstruction.

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.

Respiratory management of inhalation injury

Advances in the care of patients with major burns have led to a reduction in mortality and a change in the cause of their death. Burn shock, which accounted for almost 20 percent of burn deaths in the 1930s and 1940s, is now treated with early, vigorous fluid resuscitation and is only rarely a cause of death. Burn wound sepsis, which emerged as the primary cause of mortality once burn shock decreased in importance, has been brought under control with the use of topical antibiotics and aggressive surgical debridement. Inhalation injury has now become the most frequent cause of death in burn patients. Although mortality from smoke inhalation alone is low (0-11 percent), smoke inhalation in combination with cutaneous burns is fatal in 30 to 90 percent of patients. It has been recently reported that the presence of inhalation injury increases burn mortality by 20 percent and that inhalation injury predisposes to pneumonia. Pneumonia has been shown to independently increase burn mortality by 40 percent, and the combination of inhalation injury and pneumonia leads to a 60 percent increase in deaths. Children and the elderly are especially prone to pneumonia due to a limited physiologic reserve. It is imperative that a well organized, protocol driven approach to respiratory care of inhalation injury be utilized so that improvements can be made and the morbidity and mortality associated with inhalation injury be reduced.

Effect of particle emissions from biofuel combustion on surface activity of model and therapeutic pulmonary surfactants

This study was designed to determine the effects of particle emissions from biofuel combustion in household cooking devices, commonly used in rural India, on surface activity of model lung surfactants using Langmuir monolayers. The effect of wood and dried particles from combustion of cowdung on the surface activity of model lung surfactant dipalmitoylphosphatidylcholine (DPPC), DPPC:PG (phosphatidyl glycerol) 7:3 and the therapeutic surfactant, Exosurf, were evaluated. Dried particles from combustion of cowdung in 50wt.% mixture with DPPC elevated the γ(min) to 15.08±1.28mN/m and 50wt.% particles from combustion of wood increased minimum surface tension γ(min) to 13.46±1.70mN/m from a zero value for DPPC alone. A graded response of inhibitory potential for all three surfactants with increasing doses was found for each type of particles. An increase in the minimum surface tension achieved by surfactants in the presence of biofuel particles implies surfactant dysfunction, a greater tendency of alveolar collapse in vivo on exposure to biofuel emissions and can lead to respiratory distress.

Alterations in regional ventilation, perfusion, and shunt after smoke inhalation measured by PET

Regional changes in ventilation and perfusion occurring in the early hours after smoke inhalation injury were evaluated through the use of positron emission tomography. Five lambs were imaged before and 1, 2, and 4 h after receiving 100 breaths of cotton smoke. Utilizing a recently developed model of (13)N tracer kinetics (3), we evaluated changes in ventilation, perfusion, shunt, and regional gas content in nondependent, middle, and dependent lung zones. The data demonstrated a progressive development of regional shunt in dependent (dorsal) regions in which perfusion remained the highest throughout the study. These findings, together with decreasing regional ventilation and fractional gas content in the dependent regions, correlated with decreasing arterial Pa(O(2)) values over the course of the study. A negative correlation between regional shunt fraction and regional gas content in dependent and middle regions suggests that shunt was caused by progressive alveolar derecruitment or flooding.

Acetylcholine and tachykinin receptor antagonists attenuate wood smoke-induced bronchoconstriction in guinea pigs

To study the mechanisms of wood smoke-induced bronchoconstriction, we measured total lung resistance (RL) and dynamic lung compliance (Cdyn) in anesthetized and mechanically ventilated guinea pigs. Airway exposure to various doses of wood smoke (lauan wood; 5, 10, and 15 breaths) resulted in a dose-dependent increase in RL and decrease in Cdyn. The smoke-induced changes in RL and Cdyn were significantly attenuated by pretreatment with atropine, CP-96,345 [(2S,3S)-cis-2-(diphenylmethyl)-N-((2-methoxyphenyl)-methyl)-1-aza bicyclo(2.2.2.)-octan-3-amine; a tachykinin NK1 receptor antagonist], and SR-48,968 [(S)-N-methyl-N(4-(4-acetylamino-4-phenylpiperidino)-2-(3,4-dichlorophen yl)-butyl)benzamide; a tachykinin NK2 receptor antagonist] in combination, atropine alone, and SR-48,968 alone, but were not significantly affected by pretreatment with the inactive enantiomers of CP-96,345 and SR-48,968, CP-96,345 alone, indomethacin (a cyclooxygenase inhibitor), and MK-571 [((3-(3-(2-(7-chloro-2-quinolinyl)ethenyl)phenyl((3-dimethyl amino-3-oxo-propyl)thio)methyl)propanoic acid; a leukotriene D4 receptor antagonist]. The activity of airway neutral endopeptidase, a major enzyme for tachykinin degradation, was not significantly influenced by wood smoke during the development of bronchoconstriction. We conclude that: (1) both cholinergic mechanisms and endogenous tachykinins, but not cyclooxygenase products or leukotriene D4, play an important role in the acute bronchoconstriction induced by wood smoke, and (2) the contribution of tachykinins to this airway response is primarily mediated via the activation of tachykinin NK2 receptors, but is not associated with inactivation of the airway neutral endopeptidase.

The comparison of early fluid therapy in extensive flame burns between inhalation and noninhalation injuries

Over the last half century, advances in treatment have changed the principal cause of death in burn patients from burn shock and wound sepsis to pulmonary sepsis, of which inhalation injury has always played a key role in morbidity and mortality. Even though Navar et al., Am. J. Surg. 1985;150:716-720 have noted that patients with inhalation injury had a mean fluid requirement of 5.8 ml/kg/% burn to achieve resuscitation from early burn shock, while patients without inhalation injury required only a mean fluid of 4.0 ml/kg/% burn, to achieve successful resuscitation in inhalation injured patients with minimum but adequate fluid has always been a challenge. To further define the difference of early fluid therapy between inhalation and noninhalation in extensively burned patients, a retrospective analysis was carried out in the Tri-Service General Hospital. Sixty-two flame burned patients (aged from 16 to 81 years-old with a mean age of 33.2+/-15.1 years: with burn size ranging from 30% to 98% TBSA with a mean burn size of 60.5+/-22.7%; 26 with inhalation injury; noninhalation 36) were reviewed during a 5-year period. The Parkland formula is the initial choice of fluid regimen with 4 ml/kg/% burn and the amount of replacement is monitored by urine output and is titrated to maintain urine output between 0.5 and 1.0 ml/kg/h. The mean amounts of fluid requirements of both inhalation and noninhalation burned patients were 3.1 +/- 1.0 and 2.3+/-0.8 ml/kg/% burn respectively (p < 0.05). Our study showed less fluid requirement for both inhalation and noninhalation injured patients in comparison with the Navar study and Parkland predictions in the first 24 h postburn. Furthermore, the inhalation injured patients definitely required volumes of fluid in excess of those required in noninhalation injured cases.

Intrabronchial surfactant application in cases of inhalation injury: first results from patients with severe burns and ARDS

Damage to the respiratory tract caused by inhalation of toxic products of combustion with subsequent development of an acute respiratory distress syndrome (ARDS) is one of the main causes of death in burn patients. Treatment with an exogenous surfactant is a therapeutic option for which there has previously been no empirical data. We report on four severely burned patients with deep partial thickness and full thickness burns of between 40 and 70 per cent body surface area (BSA), and with inhalation injury complicated by ARDS. These patients were treated once or more than once with bovine surfactant replacement (Alveofact). In addition to biophysical and biochemical analysis, the influence of this substance on oxygenation and lung function were evaluated. After the limits of mechanical ventilation had been reached, bronchoscopic intrabronchial administration of surfactant was followed by temporarily improved gas exchange with an increase in arterial O2 partial pressure (PaO2), accompanied by a reduction in inspiratory O2 concentration (FiO2), and also improved lung compliance. All the patients survived in spite of an initially unfavourable prognosis. Replacement of exogenous surfactant in the treatment of inhalation traumatized severe burn patients with ARDS appears to show considerable promise as an approach to improving the survival chances of these high-risk patients.

Pulmonary complications in inhalation injuries with associated cutaneous burn

This retrospective study of 100 consecutive patients with inhalation injury documents that adult respiratory distress syndrome (ARDS) and pneumonia are common complications. Pulmonary complications cause or directly contribute to death in 77% of patients with combined inhalation and cutaneous burn injury. Additionally, the high fluid requirements of these patients worsens their pulmonary injury and is associated with adverse outcome. Independent factors predictive of death include ARDS and expected fluid requirements as well as age and percentage of total body surface area burned. An abnormal chest roentgenogram in the first 48 hours after injury is also associated with death. The development of ARDS is predicted by the actual volume of fluid resuscitation, despite normal pulmonary wedge pressure or normal central venous pressure reflecting increased microvascular permeability. These findings indicate a need for reevaluation of fluid resuscitation of patients with inhalation injury.

Segmental pulmonary vascular resistance following wood smoke inhalation

OBJECTIVES

To locate the specific site (i.e., pulmonary arteries, veins, or capillaries) of increased pulmonary vascular resistance after wood smoke inhalation and to demonstrate whether the prostanoids, thromboxane B2 or 6-keto-prostaglandin F1 alpha, play a role in these vascular resistance changes.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Laboratory at a university medical center.

SUBJECTS

Five mongrel dogs.

INTERVENTIONS

The isolated canine left lower lobe preparation was used to measure changes in the pressure drop across the pulmonary arteries, veins, and capillaries. The left lower lobe was surgically isolated and perfused by a pump primed with autologous blood. The arterial and venous occlusion technique and the vascular pressure-flow relationship were used to assess changes in pulmonary vascular resistance. After baseline measurements, the left lower lobe was exposed to wood smoke for 2.5 mins and measurements were repeated.

MEASUREMENTS AND MAIN RESULTS

Smoke exposure caused an immediate (5 mins post-inhalation) increase in the total pressure gradient across the lobe (baseline = 9.8 +/- 0.5 torr [1.3 +/- 0.06 kPa]); smoke inhalation = 24.3 +/- 3.9 torr [3.24 +/- 0.5 kPa]; p < .05). Total pressure drop was partitioned longitudinally into pressure drops across arteries, veins, and the middle vessels. The increase in total pressure drop was associated with a moderate increase in the pressure drop across the middle vessels (baseline = 1.1 +/- 0.2 torr [0.14 +/- 0.02 kPa]; smoke inhalation = 5.2 +/- 1.1 torr [0.69 +/- 0.14 kPa]; p < .05); a large increase in the pressure drop across the veins (baseline = 4.8 +/- 1.3 torr [0.64 +/- 0.17 kPa]; smoke inhalation = 20.7 +/- 3.4 torr [2.7 +/- 0.45 kPa]; p < .05), and no significant change in the pressure drop across the arteries (baseline = 3.7 +/- 0.4 torr [0.49 +/- 0.05 kPa]; smoke inhalation = 4.8 +/- 0.5 torr [0.64 +/- 0.06 kPa]; p = NS). Increases in the pressure drop across the middle and venous vessels were transient and no longer significantly different from baseline 15 mins after smoke inhalation. Similarly, analysis of the pulmonary artery/blood flow data demonstrated that the mean slope and pressure intercept were greater than baseline only at 5 mins postsmoke inhalation (p < .05). Thromboxane B2 did not significantly change from baseline values after smoke exposure and prostaglandin F1 alpha demonstrated a slight but significant decrease 30 mins postsmoke. Pulmonary edema was measured gravimetrically (wet/dry weight ratio) and smoke significantly increased lung water in the left lower lobe (wet/dry weight ratio = 6.55 +/- 0.4) as compared with the normal left upper lobe (wet/dry weight ratio = 4.97 +/- 0.2).

CONCLUSIONS

We conclude that smoke causes an intense but transient increase in the pressure drop across the venous segment that may accelerate the formation of pulmonary edema, which is not mediated by changes in thromboxane B2 or prostaglandin F1 alpha.

Diagnosis and treatment of smoke inhalation

Inhalation remains the most frequent and serious comorbid event that occurs in thermally injured patients. A thorough understanding of the pathophysiology enables individualization of therapy and appropriate triage of patients. We summarize our current knowledge of the pathophysiology, diagnosis, and treatment of inhalation injury, with a focus on newer treatment strategies that are evolving secondary to laboratory research.

Effects of wood and cotton smoke on the surface properties of pulmonary surfactant

The effects of wood and cotton smoke and several known smoke components on the dynamic surface activity of pulmonary surfactant were characterized with a modified Wilhelmy balance. Surfactant was harvested by saline lavage from dog lungs, placed in the balance and a control surface tension/area isotherm (y-A) and surface tension at minimum area (control y/min = 6.6 +/- 1.6 dynes/cm) measured. Hysteresis area (HA), recruitment index (RI), and stability index (SI) were calculated. Following control measurements, smoke (wood or cotton) was gently blown over the surfactant in the balance. Similarly, each of the individual smoke components or Liquid smoke (prepared by bubbling wood smoke through saline) were injected onto the balance. Wood smoke significantly (P < 0.05) altered all surface properties measured, increasing ymin (22.0 +/- 1.6 dynes/cm) and decreasing HA, RI, and SI as compared to control; cotton smoke exposure had almost no effect on surfactant function. A supplementary dose of surfactant was added to the balance, following wood smoke exposure, which decreased ymin (9.4 +/- 2.6 dynes/cm, P = NS vs control) but not the other parameters to control. Acrolein, formaldehyde, and HCl had little effect on any of the surface properties measured whereas isobutyraldehyde and liquid smoke altered the y-A curve but did not increase ymin. These data demonstrate that wood but not cotton smoke inhibit surfactant function, however, surfactant function can be restored, following deactivation by smoke, suggesting that surfactant replacement therapy for victims of severe smoke inhalation may be of benefit.

Comparison of high-frequency jet to conventional mechanical ventilation in the treatment of severe smoke inhalation injury

The pathophysiology of smoke inhalation includes surfactant inhibition and pulmonary vascular injury leading to a high permeability pulmonary oedema. It has been shown in surfactant deficient animal models that methods of ventilation (i.e. high-frequency ventilation - HFV) avoiding a large pressure excursion (i.e. pressure change from end expiration to peak inspiration) improves oxygenation and decreases hyaline membrane formation. Therefore, we compared HFV with conventional mechanical ventilation (CMV) on lung function in an acute animal model of smoke inhalation (SI). Mongrel dogs were anaesthetized, surgically prepared for haemodynamic and blood gas monitoring, and placed on either CMV (n = 6) or HFV (n = 7). Following baseline (BL) measurements both groups were ventilated with wood smoke for 10 min. Ventilator settings were not adjusted from baseline following smoke inhalation in either groups; positive and expiratory pressure (PEEP, approximately 6 mmHg) was added in both groups following smoke exposure. At the conclusion of the study (4 h postsmoke inhalation) lung samples were taken for surfactant function and lung water measurements. Smoke inhalation immediately increased the A-a gradient (CMV-BL = 6.9 +/- 2.4 to CMV-SI = 77.3 +/- 1.9; HFV-BL = 10.5 +/- 2.7; HFV-SI = 72.8 +/- 3.7 mmHg), venous admixture (CMV-BL = 6.9 +/- 2.8 to CMV-SI 69.8 +/- 6.6; HFV-BL = 7 +/- 1.7 to HFV-SI = 60.4 +/- 7.9 per cent) and decreased Pao2 (CMV-BL = 110 +/- 3.4 to CMV-SI = 28 +/- 3.5; HFV-BL = 103 +/- 3.6 to HFV-SI = 31 +/- 1.7 mmHg) to a similar level in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Exosurf treatment following wood smoke inhalation

Pulmonary surfactant deactivation is an important factor in the pathophysiology caused by wood smoke inhalation. Surfactant replacement is beneficial in treatment of surfactant-deficient neonates and possibly the adult respiratory distress syndrome (ARDS). In this study, the effect of exogenous Exosurf treatment for acute wood smoke injury was examined in four groups of rabbits. All groups were anaesthetized, placed on a ventilator, and surgically prepared for haemodynamic, peak airway pressure (P(aw)), and blood gas measurements. Rabbits were monitored for 2 h following smoke or sham smoke inhalation. At the conclusion of the experiment pulmonary oedema and surfactant function were measured. A Control group (n = 5) was followed without intervention. A Smoke group (n = 4) was ventilated with wood smoke for 3 min. A third group (Smoke+Exo, n = 4) was subjected to smoke followed by pulmonary instillation of Exosurf (5 ml/kg). Saline (5 ml/kg) was instilled into the lungs of the fourth group (n = 3) as a control for Exosurf instillation. Saline, Smoke and Smoke+Exo all significantly lowered PO2 and elevated P(aw) compared to baseline and the Control group. Exosurf treatment did not reduce the pulmonary oedema or restore surfactant function caused by smoke exposure. This study indicates that wood smoke inhalation acutely damages the lung and that administration of Exosurf by instillation is not an effective treatment.

Smoke inhalation: diagnosis and treatment

Smoke inhalation, defined as airway or pulmonary parenchymal injury resulting from the inhalation of toxic combustion products, presents with a wide range of severity in patients with and without skin burns. In patients with severe injuries, the diagnosis is obvious on the basis of the history and clinical presentation; in patients with less severe injuries or those in whom the clinical consequences are delayed, diagnostic precision is difficult because diagnostic clues provide only indirect information. There is no specific treatment so diagnosis is not critical for patient management. Patients at risk include 20% to 30% of flame burn victims who should receive vigorous supportive care. The mortality rate of smoke inhalation victims without a burn is < 10%. With a burn the mortality rate is 30% to 50%, suggesting that thermal injury or its treatment is responsible for further lung damage. Endotracheal intubation provides definitive treatment for obstructed or soon-to-be obstructed patients. However the diagnosis of smoke inhalation per se is not an indication for airway intubation and respiratory support; 12% of patients without a burn require intubation versus 62% of those with a burn. A translaryngeal tube can be converted to a tracheotomy safely in burn victims; tracheotomies are easier to manage if burns of the neck are excised and grafted prior to placement. Mechanical ventilation with positive end expiratory pressure (PEEP) is the treatment for the pulmonary injury. The early lesions of smoke inhalation often progress in the context of sepsis and other complications of the burn illness to a clinical state consistent with adult respiratory distress syndrome.

Methylprednisolone does not protect the lung from inhalation injury

Most clinical studies suggest that corticosteroids are contraindicated in the treatment of acute smoke inhalation. However, they are still used in critical situations with the hope that they might reverse the acute pathophysiological responses to smoke inhalation and thus reduce the severity of the illness or make survival possible. These experiments were done to study the effect of methylprednisolone on the response to smoke inhalation in anaesthetized mongrel dogs. Three experimental protocols were followed: (I) haemodynamics, gas exchange, lung compliance, and lung water were evaluated; (II) pulmonary vascular permeability was assessed by cannulating the afferent tracheobronchial lymphatic and calculating the osmotic reflection coefficient (sigma d) at high lung lymph flows; (III) pulmonary surfactant function was studied using a Wilhelmy balance. Methylprednisolone alone did not alter any measured values compared with those seen in control animals. Treatment with methylprednisolone (30 mg/kg) prior to smoke exposure did not attenuate any of the adverse responses typically seen after smoke inhalation. These data indicate that methylprednisolone does not protect the lung from the acute physiological consequences of inhalation injury.

Effects of smoke inhalation on surfactant phospholipids and phospholipase A2 activity in the mouse lung

The effects of smoke inhalation on the pulmonary surfactant system were examined in mice exposed for 30 minutes to smoke generated from the burning of polyurethane foam. At 8 or 12 hours after exposure, surfactants were isolated separately from lung lavage (extracellular surfactant) and residual lung tissue (intracellular surfactant) for phospholipid analysis. Calcium-dependent phospholipase A2 (PLA2) was measured on a microsomal fraction prepared from the tissue homogenate. Smoke inhalation produced a twofold increase in extracellular surfactant total phospholipid. While there was no change in the total phospholipid or phosphatidylcholine (PC) content of the intracellular surfactant, smoke inhalation significantly decreased the disaturated species of PC (DSPC). The specific activity of PLA2 was reduced by more than 50% in both groups of exposed mice. Smoke inhalation appears to result in selective depletion of the DSPC of intracellular surfactant and PLA2 involved in its synthesis. This depletion may be compensated for by increased secretion or slower breakdown of the material present in the extracellular compartment.

Managing smoke inhalation injuries

Inhalation injuries most often occur with cutaneous burns, and the likelihood of an inhalation injury increases incrementally with age of the patient and size of the burn. Damage to the pulmonary parenchymal tissue manifests as increased capillary permeability leading to excessive lung fluid formation and increasing hypoxia. An inhalation injury may be diagnosed using observation of indirect criteria in conjunction with fiberoptic bronchoscopy, xenon 133 radiospirometry, and/or measurement of extravascular lung water. Initially, carbon monoxide poisoning threatens the patient's oxygenation capacity. High-flow oxygen therapy reduces the half-life of carbon monoxide to an acceptable period. The patient proceeds through three stages: pulmonary insufficiency, pulmonary edema, and bronchopneumonia. Treatment is directed toward supporting oxygenation using endotracheal intubation with mechanical ventilation, humidification of inspired air, early mobilization, chest physiotherapy, antibiotics for documented infection, and adequate systemic hydration.

Smoke inhalation injury in sheep

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Inhalation injuries

Inhalation injuries occur in approximately one-third of all major burns and account for a significant number of deaths in those burn patients each year. Victims die as a result of carbon monoxide poisoning, hypoxia, and smoke inhalation. These deaths can occur without thermal wounds as well as with burn injuries. There are three distinct problems with inhalation injuries: thermal burns of the upper airway, carbon monoxide poisoning, and smoke inhalation. Each has different symptoms and signs, different treatment, and different prognosis. Thermal burns occurring in the upper airway are usually manifested within 48 hours of injury. Diagnosis is made by direct visualization of the upper airway, looking for signs of thermal injury. Admission for observation with humidified oxygen, attentive pulmonary toilet, bronchodilators as needed, and prophylactic endotracheal intubation as indicated are the mainstays of treatment. Resolution of the injury usually occurs within days. Carbon monoxide poisoning, the most common cause of death in inhalation injury, is a result of combustion. Symptoms and signs correlate with blood levels, but arterial blood gases are used to determine the degree of carbon monoxide intoxication. Treatment is based on the principle that carbon monoxide dissociation occurs much faster if the patient is placed on 100% oxygen. Occasionally the patient's symptoms may persist or get worse despite adequate treatment. Smoke inhalation significantly damages normal respiratory physiology, resulting in injury progressing from acute pulmonary insufficiency to pulmonary edema to bronchopneumonia, depending on the severity of exposure. Diagnosis is based on history, but clinical findings, arterial blood gases, and fiberoptic bronchoscopy are helpful. Treatment is supportive with careful attention paid to fluid resuscitation in the patient with burns.(ABSTRACT TRUNCATED AT 250 WORDS)

Smoke inhalation

An attempt has been made to review the characteristics of fire and smoke and the epidemiology of smoke inhalation to identify some of the many variables which interact to control the severity of the injury. An experimental model appropriate to study the pulmonary injury of smoke victims who survive to enter the health care system is described. Experiments which define how smoke damages the lung are reviewed in an effort to explain why the smoke-damaged lung is vulnerable to additional stress and why those with an injured lung and a burn have such a high mortality rate.

Effects of crystalloid on lung fluid balance after smoke inhalation

Inhalation injury occurs in 21% of flame burn victims who require large fluid volumes for resuscitation and have a mortality rate greater than 30%. This study was done to determine how vulnerable the smoke-injured lung is to fluid accumulation when crystalloids are infused rapidly. Mongrel dogs were exposed to smoke and 10% body-weight Ringer's lactate in three groups: (I) fluid only, (II) smoke only, and (III) smoke and fluid. The increase in wet-dry lung weight ratio was 2% in Group I, 28% in Group II, and 42% in Group III, consistent with pulmonary edema present only in Group III. The decrease in colloid oncotic pressure was similar in both of the groups that were given fluid, and the rise in the surface tension minimum of lung extracts was similar in both of the groups that were exposed to smoke. The smoke-injured lung loses the ability to protect itself when challenged with fluid. Reduced oncotic pressure is not responsible. Changes in microvascular pressure, endothelial and epithelial damage, and surfactant inactivation interact to cause this increase in extravascular lung water.

Clearance of aerosolized 99mTc-diethylenetriaminepentacetate before and after smoke inhalation

The pulmonary clearance of aerosolized 99mTc-diethylenetriaminepentacetate (DTPA) was studied in mongrel dogs immediately after exposure to wood smoke to see if a sensitive, objective way of assessing the degree of pulmonary injury might be found. Animals were studied in four groups as follows: control, following five minutes, two minutes, and 15 seconds of smoke exposure. Chest roentgenograms and 133Xe scans were taken before and after smoke exposure. The DTPA clearance was more sensitive in detecting injury than either of these imaging techniques. The DTPA clearance rates increased in a dose responsive way following smoke inhalation: 2.4 percent and 12.1 percent excreted per minute for control animals and those exposed to five minutes of smoke, respectively. Seven patients in a clinical trial of DTPA following smoke exposure are described; their DTPA clearance rates were all normal, although five were active cigarette smokers. Despite encouraging results in animal experiments, DTPA clearance studies may be of little practical value in the clinical setting of acute inhalation injury.

Early effects of inhalation injury on lung mechanics and pulmonary perfusion

We investigated the early effects of a rather large amount of cotton-smoke on lung mechanics and pulmonary perfusion. Under halothane anesthesia 18 ewes were intubated with a double-lumen tube. In 6 sheep the left lung was exposed to smoke, in another 6 the right lung. A sham group of 6 sheep was insufflated with air instead of smoke. Prior to and 30-45 min following the smoking- (sham-) procedure the following parameters were determined for the smoke- (sham-) exposed and the contralateral lung: static compliance, inspiratory airway resistance, and physiologic dead space ratio. In addition MAP, MPAP, WP, and CO were recorded. The data indicate that inhalation of large amounts of smoke has no major direct effects on pulmonary mechanics and perfusion in the early post-injury period. Only an increase in airway resistance of the smoke exposed lungs was found, which must be attributed to a local reflex mechanism.

A dose-responsive model of smoke inhalation injury. Severity-related alteration in cardiopulmonary function

The dose responsiveness of selected physiologic indices was studied in a sheep model of smoke inhalation injury. In this model, graded severity of injury was achieved by changing the contact time with smoke (defined by "unit"), whereas other variables were kept constant. Blood gas and cardiopulmonary indices were measured in 70 sheep, including 12 controls, either 24 or 72 hours after exposure to 3, 6, 9, 12, 15, or 18 units of smoke. A 12-unit dose of smoke was fatal within 72 hours and an 18-unit dose was fatal within 24 hours. The best correlation between smoke dose and response was observed in arterial oxygen tension 24 hours after exposure. At 24 hours, most of the cardiopulmonary indices showed significant change only after a 12-unit exposure. Although the exact shape of the dose-response curve could not be defined, sigmoid or curved linear shape was suggested, reflecting the progressive deterioration.

Pulmonary injury in burned patients

Inhalation injury has emerged as the number one cause of fatality in the burn patient. Fiberoptic bronchoscopy and 133Xe scanning complement traditional clinical signs of inhalation injury and have led to discovery of a higher incidence of these injuries among patients with burns. Patients with inhalation injury typically demonstrate three stages: acute pulmonary insufficiency, pulmonary edema, and bronchopneumonia, all of which carry at least 50 per cent mortality rates. The major early pathophysiologic changes in the lungs of burned patients are related to upper-airway obstruction and lower-airway permeability edema. Treatment consists of intubation for signs of respiratory distress, pulmonary toilet, humidification of inspired air, and antibiotics for documented infection.