Role of tidal volume, FRC, and end-inspiratory volume in the development of pulmonary edema following mechanical ventilation

Mechanical ventilation with high peak inspiratory pressure and large tidal volume (VT) produces permeability pulmonary edema. Whether it is mean or peak inspiratory pressure (i.e., mean or end-inspiratory volume) that is the major determinant of ventilation-induced lung injury is unsettled. Rats were ventilated with increasing tidal volumes starting from different degrees of FRC that were set by increasing end-expiratory pressure during positive-pressure ventilation. Pulmonary edema was assessed by the measurement of extravascular lung water content. The importance of permeability alterations was evaluated by measurement of dry lung weight and determination of albumin distribution space. Pulmonary edema with permeability alterations occurred regardless of the value of positive end-expiratory pressure (PEEP), provided the increase in VT was large enough. Similarly, edema occurred even during normal VT ventilation provided the increase in PEEP was large enough. Furthermore, moderate increases in VT or PEEP that were innocuous when applied alone, produced edema when combined. The effect of PEEP was not the consequence of raised airway pressure but of the increase in FRC since similar observations were made in animals ventilated with negative inspiratory pressure. However, although permeability alterations were similar, edema was less marked in animals ventilated with PEEP than in those ventilated with zero end-expiratory pressure (ZEEP) with the same end-inspiratory pressure. This "beneficial" effect of PEEP was probably the consequence of hemodynamic alterations. Indeed, infusion of dopamine to correct the drop in systemic arterial pressure that occurred during PEEP ventilation resulted in a significant increase in pulmonary edema. In conclusion, rather than VT or FRC value, the end-inspiratory volume is probably the main determinant of ventilation-induced edema. Hemodynamic status plays an important role in modulating the amount of edema during lung overinflation but does not fundamentally modify the characteristics of this edema which is consistently associated with major permeability alterations. These results may be relevant for ventilatory strategies during acute respiratory failure.

Early detection of type III procollagen peptide in acute lung injury. Pathogenetic and prognostic significance

The fibroproliferative reaction to acute lung injury may limit restoration of normal lung function and increase mortality in patients with acute lung injury. A biologic marker of collagen synthesis in the lung may be useful for studying the pathogenesis of acute lung injury and for identifying patients with acute lung injury who are at high risk for death and might benefit from new therapeutic modalities. Using an immunoassay, type III procollagen NH2 terminal peptide was measured in the pulmonary edema fluid of 44 patients with either acute lung injury or hydrostatic pulmonary edema (control group) within the first 24 h after endotracheal intubation for acute respiratory failure. Patients with acute lung injury (n = 33) or hydrostatic edema (n = 11) had the same degree of lung dysfunction as measured by the severity of oxygenation defect, the level of positive end-expiratory pressure, the decrease in static lung compliance, and the extent of infiltrates on the chest radiograph. However, the median procollagen III level was 5-fold higher in the pulmonary edema fluid of patients with acute lung injury than in the patients with hydrostatic pulmonary edema (p = 0.0001). Of the 33 patients with acute lung injury, 21 patients died and 12 lived. Nonsurvivors had significantly higher procollagen III levels than did survivors (p = 0.05). The positive and negative predictive values for nonsurvival for a procollagen III level > or = 1.75 U/ml were 74 and 83%, respectively. The relative risk of dying in the presence of a procollagen III value > or = 1.75 U/ml was 4.5 (95% CI, 0.7 to 27). Collagen synthesis in the lung, as reflected by elevated levels of procollagen III in pulmonary edema fluid, begins within the first 24 h of acute lung injury concurrent with the acute phase of increased endothelial and epithelial permeability to protein. This evidence suggests that fibrosing alveolitis begins much earlier in the course of clinical acute lung injury than has previously been appreciated. In addition, the presence of an elevated level of procollagen III is an early predictor of poor outcome. Thus, elevation of procollagen III in pulmonary edema fluid may have both pathogenetic and prognostic significance in patients with acute lung injury.

A Simple Method for Estimating Respiratory Solute Dilution in Exhaled Breath Condensates

Exhaled breath condensates have been widely used to detect inflammatory mediators in the fluid that covers airway surfaces of patients with inflammatory lung disorders. This approach is much less invasive than bronchoalveolar lavage, but respiratory droplets are markedly diluted by large and variable amounts of water vapor. We estimated the dilution of respiratory droplets by comparing concentrations of nonvolatile, reference indicators (total nonvolatile cations, urea or conductivity) in 18 normal subjects with normal plasma concentrations by assuming similar concentrations in the respiratory fluid and plasma. The volatile cation, NH4+ (most of which is delivered as NH3 gas from the mouth), represented 93 +/- 3% (SEM) of the condensate cations. More than 99% of the NH4+ was removed by lyophilization, making it possible to use conductivity to estimate total nonvolatile ionic concentrations and facilitating analysis of urea. Conductivity was significantly correlated with electrolyte and urea concentrations. Estimates of dilution based on total cations, conductivity, and urea were not significantly different (cations: 20,472 +/- 2,516; conductivity: 21,019 +/- 2,427; and urea: 18,818 +/- 2,402). These observations suggest that the conductivity of lyophilized samples can be used as an inexpensive, simple, and reliable method for estimating dilution of nonvolatile, hydrophilic mediators in condensates.

Atelectasis causes gas exchange impairment in the anaesthetised horse

The anatomical basis of gas exchange impairment in the anaesthetised horse was studied by computerised tomography (CT; three shetland ponies) and morphological analysis (one pony and three horses). By means of CT, densities were seen in dependent lung regions early during anaesthesia, both with spontaneous breathing and with mechanical ventilation. The densities remained for some time where they had initially been created when the animal was turned from dorsal to sternal recumbency. Deep insufflation of the lungs reduced the dense area. Gas exchange was impaired roughly in proportion to the dense area. On histological analysis, the densities were atelectatic and congested with blood. Gravimetry showed no more extravascular water per unit lung tissue in the atelectatic than in the 'normal' regions, and the blood content was increased only slightly. It is concluded that the horse develops atelectasis in dependent lung regions early during anaesthesia in dorsal recumbency, and that atelectasis is the most likely explanation for the large shunt and impaired arterial oxygenation regularly seen during anaesthesia.

Exhaled breath condensate in children: pearls and pitfalls

Exhaled breath condensate (EBC) is a rapidly growing field of research in respiratory medicine. Airway inflammation is a central feature of chronic lung diseases, like asthma, cystic fibrosis, bronchopulmonary dysplasia and primary ciliary dyskinesia. EBC may be a useful technique for non-invasive assessment of markers of airway inflammation. The non-invasive character of EBC "inflammometry" and the general lack of appropriate techniques makes it particularly interesting for paediatrics. We provide a detailed update on the methods currently used for EBC collection and measurement of mediators. We emphasize on paediatric data. The apparent simplicity of the EBC method must not be overstated, as numerous methodological pitfalls have yet to overcome. Comparison and interpretation of data on this rapidly growing field of research is mainly hampered by the lack of standardization and the lack of specific high-sensitivity immunochemical or colorimetric assays. The initiative of the European Respiratory Society to institute a task force on this topic is a first step towards a uniform technique of EBC. Meanwhile, when using this technique or when interpreting research data, one should be fully aware of the possible methodological pitfalls.

Steady-state intrapulmonary concentrations of moxifloxacin, levofloxacin, and azithromycin in older adults

STUDY OBJECTIVE

To determine the steady-state, extracellular, and intracellular pulmonary disposition of moxifloxacin (MXF), levofloxacin (LEVO), and azithromycin (AZI) relative to that of the plasma over a 24-h dosing interval.

DESIGN

Randomized, multicenter, open-label investigation.

PATIENTS

Forty-seven older adults (mean [+/- SD] age, 62 +/- 13 years) undergoing diagnostic bronchoscopy.

INTERVENTIONS

Oral administration of MXF, 400 mg, LEVO, 500 mg daily for five doses, or AZI, 500 mg for one dose, then 250 mg daily for four doses. BAL and venipuncture were completed at 4, 8, 12, or 24 h following the administration of the last dose.

MEASUREMENTS AND RESULTS

Steady-state MXF, LEVO, and AZI concentrations were determined in the plasma, epithelial lining fluid (ELF), and alveolar macrophages (AMs). The concentrations of all three agents were greatest in the AMs followed by the ELF compared to the plasma. Plasma concentrations were similar to those previously reported with these agents. The mean ELF concentrations at 4, 8, 12, and 24 h were as follows: MXF, 11.7 +/- 11.9, 7.8 +/- 5.1, 10.5 +/- 3.7, and 5.7 +/- 6.3 micro g/mL, respectively; LEVO, 15.2 +/- 4.5, 10.2 +/- 6.7, 6.9 +/- 4.4, and 2.9 +/- 1.7 micro g/mL, respectively; and AZI, 0.6 +/- 0.4, 0.7 +/- 0.4, 0.9 +/- 0.5, and 0.9 +/- 0.7 micro g/mL, respectively. The AM concentrations at 4, 8, 12, and 24 h were as follows: MXF, 47.7 +/- 47.6, 123.3 +/- 126.4, 26.2 +/- 19.4, and 32.8 +/- 16.5 micro g/mL, respectively; LEVO, 28.5 +/- 30.2, 26.1 +/- 15.7, 28.3 +/- 12.6, and 8.2 +/- 6.1 micro g/mL, respectively; and AZI, 71.8 +/- 50.1, 73.8 +/- 75.3, 155.9 +/- 81.3, and 205.2 +/- 256.3 micro g/mL, respectively.

CONCLUSIONS

The intrapulmonary concentrations of MXF, LEV, and AZI were superior to those obtained in the plasma. The AM concentrations of all agents studied were more than adequate relative to the minimum concentration required to inhibit 90% of the organism population (MIC(90)) of the common intracellular pathogens (< 1 micro g/mL). These data indicate that attainable extracellular concentrations of AZI are insufficient to reliably eradicate Streptococcus pneumoniae, based on the agent's current minimum inhibitory concentration profile, whereas the mean concentrations of MXF and LEVO in the ELF exceed the MIC(90) of the S pneumoniae population. Moreover, MXF concentrations exceeded the S pneumoniae susceptibility breakpoint (1.0 micro g/mL) at all time points, while 2 of 15 concentrations (13%) failed to maintain LEVO concentrations above the breakpoint (2.0 micro g/mL) throughout the dosing interval.

Cadaver lung donors: effect of preharvest ventilation on graft function

The pulmonary donor pool would increase substantially if lungs could be safely transplanted after cessation of circulation. To determine whether ventilation of cadaver lungs could improve graft function, canine donors were sacrificed and then ventilated with 100% oxygen (n = 6) or 100% nitrogen (n = 6); 6 served as nonventilated controls. Four hours after death, the lungs were flushed with modified Euro-Collins solution and harvested. Controls were ventilated with 100% oxygen only during flush and harvest. Recipients were rendered dependent on the transplanted lung by occlusion of the right pulmonary artery and bronchus 1 hour after transplantation. Ventilation was maintained at a constant inspired oxygen fraction of 0.4. Four controls died of pulmonary edema shortly after occlusion of the native lung. The mean arterial oxygen tensions in the oxygen-ventilated, nitrogen-ventilated, and control groups at the end of 8 hours were 81 mm Hg (n = 4), 88 mm Hg (n = 3), and 55 mm Hg (n = 2), respectively. Postmortem oxygen ventilation improved early recipient survival and gas exchange. Postmortem nitrogen ventilation improved early gas exchange and delayed recipient death compared with non-ventilated controls. The mechanics of ventilation appears to confer a functional advantage independent of a continued supply of oxygen. Transplantation of lungs harvested from cadavers after cessation of circulation might be feasible.

Aerosolized beta(2)-adrenergic agonists achieve therapeutic levels in the pulmonary edema fluid of ventilated patients with acute respiratory failure

OBJECTIVE

Experimental studies demonstrate that beta-adrenergic agonists markedly stimulate alveolar fluid clearance if concentrations of 10(-6) M are achieved in alveolar fluid. However, no studies have determined whether aerosolized beta-adrenergic agonists are delivered to the distal air spaces of the lung in therapeutic concentrations in patients with pulmonary edema.

DESIGN AND SETTING

This retrospective study measured albuterol levels in the pulmonary edema fluid and plasma from mechanically ventilated patients with pulmonary edema from a hydrostatic mechanism ( n=10) or from acute lung injury ( n=12).

MEASUREMENTS AND RESULTS

After a total aerosolized albuterol dose of 4.2+/-3.2 mg in the prior 6 h the median pulmonary edema fluid albuterol level was 1,250 ng/ml (10(-6) M) in patients with hydrostatic pulmonary edema; after 3.5+/-2.6 mg the figure was 1,240 ng/ml (10(-6) M) in patients with pulmonary edema from acute lung injury. Plasma albuterol levels were much lower, with a median of 5.2 ng/ml (0.01 x 10(-6) M) in patients with hydrostatic pulmonary edema and 3.1 ng/ml (0.01 x 10(-6) M) in patients with pulmonary edema from acute lung injury.

CONCLUSIONS

These results provide the first evidence that levels of beta-adrenergic agonists that are physiologically efficacious in experimental models can be achieved with conventional delivery systems in ventilated, critically ill patients with acute respiratory failure from pulmonary edema.

Adrenal epinephrine increases alveolar liquid clearance in a canine model of neurogenic pulmonary edema

Case reports of neurogenic pulmonary edema (NPE) often indicate that the edema resolves quickly. Because plasma epinephrine concentration may be elevated in NPE, and epinephrine has been shown to increase the rate of alveolar liquid clearance (ALC), we determined if ALC was increased in a canine model of NPE produced by the intracisternal administration of veratrine. ALC was determined by instilling autologous plasma into a lower lung lobe and using the increase in instillate protein concentration after 4 h to calculate the volume of fluid cleared from the airspaces by mass balance. To prevent pulmonary hypertension and edema, which would confound the mass balance analysis, carotid arterial blood was allowed to drain into a reservoir as pulmonary arterial pressure started to rise after veratrine administration. ALC in animals administered veratrine (n = 6) was 30.4 +/- 1.6 (SE)% of the instilled volume compared with 14.1 +/- 2.1% observed in control animals. The increase in ALC could be inhibited by adrenalectomy, beta2-adrenergic blockade using ICI 118,551, or sodium channel blockade using amiloride and could be duplicated by infusing epinephrine to increase plasma epinephrine concentration to levels observed in NPE. These data indicate that the increased ALC was mediated by adrenal epinephrine and suggest that edema resolution in patients with NPE might be accelerated by endogenous epinephrine.

Alveolar granulocyte colony-stimulating factor and alpha-chemokines in relation to serum levels, pulmonary neutrophilia, and severity of lung injury in ARDS

OBJECTIVES

To determine granulocyte colony-stimulating factor (G-CSF), epithelial neutrophil-activating peptide (ENA)-78, and interleukin (IL)-8 in BAL fluid (BALF), epithelial lining fluid (ELF), and serum for establishing the concentration gradient of G-CSF, ENA-78, and IL-8 between the blood and the alveolar space in ARDS and acute lung injury (ALI); and to evaluate the relationship of G-CSF, IL-8, and ENA-78 to pulmonary neutrophilia and severity of lung injury.

DESIGN

Prospective study.

SETTING

An adult trauma/surgical ICU.

PATIENTS

Nineteen patients with ARDS and 10 patients with ALI.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

BAL and blood sampling simultaneously within 12 h and 24 h after onset of ARDS/ALI; G-CSF was detected in BALF in 18 of 19 patients with ARDS, in 7 of 10 patients with ALI, and in all serum samples. G-CSF in BALF and serum was significantly higher in ARDS than in ALI. ENA-78 was detected in BALF in 14 of 19 patients with ARDS, in 8 of 10 patients with ALI, and in serum of all patients. Levels in BALF and serum were not different between ARDS and ALI. IL-8 was detected in all patients; concentrations in BALF in ARDS were significantly higher than in ALI. Concentrations of G-CSF, ENA-78, and IL-8 in ELF were significantly higher than in serum. G-CSF in BALF and serum and IL-8 in BALF correlated positively with pulmonary neutrophilia. G-CSF in serum and IL-8 in BALF correlated negatively with PaO(2)/fraction of inspired oxygen (FIO(2)) ratio. However, ENA-78 did not show a correlation with neutrophil count or with PaO(2)/FIO(2) ratio.

CONCLUSIONS

G-CSF may be pathophysiologically important for accumulation and activation of neutrophils in ARDS. Local G-CSF production is the likely driving force for neutrophils rather than elevation of circulating levels. In comparison to ENA-78, IL-8 seems to be the predominant neutrophil chemoattractant in the early phase of ARDS.

Pulmonary interstitial pressure in anesthetized paralyzed newborn rabbits

In anesthetized paralyzed term newborn rabbits at various postgestational ages (from birth up to 16 days), we measured by micropuncture technique the hydraulic pressure of the pulmonary interstitium (Pip), the extrapleural parietal interstitium, and the pleural liquid. Birth data refer to cesarian-delivered nonbreathing rabbits. Pip increased from 0.5 +/- 2 to 6 +/- 0.7 cmH2O from birth up to 2 h and then decreased, becoming subatmospheric at 5 h and attaining -6 +/- 1.6 cmH2O at 16 days. Over the same period of time, pressure in the extrapleural parietal interstitium and the pleural liquid remained fairly constant at an average value of approximately -1.5 and -2 cmH2O, respectively. The wet-to-dry weight ratio of the lungs decreased from 7.8 +/- 0.4 to 4.9 +/- 0.1 at 16 days. Plasma protein concentration was 4.2 +/- 0.4 g/dl at birth, decreased to 3.2 +/- 0.5 g/dl at 1 h from delivery, and increased back to 4 +/- 0.6 g/dl at 16 days. Pleural liquid protein concentration was 3 +/- 0.1 g/dl at birth and decreased to 1.2 +/- 0.2 g/dl at 16 days. In the first hours of postnatal life, the marked increase in Pip appears to be a key factor in favoring fluid clearance from pulmonary interstitium into the pulmonary capillaries and the pleural space. This factor vanishes after approximately 6 h because of the marked decrease in Pip.

Elevated levels of interleukin-8 and leukotriene B4 in pulmonary edema fluid of a patient with reexpansion pulmonary edema

We experienced a case of reexpansion pulmonary edema (RPE) after surgical treatment of pneumothorax. In this case, protein leakage and polymorphonuclear leukocyte (PMN) accumulation were observed in the reexpanded lung. Interleukin-8 and leukotriene B4 in edema fluid were increased at the onset of RPE. PMN elastase was also increased, though its peak was delayed. The plasma level of P-selectin, which mediates adhesion between PMN and endothelium, was elevated. We speculate that some of these fluid mediators may play important roles in chemotaxis and activation of PMN in the development of RPE.

Lung management during cardiopulmonary bypass: influence on extravascular lung water

Progressive respiratory insufficiency secondary to cardiopulmonary bypass (CPB) is still a hazard after cardiac surgery. Pathophysiologically, impaired capillary endothelial integrity seems to be the fundamental lesion, followed by increased interstitial fluid accumulation. The reasons for this pulmonary damage are controversial; however, management of the nonperfused lungs during CPB has been widely neglected and may be partly responsible. In this study, 90 patients undergoing coronary artery bypass grafting were randomly divided into six groups (15 patients each) with different management of the lungs during CPB: group 1, lungs collapsed (0/0); group 2, static inflation with +5 cm H2O and F1O2 1.0 (+5/1.0); group 3, static inflation with +5 cm H2O and F1O2 0.21 (+5/0.21); group 4, static inflation with +15 cm H2O and F1O2 1.0 (+15/1.0); group 5, static inflation with +15 cm H2O and F1O2 0.21 (+15/0.21); and group 6, controlled mechanical ventilation as before start of CPB (positive end-expiratory pressure [PEEP] +5 cm H2O; F1O2 1.0) (ventilation). In addition to hemodynamic monitoring, extravascular lung water (EVLW) was measured by means of a double-indicator dilution technique with heat and indocyanine green. Measurements were performed after induction of anesthesia, before onset of CPB, and immediately after weaning from bypass, as well as 60 minutes and 5 hours after termination of CPB. Pulmonary gas exchange (PaO2) and intrapulmonary shunting (Qs/Qt) were also measured. Starting from comparable, normal baseline values, EVLW was increased in all groups after weaning from CPB, with the most pronounced increase in group 4 (maximum, +35%) and group 5 (+40%).(ABSTRACT TRUNCATED AT 250 WORDS)

Immediate application of positive-end expiratory pressure is more effective than delayed positive-end expiratory pressure to reduce extravascular lung water

OBJECTIVE

To determine by the measurement of extravascular lung water (EVLW) whether the timing of positive-end expiratory pressure (PEEP) application influences the intensity of lung injury.

DESIGN

Animal experimental study.

SETTING

Animal experimental laboratory.

SUBJECTS

Mixed-breed pigs (n = 18), aged 4 to 5 mos, weighing 25 to 30 kg.

INTERVENTIONS

The animals were anesthetized and tracheotomized, after which a permeability pulmonary edema was instigated by infusing oleic acid (0.1/kg) into the central vein. All animals were then randomly divided into three groups. In group 1 (n = 5), 10 cm H2O of PEEP was applied immediately after the oleic acid infusion and maintained throughout the 6 hrs of the experiment. Group 2 (n = 7) received the same level of PEEP 120 mins after the insult for 4 hrs. Group 3 (n = 6), the control group, was ventilated without PEEP for the six hrs of the experiment.

MEASUREMENTS AND MAIN RESULTS

At the end of the experiment, EVLW was calculated by gravimetric method. EVLW in group 1 (11.46+/-2.00 mL/kg) was significantly less than in group 2 (19.12+/-2.62 mL/kg) and group 3 (25.81+/-1.57 mL/kg), (p<.0001). Oxygenation also showed important differences by the end of the experiment when the Pao2/Fio2 ratio was significantly better in group 1 (467+/-73) than in group 2 (180+/-82) and group 3 (39+/-9), (p<.0001).

CONCLUSIONS

The application of 10 cm H2O of PEEP reduces EVLW in a time-dependent manner and maximum protective effect is achieved if it is applied immediately after lung injury production.

A novel leukotriene B4-receptor antagonist in endotoxin shock: a prospective, controlled trial in a porcine model

OBJECTIVE

To evaluate the hypothesis that treatment with LY255283, a novel leukotriene B4-receptor antagonist, is beneficial in an animal model of the adult respiratory distress syndrome induced by endotoxin.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Laboratory at a large university medical center.

SUBJECTS

Twenty-five, immature, random-bred swine.

INTERVENTIONS

Four groups of pigs were studied: the LPS group of animals (n = 6) were infused with Escherichia coli lipopolysaccharide (strain 0111:B4, 250 micrograms/kg) from 0 to 60 mins; the LPS + 255283 group of animals (n = 6) were infused with lipopolysaccharide as above, but were also treated with LY255283 (30 mg/kg, then 10 mg/kg/hr), beginning at -15 mins; the 255283 group of animals (n = 6) were infused with the same dose of LY255283, but were not challenged with lipopolysaccharide; and the RL control group of subjects (n = 7) received only the lactated Ringer's solution vehicle. Beginning at 30 mins, all groups were infused with dextran-70 solution as needed to maintain cardiac output at 90% to 110% of baseline value.

MEASUREMENTS AND MAIN RESULTS

Treatment with LY255283 significantly (p < .05) ameliorated lipopolysaccharide-induced systemic arterial hypotension, pulmonary arterial hypertension, and arterial hypoxemia. Treatment with this drug also abrogated lipopolysaccharide-induced increases in pulmonary extravascular water content and bronchoalveolar lavage fluid protein concentration.

CONCLUSIONS

These data suggest that leukotriene B4 may be an important mediator of acute lung injury in this porcine model of septic shock and acute lung injury. Further studies to assess the specificity of LY255283 as a leukotriene B4 antagonist are necessary in order to exclude the possibility that the beneficial effects of this compound are due to pharmacologic actions other than the blockade of LTB4 receptors.

Local Pseudomonas instillation induces contralateral lung injury and plasma cytokines

We investigated whether local bacterial instillation leads to lung injury in noninstilled lung regions and examined local and systemic cytokine accumulation. Rats were challenged by intrabroncheal instillation of Pseudomonas aeruginosa, 10(7) colony-forming units (CFU) (HD group, n = 11), 4 x 10(6) CFU (LD group, n = 10), or saline (control group, n = 12). 99mTc-labeled macroaggregated albumin was added to the P. aeruginosa or saline solution for later documentation of the instilled area. At 4 h the right lung, including instilled segment, and the left lung were sampled. Lung injury was assessed by lung tissue to plasma 125I-labeled albumin (T/P) and lung wet-dry (W/D) ratios. We measured plasma and bronchoalveolar lavage fluid (BALF) levels of tumor necrosis factor (TNF) and cytokine-induced neutrophil chemoattractant (CINC). HD bacterial instillation induced neutrophil recruitment and TNF and CINC elevation in BALF (p < 0.05) associated with increased T/P (p < 0.005) and W/D (p < 0.05) ratios in both instilled and the noninstilled lungs as compared with the saline-instilled and noninstilled controls. LD bacterial instillation induced neutrophil recruitment and TNF and CINC elevation only in the instilled lung (p < 0.05), and not in the noninstilled lung, and did not increase the T/P or W/D ratio. Plasma levels of TNF and CINC were increased in the HD, but not the LD, group when compared with the saline controls (p < 0.05). These data indicate that, when the dose is high enough to cause an excess inflammatory response, local bacterial instillation leads to neutrophil sequestration, lung injury, and cytokine elevation in the noninstilled lung associated with systemic cytokine release.

The nitric oxide synthase cofactor tetrahydrobiopterin reduces allograft ischemia-reperfusion injury after lung transplantation

OBJECTIVE

Exogenous nitric oxide reduces ischemia-reperfusion injury after solid organ transplantation. Tetrahydrobiopterin, an essential cofactor for nitric oxide synthases, may restore impaired endothelium-dependent nitric oxide synthesis. We evaluated whether tetrahydrobiopterin administration to the recipient attenuates lung reperfusion injury after transplantation in swine.

METHODS

Unilateral left lung transplantation was performed in 15 weight-matched pigs (24-31 kg). Donor lungs were flushed with 1.5 L cold (1 degrees C) low-potassium-dextran solution and preserved for 20 hours. Group I animals served as controls. Group II and III animals were treated with a bolus of tetrahydrobiopterin (20 mg/kg). In addition, in group III a continuous infusion of tetrahydrobiopterin (10 mg/kg per hour over 5 hours) was given. One hour after reperfusion, the recipient right lung was occluded. Cyclic guanosine monophosphate levels were measured in the pulmonary venous and central venous blood. Extravascular lung water index, hemodynamic variables, lipid peroxidation, and neutrophil migration to the allograft were assessed.

RESULTS

In group III a significant reduction of extravascular lung water was noted in comparison with the controls (P =.0047). Lipid peroxidation in lung allograft tissue was significantly reduced in group II (P =.0021) and group III ( P =. 0077) in comparison with group I. Pulmonary venous levels of cyclic guanosine monophosphate increased up to 23 +/- 1 pmol/mL at 5 hours in group II and up to 40 +/- 1 pmol/mL in group III (group I, 4.1 +/- 0.5 pmol/mL [I vs III]; P <.001), whereas central venous levels of cyclic guanosine monophosphate were unchanged in all groups.

CONCLUSION

Tetrahydrobiopterin administration during lung allograft reperfusion may reduce posttransplantation lung edema and oxygen-derived free radical injury in the graft. This effect is mediated by local enhancement of the nitric oxide/cyclic guanosine monophosphate pathway.

Pulmonary fluid flow challenges for experimental and mathematical modeling

Modeling the flow of fluid in the lungs, even under baseline healthy conditions, presents many challenges. The complex rheology of the fluids, interaction between fluids and structures, and complicated multi-scale geometry all add to the complexity of the problem. We provide a brief overview of approaches used to model three aspects of pulmonary fluid and flow: the surfactant layer in the deep branches of the lung, the mucus layer in the upper airway branches, and closure/reopening of the airway. We discuss models of each aspect, the potential to capture biological and therapeutic information, and open questions worthy of further investigation. We hope to promote multi-disciplinary collaboration by providing insights into mathematical descriptions of fluid-mechanics in the lung and the kinds of predictions these models can make.

Protective effects of low tidal volume ventilation in a rabbit model of Pseudomonas aeruginosa-induced acute lung injury

OBJECTIVE

To determine whether low "stretch" mechanical ventilation protects animals from clinical sepsis after direct acute lung injury with Pseudomonas aeruginosa as compared with high "stretch" ventilation.

DESIGN

Prospective study.

SETTING

Experimental animal laboratory.

SUBJECTS

Twenty-seven anesthetized and paralyzed rabbits.

INTERVENTIONS

P. aeruginosa (109 colony forming units) was instilled into the right lungs of rabbits that were then ventilated at a tidal volume of either 15 mL/kg (n = 11) or 6 mL/kg (n = 7) for 8 hrs. Control animals were ventilated at a tidal volume of either 15 mL/kg (n = 4) or 6 mL/kg (n = 5) for 8 hrs, but an instillate without bacteria was used. A positive end-expiratory pressure of 3-5 cm H2O was used for all experiments. Radiolabeled albumin was used as a marker of alveolar epithelial permeability.

MEASUREMENTS AND MAIN RESULTS

Hemodynamics, arterial blood gas determination, alveolar permeability, wet-to-dry ratios on lungs, and time course of bacteremia were determined. When final values were compared with the values at the beginning of the experiment, there were significant decreases in mean arterial pressure (from 104 +/- 15 to 57 +/- 20 mm Hg), pH (from 7.46 +/- 0.04 to 7.24 +/- 15), Pao2 (from 528 +/- 35 to 129 +/- 104 torr [70.4 +/- 4.7 to 17.2 +/- 13.9 kPa]), and temperature (from 38.2 +/- 1 to 36.2 +/- 1.2 degrees C) in the high tidal volume group, whereas no significant differences were found in the low tidal volume group. Decreased alveolar permeability was shown in the low tidal volume group, as was decreased extravascular lung water in the uninstilled lung in the low tidal volume group (12.7 +/- 2.5 vs. 4.3 +/- 0.45 g H2O/g dry lung). No noteworthy difference was noted in the time course of bacteremia, although there was a trend toward earlier bacteremia in the high tidal volume group.

CONCLUSIONS

In our animal model of P. aeruginosa-induced acute lung injury, low tidal volume ventilation was correlated with improved oxygenation, hemodynamic status, and acid-base status as well as decreased alveolar permeability and contralateral extravascular lung water.

Aquaporin channels may modulate ventilator-induced lung injury

Adult Respiratory Distress Syndrome is a disease with functional lung heterogeneity and thus a ventilator-delivered breath may over-distend non-involved areas. In rats we examined ventilator-delivered tidal volume (TV) breaths of 7 and 20 ml/kg on lung water as evidence of lung injury. We examined the role of aquaporins on ventilator-induced lung injury (VILI) by infusing HgCl(2) which inhibits aquaporins by binding cysteine. Wet to dry lung weight ratio (W/D) as evidence of lung water was 4.47+/-0.1 SEM in controls, 4.6+/-0.1 and 5.5+/-0.2 (P<0.05) in rats ventilated at 7 and 20 ml/kg, respectively. Pulmonary artery pressure (PAP) rose from 23+/-1 to 26+/-1 mmHg (P<0.05, n=7) and cardiac output fell from 104+/-2 to 67+/-3 ml/min (P<0.05) in rats ventilated at 20 ml/kg. Left ventricular end diastolic pressure (n=3) was unchanged. Evans Blue dye, an albumin marker, increased from a control 37+/-11 to 97+/-41 mg/g wet lung in TV 20 rats (P<0.05). HgCl(2) infused slowly by tail vein did not significantly raise PAP, but did increase W/D to 6+/-0.2 (P<0.05) in rats ventilated at 20 ml/kg but not at 7 ml/kg. Equimolar cysteine infusions prevented the HgCl(2) from increasing the W/D above that seen with TV 20 ml/kg. Thus ventilation with TV of 20 ml/kg produced a protein-rich lung edema. Aquaporin channels may have a protective effect in VILI.

Aerosolized deferoxamine prevents lung and systemic injury caused by smoke inhalation

We assessed the role of oxidant release at the airway mucosal surface on airway injury and systemic response to a severe smoke insult. Adult sheep (n = 20) were insufflated with well-characterized smoke from burning cotton toweling. A standardized dose of 12 breaths of smoke with a tidal volume of 20 ml/kg was given under anesthesia. Sheep were awakened, monitored for 24 h, and killed; data were compared with control sheep. Sheep were given 1) humidified oxygen, 2) continuous aerosol of 10% deferoxamine (DFO)-pentastarch solution beginning after smoke, 3) DFO-alone aerosol, or 4) pentastarch-alone aerosol. DFO has antioxidant properties directly and chelates iron. Severe respiratory failure occurred in all but DFO-pentastarch group. Shunt fraction increased from a control of 4%. Histological assessment revealed severe airway mucosal edema, ulceration, bronchorrhea, and severe atelectasis but only moderate alveolar edema. Increased lipid peroxides were also noted in free airway fluid and in bronchoalveolar lavage fluid. In addition, oxygen consumption increased by 75%, fluid requirements increased threefold, and protein-rich systemic soft tissue lymph flow doubled, all significant increases compared with control sheep. No significant physiological or histological changes were noted in DFO-pentastarch aerosol group. We conclude that 1) oxidants possibly initiated through free iron release are involved in severe smoke-induced airway injury and resulting systemic inflammatory response, probably through an amplified oxidant injury and 2) an aerosol of a DFO-pentastarch complex prevents the injury process, whereas DFO alone is not effective as an aerosol.

How important is the measurement of extravascular lung water?

PURPOSE OF REVIEW

Accurate quantification of extravascular lung water is an important issue in the management of patients with pulmonary edema. The single transpulmonary thermal indicator method has been available since the late 1990s. Its simplicity and easy application make it clinically attractive.

RECENT FINDINGS

Several experimental studies have confirmed the accuracy of the single transpulmonary thermal indicator technique in comparisons with postmortem gravimetric method. Whereas changes in extravascular lung water of less than 100-200% are undetectable by other clinically applicable methods of lung injury assessment (chest radiograph and oxygenation), the single transpulmonary indicator has proven highly sensitive to small (10-20%) increases and is therefore useful to detect incipient pulmonary edema. In patients with sepsis or acute respiratory distress syndrome, extravascular lung water measurement offers information unobtainable by other means.

SUMMARY

Extravascular lung water can be considered a relevant parameter that contributes to rational management of fluid and vasoactive therapy of many critically ill patients and offers a fuller picture of their overall lung function.

Measurements of extracellular fluid volume in highly perfused organs and lung water in hypo- and hypervolaemic dogs

The purpose of this study was to identify whether the central extracellular fluid volume status following hypo- and hypervolaemia can be measured by the initial distribution volume of glucose or by the extravascular lung water. These two estimates were compared with the initial distribution volume of sucrose which has been used as an indicator for the measurement of the extracellular fluid volume. The above three estimates were determined by the administration of glucose, chilled saline and sucrose solutions, before and after haemorrhage (30 mL kg-1), and subsequent fluid load (lactated Ringer's solution 90 mL kg-1). The distribution volumes of glucose and sucrose decreased after haemorrhage and increased after fluid load compared with normovolaemic values, and a linear correlation was obtained between these two distribution volumes (r = 0.93, P < 0.001, n = 36). However, the extravascular lung water remained statistically unchanged throughout the procedure, despite a weak linear correlation with the sucrose distribution volume (r = 0.38, n = 33, P < 0.05). These results indicate that the initial distribution volume of glucose is more useful as an indicator of the central extracellular fluid volume status than the extravascular lung water.

Lung fluid dynamics and supply dependency of oxygen uptake during experimental endotoxic shock and volume resuscitation

BACKGROUND AND METHODS

We studied the effect of volume resuscitation on lung fluid balance and systemic oxygen extraction during septic shock in eight anesthetized dogs. Sepsis was induced using a 2-hr continuous infusion of Escherichia coli endotoxin at 0.25 micrograms/min.kg. Relationships between oxygen uptake (VO2) and oxygen supply (DO2) were performed acutely during stepwise controlled decrements in cardiac output by progressive inflation of an intracardiac balloon. At each stage, DO2 and corresponding VO2 were measured independently and the individual critical DO2 level was referred to as the point below which the relationship held. The slope of such a constructed relationship was defined as the maximal oxygen extraction ratio. Lung fluid balance was assessed by measurements of extravascular lung water. All values were studied at baseline, after endotoxin insult, and after reversing hypotension by a 10% dextran infusion.

RESULTS

Endotoxin infusion led to a shock state that associated hypotension (from 135 to 63 mm Hg) with increases in blood lactate (from 0.53 to 3.9 mmol/L). The mean critical DO2 and maximal oxygen extraction ratio were significantly altered from 7.9 to 17.8 mL/min.kg and from 0.81 to 0.38, respectively. After reversing hypotension by 28 mL/kg colloid infusion, the critical DO2 (11.4 mL/min.kg) and maximal oxygen extraction ratio (0.48) were significantly improved. However, restoration of normal values required a state of fluid overload by further dextran infusion (8 mL/kg). At the end of the fluid challenge, extravascular lung water significantly increased from 6.4 to 17.4 mL/kg.

CONCLUSIONS

These data suggest that volume loading may reverse endotoxin-induced peripheral perfusion abnormalities. However, substantial pulmonary edema may occur, possibly jeopardizing the beneficial effects of fluid expansion.

Lung protein leakage in feline septic shock

The aim of the present study was to explore lung microvascular leakage of protein and water in a feline model of septic shock, using a double isotope technique with external gamma camera detection and gravimetric lung water measurements. The experiments were performed on artificially ventilated cats. One group of cats (n = 8) was given an infusion of live Escherichia coli bacteria, and another group (n = 5) served as a control group receiving saline. Plasma transferrin was radiolabeled in vivo with indium-113m-chloride, and erythrocytes were labeled with technetium-99m. The distribution of these isotopes in the lungs was continuously measured with a gamma camera. A normalized slope index (NSI) was calculated, indicative of the transferrin accumulation corrected for changes in local blood volume that reflect protein leakage. In the septic group there was a protein leakage after bacterial infusion, with a NSI of 39 x 10(-4) +/- 5 x 10(-4) min-1 (mean +/- SEM), and the PaO2 diminished from 21 +/- 1 to 9.5 +/- 1 kPa. In control cats a slight protein leakage with a NSI of 9 +/- 10(-4) +/- 2 x 10(-4) min-1 was detected, probably caused by the operative procedure, but PaO2 did not change. Wet-to-dry-weight ratios of postmortem lungs were not significantly different between the groups. It was concluded that an intravenous infusion of live E. coli bacteria induces a lung capillary protein leakage without increased lung water and a concomitantly disturbed gas exchange.(ABSTRACT TRUNCATED AT 250 WORDS)