Injurious mechanical ventilation in the normal lung causes a progressive pathologic change in dynamic alveolar mechanics

Use of a Portable Mechanical Ventilator during Cardiopulmonary Resuscitation is Feasible, Improves Respiratory Parameters, and Prevents the Decrease of Dynamic Lung Compliance

BACKGROUND

For practical and protective ventilation during cardiopulmonary resuscitation (CPR), a 150-grams mechanical ventilator (VLP2000E) that limits peak inspiratory pressure (PIP) during simultaneous ventilation with chest compressions was developed.

OBJECTIVES

To evaluate the feasibility of VLP2000E ventilation during CPR and to compare monitored parameters versus bag-valve ventilation.

METHODS

A randomized experimental study with 10 intubated pigs per group. After seven minutes of ventricular fibrillation, 2-minute CPR cycles were delivered. All animals were placed on VLP2000E after achieving return of spontaneous circulation (ROSC).

RESULTS

Bag-valve and VLP2000E groups had similar ROSC rate (60% vs. 50%, respectively) and arterial oxygen saturation in most CPR cycles, different baseline tidal volume [0.764 (0.068) vs. 0.591 (0.123) L, p = 0.0309, respectively] and, in 14 cycles, different PIP [52 (9) vs. 39 (5) cm H2O, respectively], tidal volume [0.635 (0.172) vs. 0.306 (0.129) L], ETCO2[14 (8) vs. 27 (9) mm Hg], and peak inspiratory flow [0.878 (0.234) vs. 0.533 (0.105) L/s], all p < 0.0001. Dynamic lung compliance (≥ 0.025 L/cm H2O) decreased after ROSC in bag-valve group but was maintained in VLP2000E group [0.019 (0.006) vs. 0.024 (0.008) L/cm H2O, p = 0.0003].

CONCLUSIONS

VLP2000E ventilation during CPR is feasible and equivalent to bag-valve ventilation in ROSC rate and arterial oxygen saturation. It produces better respiratory parameters, with lower airway pressure and tidal volume. VLP2000E ventilation also prevents the significant decrease of dynamic lung compliance observed after bag-valve ventilation. Further preclinical studies confirming these findings would be interesting.

Acinar micromechanics in health and lung injury: what we have learned from quantitative morphology

Within the pulmonary acini ventilation and blood perfusion are brought together on a huge surface area separated by a very thin blood-gas barrier of tissue components to allow efficient gas exchange. During ventilation pulmonary acini are cyclically subjected to deformations which become manifest in changes of the dimensions of both alveolar and ductal airspaces as well as the interalveolar septa, composed of a dense capillary network and the delicate tissue layer forming the blood-gas barrier. These ventilation-related changes are referred to as micromechanics. In lung diseases, abnormalities in acinar micromechanics can be linked with injurious stresses and strains acting on the blood-gas barrier. The mechanisms by which interalveolar septa and the blood-gas barrier adapt to an increase in alveolar volume have been suggested to include unfolding, stretching, or changes in shape other than stretching and unfolding. Folding results in the formation of pleats in which alveolar epithelium is not exposed to air and parts of the blood-gas barrier are folded on each other. The opening of a collapsed alveolus (recruitment) can be considered as an extreme variant of septal wall unfolding. Alveolar recruitment can be detected with imaging techniques which achieve light microscopic resolution. Unfolding of pleats and stretching of the blood-gas barrier, however, require electron microscopic resolution to identify the basement membrane. While stretching results in an increase of the area of the basement membrane, unfolding of pleats and shape changes do not. Real time visualization of these processes, however, is currently not possible. In this review we provide an overview of septal wall micromechanics with focus on unfolding/folding as well as stretching. At the same time we provide a state-of-the-art design-based stereology methodology to quantify microarchitecture of alveoli and interalveolar septa based on different imaging techniques and design-based stereology.

Assessment of hemodynamics, blood gases, and lung histopathology of healthy Pig model on two different mechanical ventilators

In response to COVID-19 global crisis and arising from social responsibility, efforts have been exerted to promptly research, develop and manufacture ICU ventilators locally to meet the spike in demand. This study aimed at: Evaluating the safety and performance of a newly developed mechanical ventilator; EZVent compared to a commercial ventilator regarding hemodynamics, arterial blood gases (ABG), lung inflammatory markers, and histopathology in a healthy pig model using three different ventilation modes. Methods: Eight adult male pigs were anesthetized and randomly assigned into two equal groups: Commercial vent and EZVent group, the animals of which were ventilated using a standard commercial ventilator and EZVent, respectively. On every animal, three ventilation modes were tested, each mode for 30 min: CMV-VC, CMV-PC, and CPAP-PS modes. Vital signs, ECG, Lung Mechanics (LM), and ABG were measured before ventilation and after 30 min of ventilation of each mode. After animals’ euthanasia, histological examinations of lung samples including morphometric assessment of alveolar edema, alveolar wall thickening, and the mean number of inflammatory cellular infiltrate/cm² of lung tissue were analyzed. TNF-α and Il-6 expression and localization in lung tissue were assessed by western blot and immunohistochemistry. Results: The vital signs, LM, ABG, morphometric analysis, and histopathological score during the different ventilation modes showed non-significant differences between the study groups. TNF-α and IL-6 were minimally expressed in the bronchiolar epithelium and the alveolar septa. Their increased expression level was insignificant. Conclusion: EZVent is equivalent to the commercial ventilator regarding its safety and efficacy.

Non-Intubated Thoracic Surgery: Standpoints and Perspectives

Non-intubated video-assisted thoracic surgery (NI-VATS) combines the advantages of a non-intubated surgery with the benefits of a minimally invasive approach. First, NI-VATS is performed in the case of fragile patients when general anesthesia and/or orotracheal intubation can be foreseen as inconvenient. However, NI-VATS indications have been increasingly extended to different patient conditions, considering the increasingly assessed safety and feasibility of the procedure. Currently, the NI-VATS approach is used worldwide for different thoracic surgery procedures, including the management of malignant pleural effusion, surgical treatment of empyema, anatomical and non-anatomical lung resection, and other indications. In fact, this approach has shown to be less impactful than VATS under general anesthesia, allowing for shortened hospitalization and faster recovery after surgery. Besides, NI-VATS is associated with fewer pulmonary complications, less respiratory distress, and a mild systemic inflammatory reaction. For these reasons, this approach should be considered not only in patients with poor cardiac or respiratory function (general functional reserve), but also in other eligible conditions.

We explored the anesthetic and surgical aspects of such an approach, including the management of analgesia, cough reflex, depth of sedation, and intraoperative technical issues to put this approach in perspective.

Non-intubated Thoracoscopic Surgery-Tips and Tricks From Anesthesiological Aspects: A Mini Review

Background

In the last few decades, surgical techniques have been developed in thoracic surgery, and minimally invasive strategies such as multi-and uniportal video-assisted thoracic surgery (VATS) have become more favorable even for major pulmonary resections. With this surgical evolution, the aesthetic approach has also changed, and a paradigm shift has occurred. The traditional conception of general anesthesia, muscle relaxation, and intubation has been re-evaluated, and spontaneous breathing plays a central role in our practice by performing non-intubated thoracoscopic surgeries (NITS-VATS).

Methods

We performed a computerized search of the medical literature (PubMed, Google Scholar, Scopus) to identify relevant articles in non-intubated thoracoscopic surgery using the following terms [(non-intubated) OR (non-intubated) OR (awake) OR (tubeless) OR (regional anesthesia)] AND [(VATS) OR (NIVATS)], as well as their Medical Subject Headings (MeSH) terms.

Results

Based on the outcomes of the reviewed literature and our practice, it seems that pathophysiological concerns can be overcome by proper surgical and anesthetic management. All risks are compensated by the advantageous physiological changes that result in better patient outcomes. With the maintenance of spontaneous breathing, the incidence of potential adverse effects of mechanical ventilation, such as ventilator-induced lung injury and consequent postoperative pulmonary complications, can be reduced. The avoidance of muscle relaxants also results in the maintenance of contraction of the dependent hemidiaphragm and lower airway pressure levels, which may lead to better ventilation-perfusion matching. These techniques can be challenging for surgeons as well as for anesthetists; hence, a good knowledge of physiological and pathophysiological changes, clear inclusion and exclusion and intraoperative conversion criteria, and good communication between team members are essential.

Conclusion

NITS-VATS seems to be a feasible and safe method in selected patients with evolving importance as a part of the minimally invasive surgical and anesthetic conception and has a role in reducing perioperative complications, which is crucial in the thoracic surgical patient population.

Converting to Intubation During Non-intubated Thoracic Surgery: Incidence, Indication, Technique, and Prevention

Traditionally, intubated general anesthesia with one-lung ventilation is standard in thoracoscopic surgery. However, in recent decades, non-intubated thoracoscopic surgery (NITS) has become an alternative method to minimize the adverse effects of intubated general anesthesia. Non-intubated procedures result in fewer adverse events than tracheal intubation and general anesthesia, such as intubation-related airway injury, ventilation-induced lung injury, prolonged hospital stay, and postoperative nausea and vomiting. Despite these benefits, surgeons must consider the possibility of converting to intubation during NITS as the conversion rate is between 2 and 11%, varying between regions and learning time. The conversion rate is also affected by race, body size, the learning curve, and the surgical team's preferred methods. There are surgical (e.g., significant respiratory movements, uncontrolled bleeding, hindered surgical fields, large tumor sizes, adhesions) and anesthetic (e.g., hypoxemia, hypercapnia, airway spasms) reasons for converting to intubation. When a conversion is deemed necessary by the surgical team, the members should be well-prepared and act rapidly. Anesthesiologists should also feel comfortable intubating patients in the lateral decubitus position with or without bronchoscopic guidance. Patient selection is the key factor for avoiding conversion into an intubated surgery. Patients with an American Society of Anesthesiologists grade 2 or less, a body mass index <25, and less surgical complexity may be good candidates for NITS. Careful monitoring, adequate anesthesia depth, an experienced surgical team, and sufficient preparation can also prevent conversion. Conversion from a non-intubated into intubated thoracic surgery is unwanted but not inevitable. Therefore, NITS can be successful when performed on select patients by a well-prepared and experienced surgical team and is worthy of recommendation owing to its non-invasiveness.

Multiple organ dysfunction syndrome: Contemporary insights on the clinicopathological spectrum

Multiorgan dysfunction syndrome (MODS) remains a major complication and challenge to treat patients with critical illness in different intensive care unit settings. The exact mechanism and pathophysiology of MODS is complex and remains unexplored. We reviewed the literature from January 2011 to August 2019 to analyze the underlying mechanisms, prognostic factors, MODS scoring systems, organ systems dysfunctions, and the management of MODS. We used the search engines PubMed, MEDLINE, Scopus, and Google Scholar with the keywords "multiple organ dysfunction syndrome," "intensive care units," "multiorgan failure," "MODS scoring system," and "MODS management." The initial search yielded 3550 abstracts, of which 91 articles were relevant to the scope of the present article. A better understanding of a disease course will help differentiate the signs of an intense inflammatory response from the early onset of sepsis and minimize the inappropriate use of medications. This, in turn, will promote organtargeted therapy and prevent occurrence and progression of MODS.

Mechanical Ventilation Lessons Learned From Alveolar Micromechanics

Morbidity and mortality associated with lung injury remains disappointingly unchanged over the last two decades, in part due to the current reliance on lung macro-parameters set on the ventilator instead of considering the micro-environment and the response of the alveoli and alveolar ducts to ventilator adjustments. The response of alveoli and alveolar ducts to mechanical ventilation modes cannot be predicted with current bedside methods of assessment including lung compliance, oxygenation, and pressure-volume curves. Alveolar tidal volumes (Vt) are less determined by the Vt set on the mechanical ventilator and more dependent on the number of recruited alveoli available to accommodate that Vt and their heterogeneous mechanical properties, such that high lung Vt can lead to a low alveolar Vt and low Vt can lead to high alveolar Vt. The degree of alveolar heterogeneity that exists cannot be predicted based on lung calculations that average the individual alveolar Vt and compliance. Finally, the importance of time in promoting alveolar stability, specifically the inspiratory and expiratory times set on the ventilator, are currently under-appreciated. In order to improve outcomes related to lung injury, the respiratory physiology of the individual patient, specifically at the level of the alveolus, must be targeted. With experimental data, this review highlights some of the known mechanical ventilation adjustments that are helpful or harmful at the level of the alveolus.

A Physiologically Informed Strategy to Effectively Open, Stabilize, and Protect the Acutely Injured Lung

Acute respiratory distress syndrome (ARDS) causes a heterogeneous lung injury and remains a serious medical problem, with one of the only treatments being supportive care in the form of mechanical ventilation. It is very difficult, however, to mechanically ventilate the heterogeneously damaged lung without causing secondary ventilator-induced lung injury (VILI). The acutely injured lung becomes time and pressure dependent, meaning that it takes more time and pressure to open the lung, and it recollapses more quickly and at higher pressure. Current protective ventilation strategies, ARDSnet low tidal volume (LVt) and the open lung approach (OLA), have been unsuccessful at further reducing ARDS mortality. We postulate that this is because the LVt strategy is constrained to ventilating a lung with a heterogeneous mix of normal and focalized injured tissue, and the OLA, although designed to fully open and stabilize the lung, is often unsuccessful at doing so. In this review we analyzed the pathophysiology of ARDS that renders the lung susceptible to VILI. We also analyzed the alterations in alveolar and alveolar duct mechanics that occur in the acutely injured lung and discussed how these alterations are a key mechanism driving VILI. Our analysis suggests that the time component of each mechanical breath, at both inspiration and expiration, is critical to normalize alveolar mechanics and protect the lung from VILI. Animal studies and a meta-analysis have suggested that the time-controlled adaptive ventilation (TCAV) method, using the airway pressure release ventilation mode, eliminates the constraints of ventilating a lung with heterogeneous injury, since it is highly effective at opening and stabilizing the time- and pressure-dependent lung. In animal studies it has been shown that by “casting open” the acutely injured lung with TCAV we can (1) reestablish normal expiratory lung volume as assessed by direct observation of subpleural alveoli; (2) return normal parenchymal microanatomical structural support, known as alveolar interdependence and parenchymal tethering, as assessed by morphometric analysis of lung histology; (3) facilitate regeneration of normal surfactant function measured as increases in surfactant proteins A and B; and (4) significantly increase lung compliance, which reduces the pathologic impact of driving pressure and mechanical power at any given tidal volume.

The micromechanics of lung alveoli: structure and function of surfactant and tissue components

The mammalian lung´s structural design is optimized to serve its main function: gas exchange. It takes place in the alveolar region (parenchyma) where air and blood are brought in close proximity over a large surface. Air reaches the alveolar lumen via a conducting airway tree. Blood flows in a capillary network embedded in inter-alveolar septa. The barrier between air and blood consists of a continuous alveolar epithelium (a mosaic of type I and type II alveolar epithelial cells), a continuous capillary endothelium and the connective tissue layer in-between. By virtue of its respiratory movements, the lung has to withstand mechanical challenges throughout life. Alveoli must be protected from over-distension as well as from collapse by inherent stabilizing factors. The mechanical stability of the parenchyma is ensured by two components: a connective tissue fiber network and the surfactant system. The connective tissue fibers form a continuous tensegrity (tension + integrity) backbone consisting of axial, peripheral and septal fibers. Surfactant (surface active agent) is the secretory product of type II alveolar epithelial cells and covers the alveolar epithelium as a biophysically active thin and continuous film. Here, we briefly review the structural components relevant for gas exchange. Then we describe our current understanding of how these components function under normal conditions and how lung injury results in dysfunction of alveolar micromechanics finally leading to lung fibrosis.

Non-intubated thoracoscopic surgery for decortication of empyema under thoracic epidural anesthesia: a case report

General anesthesia is the main strategy for almost all thoracic surgeries. However, a growing body of literature has reported successful cases of non-intubated thoracic surgery with regional anesthesia. This alternative strategy not only prevents complications related to general anesthesia, such as lung injury, incomplete re-expansion and intubation related problems, but also accords with trends of shorter hospital stay and lower overall costs. We experienced a successful case of non-intubated thoracoscopic decortication for a 68-year-old man who was diagnosed as empyema while the patient kept spontaneously breathing with moderate sedation under thoracic epidural anesthesia. The patient showed a fast recovery without concerns of general anesthesia related complications and effective postoperative analgesia through thoracic epidural patient-controlled analgesia device. This is the first report of non-intubated thoracoscopic surgery under thoracic epidural anesthesia in Korea, and we expect that various well designed prospective studies will warrant the improvement of outcomes in non-intubated thoracoscopic surgery.

Mechanical ventilation in acute respiratory distress syndrome: The open lung revisited

Acute respiratory distress syndrome (ARDS) is still related to high mortality and morbidity rates. Most patients with ARDS will require ventilatory support. This treatment has a direct impact upon patient outcome and is associated to major side effects. In this regard, ventilator-associated lung injury (VALI) is the main concern when this technique is used. The ultimate mechanisms of VALI and its management are under constant evolution. The present review describes the classical mechanisms of VALI and how they have evolved with recent findings from physiopathological and clinical studies, with the aim of analyzing the clinical implications derived from them. Lastly, a series of knowledge-based recommendations are proposed that can be helpful for the ventilator assisted management of ARDS at the patient bedside.

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

BACKGROUND

Doppler 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.

FINDINGS

Three 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.

CONCLUSIONS

Lung 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.

Ultrasonography for the assessment of lung recruitment maneuvers

Lung collapse is a known complication that affects most of the patients undergoing positive pressure mechanical ventilation. Such atelectasis and airways closure lead to gas exchange and lung mechanics impairment and has the potential to develop an inflammatory response in the lungs. These negative effects of lung collapse can be reverted by a lung recruitment maneuver (RM) i.e. a ventilatory strategy that resolves lung collapse by a brief and controlled increment in airway pressures. However, an unsolved question is how to assess such RM at the bedside. The aim of this paper is to describe the usefulness of lung sonography (LUS) to conduct and personalize RM in a real-time way at the bedside. LUS has favorable features to assess lung recruitment due to its high specificity and sensitivity to detect lung collapse together with its non-invasiveness, availability and simple use.

Non-intubated video-assisted thoracic surgery: where does evidence stand?

In recent years, non-intubated video-assisted thoracic surgery (NIVATS) strategies are gaining popularity worldwide. The main goal of this surgical practice is to achieve an overall improvement of patients' management and outcome thanks to the avoidance of side-effects related to general anesthesia (GA) and one-lung ventilation. The spectrum of expected benefits is multifaceted and includes reduced postoperative morbidity, faster discharge, decreased hospital costs and a globally reduced perturbation of patients' well-being status. We have conducted a literature search to evaluate the available evidence on this topic. Meta-analysis of collected results was also done where appropriate. Despite some fragmentation of data and potential biases, the available data suggest that NIVATS operations can reduce operative morbidity and hospital stay when compared to equipollent procedures performed under GA. Larger, well designed prospective studies are thus warranted to assess the effectiveness of NIVATS as far as to investigate comprehensively the various outcomes. Multi-institutional and multidisciplinary cooperation will be welcome to establish uniform study protocols and to help address the questions that are to be answered yet.

Differential modulation of claudin 4 expression and myosin light chain phosphorylation by thyroid function in lung injury

BACKGROUND

Trauma and ventilator-induced lung injury is often associated with endothelial-epithelial barriers breakdown, which may lead to multiple system organ failure (MSOF) and death in critically ill patients. Although molecular mechanism involved in MSOF is not known, junctional opening is believed to happen. In vitro, thyroid hormones inhibit myosin light chain (MLC) phosphorylation and may, thus, inhibit cellular contraction and junctional opening. Trauma is also associated with tissue hypo-thyroid state. Therefore, we examined the effects of thyroid function on expression of phospho-MLC (pp-MLC) and claudin 4 (Clud4), key proteins involved in regulation of junctional tightness, in lung injury.

METHODS

Rats were rendered hypo-thyroid (Hypo) or hyperthyroid (Hyper) by adding methimazole or levo-thyroxine, respectively, to their drinking water. Untreated euthyroid (Eue) animals were used as control. Lung pp-MLC and Clud4 proteins were assessed by western blotting and in situ immunodetection, respectively. Lung injury was induced by high tidal volume mechanical ventilation.

RESULTS

Lung injury was significantly enhanced in Hypo animals and attenuated in Hyper animals. Parallel changes in expression of lung pp-MLC were detected. Alterations in lung histomorphology correlated with the level of pp-MLC. Expression of alveolar and bronchiolar Clud4 protein was differentially affected by the state of thyroid gland.

CONCLUSIONS

Our data suggest that thyroid function plays significant role in lung injury perhaps by modulating expression of the proteins involved in junctional tightness. Besides, they strongly support the idea that the tissue hypo-thyroid state may contribute to endothelial-epithelial barriers breakdown associated with trauma.

Real-time images of tidal recruitment using lung ultrasound

Background

Ventilator-induced lung injury is a form of mechanical damage leading to a pulmonary inflammatory response related to the use of mechanical ventilation enhanced by the presence of atelectasis. One proposed mechanism of this injury is the repetitive opening and closing of collapsed alveoli and small airways within these atelectatic areas—a phenomenon called tidal recruitment. The presence of tidal recruitment is difficult to detect, even with high-resolution images of the lungs like CT scan. The purpose of this article is to give evidence of tidal recruitment by lung ultrasound.

Findings

A standard lung ultrasound inspection detected lung zones of atelectasis in mechanically ventilated patients. With a linear probe placed in the intercostal oblique position. We observed tidal recruitment within atelectasis as an improvement in aeration at the end of inspiration followed by the re-collapse at the end of expiration. This mechanism disappeared after the performance of a lung recruitment maneuver.

Conclusions

Lung ultrasound was helpful in detecting the presence of atelectasis and tidal recruitment and in confirming their resolution after a lung recruitment maneuver.

Electronic supplementary material

The online version of this article (doi:10.1186/s13089-015-0036-2) contains supplementary material, which is available to authorized users.

Dead space during one-lung ventilation

PURPOSE OF REVIEW

Describe the importance of monitoring dead space during thoracic surgery, specifically during one-lung ventilation.

RECENT FINDINGS

The concept of dead space has gained renewed interest among anesthesiologists ever since breath-by-breath measurement by volumetric capnography became available. Monitoring dead space during thoracic surgery assesses the ventilatory deficiencies related to increases in instrumental, airway and/or alveolar dead space, when ventilating patients with positive pressure and double-lumen tubes. Another interesting use of such monitoring is to detect ventilator-induced lung injury due to tidal overdistension. This type of injury threatens the fragile lungs especially during one-lung ventilation and can clinically be recognized as an increase in airway and alveolar dead space above normal values. To date, lung protective ventilation is based on the use of low tidal volumes and airway pressures to decrease overdistension. It has been shown to reduce the incidence of postoperative pulmonary complications after thoracic surgeries. However, such a ventilatory strategy impairs ventilation and induces hypercapnia due to increases in dead space. Therefore, continuous assessment of dead space is helpful in guiding ventilation and avoiding overdistension while maintaining the elimination of CO(2) during thoracic surgery sufficiently high.

SUMMARY

Monitoring dead space helps anesthesiologists monitor the status of the lung and find appropriate ventilatory settings during thoracic surgeries.

Airway pressure release ventilation reduces conducting airway micro-strain in lung injury

BACKGROUND

Improper mechanical ventilation can exacerbate acute lung damage, causing a secondary ventilator-induced lung injury (VILI). We hypothesized that VILI can be reduced by modifying specific components of the ventilation waveform (mechanical breath), and we studied the impact of airway pressure release ventilation (APRV) and controlled mandatory ventilation (CMV) on the lung micro-anatomy (alveoli and conducting airways). The distribution of gas during inspiration and expiration and the strain generated during mechanical ventilation in the micro-anatomy (micro-strain) were calculated.

STUDY DESIGN

Rats were anesthetized, surgically prepared, and randomized into 1 uninjured control group (n = 2) and 4 groups with lung injury: APRV 75% (n = 2), time at expiration (TLow) set to terminate appropriately at 75% of peak expiratory flow rate (PEFR); APRV 10% (n = 2), TLow set to terminate inappropriately at 10% of PEFR; CMV with PEEP 5 cm H2O (PEEP 5; n = 2); or PEEP 16 cm H2O (PEEP 16; n = 2). Lung injury was induced in the experimental groups by Tween lavage and ventilated with their respective settings. Lungs were fixed at peak inspiration and end expiration for standard histology. Conducting airway and alveolar air space areas were quantified and conducting airway micro-strain was calculated.

RESULTS

All lung injury groups redistributed inspired gas away from alveoli into the conducting airways. The APRV 75% minimized gas redistribution and micro-strain in the conducting airways and provided the alveolar air space occupancy most similar to control at both inspiration and expiration.

CONCLUSIONS

In an injured lung, APRV 75% maintained micro-anatomic gas distribution similar to that of the normal lung. The lung protection demonstrated in previous studies using APRV 75% may be due to a more homogeneous distribution of gas at the micro-anatomic level as well as a reduction in conducting airway micro-strain.

Computational Models of Ventilator Induced Lung Injury and Surfactant Dysfunction

Managing acute respiratory distress syndrome (ARDS) invariably involves the administration of mechanical ventilation, the challenge being to avoid the iatrogenic sequellum known as ventilator-induced lung injury (VILI). Devising individualized ventilation strategies in ARDS requires that patient-specific lung physiology be taken into account, and this is greatly aided by the use of computational models of lung mechanical function that can be matched to physiological measurements made in a given patient. In this review, we discuss recent models that have the potential to serve as the basis for devising minimally injurious modes of mechanical ventilation in ARDS patients.

From "awake" to "monitored anesthesia care" thoracic surgery: A 15 year evolution

Although general anesthesia still represents the standard when performing thoracic surgery, the interest toward alternative methods is increasing. These have evolved from the employ of just local or regional analgesia techniques in completely alert patients (awake thoracic surgery), to more complex protocols entailing conscious sedation and spontaneous ventilation. The main rationale of these methods is to prevent serious complications related to general anesthesia and selective ventilation, such as tracheobronchial injury, acute lung injury, and cardiovascular events. Trends toward shorter hospitalization and reduced overall costs have also been indicated in preliminary reports. Monitored anesthesia care in thoracic surgery can be successfully employed to manage diverse oncologic conditions, such as malignant pleural effusion, peripheral lung nodules, and mediastinal tumors. Main non-oncologic indications include pneumothorax, emphysema, pleural infections, and interstitial lung disease. Furthermore, as the familiarity with this surgical practice has increased, major operations are now being performed this way. Despite the absence of randomized controlled trials, there is preliminary evidence that monitored anesthesia care protocols in thoracic surgery may be beneficial in high-risk patients, with non-inferior efficacy when compared to standard operations under general anesthesia. Monitored anesthesia care in thoracic surgery should enter the armamentarium of modern thoracic surgeons, and adequate training should be scheduled in accredited residency programs.

Automated alerting and recommendations for the management of patients with preexisting hypoxia and potential acute lung injury: a pilot study

BACKGROUND

Acute lung injury (ALI) is associated with high mortality. Low tidal volume (Vt) ventilation has been shown to reduce mortality in ALI patients in the intensive care unit. Anesthesiologists do not routinely provide lung-protective ventilation strategies to patients with ALI in the operating room. The authors hypothesized that an alert, recommending lung-protective ventilation regarding patients with potential ALI, would result in lower Vt administration.

METHODS

The authors conducted a randomized controlled trial on anesthesia providers caring for patients with potential ALI. Patients with an average or last collected ratio of partial pressure of arterial oxygen to inspired fraction of oxygen less than 300 were randomized to providers being sent an alert with a recommended Vt of 6 cc/kg predicted body weight or conventional care. Primary outcomes were Vt/kg predicted body weight administered to patients. Secondary outcomes included ventilator parameters, length of postoperative ventilation, and death.

RESULTS

The primary outcome was a clinically significant reduction in mean Vt from 508-458 cc (P = 0.033), with a reduction in Vt when measured in cc/kg predicted body weight from 8 to 7.2 cc/kg predicted body weight (P = 0.040). There were no statistically significant changes in other outcomes or adverse events associated with either arm.

CONCLUSIONS

Automated alerts generated for patients at risk of having ALI resulted in a statistically significant reduction in Vt administered when compared with a control group. Further research is required to determine whether a reduction in Vt results in decreased mortality and/or postoperative duration of mechanical ventilation.

Linking the development of ventilator-induced injury to mechanical function in the lung

Management of ALI/ARDS involves supportive ventilation at low tidal volumes (V t) to minimize the rate at which ventilator induced lung injury (VILI) develops while the lungs heal. However, we currently have few details to guide the minimization of VILI in the ALI/ARDS patient. The goal of the present study was to determine how VILI progresses with time as a function of the manner in which the lung is ventilated in mice. We found that the progression of VILI caused by over-ventilating the lung at a positive end-expiratory pressure of zero is accompanied by progressive increases in lung stiffness as well as the rate at which the lung derecruits over time. We were able to accurately recapitulate these findings in a computational model that attributes changes in the dynamics of recruitment and derecruitment to two populations of lung units. One population closes over a time scale of minutes following a recruitment maneuver and the second closes in a matter of seconds or less, with the relative sizes of the two populations changing as VILI develops. This computational model serves as a basis from which to link the progression of VILI to changes in lung mechanical function.

In situ methods for assessing alveolar mechanics

Lung mechanics are an important determinant of physiological and pathophysiological lung function. Recent light microscopy studies of the intact lung have furthered the understanding of lung mechanics but used methodologies that may have introduced artifacts. To address this concern, we employed a short working distance water immersion objective to capture confocal images of a fluorescently labeled alveolar field on the costal surface of the isolated, perfused rat lung. Surface tension held a saline drop between the objective tip and the lung surface, such that the lung surface was unconstrained. For comparison, we also imaged with O-ring and coverslip; with O-ring, coverslip, and vacuum pressure; and without perfusion. Under each condition, we ventilated the lung and imaged the same region at the endpoints of ventilation. We found use of a coverslip caused a minimal enlargement of the alveolar field; additional use of vacuum pressure caused no further dimensional change; and absence of perfusion did not affect alveolar field dimension. Inflation-induced expansion was unaltered by methodology. In response to inflation, percent expansion was the same as recorded by all four alternative methods.

Jack of all trades: pleiotropy and the application of chemically modified tetracycline-3 in sepsis and the acute respiratory distress syndrome (ARDS)

Sepsis is a disease process that has humbled the medical profession for centuries with its resistance to therapy, relentless mortality, and pathophysiologic complexity. Despite 30 years of aggressive, concerted, well-resourced efforts the biomedical community has been unable to reduce the mortality of sepsis from 30%, nor the mortality of septic shock from greater than 50%. In the last decade only one new drug for sepsis has been brought to the market, drotrecogin alfa-activated (Xigris™), and the success of this drug has been limited by patient safety issues. Clearly a new agent is desperately needed. The advent of recombinant human immune modulators held promise but the outcomes of clinical trials using biologics that target single immune mediators have been disappointing. The complex pathophysiology of the systemic inflammatory response syndrome (SIRS) is self-amplifying and redundant at multiple levels. In this review we argue that perhaps pharmacologic therapy for sepsis will only be successful if it addresses this pathophysiologic complexity; the drug would have to be pleiotropic, working on many components of the inflammatory cascade at once. In this context, therapy that targets any single inflammatory mediator will not adequately address the complexity of SIRS. We propose that chemically modified tetracycline-3, CMT-3 (or COL-3), a non-antimicrobial modified tetracycline with pleiotropic anti-inflammatory properties, is an excellent agent for the management of sepsis and its associated complication of the acute respiratory distress syndrome (ARDS). The purpose of this review is threefold: (1) to examine the shortcomings of current approaches to treatment of sepsis and ARDS in light of their pathophysiology, (2) to explore the application of COL-3 in ARDS and sepsis, and finally (3) to elucidate the mechanisms of COL-3 that may have potential therapeutic benefit in ARDS and sepsis.

Beyond volutrauma in ARDS: the critical role of lung tissue deformation

Ventilator-induced lung injury (VILI) consists of tissue damage and a biological response resulting from the application of inappropriate mechanical forces to the lung parenchyma. The current paradigm attributes VILI to overstretching due to very high-volume ventilation (volutrauma) and cyclic changes in aeration due to very low-volume ventilation (atelectrauma); however, this model cannot explain some research findings. In the present review, we discuss the relevance of cyclic deformation of lung tissue as the main determinant of VILI. Parenchymal stability resulting from the interplay of respiratory parameters such as tidal volume, positive end-expiratory pressure or respiratory rate can explain the results of different clinical trials and experimental studies that do not fit with the classic volutrauma/atelectrauma model. Focusing on tissue deformation could lead to new bedside monitoring and ventilatory strategies.

High tidal volume ventilation is not deleterious in infant rats exposed to severe hemorrhage

BACKGROUND

Both high tidal volume (V(T)) ventilation and hemorrhage induce acute lung injury in adult rodents. It is not known whether injurious ventilation augments lung injury in infant rats exposed to severe hemorrhage.

METHODS

Two-week-old rats were allocated for ventilation with VT 7 mL/kg and positive end-expiratory pressure (PEEP) 5 cm H₂O (low V(T)) or V(T) 21 mL/kg and PEEP 1 (high V(T)) for 4 hours. Additional rats were subjected to volume-controlled hemorrhage and delayed saline resuscitation, followed by low V(T) or high V(T) ventilation for 4 hours. Nonventilated control groups were also included. Airway resistance and the coefficient of tissue elastance were derived from respiratory input impedance measurements using the low-frequency forced oscillation technique. Pressure-volume curves were obtained at baseline and at the end of the study. Interleukin-6, macrophage inflammatory protein-2, and tumor necrosis factor alpha were determined in bronchoalveolar lavage fluid (BALF) and serum.

RESULTS

In both healthy and hemorrhage-exposed animals, high V(T) resulted in reduced elastance (better lung compliance) and increased transcutaneous oxygen saturation. Interleukin-6 in BALF was greater in ventilated animals when compared with nonventilated controls, but not different among ventilated groups. No significant differences were found for all other inflammatory mediators, total protein concentration in BALF, and histology.

CONCLUSION

High V(T) ventilation with low PEEP improves respiratory system mechanics without causing additional damage to healthy and hemorrhage-exposed infant rats after 4 hours of ventilation. This study highlights the tolerance to high V(T) ventilation in infant rats and underscores the need for age-specific animal models.

Titration of mean airway pressure and FiO2 during high frequency oscillatory ventilation in a porcine model of acute lung injury

BACKGROUND

High frequency oscillatory ventilation (HFOV) is frequently utilized for patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). However, precise criteria to titrate mean airway pressure (mPaw) and FiO(2) as the patient's condition improves are lacking. We hypothesized that reducing mPaw and FiO(2) too quickly after reaching target arterial oxygen saturation levels would promote ventilator induced lung injury (VILI).

MATERIALS AND METHODS

ALI was induced by instilling 3% Tween 20. Pigs were placed supine and received 30 min of nonprotective ventilation. Pigs were separated into two groups: HFOV constant (HFOVC, n = 3) = constant mPaw and FiO(2) for the duration; HFOV titrated (HFOVT, n = 4) = FiO(2) and/or mPaw were reduced every 30 min if the oxygen saturation remained between 88%-95%. Hemodynamic and pulmonary measurements were made at baseline, after lung injury, and every 30 min during the 6-h study. Lung histopathology was determined by quantifying alveolar hyperdistension, fibrin, congestion, atelectasis, and polymorphonuclear leukocyte (PMN) infiltration.

RESULTS

Oxygenation was significantly lower in the HFOVT group compared to the HFOVC group after 6 h. Lung histopathology was significantly increased in the HFOVT group in the following categories: PMN infiltration, alveolar hyperdistension, congestion, and fibrin deposition.

CONCLUSIONS

Rapid reduction of mPaw and FiO(2) in our ALI model significantly reduced oxygenation, but, more importantly, caused VILI as evidenced by increased lung inflammation and alveolar hyperdistension. Specific criteria for titration of mPaw and inspired oxygen are needed to maximize the lung protective effects of HFOV while maintaining adequate gas exchange.

The physical basis of ventilator-induced lung injury

Although mechanical ventilation (MV) is a life-saving intervention for patients with acute respiratory distress syndrome (ARDS), it can aggravate or cause lung injury, known as ventilator-induced lung injury (VILI). The biophysical characteristics of heterogeneously injured ARDS lungs increase the parenchymal stress associated with breathing, which is further aggravated by MV. Cells, in particular those lining the capillaries, airways and alveoli, transform this strain into chemical signals (mechanotransduction). The interaction of reparative and injurious mechanotransductive pathways leads to VILI. Several attempts have been made to identify clinical surrogate measures of lung stress/strain (e.g., density changes in chest computed tomography, lower and upper inflection points of the pressure-volume curve, plateau pressure and inflammatory cytokine levels) that could be used to titrate MV. However, uncertainty about the topographical distribution of stress relative to that of the susceptibility of the cells and tissues to injury makes the existence of a single 'global' stress/strain injury threshold doubtful.

The physical basis of ventilator-induced lung injury

Although mechanical ventilation (MV) is a life-saving intervention for patients with acute respiratory distress syndrome (ARDS), it can aggravate or cause lung injury, known as ventilator-induced lung injury (VILI). The biophysical characteristics of heterogeneously injured ARDS lungs increase the parenchymal stress associated with breathing, which is further aggravated by MV. Cells, in particular those lining the capillaries, airways and alveoli, transform this strain into chemical signals (mechanotransduction). The interaction of reparative and injurious mechanotransductive pathways leads to VILI. Several attempts have been made to identify clinical surrogate measures of lung stress/strain (e.g., density changes in chest computed tomography, lower and upper inflection points of the pressure-volume curve, plateau pressure and inflammatory cytokine levels) that could be used to titrate MV. However, uncertainty about the topographical distribution of stress relative to that of the susceptibility of the cells and tissues to injury makes the existence of a single 'global' stress/strain injury threshold doubtful.

Automated analysis of intratidal dynamics of alveolar geometry from microscopic endoscopy

Alveolar parenchyma, the gas exchange area of the respiratory system, is prone to mechanical damage during mechanical ventilation. Development of lung protective ventilation strategies therefore requires a better understanding of alveolar dynamics during mechanical ventilation. In this paper, we propose a novel method for automated analysis of the intratidal geometry of subpleural alveoli based on the evaluation of video frames recorded from alveolar microscopy in an experimental setting. Our method includes the recording with a microscopic endoscope, feature extraction from image data, the analysis of a single frame, the tracking and analysis of single alveoli in a video sequence, and the evaluation of the obtained sequence of alveolar geometry data. Our method enables automated analysis of 2-D alveolar geometry with sufficient temporal resolution to follow intratidal dynamics. The developed method and the reproducibility of the results were successfully validated with manually segmented video frames.

Acute lung injury and outcomes after thoracic surgery

PURPOSE OF REVIEW

The present review evaluates the evidence available in the literature tracking perioperative mortality and morbidity as well as the pathogenesis and management of acute lung injury (ALI) in patients undergoing thoracotomy.

RECENT FINDINGS

Over the last decade, despite increasing age and comorbid conditions, the operative mortality has remained unchanged for patients undergoing lung resection, whereas procedure-related complications have declined. Better clinical outcomes are achieved in high-volume hospitals and when procedures are performed by a thoracic surgeon. Postthoracotomy ALI has become the leading cause of operative death, its incidence has remained stable (2-5%) and earlier diagnosis can be made by assessing the extravascular lung water volume with the single-indicator dilution technique. The pathogenesis of ALI implicates a multiple-hit sequence of various triggering factors (e.g. oxidative stress and surgical-induced inflammation) in addition to injurious ventilatory settings and genetic predisposition.

SUMMARY

Knowledge of the perioperative risk factors of major complications and understanding of the mechanisms of postthoracotomy ALI enable anesthesiologists to implement 'protective' lung strategies including the use of low tidal volume (VT) with recruitment maneuvers, a goal-directed fluid approach and prophylactic treatment with inhaled beta2-adrenergic agonists.

Aerosolised surfactant generated by a novel noninvasive apparatus reduced acute lung injury in rats

Introduction

Exogenous surfactant has been explored as a potential therapy for acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). In the present study, a nebuliser driven by oxygen lines found in the hospital was developed to deliver aerosolised porcine pulmonary surfactant (PPS). We hypothesised that aerosolised surfactant inhaled through spontaneous breathing may effectively reduce severe lung injury.

Methods

Rats were intravenously injected with oleic acid (OA) to induce ALI and 30 minutes later they were divided into five groups: model (injury only), PPS aerosol (PPS-aer), saline aerosol (saline-aer), PPS instillation (PPS-inst), and saline instillation (Saline-Inst). Blood gases, lung histology, and protein and TNF-α concentrations in the bronchoalveolar lavage fluid (BALF) were examined.

Results

The PPS aerosol particles were less than 2.0 μm in size as determined by a laser aerosol particle counter. Treatment of animals with a PPS aerosol significantly increased the phospholipid content in the BALF, improved lung function, reduced pulmonary oedema, decreased total protein and TNF-α concentrations in BALF, ameliorated lung injury and improved animal survival. These therapeutic effects are similar to those seen in the PPS-inst group.

Conclusions

This new method of PPS aerosolisation combines the therapeutic effects of a surfactant with partial oxygen inhalation under spontaneous breathing. It is an effective, simple and safe method of administering an exogenous surfactant.

The role of time and pressure on alveolar recruitment

Inappropriate mechanical ventilation in patients with acute respiratory distress syndrome can lead to ventilator-induced lung injury (VILI) and increase the morbidity and mortality. Reopening collapsed lung units may significantly reduce VILI, but the mechanisms governing lung recruitment are unclear. We thus investigated the dynamics of lung recruitment at the alveolar level. Rats (n = 6) were anesthetized and mechanically ventilated. The lungs were then lavaged with saline to simulate acute respiratory distress syndrome (ARDS). A left thoracotomy was performed, and an in vivo microscope was placed on the lung surface. The lung was recruited to three recruitment pressures (RP) of 20, 30, or 40 cmH(2)O for 40 s while subpleural alveoli were continuously filmed. Following measurement of microscopic alveolar recruitment, the lungs were excised, and macroscopic gross lung recruitment was digitally filmed. Recruitment was quantified by computer image analysis, and data were interpreted using a mathematical model. The majority of alveolar recruitment (78.3 +/- 7.4 and 84.6 +/- 5.1%) occurred in the first 2 s (T2) following application of RP 30 and 40, respectively. Only 51.9 +/- 5.4% of the microscopic field was recruited by T2 with RP 20. There was limited recruitment from T2 to T40 at all RPs. The majority of gross lung recruitment also occurred by T2 with gradual recruitment to T40. The data were accurately predicted by a mathematical model incorporating the effects of both pressure and time. Alveolar recruitment is determined by the magnitude of recruiting pressure and length of time pressure is applied, a concept supported by our mathematical model. Such a temporal dependence of alveolar recruitment needs to be considered when recruitment maneuvers for clinical application are designed.

Alveolar instability caused by mechanical ventilation initially damages the nondependent normal lung

BACKGROUND

Septic shock is often associated with acute respiratory distress syndrome, a serious clinical problem exacerbated by improper mechanical ventilation. Ventilator-induced lung injury (VILI) can exacerbate the lung injury caused by acute respiratory distress syndrome, significantly increasing the morbidity and mortality. In this study, we asked the following questions: what is the effect of the lung position (dependent lung versus nondependent lung) on the rate at which VILI occurs in the normal lung? Will positive end-expiratory pressure (PEEP) slow the progression of lung injury in either the dependent lung or the nondependent lung?

MATERIALS AND METHODS

Sprague-Dawley rats (n = 19) were placed on mechanical ventilation, and the subpleural alveolar mechanics were measured with an in vivo microscope. Animals were placed in the lateral decubitus position, left lung up to measure nondependent alveolar mechanics and left lung down to film dependent alveolar mechanics. Animals were ventilated with a high peak inspiratory pressure of 45 cmH2O and either a low PEEP of 3 cmH2O or a high PEEP of 10 cmH2O for 90 minutes. Animals were separated into four groups based on the lung position and the amount of PEEP: Group I, dependent + low PEEP (n = 5); Group II, nondependent + low PEEP (n = 4); Group III, dependent + high PEEP (n = 5); and Group IV, nondependent + high PEEP (n = 5). Hemodynamic and lung function parameters were recorded concomitant with the filming of alveolar mechanics. Histological assessment was performed at necropsy to determine the presence of lung edema.

RESULTS

VILI occurred earliest (60 min) in Group II. Alveolar instability eventually developed in Groups I and II at 75 minutes. Alveoli in both the high PEEP groups were stable for the entire experiment. There were no significant differences in arterial PO2 or in the degree of edema measured histologically among experimental groups.

CONCLUSION

This open-chest animal model demonstrates that the position of the normal lung (dependent or nondependent) plays a role on the rate of VILI.