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

Inhalation injury is associated with long-term employment outcomes in the burn population: Findings from a cross-sectional examination of the Burn Model System National Database

Introduction

Inhalation injuries carry significant acute care burden including prolonged ventilator days and length of stay. However, few studies have examined post-acute outcomes of inhalation injury survivors. This study compares the long-term outcomes of burn survivors with and without inhalation injury.

Methods

Data collected by the Burn Model System National Database from 1993 to 2019 were analyzed. Demographic and clinical characteristics for adult burn survivors with and without inhalation injury were examined. Outcomes included employment status, Short Form-12/Veterans Rand-12 Physical Composite Score (SF-12/VR-12 PCS), Short Form-12/Veterans Rand-12 Mental Composite Score (SF-12/VR-12 MCS), and Satisfaction With Life Scale (SWLS) at 24 months post-injury. Regression models were used to assess the impacts of sociodemographic and clinical covariates on long-term outcome measures. All models controlled for demographic and clinical characteristics.

Results

Data from 1,871 individuals were analyzed (208 with inhalation injury; 1,663 without inhalation injury). The inhalation injury population had a median age of 40.1 years, 68.8% were male, and 69% were White, non-Hispanic. Individuals that sustained an inhalation injury had larger burn size, more operations, and longer lengths of hospital stay (p<0.001). Individuals with inhalation injury were less likely to be employed at 24 months post-injury compared to survivors without inhalation injury (OR = 0.63, p = 0.028). There were no significant differences in PCS, MCS, or SWLS scores between groups in adjusted regression analyses.

Conclusions

Burn survivors with inhalation injury were significantly less likely to be employed at 24 months post-injury compared to survivors without inhalation injury. However, other health-related quality of life outcomes were similar between groups. This study suggests distinct long-term outcomes in adult burn survivors with inhalation injury which may inform future resource allocation and treatment paradigms.

Animal models of smoke inhalation injury and related acute and chronic lung diseases

Smoke inhalation injury leads to various acute and chronic lung diseases and thus is the dominant cause of fire-related fatalities. In a search for an effective treatment and validation of therapies different classes of animal models have been developed, which include both small and large animals. These models have advanced our understanding of the mechanism of smoke inhalation injury, enabling a better understanding of pathogenesis and pathophysiology and development of new therapies. However, none of the animal models fully mirrors human lungs and their pathologies. All animal models have their limitations in replicating complex clinical conditions associated with smoke inhalation injury in humans. Therefore, for a correct interpretation of the results and to avoid bias, a precise understanding of similarities and differences of lungs between different animal species and humans is critical. We have reviewed and presented comprehensive comparison of different animal models and their clinical relevance. We presented an overview of methods utilized to induce smoke inhalation injuries, airway micro-/macrostructure, advantages and disadvantages of the most commonly used small and large animal models.

The renaissance man of burn surgery: Basil A. Pruitt, Jr

Dr. Basil A. Pruitt Jr., a consummate clinical and translational surgeon-scientist, has spent over half a century at the forefront of an advancing standard of burn care. Commanding the US Army Institute for Surgical Research in San Antonio, he trained generations of leading burn clinicians and allied scientists. At his direction, there were forged discoveries in resuscitation from shock, treatment of inhalation injury, control of burn-related infections, prevention of iatrogenic complications, and understanding the sympathetic, endocrine, and immune responses to burn injury. Most consequentially, this team was among the first to recognize and define alterations in the basal metabolic rate and thermoregulation consequent to burn injury. These investigations prompted groundbreaking insights into the coordinated nervous, autonomic, endocrine, immune, and metabolic outflows that a severely burned patient uses to remain alive and restore homeostasis. Marking his scientific consequence, many of his reports continue to bear fruit when viewed through a contemporary lens. This article summarizes some of the major findings of his career thus far and is intended to complement a Festschrift recently held in his honor.

A model of recovery from inhalation injury and cutaneous burn in ambulatory swine

Inhalation injury commonly accompanies thermal injury, increasing the likelihood of mortality and multiple organ dysfunction (MOD). Large animal models have given important insight into the pathophysiology of this injury; however recapitulating late MOD has remained difficult. The current report describes experiments using a smoke inhalation and burn model, with follow-up of ambulatory swine for 14days with bronchoscopy, CT scanning, and bronchoalveolar lavage fluid (BALF)/blood collection. Clinically, animals cleared airway damage in the first several days after-injury. This was mirrored with erythematous airways on day 2 after-injury, which resolved by the end of the experiment, as did parenchymal damage seen on CT. An initial rise in the protein content of BALF immediately after-injury was followed by a dramatic increase in the concentration of leukocytes. Circulating neutrophils increased while lymphocytes decreased; both correlated with cell counts in BALF. IL8 levels in BALF increased 30-fold and remained elevated throughout the experiment. IL1ra increased circulation immediately after-injury, and afterwards in BALF. Other cytokines (TNFα, IL12) transiently increased in BALF (and decreased in circulation) on day 2. Taken together, these results display a remarkable capability for the lungs to recover in the absence of intubation, with further evidence of the role of cytokines such as IL8 and IL1ra. The possible exacerbating effects of clinical practices such as ventilation and bronchoscopies should be considered.

An historical perspective on advances in burn care over the past 100 years

The accelerated pace of clinical and laboratory research over the past century and application of the research findings to patient care have resulted in unprecedented survival of burned patients in all age groups. Resuscitation based on an understanding of the nature and magnitude of the multisystem response to injury now prevents burn shock; effective topical antimicrobial chemotherapy and early excision prevent wound toxemia and sepsis; biologic and bioengineered dressings compensate for the missing skin; and broad spectrum metabolic support regimens prevent exhaustion and accelerate convalescence. Rehabilitation programs have also been developed to restore physical function and permit the burn patient to reenter society as a productive individual.

Tracheobronchial Stenosis Following Sulfur Mustard Inhalation

Sulfur mustard inhalation leads to different respiratory complications. In this article, we describe late stenotic effects of mustard gas inhalation on major airways. About 15 yr after exposure, suspect cases suffering from severe respiratory disorders underwent complete workup for central airway stenosis. Patients were evaluated with bronchoscopy and tracheal computerized tomography scan. The mean age of patients was 43+/-8 yr. The mean exposure time was 16+/-0.7 yr. The mean time between injury and diagnosis of tracheobronchial stenosis was 11.7+/-4.8 yr. Among the 33 referred cases with no other risk factor of stenosis, 8 cases had significant stenosis in their major airways, confirmed by tracheal computerized tomography scan and bronchoscopy. We conclude that direct toxic effects of sulfur mustard can lead to tracheobronchial stenosis with different degrees of involvement ranging from diffuse tracheal stenosis to stenosis of the isolated left main bronchus or glottic and subglottic stenosis.

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.

Base deficit and alveolar-arterial gradient during resuscitation contribute independently but modestly to the prediction of mortality after burn injury

The main determinants of mortality after burn injury that can be measured on admission include age, total burn size (% burn), and inhalation injury (INHAL). Other variables, measured during resuscitation, may provide additional information about injury severity. We assessed the utility of early arterial blood gas (ABG) data in predicting mortality after burn injury. Data were limited to samples obtained during the first 2 days after burn injury and to those obtained during high-frequency percussive ventilation. Mean values for each patient's ABG data were calculated; subsequent analysis used these derived variables. Logistic regression analysis (LRA) was used to generate a mortality predictor using burn, age (as a cubic age score, AGE), and INHAL. LRA was then repeated with the ABG variables. A total of 162 patients were included. By univariate analysis, death was associated with increased alveolar-arterial gradient (AaDO2), AGE, % burn, full-thickness burn size, INHAL, and with decreased pH and base excess. LRA of % burn, AGE, INHAL, and full-thickness burn size retained the first three variables. The addition of ABG data demonstrated that mean burn excess and mean AaDO2 also contributed independently to mortality. However, there was no difference in accuracy (86%) between the two equations. By Kaplan Meier analysis, AaDO2 but not BE predicted earlier death in those who died. Measured during resuscitation, metabolic acidosis (ie, a base deficit) and oxygenation failure (ie, increased AaDO2) contributed independently, but modestly, to ultimate mortality after burn injury. The inclusion of these variables did not improve predictive accuracy. Whether therapies targeted at these endpoints would improve outcome is unknown.

Acute respiratory distress syndrome secondary to inhalation of chlorine gas in sheep

BACKGROUND

Toxic industrial chemicals (TICs) are potential terrorist weapons. Several TICs, such as chlorine, act primarily on the respiratory tract, but knowledge of the pathophysiology and treatment of these injuries is inadequate. This study aims to characterize the acute respiratory distress syndrome (ARDS) caused by chlorine gas (Cl2) inhalation in a large-animal model.

METHODS

Anesthetized female sheep were ventilated with 300 L of a Cl2/air/oxygen mixture for 30 minutes. In phase 1 (n = 35), doses were 0 ppm (Group 1, n = 6); 120 ppm (Group 2, n = 6); 240 to 350 ppm (Group 3, n = 11); and 400 to 500 ppm (Group 4, n = 12). In phase 2 (n = 17), doses were 0 ppm (Group 5, n = 5); 60 ppm (Group 6, n = 5); and 90 ppm (Group 7, n = 7), and the multiple inert gas elimination technique (MIGET) was used to characterize the etiology of hypoxemia. Computed tomography (CT) scans were performed daily for all animals.

RESULTS

In Phase 1, lung function was well maintained in Group 1; Cl2 caused immediate and sustained acute lung injury (PaO2-to-FiO2 ratio, PFR<3.0) in Group 2 and ARDS (PFR<2.0) in Groups 3 and 4. All animals in Groups 1 and 2 survived 96 hours. Kaplan-Meier analysis showed dose-related differences in survival (log-rank test, p < 0.0001). Logistic regression identified 280 ppm as the lethal dose 50%. CT and histopathology demonstrated lesions of both small airways and alveoli. In Phase 2, MIGET showed diversion of blood flow from normal to true-shunt lung compartments and, transiently, to poorly ventilated compartments.

CONCLUSIONS

Cl2 causes severe, dose-related lung injury, with features seen in both smoke inhalation and in ARDS secondary to systemic disease. This model will be used to test new therapeutic modalities.

Assessment of oxidative stress in lungs from sheep after inhalation of wood smoke

To elucidate potential dose-dependent mechanisms associated with wood smoke inhalation injury, the present study evaluated antioxidant status and the extent of pulmonary injury in sheep after graded exposure to smoke. Adult, male sheep (n=4-5 per group) were anesthetized and received 0, 5, 10 or 16 units of cooled western pine bark smoke, corresponding to 0, 175, 350 and 560 s, respectively, of smoke dwell time in the airways and lung. Smoke was mixed at a 1:1 ratio with 100% O2 to minimize hypoxia. Plasma and expired breath samples were collected pre-smoke, and 6, 12, 18, 24, 36 and 48 h after smoke exposure. Sheep were euthanatized 48 h after smoke exposure and lung and airway sections were evaluated histologically for injury and biochemically for indices of oxidative stress. Plasma thiobarbituric acid reactive substances (TBARS) were 66 and 69% higher than controls after moderate and severe smoke exposure at 48 h, whereas total antioxidant potential was not statistically different among groups at any time after exposure. Lung TBARS showed a dose-dependent response to smoke inhalation and were approximately 2-, 3- and 4-fold higher, respectively, than controls after exposure to 5, 10 and 16 units of smoke. Lung myeloperoxidase (MPO) activity was also higher in smoke-exposed animals than controls, and MPO activity was markedly elevated (19- and 22-fold higher than controls in right apical and medial lobes) in response to severe smoke exposure. Smoke exposure also induced a dose-dependent injury to tracheobronchial epithelium and lung parenchyma. Taken together these data show that few indices of oxidative stress responded in a dose-dependent manner to graded doses of smoke inhalation, although most of the indices measured in lung were affected by the highest dose of smoke. Additional time course studies are necessary to determine whether these oxidants are a cause or a consequence of the airway and lung injury associated with exposure to wood smoke.

Assessment of Severity of Ovine Smoke Inhalation Injury by Analysis of Computed Tomographic Scans

BACKGROUND

Our goal was to evaluate computed tomographic (CT) scans of the chest as a means of stratifying smoke inhalation injury (SII) severity.

METHODS

Twenty anesthetized sheep underwent graded SII: group I, no smoke; group II, 5 smoke units; group III, 10 units; and group IV, 16 units. CT scans were obtained at 6, 12, and 24 hours after injury. Each quadrant of each slice was scored subjectively: 0 = normal, 1 = interstitial markings, 2 = ground-glass appearance, and 3 = consolidation. The sum of all scores was the radiologist's score (RADS) for that scan. Computerized analysis of three-dimensional reconstructed scans was also performed, based on Hounsfield unit ranges: hyperinflated, -1,000 to -900; normal, -899 to -500; poorly aerated, -499 to -100; and nonaerated, -99 to +100. The fraction of abnormal lung tissue (FALT) was computed from poorly aerated, nonaerated, and total volumes. Mean gray-scale density (DENS) was also computed.

RESULTS

SII resulted in severity- and time-related changes in oxygenation (alveolar-arterial gradient), ventilation (respiratory rate-pressure product), DENS, FALT, and RADS. Ordinal logistic regression generated a predictive model for severity of injury (r2 = 0.623, p = 0.001), retaining RADS at 24 hours and rejecting the other variables.

CONCLUSION

At 24 hours, CT scanning enabled SII severity stratification; qualitative evaluation (RADS) outperformed current semiautomated methods (DENS, FALT).

Effects of heparin and lisofylline on pulmonary function after smoke inhalation injury in an ovine model

OBJECTIVE

This study evaluates the effects of heparin alone and in combination with lisofylline, 1-(5-R-hydroxyhexyl)3,7-dimethylxanthine, on severe smoke injury.

DESIGN

Prospective animal study with concurrent controls.

SETTING

An animal laboratory.

SUBJECTS

Eighteen 1-yr-old female sheep, weighing 24-32 kg.

INTERVENTIONS

After smoke exposure and tracheostomy, animals were divided into three groups. Group S (n = 6) received nebulized saline through an endotracheal tube every 4 hrs for 48 hrs. Group H (n = 6) received 10,000 units of nebulized heparin every 4 hrs. Group LH (n = 6) was treated with nebulized heparin and intravenous infusion of lisofylline (10 mg x kg(-1) x hr(-1)) for 48 hrs after a bolus injection (20 mg/kg). Animals initially breathed room air spontaneously. If PaO2 was <50 torr and PaCO2 >60 torr, animals were mechanically ventilated. Sheep were killed 48 hrs postinjury.

MEASUREMENTS AND MAIN RESULTS

Blood gases were measured serially. At 48 hrs, ventilation perfusion distribution mismatching was analyzed by using the multiple inert gas elimination technique. Lung malondialdehyde was determined. The postinjury increase in alveolar-arterial oxygen tension gradient (LH, 36.7 +/- 3.5 vs. S, 89.0 +/- 24.6 torr at 48 hrs) was significantly attenuated in those animals receiving LH. The percentage of pulmonary shunt, Qs/Qt (LH, 20.8 +/- 4.9 vs. S, 36.6 +/- 4.6%), and the percentage of animals that required ventilation (LH, 0 vs. S, 67%) were significantly reduced in LH. Multiple inert gas elimination technique study showed that the true shunt fraction was decreased in LH. Lung malondialdehyde was significantly less in LH (LH, 0.33 +/- 0.06 vs. S, 0.56 +/- 0.09 nmol/mg protein). There was no significant difference in any of these variables between H and S.

CONCLUSION

Treatment with heparin alone did not attenuate pulmonary dysfunction after severe smoke injury. Combined treatment with nebulized heparin and systemic lisofylline had beneficial effects on pulmonary function in association with a decrease in blood flow to poorly ventilated areas and less lipid peroxidation.

Effects of burns on inhalation injury in sheep: a 5-day study

BACKGROUND

We have previously reported that infliction of thermal injury immediately after smoke exposure did not accentuate pulmonary dysfunction during the subsequent 48 h. The purpose of this study was to determine whether thermal injury would aggravate pulmonary dysfunction during a longer postinjury period of 5 days.

METHODS

Six sheep (G1) received 12 units of smoke inhalation injury (SII) alone; seven sheep (G2) received a 40% full-thickness scald burn immediately after SII. All sheep were resuscitated with lactated Ringer's solution for the first 48 h. After 48 h, animals were fed food and water ad libitum. Cardiopulmonary variables and blood gases were measured serially. At the end of the 5-day experimental period, VA/Q distribution was analyzed using the multiple inert gas elimination technique (MIGET). Lung wet to dry (W/D) weight ratios and malondialdehyde (MDA) concentrations were determined.

RESULTS

Cardiac index in G2 significantly increased and remained higher compared with G1. There was no difference in A-aDO(2) between the two groups. There was also no difference between the two groups by MIGET study, or in terms of lung MDA and W/D weight ratios. None of the animals manifested symptoms of infection.

CONCLUSION

Despite the difference in the hemodynamic changes induced by the addition of a 40% burn to smoke inhalation injury, pulmonary dysfunction was not accentuated during the 5-day study period in the absence of infection.

Delayed partial liquid ventilation shows no efficacy in the treatment of smoke inhalation injury in swine

In an earlier neonatal porcine model of smoke inhalation injury (SII), immediate postinjury application of partial liquid ventilation (PLV) had dramatic beneficial effects on lung compliance, oxygenation, and survival over a 24-h period. To explore the efficacy of PLV following SII, we treated animals at 2 and 6 h after SII and followed them for 72 h. Pigs weighing 8–12 kg were sedated and pharmacologically paralyzed, given a SII, and placed on volume-cycled, pressure-limited ventilation. Animals were randomized to three groups: group I (+SII, no PLV, n = 8), group II(+SII, PLV at 2 h, n = 6), and group III (+SII, PLV at 6 h, n = 7). Ventilatory parameters and arterial blood gasses were obtained at scheduled intervals. The PLV animals ( groups II and III) followed a worse course than group I (no PLV); PLV groups had higher peak and mean airway pressures, oxygenation index, and rate-pressure product (a barotrauma index) and lower lung compliance and arterial partial pressure of oxygen-to-inspired oxygen fraction ratio (all P < 0.05). PLV conferred no survival advantage. The reported beneficial effects of PLV with other models of acute lung injury do not appear to extend to the treatment of SII when PLV is instituted in a delayed manner. This study was not able to validate the previously reported beneficial effects of PLV in SII and actually found deleterious effects, perhaps reflecting the predominance of airway over alveolar disease in SII.

Half-life of blood carboxyhemoglobin after short-term and long-term exposure to carbon monoxide

BACKGROUND

In models of smoke inhalation injury and carbon monoxide poisoning blood carboxy-hemoglobin (COHb) levels decrease faster than predicted by the generally recognized half-life of COHb. We studied the effects of duration of exposure to carbon monoxide (CO) on the subsequent CO elimination.

METHODS

Each of four sheep were insufflated with CO gas mixtures either for a few minutes (short-term exposure) or for several hours (long-term exposure), then ventilated with air for 3 hours. Serial COHb concentrations were analyzed by using a two-compartment, single central outlet mathematical model.

RESULTS

Short-term exposures exhibited biphasic decreases of COHb concentration compatible with a two-compartment model; an initial rapid decrease (half-life 5.7 +/- 1.4 minutes) was followed by a slower phase (103 +/- 20.5 minutes). Long-term exposures exhibited almost monophasic decreases, which were nevertheless compatible with the model (half-life, 21.5 +/- 2.1 and 118 +/- 11.2 minutes).

CONCLUSION

This study demonstrated different patterns of CO elimination curve, which suggests distribution of CO to two compartments having different rates of equilibration.

Acute lung injury, acute respiratory distress syndrome and inhalation injury: an overview

Acute Lung Injury (ALI) and the Acute Respiratory Distress Syndrome (ARDS) are severe respiratory diseases that have a very poor prognosis and have numerous causes. Despite a great deal of research and investigation since the initial description of ARDS 30 years ago many questions about the pathogenesis, treatment and outcome of the disease remain unanswered. Although there is evidence to suggest that outcome of ALI and ARDS is improving, the reasons why are unknown and there is not yet a well developed treatment for these diseases. Inhalation injury resulting from exposure to pyrolysis and combustion atmospheres is among the causes of ALI/ARDS. Little is known of the mechanisms of fire related inhalation injury that results in the development of ALI/ARDS. There is a paucity of information about fire atmosphere exposure response relationships for smoke-induced inhalation injury. Although there is considerable information about the pulmonary toxicity of many of the more common constituents of fire atmospheres, little is known about the pulmonary toxicity of mixtures of these constituents. Fire related pulmonary health risks are of particular concern to the Navy due to the limited opportunity to escape the inhalation hazards posed by shipboard fires. Consequently the Naval Medical Research Institute Detachment (Toxicology) has undertaken a research program to develop research models of combustion atmosphere induced ALI/ARDS which can be exploited to systematically address some of the questions surrounding fire related ALI/ARDS. ALI/ARDS has been the topic of a vast amount of research, numerous symposia, working groups and their published proceedings, book chapters, and books. Less information is available regarding experimental models of smoke induced lung damage, however the literature on the subject is extensive. Consequently this article is intended to provide the reader with a primer or cursory "overview" of ALI and ARDS from a toxicological perspective and should not be considered comprehensive.

Ventilation-perfusion alterations after smoke inhalation injury in an ovine model

To study the pathophysiological mechanism of progressive hypoxemia after smoke inhalation injury, alterations in ventilation-perfusion ratio (VA/Q) were studied in an ovine model by using the multiple inert gas elimination technique. Because ethane was detected in expired gas of some sheep, we replaced ethane with krypton, which was a unique application of the multiple inert gas elimination technique when one of the experimental gases is present in the inspirate. Severity-related changes were studied 24 h after injury in control and mild, moderate, and severe inhalation injury groups. Time-related changes were studied in controls and sheep with moderate injury at 6, 12, 24, and 72 h. Arterial PO2 decreased progressively with severity of injury as well as with time. In smoke-exposed animals, blood flow was recruited to low VA/Q compartment (0 < VA/Q < 0.1; 17.6 +/- 10.6% of cardiac output, 24 h, moderate injury) from normal VA/Q compartment (0.1 < VA/Q < 10). However, increases in true shunt (VA/Q = 0; 5.6 +/- 2.5%, 24 h, moderate injury) and dead space were not consistent findings. The VA/Q patterns suggest the primary change in smoke inhalation injury to be a disturbance of ventilation.

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.

Upper airway compromise after inhalation injury. Complex strictures of the larynx and trachea and their management

OBJECTIVE

Strictures of the upper airway caused by burns have features distinct from other benign stenoses. The authors reviewed their experience with burn-related stenoses to define the principles of treatment.

SUMMARY BACKGROUND DATA

The combined effects of inhaled gases and heat in burn victims produce an intense, often transmural, inflammation of the airway, further complicated by intubation. The incidence of laryngotracheal strictures in survivors of inhalation injury is high, but the reported experience with their treatment is limited and often unduly separated into injuries of larynx and trachea.

METHODS

Presentation, treatment, and long-term follow-up are reviewed in 9 women and 9 men age 9 to 63 years, who were evaluated over a 22 year period for chronic airway compromise after inhalation injury. There were 18 tracheal stenoses, 14 subglottic strictures, and 2 main bronchial stenoses. Laryngotracheal strictures stenosis. T-tubes were placed in 15 patients, in low subglottic or tracheal stenosis below the vocal cords, in high subglottic stenosis through the vocal cords, and as a stent after resection of subglottic stenosis.

RESULTS

There were two deaths during follow-up, one from respiratory failure and one from an unrelated cause. Two patients underwent evaluation only. Early in this series, one tracheal and one laryngotracheal resection resulted in prompt restenosis. Of the remaining 14 patients, 9 are without airway support from 2 to 20 years later. Four have permanent tracheal tubes. One patient required tracheostomy 8 years after successful subglottic reconstruction.

CONCLUSIONS

Strictures of the upper airway related to inhalation injury are associated with prolonged inflammation and involve larynx and trachea in a majority of patients. These complex injuries respond to prolonged tracheal stenting (mean, 28 months) and resection or stenting of subglottic stenoses with recovery of a functional airway and voice in most patients. Early tracheal resection should be avoided.

The role of inhalation injury in burn trauma. A Canadian experience

From 1977 to 1987, 1705 thermally injured patients were admitted to the Firefighters' Burn Center at the University of Alberta Hospitals. Thirteen hundred forty-four were male (78.8%) and 361 were female (21.2%), with a mean total burn surface area (TBSA) of 15.1 (SEM +/- 0.4%) and a range of 1% to 99% TBSA. Sixteen hundred thirty-five patients survived to be discharged from hospital, with an overall survival rate of 95.9%. One hundred twenty-four burn patients (7.3%) suffered concomitant inhalation injury diagnosed by bronchoscopy. Patients with inhalation injury suffered from larger TBSA (39.7% +/- 2.8% versus 12.2% +/- 0.3%; p less than 0.01) than those without inhalation injury. Inhalation injury increased the number of deaths from burn injury (34.7% versus 1.7%; p less than 0.01) independent of age and TBSA. Inhalation injury was associated with a threefold prolongation of hospital stay (23.7 +/- 0.7 versus 74.4 +/- 6.2 days; p less than 0.01) and was independent of age and TBSA. Multifactorial probit analysis was performed for both inhalation- and noninhalation-injured burned patients to allow TBSA and age adjusted rates of mortality for the burn population presented. The maximum detrimental effects of inhalation injury in burn patient outcome occurred when it coexisted with moderate (15% to 29% TBSA) to large (30% to 69% TBSA) thermal injuries. These data demonstrate that inhalation injury is an important comorbid factor in burn injury that increases the number of deaths substantially. Most importantly such injuries also independently prolong the duration of hospitalization in a highly unpredictable fashion as compared to patients with cutaneous burns only. As such our data illustrate the extreme importance of inhalation injury as a comorbid factor following thermal injury and reveal the present limitations for accurate quantification of the magnitude of respiratory tract injury accompanying thermal trauma.

Smoke inhalation injury in sheep

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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.