Lymphatics and lymph in acute lung injury

Spontaneous breathing promotes lung injury in an experimental model of alveolar collapse

Vigorous spontaneous breathing has emerged as a promotor of lung damage in acute lung injury, an entity known as “patient self-inflicted lung injury”. Mechanical ventilation may prevent this second injury by decreasing intrathoracic pressure swings and improving regional air distribution. Therefore, we aimed to determine the effects of spontaneous breathing during the early stage of acute respiratory failure on lung injury and determine whether early and late controlled mechanical ventilation may avoid or revert these harmful effects. A model of partial surfactant depletion and lung collapse was induced in eighteen intubated pigs of 32 ±4 kg. Then, animals were randomized to (1) SB‐group: spontaneous breathing with very low levels of pressure support for the whole experiment (eight hours), (2) Early MV-group: controlled mechanical ventilation for eight hours, or (3) Late MV-group: first half of the experiment on spontaneous breathing (four hours) and the second half on controlled mechanical ventilation (four hours). Respiratory, hemodynamic, and electric impedance tomography data were collected. After the protocol, animals were euthanized, and lungs were extracted for histologic tissue analysis and cytokines quantification. SB-group presented larger esophageal pressure swings, progressive hypoxemia, lung injury, and more dorsal and inhomogeneous ventilation compared to the early MV-group. In the late MV-group switch to controlled mechanical ventilation improved the lung inhomogeneity and esophageal pressure swings but failed to prevent hypoxemia and lung injury. In a lung collapse model, spontaneous breathing is associated to large esophageal pressure swings and lung inhomogeneity, resulting in progressive hypoxemia and lung injury. Mechanical ventilation prevents these mechanisms of patient self-inflicted lung injury if applied early, before spontaneous breathing occurs, but not when applied late.

Duodenum edema due to reduced lymphatic drainage leads to increased inflammation in a porcine endotoxemic model

Background

Interventions, such as mechanical ventilation with high positive end-expiratory pressure (PEEP), increase inflammation in abdominal organs. This effect could be due to reduced venous return and impaired splanchnic perfusion, or intestinal edema by reduced lymphatic drainage. However, it is not clear whether abdominal edema per se leads to increased intestinal inflammation when perfusion is normal. The aim of the presented study was to investigate if an impaired thoracic duct function can induce edema of the abdominal organs and if it is associated to increase inflammation when perfusion is maintained normal. In a porcine model, endotoxin was used to induce systemic inflammation. In the Edema group (n = 6) the abdominal portion of the thoracic duct was ligated, while in the Control group (7 animals) it was maintained intact. Half of the animals underwent a diffusion weighted-magnetic resonance imaging (DW-MRI) at the end of the 6-h observation period to determine the abdominal organ perfusion. Edema in abdominal organs was assessed using wet–dry weight and with MRI. Inflammation was assessed by measuring cytokine concentrations in abdominal organs and blood as well as histopathological analysis of the abdominal organs.

Results

Organ perfusion was similar in both groups, but the Edema group had more intestinal (duodenum) edema, ascites, higher intra-abdominal pressure (IAP) at the end of observation time, and higher cytokine concentration in the small intestine. Systemic cytokines (from blood samples) correlated with IAP.

Conclusions

In this experimental endotoxemic porcine model, the thoracic duct’s ligation enhanced edema formation in the duodenum, and it was associated with increased inflammation.

Pulmonary Interstitial Matrix and Lung Fluid Balance From Normal to the Acutely Injured Lung

This review analyses the mechanisms by which lung fluid balance is strictly controlled in the air-blood barrier (ABB). Relatively large trans-endothelial and trans-epithelial Starling pressure gradients result in a minimal flow across the ABB thanks to low microvascular permeability aided by the macromolecular structure of the interstitial matrix. These edema safety factors are lost when the integrity of the interstitial matrix is damaged. The result is that small Starling pressure gradients, acting on a progressively expanding alveolar barrier with high permeability, generate a high transvascular flow that causes alveolar flooding in minutes. We modeled the trans-endothelial and trans-epithelial Starling pressure gradients under control conditions, as well as under increasing alveolar pressure (Palv) conditions of up to 25 cmH2O. We referred to the wet-to-dry weight (W/D) ratio, a specific index of lung water balance, to be correlated with the functional state of the interstitial structure. W/D averages ∼5 in control and might increase by up to ∼9 in severe edema, corresponding to ∼70% loss in the integrity of the native matrix. Factors buffering edemagenic conditions include: (i) an interstitial capacity for fluid accumulation located in the thick portion of ABB, (ii) the increase in interstitial pressure due to water binding by hyaluronan (the "safety factor" opposing the filtration gradient), and (iii) increased lymphatic flow. Inflammatory factors causing lung tissue damage include those of bacterial/viral and those of sterile nature. Production of reactive oxygen species (ROS) during hypoxia or hyperoxia, or excessive parenchymal stress/strain [lung overdistension caused by patient self-induced lung injury (P-SILI)] can all cause excessive inflammation. We discuss the heterogeneity of intrapulmonary distribution of W/D ratios. A W/D ∼6.5 has been identified as being critical for the transition to severe edema formation. Increasing Palv for W/D > 6.5, both trans-endothelial and trans-epithelial gradients favor filtration leading to alveolar flooding. Neither CT scan nor ultrasound can identify this initial level of lung fluid balance perturbation. A suggestion is put forward to identify a non-invasive tool to detect the earliest stages of perturbation of lung fluid balance before the condition becomes life-threatening.

Transpulmonary thermodilution detects rapid and reversible increases in lung water induced by positive end-expiratory pressure in acute respiratory distress syndrome

PURPOSE

It has been suggested that, by recruiting lung regions and enlarging the distribution volume of the cold indicator, increasing the positive end-expiratory pressure (PEEP) may lead to an artefactual overestimation of extravascular lung water (EVLW) by transpulmonary thermodilution (TPTD).

METHODS

In 60 ARDS patients, we measured EVLW (PiCCO2 device) at a PEEP level set to reach a plateau pressure of 30 cmH₂O (HighPEEP_start) and 15 and 45 min after decreasing PEEP to 5 cmH₂O (LowPEEP_15' and LowPEEP_45', respectively). Then, we increased PEEP back to the baseline level (HighPEEP_end). Between HighPEEP_start and LowPEEP_15', we estimated the degree of lung derecruitment either by measuring changes in the compliance of the respiratory system (Crs) in the whole population, or by measuring the lung derecruited volume in 30 patients. We defined patients with a large derecruitment from the other ones as patients in whom the Crs changes and the measured derecruited volume were larger than the median of these variables observed in the whole population.

RESULTS

Reducing PEEP from HighPEEP_start (14 ± 2 cmH₂O) to LowPEEP_15' significantly decreased EVLW from 20 ± 4 to 18 ± 4 mL/kg, central venous pressure (CVP) from 15 ± 4 to 12 ± 4 mmHg, the arterial oxygen tension over inspired oxygen fraction (PaO₂/FiO₂) ratio from 184 ± 76 to 150 ± 69 mmHg and lung volume by 144 [68-420] mL. The EVLW decrease was similar in "large derecruiters" and the other patients. When PEEP was re-increased to HighPEEP_end, CVP, PaO₂/FiO₂ and EVLW significantly re-increased. At linear mixed effect model, EVLW changes were significantly determined only by changes in PEEP and CVP (p < 0.001 and p = 0.03, respectively, n = 60). When the same analysis was performed by estimating recruitment according to lung volume changes (n = 30), CVP remained significantly associated to the changes in EVLW (p < 0.001).

CONCLUSIONS

In ARDS patients, changing the PEEP level induced parallel, small and reversible changes in EVLW. These changes were not due to an artefact of the TPTD technique and were likely due to the PEEP-induced changes in CVP, which is the backward pressure of the lung lymphatic drainage. Trial registration ID RCB: 2015-A01654-45. Registered 23 October 2015.

Static and Dynamic Transpulmonary Driving Pressures Affect Lung and Diaphragm Injury during Pressure-controlled versus Pressure-support Ventilation in Experimental Mild Lung Injury in Rats

BACKGROUND

Pressure-support ventilation may worsen lung damage due to increased dynamic transpulmonary driving pressure. The authors hypothesized that, at the same tidal volume (VT) and dynamic transpulmonary driving pressure, pressure-support and pressure-controlled ventilation would yield comparable lung damage in mild lung injury.

METHODS

Male Wistar rats received endotoxin intratracheally and, after 24 h, were ventilated in pressure-support mode. Rats were then randomized to 2 h of pressure-controlled ventilation with VT, dynamic transpulmonary driving pressure, dynamic transpulmonary driving pressure, and inspiratory time similar to those of pressure-support ventilation. The primary outcome was the difference in dynamic transpulmonary driving pressure between pressure-support and pressure-controlled ventilation at similar VT; secondary outcomes were lung and diaphragm damage.

RESULTS

At VT = 6 ml/kg, dynamic transpulmonary driving pressure was higher in pressure-support than pressure-controlled ventilation (12.0 ± 2.2 vs. 8.0 ± 1.8 cm H2O), whereas static transpulmonary driving pressure did not differ (6.7 ± 0.6 vs. 7.0 ± 0.3 cm H2O). Diffuse alveolar damage score and gene expression of markers associated with lung inflammation (interleukin-6), alveolar-stretch (amphiregulin), epithelial cell damage (club cell protein 16), and fibrogenesis (metalloproteinase-9 and type III procollagen), as well as diaphragm inflammation (tumor necrosis factor-α) and proteolysis (muscle RING-finger-1) were comparable between groups. At similar dynamic transpulmonary driving pressure, as well as dynamic transpulmonary driving pressure and inspiratory time, pressure-controlled ventilation increased VT, static transpulmonary driving pressure, diffuse alveolar damage score, and gene expression of markers of lung inflammation, alveolar stretch, fibrogenesis, diaphragm inflammation, and proteolysis compared to pressure-support ventilation.

CONCLUSIONS

In the mild lung injury model use herein, at the same VT, pressure-support compared to pressure-controlled ventilation did not affect biologic markers. However, pressure-support ventilation was associated with a major difference between static and dynamic transpulmonary driving pressure; when the same dynamic transpulmonary driving pressure and inspiratory time were used for pressure-controlled ventilation, greater lung and diaphragm injury occurred compared to pressure-support ventilation.

The post-cardiac arrest syndrome: A case for lung-brain coupling and opportunities for neuroprotection

Systemic inflammation and multi-organ failure represent hallmarks of the post-cardiac arrest syndrome (PCAS) and predict severe neurological injury and often fatal outcomes. Current interventions for cardiac arrest focus on the reversal of precipitating cardiac pathologies and the implementation of supportive measures with the goal of limiting damage to at-risk tissue. Despite the widespread use of targeted temperature management, there remain no proven approaches to manage reperfusion injury in the period following the return of spontaneous circulation. Recent evidence has implicated the lung as a moderator of systemic inflammation following remote somatic injury in part through effects on innate immune priming. In this review, we explore concepts related to lung-dependent innate immune priming and its potential role in PCAS. Specifically, we propose and investigate the conceptual model of lung-brain coupling drawing from the broader literature connecting tissue damage and acute lung injury with cerebral reperfusion injury. Subsequently, we consider the role that interventions designed to short-circuit lung-dependent immune priming might play in improving patient outcomes following cardiac arrest and possibly other acute neurological injuries.

Ventilator-induced Lung Injury

Prevention of ventilator-induced lung injury (VILI) can attenuate multiorgan failure and improve survival in at-risk patients. Clinically significant VILI occurs from volutrauma, barotrauma, atelectrauma, biotrauma, and shear strain. Differences in regional mechanics are important in VILI pathogenesis. Several interventions are available to protect against VILI. However, most patients at risk of lung injury do not develop VILI. VILI occurs most readily in patients with concomitant physiologic insults. VILI prevention strategies must balance risk of lung injury with untoward side effects from the preventive effort, and may be most effective when targeted to subsets of patients at increased risk.

Fluconazole treatment of intrauterine Candida albicans infection in fetal sheep

BACKGROUND

Intrauterine Candida albicans infection causes severe fetal inflammatory responses and fetal injury in an ovine model. We hypothesized that intra-amniotic antifungal therapy with fluconazole would decrease the adverse fetal effects of intra-amniotic C. albicans in sheep.

METHODS

Sheep received an intra-amniotic injection of 10(7) colony-forming units C. albicans. After 2 d, animals were then randomized to: (i) intra-amniotic and fetal intraperitoneal saline with delivery after 24 h (3 d C. albicans group); (ii) intra-amniotic and fetal intraperitoneal injections of fluconazole with delivery after either 24 h (3 d C. albicans plus 1 d fluconazole group) or 72 h (5 d C. albicans plus 3 d fluconazole group). Controls received intra-amniotic injections of saline followed by intra-amniotic and fetal intraperitoneal fluconazole injections.

RESULTS

Intra-amniotic C. albicans caused severe fetal inflammatory responses characterized by decreases in lymphocytes and platelets, an increase in posterior mediastinal lymph node weight and proinflammatory mRNA responses in the fetal lung, liver, and spleen. Fluconazole treatment temporarily decreased the pulmonary and chorioamnion inflammatory responses.

CONCLUSION

The severe fetal inflammatory responses caused by intra-amniotic C. albicans infection were transiently decreased with fluconazole. A timely fetal delivery of antimicrobial agents may prevent fetal injury associated with intrauterine infection.

Oral, nasal and pharyngeal exposure to lipopolysaccharide causes a fetal inflammatory response in sheep

Background

A fetal inflammatory response (FIR) in sheep can be induced by intraamniotic or selective exposure of the fetal lung or gut to lipopolysaccharide (LPS). The oral, nasal, and pharyngeal cavities (ONP) contain lymphoid tissue and epithelium that are in contact with the amniotic fluid. The ability of the ONP epithelium and lymphoid tissue to initiate a FIR is unknown.

Objective

To determine if FIR occurs after selective ONP exposure to LPS in fetal sheep.

Methods

Using fetal recovery surgery, we isolated ONP from the fetal lung, GI tract, and amniotic fluid by tracheal and esophageal ligation and with an occlusive glove fitted over the snout. LPS (5 mg) or saline was infused with 24 h Alzet pumps secured in the oral cavity (n = 7–8/group). Animals were delivered 1 or 6 days after initiation of the LPS or saline infusions.

Results

The ONP exposure to LPS had time-dependent systemic inflammatory effects with changes in WBC in cord blood, an increase in posterior mediastinal lymph node weight at 6 days, and pro-inflammatory mRNA responses in the fetal plasma, lung, and liver. Compared to controls, the expression of surfactant protein A mRNA increased 1 and 6 days after ONP exposure to LPS.

Conclusion

ONP exposure to LPS alone can induce a mild FIR with time-dependent inflammatory responses in remote fetal tissues not directly exposed to LPS.

Mechanical ventilation and intra-abdominal hypertension: 'Beyond Good and Evil'

Intra-abdominal hypertension is frequent in surgical and medical critically ill patients. Intra-abdominal hypertension has a serious impact on the function of respiratory as well as peripheral organs. In the presence of alveolar capillary damage, which occurs in acute respiratory distress syndrome (ARDS), intra-abdominal hypertension promotes lung injury as well as edema, impedes the pulmonary lymphatic drainage, and increases intra-thoracic pressures, leading to atelectasis, airway closure, and deterioration of respiratory mechanics and gas exchange. The optimal setting of mechanical ventilation and its impact on respiratory function and hemodynamics in ARDS associated with intra-abdominal hypertension are far from being assessed. We suggest that the optimal ventilator management of patients with ARDS and intra-abdominal hypertension would include the following: (a) intra-abdominal, esophageal pressure, and hemodynamic monitoring; (b) ventilation setting with protective tidal volume, recruitment maneuver, and level of positive end-expiratory pressure set according to the 'best' compliance of the respiratory system or the lung; (c) deep sedation with or without neuromuscular paralysis in severe ARDS; and (d) open abdomen in selected patients with severe abdominal compartment syndrome.

Effects of different tidal volumes in pulmonary and extrapulmonary lung injury with or without intraabdominal hypertension

PURPOSE

We hypothesized that: (1) intraabdominal hypertension increases pulmonary inflammatory and fibrogenic responses in acute lung injury (ALI); (2) in the presence of intraabdominal hypertension, higher tidal volume reduces lung damage in extrapulmonary ALI, but not in pulmonary ALI.

METHODS

Wistar rats were randomly allocated to receive Escherichia coli lipopolysaccharide intratracheally (pulmonary ALI) or intraperitoneally (extrapulmonary ALI). After 24 h, animals were randomized into subgroups without or with intraabdominal hypertension (15 mmHg) and ventilated with positive end expiratory pressure = 5 cmH(2)O and tidal volume of 6 or 10 ml/kg during 1 h. Lung and chest wall mechanics, arterial blood gases, lung and distal organ histology, and interleukin (IL)-1β, IL-6, caspase-3 and type III procollagen (PCIII) mRNA expressions in lung tissue were analyzed.

RESULTS

With intraabdominal hypertension, (1) chest-wall static elastance increased, and PCIII, IL-1β, IL-6, and caspase-3 expressions were more pronounced than in animals with normal intraabdominal pressure in both ALI groups; (2) in extrapulmonary ALI, higher tidal volume was associated with decreased atelectasis, and lower IL-6 and caspase-3 expressions; (3) in pulmonary ALI, higher tidal volume led to higher IL-6 expression; and (4) in pulmonary ALI, liver, kidney, and villi cell apoptosis was increased, but not affected by tidal volume.

CONCLUSIONS

Intraabdominal hypertension increased inflammation and fibrogenesis in the lung independent of ALI etiology. In extrapulmonary ALI associated with intraabdominal hypertension, higher tidal volume improved lung morphometry with lower inflammation in lung tissue. Conversely, in pulmonary ALI associated with intraabdominal hypertension, higher tidal volume increased IL-6 expression.

Toward managing chronic rejection after lung transplant: the fate and effects of inhaled cyclosporine in a complex environment

The fate and effects of inhaled cyclosporine A (CsA) are considered after deposition on the lung surface. Special emphasis is given to a post-lung transplant environment and to the potential effects of the drug on the various cell types it is expected to encounter. The known stability, metabolism, pharmacokinetics and pharmacodynamics of the drug have been reviewed and discussed in the context of the lung microenvironment. Arguments support the contention that the immuno-inhibitory and anti-inflammatory effects of CsA are not restricted to T-cells. It is likely that pharmacologically effective concentrations of CsA can be sustained in the lungs but due to the complexity of uptake and action, the elucidation of effective posology must ultimately rely on clinical evidence.

Noninvasive measurement of edema in partial thickness burn wounds

A lack of noninvasive tools to quantify edema has limited our understanding of burn wound edema pathophysiology in a clinical setting. Near-infrared spectroscopy (NIR) is a new noninvasive tool able to measure water concentration/edema in tissue. The purpose of this study was to determine whether NIR could detect water concentration changes or edema formation in acute partial-thickness burn injuries. Adult burn patients within 72 hours postinjury, thermal etiology, partial-thickness burn depth, and <20% TBSA were included. Burn wounds were stratified into partial-thickness superficial or deep wounds based on histology and wound healing time. NIR devices were used to quantify edema in a burn and respective control sites. The sample population consisted of superficial (n = 12) and deep (n = 5) partial-thickness burn injuries. The patients did not differ with respect to age (40 +/- 15 years), TBSA (5 +/- 4%), and mean time for edema assessment (2 days). Water content increased 15% in burned tissue compared with the respective control regions. There were no differences in water content at the control sites. At 48 hours, deep partial-thickness injuries showed a 23% increase in water content compared with 18% superficial partial-thickness burns. NIR could detect differences in water content or edema formation in partial-thickness burns and unburned healthy regions. NIR holds promise as a noninvasive, portable clinical tool to quantify water content or edema in burn wounds.

Modulation of fetal inflammatory response on exposure to lipopolysaccharide by chorioamnion, lung, or gut in sheep

OBJECTIVE

We hypothesized that fetal lipopolysaccharide exposures to the chorioamnion, lung, or gut would induce distinct systemic inflammatory responses.

STUDY DESIGN

Groups of 5-7 time-mated ewes were used to surgically isolate the fetal respiratory and the gastrointestinal systems from the amniotic compartment. Outcomes were assessed at 124 days gestational age, 2 days and 7 days after lipopolysaccharide (10 mg, Escherichia coli 055:B5) or saline solution infusions into the fetal airways or amniotic fluid.

RESULTS

Lipopolysaccharide induced systemic inflammatory changes in all groups in the blood, lung, liver, and thymic lymphocytes. Changes in lymphocytes in the posterior mediastinal lymph node draining lung and gut, occurred only after direct contact of lipopolysaccharide with the fetal lung or gut.

CONCLUSION

Fetal systemic inflammatory responses occurred after chorioamnion, lung, or gut exposures to lipopolysaccharide. The organ responses differed based on route of the fetal exposure.

Intralobular pulmonary lymphatic distribution in normal human lung using D2-40 antipodoplanin immunostaining

It has been assumed for a long time that except for limited areas close to respiratory bronchioles or their satellite arteries, there is no evidence of lymphatic vessels deep in the pulmonary lobule. An immunohistochemical study using the D2-40 monoclonal antibody was performed on normal pulmonary samples obtained from surgical specimens, with particular attention to the intralobular distribution of lymphatic vessels. This study demonstrated the presence of lymphatics not only in the connective tissue surrounding the respiratory bronchioles but also associated with intralobular arterioles and/or small veins even less than 50 mum in diameter. A few interlobular lymphatic vessels with a diameter ranging from 10 mum to 20 mum were also observed further away, in interalveolar walls. In conclusion, this study, using the D2-40 monoclonal antibody, demonstrated the presence of small lymphatic channels within the normal human pulmonary lobules, emerging from interalveolar interstitium, and around small blood vessels constituting the paraalveolar lymphatics. This thin intralobular lymphatic network may play a key pathophysiological role in a wide variety of alveolar and interstitial lung diseases and requires further investigation.

Altered pharmacology in the Intensive Care Unit patient

Critically ill patients, not infrequently present alterations of physiological parameters that determine the success/failure of therapeutic interventions as well as the final outcome. Sepsis and polytrauma are two of the most common and complex syndromes occurring in Intensive Care Unit (ICU) and affect drug absorption, disposition, metabolism and elimination. Pharmacological management of ICU patients requires consideration of the unique pharmacokinetics associated with these clinical conditions and the likely occurrence of drug interaction. Rational adjustment in drug choice and dosing contributes to the appropriateness of treatment of those patients.