The pathogenesis of pulmonary edema

Pathogenesis of Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a syndrome of acute respiratory failure caused by noncardiogenic pulmonary edema. Despite five decades of basic and clinical research, there is still no effective pharmacotherapy for this condition and the treatment remains primarily supportive. It is critical to study the molecular and physiologic mechanisms that cause ARDS to improve our understanding of this syndrome and reduce mortality. The goal of this review is to describe our current understanding of the pathogenesis and pathophysiology of ARDS. First, we will describe how pulmonary edema fluid accumulates in ARDS due to lung inflammation and increased alveolar endothelial and epithelial permeabilities. Next, we will review how pulmonary edema fluid is normally cleared in the uninjured lung, and describe how these pathways are disrupted in ARDS. Finally, we will explain how clinical trials and preclinical studies of novel therapeutic agents have further refined our understanding of this condition, highlighting, in particular, the study of mesenchymal stromal cells in the treatment of ARDS.

Lung-Kidney Cross-Talk

Awareness of the multifaceted lung and kidney interactions in the critically ill has increased considerably. Cardiogenic and noncardiogenic pulmonary edema represent two entities of pulmonary edema and differ significantly in terms of alveolar fluid clearance. Acute lung injury describes the breakdown of normal lung architecture with development of a high-permeability noncardiogenic pulmonary edema resulting from an inflammation/oxidant-mediated injury to the alveolar-capillary barrier and downregulation of the epithelial active ion transport system. Acute kidney injury is the most common organ dysfunction in patients with acute respiratory distress syndrome. It may develop as a result of blood gas disturbances that compromise renal blood flow and renal compensatory mechanisms; pulmonary hypertension, which may aggravate renal impairment by causing renal congestion and tissue edema; and mechanical ventilation–induced alterations, including systemic release of mediators, all which promote end-organ cell injury. Acute kidney injury, on the other hand, may initiate and perpetuate lung injury resulting from fluid overload and the systemic release of mediators that promote increased pulmonary vascular permeability, lung inflammation, and apoptosis, and breakdown of the transepithelial electrolyte and water transport, ultimately leading to respiratory failure. It is hoped that an in-depth understanding of the factors influencing lung-kidney interactions will encourage physicians to explore and develop new strategies for the benefit of the patient.

This chapter will:1

Review the pathophysiology of acute lung injury.

2

Summarize the emerging understanding of lung-kidney cross-talk in the critically ill patient.

3

Identify the mechanisms by which acute kidney injury may potentiate acute lung injury.

Suffocation From Balloon Bronchoplasty

Negative pressure pulmonary edema is a well-described complication of upper airway obstruction. However, the simultaneous occurrence of blood-stained secretions and petechial tracheobronchial hemorrhage are rarely recognized and a potential complication of transient intentional occlusion of the airways. We described a case of "hemorrhagic bronchial mucosa syndrome" and asymptomatic blood-tinged pulmonary edema after balloon bronchoplasty for a concentric tracheal stenosis using a flexible bronchoscopy. This was characterized by interval appearance of diffuse petechial tracheobronchial bleeding and a persistent blood-tinged alveolar effluent after sustained occlusion of the airway. The simultaneous occurrence of both phenomena in this patient suggests different degrees of injury in a common pathogenic spectrum. We postulate that sustained, complete occlusion of the airway produces variable degrees of mechanical disruption of the bronchial and alveolar vasculature that lead to the development of negative pressure pulmonary edema and tracheobronchial hemorrhage. In this case, the syndrome was self-limited and without major consequences but highlights an unrecognized potential complication of balloon bronchoplasty.

Alveolar Fluid Clearance in Pathologically Relevant Conditions: In Vitro and In Vivo Models of Acute Respiratory Distress Syndrome

Critically ill patients with respiratory failure from acute respiratory distress syndrome (ARDS) have reduced ability to clear alveolar edema fluid. This reduction in alveolar fluid clearance (AFC) contributes to the morbidity and mortality in ARDS. Thus, it is important to understand why AFC is reduced in ARDS in order to design targeted therapies. In this review, we highlight experiments that have advanced our understanding of ARDS pathogenesis, with particular reference to the alveolar epithelium. First, we review how vectorial ion transport drives the clearance of alveolar edema fluid in the uninjured lung. Next, we describe how alveolar edema fluid is less effectively cleared in lungs affected by ARDS and describe selected in vitro and in vivo experiments that have elucidated some of the molecular mechanisms responsible for the reduced AFC. Finally, we describe one potential therapy that targets this pathway: bone marrow-derived mesenchymal stem (stromal) cells (MSCs). Based on preclinical studies, MSCs enhance AFC and promote the resolution of pulmonary edema and thus may offer a promising cell-based therapy for ARDS.

Pulmonary Edema and Hypoxic Respiratory Failure

OBJECTIVES

The purpose of this chapter is to outline the causes, physiology, pathophysiology, and management strategies for hydrostatic and permeability pulmonary edema and hypoxic respiratory failure.

DATA SOURCE

MEDLINE and PubMed.

CONCLUSION

The pulmonary parenchyma and vasculature are at high risk in conditions where injury occurs to the lung and or heart. A targeted approach that uses strategies that optimize the particular pathophysiology of the parenchyma and vasculature is required.

Resolution of pulmonary edema. Thirty years of progress

In the last 30 years, we have learned much about the molecular, cellular, and physiological mechanisms that regulate the resolution of pulmonary edema in both the normal and the injured lung. Although the physiological mechanisms responsible for the formation of pulmonary edema were identified by 1980, the mechanisms that explain the resolution of pulmonary edema were not well understood at that time. However, in the 1980s several investigators provided novel evidence that the primary mechanism for removal of alveolar edema fluid depended on active ion transport across the alveolar epithelium. Sodium enters through apical channels, primarily the epithelial sodium channel, and is pumped into the lung interstitium by basolaterally located Na/K-ATPase, thus creating a local osmotic gradient to reabsorb the water fraction of the edema fluid from the airspaces of the lungs. The resolution of alveolar edema across the normally tight epithelial barrier can be up-regulated by cyclic adenosine monophosphate (cAMP)-dependent mechanisms through adrenergic or dopamine receptor stimulation, and by several cAMP-independent mechanisms, including glucocorticoids, thyroid hormone, dopamine, and growth factors. Whereas resolution of alveolar edema in cardiogenic pulmonary edema can be rapid, the rate of edema resolution in most patients with acute respiratory distress syndrome (ARDS) is markedly impaired, a finding that correlates with higher mortality. Several mechanisms impair the resolution of alveolar edema in ARDS, including cell injury from unfavorable ventilator strategies or pathogens, hypoxia, cytokines, and oxidative stress. In patients with severe ARDS, alveolar epithelial cell death is a major mechanism that prevents the resolution of lung edema.

Fluid management in critically ill patients: the role of extravascular lung water, abdominal hypertension, capillary leak, and fluid balance

INTRODUCTION

Capillary leak in critically ill patients leads to interstitial edema. Fluid overload is independently associated with poor prognosis. Bedside measurement of intra-abdominal pressure (IAP), extravascular lung water index (EVLWI), fluid balance, and capillary leak index (CLI) may provide a valuable prognostic tool in mechanically ventilated patients.

METHODS

We performed an observational study of 123 mechanically ventilated patients with extended hemodynamic monitoring, analyzing process-of-care variables for the first week of ICU admission. The primary outcome parameter was 28-day mortality. ΔmaxEVLWI indicated the maximum difference between EVLWI measurements during ICU stay. Patients with a ΔmaxEVLWI <-2 mL/kg were called 'responders'. CLI was defined as C-reactive protein (milligrams per deciliter) over albumin (grams per liter) ratio and conservative late fluid management (CLFM) as even-to-negative fluid balance on at least two consecutive days.

RESULTS

CLI had a biphasic course. ΔmaxEVLWI was lower if CLFM was achieved and in survivors (-2.4 ± 4.8 vs 1.0 ± 5.5 mL/kg, p = 0.001; -3.3 ± 3.8 vs 2.5 ± 5.3 mL/kg, p = 0.001, respectively). No CLFM achievement was associated with increased CLI and IAPmean on day 3 and higher risk to be nonresponder (odds ratio (OR) 2.76, p = 0.046; OR 1.28, p = 0.011; OR 5.52, p = 0.001, respectively). Responders had more ventilator-free days during the first week (2.5 ± 2.3 vs 1.5 ± 2.3, p = 0.023). Not achieving CLFM and being nonresponder were strong independent predictors of mortality (OR 9.34, p = 0.001 and OR 7.14, p = 0.001, respectively).

CONCLUSION

There seems to be an important correlation between CLI, EVLWI kinetics, IAP, and fluid balance in mechanically ventilated patients, associated with organ dysfunction and poor prognosis. In this context, we introduce the global increased permeability syndrome.

Methods of Measuring Lung Water

Pulmonary oedema can result from both cardiogenic and non-cardiogenic aetiologies and is a cause of considerable morbidity and mortality. Accurate methods of quantifying pulmonary oedema are needed for both clinical and research purposes. Applications could include early recognition, and thus prevention, of impending decompensation in heart failure patients, guidance of fluid management in patients with established pulmonary oedema, and as a pharmacodynamic outcome measure for early clinical trials of drugs for the treatment of pulmonary oedema. Magnetic resonance imaging, computed tomography, positron emission tomography, electrical impedance, and thermodilution methods have all been used with the aim of measuring lung water. These methods differ in their accuracy, cost, ionising radiation dose, invasiveness, portability, and ability to provide dynamic measures. To date, none have been established as a ‘gold standard’ clinical measurement to improve clinical outcomes or to assist drug development. This review aims to discuss each of these methods in turn, focussing on advantages, limitations, and possible future development and applications.

Extravascular lung water index and global end-diastolic volume index should be corrected in children

PURPOSE

The aim of the present study was to explain why extravascular lung water index (EVLWI) is higher and why global end-diastolic blood volume index (GEDVI) is lower in young children when measured with the PiCCO system (Pulsion, Munich, Germany).

MATERIALS AND METHODS

We pooled available data from literature from children concerning organ weight derived from autopsy studies and computed tomographic lung measurements. These data include age, height, body weight, body surface area (BSA), and lung and heart weights. For standard, age-dependent weight and height, we used published data from the World Health Organization. From the available data, we calculated the lung weight-to-body weight ratio, the heart weight-to-BSA ratio, and the end-diastolic volume-to-BSA ratio. We compared these ratios to body growth and development.

RESULTS

Lung weight develops more slowly and with less magnitude than does body weight. In addition, the (relatively) greater lung weight in younger children results in a higher amount of pulmonary blood volume. This explains the higher EVLWI in young children. End-diastolic blood volume and heart weight increase faster and are more pronounced compared with BSA. This explains the lower GEDVI in young children. We propose correction factors for comparing EVLWI and GEDVI with adult reference values.

CONCLUSIONS

Extravascular lung water index is higher and GEDVI is lower in young children because of changing organ-to-body weight relationships during growth.

Pulmonary Vascular Disease

The pulmonary vasculature is an anatomic compartment that is frequently overlooked in the histologic review of lung biopsy samples, other than those obtained specifically to assess pulmonary vascular disease.1 Though often of a nonspecific nature, the histologic pattern of vascular remodeling may at times suggest its underlying pathogenesis and provide clues to the cause of pulmonary hypertension.2 Disproportionately severe vascular pathology may further indicate alternate disease processes, such as congestive heart failure or thromboemboli, contributing to the patient’s overall respiratory condition.

Pulmonary edema and cardiac dysfunction following subarachnoid hemorrhage

BACKGROUND

Pulmonary edema (PE) can occur in the early or late period following subarachnoid hemorrhage (SAH). The incidence of each type of PE is unknown and the association with ventricular dysfunction, both systolic and diastolic, has not been described.

METHODS

Retrospective chart review of 178 consecutive patients with SAH surgically treated over a three-year period. Patients with pulmonary edema diagnosed by a radiologist were included. Early onset SAH was defined as occurring within 12 hours. Cardiac function at the time of the PE was analyzed using hemodynamic and echocardiographic criteria of systolic and diastolic dysfunction. Pulmonary edema was observed in 42 patients (28.8%) and was more often delayed (89.4%). Evidence of cardiac involvement during PE varied between 40 to 100%.

RESULTS AND CONCLUSIONS

Pulmonary edema occurs in 28.8% of patients after SAH, and is most commonly delayed. Cardiac dysfunction, both systolic and diastolic, is commonly observed during SAH and could contribute to the genesis of PE after SAH.

The timing of fracture treatment in polytrauma patients: relevance of damage control orthopedic surgery

Information illustrating the benefits of fracture stabilization after multiple trauma has been gathering for almost a century. At the turn of the last century, the introduction of the Thomas splint clearly demonstrated the importance of skeletal stabilization in the management of these patients. The introduction of standardized surgical treatment for fractures in the early 1950s is considered today as the turning point in the care of the polytraumatized patient. With the knowledge acquired, the application of early operative fixation of fractures in severely injured patients in the 1980s has yielded to the concept of early total care of all fractures. Yet, in distinct patient subgroups with severe thoracic injuries and very high injury severity scores, this concept has been associated with adverse outcomes. Therefore, in a further era that began in the 1990s, a different approach has been favored for these subgroups. It recommends early (initial) temporary stabilization followed by secondary definitive osteosynthesis of major fractures in patients at high risk of developing systemic complications. In the last decade, attempts have been made to determine which patients benefit from early total care and which ones should undergo a secondary definitive approach. This manuscript provides a historical overview on the changing treatment of fractures and summarizes the evolution of "damage control orthopedic surgery."

Beta-adrenergic agonist therapy accelerates the resolution of hydrostatic pulmonary edema in sheep and rats

To determine whether beta-adrenergic agonist therapy increases alveolar liquid clearance during the resolution phase of hydrostatic pulmonary edema, we studied alveolar and lung liquid clearance in two animal models of hydrostatic pulmonary edema. Hydrostatic pulmonary edema was induced in sheep by acutely elevating left atrial pressure to 25 cmH(2)O and instilling 6 ml/kg body wt isotonic 5% albumin (prepared from bovine albumin) in normal saline into the distal air spaces of each lung. After 1 h, sheep were treated with a nebulized beta-agonist (salmeterol) or nebulized saline (controls), and left atrial pressure was then returned to normal. beta-Agonist therapy resulted in a 60% increase in alveolar liquid clearance over 3 h (P < 0.001). Because the rate of alveolar fluid clearance in rats is closer to human rates, we studied beta-agonist therapy in rats, with hydrostatic pulmonary edema induced by volume overload (40% body wt infusion of Ringer lactate). beta-Agonist therapy resulted in a significant decrease in excess lung water (P < 0.01) and significant improvement in arterial blood gases by 2 h (P < 0.03). These preclinical experimental studies support the need for controlled clinical trials to determine whether beta-adrenergic agonist therapy would be of value in accelerating the resolution of hydrostatic pulmonary edema in patients.

Altered endothelial function in lambs with pulmonary hypertension and acute lung injury

Acute lung injury produces pulmonary hypertension, altered vascular reactivity, and endothelial injury. To determine whether acute lung injury impairs the endothelium-dependent regulation of pulmonary vascular tone, 16 lambs were studied during U46619-induced pulmonary hypertension without acute lung injury, or air embolization-induced pulmonary hypertension with acute lung injury. The hemodynamic responses to endothelium-dependent (acetylcholine, ATP, ET-1, and 4 Ala ET-1 [an ETb receptor agonist]) and endothelium-independent (nitroprusside and isoproterenol) vasodilators were compared. During U46619-induced pulmonary hypertension, all vasodilators decreased pulmonary arterial pressure and vascular resistance (P < 0.05). During air embolization-induced pulmonary hypertension, the pulmonary vasodilating effects of acetylcholine, ATP, and 4 Ala ET-1 were attenuated (P < 0.05); the pulmonary vasodilating effects of nitroprusside and isoproterenol were unchanged; and the pulmonary vasodilating effects of ET-1 were reversed, producing pulmonary vasoconstriction (P < 0.05). During air embolization, the pulmonary vasoconstricting effects of ET-1 were blocked by BQ 123, an ETa receptor antagonist. The systemic effects of the vasoactive drugs were similar during both conditions. We conclude that pulmonary hypertension with acute lung injury induced by air embolization results in endothelial dysfunction; there is selective impairment of endothelium-dependent pulmonary vasodilation and an altered response to ET-1 from pulmonary vasodilation to vasoconstriction. This altered response to ET-1 is associated with decreased ETb receptor-mediated vasodilation and increased ETa receptor-mediated vasoconstriction. Endothelial injury and dysfunction account, in part, for the altered regulation of pulmonary vascular tone during pulmonary hypertension with acute lung injury.

The measurement of lung water

INTRODUCTION: In this review, we compare the spectrum of currently available methods for quantifying pulmonary edema in patients. REVIEW: Imaging and indicator dilution techniques comprise the most common strategies for measuring lung water at the bedside. The most accurate (within 10% of the gravimetric gold standard) and most reproducible (< 5% between-test variation) are also, unfortunately, the most expensive and most difficult to implement for purposes of large-scale clinical trials or for routine clinical practice. CONCLUSION: The standard chest radiograph remains the best screening test for the detection of pulmonary edema. Indicator-dilution techniques are probably the best available method at present for quantitation in patient groups.

Alveolar epithelial fluid clearance persists in the presence of moderate left atrial hypertension in sheep

The effect of moderate left atrial (LA) hypertension on alveolar liquid clearance (ALC) was investigated in anesthetized, ventilated sheep, surgically prepared to measure lung lymph flow as well as hemodynamics. To simulate alveolar edema, 3-4 ml/kg of isosmolar 5% albumin in Ringer lactate were instilled into each lower lobe, and ALC was measured. After 4 h of LA hypertension (24 cmH2O), ALC was similar to that in control sheep (31 +/- 3% with LA hypertension vs. 34 +/- 10% with normal LA pressure). Because plasma epinephrine levels were moderately elevated in the presence of LA hypertension, ALC was then studied in the presence of LA hypertension following bilateral adrenalectomy. Without endogenous release of epinephrine, ALC was significantly reduced compared with normal LA pressure (20 +/- 7% compared with 34 +/- 10%, P < 0.05). Thus endogenous catecholamines caused a submaximal stimulation of ALC in the presence of LA hypertension. Exogenous administration of aerosolized beta2-agonist therapy with salmeterol increased ALC in the presence of normal LA pressure but had no stimulatory effect in the presence of moderate LA hypertension. Therefore, we tested the hypothesis that endogenous release of atrial natriuretic factor (ANF) may downregulate alveolar epithelial Na+ and fluid transport in the presence of LA hypertension. There was a modest twofold increase in plasma ANF levels after LA hypertension. Additional in vitro studies demonstrated that, in the presence of beta2-agonist stimulation, ANF decreased Na+ pump activity (Na+-K+-ATPase) in isolated rat alveolar epithelial type II cells. ANF may downregulate vectorial Na+ and fluid transport stimulated by endogenous or exogenous beta-adrenergic agonist stimulation in the presence of LA hypertension. In summary, ALC continues even in the presence of moderate LA hypertension. Aerosolized beta2-adrenergic agonist therapy significantly increased ALC, but only when LA pressure was normal.

Acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) is a serious and complex clinical problem that often threatens the lives of patients. Emerging clinical data suggest that the survival of patients with this disorder may have improved during the last two decades, presumably because of advances in supportive medical care. Among the supportive therapies used to treat patients with ARDS, none is more complex than mechanical ventilation. New strategies for administering mechanical ventilation to patients with ARDS may reduce the occurrence of iatrogenic volotrauma and oxygen toxicity, accounting in part for the recently observed improvements in patient survival. Prevention and cure of ARDS have remained elusive goals because of the lack of specific therapies directed against the known pathogenic factors. Ongoing investigations are aimed at identifying specific therapies to interrupt the mechanisms of inflammation and lung injury responsible for this syndrome. Until such therapies become available, clinicians caring for patients with ARDS should attempt to minimize additional morbidity and mortality resulting from nosocomial infections and iatrogenic injuries.

Bronchoscopic findings in post-obstructive pulmonary oedema

PURPOSE

To present the first photographed bronchoscopic findings associated with negative pressure pulmonary oedema (NPPE).

CLINICAL FEATURES

A previously healthy patient underwent anterior C3-C4 disc removal and arthrodesis. Following tracheal extubation he developed acute respiratory distress manifested as stridor, tachypnoea, restlessness, and desaturation. Once the trachea was reintubated, he displayed the classic findings of pulmonary oedema. Bronchoscopy was performed to confirm tracheal tube position and to rule out tracheal injury secondary to surgical manipulation. Diffuse punctate haemorrhages were noted throughout the visualised tracheobronchial tree.

CONCLUSION

We believe that these haemorrhages represent disruption of the bronchial vasculature and may contribute to the clinical presentation of NPPE.

Fluid balance during pulmonary edema. Is fluid gain a marker or a cause of poor outcome?

STUDY OBJECTIVE

To evaluate the importance of fluid balance and changes in extravascular lung water (EVLW) on survival in the ICU and short-term outcome in patients with pulmonary edema.

DESIGN

Retrospective analysis of data (sorting by survival and "treatment received") from a recent randomized controlled trial of fluid restriction in this population.

SETTING

Medical ICU of a university-affiliated, tertiary-care medical center.

PATIENTS

Eighty-nine patients (from the previously mentioned study) requiring pulmonary artery catheterization with abnormally high EVLW (greater than 7 ml/kg).

MEASUREMENTS AND RESULTS

When analyzed by survival, the survivors had no significant fluid gain or change in EVLW but decreased wedge pressure and body weight, compared to nonsurvivors. When analyzed by fluid balance, patients who gained less than 1 L of fluid by 36 hours into the study had a better rate of survival (74 percent) than the rest (50 percent; p less than 0.05). Also, the median duration of days on the ventilator, ICU days, and days of hospitalization was approximately half as long for each variable in the group with less than 1 L of fluid gain. Even accounting for baseline differences in the severity of illness, fluid balance was an independent predictor of survival (p less than 0.05). When analyzed by whether or not EVLW decreased by more than 15 percent between the first and last measurement, only patients with ARDS or sepsis had decreased days on the ventilator and ICU days.

CONCLUSIONS

These data support the concept that positive fluid balance per se is at least partially responsible for poor outcome in patients with pulmonary edema and defend the strategy of attempting to achieve a negative fluid balance if tolerated hemodynamically.

Differential responses of the endothelial and epithelial barriers of the lung in sheep to Escherichia coli endotoxin

Although intravenous Escherichia coli endotoxin has been used extensively in experimental studies to increase lung endothelial permeability, the effect of E. coli endotoxin on lung epithelial permeability has not been well studied. To examine this issue in sheep, bidirectional movement of protein across the lung epithelial barrier was studied by labeling the vascular space with 131I-albumin and by instilling 3 ml/kg of an isosmolar protein solution with 125I-albumin into the alveoli. E. coli endotoxin was administered according to one of three protocols: intravenous alone (5-500 micrograms/kg), intravenous (5 micrograms/kg) plus low-dose alveolar endotoxin (10 micrograms/kg), and high-dose alveolar endotoxin alone (50-100 micrograms/kg). Alveolar liquid clearance was estimated based on the concentration of the instilled native protein. Sheep were studied for either 4 or 24 h. Although intravenous E. coli endotoxin produced a marked increase in transvascular protein flux and interstitial pulmonary edema, there was no effect on the clearance of either the vascular (131I-albumin) or the alveolar (125I-albumin) protein tracer across the epithelial barrier. High-dose alveolar E. coli endotoxin caused a 10-fold increase in the number of leukocytes, particularly neutrophils, that accumulated in the air spaces. In spite of the marked chemotactic effect of alveolar endotoxin, there was no change in the permeability of the epithelial barrier to the vascular or alveolar protein tracers. Also, alveolar epithelial liquid clearance was normal. Morphologic studies confirmed that the alveolar epithelial barrier was not injured by either intravenous or alveolar E. coli endotoxin. Thus, the alveolar epithelium in sheep is significantly more resistant than the lung endothelium to the injurious effects of E. coli endotoxin.

Peripheral vascular permeability following a thermal injury to the airway

Effects of thermal injury to the airway on the vascular permeability in the region of head and neck, were studied in the canine models. The thermal airway injury was produced by an inhalation of a gas burner's flame through the metallic tracheostomy cannula. The changes in vascular permeability were evaluated by calculating the reflection coefficient, which was obtained by the protein washdown technique into lymph. The reflection coefficient after the flame inhalation did not show any increases, while it increased significantly after a histamine infusion into the carotic artery. We concluded, that the vascular permeability in the unburned area does not increase at least in the first 3 hr after a thermal injury to the airway.

Acute preload effects of furosemide

Acute preload effects (as reflected by the pulmonary capillary wedge pressure [PCWP]) of an intravenous furosemide bolus were studied in 33 patients. In those patients receiving no vasoactive drug and in those receiving predominantly preload reducing agents, there was an initial rise in PCWP up until 15 minutes followed by a diuresis-induced fall in PCWP below baseline levels at 1 h. Patients who were receiving preload and significant afterload reduction showed an immediate drop in PCWP which was sustained. This trend is independent of underlying pathology or dose of furosemide used. It is postulated that furosemide causes an early deleterious release of endogenous vasoconstrictors which may be blocked by combined preload and afterload reduction.

Ultrastructural morphogenesis of 4-ipomeanol-induced bronchiolitis and interstitial pneumonia in calves

The two objectives of this research were 1) to describe the ultrastructural morphogenesis of pulmonary damage and repair induced in calves after treatment with 4-ipomeanol and 2) to characterize infiltrating pulmonary inflammatory cells by bronchoalveolar lavage. Interstitial edema was observed as early as 4 hours after intravenous injection of 4-ipomeanol (5 mg/kg body weight) and progressed to severe alveolar edema by 72 hours. Damage to type I alveolar epithelial cells and terminal bronchiolar nonciliated cells included dilation of endoplasmic reticulum and perinuclear envelopes and was present at 4 hours after treatment. Necrosis and sloughing of these cells from basement membranes occurred at times from 12 to 96 hours after treatment. Alveolar capillary endothelial cells had mild dilation of endoplasmic reticulum at times from 12 to 72 hours after treatment. Necrosis of endothelial cells was not observed. Inflammatory cell infiltrates in bronchioles and alveoli were dominated by macrophages and neutrophils. Significant elevations (P less than 0.05) in numbers of neutrophils and macrophages were recovered by bronchoalveolar lavage at times from 24 to 96 hours after 4-ipomeanol-treatment. Hyperplasia of nonciliated bronchiolar epithelial cells and of type II alveolar epithelial cells were observed at 72 and 96 hours after treatment. The results indicate that type I alveolar epithelial cells and nonciliated bronchiolar epithelial cells are most susceptible to 4-ipomeanol-induced damage and necrosis in calves. 4-ipomeanol-induced pulmonary edema in calves occurs prior to ultrastructurally-demonstrable, mild, alveolar capillary endothelial cell damage.

Modern approaches to the therapy of septic shock

Bacteremia from gram-negative rods is a great cause of concern for hospital physicians today. Shock-complicating gram-negative sepsis has a mortality rate of 60% and above, despite early diagnosis and treatment. Intensive research efforts have shown new pathophysiological mechanisms and mediators involved in septic shock, with changes in recommended treatment protocols. In this report, the authors review the use of corticosteroids, fibronectin, naloxone hydrochloride, and immunotherapy, with emphasis on theoretical considerations and relevant clinical experience. Although these treatment methods may have been promising initially, data from large double-blind human trials are either lacking or unencouraging. While continued research and modern therapeutic approaches should improve future survival rates from septic shock, use of the therapies reviewed should be considered experimental at this time.

Negative pressure pulmonary oedema secondary to airway obstruction in an intubated infant

We report the case of a healthy one-month-old male infant who underwent an uneventful endotracheal anaesthetic for hernia repair. During transport to the recovery room (a less than 30 second trip), the endotracheal tube in the spontaneously breathing infant became obstructed, possibly due to impaction of the tip in the right main bronchus. Restoration of the airway was followed by fulminant pulmonary oedema. Several days of vigorous respiratory and pharmacologic therapy were required for resolution of the infant's respiratory distress. We review other reported cases of acute airway obstruction associated with pulmonary oedema in children and briefly describe the proposed mechanisms. The difficulties of gauging proper endotracheal tube depth in the infant are noted. This case report demonstrates the importance of continuous monitoring during patient transport to the recovery room.

Acute cardiogenic pulmonary edema: clinical and noninvasive evaluation

Left ventricular echocardiograms performed within ninety-six hours of admission were prospectively correlated with the clinical course in 87 consecutive patients admitted with acute pulmonary edema. Patients were stratified into four groups based on their two-dimensional echocardiogram: hyperdynamic, normal, mildly reduced, and severely reduced. Echocardiographic estimates of left ventricular function were compared with their ejection fraction measured by the gated radioisotope technique. The authors found that 48% of the patients were either normal or hyperdynamic (38% and 10% respectively). Patients in these two groups had a greater incidence of left ventricular hypertrophy (wall thickness greater than 13 mm) (66% vs 39%, p less than .05), hypertension on admission (BP greater than 160/100) (66% vs 41%, p = .05), and smaller end-diastolic dimension (p less than .05) than those with decreased left ventricular function. The authors conclude that echocardiography is a good screening test of left ventricular function in patients presenting with pulmonary edema. Patients with normal or increased left ventricular systolic function should be evaluated for correctable or treatable causes of acute pulmonary edema.

Prevention of acute pulmonary edema after bone marrow transplantation

In a retrospective review of 21 bone marrow transplantation procedures (BMT), we identified ten episodes of acute pulmonary edema coinciding with significant weight gain in the second week after BMT. When we prospectively observed nine consecutive BMT recipients, six patients developed acute pulmonary edema associated with significant (p less than 0.05) weight gain and an increase in echocardiographically determined left ventricular end diastolic diameter. These findings led to a prospective prophylactic intervention study of 30 consecutive BMT patients. Prophylactic intervention consisting of reduced fluid volume of parenteral alimentation, and diuretic therapy was instituted at any clinical sign of fluid overload. No episode of pulmonary edema occurred. The dramatic difference--acute pulmonary edema occurred in 16/30 untreated vs 0/30 treated cases--suggests that this post-BMT complication is critically related to fluid balance and can be prevented by careful clinical examination, close monitoring of weight change, avoidance of fluid overload and the appropriate use of diuretic therapy.

Effects of plasmapheresis and of hypoproteinemia on lung liquid conductance in awake sheep

The Starling equation, which describes net transvascular liquid flow, does not include the possibility that a reduction in plasma protein concentration may have a direct effect on lung liquid conductance or microvascular protein permeability. Nevertheless, both effects have been reported. Since these results were not predictable, we wondered whether the changes were due to the decrease in plasma protein concentration or to the process by which protein depletion was accomplished (batch plasmapheresis which involves considerable handling of blood). To separate these factors, we did control (sham) and protein removal plasmapheresis in awake sheep by two plasmapheresis methods (batch and continuous-flow). We monitored pulmonary hemodynamics, measured lung lymph flow, and determined protein concentrations in lymph and plasma. We calculated or measured the protein osmotic pressures of plasma and lymph. After control plasmapheresis, lymph flow increased and lymph:plasma protein concentration decreased but had returned to baseline levels by 4 hours. After protein removal plasmapheresis, the changes persisted for 24 hours. However, lung microvascular conductance (filtration coefficient) was not increased, except during the first 4-hour period. The changes in lymph flow and protein concentration ratio are explained using a simple two-pore model. We conclude that, over the range studied, hypoproteinemia does not increase lung microvascular liquid conductance or protein permeability.

The uncertain role of the neutrophil in increased permeability pulmonary edema

The intrapulmonic accumulation of neutrophils is a relatively common finding in certain animal models of increased permeability pulmonary edema and in humans with the adult respiratory distress syndrome. The release of toxic oxygen radicals from these cells can result in acute lung injury. Whether these cells mediate the increased permeability in all models of increased permeability pulmonary edema remains controversial. This review will examine the role of the neutrophils in various models of increased permeability pulmonary edema.

Hyperoxia and paraquat alter the kinetics of platelet serotonin uptake

Platelets and serotonin (5-HT) have been increasingly implicated in the pathophysiological response to lung microvascular injury. These experiments were undertaken to study the effect of agents known to injure the pulmonary microvasculature on platelet function, i.e., 5-HT uptake kinetics. Mice were exposed to 100% normobaric oxygen (24 to 96 hr) or pretreated ip (3 to 24 hr) with paraquat dichloride (50 mg/kg), diquat dibromide (68 mg/kg), or alpha-naphthylthiourea (ANTU, 10 mg/kg). Mouse platelet 5-HT accumulation was described by a saturable uptake system, possessing high affinity and low capacity, acting in conjunction with passive diffusion. The kinetic constants for the saturable uptake system in control mice were Km 3.37 +/- 0.32 X 10(-7) M and Vmax 46.7 +/- 3.5 pmol 10(8) platelets-1 min-1. Exposure to oxygen for 24 hr resulted in an increased affinity, Km 1.91 +/- 0.67 X 10(-7) M, and a decreased Vmax, 20.0 +/- 5.0 pmol 10(8) platelets-1 4 min-1, with no change in the passive diffusion component. Pretreatment with paraquat (3 hr) produced similar changes (Km 1.71 +/- 0.27 X 10(-7) M and Vmax 15.8 +/- 1.6 pmol 10(8) platelets-1 4 min-1), while diquat and ANTU failed to alter the kinetics of platelet 5-HT uptake. These changes appeared to require a pulmonary toxicant capable of generating a flux of oxygen radicals, and were not due to either the presence of residual toxicant, the presence of an endogenous inhibitor in platelet-rich plasma, or changes in the platelet content of endogenous 5-HT. This study has shown that hyperoxia and paraquat affect platelet function, and suggests that this alteration may contribute to the pathophysiological response of the pulmonary microvasculature to injury produced by these agents.

The synergistic influence of the intravascular starling forces on pulmonary microvascular solute flux in human ARDS

To assess the importance of the intravascular Starling forces on the pulmonary microvascular flux of solutes in ARDS, the clearance from blood to pulmonary edema fluid of a small-molecular-weight hydrophilic radiotracer, indium-111-DTPA, and a large-molecular-weight radiotracer, iodine-125-HSA, in patients with noncardiac pulmonary edema was measured. Since permeability changes of the pulmonary microvessels in ARDS are likely not homogeneous, the severity of the permeability lesion according to the magnitude of I-HSA flux was predefined. A significant positive correlation between the clearance of In-DTPA and the Pmv-pi mv gradient was found both in patients with a "moderate" (R2 = 0.46, P less than 0.01) and "severe" (R2 = 0.45 P less than 0.01) increase in microvascular permeability. The clearance of I-HSA from blood to edema fluid was also positively correlated with the Pmv and the Pmv-pi gradient. Therefore, even though ARDS is primarily characterized by a spectrum of change in permeability within the pulmonary microvasculature, the flux of both small- and large-molecular-weight solutes remains synergistically modulated by the measurable intravascular Starling forces.

Hyperoxia alters platelet disposition of serotonin

Exposure of mice to normobaric 100% oxygen for 24-96 h is known to damage the pulmonary capillary endothelium and alter the disposition of serotonin (5-hydroxytryptamine, 5-HT). We now report that such exposure increased the concentration of platelets and decreased the platelet content of 5-HT and a tracer dose of [3H]5-HT. After 48 h of hyperoxia exposure, the platelet concentration was elevated to 121% of air-exposed control values and the content of 5-HT and [3H]5-HT/10(9) platelets was decreased 76% and 57%, respectively. Kinetic analysis of the platelet 5-HT uptake process indicated that hyperoxia exposure caused an increased affinity and decreased velocity of transport. After 48 h of oxygen exposure the Km for platelet 5-HT uptake was 1.91 +/- 0.67 X 10(-7) M and the Vmax 30.1 +/- 4.6 pmol/10(8) platelets/4 min compared to air-exposed control values of Km 3.37 +/- 0.32 X 10(-7) M and Vmax 46.7 +/- 3.5 pmol/10(8) platelets/4 min, respectively. These changes in platelet 5-HT uptake and disposition may contribute to the pathophysiology of the pulmonary microvascular response to hyperoxia-induced injury.

A role for serotonin in alpha-naphthylthiourea-induced pulmonary edema

alpha-Naphthylthiourea (ANTU) damages the pulmonary capillary endothelium producing a marked pulmonary edema. Since the pulmonary microvasculature regulates the circulating levels of serotonin (5-HT), the role of 5-HT in the pathophysiology of ANTU-induced pulmonary edema was examined. Mice treated with ANTU (10 mg/kg, ip) rapidly developed pulmonary edema which was maximal at 3 hr and was resolved by 12 hr. The lung content of both endogenous 5-HT and a tracer dose of 5-[3H]HT paralleled the time course of the development and resolution of the pulmonary edema. ANTU produced a significant thrombocytopenia (58 to 72%) at all time points, and an elevated platelet content of 5-HT and 5-[3H]HT during the resolution phase (6 to 12 hr). Drugs possessing select effects on 5-HT were shown to alter the edematogenic response to ANTU. Fluoxetine, a selective inhibitor of 5-HT uptake, potentiated the pulmonary edema, while clorgyline, an irreversible inhibitor of type A monoamine oxidase, was without effect. Reserpine which depletes 5-HT stores prevented both thrombocytopenia and pulmonary edema in response to ANTU. Reloading the lung and platelet 5-HT stores of reserpinized animals reestablished the normal response to ANTU. Pretreatment with the selective 5-HT2 receptor antagonist, ketanserin, prevented the thrombocytopenia, the increase in lung content of 5-HT and 5-[3H]HT, and prevented the edematogenic response to ANTU by 70%. These data indicate a major role for 5-HT in the pathophysiology of acute lung microvascular injury produced by ANTU.

Toxicity of oxygen radicals in cultured pulmonary endothelial cells

Superoxide dismutase and catalase, which catalytically remove O-2 and H2O2, respectively, each separately protected cultured pulmonary artery endothelial cells from loss of membrane integrity after exposure to oxygen radicals generated either cellularly (polymorphonuclear leukocytes) or chemically (dihydroxyfumarate). Nicotinamide, a precursor of nicotinamide-adenine dinucleotide (NAD) and an inhibitor of ADP-ribose synthetase, also protected cultured endothelial cells from loss of membrane integrity in a concentration-dependent manner after exposure to DHF.

Effects of sequential periods of intracranial hypertension on lung fluid balance

Pulmonary hemodynamics and fluid and protein exchange were examined in dogs subjected to three successive periods of intracranial hypertension. Results indicate that the alteration in lung fluid balance is due to increased microvascular surface area following capillary recruitment. The relationship to the mechanism of neurogenic pulmonary edema is discussed.

Reparative changes following oxygen-induced lung injury: effect on serotonin disposition and metabolism

Exposure of mice to normobaric 100% oxygen for 72 hr has been shown to damage lung capillary endothelial cells and to markedly alter the pulmonary disposition and metabolism of endogenous serotonin (5-HT) and exogenous [3H]5-HT in a time-dependent manner. We have extended these studies to examine the reparative changes occurring in lung following moderate oxygen-induced injury. Pulmonary angiotensin converting enzyme (ACE) activity, a biochemical marker of endothelial cell injury, was decreased after a 72-hr oxygen exposure and progressively increased above control levels during the recovery period (130%, 168 hr) and paralleled lung protein content. The pulmonary disposition of [3H]5-HT also provided an index of endothelial cell function. Lung levels of [3H]5-HT were elevated 183% (0 hr) and 200% (24 hr) and returned to control values by 72 hr of air recovery. Pulmonary edema followed a similar time-course that corresponded to reported ultrastructural changes. The circulating platelet concentration progressively decreased from control values at 0 hr to 68% of control of 168 hr. In contrast to lung where 5-HT was significantly elevated during the early reparative period, platelet 5-HT content was significantly decreased and, like lung, returned to control values by 72 hr. The two forms of lung monoamine oxidase (MAO) showed different responses during the reparative phase. Type A MAO was slightly elevated throughout the recovery period. In contrast, type B MAO was decreased at 0 hr but increased throughout the reparative phase, being significantly elevated 128% at 72 hr and 139% at 168 hr. These data suggest that the lung is capable of readily recovering from moderate oxygen-induced injury and that certain biochemical parameters described herein provide useful indices of pulmonary microvascular function.

Pulmonary edema induced by high intravenous doses of diatrizoate in the rat

Using a simple, sensitive model, it has been demonstrated that intravenous administration of high doses of contrast medium can induce pulmonary edema in non-anesthetized rats. The degree of edema formation, which is dependent on the rate of injection as well as dose, is greatest immediately after injection and then decreases slowly. The amount of fluid accumulation in the lungs is related to the chemotoxicity of the medium as other solutions of equivalent hyperosmolality did not induce the same degree of pulmonary edema.

Effect of changes in pleural pressure on fluid filtration rate in expanded and collapsed rabbit lungs

Eight isolated rabbit lungs were suspended from a force-displacement transducer and perfused at constant flow. The pressure surrounding the lungs ("pleural" pressure) was then reduced from -0.5 kPa to -1.0 and -1.5 kPa, and the rate of weight gain recorded. The step reductions in "pleural" pressure produced greater increases in pulmonary vascular volume and fluid filtration rate when the lungs were collapsed than when they were expanded, thus suggesting that the change in "pleural" pressure was more effectively transmitted to the perimicrovascular space when the lung was collapsed. These observations may help to explain the phenomenon of re-expansion pulmonary oedema.