High frequency percussive ventilation in burn patients: hemodynamics and gas exchange

High frequency percussive ventilation (HFPV) is a recent ventilatory mode, which combines conventional cycles with high frequency percussions. HFPV was initially instituted as salvage therapy after acute respiratory failure following smoke inhalation injury achieving in each case a dramatic improvement of blood oxygenation, PaCO(2) and ventilatory pressures. This study investigates the influence of HFPV on hesmodynamics, blood oxygenation and ventilatory parameters in eight stable ICU burn patients requiring artificial ventilatory support during a postoperative period following traumatic injury. Periods of 2h were analysed receiving conventional ventilation and HFPV with a high frequency of 400 and 800 cycles/min. Hemodynamic data were not significantly modified; peak inspiratory pressure was significantly lower under HFPV but mean airway pressure was unchanged. Blood oxygenation and CO(2) elimination were significantly improved under HFPV. No side effects were noted. These observations suggest that HFPV could improve pulmonary gas exchanges under lower peak pressures and without hemodynamic compromise. HFPV could represent an interesting alternative open lung strategy method to improve alveolar recruitment.

Cepharanthin, an alkaloid from Stephania cepharantha, inhibits increased pulmonary vascular permeability in an ovine model of sepsis

Sepsis is a life-threatening event when it occurs in patients suffering from smoke inhalation injury. Pneumonia is one of the most frequent sources of infection in sepsis. Activated leukocytes likely play a role in the pathogenesis of sepsis. Cepharanthin is a biscoclaurine alkaloid that reportedly inhibits the activation of neutrophils. In this study, we investigated the effects of cephranthin on a post-smoke inhalation model of sepsis in sheep. Female sheep (n = 15) were surgically prepared for the study. After 5 days recovery from the operative procedures, tracheostomy was performed in all animals and 48 breaths of cotton smoke (<40 degrees C) were given via a modified bee smoker under halothane anesthesia. After smoke insufflation, Pseudomonas aeruginosa (5 x 109 cfu/kg) was instilled into the airway using a bronchoscope. All of the animals were mechanically ventilated with 100% O(2). Cepharanthin (1.3 mg/kg/h) was infused in five sheep continuously beginning 1 h after the insult and thereafter for the remainder of the 24-h study period. Control animals (n = 6) were treated with 5% dextrose as a vehicle control. Cepharanthin significantly attenuated changes in lung histology as well as in lung wet/dry weight ratio. An in vitro study revealed that cepharanthin inhibited the release of neutrophil elastase from isolated neutrophils stimulated with either formyl-methyl-leucyl-phenylalanine (fMLP) or phorbol myristate acetate with an IC(50) of 60 microM. Cepharanthin also inhibited the fMLP-induced increase in intracellular calcium levels of neutrophils. This result indicates cepharanthin inhibits protein kinase C or a more downstream signaling pathway in neutrophil activation. In conclusion, cepharanthin attenuates acute lung injury and septic shock after smoke inhalation in sheep.

Combined Smoke Inhalation and Scald Burn in the Rat

The combination of burn injury with smoke inhalation from fires significantly increases mortality. The mechanism of increased mortality is poorly understood but has been associated with multiple organ dysfunction syndrome, including cardiac dysfunction. Impaired cardiac function correlates with decreased survival in burn patients. We investigated smoke inhalation from burning cotton combined with a 40% body surface area, third-degree burn during the first 4 hours after injury in rats. In the early phase after injury, burn caused a significant rise in lung neutrophil infiltration but no increase in lung water. Smoke led to a rise in lung water but only a mild increase in neutrophil infiltration. Combined smoke and burn did not increase neutrophil accumulation or lung water above that which occurred with either injury alone. Only in combined smoke and burn was there a drop in cardiac output and stroke volume with pulmonary edema and lung neutrophil influx.

Pathophysiological basis of smoke inhalation injury

Smoke inhalation injury results in serious respiratory failure. When smoke inhalation injury is combined with burn injury or pneumonia, the physiological responses are different and more severe than those of smoke inhalation injury alone. Treatment strategies should be planned based on these pathophysiological aspects.

[Effects of smoke inhalation injury on the phagocytic function of rat alveolar macrophage and on neutrophil apoptosis]

OBJECTIVE

To investigate the effects of smoke inhalation injury on the phagocytic function of rat alveolar macrophages and neutrophil apoptosis.

METHODS

Wistar rats inflicted with smoke inhalation injury were employed in the study. Fifty-four Wistar rats were randomly divided into normal control (N, n = 6) and inhalation injury (I, n = 48) groups. Alveolar macrophages were harvested from the BALF (bronchoalveolar lavage fluid) in I group of rats at 2, 6, 12 and 24 postburn hours (PBHs) and on 2, 3, 4 and 5 postburn days (PBDs). The dynamic change in the phagocytosis of chicken erythrocytes by alveolar macrophages in vitro was observed. The positive rate of myeloperoxidase (MPO) staining of alveolar macrophages (AMs) by MPO staining method was observed, so as to indirectly reflect neutrophil apoptosis and the phagocytosis o apoptotic neutrophils by AMs. Furthermore, the dynamic change in the inflammatory cell apoptosis within BALF was monitored by flow cytometry.

RESULTS

(1) he phagocytosis of chicken erythrocytes by AMs was decreased during early postburn stage (2 - 6 PBHs) but recovered after 12 PBHs. (2) The positive MPO staining of AMs was increased gradually after injury and reached top level at 24 PBHs, but decreased during 2 - 5 PBDs. (3) The apoptotic rate within BALF was around 3.02% - 12.95% and rose to peak value at 24 PBHs.

CONCLUSION

There was increased apoptosis of inflammatory cells within BALF. The resolution process of inflammation after smoke inhalation injury involved neutrophil apoptosis and the phagocytosis of apoptotic neutrophils by AMs.

Environmental insults: smoke inhalation, submersion, diving, and high altitude

In the expanding search for recreation, we spend more and more of our time in various environments. Whether the air is thin or compressed or smoke-filled or there is no air at all, emergency physicians continue to meet and treat the various pulmonary emergencies that the environment may create. The authors present the background, diagnosis, and management of a few of the more common pulmonary emergencies that the environment may produce.

Acute inhalation injury

The lungs can be an efficient means for the absorption of inhaled toxicants, resulting in airway and pulmonary injury or systemic toxicity. Although a few specific antidotes exist for inhaled toxicants, the syndrome of acute inhalation injury and clinical therapeutics are linked by common pathways of pathophysiology. Understanding the mechanisms of inhalation injury and occupation- or situation-specific toxicants can simplify the decision-making process for the out-of-hospital emergency responder and the emergency physician when confronted with a patient and the myriad of potential inhaled toxicants.

Effects of exogenous surfactant supplementation and partial liquid ventilation on acute lung injury induced by wood smoke inhalation in newborn piglets

OBJECTIVE

To investigate the beneficial effects of exogenous surfactant supplementation (ESS) and partial liquid ventilation (PLV) in treating acute lung injury induced by wood smoke inhalation.

DESIGN

A prospective, randomized, controlled, multigroup study.

SETTING

An animal research laboratory at a medical center.

SUBJECTS

Newborn piglets (n = 29; 1.80 +/- 0.06 kg) of either sex.

INTERVENTIONS

Animals were ventilated with a tidal volume of 15 mL/kg, a rate of 30 breaths/min, a positive end-expiratory pressure of 5 cm H(2)O, and an Fio(2) of 1.0. After the induction of acute lung injury by wood smoke inhalation, animals were randomly assigned to receive either conventional mechanical ventilation (CMV) or PLV with or without ESS pretreatment. Animals were grouped as CMV, ESS-CMV, PLV, and ESS-PLV.

MEASUREMENTS AND MAIN RESULTS

Arterial blood gases, cardiovascular hemodynamics, dynamic lung compliance, and total lung injury scores were measured. After smoke inhalation, all four groups displayed similar high arterial carboxyhemoglobin levels, low Pao(2) (<150 mm Hg), and low dynamic lung compliance (<66% of its baseline). In the CMV group, these deleterious conditions remained during the 4-hr observation period, and severe lung injury was noted histologically. All treatment groups demonstrated a significant increase in Pao(2) compared with the CMV group. In addition, both the PLV and ESS-PLV groups displayed significant improvements in dynamic lung compliance and in their histologic outcomes. Nevertheless, none of the variables measured in the PLV group differed from those measured in the ESS-PLV group.

CONCLUSIONS

In a newborn piglet model of smoke inhalation injury, PLV or ESS improved oxygenation. PLV compared favorably with ESS in its greater improvements in lung compliance and lung pathology. However, the combined therapy of ESS and PLV was not clearly superior to PLV alone during the observation period.

P-selectin blockade fails to improve acute lung injury in sheep

Accumulation of neutrophils in the lung contributes to the endothelial damage in the tissue associated with acute respiratory distress syndrome. This initial recruitment of neutrophils within the pulmonary microvasculature may involve P-selectin. Thus we hypothesized that an antibody against P-selectin would reduce pulmonary damage. Sheep were chronically instrumented and prepared. The first group received 40% body surface area third-degree burns with 48 breaths of cotton smoke and 1 mg/kg of anti-(P-selectin) antibody (termed 3D4) 1 h post injury (n = 5). The second group (non-treated) received the same injury but no antibody treatment (n = 6). The third group comprised of sham animals without any injury or antibody treatment (n = 6). Sheep were studied for 48 h during which they were uniformly resuscitated with Ringer's lactate solution by following the Parkland formula. All the animals were mechanically ventilated. In the non-treated injured group, the arterial partial pressure of O(2) ('PaO(2)')/inspired fraction of O(2) ('F(i)O(2)') ratio dropped to 168+/-30 at 48 h, whereas the lung lymph flow increased to an average of 46+/-9 ml/h (10-fold of baseline). These changes were not prevented by an anti-(P-selectin) antibody. The plasma and lymph nitrate/nitrite levels were lower in the antibody-treated group than in the non-treated group. The lymph conjugated dienes were significantly lower in the treated animals. However, lung myeloperoxidase activity and lung tissue conjugated dienes were significantly increased in the treated animals compared with the non-treated injured controls. In conclusion, although the anti-(P-selectin) antibody did not protect against lung injury during the initial 48 h of burn and smoke, it decreased some aspects of injury in the peripheral microcirculation.

Lung function and airway inflammation in rats following exposure to combustion products of carbon-graphite/epoxy composite material: comparison to a rodent model of acute lung injury

Pulmonary function and inflammation in the lungs of rodents exposed by inhalation to carbon/graphite/epoxy advanced composite material (ACM) combustion products were compared to that of a rodent model of acute lung injury (ALI) produced by pneumotoxic paraquat dichloride. This investigation was undertaken to determine if short-term exposure to ACM smoke induces ALI; and to determine if smoke-related responses were similar to the pathogenic mechanisms of a model of lung vascular injury. We examined the time-course for mechanical lung function, infiltration of inflammatory cells into the lung, and the expression of three inflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha), macrophage inflammatory protein-2 (MIP-2) and interferon-gamma (IFN-gamma). Male Fischer-344 rats were either exposed to 26.8-29.8 g/m(3) nominal concentrations of smoke or were given i.p. injections of paraquat dichloride. Measurements were determined at 1, 2, 3, and 7 days post exposure. In the smoke-challenged rats, there were no changes in lung function indicative of ALI throughout the 7-day observation period, despite the acute lethality of the smoke atmosphere. However, the animals showed signs of pulmonary inflammation. The expression of TNF-alpha was significantly increased in the lavage fluid 1 day following exposure, which preceded the maximum leukocyte infiltration. MIP-2 levels were significantly increased in lavage fluid at days 2, 3, and 7. This followed the leukocyte infiltration. IFN-gamma was significantly increased in the lung tissue at day 7, which occurred during the resolution of the inflammatory response. The paraquat, which was also lethal to a small percentage of the animals, caused several physiologic changes characteristic of ALI, including significant decreases in lung compliance, lung volumes/capacities, distribution of ventilation, and gas exchange capacity. The expression of TNF-alpha and MIP-2 increased significantly in the lung tissue as well as in the lavage fluid. Increased MIP-2 levels also preceded the maximum neutrophil infiltration. The differences in the time-course and primary site of TNF-alpha, MIP-2, and IFN-gamma expression; and the differences in the temporal relationship between their expression and infiltration of inflammatory cells may have accounted for the differences in lung function between paraquat treated and ACM smoke exposed animals.

Recombinant antithrombin attenuates pulmonary inflammation following smoke inhalation and pneumonia in sheep

OBJECTIVE

The interaction between coagulation and inflammation has become one of the major topics in critical care medicine. In the present study, we investigated the effect of posttreatment of sepsis with recombinant human antithrombin.

DESIGN

Experimental laboratory in a university hospital.

SETTING

University laboratory.

SUBJECTS

Female merino ewes (n = 16).

INTERVENTIONS

After 1 wk of recovery from the surgical preparation, a tracheotomy was performed followed by insufflation of 48 breaths of cotton smoke (<40 degrees C). Afterward, a stock solution of live (5 x 10(11) colony-forming units) was instilled in the both lung lobes through a bronchoscope. All sheep were mechanically ventilated employing 100% oxygen. An infusion of recombinant human antithrombin (100 units x kg(-1) x 24 hrs(-1), intravenously; n = 6) or saline (n = 6) was started 1 hr after injury. Sham control animals (n = 4) were surgically prepared but not insufflated with smoke and bacteria. Lung histologic changes were evaluated by a scoring system.

MEASUREMENTS AND MAIN RESULTS

The infusion of recombinant human antithrombin maintained the baseline antithrombin activity throughout the study; in the saline-treated group, antithrombin activity decreased significantly. The lung wet/dry weight ratio and the histology score (combined scores for congestion, edema, inflammation, and hemorrhage) were significantly increased by the insult, but recombinant human antithrombin attenuated these responses. More than 30% of both bronchi and bronchioles were obstructed by cast formation after smoke inhalation and pneumonia. The cast was composed of epithelial cells, neutrophils, mucus, and fibrin. The obstruction was significantly improved by recombinant human antithrombin infusion. Arterial pressure and urine output were also attenuated in recombinant human antithrombin-treated animals. The increases in plasma nitrate/nitrite concentrations and pulmonary shunt fraction after the injury were not attenuated by recombinant human antithrombin.

CONCLUSION

Posttreatment by recombinant human antithrombin was effective in treating acute lung injury after smoke inhalation and pneumonia in sheep. We hypothesize that the decrease in antithrombin activity during sepsis might induce severe airway obstruction and that supplementation with antithrombin inhibits this decrease.

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

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

[Comparative efficacy of various massage techniques in the rehabilitation treatment of patients with inhalation trauma early after admission to the hospital]

67 patients with inhalation trauma of 90 patients with acute thermal trauma and 23 healthy controls participated in the trial. External respiration function was assessed on the spirograph SPIROSIFT-3000 (Fukuda Densy, Japan). The injured patients have undergone chest vibromassage (n = 23), vibromassage of Zakhariin-Head zones (trachea-bronchi-lungs) (n = 22), manual chest massage (n = 22). Improvement of clinical and external respiration parameters was more significant in patients exposed to vibromassage of the trachea-bronchi-lungs zones.

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

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

[Clinical analysis of 333 cases of inhalation injury in burned children]

OBJECTIVE

To analyze the clinical features of inhalation injury in children, with the aim of improving its management.

METHODS

The incidence of inhalation injury in 333 cases of burned children was analyzed in terms of burn area, shock, infection and prognosis.

RESULTS

The incidences of shock and bacteremia were 41.14% and 18.92%, and those of moderate and severe inhalation injury were 58.76% and 31.96% respectively in burned children with inhalation injury. Bacteremia developed in 24.82% of the patients with shock. Among 67 patients who ultimately died, 58.21% of them were complicated with bacteremia ending in 34.33% of mortality. Early tracheostomy was beneficial in that less fluids were required for resuscitation.

CONCLUSION

Burn infection was an important factor affecting the prognosis of inhalation injury. And inhalation injury and shock were major inducers of burn infection. Early application of wide spectrum antibiotics and shock management were helpful in lowering of burn infection rate. Early tracheostomy might be beneficial to burn shock management.

Effects of manganese superoxide dismutase, when given after inhalation injury has been established

OBJECTIVES

To determine whether treatment with manganese superoxide dismutase (MnSOD), given intravenously after inhalation injury has been established, improves oxygenation and lung fluid balance.

DESIGN

Randomized, controlled intervention trial.

SETTING

University research laboratory.

SUBJECTS

Twenty-four chronically instrumented awake ewes with lung lymph fistulas.

INTERVENTIONS

After smoke inhalation with 48 breaths of cotton smoke, the animals were assigned randomly to a control group (n = 6) or a treatment group, receiving 1000 units of MnSOD/kg (n = 6), 3000 units of MnSOD/kg (n = 6), or 9000 units of MnSOD/kg (n = 6) intravenously 1 hr after smoke inhalation.

MEASUREMENTS AND MAIN RESULTS

Different from the other three groups, in the group that received 3000 units of MnSOD, cardiac output and Pao2/Fio2 ratio did not significantly decrease throughout the experimental period. Apart from higher oxygen consumption in the group receiving 3000 units of MnSOD 24 hrs after smoke inhalation (263 +/- 44 mL/min vs. 182 +/- 36 mL/min; p < 0.05), no significant differences between treatment groups and control group were observed.

CONCLUSIONS

Treatment with MnSOD given after smoke inhalation seems to be less effective then pretreatment with MnSOD, which was reported in previous studies to reduce the degree of inhalation injury.

[Acute respiratory insufficiency in burn patients from smoke inhalation]

Respiratory injuries by smoke inhalation are one of the most frequent reasons for acute respiratory failure in burn victims. They are most often of chemical origin and are responsible of a 20 to 70% increase of the mortality compared to the mortality of patients with similar burn injuries, but without inhalation lesions. They are often associated to a certain degree to other factors of acute respiratory failure: superior air way obstruction by oedema in face and neck burns, thoracic expansion hindrance due to thoracic burns, lung trauma lesions by blast injury. The generalized inflammatory reaction due to the extent of burns and an initial inadequate resuscitation are worsening factors. The inflammatory process may be responsible of lung injuries similar to those induced by smoke inhalation, even when there is no inhalation. The treatment remains symptomatic and based on the oxygen therapy, mechanical ventilation, prevention of infections and maintain of homeostasis by hydroelectrolytic adequate resuscitation. The nitric oxyde associated to the almitrin allows in a certain number of cases to minimize intra pulmonary shunting and to normalize the VA/O ratio. The development of treatments allowing to modulate inflammatory mediators may lead to news therapies in the future.

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.

Rapid decline in sputum IL-10 concentration following occupational smoke exposure

The acute effects of smoke exposure on inflammatory mediators such as interleukin-10 (IL-10), interleukin-8 (IL-8), and tumor necrosis factor-alpha (TNF-alpha) are not well understood. Our study was designed to measure sputum concentrations of these cytokines in firefighters following low-level smoke exposure. At baseline, participating firefighters underwent blood collection, pulmonary function testing, and sputum induction through inhalation of nebulized hypertonic saline. Study participants later performed overhaul of a structural fire, during which time they wore cartridge respirators and were monitored for smoke exposure. Overhaul involves searching for and extinguishing hidden sources of combustion. One hour following overhaul, blood, pulmonary function data, and induced sputum were again collected. IL-10, IL-8, and TNF-alpha concentrations were measured by enzyme-linked immunosorbent assay (ELISA) in sputum supernatant. In 17 firefighters, baseline sputum IL-10 concentrations were 57.0 +/- 56.8 pg/L, and declined to 16.9 +/- 27.2 pg/L following overhaul (p =.02). No significant changes were observed in sputum IL-8 and TNF-alpha concentrations. Forced vital capacity (FVC) declined significantly in study participants following overhaul. Serum concentrations of Clara-cell protein and surfactant-associated protein A increased significantly following overhaul, indicating increased lung permeability. IL-10 concentrations appear to be exquisitely sensitive to smoke, and studies of IL-10 in sputum should control for recent exposure. Reduced suppression of inflammation by IL-10 may be a mechanism by which low-level smoke exposure causes lung injury.

Interleukin-8, aquaporin-1, and inducible nitric oxide synthase in smoke and burn injured sheep treated with percutaneous carbon dioxide removal

We previously showed that a percutaneous arteriovenous gas exchanger was effective in removing CO2 and reversing respiratory failure in an ovine model of adult respiratory distress syndrome (ARDS) produced by smoke inhalation and burn injury (Alpard et al., Ann Surg 230:215-224, 1999). In this study, we tested the hypothesis that arteriovenous CO2 removal (AVCO2R) lessened endogenous inflammation in the lung. Myeloperoxidase activity, aquaporin-1 (AQP-1), interleukin-8 (IL-8), and inducible nitric oxide synthase mRNAs as well as aquaporin-1, and IL-8 protein were measured in ovine lung tissue. Lung tissue was taken at 96 h (time of sacrifice) from animals with combined smoke inhalation and 40% third degree dermal burn and subsequently treated with AVCO2R or sham (ventilator alone) after onset of ARDS (PaO2:FiO2 ratio of < 200). Myeloperoxidase activity was 1.862 +/- 0.302 U/mg protein in the ventilator group and 0.830 +/- 0.141 in the AVCO2R plus ventilator group. AQP-1 mRNA was 140,482 +/- 31,702 copies/microg total RNA in the ventilator group and 61,854 +/- 22,433 copies/microg total RNA in the AVCO2R plus ventilator group (p = 0.076). mRNA for IL-8 mRNA in the ventilator alone treated animals was 74,000 +/- 3,300 copies/microg total RNA compared to < 1,000 copies/microg total RNA in the ventilator plus AVCO2R group. This result was highly significant (p < 0.001) Inducible nitric oxide synthase mRNA was 7,853 +/- 2,229 copies/microg total RNA for the AVCO2R group and 5,854 +/- 2,070 copies/microg total RNA for the ventilator managed animals. These differences were not statistically significant (p = 0.54). Percutaneous AVCO2R produced a specific decrease in IL-8 in the smoke and burn injured animals. Furthermore, this effect was consistent with cell signaling mechanisms that increase the expression of IL-8 by cyclic stretching and the observed reduction in the number of neutrophils in the lung parenchyma. Therefore, we speculate that the mechanism by which CO2 removal exerts a beneficial effect may be due to both decreases in ventilatory requirements, with an accompanying reduction in alveolar stretching, and reduction of neutrophil numbers in lung tissue.

Pathophysiological analysis of combined burn and smoke inhalation injuries in sheep

We investigated the pathophysiological alterations seen with combined burn and smoke inhalation injuries by focusing on pulmonary vascular permeability and cardiopulmonary function compared with those seen with either burn or smoke inhalation injury alone. To estimate the effect of factors other than injury, the experiments were also performed with no injury in the same experimental setting. Lung edema was most severe in the combined injury group. Our study revealed that burn injury does not affect protein leakage from the pulmonary microvasculature, even when burn is associated with smoke inhalation injury. The severity of lung edema seen with the combined injury is mainly due to augmentation of pulmonary microvascular permeability to fluid, not to protein. Cardiac dysfunction after the combined injury consisted of at least two phases. An initial depression was mostly related to hypovolemia due to burn injury. It was improved by a large amount of fluid resuscitation. The later phase, which was indicated to be a myocardial contractile dysfunction independent of the Starling equation, seemed to be correlated with smoke inhalation injury.

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.

Hemodynamic Stability During Arteriovenous Carbon Dioxide Removal for Adult Respiratory Distress Syndrome: A Prospective Randomized Outcomes Study in Adult Sheep

To evaluate the ability of arteriovenous carbon dioxide removal (AVCO2R) to maintain hemodynamic stability during treatment of adult respiratory distress syndrome (ARDS), we used our smoke/burn, LD40 sheep model of ARDS. With onset of ARDS (PaO2/FiO2 < 200) animals were randomized to AVCO2R (n = 20) or SHAM (n = 8). With AVCO2R, the carotid artery (10-14 F) and jugular vein (14-16 F) were cannulated; SHAM received identical management, sparing the vessels. AVCO2R maintained stable hemodynamics compared to SHAM at 48 hours; heart rate (114.8+/-6.1 vs. 110.1+/-11.0 beats/min.), mean arterial pressure (112+/-5.1 vs. 107.0+/-8.5 mm Hg), cardiac output (7.4+/-0.5 vs. 7.5+/-0.9 L/min.), pulmonary arterial pressure (26+/-2.4 vs. 21+/-1.3 mm Hg), pulmonary arterial wedge pressure (14.1+/-1.8 vs. 14.0+/-1.2 mm Hg), and central venous pressure (7+/-1.6 vs. 8+/-0.9 mm Hg). At 48 hours, AVCO2R allowed significant reductions (p<0.05) in minute ventilation (13.6+/-2.5 to 7.6+/-0.8 L/min); tidal volume (TV) (389.4+/-24.1 to 295.0+/-10.1 ml); peak inspiratory pressure (PIP) (25.4+/-9.2 to 18.8+/-2.5 cm H2O); RR (27.5+/-0.7 to 21.6+/-1.8 breaths/min); and FiO2 (0.96+/-0.00 to 0.48+/-0.2) while normocapnia was maintained. AVCO2R is an effective method of CO2 removal during severe respiratory failure that is hemodynamically well tolerated.

Role of nitric oxide in vascular permeability after combined burns and smoke inhalation injury

Patients with severe burn and/or smoke inhalation injury suffer both systemic and pulmonary vascular hyperpermeability. We hypothesized that nitric oxide (NO) produced by inducible nitric oxide synthase (iNOS) plays a role in the changes in microvascular permeability seen with this injury. To test the hypothesis, we administered mercaptoethylguanidine (MEG), a selective iNOS inhibitor, to conscious sheep subjected to a combined smoke inhalation and third-degree burn injury to 40% of total body surface area. The sheep were surgically prepared for chronic study with lung and prefemoral lymph fistulas in order to estimate microvascular permeability. Both the groups and a control group of animals showed an increase in iNOS protein and message in their lungs. The control animals showed significant increases in either plasma or lymph NO2-/NO3- (NOx) concentration at 24 h after injury, with associated cardiac depression and hemoconcentration. The airway epithelium stained for nitrotyrosine. In the treatment group, NOx did not increase significantly in plasma or lymph throughout the experiment, there was no nitrotyrosine staining, hemodynamic depression was not observed, and the fluid requirement was significantly less than in the control group. Changes in pulmonary microvascular permeability were significantly suppressed by inhibition of iNOS. However, there was no significant difference between the two study groups in the microvascular permeability of burned tissue. These data suggest that NO produced by iNOS plays an important role in the changes in systemic and pulmonary microvascular permeability in combined smoke inhalation/third-degree burn injury, but does not affect the vascular permeability of third-degree-burned tissue in this type of injury.

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.

The effect of inducible nitric oxide synthase (iNOS) inhibition on smoke inhalation injury in sheep

Recent studies on smoke inhalation injury have been focused on nitric oxide (NO) as an essential factor of progressive lung injury. We studied the effects of inducible nitric oxide synthase (iNOS) inhibition on inhalation injury in sheep. Sheep (n = 14) were prepared surgically for chronic study. After recovery period, the sheep received 48 breaths of cotton smoke. The animals were then randomised into two groups: MEG group [30 mg/kg mercaptoethylguanidine (MEG), selective inhibitor of iNOS and peroxynitrite scavenger, was given 1 h after injury and then 8 h for 41 h, n = 7] and control group (0.9% NaCl, n = 7). All animals were ventilated mechanically, and airway blood flow was measured using colored microspheres. In the control group, following significant increase in airway blood flow, deterioration in the PaO2/FiO2 ratio was observed. Whereas in the MEG group, it was not observed. In addition, the MEG group did not show significant increase in pulmonary vascular resistance and intrapulmonary shunt fraction. Lung wet/dry ratios, a marker of pulmonary edema, were significantly lower in the MEG group. At 48 h after injury, lung tissue-conjugated dienes, an index of lung oxidative tissue injury, were significantly lower in the MEG group than in the control group. Our data suggest that 1) iNOS-NO produced in the airway circulation plays a major role on the significant increase in airway blood flow, which may contribute to the spread of injury from injured airway to the lung parenchyma; 2) iNOS-NO induced in the pulmonary circulation contributes to the loss of hypoxic pulmonary vasoconstriction; and 3) iNOS-NO plays an important role on the lung oxidative tissue injury.

[The effects of NAC on the expression and activity of SPA in rats inflicted by smoke inhalation injury]

OBJECTIVE

To investigate the effects of NAC (N-acetyl-L-cysteine) on the expression and activity of SPA (surfactant-associated protein A) in rats inflicted by smoke inhalation injury.

METHODS

Wistar rats inflicted with smoke inhalation injury were employed as the model. The expression of SPA mRNA, the static pulmonary compliance, the surface tension of the alveolar lavage and the morphology of lamellae bodies (LB) of type II alveolar cells were examined.

RESULTS

After the application of NAC, there exhibited an increase in SPA mRNA expression and static pulmonary compliance, and the restoration of the BAL surface tension to normal.

CONCLUSION

The application of NAC could promote the expression of SPA mRNA after smoke inhalation injury and improve the SPA-related function.

New clinically relevant sheep model of severe respiratory failure secondary to combined smoke inhalation/cutaneous flame burn injury

OBJECTIVES

To develop a predictable, dose-dependent, clinically relevant model of severe respiratory failure associated with a 40% total body surface area, full-thickness (third-degree) cutaneous flame burn and smoke inhalation injury in adult sheep.

DESIGN

Model development.

SETTING

Research laboratory.

SUBJECTS

Adult female sheep (n = 22).

INTERVENTIONS

Animals were divided into three groups, determined by the number of smoke breaths administered (24, 36, 48) for a graded inhalation injury. The smoke was insufflated into a tracheostomy with a modified bee smoker at airway temperatures <40 degrees C. All animals concurrently received a 40% total body surface area (third-degree) cutaneous flame burn to the body (flanks). After injury, the animals were placed on volume-controlled ventilation to achieve PaO2 >60 mm Hg and PaCO2 <40 mm Hg. Arterial blood gases and ventilator settings were monitored every 6 hrs postinjury for up to 7 days.

MEASUREMENTS AND MAIN RESULTS

All animals survived the induction of injury. In the 24 smoke breath/40% total body surface area burn (24/40) group, PaO2/F(IO2) never decreased below 300, and peak inspiratory pressure was consistently <14 cm H2O with normal arterial blood gases throughout the observation period. With 36 smoke breaths/40% total body surface area burn (36/40) (n = 7), all animals had PaO2/F(IO2) of <200 and peak inspiratory pressure of 26 cm H2O within 40-48 hrs, as 30% died during the study period. With 48 smoke breaths/40% total body surface area burn (48/40) (n = 12), all animals developed respiratory distress syndrome (RDS) in 24-30 hrs, but none survived the experimental period.

CONCLUSIONS

Development of RDS by smoke and cutaneous flame bum injury depends on smoke inhalation dose. A combination of 36 breaths of smoke and a 40% total body surface area (third-degree) cutaneous flame burn injury can induce severe RDS (PaO2/F(IO2) <200) within 40-48 hrs to allow evaluation of various treatment modalities of RDS.

Effects of an L-selectin antibody on the pulmonary and systemic manifestations of severe smoke inhalation injuries in sheep

Sheep were treated with either lymphocyte adhesion molecule (LAM)1-3, an antibody against L-selectin, (40 mg 1 hour before smoke inhalation and 35 mg 24 hours after smoke inhalation; n = 6) or equivalent volumes of 0.9% saline solution (n = 6). After the smoke inhalation injuries, the PaO2/FIO2 ratio declined in both groups until 40 hours after the injuries, when a trend toward improvement was noted in the group that received LAM1-3. Lung lymph flow increased in both groups until 36 hours after the smoke inhalation injuries and then significantly decreased in the group that received LAM1-3. Forty-eight hours after the smoke inhalation injuries, there was a significant decrease in the ratio of wet-dry lung weight and in preservation of the reflection coefficient in the group that received LAM1-3 (P < .05). Histopathologic examination showed no differences between the groups in the pulmonary morphology associated with smoke inhalation. A reduction in splanchnic blood flow was noted in the control group (P < .05); this reduction was attenuated by treatment with LAM1-3. The delayed pulmonary effects and improved splanchnic blood flow suggested that LAM1-3 attenuated the development of a systemically induced secondary lung injury rather than of the primary lung injury associated with smoke inhalation.

[Smoke poisoning]

SYSTEMIC AND LOCAL EFFECT: Smoke inhalation causes systemic and local, mainly respiratory, toxicity due to the asphyxiant and irritant properties of toxic gases.

OXYGEN DEPRIVATION AND INTOXICATION

The syndrome of oxygen deprivation and intoxication by asphyxiant gases is caused by combustion-induced oxygen deprivation and exposure to carbon monoxide (CO) and cyanide (CN), but also to other toxic gases. A loss of consciousness is a good sign of systemic toxicity; however, the respective role of CO, CN and other toxic gases cannot be determined. The presence of apnea, lactic acidosis, and severe cardiovascular disturbances is consistent with CN poisoning. A correlation exists between blood CO concentration determined on a sample obtained at the site of the fire, and the occurrence and severity of the clinical disorders.

IRRITANT GASES INTOXICATION

This syndrome explains the mucosal injury affecting the eyes and the lungs. These complications are better diagnosed by clinical examination rather than by various investigations such as chest X-ray or fiberoptic bronchoscopy. Dysphonia is always a sign of severe poisoning.

CLINICAL COURSE

In non-burned victims, delayed neurological and respiratory complications can be observed. Oxygen administration is the cornerstone supportive therapy. Hyperbaric oxygen should be discussed according to the severity of the syndrome of oxygen deprivation and intoxication by asphyxiant gases. In case of cyanide poisoning, a safe and effective antidote should be given; hydroxocobalamine seems to be the drug of choice. Supportive treatment is efficient to treat respiratory failure. Endotracheal intubation should be considered in patients exhibiting early dysphonia associated with dyspnea.

Interleukin-8 mediates injury from smoke inhalation to both the lung endothelial and the alveolar epithelial barriers in rabbits

Although prior studies have shown that smoke inhalation causes lung endothelial injury and formation of pulmonary edema, there is no information about the effect of smoke inhalation on the function of the alveolar epithelial barrier. Therefore, the primary objective of this study was to determine the effect of smoke-induced lung injury on the alveolar epithelial barrier in a rabbit experimental model. The second objective was to investigate whether pretreatment with a monoclonal anti-interleukin (IL)-8 antibody prevented alveolar epithelial barrier injury after smoke inhalation. Anesthetized rabbits were tracheotomized and were insufflated with cooled smoke generated from burning cotton cloth (75 breaths). In some experiments, anti-IL-8 antibody or an irrelevant antibody (2 mg/¿g) was given intravenously 5 min before insufflation of cotton smoke. Smoke inhalation caused a significant increase in the alveolar epithelial permeability to protein and a 40% reduction in the fluid transport capacity of the alveolar epithelium. Pretreatment with anti-IL-8 antibody, but not with an irrelevant-isotype antibody, significantly reduced the smoke-mediated increase in bidirectional transport of protein across the alveolar epithelium, and restored alveolar liquid clearance to a normal level. The results of the study show that smoke inhalation causes injury to both the alveolar epithelial barrier and the lung endothelium, and that IL-8 is an important mediator of this injury.

Increased group IV cytosolic phospholipase A2 activity in lungs of sheep after smoke inhalation injury

Increased phospholipase A2 (PLA2) activity was measured in cytosolic fractions of lungs from sheep exposed to smoke from burning cotton or to synthetic smoke consisting of carbon and acrolein, a cotton smoke toxin. Three peaks of PLA2 activity were identified by heparin-Sepharose chromatography. The heparin-nonbinding PLA2 activity was twofold higher in the extracts from lungs exposed to smoke than in normal lungs. This activity was identified as the group IV 85-kDa cytosolic PLA2 (cPLA2). The activities of the forms of PLA2 that bound to heparin did not change after smoke exposure. Those activities showed a pH optimum of 9.0, required a millimolar Ca2+ concentration for full activity, and were inhibited by 5 mM dithiothreitol. One activity eluted at an NaCl concentration typical for group Ib and V PLA2 and had the expected substrate specificity. The other form of lung PLA2 that bound heparin was a group II PLA2. Lung myeloperoxidase activity increased progressively with increased exposure to smoke. cPLA2 was identified in sheep neutrophils. With 30 breaths of smoke exposure, there was an increase in cPLA2 activity without a difference in immunoreactivity on Western blot, indicating that the increased activity was not due to increased amounts of protein. In conclusion, smoke induces increases in resident lung cell cPLA2 activity that is likely responsible for eicosanoid production, leading to lung inflammation and bronchoconstriction.

Neonatal capsaicin treatment alters immediate ventilatory responses to inhaled wood smoke in rats

Neonatal capsaicin treatment chronically ablates unmyelinated C fibers, yet also destroys a small amount of myelinated fibers. Inhalation of wood smoke evokes respiratory reflexes resulting from stimulation of both lung C-fiber nerve endings (unmyelinated afferents) and irritant receptors (myelinated afferents). This study investigated the influences of neonatal capsaicin treatment on the immediate ventilatory responses to inhaled wood smoke in adult rats. Inhalation of wood smoke (approximately 6 ml) via a tracheostomy immediately triggered only an augmented inspiration in 16 rats neonatally treated with capsaicin (50 mg/kg, subcutaneous injection). In contrast, inhaled wood smoke evoked a slowing of respiration in 11 neonatal vehicle-treated rats and an augmented inspiration in another five. The inability to exhibit the slowing of respiration and the persistence of the augmented inspiration in capsaicin-treated rats are consistent with our hypothesis that these two reflex responses originate from stimulation of lung vagal C-fiber afferents and irritant receptors, respectively. Since all capsaicin-treated rats responded to smoke with an augmented inspiration, it is further suggested that neonatal capsaicin treatment selectively impairs the reflex functions of C-fiber afferents and well preserves the reflex functions of lung irritant receptors.

Role of L-selectin in physiological manifestations after burn and smoke inhalation injury in sheep

The effects of a monoclonal antibody against L-selectin [leukocyte adhesion molecule (LAM)1-3] on microvascular fluid flux were determined in conscious sheep subjected to a combined injury of 40% third-degree burn and smoke inhalation. This combined injury induced a rapid increase in systemic prefemoral lymph flow (sQlymph) from the burned area and a delayed-onset increase in lung lymph flow. The initial increase in sQlymph was associated with an elevation of the lymph-to-plasma oncotic pressure ratio; consequently, it leads to a predominant increase in the systemic soft tissue permeability index (sPI). In an untreated control group, the increased sPI was sustained beyond 24 h after injury. Pretreatment with LAM1-3 resulted in earlier recovery from the increased sPI, although the initial responses in sQlymph and sPI were identical to those in the nontreatment group. The delayed-onset lung permeability changes were significantly attenuated by pretreatment with LAM1-3. These findings indicate that both leukocyte-dependent and -independent mechanisms are involved in the pathogenesis that occurs after combined injury with burn and smoke inhalation.

Smoke inhalation injury

Pulmonary injury due to smoke inhalation is a significant cause of death in fire victims. Singed nasal hair and carbonaceous sputum are easily recognized warning signs, but other subtle clues should prompt thorough evaluation and aggressive treatment. Dr Lee-Chiong describes the basic mechanisms of injury and discusses how to assess and manage complications caused by smoke inhalation.

Altered systemic organ blood flow after combined injury with burn and smoke inhalation

Systemic organ blood flow was longitudinally determined with fluorescent microspheres after severe thermal injury in unanesthetized sheep. After chronic instrumentation, 20 sheep were subjected to combined injury with 40% body surface area third-degree burn and 48 breaths of cotton smoke insufflation. During the next 72 h of the experimental period, all animals were resuscitated with Ringer's lactate following the Parkland formula. To test the effect of systemic administration of ibuprofen, animals were assigned to the control group (n=11) or the ibuprofen group (n=9). In the ibuprofen group, animals received ibuprofen as a 12 mg/kg bolus injection 1 h after injury and 6 mg/kg/h as a continuous infusion for the next 47 h. After this combined injury, animals exhibited a biphasic hemodynamic alteration, with an initial shock period and a later hyperdynamic period, a phenomenon often seen in severely burned patients. Among multiple organs, the splanchnic organs exhibited more dominant and sustained decreases in regional blood flow, whereas heart and kidney blood flow were maintained at more than 90% of baseline level even in the initial hypovolemic phase. In the postresuscitation period, no organ except the heart showed increased regional blood flow, despite a more than 20% increase in cardiac output. Ibuprofen had effects on early recovery from the initial shock period, and it improved intestinal organ blood flow, suggesting a potential benefit of this drug for severe thermal injury.

Inhibitory effect of inhaled wood smoke on the discharge of pulmonary stretch receptors in rats

We investigated the inhibition of slowly adapting pulmonary stretch receptors (PSRs) by inhaled wood smoke. Impulses were recorded from PSRs in 68 anesthetized, open-chest, and artificially ventilated rats. Eighty-one of one hundred five PSRs were inhibited within one or two breaths when 6 ml of wood smoke were delivered into the lungs. As a group (n = 105), PSR activity significantly decreased from a baseline of 19.0 +/- 1.3 (SE) to a lowest level of 12.9 +/- 1.2 impulses/breath at the fourth or fifth breath after smoke delivery. This afferent inhibition usually persisted for 5-18 breaths. In contrast, smoke delivery did not affect transpulmonary pressure. Delivery of gas-phase smoke or a hypercapnic gas mixture containing CO2 at a concentration (15%) matching that in the smoke produced a nearly identical inhibition in the same PSRs (n = 10). This afferent inhibition was largely prevented by pretreatment with acetazolamide (an inhibitor of carbonic anhydrase; n = 10) but was not affected by pretreatment with the vehicle for acetazolamide (n = 8) or isoproterenol (a bronchodilator; n = 10). These results suggest that 1) an increase in H+ concentration resulting from hydration of CO2 in the smoke may be responsible for the inhibitory effect of wood smoke on the discharge of PSRs and 2) changes in lung mechanics are not the cause of this afferent inhibition.

Effect of reduced bronchial circulation on lung fluid flux after smoke inhalation in sheep

We determined the effect of reduced bronchial blood flow on lung fluid flux through changes in lung lymph flow, lung wet weight-to-dry weight (wet/dry) ratios, and pulmonary microvascular reflection coefficient (sigma). In the first of two surgical procedures, Merino ewes (n = 21) were surgically prepared for chronic study. Five to seven days later, in a second operation, the bronchial artery of the injection group (n = 7) was ligated, and 4 ml of 70% ethanol were injected into the bronchial artery to cause sclerosis of the airway circulation. In the ligation group (n = 7), only the bronchial artery was ligated. In the sham group (n = 7), the bronchial artery was surgically exposed but left intact without ligation or ethanol injection. One day after these operations the animals received a tracheotomy and 48 breaths of cotton smoke. The value of sigma was determined at two points: 24 h before the second surgical procedure and 24 h after smoke inhalation. Lung lymph flow, blood-gas parameters, and hemodynamic data were measured every 4 h after injury. At the end of investigation, samples of lung were taken for determination of blood-free wet/dry ratio. In the sham group, inhalation injury induced a gradual increase in pulmonary vascular resistance and lung lymph flow, which was associated with deterioration of oxygenation. Reduction of the bronchial blood flow attenuated these pathophysiological changes, and the degree of this attenuation was greater in the injection group than in the ligation group. The value of sigma was significantly higher after smoke inhalation in the injection group compared with the sham group (0.77 +/- 0.04 vs. 0.61 +/- 0.03, means +/- SE) at 24 h. The mean wet/dry ratio value of the injection group animals was 30% less than that of the sham group. Our data show that the bronchial circulation contributes to edema formation in the lung occurring after acute lung injury with smoke inhalation.

The usefulness of combined high-frequency percussive ventilation during acute respiratory failure after smoke inhalation

Inhalation injury and bacterial pneumonia represent some of the most important causes of mortality in burn patients. We describe 11 severely burned patients with acute respiratory failure due to inhalation injury who did not respond adequately to conventional respiratory support. High-frequency percussive ventilation (HFPV) is a recent ventilatory mode, which combines the advantages of conventional ventilation with some of those of high-frequency ventilation. Seven patients developed pulmonary infection during the acute phase; one patient died of multiple organ failure on day 25. All the other patients survived; two developed bronchiolitis obliterans symptoms before discharge. No side-effects were noted and haemodynamic tolerance of HFPV was excellent. Our findings suggest that HFPV can improve pulmonary function and gas exchange in these catastrophic pulmonary failures following inhalation injury.

Prolonged hemodynamic stability during arteriovenous carbon dioxide removal for severe respiratory failure

OBJECTIVE

The effects of prolonged arteriovenous carbon dioxide removal on hemodynamics during severe respiratory failure were evaluated in adult sheep with severe smoke inhalation injury.

METHODS

Adult female sheep (n = 6,33.8 +/- 5.2 kg) were subjected to intratracheal cotton severe smoke insufflation to a mean carboxyhemoglobin level of 83% +/- 3%. Twenty-four hours after injury, a low-resistance 2.5 m2 membrane oxygenator was placed in a carotid-to-jugular pumpless arteriovenous shunt at unrestricted flow to allow complete carbon dioxide removal and reductions in ventilator support. Animals remained conscious, and heart rate, cardiac output, mean arterial pressure, and pulmonary arterial pressure were measured at baseline, after injury, and daily during support with the arteriovenous carbon dioxide removal circuit for 7 days.

RESULTS

All animals survived the study period. Carbon dioxide removal ranged from 99.7 +/- 13.7 to 152.2 +/- 16.2 ml/min, and five (83%) of the six animals were successfully weaned from the ventilator before day 7. During full support with the arteriovenous carbon dioxide removal circuit, shunt flow ranged from 1.24 +/- 0.06 to 1.43 +/- 0.08 L/min and accounted for 20.1% +/- 1.4% to 25.9% +/- 2.4% of cardiac output. No statistically significant changes in heart rate, cardiac output, mean arterial pressure, or pulmonary artery pressure were demonstrated over the study course despite the extracorporeal shunt flow.

CONCLUSIONS

Arteriovenous carbon dioxide removal as a simplified means of extracorporeal gas exchange support is relatively safe without adverse hemodynamic effects or complications.

Lung compliance, airway resistance, and work of breathing in children after inhalation injury

Pathophysiologic changes associated with inhalation injury make mechanical ventilation in children a challenge. Decreased lung compliance and increased airway resistance after inhalation injury may lead to elevated airway pressures and barotrauma. Previous studies have shown significant decreases in the incidence of pneumonia and death in adult patients with inhalation injury treated with high-frequency percussive ventilation (HFPV) as compared with conventional mechanical ventilation (CMV). No studies to date have compared lung compliance, airway resistance, or work of breathing in children being treated with HFPV versus CMV. The purpose of this study was to evaluate lung compliance, airway resistance, and work of breathing in pediatric patients with inhalation injury who required mechanical ventilation. Ten children with bronchoscopically identified inhalation injury requiring mechanical ventilation were studied. Five children received CMV and five children received HFPV. All patients were treated according to our standard inhalation injury protocol. Based on our data and patient population, children receiving ventilation with the HFPV have a significant decrease in the work of breathing as compared with CMV.

Plasma catalase and glutathione levels are decreased in response to inhalation injury

We determined the effect of a severe smoke exposure on plasma oxidant and antioxidant activity. Adult sheep were given a smoke exposure while under anesthesia that produced a carboxyhemoglobin level of 45% +/- 3%. Twelve sheep were studied; six were given smoke alone and volume-resuscitated with sufficient lactated Ringer's solution to maintain baseline hemodynamics. This response was compared with six control sheep during a 6-hour period. The smoke inhalation injury produced a significant increase in plasma hydrogen peroxide and a significant decrease in plasma lipid peroxidation. Circulating lipid peroxidation did not correlate with tissue lipid peroxidation because lung and liver lipid peroxidation were significantly increased. The plasma antioxidants glutathione, catalase, and vitamin E were significantly reduced in response to the injury. Vitamin C remained unchanged from control. Circulatory failure is not a key element in this study, because lactate levels were controlled with volume resuscitation. The degree of smoke inhalation to the airway produced distant organ lipid peroxidation and a decrease in circulating antioxidants--without producing an increase in circulating lipid peroxidation. Maintaining circulating antioxidants may prevent distant organ lipid peroxidation and may be of clinical use in devising treatment strategies for smoke inhalation injury with the availability of antioxidants.

Effects of burns on inhalation injury

BACKGROUND

There are few studies of smoke injury combined with thermal burn.

METHODS

Seven sheep (G1) received smoke injury alone; eight (G2) received a 40% full-thickness scald burn immediately after smoke injury. All animals were resuscitated with lactated Ringer's solution and killed 48 hours after injury. Cardiopulmonary variables and blood gases were measured serially. Ventilation perfusion distribution was analyzed using the multiple inert gas elimination technique. Lung wet to dry weight ratio and malondialdehyde levels were determined.

RESULTS

G2 resulted in early significant hemodynamic changes. Serum total protein concentration was significantly lower and malondialdehyde significantly higher in G2. However, PaO2, lung wet to dry weight ratio, and ventilation perfusion mismatching in G2 did not differ from those in G1.

CONCLUSIONS

Although the addition of burn injury exaggerated the lung lipid peroxidation and hypoproteinemia in the presence of more pronounced hemodynamic changes, the pulmonary dysfunction was not accentuated.

Reflex apneic response evoked by laryngeal exposure to wood smoke in rats: neural and chemical mechanisms

We investigated the neural and chemical mechanisms contributing to the immediate ventilatory responses to laryngeal exposure to wood smoke in anesthetized Sprague-Dawley rats. Five milliliters of wood smoke were delivered into a functionally isolated larynx at a constant flow rate of 1.4 ml/s while the animals breathed spontaneously. Within 1 s after exposure, laryngeal wood smoke consistently triggered an apnea in each of the 42 rats tested. The apneic duration reached 1,636.4 +/- 105.4 (SE) % (n = 42) of the baseline expiratory duration. This apneic response was not affected by denervation of recurrent laryngeal nerves (n = 6) or by removal of smoke particulates (n = 14), but it was totally eliminated by topical application of an anesthetic (n = 8; lidocaine hydrochloride, 8%) to the laryngeal mucosa or by sectioning of the superior laryngeal nerves (n = 42). Furthermore, laryngeal application of a hydroxyl radical scavenger (dimethylthiourea; 500 mg/ml; n = 8) greatly diminished or abolished the smoke-induced apneic response, but it did not affect the apneic response evoked by laryngeal exposure to air saturated with 6% ammonia. These results suggest that the immediate apneic response to laryngeal wood smoke is a reflex resulting from the stimulation of the superior laryngeal afferents by the gas phase of wood smoke and that the stimulation is mediated through a hydroxyl radical mechanism.

Temperature profiles during resuscitation predict survival following burns complicated by smoke inhalation injury

Temperature and resuscitation profiles of 15 non-survivors were compared with matched survivors of major burns. All patients were intubated and ventilated for smoke inhalation injury, survived more than 3 days postburn and had a cutaneous burn greater than 15 per cent of the body surface area (mean 32.3 +/- 11.0 per cent SD). Cases were matched for similar ages (within 10 years) and total body surface area burn (within 10 per cent). The rate of core temperature rise following admission to the burn unit was significantly greater in survivors (mean 0.46 +/0 0.18 degree C/h) compared with matched non-survivors (mean 0.30 +/- 0.15 degrees C/h; p < 0.01). Core temperature increased at a rate of 0.27 degrees C/h or greater in all survivors, whereas 7 non-survivors raised their core temperature at a rate less than this. The rate of skin temperature rise was also significantly greater in the survivors (mean 1.35 +/- 0.91 degrees C/h) compared with matched non-survivors (mean 0.63 +/- 0.43 degrees C/h, p < 0.01). In 13/15 survivors, the skin temperature increased at a rate of 0.6 degree C/h or greater, whereas in 8/15 non-survivors skin temperature increased at a rate less than this. There was a negative relationship between initial core temperature and delay from time of burn to admission to the burns unit in non-survivors (correlation coefficient = -0.92; p < 0.01), whereas there was no effect of delay in the survivors. These findings suggest that patients with a high mortality probability can be detected early in their clinical course by means of temperature profiles.