Atelectatic Lung Research Articles

Single-lung ventilation and oxidative stress: a different perspective on a common practice.

To summarize what is currently known about the relationship between single-lung ventilation (SLV), oxidative stress, and postoperative disruption of organ function. SLV produces progressive alelectasis that is associated with hypoxic pulmonary vasoconstriction and redistribution of blood flow away from the nonventilated lung. This local tissue hypoxia induces the generation of reactive oxygen and reactive nitrogen species, an effect subsequently amplified by lung re-expansion consistent with well described hypoxia/reperfusion responses. Both experimental and clinical data indicate that the magnitude of oxidative and nitrosative stress is related to the duration of SLV and that these stresses affect not only the collapsed/re-expanded lung, but other organs as well. SLV and subsequent re-expansion of atelectatic lung are associated with the generation of reactive oxygen and nitrogen species that may modulate persistent systemic effects.

A Huge Thrombus-Containing Pulmonary Artery Aneurysm

Pulmonary artery aneurysms are very rare entities that may be caused by several diseases. One of its causes is infection by Bilharziasis which is an endemic disease in Egypt. We report a case of a male patient presented by dyspnea and his chest x-ray showed a huge pulmonary artery as well as an atelectatic lung lobe. Final diagnosis was done using echocardiography that showed a huge pulmonary artery aneurysm containing a very large organized thrombus.

Regional distribution of ventilation in horses in dorsal recumbency during spontaneous and mechanical ventilation assessed by electrical impedance tomography: a case series

ObjectiveTo evaluate the regional distribution of ventilation in horses during spontaneous breathing and controlled mechanical ventilation (CMV) using electrical impedance tomography (EIT). Study designProspective, experimental case series. AnimalsFour anaesthetized experimental horses. MethodsHorses were anaesthetized with isoflurane in an oxygen-air mixture and medetomidine continuous rate infusion, placed in dorsal recumbency with an EIT belt around the thorax, and allowed to breathe spontaneously until PaCO2 reached 13.3 kPa (100 mmHg), when volume CMV was started. For each horse, the EIT signal was recorded for at least 2 minutes immediately before (T1), and at 30 (n = 3) or 60 (n = 1) minutes after the start of CMV (T2). The centre of ventilation (CoV), dependent silent spaces (DSS) (likely to represent atelectatic lung areas), non-dependent silent spaces (NSS) (likely to represent lung areas with low ventilation) and total ventilated area (TVA) were evaluated. Cardiac output (CO) was measured and venous admixture and oxygen delivery (DO2) were calculated at T1 and T2. Data are presented as median and range. ResultsAfter the initiation of CMV, the CoV moved ventrally towards the non-dependent lung by 10% [from 57.4% (49.6–60.2%) to 48.3% (41.9–54.4%)]. DSS increased [from 4.1% (0.2–13.9%) to 18.7% (7.5–27.5%)], while NSS [21.7% (9.4–29.2%) to 9.9% (1.0–20.7%)] and TVA [920 (699–1051) to 837 (662–961) pixels] decreased. CO, venous admixture and DO2 also decreased. Conclusions and clinical relevanceIn spontaneously breathing anaesthetized horses in dorsal recumbency, ventilation was essentially centred within the dependent dorsal lung regions and moved towards non-dependent ventral regions as soon as CMV was started. This shows a major lack of ventilation in the dependent lung, which may be indicative of atelectasis.

Doppler images of intra-pulmonary shunt within atelectasis in anesthetized children.

BackgroundDoppler images of pulmonary vessels in pulmonary diseases associated with subpleural consolidations have been described. Color Doppler easily identifies such vessels within consolidations while spectral Doppler analysis allows the differentiation between pulmonary and bronchial arteries. Thus, Doppler helps in diagnosing the nature of consolidations. To our knowledge, Doppler analysis of pulmonary vessels within anesthesia-induced atelectasis has never been described before. The aim of this case series is to demonstrate the ability of lung ultrasound to detect the shunting of blood within atelectatic lung areas in anesthetized children.FindingsThree anesthetized and mechanically ventilated children were scanned in the supine position using a high-resolution linear probe of 6–12 MHz. Once subpleural consolidations were detected in the most dependent posterior lung regions, the probe was rotated such that its long axis followed the intercostal space. In this oblique position, color Doppler mapping was performed to detect blood flow within the consolidation. Thereafter, pulsed waved spectral Doppler was applied in the previously identified vessels during a short expiratory pause, which prevented interferences from respiratory motion. Different flow patterns were identified which corresponded to both, pulmonary and bronchial vessels. Finally, a lung recruitment maneuver was performed which leads to the complete resolution of the aforementioned consolidation thereby confirming the pathophysiological entity of anesthesia-induced atelectasis.ConclusionsLung ultrasound is a non-invasive imaging tool that not only enables the diagnosis of anesthesia-induced atelectasis in pediatric patients but also analysis of shunting blood within this consolidation.Electronic supplementary materialThe online version of this article (doi:10.1186/s13089-016-0055-7) contains supplementary material, which is available to authorized users.

Lavage-induced Surfactant Depletion in Pigs As a Model of the Acute Respiratory Distress Syndrome (ARDS).

Various animal models of lung injury exist to study the complex pathomechanisms of human acute respiratory distress syndrome (ARDS) and evaluate future therapies. Severe lung injury with a reproducible deterioration of pulmonary gas exchange and hemodynamics can be induced in anesthetized pigs using repeated lung lavages with warmed 0.9% saline (50 ml/kg body weight). Including standard respiratory and hemodynamic monitoring with clinically applied devices in this model allows the evaluation of novel therapeutic strategies (drugs, modern ventilators, extracorporeal membrane oxygenators, ECMO), and bridges the gap between bench and bedside. Furthermore, induction of lung injury with lung lavages does not require the injection of pathogens/endotoxins that impact on measurements of pro- and anti-inflammatory cytokines. A disadvantage of the model is the high recruitability of atelectatic lung tissue. Standardization of the model helps to avoid pitfalls, to ensure comparability between experiments, and to reduce the number of animals needed.

Sonographic appearance of bronchial carcinoma in atelectasis versus flooded lung

Background: Sonography of central lung tumours is limited, when surrounded by gaseous lung. Only in cases of bronchial- pleural invasion or when atelectatic lung serves as acoustic contact it becomes imageable. Further it has been shown that One Lung Flooding (OLF) is safe and enables sonographically examination of lung in-vivo. For ultrasound guided interventions the tumour demarcation from lung tissue is essential. Therefore the visualization of lung tumours in flooded and atelectatic condition was assessed.

Lung-Centered Open Heart Surgery: A Call for a Paradigm Change.

Lung-Centered Open Heart Surgery: A Call for a Paradigm Change.

Reexpansion of atelectasis caused by use of continuous positive airway pressure (CPAP) before radiation therapy (RT)

IntroductionAlthough radiation therapy (RT) is an effective treatment for malignant atelectasis, its accurate delivery is challenging because of difficulty differentiating between tumor and atelectatic lung. Furthermore, reexpansion of lung during treatment repositions tumor and normal structures necessitating replanning to ensure treatment accuracy. Facilitating lung reexpansion before initiation of RT may improve RT treatment accuracy, spare normal tissue, and reduce obstructive symptoms. We report a case of reexpansion of right upper lobe (RUL) atelectasis caused by use of continuous positive airway pressure (CPAP) before RT. Case reportA 52-year-old woman presented with dyspnea and cough. Imaging studies showed an RUL mass with atelectasis. Bronchoscopy showed extrinsic compression of the RUL and middle lobe bronchi. Biopsy showed small cell lung cancer. Staging with positron emission tomography-computed tomography (CT) and contrast enhanced CT of brain showed no other disease. Following 4 cycles of platinum-based chemotherapy, CT imaging showed a decrease in tumor volume, but persistent RUL atelectasis. She agreed to participate in an institutional study to evaluate the use of CPAP to reduce respiratory motion and immobilize tumors during RT. During CPAP training, she complained of vertigo, headache, and weakness and refused simulation. The next day she reported less dyspnea and completed training and CT simulation without difficulty. CT simulation with CPAP showed reexpansion of the RUL. Lung volume increased from 2170 to 3767 mL (74 %). Gross tumor volume, clinical volume, and planning volume decreased 46%, 45%, and 38%, respectively. Mean lung dose and mean heart dose decreased 20% and 51%, respectively. CPAP was used daily for 1 hour before and during treatment. Cone beam CT scans showed that the RUL remained inflated throughout treatment. ConclusionThis is the first reported use of CPAP for reexpansion of atelectasis before RT planning and treatment. Reexpansion of atelectasis improved RT planning, decreased dose to uninvolved lung, and removed the need for replanning. Further study of CPAP as an initial intervention to improve RT delivery in patients with malignant atelectasis is warranted.

Spontaneous Hemothorax Caused by a Ruptured Atypical Carcinoid Tumor: A Very Rare Case

: Neoplasm is one of the primary causes of spontaneous hemothorax. When spontaneous hemothorax is present, it is essential to detect the surgically corrective cause in order to successfully control this life-threatening condition. Undergoing an imaging evaluation, such as by enhanced computed tomography (CT), is especially important in a patient with spontaneous hemothorax. Herein, we report on a case of spontaneous hemothorax that was caused by a ruptured atypical carcinoid tumor in the right lower lobe. This hypervascular and peripherally located tumor was initially missed by both an unenhanced and enhanced chest CT because intra-tumoral bleeding and the hypervascular nature of this tumor caused similar high density when compared to the loculated hemothorax along the right major fissure and the surrounding atelectatic lung. Consequently, the tumor was obscured by the massive hemothorax and surrounding atelectatic lung on the initial chest CT. However, a second chest CT taken after tube drainage of the massive hemothorax informed the correct diagnosis.

Acute histopathological effects of cryotherapy on lung tissue

Background: Cryotherapy is an actual treatment and diagnostic method in many fields of medicine. We aimed to evaluate the acute histopathological effects of cryotherapy application on lung tissue. Materials and Methods: In this study 10 male rabbits were used. After providing single lung ventilation of the rabbits, clamshell incision was performed for exploration. Four different cryotherapy applications were performed to determine the different histopathologic changes on atelectatic and ventilated lung, also the difference between one versus two-cycle applications. After all applications, firstly, air leak was checked, then specimens were taken to analyze the acute histopathologic effects. Results: After cryotherapy application, no air leak was detected on ventilated rabbit lung with a pressure of 30 cmH2O. There was no bleeding from lung tissue, but macroscopic parenchymal hematoma developed. The depth of necrosis in lung tissue was evaluated with histopathological analysis. In all samples, alveolar edema and congestion were observed but there was no statistical difference between the depth of necrosis regarding with different cryotherapy applications. Conclusions: This study indicated that different applications of cryotherapy on lung parenchyma is a safe method and do not affect the depth of necrosis in a statistically significant degree.

Lung recruitment tools

Increased understanding of the mechanical and physical properties of the lungs and gas flow has allowed considerable advances in the field of mechanical ventilation and lung protection. Maintaining laminar flow, ‘the physiological flow’, and preventing turbulent flow during mechanical ventilation prevent atelectasis and help keep the lung open. This protects the lung from ventilator-induced lung injury (VILI). Analysis of the pressure–volume ( P/V ) curve of the respiratory system is the basis for maintaining lung protection. Lung volumes affect the dynamics of the lung and usually have a significant effect on the flow, airway resistance, lung compliance, ventilation–perfusion ratio and recruitment. Functional residual capacity (FRC) has a significant role in maintaining the structure and function of the lung, and the relationship between the FRC and closing volume (CV) is more important than considering the FRC and CV alone. Positive end-expiratory pressure (PEEP), by preventing and/or recruiting atelectatic lung regions, can maintain the lung structure and protects against VILI. The optimal PEEP, still controversial, can be determined using the following methods: (1) a decremental PEEP trial after recruitment manoeuvres with P aO2 and lung compliance guidance; (2) (quasi) static approaches or dynamic approaches based on the P/V curve; (3) based on the F iO2/PEEP table with oxygenation guidance; (4) PEEP guided by oesophageal pressure; (5) based on a computerized tomography scan or chest radiograph; and (6) using electrical impedance tomography. Recruitment manoeuvres can help to recruit atelectatic lung regions and can be accomplished by raising the transpulmonary pressure periodically and briefly to a higher level than that achieved during tidal ventilation. Clinical and experimental studies has been conducted to identify the durability of the beneficial effects of recruitment manoeuvres, when and how to perform them, early or late in the course of acute respiratory distress syndrome and with high or low PEEP, and which categories of patients will benefit from them.

Emphysematous lesions in the right cranial lung lobe and torsion of the right medial lung lobe in a British shorthair cat: a case report

A three-year-old male British shorthair cat that had exhibited progressive lethargy and intermittent dyspnoea for 14 days was referred for evaluation of acute respiratory deterioration. Clinical findings included rapid and shallow breathing, pale mucous membranes, sound suppression on the right side, and a subcutaneous haematoma in the right epigastric area. Serum biochemistry analysis showed leukocytosis and thrombocytosis. Radiographs revealed hydropneumothorax, a broken eighth right rib, atelectatic right cranial lung lobe (RCrL), and consolidation of the right middle lobe (RML). Doppler examination revealed sonographic changes in the echotexture of both lobes and venous flow was absent in the twisted RML. Furthermore, bronchoscopy showed proximal narrowing of the cat’s RML bronchus. Exploratory surgery via medial sternotomy confirmed torsion of the RML and identified deteriorated gas-containing lesions in the collapsed RCrL. Both lung lobes were removed by standard lobectomy, and postoperative recovery was without major complications. Histopathological examination diagnosed multiple bullae and blebs, with significant subpleural haemorrhages in the atelectatic RCrL, whereas tissue congestion with haemorrhages, necrosis, and thrombosis typical for lung lobe torsion were observed in the RML. No other underlying aetiology was apparent. Two months post-operatively, the cat presented with similar acute onset of dyspnoea and spontaneous pneumothorax and was euthanised at the owner’s request. The autopsy revealed identical new emphysematous changes in the contra-lateral lung lobes that had been absent at the time of surgery. Emphysematous lesions, regardless of their origin, should be considered in the etiopathology of lung lobe torsion.

Atelectasis causes alveolar hypoxia-induced inflammation during uneven mechanical ventilation in rats.

BackgroundPatients with acute respiratory distress syndrome receiving mechanical ventilation show inhomogeneous lung aeration. Atelectasis during uneven mechanical ventilation leads to alveolar hypoxia and could therefore result in lung inflammation and injury. We aimed to elucidate whether and how atelectasis causes alveolar hypoxia-induced inflammation during uneven mechanical ventilation in an open-chest differential-ventilation rat model.MethodsWe first investigated inflammatory and histological changes in the bilateral lungs of unilaterally ventilated rats, in which the right lung was atelectatic and the left lung was ventilated with high tidal volume (HTV). In the next series, we investigated the effects of normal tidal volume (NTV) ventilation of the right lungs with 60 % O2 or 100 % N2 during HTV ventilation of the left lungs. Then, proinflammatory cytokine secretions were quantified from murine lung epithelial (MLE15) and murine alveolar macrophage (MH-S) cells cultured under a hypoxic condition (5 % O2) mimicking atelectasis. Further, activities of nuclear factor (NF)-κB and hypoxia-inducible factor (HIF)-1 were assessed in the nonventilated atelectatic lung and MLE15 cells cultured under the hypoxic condition. Finally, effects of NF-κB inhibition and HIF-1α knockdown on the cytokine secretions from MLE15 cells cultured under the hypoxic condition were assessed.ResultsThe nonventilated atelectatic lungs showed inflammatory responses and minimal histological changes comparable to those of the HTV-ventilated lungs. NTV ventilation with 60 % O2 attenuated the increase in chemokine (C-X-C motif) ligand (CXCL)-1 secretion and neutrophil accumulation observed in the atelectatic lungs, but that with 100 % N2 did not. MLE15 cells cultured with tumor necrosis factor (TNF)-α under the hypoxic condition showed increased CXCL-1 secretion. NF-κB and HIF-1α were activated in the nonventilated atelectatic lungs and MLE15 cells cultured under the hypoxic condition. NF-κB inhibition abolished the hypoxia-induced increase in CXCL-1 secretion from MLE15 cells, while HIF-1α knockdown augmented it.ConclusionsAtelectasis causes alveolar hypoxia-induced inflammatory responses including NF-κB-dependent CXCL-1 secretion from lung epithelial cells. HIF-1 activation in lung epithelial cells is an anti-inflammatory response to alveolar hypoxia in atelectatic lungs.

Effect of surfactant on regional lung function in an experimental model of respiratory distress syndrome in rabbit.

We assessed the changes in regional lung function following instillation of surfactant in a model of respiratory distress syndrome (RDS) induced by whole lung lavage and mechanical ventilation in eight anaesthetized, paralyzed, and mechanically ventilated New Zealand White rabbits. Regional specific ventilation (sV̇) was measured by K-edge subtraction synchrotron computed tomography during xenon washin. Lung regions were classified as poorly aerated (PA), normally aerated (NA), or hyperinflated (HI) based on regional density. A functional category was defined within each class based on sV̇ distribution (High, Normal, and Low). Airway resistance (Raw), respiratory tissue damping (G), and elastance (H) were measured by forced oscillation technique at low frequencies before and after whole lung saline lavage-induced (100 ml/kg) RDS, and 5 and 45 min after intratracheal instillation of beractant (75 mg/kg). Surfactant instillation improved Raw, G, and H (P < 0.05 each), and gas exchange and decreased atelectasis (P < 0.001). It also significantly improved lung aeration and ventilation in atelectatic lung regions. However, in regions that had remained normally aerated after lavage, it decreased regional aeration and increased sV̇ (P < 0.001) and sV̇ heterogeneity. Although surfactant treatment improved both central airway and tissue mechanics and improved regional lung function of initially poorly aerated and atelectatic lung, it deteriorated regional lung function when local aeration was normal prior to administration. Local mechanical and functional heterogeneity can potentially contribute to the worsening of RDS and gas exchange. These data underscore the need for reassessing the benefits of routine prophylactic vs. continuous positive airway pressure and early "rescue" surfactant therapy in very immature infants.

Variability in Mechanical Ventilation: What's All the Noise About?

Controlled mechanical ventilation is characterized by a fixed breathing frequency and tidal volume. Physiological and mathematical models have demonstrated the beneficial effects of varying tidal volume and/or inspiratory pressure during positive-pressure ventilation. The addition of noise (random changes) to a monotonous nonlinear biological system, such as the lung, induces stochastic resonance that contributes to the recruitment of collapsed alveoli and atelectatic lung segments. In this article, we review the mechanism of physiological pulmonary variability, the principles of noise and stochastic resonance, and the emerging understanding that there are beneficial effects of variability during mechanical ventilation.

Regulation of PACAP receptors in respiratory distress syndrome (RDS) of preterms and newborns

s of the 51st Workshop for Pediatric Research 51st Workshop for Pediatric Research Gottingen, Germany 16-17 April 2015 This supplement has not been sponsored. Meeting abstracts Background Prevalence of respiratory distress syndrome (RDS) caused by primary surfactant deficiency reaches 50% in infants below 32 weeks of gestational age. Increased alveolar surface tension leads to atelectatic and/or dystelectatic lung areas followed by inflammation resulting in development of a bronchopulmonary dysplasia (BPD) in 8% of these children. Standard RDS treatment consists of administration of exogenous surfactant. With the introduction of less invasive application (LISA) of exogenous surfactant, the use of Surfactant has significantly increased. Pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors (VPAC1, VPAC2, PAC1) trigger inflammatory reactions as well as anti-inflammatory processes. Materials and methods Using cell cultures, FACS and ELISA methods we analyzed surfactant effects on inflammation and PACAP-regulation and of its receptors in vivo and ex vivo. Results We were able to show that lipopolysaccharide (LPS) in prestimulated cells (PBMC) after surfactant treatment resulted in a significant up-regulation of pro-inflammatory interleukin (IL)-8. In tracheal secretory cells of surfactant-treated neonates we found an up-regulation of pro-inflammatory receptor VPAC1. Furthermore, in cell cultures we identified changes in the proliferation rates. Amniotic infection syndrome (AIS) is one of the major causes for premature birth resulting in RDS requiring exogenous surfactant. After pre-stimulation of PBMCs and subsequent addition of surfactant, pro-inflammatory signals were fortified. These results were confirmed by analysis of tracheal secretions of preterms and newborns. Conclusions Current findings may imply that safety and efficacy of routine surfactant administration should be reassessed as surfactant potentially triggers pulmonary inflammation and thus may contribute to BPD development.

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.

Effects of pulse-delivered inhaled nitric oxide administration on pulmonary perfusion and arterial oxygenation in dorsally recumbent isoflurane-anesthetized horses.

To image the spatial distribution of pulmonary blood flow by means of scintigraphy, evaluate ventilation-perfusion (VA/Q) matching and pulmonary blood shunting (Qs/Qt) by means of the multiple inert gas elimination technique (MIGET), and measure arterial oxygenation and plasma endothelin-1 concentrations before, during, and after pulse-delivered inhaled nitric oxide (PiNO) administration to isoflurane-anesthetized horses in dorsal recumbency. 3 healthy adult Standardbreds. Nitric oxide was pulsed into the inspired gases in dorsally recumbent isoflurane-anesthetized horses. Assessment of VA/Q matching, Qs/Qt, and Pao2 content was performed by use of the MIGET, and spatial distribution of pulmonary blood flow was measured by perfusion scintigraphy following IV injection of technetium Tc 99m-labeled macroaggregated human albumin before, during, and 30 minutes after cessation of PiNO administration. During PiNO administration, significant redistribution of blood flow from the dependent regions to the nondependent regions of the lungs was found and was reflected by improvements in VA/Q matching, decreases in Qs/Qt, and increases in Pao2 content, all of which reverted to baseline values at 30 minutes after PiNO administration. Administration of PiNO in anesthetized dorsally recumbent horses resulted in redistribution of pulmonary blood flow from dependent atelectatic lung regions to nondependent aerated lung regions. Because hypoxemia is commonly the result of atelectasis in anesthetized dorsally recumbent horses, the addition of nitric oxide to inhaled gases could be used clinically to alleviate hypoxemia in horses during anesthesia.

Stress concentration around an atelectatic region: A finite element model

Lung parenchyma surrounding an atelectatic region is thought to be subjected to increased stress compared with the rest of the lung. Using 37 hexagonal cells made of linear springs, Mead et al. (1970) measured a stress concentration greater than 30% in the springs surrounding a stiffer central cell. We re-examine the problem using a 2D finite element model of 500 cells made of thin filaments with a non-linear stress–strain relationship. We study the consequences of increasing the central stiff region from one to nine contiguous cells in regular hexagonal honeycombs and random Voronoi honeycombs. The honeycomb structures were uniformly expanded with strains of 15%, 30%, 45% and 55% above their resting, non-deformed geometry. The curve of biaxial stress vs. fractional area change has a similar shape to that of the pressure–volume curve of the lung, showing an initial regime with relatively flat slope and a final regime with decreasing slope, tending toward an asymptote. Regular honeycombs had little variability in the maximum stress in radially oriented filaments adjacent to the central stiff region. In contrast, some filaments in random Voronoi honeycombs were subjected to stress concentration approximately 16 times the average stress concentration in the radially oriented filaments adjacent to the stiff region. These results may have implications in selecting the appropriate strategy for mechanical ventilation in ARDS and defining a “safe” level of alveolar pressure for ventilating atelectatic lungs.

Monitoring of oesophageal pressure.

Studies in patients with acute respiratory distress syndrome (ARDS) have been unable to demonstrate a survival advantage with higher levels of positive end-expiratory pressure (PEEP) to open atelectatic lung regions or prevent their cyclic collapse. This review will discuss the challenges of accurately measuring pleural pressure with balloon-tipped catheters in the oesophagus, and the utility of such pressure monitoring to set PEEP and assess lung mechanics, focusing on patients with ARDS. Recent investigations have suggested that the monitoring of oesophageal pressure in ARDS patients may help individualize PEEP settings to optimize lung recruitment based on transpulmonary pressure. Changes in oesophageal pressure likely accurately reflect global changes in pleural pressure in supine patients with ARDS. However, absolute oesophageal pressure values in such patients may be subject to local artefacts and may substantially overestimate pleural pressure in other lung regions. Setting PEEP high enough to achieve a targeted end-expiratory transpulmonary pressure in the region of the oesophageal balloon catheter could overdistend other lung regions. Measurement of oesophageal pressure is feasible, but its clinical utility to titrate PEEP, compared with routine assessment, awaits experimental confirmation.