Extracorporeal carbon dioxide removal and low-frequency positive-pressure ventilation. Improvement in arterial oxygenation with reduction of risk of pulmonary barotrauma in patients with adult respiratory distress syndrome

Bioengineering Progress in Lung Assist Devices

Artificial lung technology is advancing at a startling rate raising hopes that it would better serve the needs of those requiring respiratory support. Whether to assist the healing of an injured lung, support patients to lung transplantation, or to entirely replace native lung function, safe and effective artificial lungs are sought. After 200 years of bioengineering progress, artificial lungs are closer than ever before to meet this demand which has risen exponentially due to the COVID-19 crisis. In this review, the critical advances in the historical development of artificial lungs are detailed. The current state of affairs regarding extracorporeal membrane oxygenation, intravascular lung assists, pump-less extracorporeal lung assists, total artificial lungs, and microfluidic oxygenators are outlined.

RNAi therapeutic strategies for acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS), replacing the clinical term acute lung injury, involves serious pathophysiological lung changes that arise from a variety of pulmonary and nonpulmonary injuries and currently has no pharmacological therapeutics. RNA interference (RNAi) has the potential to generate therapeutic effects that would increase patient survival rates from this condition. It is the purpose of this review to discuss potential targets in treating ARDS with RNAi strategies, as well as to outline the challenges of oligonucleotide delivery to the lung and tactics to circumvent these delivery barriers.

The role of extra-corporeal membrane oxygenation (ECMO) in the treatment of diffuse alveolar haemorrhage secondary to ANCA-associated vasculitis: report of two cases and review of the literature

Diffuse alveolar haemorrhage (DAH) secondary to anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) is a rare life-threatening condition presenting with severe respiratory failure. The management of AAV-related DAH consists of remission induction immunosuppressive therapy, which requires time to be effective, with significant fatality rates despite appropriate treatment. Extracorporeal membrane oxygenation (ECMO) can support gas exchanges providing the time necessary for immunosuppressive treatment to control the underlying disease in cases refractory to the conventional ventilation techniques. Despite severe preexisting bleeding has been considered a relative contraindication, ECMO has proven to be life-saving in several cases of respiratory failure associated with pulmonary haemorrhage due to various causes, including AAV. We reviewed the clinical presentation and course of two patients affected by AAV-related DAH treated at our Institution between 2012 and 2017, whose management required the use of veno-venous ECMO. We reviewed the current literature on the role of ECMO in the support of these patients. In both patients, ECMO provided life support and allowed disease control, in combination with immunosuppressive treatment. Despite systemic anticoagulation, clinical improvement was achieved without exacerbation of the pulmonary bleeding. We performed a literature review, and summarized available data confirming the effectiveness and safety of ECMO in AAV-related DAH. ECMO has a life-saving role in the management of patients with severe respiratory failure due to ANCA-associated pulmonary capillaritis.

Hemorrhage under veno-venous extracorporeal membrane oxygenation in acute respiratory distress syndrome patients: a retrospective data analysis

Background

Despite being still invasive and challenging, technical improvement has resulted in broader and more frequent application of extracorporeal membrane oxygenation (ECMO), to prevent hypoxemia and to reduce invasiveness of mechanical ventilation (MV). Heparin-coated ECMO-circuits are currently standard of care, in addition to heparin based anticoagulation (AC) regimen guided by activated clotting time (ACT) or activated partial thromboplastin time (aPTT). Despite these advances, a reliable prediction of hemorrhage is difficult and the risk of hemorrhagic complication remains unfortunately high. We hypothesized, that there are coagulation parameters that are indices for a higher risk of hemorrhage under veno-venous (VV)-ECMO therapy.

Methods

Data from 36 patients with severe respiratory failure treated with VV-ECMO at a University Hospital intensive care unit (ICU) were analyzed retrospectively. Patients were separated into two groups based on severity of hemorrhagic complications and transfusion requirements. The following data were collected: demographics, hemodynamic data, coagulation samples, transfusion requirements, change of ECMO-circuit during treatment and adverse effects, including hemorrhage and thrombosis.

Results

In this study 74 hemorrhagic events were observed, one third of which were severe. Patients suffering from severe hemorrhage had a lower survival rate on VV-ECMO (43% vs. 91%; P=0.002) and in ICU (36% vs. 86%; P=0.002). SAPS II, factor VII and X were different between mild and severe hemorrhage group.

Conclusions

Severe hemorrhage under VV-ECMO is associated with higher mortality. Only factor VII and X differed between groups. Further clinical studies are required to determine the timing of initiation and targets for AC therapies during VV-ECMO.

Extracorporeal techniques in acute respiratory distress syndrome

Extracorporeal membrane oxygenation (ECMO) was first introduced for patients with acute respiratory distress syndrome (ARDS) in the 1970s. However, enthusiasm was tempered due to the high mortality seen at that time. The use of ECMO has grown considerably in recent years due to technological advances and the evidence suggesting potential benefit. While the efficacy of ECMO has yet to be rigorously demonstrated with high-quality evidence, it has the potential not only to have a substantial impact on outcomes, including mortality, but also to change the paradigm of ARDS management.

Successful Treatment of Refractory Hypoxemia Secondary to Disseminated Histoplasmosis Using Extracorporeal Membrane Oxygenation Support

Refractory hypoxemia secondary to acute respiratory distress syndrome (ARDS) is associated with high mortality. Extracorporeal membraneoxygenation (ECMO) is an accepted strategy for treating refractory hypoxemia in patients with ARDS but is relatively contraindicated in the setting of systemic infections. We present a case of successful ECMO use in a host with refractory hypoxemia secondary to disseminated histoplasmosis with fungemia and discuss our management approach to this difficult patient.

Current Applications for the Use of Extracorporeal Carbon Dioxide Removal in Critically Ill Patients

Mechanical ventilation in patients with respiratory failure has been associated with secondary lung injury, termed ventilator-induced lung injury. Extracorporeal venovenous carbon dioxide removal (ECCO₂R) appears to be a feasible means to facilitate more protective mechanical ventilation or potentially avoid mechanical ventilation in select patient groups. With this expanding role of ECCO₂R, we aim to describe the technology and the main indications of ECCO₂R.

Hypoxemic Respiratory Failure: Evidence, Indications, and Exclusions

ECMO is increasingly being used to manage severe ARDS with refractory hypoxemia and hypercapnia, and to facilitate lung-protective ventilation and minimize ventilator-associated lung injury. However, there is limited high-level evidence to support its use. Early randomized trials did not show a benefit, though these studies were hampered by high mortality rates, limited experience with ECMO, and antiquated technology. Since the advent of more advanced circuit components and increased experience with the use of this technology, survival rates with ECMO for ARDS have improved. There is only one randomized trial to date which used a more modern ECMO circuit. This trial, which has significant limitations, demonstrated a survival benefit from referral to a specialized center for consideration for ECMO. However, a prospective randomized trial comparing ECMO, using modern equipment, to standard-of-care mechanical ventilation has yet to be performed. There are no universally accepted guidelines for initiation of ECMO for ARDS, however suggested criteria include PaO₂ to FIO₂ ratio less than 80, uncompensated respiratory acidosis, and excessively high plateau airway pressures despite optimal ventilator management. Relative contraindications include prolonged ventilation at high airway pressures or high FIO₂, contraindications to anticoagulation, and concurrent severe, irreversible comorbidities.

Extracorporeal gas exchange for acute respiratory failure in adult patients: a systematic review

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2015 and co-published as a series in Critical Care. Other articles in the series can be found online at http://ccforum.com/series/annualupdate2015. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Mechanical ventilation during extracorporeal life support (ECLS): a systematic review

PURPOSE

In patients with acute respiratory distress syndrome (ARDS), extracorporeal life support (ECLS) has been utilized to support gas exchange and mitigate ventilator-induced lung injury (VILI). The optimal ventilation settings while on ECLS are unknown. The purpose of this systematic review is to describe the ventilation practices in patients with ARDS who require ECLS.

METHODS

We electronically searched MEDLINE, EMBASE, CENTRAL, AMED, and HAPI (inception to January 2015). Studies included were randomized controlled trials, observational studies, or case series (≥4 patients) of ARDS patients undergoing ECLS. Our review focused on studies describing ventilation practices employed during ECLS for ARDS.

RESULTS

Forty-nine studies (2,042 patients) met our inclusion criteria. Prior to initiation of ECLS, at least one parameter consistent with injurious ventilation [tidal volume >8 mL/kg predicted body weight (PBW), peak pressure >35 cmH2O (or plateau pressure >30 cmH2O), or FiO2 ≥0.8] was noted in 90% of studies. After initiation of ECLS, studies reported median [interquartile range (IQR)] reductions in: tidal volume [2.4 mL/kg PBW (2.2-2.9)], plateau pressure [4.3 cmH2O (3.5-5.8)], positive end-expiratory pressure (PEEP) [0.20 cmH2O (0-3.0)], and FiO2 [0.40 (0.30-0.60)]. Median (IQR) overall mortality was 41 % (31-51%).

CONCLUSIONS

Reduction in the intensity of mechanical ventilation in patients with ARDS supported by ECLS is common, suggesting that clinicians may be focused on reducing VILI after ECLS initiation. Future investigations should focus on establishing the optimal ventilatory strategy for patients with ARDS who require ECLS.

Extracorporeal circulatory approaches to treat acute respiratory distress syndrome

The early history of extracorporeal membrane oxygenation (ECMO) for adult patients with the acute respiratory distress syndrome (ARDS) evolved slowly over decades, a consequence of extracorporeal technology with high risk and unclear benefit. However, advances in component technology, accumulating evidence, and growing experience in recent years have resulted in a resurgence of interest in ECMO. Extracorporeal support, though currently lacking high-level evidence, has the potential to improve outcomes, including survival, in ARDS. In the near future, novel extracorporeal management strategies may, in fact, lead to a new paradigm in the approach to certain patients with ARDS.

Extracorporeal carbon dioxide removal for patients with acute respiratory failure secondary to the acute respiratory distress syndrome: a systematic review

Acute respiratory distress syndrome (ARDS) continues to have significant mortality and morbidity. The only intervention proven to reduce mortality is the use of lung-protective mechanical ventilation strategies, although such a strategy may lead to problematic hypercapnia. Extracorporeal carbon dioxide removal (ECCO₂R) devices allow uncoupling of ventilation from oxygenation, thereby removing carbon dioxide and facilitating lower tidal volume ventilation. We performed a systematic review to assess efficacy, complication rates, and utility of ECCO₂R devices. We included randomised controlled trials (RCTs), case-control studies and case series with 10 or more patients. We searched MEDLINE, Embase, LILACS (Literatura Latino Americana em Ciências da Saúde), and ISI Web of Science, in addition to grey literature and clinical trials registries. Data were independently extracted by two reviewers against predefined criteria and agreement was reached by consensus. Outcomes of interest included mortality, intensive care and hospital lengths of stay, respiratory parameters and complications. The review included 14 studies with 495 patients (two RCTs and 12 observational studies). Arteriovenous ECCO₂R was used in seven studies, and venovenous ECCO₂R in seven studies. Available evidence suggests no mortality benefit to ECCO₂R, although post hoc analysis of data from the most recent RCT showed an improvement in ventilator-free days in more severe ARDS. Organ failure-free days or ICU stay have not been shown to decrease with ECCOvR. Carbon dioxide removal was widely demonstrated as feasible, facilitating the use of lower tidal volume ventilation. Complication rates varied greatly across the included studies, representing technological advances. There was a general paucity of high-quality data and significant variation in both practice and technology used among studies, which confounded analysis. ECCO₂R is a rapidly evolving technology and is an efficacious treatment to enable protective lung ventilation. Evidence for a positive effect on mortality and other important clinical outcomes is lacking. Rapid technological advances have led to major changes in these devices and together with variation in study design have limited applicability of analysis. Further well-designed adequately powered RCTs are needed.

Extracorporeal CO(2) removal in ARDS

Acute respiratory distress syndrome remains one of the most clinically vexing problems in critical care. As technology continues to evolve, it is likely that extracorporeal CO(2) removal devices will become smaller, more efficient, and safer. As the risk of extracorporeal support decreases, devices' role in acute respiratory distress syndrome patients remains to be defined. This article discusses the functional properties and management techniques of CO(2) removal and intracorporeal membrane oxygenation and provides a glimpse into the future of long-term gas-exchange devices.

Use of extracorporeal life support to support patients with acute respiratory distress syndrome due to H1N1/2009 influenza and other respiratory infections

A large proportion of critically ill H1N1/2009 patients with respiratory failure subsequently developed ARDS and, to date, about 400 patients receiving extracorporeal life support (ECLS) have been accounted for globally, with a reported survival rate from 63% to 79%. The survival rates of patients with ARDS due to non-H1N1/2009 infections are similar. There is no definite evidence to suggest that patient outcomes are changed by ECLS, but its use is associated with serious short-term complications. ECLS relies on an extracorporeal circuit, with extracorporeal membrane oxygenation (ECMO) and pumpless interventional lung assist (ILA) being the two major types employed in ARDS. Both have the potential to correct respiratory failure and related haemodynamic instability. There are only a very limited number of clinical trials to test either and, although ECLS has been used in treating H1N1/2009 patients with ARDS with some success, it should only be offered in the context of clinical trials and in experienced centres.

Acute lung injury and the acute respiratory distress syndrome: a clinical review

Acute respiratory distress syndrome and acute lung injury are well defined and readily recognised clinical disorders caused by many clinical insults to the lung or because of predispositions to lung injury. That this process is common in intensive care is well established. The mainstay of treatment for this disorder is provision of excellent supportive care since these patients are critically ill and frequently have coexisting conditions including sepsis and multiple organ failure. Refinements in ventilator and fluid management supported by data from prospective randomised trials have increased the methods available to effectively manage this disorder.

Artificial lung: progress and prototypes

Lung disease is the fourth leading cause of death (one in seven deaths) in the USA. Acute respiratory distress syndrome (ARDS) affects approximately 150,000 patients a year in the USA, and an estimated 16 million Americans are afflicted with chronic lung disease, accounting for 100,000 deaths per year. Medical management is the standard of care for initial therapy, but is limited by the progression of disease. Chronic mechanical ventilation is readily available, but is cumbersome, expensive and often requires tracheotomy with loss of upper airway defense mechanisms and normal speech. Lung transplantation is an option for less than 1100 patients per year since demand has steadily outgrown supply. For the last 15 years, the authors' group has studied ARDS in order to develop viable alternative treatments. Both extracorporeal gas exchange techniques, including extracorporeal membrane oxygenation, extracorporeal and arteriovenous CO(2) removal, and intravenous oxygenation, aim to allow for a less injurious ventilatory strategy during lung recovery while maintaining near-normal arterial blood gases, but precludes ambulation. The paracorporeal artificial lung (PAL), however, redefines the treatment of both acute and chronic respiratory failure with the goal of ambulatory total respiratory support. PAL prototypes tested on both normal sheep and the absolute lethal dose smoke/burn-induced ARDS sheep model have demonstrated initial success in achieving total gas exchange. Still, clinical trials cannot begin until bio- and hemodynamic compatibility challenges are reconciled. The PAL initial design goals are for a short-term (weeks) bridge to recovery or transplant, but eventually, for long-term support (months).

Adjuncts to Mechanical Ventilation in ARDS

Since its first description, acute respiratory distress syndrome has been characterized by abnormal physiologic and gas exchange properties of the lungs. Many adjunctive therapies have been developed to reduce the stresses of mechanical ventilation on already damaged lungs. We examined the mechanism of action and the latest clinical trial information of several adjunctive therapies including prone positioning, nitric oxide, extracorporeal membrane oxygenation, arterial venous carbon dioxide removal, and liquid ventilation. While all of these therapies have demonstrated short-term improvements in arterial blood gases and in the limitation of lung injury, none have shown an evidence-based survival benefit.

Acute respiratory distress syndrome

Several combination therapies have been described throughout this article: in all likelihood, it is combination therapy that will allow improved survival of ARDS patients. As medicine moves into the future, clinical trials evaluating the efficacy of therapies for ARDS will be performed. In human critical care medicine, a large forward step was taken when ALI and ARDS were clearly defined. Unfortunately. as good as the definition is, ALI and ARDS occur secondary to many different underlying pathologic processes,perhaps obscuring the benefits of certain therapies for ARDS based on the underlying condition, for example, trauma versus sepsis. Selection of patients entering any ARDS trial is crucial: not only must those patients meet the strict definition of ARDS but the underlying disease process should be clearly identified. Identification of patients suffering from different disease processes before the onset of ARDS will allow for stratification of outcomes according to the intervention and the underlying pathology--comparing apples to apples and not to oranges. We are in a unique position in veterinary medicine. Although frequently financially limited by our clients, we have the opportunity to achieve several goals. First, we need to clearly define what constitutes ALI and ARDS in veterinary medicine. Do we want to rely on the human definitions? Probably not; however, as a group, we need to determine what we will accept as definitions. For example, we may not be able perform right heart catheterizations on all our patients to meet the wedge pressure requirement of human beings of less than 18 mm Hg. Do we agree that a PAOP of less than 18 mmHg is appropriate for animals, and is it appropriate for all animals? Will we accept another measure, for example, pulmonary artery diameter increases with echocardiographic evidence of acceptable left heart function? What is acceptable left heart function? As veterinarians, what do we consider to be hypoxemia? Is it the same in all species that we work with? What do we define as acute onset? Most human ARDS cases occur while patients are in hospital being treated for other problems, whereas many of our patients present already in respiratory distress. If we are unable to ventilate patients for economic or practical reasons, what do we use as the equivalent of the Pao2/Flo, ratio'? Reliance on the pathologist is not reasonable, because many disease processes can look similar to ARDS under the microscope. If anything, ALI and ARDS are clinical diagnoses. It is time for veterinarians to reach a consensus on the definition for ALI and ARDS in our patients. Only when we have a consensus of definition can rational prospective clinical trials of therapies be designed.

Extracorporeal gas exchange with the DeltaStream rotary blood pump in experimental lung injury

In most severe cases of the acute respiratory distress syndrome, veno-venous extracorporeal membrane oxygenation (ECMO) can be used to facilitate gas exchange. However, the clinical use is limited due to the size and the concomitant risk of severe adverse events of conventionally-used centrifugal blood pumps with high extracorporeal blood volumes. The DeltaStream blood pump is a small-sized rotary blood pump that may reduce extracorporeal blood volume, foreign surfaces, contact activation of the coagulation system, and blood trauma. The aim of the present study was to test the safety and efficacy of the DeltaStream pump for ECMO in animals with normal lung function and experimental acute lung injury (ALI). Therefore, veno-venous ECMO was performed for 6 hours in mechanically ventilated pigs with normal lung function (n=6) and with ALI induced by repeated lung lavage (n=6) with a blood flow of 30% of the cardiac output. Gas flow with a FiO2 of 1.0 was set to equal blood flow. With a mean activated clotting time of 121 +/- 22 s, no circulatory impairment or thrombus formation was revealed during ECMO. Furthermore, free plasma Hb did not increase. In controls, hemodynamics and gas exchange remained unchanged. In animals with ALI, hemodynamics remained stable and gas transfer across the extracorporeal oxygenators was optimal, but only in 2 animals was a marked increase in PaO2 observed. CO2 removal was efficacious in all animals. We concluded that the DeltaStream blood pump may be used for veno-venous ECMO without major blood damage or hemodynamic impairment.

Artificial lungs: a new inspiration

An estimated 16 million Americans are afflicted with some degree of chronic obstructive pulmonary disease (COPD), accounting for 100,000 deaths per year. The only current treatment for chronic irreversible pulmonary failure is lung transplantation. Since the widespread success of single and double lung transplantation in the early 1990s, demand for donor lungs has steadily outgrown the supply. Unlike dialysis, which functions as a bridge to renal transplantation, or a ventricular assist device (VAD), which serves as a bridge to cardiac transplantation, no suitable bridge to lung transplantation exists. The current methods for supporting patients with lung disease, however, are not adequate or efficient enough to act as a bridge to transplantation. Although occasionally successful as a bridge to transplant, ECMO requires multiple transfusions and is complex, labor-intensive, time-limited, costly, non-ambulatory and prone to infection. Intravenacaval devices, such as the intravascular oxygenator (IVOX) and the intravenous membrane oxygenator (IMO), are surface area limited and currently provide inadequate gas exchange to function as a bridge-to-recovery or transplant. A successful artificial lung could realize a substantial clinical impact as a bridge to lung transplantation, a support device immediately post-lung transplant, and as rescue and/or supplement to mechanical ventilation during the treatment of severe respiratory failure.

Effects of ultrafiltration, dialysis, and temperature on gas exchange during hemodiafiltration: a laboratory experiment

To study gas exchange in the filter during continuous venovenous hemodiafiltration (CVVHDF), an air-tight heated mixing chamber with adjustable CO2 supply was constructed and connected to a CVVHDF monitor. Bicarbonate-free crystalloid (Part 1) and packed red blood cell (Part 2) solutions were circulated at 150 ml x min(-1). Gas exchange expressed as pre-postfilter difference in CO2 and O2 contents was measured at different CVVHDF settings and temperatures of circulating and dialysis solutions. Ultrafiltration was most efficacious for CO2 removal (at 1,000 ml x h(-1) ultrafiltration CO2 losses reached 13% of prefilter CO2 content). Addition of dialysis (1,000 ml x h(-1)) increased CO2 loss to 17% and at maximal parameters (filtration 3,000 ml x h(-1), dialysis 2,500 ml x h(-1)), the loss of CO2 amounted to 35% of prefilter content. Temperature changes of circulating and/or dialysis fluids had no significant impact on CO2 losses. The O2 exchange during CVVHDF was negligible. Currently used CVVHDF is only marginally effective in CO2 removal. Higher volume ultrafiltration combined with dialysis can be expected to reach clinical significance.

Treatment of ARDS

Improved understanding of the pathogenesis of acute lung injury (ALI)/ARDS has led to important advances in the treatment of ALI/ARDS, particularly in the area of ventilator-associated lung injury. Standard supportive care for ALI/ARDS should now include a protective ventilatory strategy with low tidal volume ventilation by the protocol developed by the National Institutes of Health ARDS Network. Further refinements of the protocol for mechanical ventilation will occur as current and future clinical trials are completed. In addition, novel modes of mechanical ventilation are being studied and may augment standard therapy in the future. Although results of anti-inflammatory strategies have been disappointing in clinical trials, further trials are underway to test the efficacy of late corticosteroids and other approaches to modulation of inflammation in ALI/ARDS.

Thirty years of clinical trials in acute respiratory distress syndrome

OBJECTIVE

To systematically review clinical trials in acute respiratory distress syndrome (ARDS).

DATA SOURCES

Computerized bibliographic search of published research and citation review of relevant articles.

STUDY SELECTION

All clinical trials of therapies for ARDS were reviewed. Therapies that have been compared in prospective, randomized trials were the focus of this analysis.

DATA EXTRACTION

Data on population, interventions, and outcomes were obtained by review. Studies were graded for quality of scientific evidence.

MAIN RESULTS

Lung protective ventilator strategy is supported by improved outcome in a single large, prospective trial and a second smaller trial. Other therapies for ARDS, including noninvasive positive pressure ventilation, inverse ratio ventilation, fluid restriction, inhaled nitric oxide, almitrine, prostacyclin, liquid ventilation, surfactant, and immune-modulating therapies, cannot be recommended at this time. Results of small trials using corticosteroids in late ARDS support the need for confirmatory large clinical trials.

CONCLUSIONS

Lung protective ventilator strategy is the first therapy found to improve outcome in ARDS. Trials of prone ventilation and fluid restriction in ARDS and corticosteroids in late ARDS support the need for large, prospective, randomized trials.

Extracorporeal life support in the management of severe respiratory failure

ECLS is a safe and effective means to keep patients alive during severe respiratory failure that would otherwise be fatal. In addition to direct and indirect treatment of the lungs during ECLS, the technique allows days of time for study and treatment of other conditions and other organ failure. The technique has been refined in newborn infants and children, in whom survival rates are high and the technology is proven by prospective randomized trials. ECLS is usually applied to adults with respiratory failure when the mortality risk is over 80%. With these indications, the survival rate in experienced centers is 50% to 60%. A new prospective, randomized trial of ECLS in adult patients is underway in the United Kingdom. In the meantime, intensivists who are charged with the management of moribund ARDS patients who fail to respond to other methods of therapy should consider the risks versus the benefits of transferring such patients to an ECLS center.

Pathogenesis and management of respiratory insufficiency following pulmonary resection

The underlying principle of the surgical treatment of non-small-cell lung cancer (NSCLC) is complete removal of the local/regional disease within the thorax. Pulmonary resection should be as conservative as possible without compromising the adequacy of tumor removal. A multitude of factors influence the incidence and severity of complications following pulmonary resection including the pre-operative physical and psychological status of the patient, the pathologic process requiring resection, the physiologic impact of the procedure, and the addition of pre-operative or postoperative adjuvant therapy. The insidious onset of interstitial changes on chest X-ray (CXR) 1 to 2 days after pulmonary resection forewarns of respiratory distress; however, the pathophysiology of adult respiratory distress syndrome (ARDS) with progression to respiratory failure requiring mechanical ventilation and advanced critical care often unfolds. Management of patients with severe respiratory failure remains primarily supportive. "Good critical care" is the mainstay of therapy: this includes gentle mechanical ventilation to avoid ventilator-induced barotrauma and over-extension of remaining functional alveoli, diuresis, infection identification and management, and nutritional support. New therapeutic strategies that may impact on outcomes in the adult population include pressure-limited ventilation (permissive hypercapnia), inverse ratio ventilation, high-frequency jet ventilation, high-frequency oscillatory ventilation, intratracheal pulmonary ventilation, and prone position ventilation. In addition, alternative therapies such as partial liquid ventilation, inhaled nitric oxide, and extracorporeal techniques including extracorporeal membrane oxygenation (ECMO), extracorporeal carbon dioxide removal (ECCO(2)R), intravascular oxygenation (IVOX), and arteriovenous carbon dioxide removal (AVCO(2)R), provide additional modalities. A component of some or all of these strategies is finding a role in clinical practice.

Extracorporeal membrane oxygenation for severe acute respiratory failure

Extracorporeal membrane oxygenation (ECMO) is a technique for providing life support, in case the natural lungs are failing and are not able to maintain a sufficient oxygenation of the body's organ systems. ECMO technique was an adaptation of conventional cardiopulmonary bypass techniques and introduced into treatment of severe acute respiratory distress syndrome (ARDS) in the 1970s. The initial reports of the use of ECMO in ARDS patients were quite enthusiastic, however, in the following years it became clear that ECMO was only of benefit in newborns with acute respiratory failure. In neonates treated with ECMO, survival rates of 80% could be achieved. In adult patients with ARDS, two large randomized controlled trials (RCTs) published in 1979 and 1994 failed to show an advantage of ECMO over conventional treatment; survival rates were only 10% and 33%, respectively, in the ECMO groups. Since then, ECMO technology as well as conventional treatment of adult ARDS have undergone further improvements. In conventional treatment lung-protective ventilation strategies were introduced and ECMO was made safer by applying heparin-coated equipment, membranes and tubings. Many ECMO centres now use these advanced ECMO technology and report survival rates in excess of 50% in uncontrolled data collections. The question, however, of whether the improved ECMO can really challenge the advanced conventional treatment of adult ARDS is unanswered and will need evaluation by a future RCT.

A prospective comparison of atrio-femoral and femoro-atrial flow in adult venovenous extracorporeal life support

INTRODUCTION

In the United States, venovenous extracorporeal life support has traditionally been performed with atrial drainage and femoral reinfusion (atrio-femoral flow). Although flow reversal (femoro-atrial flow) may alter recirculation and extracorporeal flow, no direct comparison of these 2 modes has been undertaken.

OBJECTIVE

Our goal was to prospectively compare atrio-femoral and femoro-atrial flow in adult venovenous extracorporeal life support for respiratory failure.

METHODS

A modified bridge enabling conversion between atrio-femoral and femoro-atrial flow was incorporated in the extracorporeal circuit. Bypass was initiated in the direction that provided the highest pulmonary arterial mixed venous oxygen saturation, and the following measurements were taken: (1) maximum extracorporeal flow, (2) highest achievable pulmonary arterial mixed venous oxygen saturation, and (3) flow required to maintain the same pulmonary arterial mixed venous oxygen saturation in both directions. Flow direction was then reversed, and the measurements were repeated. Data were compared with paired t tests and are presented as mean +/- standard deviation.

RESULTS

Ten patients were studied, and 9 were included in the data analysis. Femoro-atrial bypass provided (1) higher maximal extracorporeal flow (femoro-atrial flow = 55.6 +/- 9.8 mL/kg per minute, atrio-femoral flow = 51.1 +/- 11.1 mL/kg per minute; P = .04) and (2) higher pulmonary arterial mixed venous oxygen saturation (femoroatrial flow = 89.9% +/- 6.6%, atrio-femoral flow = 83.2% +/- 4.2%; P = .006); (3) furthermore, it required less flow to maintain an equivalent pulmonary arterial mixed venous oxygen saturation (femoro-atrial flow = 37.0 +/- 12.2 mL/kg per minute, atrio-femoral flow = 46.4 +/- 8.8 mL/kg per minute; P = .04).

CONCLUSIONS

During venovenous extracorporeal life support, femoro-atrial bypass provided higher maximal extracorporeal flow, higher pulmonary arterial mixed venous oxygen saturation, and required comparatively less flow to maintain an equivalent mixed venous oxygen saturation than did atrio-femoral bypass.

An approach to the treatment of severe adult respiratory failure

OBJECTIVES

The purpose of this article is to evaluate outcome in adult patients with severe respiratory failure managed with an approach using (1) limitation of end inspiratory pressure, (2) inverse ratio ventilation, (3) titration of PEEP by SvO2, (4) intermittent prone positioning, (5) limitation of FiO2, (6) diuresis, (7) transfusion, and (8) extracorporeal life support (ECLS) if patients failed to respond.

PATIENTS AND METHODS

This study was designed as a retrospective review in the intensive care unit of a tertiary referral hospital. One-hundred forty-one consecutive patients with hypoxic (n = 135) or hypercarbic (n = 6) respiratory failure referred for consideration of ECLS between 1990 and 1996. Overall, initial PaO2/FiO2 (P/F) ratio was 75+/-5 (median = 66).

RESULTS

Lung recovery occurred in 67% of patients and 62% survived. Forty-one patients improved without ECLS (83% survived); 100 did not and were supported with ECLS (54% survived). Survival was greater in patients cannulated within 12 hours of arrival (59%) compared with those cannulated after 12 hours (40%, P < .05). Multiple logistic regression identified age, duration of mechanical ventilation before transfer, four or more dysfunctional organs, and the requirement for ECLS as independent predictors of mortality.

CONCLUSIONS

An approach that emphasizes lung protection and early implementation of extracorporeal life support is associated with high rates of survival in patients with severe respiratory failure.

Extracorporeal life support for 100 adult patients with severe respiratory failure

OBJECTIVE

The authors retrospectively reviewed their experience with extracorporeal life support (ECLS) in 100 adult patients with severe respiratory failure (ARF) to define techniques, characterize its efficacy and utilization, and determine predictors of outcome.

SUMMARY BACKGROUND DATA

Extracorporeal life support maintains gas exchange during ARF, providing diseased lungs an optimal environment in which to heal. Extracorporeal life support has been successful in the treatment of respiratory failure in infants and children. In 1990, the authors instituted a standardized protocol for treatment of severe ARF in adults, which included ECLS when less invasive methods failed.

METHODS

From January 1990 to July 1996, the authors used ECLS for 100 adults with severe acute hypoxemic respiratory failure (n = 94): paO2/FiO2 ratio of 55.7+/-15.9, transpulmonary shunt (Qs/Qt) of 52+/-22%, or acute hypercarbic respiratory failure (n = 6): paCO2 84.0+/-31.5 mmHg, despite and after maximal conventional ventilation. The technique included venovenous percutaneous access, lung "rest," transport on ECLS, minimal anticoagulation, hemofiltration, and optimal systemic oxygen delivery.

RESULTS

Overall hospital survival was 54%. The duration of ECLS was 271.9+/-248.6 hours. Primary diagnoses included pneumonia (49 cases, 53% survived), adult respiratory distress syndrome (45 cases, 51 % survived), and airway support (6 cases, 83% survived). Multivariate logistic regression modeling identified the following pre-ECLS variables significant independent predictors of outcome: 1) pre-ECLS days of mechanical ventilation (p = 0.0003), 2) pre-ECLS paO2/FiO2 ratio (p = 0.002), and 3) age (years) (p = 0.005). Modeling of variables during ECLS showed that no mechanical complications were independent predictors of outcome, and the only patient-related complications associated with outcome were the presence of renal failure (p < 0.0001) and significant surgical site bleeding (p = 0.0005).

CONCLUSIONS

Extracorporeal life support provides life support for ARF in adults, allowing time for injured lungs to recover. In 100 patients selected for high mortality risk despite and after optimal conventional treatment, 54% survived. Extracorporeal life support is extraordinary but reasonable treatment in severe adult respiratory failure. Predictors of survival exist that may be useful for patient prognostication and design of future prospective studies.

Inhalation injury treated with extracorporeal CO2 elimination

A 38-year-old male was admitted to the intensive care unit with a full-thickness burn involving 30 per cent of his total body surface area (TBSA) and severe inhalation injury. Respiratory failure developed within 54 h and CO2 could not be eliminated, even by very invasive mechanical ventilation. Because of the patient's age and the minor extent of the burned TBSA, we started extracorporeal CO2 elimination (ECCO2-R) and continued ECCO2-R for 30 days, when the patient was weaned from ECC. The clinical course during ECCO2-R was complicated by major bleeding from a thoracotomy tube, from the site of tangential excision and by four septic episodes. Lung biopsy was performed twice on day 29 (during ECCO2-R) and day 58 (after ECCO2-R) after admission and revealed bronchiolitis obliterans without tendency to recovery. The patient died of sepsis with multiorgan failure on day 81 after trauma.

High-frequency oscillatory ventilation for adult respiratory distress syndrome--a pilot study

OBJECTIVE

To evaluate the safety and effectiveness of high-frequency oscillatory ventilation using a protocol designed to recruit and maintain optimal lung volume in patients with severe adult respiratory distress syndrome (ARDS).

SETTING

Surgical and medical intensive care units in a tertiary care, military teaching hospital.

DESIGN

A prospective, clinical study.

PATIENTS

Seventeen patients, 17 yrs to 83 yrs of age, with severe ARDS (Lung Injury Score of 3.81 +/- 0.23) failing inverse ratio mechanical conventional ventilation (PaO2/FiO2 ratio of 68.6 +/- 21.6, peak inspiratory pressure of 54.3 +/- 12.7 cm H2O, positive end-expiratory pressure of 18.2 +/- 6.9 cm H2O).

INTERVENTIONS

High-frequency oscillatory ventilation was instituted after varying periods of conventional ventilation (5.12 +/- 4.3 days). We employed lung volume recruitment strategy that consisted of incremental increases in mean airway pressure to achieve a PaO2 of > or = 60 torr (> or = 8.0 kPa), with an FiO2 of < or = 0.6.

MEASUREMENTS AND MAIN RESULTS

High-frequency oscillator ventilator settings (FiO2, mean airway pressure, pressure amplitude of oscillation [delta P] frequency) and hemodynamic parameters (cardiac output, oxygen delivery [DO2]), mean systemic and pulmonary arterial pressures, and the oxygenation index (oxygenation index = [FiO2 x mean airway pressure x 100]/PaO2) were monitored during the transition to high-frequency oscillatory ventilation and throughout the course of the high-frequency protocol. Thirteen patients demonstrated improved gas exchange and an overall improvement in PaO2/FiO2 ratio (p < .02). Reductions in the oxygenation index (p < .01) and FiO2 (p < .02) at 12, 24, and 48 hrs after starting high-frequency oscillatory ventilation were observed. No significant compromise in cardiac output or DO2 was observed, despite a significant increase in mean airway pressure (31.2 +/- 10.3 to 34.0 +/- 6.7 cm H2O, p < .05) on high-frequency oscillatory ventilation. The overall survival rate at 30 days was 47%. A greater number of pretreatment days on conventional ventilation (p < .009) and an entry oxygenation index of > 47 (sensitivity 100%, specificity 100%) were associated with mortality.

CONCLUSIONS

High-frequency oscillatory ventilation is both safe and effective in adult patients with severe ARDS failing conventional ventilation. A lung volume recruitment strategy during high-frequency oscillatory ventilation produced improved gas exchange without a compromise in DO2. These results are encouraging and support the need for a prospective, randomized trial of algorithm-controlled conventional ventilation vs. high-frequency oscillatory ventilation for adults with severe ARDS.

Significant reduction in minute ventilation and peak inspiratory pressures with arteriovenous CO2 removal during severe respiratory failure

OBJECTIVES

To quantify CO2 removal using an extracorporeal low-resistance membrane gas exchanger placed in an arteriovenous shunt and evaluate its effects on the reduction of ventilatory volumes and airway pressures during severe respiratory failure induced by smoke inhalation injury.

DESIGN

Prospective study.

SETTING

Research laboratory.

SUBJECTS

Adult female sheep (n = 5).

INTERVENTIONS

Animals were instrumented with femoral and pulmonary arterial catheters and underwent an LD50 cotton smoke inhalation injury via a tracheostomy under halothane anesthesia. Twenty-four hours after smoke inhalation injury, the animals were reanesthetized and systemically heparinized for cannulation of the left carotid and common jugular vein to construct a simple arteriovenous shunt. A membrane gas exchanger was interposed within the arteriovenous shunt, and blood flow produced by the arteriovenous pressure gradient was unrestricted at the time of complete recovery from anesthesia. CO2 removal by the gas exchanger was measured as the product of the sweep gas flow (FIO2 of 1.0 at 2.5 to 3.0 L/min) and the exhaust CO2 content measured with an inline capnometer. CO2 removed by the animal's lungs was determined by the expired gas CO2 content in a Douglas bag. We made stepwise, 20% reductions in ventilator support hourly. We first reduced the tidal volume to achieve a peak inspiratory pressure of < 30 cm H2O, and then we reduced the respiratory rate while maintaining normocapnia. PaO2 was maintained by adjusting the FIO2 and the level of positive end-expiratory pressure.

MEASUREMENTS AND MAIN RESULTS

Mean blood flow through the arteriovenous shunt ranged from 1154 +/- 82 mL/min (25% cardiac output) to 1277 +/- 38 mL/min (29% cardiac output) over the 6-hr study period. The pressure gradient across the gas exchanger was always < 10 mm Hg. Maximum arteriovenous CO2 removal was 102.0 +/- 9.5 mL/min (96% of total CO2 production), allowing minute ventilation to be reduced from 10.3 +/- 1.4 L/min (baseline) to 0.5 +/- 0.0 L/min at 6 hrs of arteriovenous CO2 removal while maintaining normocapnia. Similarly, peak inspiratory pressure decreased from 40.8 +/- 2.1 to 19.7 +/- 7.5 cm H2O. PaO2 was maintained at > 100 torr (> 13.3 kPa) at maximally reduced ventilator support. Mean arterial pressure and cardiac output did not change significantly as a result of arteriovenous shunting.

CONCLUSIONS

Extracorporeal CO2 removal using a low-resistance gas exchanger in a simple arteriovenous shunt allows significant reduction in minute ventilation and peak inspiratory pressure without hypercapnia or the complex circuitry and monitoring required for conventional extracorporeal membrane oxygenation. Arteriovenous CO2 removal can be applied as an easy and cost-effective treatment to minimize ventilator-induced barotrauma and volutrauma during severe respiratory failure.

[Current aspects of acute respiratory distress syndrome in children]

Acute respiratory distress syndrome (ARDS) is a frequent condition in pediatric intensive care units. The mortality remains high despite advances in conventional mechanical ventilation and aetiological treatment. Several animal studies have documented lung injury during mechanical ventilation with high tidal volume, and clinical investigations have shown that in human ARDS, most ventilation is distributed to the small areas of remaining aerated lung resulting in overdistension of these areas and lung injury ("baby lung" theory). Nevertheless the usefulness of extrapulmonary gas exchange remains much debated. New ventilatory strategies have been developed in order to reduce ventilator-induced lung injury and to improve systemic oxygenation but multicentric randomized clinical trials are needed before these strategies can be validated.

Principles and Practice of Venovenous Extracorporeal Membrane Oxygenation

Over the past several years, the use of venovenous extracorporeal membrane oxygenation (ECMO) has increased. The primary advantage of venovenous (VV) over venoarterial (VA) ECMO is preservation of the carotid artery. Its primary disadvantage is that it does not provide circulatory support. While VV ECMO is technically similar to VA ECMO, clinical application of VV ECMO is quite different from VA ECMO. Recent clinical data show that VV ECMO is safe and effective. The purpose of this review is to discuss these differences between VV and VA ECMO, to review the various forms of VV ECMO, and finally to offer recommendations on the safe clinical use of VV ECMO.

Clinical strategies in intravascular gas exchange

Specific therapies in the management of acute pulmonary failure remain elusive, with attention being focused instead on novel supportive measures. The benefits of extracorporeal gas exchange support remain uncertain, and the perceived simplicity of intravascular gas exchange has, therefore, attracted much interest. Initial clinical experience with the intravascular oxygenator (IVOX) device confirms its safety and simplicity, but estimated mean gas-transfer values represent only 25% of basal gas-exchange requirements. The inherent limitations of IVOX as an oxygenator are discussed, providing a rationale for considering IVOX as primarily a CO2 removal device. Reappraisal of the clinical place of intravascular gas exchange and the identification of specific applications most likely to yield benefit to patients are suggested. Design modifications enhancing efficacy are anticipated, further strengthening the potential of intravascular gas-exchange devices in selected patients with pulmonary failure.

The acute respiratory distress syndrome: definitions, severity and clinical outcome. An analysis of 101 clinical investigations

OBJECTIVE

To determine possible changes in outcome from acute respiratory distress syndrome (ARDS) and to compare severity of lung injury and methods of treatment from 1967 to 1994.

DATA SOURCES

Computerized (Medline, Current Contents) and manual (Cumulated Index Medicus) literature search using the key word and/or title ARDS.

STUDY SELECTION

Only clinical studies published as full papers reporting data on both patient mortality (survival) and oxygenation index (PaO2/FIO2) were included. Single case reports, abstracts, reviews and editorials were excluded from evaluation.

DATA EXTRACTION

Relevant data were extracted in duplicate, followed by quality checks on approximately 80% of data extracted.

DATA SYNTHESIS

101 papers reporting on 3264 patients were included: 48 studies (2207 patients) were performed in the USA, 43 studies (742 patients) in Europe and 10 studies (315 patients) elsewhere. Mortality reported in these studies was 53 +/- 22% (mean +/- SD), with no apparent trend towards a higher survival (1994: 22 studies, mortality 51 +/- 19%). The mean PaO2/FIO2 ratio remained unchanged throughout the observation period (118 +/- 47 mmHg). No correlation could be established between outcome and PaO2/FIO2 or lung injury score. Patients who underwent pressure-limited ventilation had a significantly lower mortality (35 +/- 20%) than patients on volume-cycled ventilation (54 +/- 22%) or patients for whom there was no precise information on ventilatory support (59 +/- 19%). Significantly lower PaO2/FIO2 ratios (61 +/- 17 mmHg) were observed in patients prior to extracorporeal lung assist, together with mortality rates in the range of those for conventionally treated patients (55 +/- 22%).

CONCLUSIONS

The mortality of ARDS patients remained constant throughout the period studied. Therefore, the standard for outcome in ARDS should be a mortality in the 50% range. Neither PaO2/FIO2 ratio nor lung injury score was a reliable predictor for outcome in ARDS. Patients might benefit from pressure-limited ventilatory support, as well as extracorporeal lung assist. Since crucial data were missing in most clinical studies, thus preventing direct comparison, we emphasize the importance of using standardized definitions and study entry criteria.

Intracranial hypertension and adult respiratory distress syndrome: usefulness of tracheal gas insufflation

The management of increased intracranial pressure (ICP) in patients with an associated acute lung injury is difficult. High levels of PaCO2 as tolerated for permissive hypercapnia are deleterious for cerebral circulation. In such circumstances, tracheal gas insufflation (TGI), which was recently proposed to reduce PaCO2, may be of benefit. We report the cases of two patients with severe adult respiratory distress syndrome and head trauma complicated with elevated ICP. The introduction of TGI decreased PaCO2 by 17 and 26%, decreased ICP, and increased calculated cerebral perfusion pressure. We conclude that TGI could be added to a pressure-targeted strategy of ventilatory management when severe adult respiratory distress syndrome was associated to an intracranial hypertension.

Intravenacaval membrane oxygenation and carbon dioxide removal in severe acute respiratory failure

STUDY OBJECTIVE

To characterize the physiologic response to, and safety of, intravenacaval membrane oxygenation and carbon dioxide removal.

DESIGN

Interventional before-after study.

SETTING

University teaching hospital ICU.

PATIENTS

Twenty-two patients with severe acute respiratory distress syndrome (ARDS).

INTERVENTIONS

Implantation of a hollow-fiber membrane oxygenator (IVOX; CardioPulmonics; Salt Lake City, Utah) into the superior and inferior venae cavae by venotomy of the right femoral or right internal jugular vein for a duration of up to 20 days.

MEASUREMENTS

Hemodynamic measurements using pulmonary artery and systemic artery catheters, ventilator settings (FIO2, minute ventilation, peak inspiratory pressure, and positive end-expiratory pressure), arterial and mixed venous blood gases (pH, PCO2, PO2, and measured saturation), and clinical laboratory determinations (CBC, fibrinogen, plasma hemoglobin, complement C3 and C5) were obtained. Calculations of PaO2/FIO2 ratio and PaCO2-VE product were used to assess gas exchange efficacy. Microbiologic cultures were obtained from the device and wound following explantation. Survival to ICU discharge and hospital discharge were recorded.

RESULTS

Implantation was successful in 20 of 22 patients. Gas exchange rates averaged 50.4 +/- 15.8 mL.min-1 for carbon dioxide and 71.1 +/- 20.2 mL.min-1 for oxygen. A reduction in FIO2 from 0.78 +/- 0.16 to 0.63 +/- 0.21 and in VE from 177 +/- 94 mL.kg-1.min-1 to 127 +/- 58 mL.kg-1.min-1 was possible within 4 h post-implantation. By 12 h, FIO2 was reduced to 0.57 +/- 0.18. Indices of gas exchange improved significantly after implantation, with PaO2/FIO2 ratio increasing from 79 +/- 20 to 112 +/- 47 and PaCO2-VE product decreasing from 7.6 +/- 4.2 to 4.9 +/- 2.5 within 4 h. A significant reduction in peak inspiratory pressure was achieved (45 +/- 10 to 38 +/- 9 cm H2O). Major complications were blood loss during implantation requiring transfusion in 11 patients, a retroperitoneal bleed in 1 patient, and femoral deep venous thrombosis in 4 patients, but there were no long-term sequelae or IVOX-related deaths. The ICU and hospital survival were 10/20 (50%) and 8/20 (40%), respectively.

CONCLUSIONS

Intravenacaval membrane oxygen and carbon dioxide removal can provide partial respiratory support during severe respiratory failure and permit reductions in the level of mechanical ventilator support, with an acceptable safety profile.

Is tracheal gas insufflation an alternative to extrapulmonary gas exchangers in severe ARDS?

Tracheal gas insufflation (TGI) of pure oxygen combined with mechanical ventilation decreases dead space and increases CO2 clearance. In the present study, TGI was used in six patients with ARDS who met extracorporeal membrane oxygenation criteria and who were severely hypoxemic and hypercapnic despite optimal pressure-controlled ventilation. This open clinical study aimed to investigate the effects of 4 L/min continuous flow of oxygen given via an intratracheal catheter. PaCO2 decreased from 108 +/- 32 to 84 +/- 26 mm Hg (p < 0.05), and no significant change in PaO2 (68 +/- 18 vs 96 +/- 43, p = 0.06). There was no change in airway pressures and hemodynamic variables. A slight increase in end-expiratory and end-inspiratory volumes with TGI possibly occurred, as seen on tracings from respiratory inductive plethysmography (Respitrace). We conclude that TGI improves tolerance of limited pressure ventilation by removing CO2, but it may induce changes in lung volumes that are not detected by ventilator measurements.

Therapeutic optimization including inhaled nitric oxide in adult respiratory distress syndrome in a polyvalent intensive care unit

OBJECTIVE

To investigate the effects of inhaled nitric oxide (NO) in adult respiratory distress syndrome (ARDS) associated with a therapeutic optimization strategy on oxygen parameters, barotrauma, and evolution in a medical and surgical intensive care unit.

DESIGN

Prospective study.

MATERIALS AND METHODS

Twenty consecutive patients with ARDS were studied (Murray score 3.6 +/- 0.2). Eleven were surgical patients and nine were medical patients. All fulfilled the extracorporeal membrane oxygenation entry criteria. The APACHE II score predicted mortality was 39%. All were ventilated with FiO2 1 with positive end-expiratory pressure (PEEP) of 11 +/- 1 cm H2O. Therapeutic optimization included permissive hypercapnia, tracheal gas insufflation, prone position, continuous hemofiltration, treatment of infection, and pleural drainage. We used NO continuously inhaled at a concentration ranging from 5 to 10 ppm.

MEASUREMENTS AND MAIN RESULTS

After 1 hour, inhaled NO improved PaO2 in all patients except one (78 +/- 11 to 130 +/- 25 mm Hg) (p < 0.05), allowing a reduction of FiO2 and PEEP. After 24 hours, mean pulmonary arterial pressure decreased from 31 +/- 3 to 25 +/- 2 mm Hg (p < 0.05). Systemic hemodynamics were unaffected. Oxygen delivery increased from 531 +/- 135 to 603 +/- 125 mL/minute/m-2 (p < 0.05). Barotraumatic lesions were present in only one patient. Reversal of ARDS was obtained in 16 patients, of whom 14 (70%) were discharged.

CONCLUSIONS

This study was shorter to demonstrate an improvement in the survival rate. Nevertheless, these preliminary results are encouraging. Because of its safety, effectiveness, and easy use, inhaled NO should be used as a part of a therapeutic optimization protocol before considering more invasive and expensive procedures, such as extracorporeal respiratory support or intravascular oxygenation.

Reduction of ventilator settings allowed by intravenous oxygenator (IVOX) in ARDS patients

OBJECTIVE

To evaluate the possibility of reducing ventilator settings to "safe" levels by extrapulmonary gas exchange with IVOX in ARDS patients.

DESIGN

Uncontrolled open clinical study.

SETTING

Medical Intensive Care Unit of a University Hospital.

PATIENTS

6 patients with ARDS who entered into IVOX phase II clinical trials.

INTERVENTIONS

The end-point of this study was to reduce ventilator settings from the initial values, recorded on the day of inclusion, to the following: peak inspiratory pressure < 40 cmH2O, mean airway pressure < 25 cmH2O and tidal volume < 10 ml/kg. Trials to achieve this goal were made on volume-controlled ventilation within the 24 h before and after IVOX insertion. Comparison of the results achieved during these trials used Wilcoxon test.

RESULTS

Before IVOX implantation reduction of ventilator settings was not possible in the 6 patients, despite a non-significant increase in PaO2/FIO2 was achieved. IVOX permitted significant decrease in PaCO2 (from 60.5 +/- 15 to 52 +/- 11 mmHg; p = 0.02) before any modification of the ventilatory mode. After IVOX insertion, a significant decrease of the ventilator settings was performed: peak and mean airway pressures dropped from 44 +/- 10 to 36.8 +/- 6.7; p = 0.02 and from 26.3 +/- 5.6 to 22.5 +/- 3.9 cmH2O; p = 0.02, respectively. Concommitantly, PaCO2 remained unchanged and PaO2/FIO2 increased significantly from 93 +/- 28 to 117 +/- 52; p = 0.04. The interruption of oxygen flow on IVOX was associated with a slight decrease of the oxygen variables. Tolerance of IVOX was satisfactory. However, a significant decrease both in cardiac index and in pulmonary wedge pressures (from 4.5 +/- 1.2 to 3.4 +/- 9; p = 0.03 and from 16 +/- 5 to 11 +/- 2; p = 0.04, respectively) was observed.

CONCLUSION

Gas exchange achieved by IVOX allowed reduction of ventilator settings in 6 ARDS patients in whom previous attempts have failed. CO2 removal by the device, may explain these results. Efficacy of IVOX on arterial oxygenation was uncertain.

Permissive hypercapnia and intravascular oxygenator in the treatment of patients with ARDS

This open clinical study was aimed at testing the hypothesis that an intravascular oxygenator (IVOX) may help to perform permissive hypoventilation in 10 patients with severe ARDS. After initial evaluation, we tried to reduce ventilator settings before and after IVOX implantation. Before IVOX, poor clinical tolerance and worsening oxygenation did not allow for a significant decrease in ventilator settings. With IVOX, peak inspiratory pressure (PIP) was reduced from 47 to 39 cm H2O (p = 0.005) and minute ventilation from 13 +/- 3.5 to 11 +/- 3 L/min. CO2 removal by IVOX allowed a significant decrease in PaCO2 from 66 +/- 15 to 59 +/- 13 mm Hg. Improvement of oxygenation with IVOX was not significant. Furthermore, interruption of oxygen flow through IVOX did not change oxygenation variables. Tolerance of the IVOX device was good, but insertion of the device was followed by a significant decrease in both cardiac index and pulmonary wedge pressure. In conclusion, IVOX improves tolerance of hypoventilation by limiting hypercapnia in ARDS patients. These preliminary results must be confirmed by a randomized controlled study.