Altering the mechanical scenario to decrease the driving pressure

Ventilator settings resulting in decreased driving pressure (ΔP) are positively associated with survival. How to further foster the potential beneficial mediator effect of a reduced ΔP? One possibility is promoting the active modification of the lung’s “mechanical scenario” by means of lung recruitment and positive end-expiratory pressure selection. By taking into account the individual distribution of the threshold-opening airway pressures to achieve maximal recruitment, a redistribution of the tidal volume from overdistended to newly recruited lung occurs. The resulting more homogeneous distribution of transpulmonary pressures may induce a relief of overdistension in the upper regions. The gain in lung compliance after a successful recruitment rescales the size of the functional lung, potentially allowing for a further reduction in ΔP.

THAM reduces CO2-associated increase in pulmonary vascular resistance - an experimental study in lung-injured piglets

INTRODUCTION

Low tidal volume (VT) ventilation is recommended in patients with acute respiratory distress syndrome (ARDS). This may increase arterial carbon dioxide tension (PaCO2), decrease pH, and augment pulmonary vascular resistance (PVR). We hypothesized that Tris(hydroxymethyl)aminomethane (THAM), a pure proton acceptor, would dampen these effects, preventing the increase in PVR.

METHODS

A one-hit injury ARDS model was established by repeated lung lavages in 18 piglets. After ventilation with VT of 6 ml/kg to maintain normocapnia, VT was reduced to 3 ml/kg to induce hypercapnia. Six animals received THAM for 1 h, six for 3 h, and six serving as controls received no THAM. In all, the experiment continued for 6 h. The THAM dosage was calculated to normalize pH and exhibit a lasting effect. Gas exchange, pulmonary, and systemic hemodynamics were tracked. Inflammatory markers were obtained at the end of the experiment.

RESULTS

In the controls, the decrease in VT from 6 to 3 ml/kg increased PaCO2 from 6.0±0.5 to 13.8±1.5 kPa and lowered pH from 7.40±0.01 to 7.12±0.06, whereas base excess (BE) remained stable at 2.7±2.3 mEq/L to 3.4±3.2 mEq/L. In the THAM groups, PaCO2 decreased and pH increased above 7.4 during the infusions. After discontinuing the infusions, PaCO2 increased above the corresponding level of the controls (15.2±1.7 kPa and 22.6±3.3 kPa for 1-h and 3-h THAM infusions, respectively). Despite a marked increase in BE (13.8±3.5 and 31.2±2.2 for 1-h and 3-h THAM infusions, respectively), pH became similar to the corresponding levels of the controls. PVR was lower in the THAM groups (at 6 h, 329±77 dyn∙s/m(5) and 255±43 dyn∙s/m(5) in the 1-h and 3-h groups, respectively, compared with 450±141 dyn∙s/m(5) in the controls), as were pulmonary arterial pressures.

CONCLUSIONS

The pH in the THAM groups was similar to pH in the controls at 6 h, despite a marked increase in BE. This was due to an increase in PaCO2 after stopping the THAM infusion, possibly by intracellular release of CO2. Pulmonary arterial pressure and PVR were lower in the THAM-treated animals, indicating that THAM may be an option to reduce PVR in acute hypercapnia.

Maintenance of airway pressure during filter exchange due to auto-triggering

BACKGROUND

Daily routine ventilator-filter exchange interrupts the integrity of the ventilator circuit. We hypothesized that this might reduce positive airway pressure in mechanically ventilated ICU patients, inducing alveolar collapse and causing impaired oxygenation and compliance of the respiratory system.

METHODS

We studied 40 consecutive ICU subjects (P(aO2)/F(IO2) ratio ≤ 300 mm Hg), mechanically ventilated with pressure-regulated volume control or pressure support and PEEP ≥ 5 cm H2O. Before the filter exchange, (baseline) tidal volume, breathing frequency, end-inspiratory plateau pressure, and PEEP were recorded. Compliance of the respiratory system was calculated; F(IO2), blood pressure, and pulse rate were registered; and P(aO2), P(aCO2), pH, and base excess were measured. Measurements were repeated 15 and 60 min after the filter exchange. In addition, a bench test was performed with a precision test lung with similar compliance and resistance as in the clinical study.

RESULTS

The exchange of the filter took 3.5 ± 1.2 s (mean ± SD). There was no significant change in P(aO2) (89 ± 16 mm Hg at baseline vs 86 ± 16 mm Hg at 15 min and 88 ± 18 mm Hg at 60 min, P = .24) or in compliance of the respiratory system (41 ± 11 mL/cm H2O at baseline vs 40 ± 12 mL/cm H2O at 15 min and 40 ± 12 mL/cm H2O at 60 min, P = .32). The bench study showed that auto-triggering by the ventilator when disconnecting from the expiratory circuit kept the tracheal pressure above PEEP for at least 3 s with pressure controlled ventilation.

CONCLUSIONS

This study showed that a short disconnection of the expiratory ventilator circuit from the ventilator during filter exchange was not associated with any significant deterioration in lung function 15 and 60 min later. This result may be explained by auto-triggering of the ventilator with high inspiratory flows during the filter exchange, maintaining airway pressure.

Impairment of neutrophilic glucocorticoid receptor function in patients treated with steroids for septic shock

Background

Glucocorticoid (GC) treatment has variable effect in sepsis. This may be explained by decreased expression or function of the glucocorticoid receptor (GR). The aim of this study was to determine GR expression and binding capacity in patients during and after sepsis.

Methods

In this prospective, non-interventional clinical study, peripheral blood and clinical data were collected from 20 adult patients at five timepoints during sepsis and 5–13 months after recovery. GR expression and binding capacity were assessed by flow cytometry.

Results

GR expression was higher in T lymphocytes from patients with septic shock compared to healthy subjects (p = 0.01). While there was no difference in GR expression between GC-treated and non-treated patients, GR binding capacity was lower in GC-treated patients at admission compared to healthy subjects (p ≤ 0.03). After the acute inflammation inflammatory phase, GR binding capacity was still lower in neutrophils of GC-treated patients, compared to healthy subjects (p = 0.01). On admission, GR binding capacity in T lymphocytes and neutrophils was inversely correlated with noradrenaline dose and lactate (p ≤ 0.03).

Conclusions

Our data suggest that GR expression is increased in T lymphocytes during septic shock regardless of GC treatment, while GR binding capacity is decreased in neutrophils in GC-treated patients. As neutrophils are the predominant circulating leucocyte in septic shock, their decreased GR binding capacity may impede the response to exogenous or endogenous glucocorticoids.

No redistribution of lung blood flow by inhaled nitric oxide in endotoxemic piglets pretreated with an endothelin receptor antagonist

Inhaled nitric oxide (INO) improves ventilation-perfusion matching and alleviates pulmonary hypertension in patients with acute respiratory distress syndrome. However, outcome has not yet been shown to improve, and nonresponse is common. A better understanding of the mechanisms by which INO acts may guide in improving treatment with INO in patients with severe respiratory failure. We hypothesized that INO may act not only by vasodilation in ventilated lung regions, but also by causing vasoconstriction via endothelin (ET-1) in atelectatic, nonventilated lung regions. This was studied in 30 anesthetized, mechanically ventilated piglets. The fall in oxygenation and rise in pulmonary artery pressure during a sepsislike condition (infusion of endotoxin) were blunted by INO 40 ppm. Endotoxin infusion increased serum ET-1, and INO almost doubled the ratio between mRNA expression of endothelin receptor A (mediating vasoconstriction) and B (mediating vasodilation and clearance of ET-1) (ET-A/ET-B) in atelectatic lung regions. INO caused a shift in blood flow away from atelectatic lung regions in the endotoxemic piglets, but not during ET receptor antagonism. We conclude that INO in short-term experiments, in addition to causing selective pulmonary vasodilation in ventilated lung regions, increases the ET-A/ET-B mRNA expression ratio in lung tissue. This might augment the vasoconstriction in atelectatic lung regions, enhancing the redistribution of pulmonary blood flow to ventilated lung regions which are reached by INO. Such vasoconstriction may be an important additional factor explaining the effect of INO.

First-time imaging of effects of inspired oxygen concentration on regional lung volumes and breathing pattern during hypergravity

PURPOSE

Aeroatelectasis can develop in aircrew flying the latest generation high-performance aircraft. Causes alleged are relative hyperoxia, increased gravity in the head-to-foot direction (+Gz), and compression of legs and stomach by anti-G trousers (AGT). We aimed to assess, in real time, the effects of hyperoxia, +Gz accelerations and AGT inflation on changes in regional lung volumes and breathing pattern evaluated in an axial plane by electrical impedance tomography (EIT).

METHODS

The protocol mimicked a routine peacetime flight in combat aircraft. Eight subjects wearing AGT were studied in a human centrifuge during 1 h 15 min exposure of +1 to +3.5Gz. They performed this sequence three times, breathing AIR, 44.5 % O2 or 100 % O2. Continuous recording of functional EIT enabled uninterrupted assessment of regional lung volumes at the 5th intercostal level. Breathing pattern was also monitored.

RESULTS

EIT data showed that +3.5Gz, compared with any moment without hypergravity, caused an abrupt decrease in regional tidal volume (VT) and regional end-expiratory lung volume (EELV) measured in the EIT slice, independently of inspired oxygen concentration. Breathing AIR or 44.5 % O2, sub-regional EELV measured in the EIT slice decreased similarly in dorsal and ventral regions, but sub-regional VT measured in the EIT slice decreased significantly more dorsally than ventrally. Breathing 100 % O2, EELV and VT decreased similarly in both regions. Inspired tidal volume increased in hyperoxia, whereas breathing frequency increased in hypergravity and hyperoxia.

CONCLUSIONS

Our findings suggest that hypergravity and AGT inflation cause airway closure and air trapping in gravity-dependent lung regions, facilitating absorption atelectasis formation, in particular during hyperoxia.

Non-lobar atelectasis generates inflammation and structural alveolar injury in the surrounding healthy tissue during mechanical ventilation

Introduction

When alveoli collapse the traction forces exerted on their walls by adjacent expanded units may increase and concentrate. These forces may promote its re-expansion at the expense of potentially injurious stresses at the interface between the collapsed and the expanded units. We developed an experimental model to test the hypothesis that a local non-lobar atelectasis can act as a stress concentrator, contributing to inflammation and structural alveolar injury in the surrounding healthy lung tissue during mechanical ventilation.

Methods

A total of 35 rats were anesthetized, paralyzed and mechanically ventilated. Atelectasis was induced by bronchial blocking: after five minutes of stabilization and pre-oxygenation with F_IO₂ = 1.0, a silicon cylinder blocker was wedged in the terminal bronchial tree. Afterwards, the animals were randomized between two groups: 1) Tidal volume (V_T) = 10 ml/kg and positive end-expiratory pressure (PEEP) = 3 cmH₂O (V_T10/PEEP3); and 2) V_T = 20 ml/kg and PEEP = 0 cmH₂O (V_T20/zero end-expiratory pressure (ZEEP)). The animals were then ventilated during 180 minutes. Three series of experiments were performed: histological (n = 12); tissue cytokines (n = 12); and micro-computed tomography (microCT; n = 2). An additional six, non-ventilated, healthy animals were used as controls.

Results

Atelectasis was successfully induced in the basal region of the lung of 26 out of 29 animals. The microCT of two animals revealed that the volume of the atelectasis was 0.12 and 0.21 cm³. There were more alveolar disruption and neutrophilic infiltration in the peri-atelectasis region than the corresponding contralateral lung (control) in both groups. Edema was higher in the peri-atelectasis region than the corresponding contralateral lung (control) in the V_T20/ZEEP than V_T10/PEEP3 group. The volume-to-surface ratio was higher in the peri-atelectasis region than the corresponding contralateral lung (control) in both groups. We did not find statistical difference in tissue interleukin-1β and cytokine-induced neutrophil chemoattractant-1 between regions.

Conclusions

The present findings suggest that a local non-lobar atelectasis acts as a stress concentrator, generating structural alveolar injury and inflammation in the surrounding lung tissue.

A ventilation strategy during general anaesthesia to reduce postoperative atelectasis

BACKGROUND

Atelectasis is common during and after general anaesthesia. We hypothesized that a ventilation strategy, without recruitment manoeuvres, using a combination of continuous positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP) and a reduced end-expiratory oxygen fraction (FETO2) before ending mask ventilation with CPAP after extubation would reduce the area of postoperative atelectasis.

METHODS

Thirty patients were randomized into three groups. During induction and emergence, inspiratory oxygen fractions (FIO2) were 1.0 in the control group and 1.0 or 0.8 in the intervention groups. No CPAP/PEEP was used in the control group, whereas CPAP/PEEP of 6 cmH2O was used in the intervention groups. After extubation, FIO2 was set to 0.30 in the intervention groups and CPAP was applied, aiming at FETO2 < 0.30. Atelectasis was studied by computed tomography 25 min postoperatively.

RESULTS

The median area of atelectasis was 5.2 cm(2) (range 1.6-12.2 cm(2)) and 8.5 cm(2) (3-23.1 cm(2)) in the groups given FIO2 1.0 with or without CPAP/PEEP, respectively. After correction for body mass index the difference between medians (2.9 cm(2)) was statistically significant (confidence interval 0.2-7.6 cm(2), p = 0.04). In the group given FIO2 0.8, in which seven patients were ex- or current smokers, the median area of atelectasis was 8.2 cm(2) (1.8-14.7 cm(2)).

CONCLUSION

Compared with conventional ventilation, after correction for obesity, this ventilation strategy reduced the area of postoperative atelectasis in one of the intervention groups but not in the other group, which included a higher proportion of smokers.

Regional distribution of lung compliance by image analysis of computed tomograms

Computed tomography (CT) can yield quantitative information about volume distribution in the lung. By combining information provided by CT and respiratory mechanics, this study aims at quantifying regional lung compliance (CL) and its distribution and homogeneity in mechanically ventilated pigs. The animals underwent inspiratory hold maneuvers at 12 lung volumes with simultaneous CT exposure at two end-expiratory pressure levels and before and after acute lung injury (ALI) by oleic acid administration. CL and the sum of positive voxel compliances from CT were linearly correlated; negative compliance areas were found. A remarkably heterogeneous distribution of voxel compliance was found in the injured lungs. As the lung inflation increased, the homogeneity increased in healthy lungs but decreased in injured lungs. Image analysis brought novel findings regarding spatial homogeneity of compliance, which increases in ALI but not in healthy lungs by applying PEEP after a recruitment maneuver.

Comprehensive multiplexed protein quantitation delineates eosinophilic and neutrophilic experimental asthma

Background

Improvements in asthma diagnosis and management require deeper understanding of the heterogeneity of the complex airway inflammation. We hypothesise that differences in the two major inflammatory phenotypes of asthma; eosinophilic and neutrophilic asthma, will be reflected in the lung protein expression profile of murine asthma models and can be delineated using proteomics of bronchoalveolar lavage (BAL).

Methods

BAL from mice challenged with ovalbumin (OVA/OVA) alone (standard model of asthma, here considered eosinophilic) or OVA in combination with endotoxin (OVA/LPS, model of neutrophilic asthma) was analysed using liquid chromatography coupled to high resolution mass spectrometry, and compared with steroid-treated animals and healthy controls. In addition, conventional inflammatory markers were analysed using multiplexed ELISA (Bio-Plex™ assay). Multivariate statistics was performed on integrative proteomic fingerprints using principal component analysis. Proteomic data were complemented with lung mechanics and BAL cell counts.

Results

Several of the analysed proteins displayed significant differences between the controls and either or both of the two models reflecting eosinophilic and neutrophilic asthma. Most of the proteins found with mass spectrometry analysis displayed a considerable increase in neutrophilic asthma compared with the other groups. Conversely, the larger number of the inflammatory markers analysed with Bio-Plex™ analysis were found to be increased in the eosinophilic model. In addition, major inflammation markers were correlated to peripheral airway closure, while commonly used asthma biomarkers only reflect central inflammation.

Conclusion

Our data suggest that the commercial markers we are currently relying on to diagnose asthma subtypes are not giving us comprehensive or specific enough information. The analysed protein profiles allowed to discriminate the two models and may add useful information for characterization of different asthma phenotypes.

Lymphatic drainage between thorax and abdomen: please take good care of this well-performing machinery…

INTRODUCTION

Patients with sepsis often receive large amounts of fluids and the presence of capillary leak, trauma or bleeding results in ongoing fluid resuscitation. This increases interstitial and intestinal edema and finally leads to intra-abdominal hypertension (IAH), which in turn impedes lymphatic drainage. Patients with IAH often develop secondary respiratory failure needing mechanical ventilation with high intrathoracic pressure or PEEP that might further alter lymphatic drainage. This review will try to convince the reader of the importance of the lymphatics in septic patients with IAH.

METHODS

A Medline and PubMed literature search was performed using the terms "abdominal pressure", "lymphatic drainage" and "ascites formation". The references from these studies were searched for relevant articles that may have been missed in the primary search. These articles served as the basis for the recommendations below.

RESULTS

Induction of sepsis with lesion of the capillary alveolar barrier results in an increased water gradient between the capillaries and the interstitium in the lungs. The drainage flow to the thoracic duct is initially increased in order to protect the lung and maintain the pulmonary interstitium as dry as possible, however this results in increased intrathoracic pressure. Sepsis also increases the permeability of the capillaries in the splanchnic beds. In analogy to the lungs the lymphatic flow in the splanchnic areas increases together with the pressure inside as a physiological response in order to limit the increase in IAP. At a critical IAP level (around 20 cmH2O) the lymph flow starts to decrease and the splanchnic water content progressively increases. The lymph flow from the abdomen to the thorax is progressively decreased resulting in increased splanchnic water content and ascites formation. The presence of mechanical ventilation with high PEEP reduces the lymph drainage further which together with the increase in IAP decreases the lymphatic pressure gradient in the splanchnic regions, with a further increase in water content and IAP triggering a vicious cycle.

CONCLUSION

Although often overlooked the role of lymphatic flow is complex but very important to determine not only the fluid balance in the lung but also in the peripheral organs. Different pathologies and treatments can markedly influence the pathophysiology of the lymphatics with dramatic effects on endorgan function.

Organ dysfunction among piglets treated with inhaled nitric oxide and intravenous hydrocortisone during prolonged endotoxin infusion

OBJECTIVE

It has previously been shown that a combination of inhaled nitric oxide (iNO) and intravenous (IV) steroid attenuates endotoxin-induced organ damage in a 6-hour porcine endotoxemia model. We aimed to further explore these effects in a 30-hour model with attention to clinically important variables.

DESIGN

Randomized controlled trial.

SETTING

University animal laboratory.

SUBJECTS

Domestic piglets (n = 30).

INTERVENTIONS

Animals were randomized into 5 groups (n = 6 each): 1) Controls, 2) LPS-only (endotoxin/lipopolysaccharide (LPS) infusion), 3) LPS + iNO, 4) LPS + IV steroid, 5) LPS + iNO + IV steroid.

MEASUREMENTS AND MAIN RESULTS

Exposure to LPS temporarily increased pulmonary artery mean pressure and impeded renal function with elevated serum creatinine and acidosis compared to a control group over the 30-hour study period. Double treatment with both iNO and IV steroid tended to blunt the deterioration in renal function, although the only significant effect was on Base Excess (p = 0.045). None of the LPS + iNO + IV steroid treated animals died during the study period, whereas one animal died in each of the other LPS-infused groups.

CONCLUSIONS

This study suggests that combined early therapy with iNO and IV steroid is associated with partial protection of kidney function after 30 hours of experimental LPS infusion.

Glucocorticoid receptor function is decreased in neutrophils during endotoxic shock

OBJECTIVES

It remains unclear whether glucocorticoid treatment can improve the outcome of sepsis. The aim of the present study was to investigate if glucocorticoid receptor (GR) expression and function is impaired in lipopolysaccharide (LPS) induced shock, and whether the time point for start of glucocorticoid treatment affects the outcome.

METHODS

Male C57BL/6J mice were administered LPS i.p. and GR expression and binding ability in blood and spleen leukocytes were analysed by flow cytometry. GR translocation was analysed using Image Stream technique. The effect of dexamethasone treatment started 2 h before or 2, 12 or 36 h after LPS administration on survival was studied.

RESULTS

Despite increased GR expression in neutrophils after LPS administration, the GR binding capacity was reduced. In addition, GR translocation was decreased in neutrophils and T lymphocytes from endotoxic mice at 12 h compared to control animals. Dexamethasone treatment improved survival only when started early (2 h) after LPS administration.

CONCLUSION

The decreased glucocorticoid responsiveness displayed by neutrophils, in combination with their increased numbers, may explain why survival is increased only when dexamethasone treatment is given early during LPS induced shock.

A practical approach to the theoretical models to calculate NO parameters of the respiratory system

Expired nitric oxide (NO) is used as a biomarker in different respiratory diseases. The recommended flow rate of 50 mL s⁻¹ (F(E)NO₀.₀₅) does not reveal from where in the lung NO production originated. Theoretical models of NO transfer from the respiratory system, linear or nonlinear approaches, have therefore been developed and applied. These models can estimate NO from distal lung (alveolar NO) and airways (bronchial flux). The aim of this study was to show the limitation in exhaled flow rate for the theoretical models of NO production in the respiratory system, linear and nonlinear models. Subjects (n = 32) exhaled at eight different flow rates between 10-350 mL s⁻¹ for the theoretical protocols. Additional subjects (n = 32) exhaled at tree flow rates (20, 100 and 350 mL s⁻¹) for the clinical protocol. When alveolar NO is calculated using high flow rates with the linear model, correction for axial back diffusion becomes negligible, -0.04 ppb and bronchial flux enhanced by 1.27. With Högman and Meriläinen algorithm (nonlinear model) the corrections factors can be understood to be embedded, and the flow rates to be used are ≤20, 100 and ≥350 mL s⁻¹. Applying these flow rates in a clinical setting any F(E)NO can be calculated necessitating fewer exhalations. Hence, measured F(E)NO₀.₀₅ 12.9 (7.2-18.7) ppb and calculated 12.9 (6.8-18.7) ppb. In conclusion, the only possibility to avoid inconsistencies between research groups is to use the measured NO values as such in modelling, and apply tight quality control to accuracies in both NO concentration and exhaled flow measurements.

Reabsorption atelectasis in a porcine model of ARDS: regional and temporal effects of airway closure, oxygen, and distending pressure

Little is known about the small airways dysfunction in acute respiratory distress syndrome (ARDS). By computed tomography (CT) imaging in a porcine experimental model of early ARDS, we aimed at studying the location and magnitude of peripheral airway closure and alveolar collapse under high and low distending pressures and high and low inspiratory oxygen fraction (FIO2). Six piglets were mechanically ventilated under anesthesia and muscle relaxation. Four animals underwent saline-washout lung injury, and two served as healthy controls. Beyond the site of assumed airway closure, gas was expected to be trapped in the injured lungs, promoting alveolar collapse. This was tested by ventilation with an FIO2 of 0.25 and 1 in sequence during low and high distending pressures. In the most dependent regions, the gas/tissue ratio of end-expiratory CT, after previous ventilation with FIO2 0.25 low-driving pressure, was significantly higher than after ventilation with FIO2 1; with high-driving pressure, this difference disappeared. Also, significant reduction in poorly aerated tissue and a correlated increase in nonaerated tissue in end-expiratory CT with FIO2 1 low-driving pressure were seen. When high-driving pressure was applied or after previous ventilation with FIO2 0.25 and low-driving pressure, this pattern disappeared. The findings suggest that low distending pressures produce widespread dependent airway closure and with high FIO2, subsequent absorption atelectasis. Low FIO2 prevented alveolar collapse during the study period because of slow absorption of gas behind closed airways.

Respiratory function during anesthesia: effects on gas exchange

Anaesthesia causes a respiratory impairment, whether the patient is breathing spontaneously or is ventilated mechanically. This impairment impedes the matching of alveolar ventilation and perfusion and thus the oxygenation of arterial blood. A triggering factor is loss of muscle tone that causes a fall in the resting lung volume, functional residual capacity. This fall promotes airway closure and gas adsorption, leading eventually to alveolar collapse, that is, atelectasis. The higher the oxygen concentration, the faster will the gas be adsorbed and the aleveoli collapse. Preoxygenation is a major cause of atelectasis and continuing use of high oxygen concentration maintains or increases the lung collapse, that typically is 10% or more of the lung tissue. It can exceed 25% to 40%. Perfusion of the atelectasis causes shunt and cyclic airway closure causes regions with low ventilation/perfusion ratios, that add to impaired oxygenation. Ventilation with positive end-expiratory pressure reduces the atelectasis but oxygenation need not improve, because of shift of blood flow down the lung to any remaining atelectatic tissue. Inflation of the lung to an airway pressure of 40 cmH2O recruits almost all collapsed lung and the lung remains open if ventilation is with moderate oxygen concentration (< 40%) but recollapses within a few minutes if ventilation is with 100% oxygen. Severe obesity increases the lung collapse and obstructive lung disease and one-lung anesthesia increase the mismatch of ventilation and perfusion. CO2 pneumoperitoneum increases atelectasis formation but not shunt, likely explained by enhanced hypoxic pulmonary vasoconstriction by CO2. Atelectasis may persist in the postoperative period and contribute to pneumonia.

Expression of the glucocorticoid receptor is decreased in experimental Staphylococcus aureus sepsis

INTRODUCTION

Glucocorticoid treatment in septic shock remains controversial after recent trials. We hypothesized that failure to respond to steroid therapy may be caused by decreased expression and/or function of glucocorticoid receptors (GR) and studied this in a mouse model of Staphylococcus aureus sepsis. The impact of timing of dexamethasone treatment was also investigated.

METHODS

Male C57BL/6J mice were intravenously inoculated with S. aureus and GR expression and binding ability in blood, spleen and lymph nodes were analysed by means of flow cytometry. GR translocation was analysed using Image Stream. Septic mice were administered dexamethasone at 22, 26, 48, 72 and 96 h after inoculation and body weight, as a sign of dehydration, was observed.

RESULTS

GR expression was decreased in septic animals, but not the ligand binding capacity. GR translocation was decreased in septic mice compared to control animals. Early dexamethasone treatment (22 and 26 h) improved clinical outcome as studied by weight gain compared to when treatment was started at later time points (48, 72 and 96 h).

CONCLUSION

Our data provide evidence that GR expression is progressively decreased in experimental sepsis and that dexamethasone has a decreased ability to translocate into the cell nucleus. This may explain why steroid treatment is only beneficial when administered early in sepsis and septic shock.