Pumpless extracorporeal lung assist (pECLA) in patients with acute respiratory distress syndrome and severe brain injury

Mechanical Ventilation in Patients with Traumatic Brain Injury: Is it so Different?

Patients with traumatic brain injury (TBI) frequently require invasive mechanical ventilation and admission to an intensive care unit. Ventilation of patients with TBI poses unique clinical challenges, and careful attention is required to ensure that the ventilatory strategy (including selection of appropriate tidal volume, plateau pressure, and positive end-expiratory pressure) does not cause significant additional injury to the brain and lungs. Selection of ventilatory targets may be guided by principles of lung protection but with careful attention to relevant intracranial effects. In patients with TBI and concomitant acute respiratory distress syndrome (ARDS), adjunctive strategies include sedation optimization, neuromuscular blockade, recruitment maneuvers, prone positioning, and extracorporeal life support. However, these approaches have been largely extrapolated from studies in patients with ARDS and without brain injury, with limited data in patients with TBI. This narrative review will summarize the existing evidence for mechanical ventilation in patients with TBI. Relevant literature in patients with ARDS will be summarized, and where available, direct data in the TBI population will be reviewed. Next, practical strategies to optimize the delivery of mechanical ventilation and determine readiness for extubation will be reviewed. Finally, future directions for research in this evolving clinical domain will be presented, with considerations for the design of studies to address relevant knowledge gaps.

Extracorporeal carbon dioxide removal for acute respiratory failure: a review of potential indications, clinical practice and open research questions

Extracorporeal carbon dioxide removal (ECCO₂R) is a form of extracorporeal life support (ECLS) largely aimed at removing carbon dioxide in patients with acute hypoxemic or acute hypercapnic respiratory failure, so as to minimize respiratory acidosis, allowing more lung protective ventilatory settings which should decrease ventilator-induced lung injury. ECCO₂R is increasingly being used despite the lack of high-quality evidence, while complications associated with the technique remain an issue of concern. This review explains the physiological basis underlying the use of ECCO₂R, reviews the evidence regarding indications and contraindications, patient management and complications, and addresses organizational and ethical considerations. The indications and the risk-to-benefit ratio of this technique should now be carefully evaluated using structured national or international registries and large randomized trials.

Noninvasive and invasive mechanical ventilation for neurologic disorders

Patients with acute neurologic injuries frequently require mechanical ventilation due to diminished airway protective reflexes, cardiopulmonary failure secondary to neurologic insults, or to facilitate gas exchange to precise targets. Mechanical ventilation enables tight control of oxygenation and carbon dioxide levels, enabling clinicians to modulate cerebral hemodynamics and intracranial pressure with the goal of minimizing secondary brain injury. In patients with acute spinal cord injuries, neuromuscular conditions, or diseases of the peripheral nerve, mechanical ventilation enables respiratory support under conditions of impending or established respiratory failure. Noninvasive ventilatory approaches may be carefully considered for certain disease conditions, including myasthenia gravis and amyotrophic lateral sclerosis, but may be inappropriate in patients with Guillain-Barré syndrome or when relevant contra-indications exist. With regard to discontinuing mechanical ventilation, considerable uncertainty persists about the best approach to wean patients, how to identify patients ready for extubation, and when to consider primary tracheostomy. Recent consensus guidelines highlight these and other knowledge gaps that are the focus of active research efforts. This chapter outlines important general principles to consider when initiating, titrating, and discontinuing mechanical ventilation in patients with acute neurologic injuries. Important disease-specific considerations are also reviewed where appropriate.

Advances in extracorporeal membrane oxygenator design for artificial placenta technology

Extreme prematurity, defined as a gestational age of fewer than 28 weeks, is a significant health problem worldwide. It carries a high burden of mortality and morbidity, in large part due to the immaturity of the lungs at this stage of development. The standard of care for these patients includes support with mechanical ventilation, which exacerbates lung pathology. Extracorporeal life support (ECLS), also called artificial placenta technology when applied to extremely preterm (EPT) infants, offers an intriguing solution. ECLS involves providing gas exchange via an extracorporeal device, thereby doing the work of the lungs and allowing them to develop without being subjected to injurious mechanical ventilation. While ECLS has been successfully used in respiratory failure in full-term neonates, children, and adults, it has not been applied effectively to the EPT patient population. In this review, we discuss the unique aspects of EPT infants and the challenges of applying ECLS to these patients. In addition, we review recent progress in artificial placenta technology development. We then offer analysis on design considerations for successful engineering of a membrane oxygenator for an artificial placenta circuit. Finally, we examine next-generation oxygenators that might advance the development of artificial placenta devices.

Update on extracorporeal carbon dioxide removal: a comprehensive review on principles, indications, efficiency, and complications

TECHNOLOGY

Extracorporeal carbon dioxide removal means the removal of carbon dioxide from the blood across a gas exchange membrane without substantially improving oxygenation. Carbon dioxide removal is possible with substantially less extracorporeal blood flow than needed for oxygenation. Techniques for extracorporeal carbon dioxide removal include (1) pumpless arterio-venous circuits, (2) low-flow venovenous circuits based on the technology of continuous renal replacement therapy, and (3) venovenous circuits based on extracorporeal membrane oxygenation technology.

INDICATIONS

Extracorporeal carbon dioxide removal has been shown to enable more protective ventilation in acute respiratory distress syndrome patients, even beyond the so-called "protective" level. Although experimental data suggest a benefit on ventilator induced lung injury, no hard clinical evidence with respect to improved outcome exists. In addition, extracorporeal carbon dioxide removal is a tool to avoid intubation and mechanical ventilation in patients with acute exacerbated chronic obstructive pulmonary disease failing non-invasive ventilation. This concept has been shown to be effective in 56-90% of patients. Extracorporeal carbon dioxide removal has also been used in ventilated patients with hypercapnic respiratory failure to correct acidosis, unload respiratory muscle burden, and facilitate weaning. In patients suffering from terminal fibrosis awaiting lung transplantation, extracorporeal carbon dioxide removal is able to correct acidosis and enable spontaneous breathing during bridging. Keeping these patients awake, ambulatory, and breathing spontaneously is associated with favorable outcome.

COMPLICATIONS

Complications of extracorporeal carbon dioxide removal are mostly associated with vascular access and deranged hemostasis leading to bleeding. Although the spectrum of complications may differ, no technology offers advantages with respect to rate and severity of complications. So called "high-extraction systems" working with higher blood flows and larger membranes may be more effective with respect to clinical goals.

Mechanical ventilation in patients with acute ischaemic stroke: from pathophysiology to clinical practice

Most patients with ischaemic stroke are managed on the ward or in specialty stroke units, but a significant number requires higher-acuity care and, consequently, admission to the intensive care unit. Mechanical ventilation is frequently performed in these patients due to swallowing dysfunction and airway or respiratory system compromise. Experimental studies have focused on stroke-induced immunosuppression and brain-lung crosstalk, leading to increased pulmonary damage and inflammation, as well as reduced alveolar macrophage phagocytic capability, which may increase the risk of infection. Pulmonary complications, such as respiratory failure, pneumonia, pleural effusions, acute respiratory distress syndrome, lung oedema, and pulmonary embolism from venous thromboembolism, are common and found to be among the major causes of death in this group of patients. Furthermore, over the past two decades, tracheostomy use has increased among stroke patients, who can have unique indications for this procedure—depending on the location and type of stroke—when compared to the general population. However, the optimal mechanical ventilator strategy remains unclear in this population. Although a high tidal volume (V_T) strategy has been used for many years, the latest evidence suggests that a protective ventilatory strategy (V_T = 6–8 mL/kg predicted body weight, positive end-expiratory pressure and rescue recruitment manoeuvres) may also have a role in brain-damaged patients, including those with stroke. The aim of this narrative review is to explore the pathophysiology of brain-lung interactions after acute ischaemic stroke and the management of mechanical ventilation in these patients.

The Feasibility of Venovenous ECMO at Role-2 Facilities in Austere Military Environments

INTRODUCTION

Venovenous extracorporeal membrane oxygenation (VV-ECMO) has been gaining use to bridge the recovery from acute respiratory distress syndrome (ARDS) refractory to conventional treatment. However, these interventions are often limited to higher echelons of military care. We present a case of lung salvage from severe ARDS in an Afghani soldier with VV-ECMO at a Role-2 (R2) facility in an austere military environment in Afghanistan.

CASE

A 25-year-old Afghani soldier presented to an R2 facility with blast lung injury and multiple penetrating injuries following an explosion. The patient underwent immediate damage control laparotomy. The abdomen was left open for subsequent washouts and ongoing resuscitation. Due to his ineligibility for evacuation and worsening ARDS, despite 5 d of conventional ventilation strategies, he was started on VV-ECMO. The patient had immediate improvements in oxygenation, which continued for 10 d. Moreover, he underwent three transportations to the operating room without accidental decannulation or disruption of the VV-ECMO device. Despite significant improvements, the patient expired on postoperative day 15, due to an overwhelming intra-abdominal sepsis.

CONCLUSION

As future advancements are sought, VV-ECMO may become a consideration for casualties with severe ARDS at the point of injury and at lower echelons of military care.

Past and present role of extracorporeal membrane oxygenation in combat casualty care: How far will we go?

Advanced extracorporeal therapies have been successfully applied in the austere environment of combat casualty care over the previous decade. In this review, we describe the historic underpinnings of extracorporeal membrane oxygenation, review the recent experience with both partial and full lung support during combat operations, and critically assess both the current status of the Department of Defense extracorporeal membrane oxygenation program and the way forward to establish long-range lung rescue therapy as a routine capability for combat casualty care.

[Topical respiratory strategies in neurocritical care]

Management of the respiratory tract and maintenance of adequate gas exchange are the basic goals of critical care. Injury to the nervous system is often accompanied by development of respiratory disorders. On the other hand, changes in the gas composition of arterial blood can cause brain damage. In addition, approaches to the patient with respiratory failure, which are used in general critical care and neurocritical care, may differ. The presented literature review is devoted to modern respiratory strategies used in neurocritical care.

Acute respiratory distress syndrome in traumatic brain injury: how do we manage it?

Traumatic brain injury (TBI) is an important cause of morbidity and mortality worldwide. TBI patients frequently suffer from lung complications and acute respiratory distress syndrome (ARDS), which is associated with poor clinical outcomes. Moreover, the association between TBI and ARDS in trauma patients is well recognized. Mechanical ventilation of patients with a concomitance of acute brain injury and lung injury can present significant challenges. Frequently, guidelines recommending management strategies for patients with traumatic brain injuries come into conflict with what is now considered best ventilator practice. In this review, we will explore the strategies of the best practice in the ventilatory management of patients with ARDS and TBI, concentrating on those areas in which a conflict exists. We will discuss the use of ventilator strategies such as protective ventilation, high positive end expiratory pressure (PEEP), prone position, recruitment maneuvers (RMs), as well as techniques which at present are used for 'rescue' in ARDS (including extracorporeal membrane oxygenation) in patients with TBI. Furthermore, general principles of fluid, haemodynamic and hemoglobin management will be discussed. Currently, there are inadequate data addressing the safety or efficacy of ventilator strategies used in ARDS in adult patients with TBI. At present, choice of ventilator rescue strategies is best decided on a case-by-case basis in conjunction with local expertise.

Acute brain trauma, lung injury, and pneumonia: more than just altered mental status and decreased airway protection

Traumatic brain injury (TBI) is a major cause of mortality and morbidity worldwide. Even when patients survive the initial insult, there is significant morbidity and mortality secondary to subsequent pulmonary edema, acute lung injury (ALI), and nosocomial pneumonia. Whereas the relationship between TBI and secondary pulmonary complications is recognized, little is known about the mechanistic interplay of the two phenomena. Changes in mental status secondary to acute brain injury certainly impair airway- and lung-protective mechanisms. However, clinical and translational evidence suggests that more specific neuronal and cellular mechanisms contribute to impaired systemic and lung immunity that increases the risk of TBI-mediated lung injury and infection. To better understand the cellular mechanisms of that immune impairment, we review here the current clinical data that support TBI-induced impairment of systemic and lung immunity. Furthermore, we also review the animal models that attempt to reproduce human TBI. Additionally, we examine the possible role of damage-associated molecular patterns, the chlolinergic anti-inflammatory pathway, and sex dimorphism in post-TBI ALI. In the last part of the review, we discuss current treatments and future pharmacological therapies, including fever control, tracheostomy, and corticosteroids, aimed to prevent and treat pulmonary edema, ALI, and nosocomial pneumonia after TBI.

Ventilatory Management of the Noninjured Lung

This article reviews aspects of mechanical ventilation in patients without lung injury, patients in the perioperative period, and those with neurologic injury or disease including spinal cord injury. Specific emphasis is placed on ventilator strategies, including timing and indications for tracheostomy. Lung protective ventilation, using low tidal volumes and modest levels of positive end-expiratory pressure, should be the default consideration in all patients requiring mechanical ventilatory support. The exception may be the patient with high cervical spinal cord injuries who requires mechanical ventilatory support. There is no consensus on the timing of tracheostomy in patients with neurologic diseases.

The contribution of arterio-venous extracorporeal lung assist to gas exchange in a porcine model of lavage-induced acute lung injury

This prospective large-animal study was performed to evaluate the contribution of arterio-venous extracorporeal lung assist (AV-ECLA) to pulmonary gas exchange in a porcine lavage-induced acute lung injury model. Fifteen healthy female pigs, weighing 50.39±3.8 kg (mean±SD), were included.

After induction of general anaesthesia and controlled ventilation, an arterial line and a pulmonary artery catheter were inserted. Saline lung lavage was performed until the PaO2 decreased to 51±16 mmHg. After a stabilization period of 60 min, the femoral artery and vein were cannulated and a low-resistance membrane lung was interposed. Under apnoeic oxygenation, variations of sweep-gas flow were performed every 20 min in order to evaluate the membrane lung's efficacy, in terms of carbon dioxide (CO2) removal and oxygen (O2) uptake. Although AV-ECLA is highly effective in eliminating CO2, if combined with apnoeic oxygenation, normocapnia was not achievable. AV-ECLA's contribution to oxygenation during severe hypoxemia was antagonized by a significant increase in the pulmonary shunt fraction.

Extracorporeal decarboxylation in patients with severe traumatic brain injury and ARDS enables effective control of intracranial pressure

INTRODUCTION

Acute respiratory distress syndrome (ARDS) with concomitant impairment of oxygenation and decarboxylation represents a complex problem in patients with increased intracranial pressure (ICP). Permissive hypercapnia is not an option to obtain and maintain lung-protective ventilation in the presence of elevated ICP. Pumpless extracorporeal lung assist (pECLA) devices (iLA Membrane Ventilator; Novalung, Heilbronn, Germany) can improve decarboxylation without aggravation associated with invasive ventilation. In this pilot series, we analyzed the safety and efficacy of pECLA in patients with ARDS and elevated ICP after severe traumatic brain injury (TBI).

METHODS

The medical records of ten patients (eight male, two female) with severe ARDS and severe TBI concurrently managed with external ventricular drainage in the neurointensive care unit (NICU) were retrospectively analyzed. The effect of pECLA on enabling lung-protective ventilation was evaluated using the difference between plateau pressure and positive end-expiratory pressure, defined as driving pressure (ΔP), during the 3 days preceding the implant of pECLA devices until 3 days afterward. The ICP threshold was set at 20 mmHg. To evaluate effects on ICP, the volume of daily cerebrospinal fluid (CSF) drainage needed to maintain the set ICP threshold was compared pre- and postimplant.

RESULTS

The ΔP values after pECLA implantation decreased from a mean 17.1 ± 0.7 cm/H2O to 11.9±0.5 cm/H2O (p = 0.011). In spite of this improved lung-protective ventilation, carbon dioxide pressure decreased from 46.6 ± 3.9 mmHg to 39.7 ± 3.5 mmHg (p = 0.005). The volume of daily CSF drainage needed to maintain ICP at 20 mmHg decreased significantly from 141.5 ± 103.5 ml to 62.2 ± 68.1 ml (p = 0.037).

CONCLUSIONS

For selected patients with concomitant severe TBI and ARDS, the application of pECLA is safe and effective. pECLA devices improve decarboxylation, thus enabling lung-protective ventilation. At the same time, potentially detrimental hypercapnia that may increase ICP is avoided. Larger prospective trials are warranted to further elucidate application of pECLA devices in NICU patients.

Curcumin inhibits apoptosis and brain edema induced by hypoxia-hypercapnia brain damage in rat models

Curcumin, extracted from South Asian spice turmeric, has been determined to have the promising ability in antioxidation and anti-inflammation. However, the effect of curcumin on treating brain damage has been not reported. In this article, the aim was to evaluate the effect of curcumin on cell apoptosis in rats exposed to hypoxia-hypercapnia and explore the therapeutic potential of curcumin in hypoxia-hypercapnia brain damage (HHBD). Sprague Dawley rats were randomly assigned into 3 groups: control group, hypoxia-hypercapnia group and curcumin group. The Fas/FasL expressions in HHBD rats treated by curcumin were measured by immunohistochemical staining and western blotting. The pathological changes of brain cells were observed by transmission electron microscope. Rats with HHBD showed significant increase of Fas/FasL expression and ultrastructural changes in brain tissue cells. Curcumin intervention effectively reversed the Fas/FasL-mediated apoptosis and HHBD-induced brain edema. Curcumin may be a potential therapeutic alternative for HHBD.

Ventilatory strategies in trauma patients

Lung injury in trauma patients can occur because of direct injury to lung or due to secondary effects of injury elsewhere for example fat embolism from a long bone fracture, or due to response to a systemic insult such as; acute respiratory distress syndrome (ARDS) secondary to sepsis or transfusion related lung injury. There are certain special situations like head injury where the primary culprit is not the lung, but the brain and the ventilator strategy is aimed at preserving the brain tissue and the respiratory system takes a second place. The present article aims to delineate the strategies addressing practical problems and challenges faced by intensivists dealing with trauma patients with or without healthy lungs. The lung protective strategies along with newer trends in ventilation are discussed. Ventilatory management for specific organ system trauma are highlighted and their physiological base is presented.

High-frequency oscillatory ventilation with tracheal gas insufflation: the rescue strategy for brain-lung interaction

The occurrence of moderate to severe acute respiratory distress syndrome due to traumatic brain injury is not uncommon and is associated with an extremely high incidence of morbidity and mortality. Owing to the complex interaction between the lung and brain, protective ventilation for the lung with lower tidal volume and higher positive end-expiratory pressure with or without mild hypercapnia might be harmful for the brain, and maintaining normocapnia or mild hypocapnia by increasing tidal volume or respiratory rate (or both) with lower positive end-expiratory pressure levels for protecting the brain might lead to ventilator-induced lung injury. Balancing the end-point between lungs and brain becomes a challenging issue, and non-conventional modes of mechanical ventilation might play a role in the more difficult clinical cases. In this commentary, the authors discuss the rationale, based on the physiologic principle of targeting both vital organs, of applying high-frequency oscillation and tracheal gas insufflation in acute respiratory distress syndrome patients with traumatic brain injury.

Transportable extracorporeal lung support for rescue of severe respiratory failure in combat casualties

BACKGROUND

Advances in oxygenator membrane, vascular cannula, and centrifugal pump technologies led to the miniaturization of extracorporeal lung support (ECLS) and simplified its insertion and use. Support of combat injuries complicated by severe respiratory failure requires critical care resources not sustainable in the deployed environment. In response to this need, a unique international military-civilian partnership was forged to create a transportable ECLS capability to rescue combat casualties experiencing severe respiratory failure.

METHODS

A multidisciplinary training and consultative relationship developed between the US military at Landstuhl Regional Medical Center (LRMC) and the University Hospital Regensburg (UHR), a German regional "lung failure" center with expertise in ECLS. ECLS circuits used were pumpless arteriovenous extracorporeal lung assist (NovaLung iLA) and pump-driven venovenous extracorporeal membrane oxygenation (PLS Quadrox D Membrane Oxygenator with Rotaflow Centrifugal Pump). US casualties supported by ECLS between June 2005 and August 2011 were identified from the LRMC Trauma Program Registry for review.

RESULTS

UHR cared for 10 US casualties supported by ECLS. The initial five patients were cannulated with arteriovenous circuits (pumpless arteriovenous extracorporeal lung assist), and the remaining five were cannulated with pump-driven venovenous circuits (extracorporeal membrane oxygenation). Four patients were cannulated in the war zone, and six patients were cannulated at LRMC after evacuation to Germany. All patients were transferred to UHR for continued management (mean, 9.6 ECLS days). In all cases, both hypoxemia and hypercapnia improved, allowing for decreased airway pressures. Nine patients were weaned from ECLS and extubated. One soldier died from progressive multiple-organ failure.

CONCLUSION

ECLS should be considered in the management of trauma complicated by severe respiratory failure. Modern ECLS technology allows these therapies to be transported for initiation outside of specialized centers even in austere settings. Close collaboration with established centers potentially allows both military and civilian hospitals with infrequent ECLS requirements to use it for initial patient stabilization before transfer for continued care.

LEVEL OF EVIDENCE

Therapeutic/care management study, level V.

High-frequency oscillation and tracheal gas insufflation in patients with severe acute respiratory distress syndrome and traumatic brain injury: an interventional physiological study

Introduction

In acute respiratory distress syndrome (ARDS), combined high-frequency oscillation (HFO) and tracheal gas insufflation (TGI) improves gas exchange compared with conventional mechanical ventilation (CMV). We evaluated the effect of HFO-TGI on PaO₂/fractional inspired O₂ (FiO₂) and PaCO₂, systemic hemodynamics, intracranial pressure (ICP), and cerebral perfusion pressure (CPP) in patients with traumatic brain injury (TBI) and concurrent severe ARDS.

Methods

We studied 13 TBI/ARDS patients requiring anesthesia, hyperosmolar therapy, and ventilation with moderate-to-high CMV-tidal volumes for ICP control. Patients had PaO₂/FiO₂ <100 mm Hg at end-expiratory pressure ≥10 cm H₂O. Patients received consecutive, daily, 12-hour rescue sessions of HFO-TGI interspersed with 12-hour periods of CMV. HFO-TGI was discontinued when the post-HFO-TGI PaO₂/FiO₂ exceeded 100 mm Hg for >12 hours. Arterial/central-venous blood gases, hemodynamics, and ICP were recorded before, during (every 4 hours), and after HFO-TGI, and were analyzed by using repeated measures analysis of variance. Respiratory mechanics were assessed before and after HFO-TGI.

Results

Each patient received three to four HFO-TGI sessions (total sessions, n = 43). Pre-HFO-TGI PaO₂/FiO₂ (mean ± standard deviation (SD): 83.2 ± 15.5 mm Hg) increased on average by approximately 130% to163% during HFO-TGI (P < 0.01) and remained improved by approximately 73% after HFO-TGI (P < 0.01). Pre-HFO-TGI CMV plateau pressure (30.4 ± 4.5 cm H₂O) and respiratory compliance (37.8 ± 9.2 ml/cm H₂O), respectively, improved on average by approximately 7.5% and 20% after HFO-TGI (P < 0.01 for both). During HFO-TGI, systemic hemodynamics remained unchanged. Transient improvements were observed after 4 hours of HFO-TGI versus pre-HFO-TGI CMV in PaCO₂ (37.7 ± 9.9 versus 41.2 ± 10.8 mm Hg; P < 0.01), ICP (17.2 ± 5.4 versus 19.7 ± 5.9 mm Hg; P < 0.05), and CPP (77.2 ± 14.6 versus 71.9 ± 14.8 mm Hg; P < 0.05).

Conclusions

In TBI/ARDS patients, HFO-TGI may improve oxygenation and respiratory mechanics, without adversely affecting PaCO₂, hemodynamics, or ICP. These findings support the use of HFO-TGI as a rescue ventilatory strategy in patients with severe TBI and imminent oxygenation failure due to severe ARDS.

Extracorporeal life support for acute respiratory distress syndromes

The morbidity and mortality of acute respiratory distress syndrome remain to be high. Over the last 50 years, the clinical management of these patients has undergone vast changes. Significant improvement in the care of these patients involves the development of mechanical ventilation strategies, but the benefits of these strategies remain controversial. With a growing trend of extracorporeal support for critically ill patients, we provide a historical review of extracorporeal membrane oxygenation (ECMO) including its failures and successes as well as discussing extracorporeal devices now available or nearly accessible while examining current clinical indications and trends of ECMO in respiratory failure.

Extracorporeal pulmonary support in severe pulmonary failure in adults: a treatment rediscovered

BACKGROUND

Severe, acute respiratory failure in adults still carries a high mortality. In recent years, improved pulmonary support techniques have been used increasingly alongside conventional treatment. About 1000 such treatments are performed in Germany annually, and the number is rising rapidly. The two types of systems currently in use involve venovenous extracorporeal membrane oxygenation (ECMO) and extracorporeal carbon dioxide elimination.

METHODS

The underlying principles, technical implementation, efficacy, and adverse effects of the new techniques are summarized in the light of a selective review of the literature, supplemented by the authors' personal experience. Recommendations are given for clinical use.

RESULTS

Currently, only limited high-quality data (from prospective randomized trials) are available to support the use of either of these techniques in adults. Veno-venous ECMO systems can effectively secure gas exchange in patients with severe respiratory failure, with experienced centers reporting survival rates from 63% to 75%. Either pump-free arteriovenous systems or low-flow ECMO systems can be used for extracorporeal carbon dioxide elimination. Complications can be serious or life-threatening and must, therefore, be rapidly recognized and treated: these include vascular injury during cannulation, venous thrombosis in a cannulated vessel, an increased hemorrhagic tendency, and thrombocytopenia.

CONCLUSION

Modern miniaturized pulmonary support systems enable protective mechanical ventilation with low tidal volumes, reduce ventilator-associated lung injury, and can improve survival rates in critically ill patients with a manageable adverse effect profile.

Carbon dioxide clearance in critical care

Lung protective ventilation limiting tidal volumes and airway pressures were proven to reduce mortality in patients with acute severe respiratory failure. Hypercapnia and hypercapnic acidosis is often noted with lung protective ventilation. While the protective effects of lung protective ventilation are well recognised, the role of hypercapnia and hypercapnic acidosis remains debatable. Some clinicians argue that hypercapnia and hypercapnic acidosis protect the lungs and may be associated with improved outcomes. To the contrary, some clinicians do not tolerate hypercapnic acidosis and use various techniques including extracorporeal carbon dioxide elimination to treat hypercapnia and acidosis. This review aims at defining the effects of hypercapnia and hypercapnic acidosis with a focus on the pros and cons of clearing carbon dioxide and the modalities that may enhance carbon dioxide clearance.

Extracorporeal Carbon Dioxide Removal (ECCO2R) in Respiratory Failure: An Overview, and where Next?

Extracorporeal carbon dioxide removal (ECCO2R) is used to facilitate protective ventilation strategies and to treat severe hypercapnic acidosis that is refractory to mechanical ventilation. There is an increasing amount of interest in the use of ECCO2R but there are no recommendations for its use that take the most recent evidence into account. In 2008, the National Institute of Health and Clinical Excellence (NICE) published guidelines on ‘Arteriovenous Extracorporeal Membrane Carbon Dioxide Removal.’1 However, since that time there have been a number of studies in the area and some significant technological advances including the introduction of commercially available VV-ECCO2R systems. The aim of this article is to provide an overview of ECCO2R, review the literature relating to its use and discuss its future role in the intensive care setting.

Clinical review: Extracorporeal membrane oxygenation

The H1N1 flu pandemic led to a wider use of extracorporeal membrane oxygenation (ECMO), proving its power in hypoxemic emergencies. The results obtained during this pandemic, more than any randomized trial, led to the worldwide acceptance of the use of membrane lungs. Moreover, as centers that applied this technique as rescue therapy for refractory hypoxemia recognized its strength and limited technical challenges, the indications for ECMO have recently been extended. Indications for veno-venous ECMO currently include respiratory support as a bridge to lung transplantation, correction of lung hyperinflation during chronic obstructive pulmonary disease exacerbation and respiratory support in patients with the acute respiratory distress syndrome, possibly also without mechanical ventilation. The current enthusiasm for ECMO in its various aspects should not, however, obscure the consideration of the potential complications associated with this life-saving technique, primarily brain hemorrhage

Acute lung injury in patients with severe brain injury: a double hit model

The presence of pulmonary dysfunction after brain injury is well recognized. Acute lung injury (ALI) occurs in 20% of patients with isolated brain injury and is associated with a poor outcome. The "blast injury" theory, which proposes combined "hydrostatic" and "high permeability" mechanisms for the formation of neurogenic pulmonary edema, has been challenged recently by the observation that a systemic inflammatory response may play an integral role in the development of pulmonary dysfunction associated with brain injury. As a result of the primary cerebral injury, a systemic inflammatory reaction occurs, which induces an alteration in blood-brain barrier permeability and infiltration of activated neutrophils into the lung. This preclinical injury makes the lungs more susceptible to the mechanical stress of an injurious ventilatory strategy. Tight CO2 control is a therapeutic priority in patients with acute brain injury, but the use of high tidal volume ventilation may contribute to the development of ALI. Establishment of a therapeutic regimen that allows the combination of protective ventilation with the prevention of hypercapnia is, therefore, required. Moreover, in patients with brain injury, hypoxemia represents a secondary insult associated with a poor outcome. Optimal oxygenation may be achieved by using an adequate FiO2 and by application of positive end-expiratory pressure (PEEP). PEEP may, however, affect the cerebral circulation by hemodynamic and CO2-mediated mechanisms and the effects of PEEP on cerebral hemodynamics should be monitored in these patients and used to titrate its application.

The advent of ECMO and pumpless extracorporeal lung assist in ARDS

Despite advances in critical care facilities and ventilation therapies acute respiratory distress syndrome (ARDS) is associated with high mortality rates. The condition can stem from a multitude of causes including pneumonia, septicemia and trauma ultimately resulting in ARDS. ARDS is characterized by respiratory insufficiency with severe hypoxemia or hypercapnia. The treatment strategy depends on the knowledge of the underlying disease. But lung-protective ventilation with adjusted positive end-expiratory pressure remains the most effective therapeutic tool despite advances in prone positioning, inhalation of nitric oxide and the use of steroids. Newer modalities including extracorporeal membrane oxygenation (ECMO) and pumpless extracorporeal lung assist (PECLA) are being increasingly introduced in critical care settings as rescue therapies in patients who fail to respond to conservative measures. We describe here the introduction and advances of both ECMO and PECLA in the management of ARDS.

[Extracorporeal membrane oxygenation and severe traumatic brain injury. Is the ECMO-therapy in traumatic lung failure and severe traumatic brain injury really contraindicated?]

Veno-venous extracorporeal membrane oxygenation (ECMO) may be lifesaving in multiple injured patients with acute respiratory distress syndrome (ARDS) due to chest trauma. To prevent circuit thrombosis or thromboembolic complications during ECMO systemic anticoagulation is recommended. Therefore, ECMO treatment is contraindicated in patients with intracranial bleeding. The management of veno-venous ECMO without systemic anticoagulation in a patient suffering from traumatic lung failure and severe traumatic brain injury is reported.

Surgical intensive care unit--the trauma surgery perspective

PURPOSE

This review addresses and summarizes the key issues and unique specific intensive care treatment of adult patients from the trauma surgery perspective.

MATERIALS AND METHODS

The cornerstones of successful surgical intensive care management are fluid resuscitation, transfusion protocol and extracorporeal organ replacement therapies. The injury-type specific complications and unique pathophysiologic regulatory mechanisms of the traumatized patients influencing the critical care treatment are discussed.

CONCLUSIONS

Furthermore, the fundamental knowledge of the injury severity, understanding of the trauma mechanism, surgical treatment strategies and specific techniques of surgical intensive care are pointed out as essentials for a successful intensive care therapy.

Nonventilatory strategies for patients with life-threatening 2009 H1N1 influenza and severe respiratory failure

Severe respiratory failure (including acute lung injury and acute respiratory distress syndrome) caused by 2009 H1N1 influenza infection has been reported worldwide. Refractory hypoxemia is a common finding in these patients and can be challenging to manage. This review focuses on nonventilatory strategies in the advanced treatment of severe respiratory failure and refractory hypoxemia such as that seen in patients with severe acute respiratory distress syndrome attributable to 2009 H1N1 influenza. Specific modalities covered include conservative fluid management, prone positioning, inhaled nitric oxide, inhaled vasodilatory prostaglandins, and extracorporeal membrane oxygenation and life support. Pharmacologic strategies (including steroids) investigated for the treatment of severe respiratory failure are also reviewed.

Ventilatory strategies for patients with acute brain injury

PURPOSE OF REVIEW

The ventilation of patients with acute brain injuries can present significant challenges. Frequently, guidelines recommending management strategies for patients with traumatic brain injuries come into conflict with what is now considered best ventilatory practice. In this review, we will explore many of these areas of conflict.

RECENT FINDINGS

The use of ventilatory strategies to control partial pressure of carbon dioxide in patients with traumatic brain injury is associated with the development of acute lung injury. Analysis of the International Mission for Prognosis And Clinical Trial (IMPACT) database has confirmed the association between hypoxia and poor neurological outcome. Although a recent meta-analysis has suggested a survival benefit for steroids in acute lung injury, the use of steroids has been associated with a worsening of outcome in patients with traumatic brain injuries and their effects on the brain have not been fully elucidated.

SUMMARY

There are unlikely to be randomized controlled trials advising how best to ventilate patients with acute brain injuries because of the heterogeneous nature of such injuries. Hypoxia should be avoided. The more widespread use of multimodal brain monitoring, including brain tissue oxygen and cerebral blood flow monitoring, may allow clinicians to tolerate a higher arterial partial pressure of carbon dioxide than has been traditional, allowing a less injurious ventilatory strategy. Modest positive end-expiratory pressure can be used. In severe respiratory failure, most 'rescue' strategies have been attempted in patients with acute brain injuries. Choice of rescue therapy at present is best decided on a case-by-case basis in conjunction with local expertise.

Evaluation of a pumpless lung assist device in hypoxia-induced pulmonary hypertension in juvenile piglets

Persistent pulmonary hypertension is an important cause of mortality and morbidity in term infants. The lung assist device (LAD) is a novel, pumpless, low-resistance extracorporeal oxygenator to supplement mechanical ventilation. The LAD may be associated with fewer complications compared with conventional extracorporeal membrane oxygenation. The objective was to test the feasibility and efficacy of the LAD in juvenile piglets with hypoxia-induced pulmonary hypertension. Pulmonary hypertension was acutely induced by hypoxia in six 3- to 4-wk-old acutely instrumented and intubated piglets. The LAD was attached between a carotid artery and jugular vein. Gas exchange and hemodynamic variables, including pulmonary arterial pressure (PAP) and cardiac output (CO), were measured. Successful LAD cannulation was achieved without complications in all animals. Extracorporeal shunt flow through the device averaged 18% of CO. The LAD achieved oxygen delivery of 20% of total oxygen consumption. PAP was reduced by 35% from 28 +/- 5 to 18 +/- 4 mm Hg (p < 0.05) and systemic Pao2 increased by 33% from 27 +/- 2 to 36 +/- 4 mm Hg (p < 0.05). Other hemodynamic variables remained stable. The novel LAD shows feasibility and efficacy in improving gas exchange and reducing PAPs in a juvenile animal model of hypoxia-induced pulmonary hypertension.

Clinical review: Ventilatory strategies for obstetric, brain-injured and obese patients

The ventilatory management of patients with acute respiratory failure is supported by good evidence, aiming to reduce lung injury by pressure limitation and reducing the duration of ventilatory support by regular assessment for discontinuation. Certain patient groups, however, due to their altered physiology or disease-specific complications, may require some variation in usual ventilatory management. The present manuscript reviews the ventilatory management in three special populations, namely the patient with brain injury, the pregnant patient and the morbidly obese patient.

Acute lung injury in patients with severe brain injury: a double hit model

The presence of pulmonary dysfunction after brain injury is well recognized. Acute lung injury (ALI) occurs in 20% of patients with isolated brain injury and is associated with a poor outcome. The "blast injury" theory, which proposes combined "hydrostatic" and "high permeability" mechanisms for the formation of neurogenic pulmonary edema, has been challenged recently by the observation that a systemic inflammatory response may play an integral role in the development of pulmonary dysfunction associated with brain injury. As a result of the primary cerebral injury, a systemic inflammatory reaction occurs, which induces an alteration in blood-brain barrier permeability and infiltration of activated neutrophils into the lung. This preclinical injury makes the lungs more susceptible to the mechanical stress of an injurious ventilatory strategy. Tight CO2 control is a therapeutic priority in patients with acute brain injury, but the use of high tidal volume ventilation may contribute to the development of ALI. Establishment of a therapeutic regimen that allows the combination of protective ventilation with the prevention of hypercapnia is, therefore, required. Moreover, in patients with brain injury, hypoxemia represents a secondary insult associated with a poor outcome. Optimal oxygenation may be achieved by using an adequate FiO2 and by application of positive end-expiratory pressure (PEEP). PEEP may, however, affect the cerebral circulation by hemodynamic and CO2-mediated mechanisms and the effects of PEEP on cerebral hemodynamics should be monitored in these patients and used to titrate its application.

Arteriovenous Extracorporeal Lung Assist Allows For Maximization Of Oscillatory Frequencies: A Large-animal Model Of Respiratory Distress

Background

Although the minimization of the applied tidal volume (VT) during high-frequency oscillatory ventilation (HFOV) reduces the risk of alveolar shear stress, it can also result in insufficient CO₂-elimination with severe respiratory acidosis. We hypothesized that in a model of acute respiratory distress (ARDS) the application of high oscillatory frequencies requires the combination of HFOV with arteriovenous extracorporeal lung assist (av-ECLA) in order to maintain or reestablish normocapnia.

Methods

After induction of ARDS in eight female pigs (56.5 ± 4.4 kg), a recruitment manoeuvre was performed and intratracheal mean airway pressure (mPaw) was adjusted 3 cmH₂O above the lower inflection point (Plow) of the pressure-volume curve. All animals were ventilated with oscillatory frequencies ranging from 3–15 Hz. The pressure amplitude was fixed at 60 cmH₂O. At each frequency gas exchange and hemodynamic measurements were obtained with a clamped and de-clamped av-ECLA. Whenever the av-ECLA was de-clamped, the oxygen sweep gas flow through the membrane lung was adjusted aiming at normocapnia.

Results

Lung recruitment and adjustment of the mPaw above Plow resulted in a significant improvement of oxygenation (p < 0.05). Compared to lung injury, oxygenation remained significantly improved with rising frequencies (p < 0.05). Normocapnia during HFOV was only maintained with the addition of av-ECLA during frequencies of 9 Hz and above.

Conclusion

In this animal model of ARDS, maximization of oscillatory frequencies with subsequent minimization of VT leads to hypercapnia that can only be reversed by adding av-ECLA. When combined with a recruitment strategy, these high frequencies do not impair oxygenation

Pumpless extracorporeal lung assist: a 10-year institutional experience

BACKGROUND

Pumpless extracorporeal lung assist (PECLA) was developed to support pulmonary function in patients with severe respiratory insufficiency.

METHODS

Since 1996, 159 patients with an age ranging from 7 to 78 years were provided with a PECLA system. Fifteen patients were referred to us by air or ground transport after insertion of the system in a peripheral hospital.

RESULTS

Main underlying lung diseases were acute respiratory distress syndrome (70.4%) and pneumonia (28.3%). Pumpless extracorporeal lung assist lasted for 0.1 to 33 days, mean 7.0 +/- 6.2 days; cumulative experience was greater than 1,300 days. Successful weaning and survival to hospital discharge was achieved in 33.1% of patients after a mean PECLA support of 8.5 +/- 6.3 days. During PECLA therapy, 48.7% of patients died, mainly as a result of multiorgan failure after a mean interval of 4.8 +/- 5.1 days. Inability to stabilize pulmonary function was noted in 3% of patients only. After PECLA, 30-day mortality was 13.6%. In a subgroup analysis, best outcome was obtained in patients after trauma.

CONCLUSIONS

Pumpless extracorporeal lung assist is a simple and efficient method to support patients with deteriorating gas exchange for prolonged periods to allow the lung protective ventilation and transportation. Best indication for use of PECLA is severe hypercapnia and moderate hypoxia.

[Pumpless extracorporeal lung assist]

The recently introduced pumpless extracorporeal lung assist (PECLA) is a remarkable alternative to the conventional extracorporeal membrane oxygenation in case of severe lung failure. By establishing a shunt between femoral artery and vein using the arterio-venous pressure gradient as a driving force through a low-resistance membrane oxygenator, PECLA provides highly effective gas-exchange by preserved cardiac function. Due to its closed system, reduced priming volume and low heparin demand, the unfavourable effects of extracorporeal membrane oxygenation can be effectively diminished. Hence the small technical, financial and personal input, the PECLA can be ideally used in district hospitals and during transport as well. Our short summary demonstrates the advantages and safety of the system proven over 123 cases.

Evidence-based therapy of severe acute respiratory distress syndrome: an algorithm-guided approach

Despite considerable research and constantly emerging treatment modalities, the mortality associated with acute respiratory distress syndrome (ARDS) has remained virtually unchanged over the last decade. Clinical studies have been unable to show a reduction in mortality for most therapeutic interventions except for low tidal volume ventilation. Failure to prove a mortality benefit might be a result of the varying severity of ARDS in the patients studied. Nevertheless, positive responses to single supportive measures (inhaled nitric oxide, prone positioning and extracorporeal membrane oxygenation) have been demonstrated in multiple trials. Criteria for administration, weaning and discontinuation of these supportive interventions have never been described in detail. In this context, implementation of an evidence-based algorithm might facilitate clinical management of severe ARDS. This review summarizes the current evidence base and proposes a new treatment algorithm that aims to prioritize the administration of advanced strategies in a multimodal approach for ARDS.

Respiratory care

PURPOSE OF THE REVIEW

Neurosurgical patients frequently develop respiratory complications, adversely affecting neurologic outcome and survival. The review summarizes current literature and management of respiratory complications associated with brain injury.

MAJOR FINDINGS

Respiratory complications are commonly associated with traumatic brain injury and subarachnoid haemorrhage. Lung-protective ventilation with reduced tidal volumes improves outcome in acute lung injury, and should be applied to neurosurgical patients in the absence of increased intracranial pressure. Weaning from the mechanical ventilation should be initiated as soon as possible, although the role of neurological status in the weaning process is not clear. Prevention of pneumonia and aspiration improves survival. In patients with difficult weaning, early bedside percutaneous tracheostomy should be considered.

FURTHER INVESTIGATIONS

Further studies are warranted to elucidate an optimal oxygenation and ventilation in brain-injured patients, weaning strategies, predictors of the failed weaning and extubation, respiratory support in patients with difficulties to wean, and early tracheostomy.