Lung microvascular transport properties measured by multiple indicator dilution methods in patients with adult respiratory distress syndrome. A comparison between patients reversing respiratory failure and those failing to reverse

Glucocorticoid Treatment in Acute Respiratory Distress Syndrome: An Overview on Mechanistic Insights and Clinical Benefit

Acute lung injury/acute respiratory distress syndrome (ALI/ARDS), triggered by various pathogenic factors inside and outside the lungs, leads to diffuse lung injury and can result in respiratory failure and death, which are typical clinical critical emergencies. Severe acute pancreatitis (SAP), which has a poor clinical prognosis, is one of the most common diseases that induces ARDS. When SAP causes the body to produce a storm of inflammatory factors and even causes sepsis, clinicians will face a two-way choice between anti-inflammatory and anti-infection objectives while considering the damaged intestinal barrier and respiratory failure, which undoubtedly increases the difficulty of the diagnosis and treatment of SAP-ALI/ARDS. For a long time, many studies have been devoted to applying glucocorticoids (GCs) to control the inflammatory response and prevent and treat sepsis and ALI/ARDS. However, the specific mechanism is not precise, the clinical efficacy is uneven, and the corresponding side effects are endless. This review discusses the mechanism of action, current clinical application status, effectiveness assessment, and side effects of GCs in the treatment of ALI/ARDS (especially the subtype caused by SAP).

Pulmonary inflammation alters the lung disposition of lipophilic amine indicators

Many lipophilic amine compounds are rapidly extracted from the blood on passage through the pulmonary circulation. The extent of their extraction in normal lungs depends on their physical-chemical properties, which affect their degree of ionization, lipophilicity, and propensity for interacting with blood and tissue constituents. The hypothesis of the present study was that changes in the tissue composition that occur during pulmonary inflammation would have a differential effect on the pulmonary extraction of lipophilic amines having different properties. If so, measurement of the extraction patterns for a group of lipophilic amines, having different physical-chemical properties, might provide a means for detecting and identifying lung tissue abnormalities. To evaluate this hypothesis, we measured the pulmonary extraction patterns for four lipophilic amines, [(14)C]diazepam, [(3)H]alfentanil, [(14)C]lidocaine, and [(14)C]codeine, along with two hydrophilic compounds, (3)HOH and [(14)C]phenylethylamine, after the bolus injection of these indicators into the pulmonary artery of isolated lungs from normal rabbits and from rabbits with pulmonary inflammation induced by an intravenous injection of complete Freund's adjuvant. The pulmonary extraction patterns, parameterized using a previously developed mathematical model, were, in fact, differentially altered by the inflammatory response. For example, the tissue sequestration rate, k(seq) (ml/s), per unit (3)HOH accessible extravascular lung water volume significantly increased for diazepam and lidocaine, but not for codeine and alfentanil. The results are consistent with the above hypothesis and suggest the potential for using lipophilic amines as indicators for detection and quantification of changes in lung tissue composition associated with lung injury and disease.

Regional measurements of pulmonary edema by using magnetic resonance imaging

A three-dimensional magnetic resonance imaging (MRI) method to measure pulmonary edema and lung microvascular barrier permeability was developed and compared with conventional methods in nine mongrel dogs. MRIs were obtained covering the entire lungs. Injury was induced by injection of oleic acid (0.021-0.048 ml/kg) into a jugular catheter. Imaging followed for 0.75-2 h. Extravascular lung water and permeability-related parameters were measured from multiple-indicator dilution curves. Edema was measured as magnetic resonance signal-to-noise ratio (SNR). Postinjury wet-to-dry lung weight ratio was 5.30 +/- 0.38 (n = 9). Extravascular lung water increased from 2.03 +/- 1.11 to 3.00 +/- 1.45 ml/g (n = 9, P < 0.01). Indicator dilution studies yielded parameters characterizing capillary exchange of urea and butanediol: the product of the square root of equivalent diffusivity of escape from the capillary and capillary surface area (D1/2S) and the capillary permeability-surface area product (PS). The ratio of D1/2S for urea to D1/2S for butanediol increased from 0.583 +/- 0.027 to 0.852 +/- 0.154 (n = 9, P < 0.05). Whole lung SNR at baseline, before injury, correlated with D1/2S and PS ratios (both P < 0.02). By using rate of SNR change, the mismatch of transcapillary filtration flow and lymph clearance was estimated to be 0.2-1.8 ml/min. The filtration coefficient was estimated from these values. Results indicate that pulmonary edema formation during oleic acid injury can be imaged regionally and quantified globally, and the results suggest possible regional quantification by using three-dimensional MRI.

Pulmonary hypertension and selective pulmonary vasodilators in acute lung injury

The pulmonary circulation and the mechanisms which generate pulmonary hypertension are reviewed. The role of these mechanisms in the common pulmonary hypertensive states are analysed, particularly those in acute lung injury. Management options are discussed, with particular emphasis on the use of selective pulmonary vasodilators.

Relative quantification of pulmonary edema with noncontrast-enhanced MRI

Pulmonary edema is a debilitating effect of acute respiratory distress syndrome. The ability to measure it noninvasively with high sensitivity and in three dimensions could be useful in not only detection but also in assessment and guidance of treatment. To this end, a three-dimensional MRI pulse sequence to measure the formation of edema was developed and tested. Another sequence was tested to measure blood flow in distal pulmonary arteries. Pulmonary edema was induced in nine dogs via venous injections of oleic acid. Edema was verified by wet-to-dry weight ratio (5.30 +/- .38) and extra-vascular lung water at baseline (2.03 +/- 1.12 ml/g dry lung weight) versus postinjury (3.00 +/- 1.45 ml/g) (P < .005). The signal-to-noise ratio within the lungs increased from 5.47 +/- 1.00 at baseline to 7.51 +/- 1.96 (P < .005), and the time course of edema formation was resolved. Results from MR phase-contrast blood flow measurements were variable. The authors conclude that the three-dimensional scan provides a sensitive relative quantification of pulmonary edema formation without the use of contrast agents or ionizing radiation.

Radionuclide assessment of pulmonary microvascular permeability

The literature has been reviewed to evaluate the technique and clinical value of radionuclide measurements of microvascular permeability and oedema formation in the lungs. Methodology, modelling and interpretation vary widely among studies. Nevertheless, most studies agree on the fact that the measurement of permeability via pulmonary radioactivity measurements of intravenously injected radiolabelled proteins versus that in the blood pool, the so-called pulmonary protein transport rate (PTR), can assist the clinician in discriminating between permeability oedema of the lungs associated with the adult respiratory distress syndrome (ARDS) and oedema caused by an increased filtration pressure, for instance in the course of cardiac disease, i.e. pressure-induced pulmonary oedema. Some of the techniques used to measure PTR are also able to detect subclinical forms of lung microvascular injury not yet complicated by permeability oedema. This may occur after cardiopulmonary bypass and major vascular surgery, for instance. By paralleling the clinical severity and course of the ARDS, the PTR method may also serve as a tool to evaluate new therapies for the syndrome. Taken together, the currently available radionuclide methods, which are applicable at the bedside in the intensive care unit, may provide a gold standard for detecting minor and major forms of acute microvascular lung injury, and for evaluating the severity, course and response to treatment.

Nitric oxide improves transpulmonary vascular mechanics but does not change intrinsic right ventricular contractility in an acute respiratory distress syndrome model with permissive hypercapnia

OBJECTIVE

To test the hypothesis that in a swine model of acute respiratory distress syndrome (ARDS) with permissive hypercapnia, inhaled nitric oxide would improve transpulmonary vascular mechanics and right ventricular workload while not changing intrinsic right ventricular contractility.

DESIGN

Prospective, randomized, controlled laboratory trial.

SETTING

University research laboratory.

SUBJECTS

Eleven swine (30 to 46 kg).

INTERVENTIONS

The swine were anesthetized, intubated, and paralyzed. After median sternotomy, pressure transducers were placed in the right ventricle, pulmonary artery, and left atrium. An ultrasonic flow probe was placed around the pulmonary artery. Ultrasonic dimension transducers were sutured onto the heart at the base, apex, left ventricle (anterior, posterior, free wall), and right ventricle (free wall). An additional transducer was placed in the interventricular septum. A surfactant depletion model of ARDS was created by saline lung lavage. Nitric oxide was administered at 2, 4, and 6 parts per million (ppm), in a random order, under the condition of permissive hypercapnia (Paco2 55 to 75 torr [7.3 to 10.0 kPa]).

MEASUREMENTS AND MAIN RESULTS

We evaluated the pulmonary vascular and right ventricular effects of permissive hypercapnia, with and without inhaled nitric oxide, by measuring variables of transpulmonary vascular mechanics and right ventricular function. These variables included mean pulmonary arterial pressure, right ventricular total power, right ventricular stroke work, transpulmonary vascular efficiency, and right ventricular intrinsic contractility. Data were obtained after lung injury under the following conditions: a) normocapnia (Paco2 35 to 45 torr [4.7 to 6.0 kPa]) and nitric oxide at 0 ppm; b) hypercapnia and nitric oxide at 0 ppm; c) hypercapnia and nitric oxide at 2, 4, and 6 ppm; and d) repeat measurements with hypercapnia and nitric oxide at 0 ppm. In ARDS with permissive hypercapnia, inhaled nitric oxide therapy (2 to 6 ppm) improved transpulmonary vascular mechanics and right ventricular workload by lowering pulmonary arterial pressure (29.6 +/- 1.3 vs. 24.6 +/- 1.0 mm Hg, p = .0001), increasing transpulmonary vascular efficiency (13.9 +/- 0.5 vs. 16.1 +/- 0.7 L/W-min, p = .0001), decreasing right ventricular total power (142 +/- 9 vs. 115 +/- 9 mW, p = .001), and decreasing right ventricular stroke work (653 +/- 37 vs. 525 +/- 32 ergs x 10(3), p = .001). Inhaled nitric oxide did not change right ventricular contractility, as measured by preload-recruitable stroke work.

CONCLUSIONS

Inhaled nitric oxide ameliorated any negative effects of hypoxic and hypercapnic pulmonary vasoconstriction. The beneficial effects of inhaled nitric oxide are related to alterations in right ventricular afterload and not intrinsic right ventricular contractility. The improved cardiopulmonary effects of inhaled nitric oxide with permissive hypercapnia potentially expand the use of nitric oxide in ARDS and other conditions in which this strategy is employed.

Inflammatory cytokines in the BAL of patients with ARDS. Persistent elevation over time predicts poor outcome

BACKGROUND

Inflammatory cytokines (ICs) are important modulators of injury and repair. ICs have been found to be elevated in the BAL of patients with both early and late ARDS. We tested the hypothesis that recurrent injury to the alveolocapillary barrier and amplification of intra-alveolar fibroproliferation observed in nonresolving ARDS is related to a persistent inflammatory response. For this purpose, we obtained serial measurements of BAL IC and correlated these levels with lung injury score (LIS), BAL indexes of endothelial permeability (albumin, total protein [TP]), and outcome.

METHODS

We prospectively studied 27 consecutive patients with severe medical ARDS. Using enzyme-linked immunosorbent assay methods, levels of tumor necrosis factor-alpha (TNF-alpha) and interleukins (IL) 1 beta, 2, 4, 6, and 8 were measured at frequent intervals in both plasma and BAL. In 22 patients, bilateral BAL was obtained on day 1 of ARDS and at weekly intervals when possible. Right and left BALs were analyzed separately for IC levels, total cell count and differential, albumin, TP, and quantitative bacterial cultures.

RESULTS

On day 1 of ARDS, the 10 nonsurvivors had significantly higher (p = 0.0002) BAL TNF-alpha, IL-1 beta, IL-6, and IL-8 levels, which remained persistently elevated over time, indicating a continuous injury process. In contrast, the 12 survivors had a lesser elevation and a rapid reduction over time. Initial BAL IL-2 and IL-4 levels were significantly higher in patients with sepsis (p = 0.006); both increased over time in survivors and nonsurvivors. BAL levels of TNF-alpha, IL-1 beta, IL-6, and IL-8 correlated with BAL albumin and TP concentrations but not with LIS or ratio of arterial oxygen tension to inspired oxygen concentration. BAL: plasma ratios were elevated for all measured cytokines, suggesting a pulmonary origin. On day 1 of ARDS, nonsurvivors had significantly higher (p = 0.04) BAL: plasma ratios for TNF-alpha, IL-1 beta, IL-6, and IL-8. Over time, BAL:plasma ratios for TNF-alpha, IL-1 beta and IL-6 remained elevated in nonsurvivors and decreased in survivors.

CONCLUSIONS

Our findings indicate that an unfavorable outcome in ARDS is associated with an initial, exaggerated, pulmonary inflammatory response that persists unabated over time. Plasma IC levels parallel changes in BAL IC levels. The BAL:plasma ratio results suggest, but do not prove, a pulmonary origin for IC production. BAL TNF-alpha, IL-1 beta, and IL-8 levels correlated with BAL indices of endothelial permeability. In survivors, reduction in BAL IC levels over time was associated with a decline in BAL albumin and TP levels, suggesting effective repair of the endothelial surface. These findings support a causal relationship between degree and duration of lung inflammation and progression of fibroproliferation in ARDS.

Sulfhemoglobinated erythrocytes as an optical intravascular tracer in the lung

Sulfhemoglobinated erythrocytes (SHb-RBC's) were examined for utility as an optical multiple indicator dilution tracer in lung studies. A device was developed to measure this tracer optically in flowing blood. Arterial blood was sampled from cannulated, anesthetized dogs and pumped through the device that measured the optical density (OD) of blood at 620 nm. This system was calibrated for increasing SHb-RBC concentrations using an unsteady-state indicator dilution procedure. Areas under optical density (delta OD) profiles were well correlated with injected SHb-RBC volumes using linear regression (r2 > 0.9). This linearity was independent of blood oxygenation, hematocrit, or pH. In vivo lung indicator dilution studies in the intact dog were performed and compared to radioisotope indicator studies using 51Cr labeled erythrocytes. Coefficient of variation (CV) between the two curves was 0.065 under baseline conditions, 0.085 for studies performed during hypoxia, and 0.073 after pH was lowered. We conclude that this device linearly measured SHb-RBC content in whole blood and that SHb-RBC is as accurate a lung indicator dilution tracer as 51Cr-erythrocytes.

Oxygen radicals--an important mediator of sepsis and septic shock

There is considerable evidence to implicate aggressive species of oxygen in the pathogenesis of organ dysfunction consequent to sepsis and septic shock. The inflammatory process appears to participate ubiquitously in this setting. A characteristic of inflammation is the involvement of activated neutrophils and their generation of aggressive oxygen species. Such species may both directly injure cells proximal to the oxidant generating cells, and may inactivate any proteolytic mechanisms normally protective against proteolytic injury caused by neutrophil elastase and other proteolytic enzymes released during inflammation. The offending agent in sepsis is most commonly envisioned as bacterial lipopolysaccharide, or endotoxin. Infusion of endotoxin into animals can reproduce much of the pathophysiology of sepsis and septic shock. In addition, administration of endotoxin to cultured cells, particularly endothelial cells, can cause responses consistent with a sequence of events that occurs in intact animals and humans. In both experimental models, it appears that aggressive oxygen species are important actors in the scenario eventuating in cell or organ injury. Of importance, the toxic consequences of these free radicals probably occurs in relatively protected spaces, including microenvironments created by close adherence between inflammatory cells and endothelial cells and the cell interior. For those reasons, the potential for antioxidants as therapy should include consideration of the volume of distribution of such substances. It is probably important that antioxidants access excluded spaces including cell interiors in order to have their maximum effect in this setting. We have studied ina preliminary way the effects of n-acetyl-cysteine, a highly permeable free radical scavenger and anti-oxidant, in patients with established ARDS.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of extravascular lung water--methods and clinical implications

The estimation of changes in extravascular lung water during different experimental and clinical conditions forms an intriguing field of research. Present methods for the measurement of lung water are difficult to apply in day-to-day clinical practice. Most methods are not only low in accuracy and sensitivity but are also invasive. A new indicator-dilution technique using heavy water and indocyanine green as diffusible and nondiffusible indicators, respectively, may provide us with a new investigative method for longterm bedside estimation of lung water.