Smoke inhalation is a multilevel insult to the pulmonary system

Inhalation injury represents an ongoing threat to patients with thermal injury. The magnitude of the disease severity is related to the multilevel insult to the pulmonary system. Asphyxiants present in inhaled smoke can compromise oxygen delivery, resulting in cell death. Also, early changes in the microcirculation of the lung parenchyma, related to polymorphonuclear cell activation and oxygen free radical production, are responsible for early pulmonary edema. Perhaps the most significant pathologic change caused by smoke inhalation is loss of the respiratory epithelium and the formation of tracheobronchial casts. The recent application of high-frequency flow interruption ventilation and intrapulmonary percussive ventilation has made the largest impact on improved survival in patients suffering from smoke inhalation.

Ventilatory support following burns and smoke-inhalation injury

The first major improvement in the treatment of burn injury came with the recognition of the importance of fluid resuscitation to prevent shock and renal failure. Subsequently, the use of topical antibiotics to control burn-wound infection and prevent invasive burn-wound sepsis led to the next significant reduction in morbidity and mortality of burn patients. Although progress has been made in the treatment of inhalation injury, the pathophysiology of the injury is still incompletely defined. A better understanding of pathogenic mechanisms will lead to the development of therapeutic agents and treatment regimens that will modulate the cascades of humoral mediators of organ dysfunction and reduce the morbidity and mortality associated with inhalation injury. The recognition of ventilator-induced lung injury has led to adoption of alternative ventilatory techniques such as high-frequency percussive ventilation, which has been shown to substantially reduce the morbidity associated with inhalation injury.

The use of perfluorocarbon-associated gas exchange to improve ventilation and decrease mortality after inhalation injury in a neonatal swine model

Patients with tracheobronchial disease frequently require mechanical ventilation during therapy and experience iatrogenic complications such as barotrauma and volutrauma. The purpose of this study was to determine whether perfluorocarbon-associated gas exchange (PAGE) results in lower ventilatory pressures and more efficient ventilation than that provided by conventional ventilation after tracheobronchial mucosal injury caused by smoke inhalation in neonatal piglets. Ten piglets were used for this prospective, randomized study. After administration of a severe smoke inhalation injury, the piglets were randomly assigned to either the perfluorocarbon or control groups. Group 1 served as the control population and received standard (time-cycled, volume-limited) mechanical ventilation. Ventilator settings were adjusted to maintain physiological pH and PO2 at the lowest tidal volume, rate, and end-expiratory pressure possible throughout the study period. Group 2 was administered intratracheal perfluorocarbon as well as identical mechanical ventilation to attain the same physiological pH and PO2. Oxygenation index, peak and mean airway pressures, and arterial blood gas levels were measured throughout the study period and subjected to statistical analysis. Histological comparison of airway and parenchymal tissues confirmed identical patterns of smoke injury in both groups. Carbon monoxide levels were the same in both groups. There was significant barotrauma and volutrauma in the control group, but none in the PAGE group. All controls died from 13 to 17 hours after injury; one PAGE pig died at 23 hours with all others surviving past 24 hours (P = .0021). Peak, plateau, and mean airway pressures were all significantly higher (P < .05) past 12 hours after injury and continued to increase until death in the controls. Arterial blood gases showed significantly (P < .05) decreased pH, PO2, and elevated PcO2 levels in the control group past 12 hours after injury. The oxygenation index was significantly elevated (P < .05) in the control group past 12 hours after injury. PAGE shows potential for improving ventilation and survival immediately after severe smoke inhalation injury and may have clinical applications in other nonhomogeneous lung injuries.

[An experiment study of reversed pulmonary hypertension with inhaled nitric oxide on smoke inhalation injury]

We evaluated the effect and mechanisms of reversed pulmonary hypertension with inhaled nitric oxide (NO) on smoke inhalation injury in the dog model, 21 dogs were divided into 3 groups randomly. Following smoke inhalation, the control group (n = 8) inhaled O2 (FiO2, 0.45) and the treated group (n = 9) inhaled O2 and 0.0045% (45 ppm) NO. Hemodynamics was serially measured for 12 hours. In addition, 4 dogs without smoke inhalation were used to study the normal lung histomophologic findings. The data were analyzed by ANOVA. After inhalation of NO, the mean pulmonary artery pressure (mPAP), pulmonary minute vessels pressure (Pmv), and pulmonary vascular resistance (PVR) were decreased significantly (P < 0.05), while the mean aortic pressure (mAP) and total peripheral resistance (TRP) were not remarkably changed (P > 0.05). The levels of cyclic guanosine monophosphate (cGMP) were increased significantly (P < 0.01). Inhaled NO may reverse pulmonary hypertension with smoke inhalation injury in dogs. The mechanism of selective pulmonary circulation was increased cGMP level in smooth cells. Inhaled NO may be recommended for clinical application.

Inhaled nitric oxide selectively reduces pulmonary hypertension after ovine smoke inhalation but does not improve oxygenation

Inhaled nitric oxide (NO) is known to selectively reduce pulmonary hypertension and improve the ventilation-perfusion relationship in subjects with lung injury of various origin. However, some forms of lung injury do not react to inhaled NO at all, or show only a reduction in pulmonary arterial pressure. Very little is known about the effects of inhaled NO after smoke inhalation injury. We investigated the effects of inhaled NO in an established model of ovine smoke inhalation injury. Chronically instrumented sheep (n = 8) had tracheostomies and were insufflated with smoke generated from burning cotton cloth (4 times at 12 breaths each). They were then connected to a ventilator with oxygen-enriched air to achieve arterial oxygen tensions within the normal range. After 48 hours, NO was added to the inspired gas in ascending concentrations of up to 100 ppm. Systemic and pulmonary hemodynamics as well as oxygen transport were analyzed. Inhaled NO dose dependently lowered the pulmonary hypertension. Concentrations higher than 20 ppm did not further reduce the pulmonary artery pressure. Right ventricular stroke work index was significantly improved owing to the reduction in pulmonary vascular resistance. Arterial oxygenation, however, was not optimized by inhaled NO, probably because of interstitial edema formation.

Predicted combustion product deposition in the human airway

Fires involving modern polymeric materials produce toxic vapours and particles of widely varying composition and size depending on available oxygen and localized temperatures. Adverse health effects of inhaled combustion-generated particles depend on physiological interactions at the airway deposition site. The present work is a theoretical investigation into the importance of airway humidity and temperature profiles, initial particle size, particle size distribution and ionic concentration on airway particle deposition. A modified numerical model accounting for hygroscopic particle growth was used to predict airway deposition of 0.1-10.0 microm mass median aerodynamic diameter (MMAD) particles. Dynamic humidity profiles were generated with an unsteady state model of heat and water vapour transport. Results suggest that for hygroscopic particles < 2.0 microm, MMAD dynamic end-inspiratory humidity profiles produce up to 250% greater predicted nasopharyngeal deposition than steady state humidity profiles. Assuming combustion products are hygroscopic, these results also suggest that less pulmonary deposition will occur than previously predicted. In addition, higher upper airway concentrations of combustion products may have significant health consequences independent of pulmonary deposition patterns.

Application of full-scale fire tests to characterize and improve the aircraft postcrash fire environment

The Federal Aviation Administration (FAA) has conducted numerous full-scale fire tests for the purpose of characterizing the postcrash cabin fire environment and developing improved fire test criteria for cabin materials. The tests consistently demonstrated the importance of cabin flashover on occupant survivability. Flashover is basically a sudden, very rapid spread of fire, generating large quantities of heat, smoke, and toxic gases that quickly fill the cabin. Before flashover, the cabin environment is largely survivable; after flashover, occupant survival becomes highly unlikely. Thermal incapacitation is more important near the fire origin and at higher elevations, whereas toxic gas incapacitation is predominant away from the fire origin and at lower elevations. The FAA has developed and adopted improved fire test methods for seat cushions (fire blocking layers) and interior panels (low heat release). In both cases, the fire test methods are consistent with full-scale test results and serve to improve occupant survivability by delaying the onset of flashover, thereby providing substantially greater available time for occupant evacuation.

Unilateral smoke inhalation in sheep: effect on left lung lymph flow with right lung injury

We previously reported that smoke inhalation to the right lung will result in damage to the air-insufflated left lung. In this study we confirm these findings and determine whether this injury is associated with an elevation in lung lymph flow and pulmonary microvascular permeability to protein as indexed by changes in reflection coefficient. Sheep (n = 12) were surgically prepared by placement of a Swan-Ganz catheter and pneumatic occluders on all pulmonary veins and the left pulmonary artery. The left lung lymphatic was selectively cannulated as shown previously (Y. Kikuchi, H. Nakazawa, and D. Traber. Am. J. Physiol. 269 (Regulatory Integrative Comp. Physiol. 38): R943-R947, 1995). All afferent lymphatics from the right lung were severed, and the right pulmonary ligament was sectioned. The caudal end of the lymph node was sectioned to remove systemic lymph contamination. The sheep were studied in the unanesthetized state 7 days later. To ensure that lymph flow was exclusively from the left lung (QLL), right pulmonary microvascular pressure was increased, a procedure that resulted in little or no change in QLL, as was previously shown. The sheep were then anesthetized, and a Carlens tube was positioned to allow separate ventilation of the right and left lung. The right lungs of five sheep and the left lungs of two sheep were insufflated with cotton smoke. Insufflation of the left lung with cotton smoke produced a fourfold increase in QLL that began 4 h after insult. Insufflation of the right lung with smoke led to a doubling of QLL that began 12 h after insult. Changes in QLL were associated with increased microvascular permeability, as indexed by the reflection coefficient. Control sheep (air insufflated into both lungs, n = 5) showed no change in QLL. Injury to the right lung resulted in damage to the left air-insufflated lung, suggesting a hematogenous mediation of the response.

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.

Effect of severe smoke inhalation injury on systemic microvascular blood flow in sheep

Multiple nonpulmonary organ dysfunction is frequently associated with acute lung injury; however, the mechanisms underlying the pathogenesis of this process are not completely understood. Decreased oxygen delivery to distant organs due to maldistribution of blood flow may be a contributing factor. We examined the effects of acute lung injury induced by smoke inhalation on microvascular blood flow to various organs in sheep. Seven sheep were prepared with arterial, venous, pulmonary artery, and left atrial catheters. After a 5 day recovery period, a tracheostomy was performed, followed by insufflation with 48 breaths of cool cotton smoke. Determination of microvascular blood flow using colored microspheres, standard hemodynamic measures, and blood gas analysis were performed before and at 12 h intervals after smoke inhalation. Animals were resuscitated to maintain left atrial pressure at +/- 2 mmHg of the baseline value and FiO2 was adjusted to maintain Sao2 at > 90%. After 48 h, sheep were killed and an autopsy was performed. Samples of trachea, left ventricle, ileum, colon, spleen, pancreas, and cortex from both kidneys were obtained for determination of microvascular blood flow. Blood flow to the trachea was substantially increased, while blood flow to the kidneys was preserved near baseline levels. Left ventricular blood flow decreased slightly; however, this decline was not statistically significant. Blood flow to ileum, colon, spleen, and pancreas was significantly decreased, particularly at 36 and 48 h after injury. These decreases were independent of changes in cardiac output or systemic oxygen delivery. It is likely that alteration in microvascular blood flow may contribute to the development of nonpulmonary organ dysfunction after acute lung injury.

Combined smoke inhalation and body surface burns injury does not necessarily imply long-term respiratory health consequences

This study was undertaken to assess the long-term respiratory health consequences of smoke inhalation in patients who are burns survivors. Patients with smoke inhalation resulting from domestic flame or fire were studied. Medical records were the primary source for the selection of the patients. Smoke inhalation was diagnosed on the basis of the visual appearance of the airways on the reported bronchoscopy. Patients who participated in the study were compared on important characteristics with those who did not participate. The participants were then assessed by questionnaire, physical examination, chest radiograph and pulmonary function tests. Twenty three out of 45 patients who had survived smoke inhalation participated in the study. Participants and nonparticipants were comparable with respect to gender, age, time since injury, aetiology of injury, and total body surface burned. Participants had more facial burns, more severe bronchoscopic findings of smoke inhalation and required intubation more frequently. Respiratory symptom assessment and pulmonary function tests were performed 45 +/- 23 months after smoke inhalation. Four patients reported an increase in dyspnoea, one an increase in cough and one an increase in phlegm. All the patients had pulmonary function tests and bronchial responsiveness (provocative concentration of histamine resulting in a 20% fall in forced expiratory volume in one second (PC20) > 16 mg.mL-1) within normal limits. The four patients complaining of increased dyspnoea had results within normal limits for cardiac and respiratory variables on maximal exertion. The present study indicates that, in burn patients, smoke inhalation resulting from a single domestic fire does not necessarily imply long-term respiratory health consequences.

Early effects of smoke inhalation on alveolar macrophage functions

Alveolar macrophage (AM) dysfunctions have been implicated in the pathogenesis of smoke inhalation lung injury. We investigated the early (within 70 min) effects of smoke inhalation on AM. The cells were recovered by bronchoalveolar lavage from rabbits ventilated with cotton smoke for 5 min followed by O2/room air for 60 min (smoke-exposed) or with room air in place of smoke (control). Smoke injury caused arterial blood carboxyhaemoglobin levels to increase 11-fold and reduced arterial blood PO2 (measured approximately 1 h postinjury) by 25 per cent. Scanning electron micrographs revealed denudation of plasmalemmal pseudopods in smoke-exposed AM. Smoke exposure suppressed both AM adherence to plastic and phagocytosis of opsonized bacteria. Basal superoxide (O2-) production was elevated in smoke-exposed AM, compared with controls, whereas PMA-stimulated O2- production was unaffected. Smoke-exposed AM had reduced basal secretion of tumour necrosis factor-alpha (TNF-alpha), but displayed a greater TNF response to stimulation with LPS than did control cells. LPS-stimulated TNF-alpha releases from control and smoke-exposed AM were suppressed by phosphodiesterase inhibitors pentoxifylline and theophylline, and were enhanced by the lipoxygenase inhibitor, MK886. The early responses of AM to smoke inhalation lung injury are consistent with activation of O2- production and priming of TNF-alpha release, concurrent with a functional down regulation of phagocytosis.

Fluid resuscitation with deferoxamine hetastarch complex attenuates the lung and systemic response to smoke inhalation

BACKGROUND

We determined the effect of infusing the iron chelator deferoxamine complexed to hetastarch on the degree of lung dysfunction and systemic abnormalities produced by a severe smoke exposure.

METHODS

Adult sheep were given a smoke exposure under anesthesia that produced a peak carboxyhemoglobin between 40% and 45%. Twenty-eight sheep were studied; eight were given smoke alone and resuscitated with sufficient lactated Ringer's solution to maintain baseline hemodynamics. Seven sheep were given a bolus plus 1 ml/kg/hr of a 10% deferoxamine-hetastarch solution for resuscitation; five were given hetastarch alone. The response was compared with eight controls during a period of 24 hours.

RESULTS

Smoke alone and smoke with hetastarch resulted in a shunt fraction of greater than 25% and a 50% decrease in compliance, severe airway inflammation, mucosal slough, atelectasis, and some alveolar edema. Increased lipid peroxides measured as malondialdehyde were present in airway fluid. In addition, oxygen consumption increased by 100% early after injury, net 24-hour positive fluid balance was almost 3 L, and a significant increase occurred in liver lipid peroxidation. The group given deferoxamine had a significantly attenuated lung response, with only modest airway damage lung dysfunction, and minimal systemic changes including a net positive fluid balance of just over 1L and no liver lipid peroxidation.

CONCLUSIONS

An iron chelator deferoxamine complexed to hetastarch, given after a severe smoke exposure, significantly attenuates the airway and the systemic inflammatory (oxidant) injury, indicating free iron release and subsequent increased oxidant activity to be a major etiologic factor.

Effects of ibuprofen on airway vascular response to cotton smoke injury

We studied the effects of ibuprofen on bronchial blood flow and myocardial function after inhalation injury. Sheep (n = 12) were chronically instrumented with cardiovascular and pulmonary catheters. After 5 days of recovery period, baseline data were collected and the sheep were divided into two groups. Group S (n = 6) were insufflated with 48 breaths of cotton smoke; while group I (n = 6) were pretreated with ibuprofen (12mg/kg bolus followed by 3 mg/kg/h continuous infusion for 24 h) and challenged with the same dose of smoke. All the animals were studied for 24h. Bronchial blood flow increased significantly in both groups throughout the experimental period; while stroke volume as well as right and left ventricular stroke work indices of both groups were significantly decreased (group I worse than group S) in the second half of the experimental period. These data suggest that vasodilatory prostaglandins do not play a major role in the bronchial vascular response to smoke inhalation injury and myocardial depression seen post injury is worse in animals treated with ibuprofen.

Burn injuries in firefighters

The authors cover the care of burn injuries from start to finish, beginning with a discussion of immediate intervention and concluding with a look at psychosocial aspects of burns. Topics in the middle include early management, evaluation of the patient and classification of the burn's severity, burn resuscitation, the pathophysiology of smoke inhalation, dressing of burn wounds, escharotomies and fasciotomies, surgical management, and rehabilitation.

Smoke inhalation among firefighters

Smoke inhalation may account for up to 75% of fire-related deaths and presents with a wide variety of complaints and findings. The authors examine the components of smoke to illustrate the patterns of smoke injury, provide useful guidelines on evaluation and management, survey current laboratory and diagnostic studies, and present their recommendations for treatment.

Pulmonary effects of firefighting

The authors examine the acute and chronic effects of exposure to smoke among firefighters and look at mortality studies for the risk of death due to nonmalignant respiratory disease and lung cancer.

The effect of smoke inhalation on bradykinin metabolism by the perfused and ventilated rat lung

The effect of smoke inhalation on bradykinin metabolism was studied in the rat lung perfused with Ringer's bicarbonate solution. After smoke (from cotton, polyester, or seat cushion material) inhalation, tritium-labeled bradykinin was added to the Ringer's bicarbonate solution, and then the lung perfusion effluent aliquots containing bradykinin and its metabolic fragments were collected after a single transpulmonary passage. For the 20 control rats without smoke inhalation, 91% of the bradykinin dose was metabolized, with Pro-Pro (I), 49%, and Arg-Pro-Pro-Gly-Phe (II), 32%, being the predominant bradykinin cleavage fragments. For 12 rats with smoke inhalation, 89% of the bradykinin dose was metabolized, with I (28%) and II (36%) being the major bradykinin cleavage fragments. The type of smoke did not significantly alter the capacity of the rat lung to metabolize bradykinin. Exposure to smoke from seat cushion material for more than 3 minutes caused pulmonary edema and thickening, and smoke exposure for more than 5 minutes caused loss of integrity at the lung alveolar-capillary interface. In contrast, exposure to cotton or polyester smoke did not cause any observable gross changes of the lung. Electron microscopic examination of lung exposed to seat cushion material smoke revealed considerable damage, with the type I epithelium existing as patches on the alveolar surface and capillary endothelium separated from the basement lamina. Thus in our model acute, short-term inhalation of smoke did not significantly alter the amount of bradykinin metabolized by the pulmonary endothelium so long as the integrity of the lung alveolar-capillary interface was maintained, although there seemed to be a moderate shift in the amount of major cleavage fragments from I to II.

Effect of phenytoin on smoke inhalation injury in sheep

To determine whether the anti-inflammatory effects of phenytoin might reduce cardiopulmonary dysfunction we studied the effects of phenytoin treatment on acute lung injury induced by smoke inhalation. Twenty-one chronically instrumented sheep were observed for 24 h after smoke inhalation injury. Myocardial contractility was evaluated by left ventricular end-systolic pressure-diameter relationship (LVESPDR) with a pair of ultrasonic transducers and strain-gauge transducer. In the control group (n = 6), uninjured sheep were given a bolus of phenytoin (12.5 mg/kg). Smoke-insufflated sheep were divided into nontreatment (n = 7) and phenytoin (n = 8) groups. Phenytoin alone had no effects in uninjured sheep except an early rise in heart rate and LVESPDR. In the group given smoke without treatment, there was a significant increase in pulmonary artery pressure and pulmonary vascular resistance index and a decrease in cardiac index. Pulmonary vascular changes were attenuated by treatment with phenytoin. Pulmonary transvascular fluid flux was evaluated by using a lung lymph fistula. LVESPDR fell in the smoke group but not in the group given phenytoin. There was a marked increase in lung lymph flow with smoke inhalation but this phenomenon was not affected by phenytoin treatment. In conclusion, phenytoin treatment reduced early hemodynamic depression.

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.

Smoke inhalation causes a delayed increase in airway blood flow to primarily uninjured lung areas

OBJECTIVE

Single lung inhalation injury causes tissue damage to the contralateral lung. We therefore examined airway blood flow after smoke inhalation in chronic instrumented sheep to get further information about the underlying pathophysiology.

DESIGN/PATIENTS

The right lung and lower trachea of 5 animals were smoke-exposed, while their left lung was air-insufflated using a split ventilation technique. Three animals, where both lungs were only air-insufflated, served as controls. Blood flow to the airway was measured using a labeled microsphere technique. All animals were studied for 24 h following smoke inhalation. Then they were sacrificed and their tissues harvested.

RESULTS

The airway blood flow to the smoke-exposed lung was elevated 11-fold immediately after inhalation injury. The bronchial blood flow to the air insufflated lung became significantly elevated 24 h post-smoke, although to a lesser extent. The control animals did not show any changes of bronchial blood flow during the observation time.

CONCLUSIONS

Damage to one lung can lead to pathophysiologic changes in the contralateral lung. This response appears to be mediated by hematogenous factors.

Impaired alveolar macrophage function in smoke inhalation injury

The high incidence of both bacterial pneumonia and the adult respiratory distress syndrome (ARDS) associated with smoke inhalation injury (SII) may result, at least in part, from smoke-induced injury to the alveolar macrophage (AM). Specifically, we hypothesized that AM antimicrobial function, ability to phagocytose apoptotic PMNs, and capacity to prevent apoptosis in PMNs are impaired by smoke. To test these hypotheses, AMs were harvested by bronchoalveolar lavage from sheep before and after the animal was exposed to cotton smoke. The two populations of AMs were incubated with Pseudomonas aeruginosa (PSA) in vitro. Normal AMs (NAMs) phagocytosed a mean of 99 +/- 11% of the PSA placed in their wells, whereas smoke-exposed AMs (SAMs) ingested only 60 +/- 8%. NAMs killed 80 +/- 8% of PSA ingested, whereas SAMs killed only 56 +/- 16% (P < 0.05). When sheep PMNs, allowed to undergo apoptosis, were incubated with the two AM populations, 66 +/- 3% of the NAMs and 40 +/- 6% of the SAMs demonstrated phagocytosis of these apoptotic PMNs (P < 0.05). Fresh sheep PMNs were incubated in unconditioned media, NAM and SAM-conditioned media, and followed over 48 hr for the development of apoptosis and maintenance of viability. The NAM-conditioned media markedly prevented apoptosis and augmented PMN survival relative to the unconditioned and SAM-conditioned media (P < 0.05). The poor antimicrobial function known to be characteristic of apoptotic PMNs, together with the directly impaired antimicrobial function of AMs, may contribute to the infectious complications of SII. If the PMNs recruited to the lung in SII are not properly supported by the AMs following smoke injury, large numbers may undergo apoptosis. If not properly disposed of by these SAMs, the apoptotic PMNs could eventually lyse, releasing tissue toxins, resulting in escalation of lung injury and leading to ARDS.

Burns and smoke inhalation

Smoke inhalation injury affects nearly one third of all major burn victims. Significant inhalation exposures must be suspected in persons who were entrapped in a closed space or who became unconscious during a fire. Each individual fire generates a characteristic smoke depending on the type of materials burnt, temperatures reached during pyrolysis, and the availability of oxygen to sustain combustion. In addition to variable amounts of thermal loads, firesmoke may contain mixtures of carbon monoxide, hydrogen cyanide, nitrogen oxides, and other highly irritating gases. Each constituent of firesmoke may potentially create pulmonary and systemic toxicities and must be considered in every victim of smoke inhalation.

Increased early postburn fluid requirements and oxygen demands are predictive of the degree of airways injury by smoke inhalation

The combination of burn and smoke inhalation was studied to determine if early hemodynamic and metabolic abnormalities would correspond with the degree of subsequent smoke-induced airways injury. Adult sheep (n = 45) given an 18% total body surface third-degree burn alone or with smoke exposures of 12 breaths of 5, 10, or 20 mL/kg tidal volume were continuously monitored with airways assessed at 4 or 24 hours. With increased smoke exposure (20 mL/kg tidal volume), oxygen consumption (VO2) in the first several hours and net positive fluid balance, especially in the first 6 hours, increased by 100% and 300%, respectively, over that seen with burn alone. The degree of increase in fluid requirement, net fluid retention, and VO2 with smoke, compared with burn alone, correlated best with the degree of airways damage quantitated at 24 hours, r = 0.83, 0.85, and 0.89, respectively. Airways damage at 4 hours did not predict the damage seen at 24 hours. Systemic changes were not caused by gas-phase toxins, such as carbon monoxide, because smoke filtered of particles had the same blood carbon monoxide control as whole smoke, but the systemic response was equal to burn alone, and there was no airways injury. The cause of the systemic changes is likely the result of the intense airways inflammation.

BW-755C diminishes smoke-induced pulmonary edema

Pulmonary edema following smoke inhalation is due to the chemical toxins in smoke and not to the heat. We have shown that acrolein, a common component of smoke, induces pulmonary edema, perhaps via release of leukotrienes. We, therefore, hypothesized that acrolein, a component of smoke from burning cotton, might have a major role in producing pulmonary edema in sheep after cotton smoke inhalation and that BW-755C, a combined cyclo- and lipoxygenase inhibitor, would prevent the edema, whereas indomethacin, a cyclooxygenase inhibitor, would not. In control anesthetized sheep (n = 7), 128 breaths of cotton smoke induced no change in pulmonary arterial pressure but induced increases (P < 0.05) in pulmonary lymph flow from 4.4 +/- 0.8 (SE) to 15 +/- 2.7 ml/h, lymph protein flux from 0.25 +/- 0.08 to 0.80 +/- 0.16 g/h, and blood-corrected wet-to-dry weight ratios from a normal value of 3.8 +/- 0.07 (n = 9) to 4.5 +/- 0.18. Indomethacin (n = 6) did not significantly prevent these changes, whereas BW-755C decreased lung lymph flow change from 5 +/- 1 to 7 +/- 2 ml/h (P = NS), lymph protein flux from 0.25 +/- 0.08 to 0.35 +/- 0.1 g/h (P = NS), and weight-to-dry ratio from normal to 3.9 +/- 2.1 (P = NS). These data suggest leukotrienes may have a role in producing cotton smoke-induced noncardiogenic pulmonary edema.

Effect of graded increases in smoke inhalation injury on the early systemic response to a body burn

OBJECTIVE

To study the early (first 24 hrs) effect of increasing lung exposure to smoke on the hemodynamic response to a modest body burn.

DESIGN

A prospective randomized study.

SETTING

Laboratory at a university medical center.

SUBJECTS

Thirty-two adult yearling female sheep.

INTERVENTIONS

Adult sheep (n = 32) were given an 18% of body surface burn; 24 sheep were then exposed to cotton toweling smoke using 12 breaths of a tidal volume of 5, 10, or 20 mL/kg. Animals were awakened, resuscitated to baseline oxygen delivery, and then killed at 24 hrs.

MEASUREMENTS AND MAIN RESULTS

Vascular pressure, cardiac output, and oxygen consumption and delivery were measured, as well as blood gases, lung and soft tissue lymph flow, and fluid balance. We found that a 5-mL/kg tidal volume smoke exposure x 12 breaths did not produce significant airway inflammation or alter the cardiopulmonary response to a burn alone. Oxygen consumption (VO2) remained at baseline and the net 24-hr positive fluid balance of 1.5 L was comparable to a burn alone. Increasing the smoke exposure to 10 mL/kg tidal volume, which produced a moderate airway injury, resulted in a significant increase in early fluid requirements, a 40% early increase in VO2, a doubling of positive fluid balance, as well as a marked increase in burn edema. However, gas exchange was not impaired. The 20-mL/kg tidal volume exposure resulted in an early 100% increase in VO2, a three-fold increase in fluid requirements at 1 to 4 hrs, compared with burn alone, in addition to a severe airway inflammation with mucosal slough and resulting impaired gas exchange.

CONCLUSIONS

The addition of a smoke exposure which produces airway inflammation and injury significantly increases early post burn systemic metabolic demands and fluid requirements, as well as the degree of burn edema and positive fluid balance compared with a burn alone. The magnitude of the accentuated response appears to correspond with the degree of airway inflammation and not with alveolar dysfunction.

Plasma copper and iron changes in sheep after left lung inhalation injury: effect of the thromboxane antagonist BM 13.177 (Solutroban)

A significant decline in plasma concentrations of copper and iron were observed in sheep exposed to preferential smoke inhalation of the left lung. The decline was evident 30 minutes after smoke inhalation, and the levels of both trace metals persisted at quite low levels for up to the 18-hour time interval after injury. From that time a gradual recover for copper but not for iron levels was observed so that by 24 hours the levels of copper were in the same range of those at baseline. Copper and iron levels showed an inverse correlation to airway peak and plateau pressures and left lung vascular resistance index and a direct correlation to left lung blood flow. Administration of BM 13.177 (Solutroban), a thromboxane antagonist, before exposure to smoke inhalation protected the sheep from the decline of copper and iron levels in plasma. In these animals airway peak and plateau pressure, left lung vascular resistance, and blood flow were also unmodified. Lipid peroxidation of the lung tissue by oxygen free radicals were lower than in those animals that did not receive BM 13.177. There was likewise a tendency of a decreased wet-to-dry weight ratios in the animals treated with BM 13.177. BM 13.177 treatment in an inhalation injury model might partly protect lung damage and parallels unchanged plasma copper and iron levels. The plasma copper and iron may therefore be an indicator of acute lung damage.

Long-term course of bronchiectasis and bronchiolitis obliterans as late complication of smoke inhalation

We describe the long-term course of a patient with bronchiectasis and bronchiolitis obliterans, both of which developed as late complications of a smoke inhalation injury. Sequential chest X-rays obtained during the observation period showed gradual progression of bronchiectasis from the saccular to the cystic type. Symptoms, spirometry and blood gas analysis, however, remained stable for 15 years. We believe that symptoms and physiological derangement were due mainly to bronchiolitis obliterans, and that once the pathophysiological condition had been established following the initial injury, it could be maintained by conservative medical management.

The effect of inhaled nitric oxide on pulmonary ventilation-perfusion matching following smoke inhalation injury

BACKGROUND

We previously reported that inhaled nitric oxide (NO) improved pulmonary function following smoke inhalation. This study evaluates the physiologic mechanism by which inhaled NO improves pulmonary function in an ovine model.

METHODS

Forty-eight hours following wood smoke exposure to produce a moderate inhalation injury, 12 animals were anesthetized and mechanically ventilated (FIO2, 0.40; tidal volume, 15 mL/kg; PEEP, 5 cm H2O) for 3 hours. For the first and third hours, each animal was ventilated without NO: for the second hour, all animals were ventilated with 40 ppm NO. Cardiopulmonary variables and blood gases were measured every 30 minutes. The multiple inert gas elimination technique (MIGET) was performed during the latter 30 minutes of each hour. The data were analyzed by ANOVA.

RESULTS

Pulmonary arterial hypertension and hypoxemia following smoke inhalation were significantly attenuated by inhaled NO compared with the values without NO (p < 0.05, ANOVA). Smoke inhalation resulted in a significant increase in blood flow distribution to low VA/Q areas (VA/Q < 0.10) with increased VA/Q dispersion. These changes were only partially attenuated by the use of inhaled NO. The SF6 (sulfur hexafluoride) retention ratio was also decreased by inhaled NO. Peak inspiratory pressures and pulmonary resistance values were not affected by inhaled NO.

CONCLUSIONS

Inhaled NO moderately improved VA/Q mismatching following smoke inhalation by causing selective pulmonary vasodilation of ventilated areas in the absence of bronchodilation. This modest effect appears to be limited by the severe inflammatory changes that occur as a consequence of smoke exposure.

Improved ventilatory function in burn patients using volumetric diffusive respiration

BACKGROUND

Volumetric diffusive respiration (VDR) offers theoretical advantages over conventional mechanical ventilation (CV) by using lower airway pressures, recruiting alveoli, and mobilizing secretions.

STUDY DESIGN

Forty-eight thermally injured pediatric patients with failing respiratory status were changed from CV to VDR. Data were obtained just before transition for CV and after stabilization on VDR, within six hours of transition.

RESULTS

Both ventilation and oxygenation were significantly improved with PaCO2 decreasing from 47 +/- 3 to 39 +/- 11 mm Hg and PaO2 increasing from 105 +/- 8 to 171 +/- 12 mm Hg after transition to VDR. Treatment with the VDR ventilator also resulted in a significant decrease in peak inspiratory pressures (PIP) from 52 +/- 2 to 38 +/- 2 cm H2O. The PaO2 to FiO2 ratio increased from 189 +/- 16 using CV, to 329 +/- 21 using VDR, suggesting an improvement in the ventilation and perfusion matching. Ventilatory efficiency, measured by the PaO2/FiO2/PIP ratio, greatly improved after transition from CV to VDR with fraction of inspired oxygen increasing from 3.9 +/- 0.4 to 10.3 +/- 1.0. Hemodynamic function (blood pressure and pulse rate) were not adversely affected by VDR.

CONCLUSIONS

The VDR ventilator is more effective than conventional ventilation for maintaining optimal gas exchange at lower airway pressures in thermally injured pediatric patients.

Role of neutrophils and nitric oxide in lung alveolar injury from smoke inhalation

We examined potential mechanisms responsible for the parenchymal lung injury seen in an animal model of smoke inhalation with concurrent inflammation. Rats injected with sterile glycogen and exposed to smoke generated by the nonflaming pyrolysis of combined Douglas fir wood and polyvinylchloride showed a 74% increase in 125I-albumin lung permeability and a fivefold increase in lung myeloperoxidase (MPO) compared with control rats. There was also a significant increase in plasma indices of oxidative injury in these animals. Compared with control animals, plasma concentrations of thiobarbituric acid reactive substances (TBARS) were elevated by 62%, the concentrations of reduced sulfhydryl groups declined by 37%, and the levels of dinitrophenylhydrazine-reactive proteins (DNPH-RP) were doubled. In addition, the plasma concentrations of nitrate (NO3-) in rats exposed to glycogen plus smoke were increased three times that of control animals. Injection of the nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), immediately after smoke exposure or induction of neutropenia using either nitrogen mustard or antineutrophil antiserum, abolished the increase in concentrations of circulating NO3-, and prevented changes in plasma concentrations of TBARS, DNPH-RP, lung MPO activity, and tissue permeability index. These data suggest that neutrophil activation and the production of nitric oxide-derived oxidants contribute to the lung and plasma indices of oxidative injury in this smoke inhalation model.

The effect of inhaled nitric oxide on smoke inhalation injury in an ovine model

Smoke inhalation is a significant comorbid factor in thermal trauma. The effect of inhaled nitric oxide (NO) on smoke inhalation injury was evaluated in an ovine model. Following smoke exposure, group 1 animals (n = 9) spontaneously breathed room air, and group 2 animals (n = 8) breathed 20 parts per million of NO in air for 48 hours. Cardiopulmonary variables and blood gases were serially measured; bronchoalveolar lavage (BAL) was performed and wet-to-dry lung weight ratios (W/D) determined at 48 hours. Pulmonary vasoconstriction following smoke inhalation was significantly attenuated by inhaled NO (p < 0.05), which exerted no apparent effect on the systemic circulation. In group 2, the serial decline in pulmonary oxygenation was less than in group 1, consistent with a smaller physiologic shunt (p < 0.05). There were no significant differences in W/D, lung compliance, BAL fluid analysis results, or histologic evaluation findings between the two groups. These results suggest that inhaled NO exerted beneficial effects on pulmonary arterial hypertension and oxygenation following smoke inhalation without apparent amelioration of airway inflammation.

Cyclooxygenase and lipoxygenase inhibition by BW-755C reduces acrolein smoke-induced acute lung injury

Inhalation of smoke containing acrolein, the most common toxin in urban fires after carbon monoxide, causes vascular injury with non-cardiogenic pulmonary edema containing potentially edematogenic eicosanoids such as thromboxane (Tx) B2, leukotriene (LT) B4, and the sulfidopeptide LTs (LTC4, LTD4, and LTE4). To determine which eicosanoids are important in the acute lung injury, we pretreated sheep with BW-755C (a combined cyclooxygenase and lipoxygenase inhibitor), U-63557A (a specific Tx synthetase inhibitor), or indomethacin (a cyclooxygenase inhibitor) before a 10-min exposure to a synthetic smoke containing carbon particles (4 microns) with acrolein and compared the results with those from control sheep that received only carbon smoke. Acrolein smoke induced a fall in arterial PO2 and rises in peak inspiratory pressure, main pulmonary arterial pressure, pulmonary vascular resistance, lung lymph flow, and the blood-free wet-to-dry weight ratio. BW-755C delayed the rise in peak inspiratory pressure and prevented the fall in arterial PO2, the rise in lymph flow, and the rise in wet-to-dry weight ratio. Neither indomethacin nor U-63557A prevented the increase in lymph flow or wet-to-dry weight ratio, although they did blunt and delay the rise in airway pressure and did prevent the rises in pulmonary arterial pressure and pulmonary vascular resistance. Thus, cyclooxygenase products, probably Tx, are responsible for the pulmonary hypertension after acrolein smoke and to some extent for the increased airway resistance but not the pulmonary edema. Prevention of high-permeability pulmonary edema after smoke with BW-755C suggests that LTB4, may be etiologic, as previous work has eliminated LTC4, LTD4, and LTE4.

Alterations of pulmonary gas exchange after superimposed carbon monoxide poisoning in acute lung injury

BACKGROUND

Smoke inhalation injury produces substantial morbidity and mortality caused both by immediate catastrophic pulmonary failure and by the subsequent development of pneumonia. Although carbon monoxide (CO) poisoning is present to a degree in nearly all instances of smoke inhalation, the importance of CO in the pathogenesis of smoke inhalation injury remains controversial because smoke contains numerous other potential pulmonary toxins such as aldehydes, chlorine gas, and hydrochloric acid. This study was performed to determine whether CO poisoning acts as a cofactor in the evolution of inhalation injury.

METHODS

Four groups of anesthetized dogs received ventilation with 1% CO in room air alone, intratracheal instillation of 2.0 ml/kg 0.1 N hydrochloric acid (HCl) alone, or acid either immediately or 30 minutes before CO. Ventilation/perfusion relationships were measured for 4 hours thereafter with the multiple inert gas elimination technique.

RESULTS

Acid instillation established 30 minutes before CO poisoning resulted in significantly decreased carboxyhemoglobin concentrations after ventilation with 1% CO in air for 10 minutes. However, CO elimination was markedly delayed in both acid-challenged groups ventilated with CO. Moreover, acid instillation immediately before CO poisoning significantly exacerbated the development of ventilation/perfusion inequality caused by the acid, because the development of shunt was accelerated.

CONCLUSIONS

CO poisoning is an important cofactor in the development of inhalation injury by acceleration of the development of ventilation/perfusion inequality after inhalation.

Unilateral smoke inhalation increases pulmonary blood flow to the injured lung

Smoke inhalation (SI) affects the homogeneity of lung perfusion possibly by increasing alveolar surface tension. Anesthetized dogs (n = 8) were ventilated with a tracheal divider and a dual ventilator. One lung (left or right) was exposed to 5 minutes of SI while the other remained on room air. Total pulmonary blood flow (cardiac output) was measured by thermal dilution and left lung blood flow was measured with an ultrasonic flow probe. Since SI is associated with elevation of alveolar surface tension (AST), we studied a second group of dogs (n = 6) in which AST was increased in one lung with aerosolized dioctyl sodium sulfosuccinate (OT). The OT elevates AST without otherwise damaging the lung. Unilateral SI resulted in systemic hypoxemia (Pao2 fell from 91 +/- 6 to 55 +/- 4 mm Hg) and increased venous admixture (9 +/- 2% to 29 +/- 4%) both of which remained different from baseline values (p < 0.05) for 2 hours. Blood flow to the smoke exposed lung increased gradually and became significantly larger than that to the contralateral normal lung 2 hours following inhalation (smoke lung = 64% +/- 6% and normal lung = 36% +/- 6% of total blood flow). Following smoke exposure, pulmonary vascular resistance (PVR) increased with time in the unexposed normal lung (baseline = 8.7 +/- 1.4; 2 hours post smoke = 22.6 +/- 7.9 mm Hg/L/min, p < 0.05); PVR did not change in the smoke injured lung.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

Smoke inhalation injury

Smoke inhalation injury in children still represents a significant cause of pulmonary disease and mortality. Carbon monoxide and other toxic products of combustion are major determinants of severity. Early hypoxemia is a contributor to over 50% of deaths. There are several clinical entities: upper airway obstruction, bronchospasm, consolidation, pulmonary edema, ARDS, and late pneumonia. Intensive care has improved outcome from burns, but pulmonary injury is still an important cause of mortality. New therapies such as high frequency ventilation may improve the outcome. Primary prevention is the most important way to reduce the poor outcome from significant exposure.

The effects of pentoxifylline on pulmonary function following smoke inhalation

Bronchopulmonary injury secondary to smoke inhalation is a significant comorbid factor following major thermal trauma. The present study evaluates the effects of pentoxifylline (PTX) on pulmonary function in an ovine model of inhalation injury. Following smoke exposure to produce a moderate inhalation injury, 16 animals were divided into two groups. Group 1 animals (n = 8) were untreated; Group 2 animals (n = 8) were treated continuously with pentoxifylline following smoke exposure. The animals were observed in the unintubated, awake state for 48 hr. Cardiopulmonary variables and blood gases were measured serially. Ventilation perfusion distribution (VA/Q), analyzed using the multiple inert gas elimination technique, and bronchoalveolar lavage (BAL) were performed at 48 hr. The wet to dry lung weight ratio was measured following necropsy. In Group 2, the progressive hypoxemia observed following smoke inhalation was attenuated with less VA/Q mismatching than in Group 1 (P < 0.05). Pulmonary hypertension secondary to increased vascular resistance was also attenuated in Group 2 (P < 0.05). In BAL fluid, polymorphonuclear leukocytes, total protein content, and conjugated dienes were less in Group 2 than in Group 1 (P < 0.05). Plasma-conjugated diene levels were also lower in Group 2 at 48 hr. Extravascular lung water and decrease in lung compliance were greater in Group 1. There was less morphologic evidence of airway injury in Group 2 compared to Group 1. The improvement of pulmonary function following treatment with PTX suggests that this agent may be useful in the management of smoke inhalation injury.

Smoke inhalation with a concurrent systemic stress results in lung alveolar injury

Smoke inhalation causes injuries to lung airways, and, at times, alveolar inflammation also develops over approximately 24 h. The pathophysiology of parenchymal lung injuries is unknown, and it is often fatal. We hypothesized that an inflammatory stress remote from the smoke-related lung insult was required for development of alveolar injuries. Spontaneously breathing rats were exposed, head only, to smoke generated by nonflaming pyrolysis (smoldering) of Douglas fir wood (DF), polyvinylchloride (PVC), or the combination of DF+PVC. Intraperitoneal injection of sterile oyster shell glycogen 4 h before smoke inhalation was used as an extra inflammatory stimulus. Histologic examinations revealed extensive airway inflammation in all smoke-exposed groups. Glycogen peritonitis alone caused no lung injuries, and in the absence of glycogen, smoke inhalation caused neither parenchymal lung injuries, assessed by [125I]bovine serum albumin (BSA) leakage, nor neutrophil infiltration, quantified by myeloperoxidase (MPO) activity. However, in rats pretreated with glycogen and studied 24 h after exposure to smoke from burning DF+PVC, [125I]BSA permeability was increased by 232 +/- 41% (SE; n = 13), MPO activity was increased 5-fold, from 2.6 +/- 0.4 (n = 7) to 13.9 +/- 1.4 (n = 19) A460/min/g lung, and histopathologic findings included extensive pulmonary inflammation. We conclude that inhalation of certain types of smoke will trigger pulmonary injury when an inflammatory process remote from the lungs is present.

Effect of increasing the tidal volume of smoke breaths on smoke-induced lung dysfunction

We determined the effect of a graded increase in lung exposure to a toxic smoke by increasing smoke tidal volume (VT) or the number of smoke breaths. Sheep were anesthetized and then insufflated with cooled cotton toweling smoke; VT was 5, 10, or 20 ml/kg, and smoke breaths were varied from 12 to 48. The smoke had a uniform particle size (3 +/- 0.4 microns diam). Peak carboxyhemoglobin levels varied from 8 +/- 2 to 45 +/- 4% in the lowest to highest exposure groups, respectively. Animals were monitored unanesthetized for 24 h, and then they were killed. Oxygenation (ratio of arterial PO2 to fraction of inspire O2) decreased from 480 +/- 21 to 200 Torr, and compliance decreased by approximately 50% in the highest smoke exposure groups, whereas only a modest decrease in oxygenation and no compliance changes were seen with lesser exposures. A moderate tracheobronchitis, some atelectasis, and no alveolar edema were noted in the lower smoke exposure groups, whereas severe tracheobronchitis, airway edema, and alveolar atelectasis were observed in the highest exposure group. Only modest alveolar flooding was noted. Impaired oxygenation and anatomic injury correlated best with the total smoke delivered (r = 0.59). Increasing VT from 5 to 20 ml/kg did not increase airway or alveolar injury if the total smoke mass delivered was maintained constant. The degree of impaired oxygenation did not correlate with measured lung water (r = 0.27) or lung lymph flow (r = 0.31).

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.

Decreased pulmonary damage in primates with inhalation injury treated with high-frequency ventilation

OBJECTIVE

This study compared two forms of high-frequency ventilation (HFV) with conventional volume ventilation (CON) in a primate model of inhalation injury to determine whether ventilatory mode was a determinant of pulmonary damage.

SUMMARY BACKGROUND DATA

The authors previously reported that the prophylactic use of high-frequency flow interruption in patients with bronchoscopically diagnosed inhalation injury requiring mechanical ventilatory support resulted in a significant decrement in mortality. They hypothesized that a reduction in ventilatory mode induced pulmonary damage was in part responsible for their clinical results.

METHODS

Fifteen adult baboons were randomized to one of three ventilatory modes (CON, high-frequency flow interruption [HFFI], or high-frequency oscillatory ventilation [HFO]) after moderate smoke injury. Ventilatory support was tailored to the same physiologic endpoints. After 7 days, the animals were killed and pulmonary pathologic changes were scored and compared. Repetitive physiologic and biochemical data were compared using analysis of variance for repeated measures.

RESULTS

Physiologic endpoints were achieved in CON and HFFI, but not in HFO. Hemodynamic variables did not differ between CON and HFFI. The barotrauma index was greater in CON compared to HFFI (p < 0.05), despite similar PO2, FIO2, AA gradient, and PCO2. Animals treated with HFFI had significantly less parenchymal damage than those treated with CON (p = 0.03) or HFO (p = 0.0008).

CONCLUSIONS

The prophylactic use of HFFI led to a significant decrement in ventilatory mode induced pulmonary damage and offers an explanation for the decreased mortality in inhalation injury patients treated with HFFI.

Does positive end-expiratory pressure significantly reduce airway blood flow?

Nutritive (systemic arterial) airway blood flow (mL/min/100 grams tissue) was studied in various size airways at four randomized levels of positive end expiratory pressure (PEEP) in smoke injured and normal lungs. Seven sheep were studied 24 hours after an isolated injury to the left lung using cotton smoke. Radioactive 15-microns microspheres were utilized to measure this airway blood flow. These data demonstrated a marked increase in systemic arterial blood flow to the airways in the injured left lung. Increasing levels of PEEP significantly reduced this hyperemic response. PEEP did not significantly affect the uninjured right lung. Systemic airway blood flow was never reduced to below normal control levels (uninjured) in either lung despite PEEP of up to 20 cm H2O. Severe reduction in airway nutritive flow, and the possibility of airway necrosis, does not appear to occur at PEEP levels of up to 20 cm H2O.

Smoke inhalation injury

Smoke inhalation injury is a complex of disease processes best understood and treated when defined in terms of the time period after injury. The early phase (0 to 36 hrs) is characterized by diagnosis and treatment of carbon monoxide and cyanide toxicity and by management of early airways edema, bronchorrhea, and bronchoconstriction with aggressive pulmonary toilet. Between 1 and 5 days, the major characteristic is airways mucosal slough, tracheobronchitis, and increasing lung water and impaired gas exchange. Pulmonary toilet and infection control, as well as close management of fluid shifts, is the major treatment. With onset of the inflammation-infection phase, the risk of nosocomial pneumonia increases markedly, as does the impairment in lung function as a result of marked increase in oxygen consumption and CO2 production. Nutrition, stress modification, avoidance of muscle fatigue, and control of infection are the key treatment modalities.

Significant enhancement of carbon dioxide removal by a new prototype IVOX

The intravenacaval blood gas exchanger (IVOX) developed by Cardiopulmonics, Inc. has been tested in animals and in human clinical trials for partial support of gas exchange (25-30%) to allow reduction in mechanical ventilatory support and barotrauma during acute respiratory failure. After recognizing the limitations of the device and limited clinical utility of removing only 25-30% of CO2 production, the authors have made design changes in the IVOX (prototypes IIA and IIB), including increased fiber number, decreased fiber length, decreased fiber diameter, and increased crimping. Nine ewes underwent placement of the IVOX prototypes in an ovine model of severe smoke inhalation injury. A modification of the original insertion technique was used to implant the prototypes. CO2 removal was directly measured from the outlet gas. O2 exchange was calculated from IVOX on/off measurements. Neither IVOX IIA nor IIB significantly changed hemodynamics when a fluid bolus (15 ml/kg) was infused before insertion. There were no significant differences between prototypes regarding thrombosis, emboli, or incidence of bleeding complications. Both prototypes significantly improved CO2 removal (60-80%) compared with that reported for an older IVOX model. The improved gas transfer by these prototypes would serve to decrease mechanical ventilatory requirements and barotrauma in the treatment of severe respiratory failure.