Effects of ultraprotective ventilation, extracorporeal carbon dioxide removal, and spontaneous breathing on lung morphofunction and inflammation in experimental severe acute respiratory distress syndrome. Anesthesiology. 2015;122:631-646. [PMID: 25371037 DOI: 10.1097/aln.0000000000000504]

[Ventilation concepts under extracorporeal membrane oxygenation (ECMO) in acute respiratory distress syndrome (ARDS)]

Extracorporeal membrane oxygenation (ECMO) is often the last resort for escalation of treatment in patients with severe acute respiratory distress syndrome (ARDS). The success of treatment is mainly determined by patient-specific factors, such as age, comorbidities, duration and invasiveness of the pre-existing ventilation treatment as well as the expertise of the treating ECMO center. In particular, the adjustment of mechanical ventilation during ongoing ECMO treatment remains controversial. Although a reduction of invasiveness of mechanical ventilation seems to be reasonable due to physiological considerations, no improvement in outcome has been demonstrated so far for the use of ultraprotective ventilation regimens.

Current knowledge gaps in extracorporeal respiratory support

Extracorporeal life support (ECLS) for acute respiratory failure encompasses veno-venous extracorporeal membrane oxygenation (V-V ECMO) and extracorporeal carbon dioxide removal (ECCO2R). V-V ECMO is primarily used to treat severe acute respiratory distress syndrome (ARDS), characterized by life-threatening hypoxemia or ventilatory insufficiency with conventional protective settings. It employs an artificial lung with high blood flows, and allows improvement in gas exchange, correction of hypoxemia, and reduction of the workload on the native lung. On the other hand, ECCO2R focuses on carbon dioxide removal and ventilatory load reduction ("ultra-protective ventilation") in moderate ARDS, or in avoiding pump failure in acute exacerbated chronic obstructive pulmonary disease. Clinical indications for V-V ECLS are tailored to individual patients, as there are no absolute contraindications. However, determining the ideal timing for initiating extracorporeal respiratory support remains uncertain. Current ECLS equipment faces issues like size and durability. Innovations include intravascular lung assist devices (ILADs) and pumpless devices, though they come with their own challenges. Efficient gas exchange relies on modern oxygenators using hollow fiber designs, but research is exploring microfluidic technology to improve oxygenator size, thrombogenicity, and blood flow capacity. Coagulation management during V-V ECLS is crucial due to common bleeding and thrombosis complications; indeed, anticoagulation strategies and monitoring systems require improvement, while surface coatings and new materials show promise. Moreover, pharmacokinetics during ECLS significantly impact antibiotic therapy, necessitating therapeutic drug monitoring for precise dosing. Managing native lung ventilation during V-V ECMO remains complex, requiring a careful balance between benefits and potential risks for spontaneously breathing patients. Moreover, weaning from V-V ECMO is recognized as an area of relevant uncertainty, requiring further research. In the last decade, the concept of Extracorporeal Organ Support (ECOS) for patients with multiple organ dysfunction has emerged, combining ECLS with other organ support therapies to provide a more holistic approach for critically ill patients. In this review, we aim at providing an in-depth overview of V-V ECMO and ECCO2R, addressing various aspects of their use, challenges, and potential future directions in research and development.

Ultraprotective versus apneic ventilation in acute respiratory distress syndrome patients with extracorporeal membrane oxygenation: a physiological study

Background

Even an ultraprotective ventilation strategy in severe acute respiratory distress syndrome (ARDS) patients treated with extracorporeal membrane oxygenation (ECMO) might induce ventilator-induced lung injury and apneic ventilation with the sole application of positive end-expiratory pressure may, therefore, be an alternative ventilation strategy. We, therefore, compared the effects of ultraprotective ventilation with apneic ventilation on oxygenation, oxygen delivery, respiratory system mechanics, hemodynamics, strain, air distribution and recruitment of the lung parenchyma in ARDS patients with ECMO.

Methods

In a prospective, monocentric physiological study, 24 patients with severe ARDS managed with ECMO were ventilated using ultraprotective ventilation (tidal volume 3 ml/kg of predicted body weight) with a fraction of inspired oxygen (FiO₂) of 21%, 50% and 90%. Patients were then treated with apneic ventilation with analogous FiO₂. The primary endpoint was the effect of the ventilation strategy on oxygenation and oxygen delivery. The secondary endpoints were mechanical power, stress, regional air distribution, lung recruitment and the resulting strain, evaluated by chest computed tomography, associated with the application of PEEP (apneic ventilation) and/or low V_T (ultraprotective ventilation).

Results

Protective ventilation, compared to apneic ventilation, improved oxygenation (arterial partial pressure of oxygen, p < 0.001 with FiO₂ of 50% and 90%) and reduced cardiac output. Both ventilation strategies preserved oxygen delivery independent of the FiO₂. Protective ventilation increased driving pressure, stress, strain, mechanical power, as well as induced additional recruitment in the non-dependent lung compared to apneic ventilation.

Conclusions

In patients with severe ARDS managed with ECMO, ultraprotective ventilation compared to apneic ventilation improved oxygenation, but increased stress, strain, and mechanical power. Apneic ventilation might be considered as one of the options in the initial phase of ECMO treatment in severe ARDS patients to facilitate lung rest and prevent ventilator-induced lung injury.

Trial registration: German Clinical Trials Register (DRKS00013967). Registered 02/09/2018. https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00013967.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40560-022-00604-9.

Extracorporeal Membrane Oxygenation in Severe Acute Respiratory Distress Syndrome: Possible Late Indication for Coronavirus Disease 2019?

Background:

There is now substantial evidence to support venovenous extracorporeal membrane oxygenation efficacy and safety for patients with severe acute respiratory distress syndrome. However, recent guidelines recommend against the initiation of extracorporeal membrane oxygenation in patients with mechanical ventilation for coronavirus disease 2019 severe acute respiratory distress syndrome for greater than 7–10 days.

Case Summary:

We report the case of a patient with coronavirus disease 2019 severe acute respiratory distress syndrome with successful late venovenous extracorporeal membrane oxygenation initiation after 20 days of mechanical ventilation. Respiratory compliance, arterial blood gases, and radiological lesions improved progressively under venovenous extracorporeal membrane oxygenation and ultraprotective ventilation. The patient was discharged from ICU.

Conclusions:

As coronavirus disease 2019 is a new and incompletely understood entity, we believe that late extracorporeal membrane oxygenation may be considered in selected patients as a bridge to recovery. Further prospective studies are, however, needed.

Toward a Long-Term Artificial Lung

Only a very small portion of end-stage organ failures can be treated by transplantation because of the shortage of donor organs. Although artificial long-term organ support such as ventricular assist devices provide therapeutic options serving as a bridge-to-transplantation or destination therapy for end-stage heart failure, suitable long-term artificial lung systems are still at an early stage of development. Although a short-term use of an extracorporeal lung support is feasible today, the currently available technical solutions do not permit the long-term use of lung replacement systems in terms of an implantable artificial lung. This is currently limited by a variety of factors: biocompatibility problems lead to clot formation within the system, especially in areas with unphysiological flow conditions. In addition, proteins, cells, and fibrin are deposited on the membranes, decreasing gas exchange performance and thus, limiting long-term use. Coordinated basic and translational scientific research to solve these problems is therefore necessary to enable the long-term use and implantation of an artificial lung. Strategies for improving the biocompatibility of foreign surfaces, for new anticoagulation regimes, for optimization of gas and blood flow, and for miniaturization of these systems must be found. These strategies must be validated by in vitro and in vivo tests, which remain to be developed. In addition, the influence of long-term support on the pathophysiology must be considered. These challenges require well-connected interdisciplinary teams from the natural and material sciences, engineering, and medicine, which take the necessary steps toward the development of an artificial implantable lung.

Impact of spontaneous breathing during mechanical ventilation in acute respiratory distress syndrome

PURPOSE OF REVIEW

Facilitating spontaneous breathing has been traditionally recommended during mechanical ventilation in acute respiratory distress syndrome (ARDS). However, early, short-term use of neuromuscular blockade appears to improve survival, and spontaneous effort has been shown to potentiate lung injury in animal and clinical studies. The purpose of this review is to describe the beneficial and deleterious effects of spontaneous breathing in ARDS, explain potential mechanisms for harm, and provide contemporary suggestions for clinical management.

RECENT FINDINGS

Gentle spontaneous effort can improve lung function and prevent diaphragm atrophy. However, accumulating evidence indicates that spontaneous effort may cause or worsen lung and diaphragm injury, especially if the ARDS is severe or spontaneous effort is vigorous. Recently, such effort-dependent lung injury has been termed patient self-inflicted lung injury (P-SILI). Finally, several approaches to minimize P-SILI while maintaining some diaphragm activity (e.g. partial neuromuscular blockade, high PEEP) appear promising.

SUMMARY

We update and summarize the role of spontaneous breathing during mechanical ventilation in ARDS, which can be beneficial or deleterious, depending on the strength of spontaneous activity and severity of lung injury. Future studies are needed to determine ventilator strategies that minimize injury but maintaining some diaphragm activity.

Extracorporeal life support and systemic inflammation

Extracorporeal life support (ECLS) encompasses a wide range of extracorporeal modalities that offer short- and intermediate-term mechanical support to the failing heart or lung. Apart from the daily use of cardiopulmonary bypass (CPB) in the operating room, there has been a resurgence of interest and utilization of veno-arterial and veno-venous extracorporeal membrane oxygenation (VA- and VV-ECMO, respectively) and extracorporeal carbon dioxide removal (ECCO₂R) in recent years. This might be attributed to the advancement in technology, nonetheless the morbidity and mortality associated with the clinical application of this technology is still significant. The initiation of ECLS triggers a systemic inflammatory response, which involves the activation of the coagulation cascade, complement systems, endothelial cells, leukocytes, and platelets, thus potentially contributing to morbidity and mortality. This is due to the release of cytokines and other biomarkers of inflammation, which have been associated with multiorgan dysfunction. On the other hand, ECLS can be utilized as a therapy to halt the inflammatory response associated with critical illness and ICU therapeutic intervention, such as facilitating ultra-protective mechanical ventilation. In addition to addressing the impact on outcome of the relationship between inflammation and ECLS, two different but complementary pathophysiological perspectives will be developed in this review: ECLS as the cause of inflammation and ECLS as the treatment of inflammation. This framework may be useful in guiding the development of novel therapeutic strategies to improve the outcome of critical illness.

Low-flow CO2 removal in combination with renal replacement therapy effectively reduces ventilation requirements in hypercapnic patients: a pilot study

Background

Lung-protective strategies are the cornerstone of mechanical ventilation in critically ill patients with both ARDS and other disorders. Extracorporeal CO₂ removal (ECCO₂R) may enhance lung protection by allowing even further reductions in tidal volumes and is effective in low-flow settings commonly used for renal replacement therapy. In this study, we describe for the first time the effects of a labeled and certified system combining ECCO₂R and renal replacement therapy on pulmonary stress and strain in hypercapnic patients with renal failure.

Methods

Twenty patients were treated with the combined system which incorporates a membrane lung (0.32 m²) in a conventional renal replacement circuit. After changes in blood gases under ECCO₂R were recorded, baseline hypercapnia was reestablished and the impact on ventilation parameters such as tidal volume and driving pressure was recorded.

Results

The system delivered ECCO₂R at rate of 43.4 ± 14.1 ml/min, PaCO₂ decreased from 68.3 ± 11.8 to 61.8 ± 11.5 mmHg (p < 0.05) and pH increased from 7.18 ± 0.09 to 7.22 ± 0.08 (p < 0.05). There was a significant reduction in ventilation requirements with a decrease in tidal volume from 6.2 ± 0.9 to 5.4 ± 1.1 ml/kg PBW (p < 0.05) corresponding to a decrease in plateau pressure from 30.6 ± 4.6 to 27.7 ± 4.1 cmH₂O (p < 0.05) and a decrease in driving pressure from 18.3 ± 4.3 to 15.6 ± 3.9 cmH₂O (p < 0.05), indicating reduced pulmonary stress and strain. No complications related to the procedure were observed.

Conclusions

The investigated low-flow ECCO₂R and renal replacement system can ameliorate respiratory acidosis and decrease ventilation requirements in hypercapnic patients with concomitant renal failure.

Trial registration NCT02590575, registered 10/23/2015.

High Visceral Adipose Tissue to Subcutaneous Adipose Tissue Ratio as a Predictor of Mortality in Acute Respiratory Distress Syndrome

BACKGROUND

We aimed to further determine the relationship between the areas of visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT), and the ratio of VAT to SAT (VAT/SAT) with the outcomes of acute respiratory distress syndrome (ARDS) patients.

METHODS

A retrospective study was performed on patients with ARDS in 7 intensive care units (ICU) of West China Hospital, Sichuan University.

RESULTS

A total of 169 patients were included in the analysis. Abdominal computed tomography scans of each patient within 24 hours of being admitted to the ICU were assessed by at least 2 investigators. Higher VAT/SAT was related with higher hospital mortality (22% vs. 44%, P = 0.003; adjusted odds ratio [aOR] 0.699, 95% CI 0.530-0.922 ([P = 0.011]). On the contrary, higher SAT and VAT were related to lower hospital mortality in ARDS (aOR 1.077, 95% CI 1.037-1.119 [P < 0.001]; aOR 1.017, 95% CI 1.004-1.030 [P = 0.011], respectively). Patients with higher SAT and VAT had shorter length of ICU stay (ICU LOS) (26.26 vs. 15.83 days, P = 0.031; 25.16 vs. 14.19 days, P = 0.007, respectively), while VAT/SAT was not related with ICU LOS. Moreover, we did not find any significant relationship either between VAT/SAT and mechanical ventilation-free days or between SAT and mechanical ventilation-free days.

CONCLUSIONS

This study suggests that VAT/SAT can contribute to adverse outcomes of patients with ARDS. However, higher SAT and VAT were related to better prognosis of ARDS patients.

Mechanical Ventilation during Extracorporeal Membrane Oxygenation in Patients with Acute Severe Respiratory Failure

Conventionally, a substantial number of patients with acute respiratory failure require mechanical ventilation (MV) to avert catastrophe of hypoxemia and hypercapnia. However, mechanical ventilation per se can cause lung injury, accelerating the disease progression. Extracorporeal membrane oxygenation (ECMO) provides an alternative to rescue patients with severe respiratory failure that conventional mechanical ventilation fails to maintain adequate gas exchange. The physiology behind ECMO and its interaction with MV were reviewed. Next, we discussed the timing of ECMO initiation based on the risks and benefits of ECMO. During the running of ECMO, the protective ventilation strategy can be employed without worrying about catastrophic hypoxemia and carbon dioxide retention. There is a large body of evidence showing that protective ventilation with low tidal volume, high positive end-expiratory pressure, and prone positioning can provide benefits on mortality outcome. More recently, there is an increasing popularity on the use of awake and spontaneous breathing for patients undergoing ECMO, which is thought to be beneficial in terms of rehabilitation.

Control of Respiratory Drive and Effort in Extracorporeal Membrane Oxygenation Patients Recovering from Severe Acute Respiratory Distress Syndrome

Background

The amount of extracorporeal carbon dioxide removal may influence respiratory drive in acute respiratory distress syndrome (ARDS) patients undergoing extracorporeal membrane oxygenation (ECMO). The authors evaluated the effects of different levels of extracorporeal carbon dioxide removal in patients recovering from severe ARDS undergoing pressure support ventilation (PSV) and neurally adjusted ventilatory assist (NAVA).

Methods

The authors conducted a prospective, randomized, crossover study on eight spontaneously breathing ARDS patients undergoing venovenous ECMO since 28 ± 20 days. To modulate carbon dioxide extraction, ECMO gas flow (GF) was decreased from baseline resting protective conditions (i.e., GF100%, set to obtain pressure generated in the first 100 ms of inspiration against an occluded airway less than 2 cm H2O, respiratory rate less than or equal to 25 bpm, tidal volume less than 6 ml/kg, and peak airway pressure less than 25 cm H2O) to GF50%-GF25%-GF0% during both PSV and NAVA (random order for ventilation mode). Continuous recordings of airway pressure and flow and esophageal pressure were obtained and analyzed during all study phases.

Results

At higher levels of extracorporeal carbon dioxide extraction, pressure generated in the first 100 ms of inspiration against an occluded airway decreased from 2.8 ± 2.7 cm H2O (PSV, GF0%) and 3.0 ± 2.1 cm H2O (NAVA, GF0%) to 0.9 ± 0.5 cm H2O (PSV, GF100%) and 1.0 ± 0.8 cm H2O (NAVA, GF100%; P &lt; 0.001) and patients’ inspiratory muscle pressure passed from 8.5 ± 6.3 and 6.5 ± 5.5 cm H2O to 4.5 ± 3.1 and 4.2 ± 3.7 cm H2O (P &lt; 0.001). In time, decreased inspiratory drive and effort determined by higher carbon dioxide extraction led to reduction of tidal volume from 6.6 ± 0.9 and 7.5 ± 1.2 ml/kg to 4.9 ± 0.8 and 5.3 ± 1.3 ml/kg (P &lt; 0.001) and of peak airway pressure from 21 ± 3 and 25 ± 4 cm H2O to 21 ± 3 and 21 ± 5 cm H2O (P &lt; 0.001). Finally, transpulmonary pressure linearly decreased when the amount of carbon dioxide extracted by ECMO increased (R2 = 0.823, P &lt; 0.001).

Conclusions

In patients recovering from ARDS undergoing ECMO, the amount of carbon dioxide removed by the artificial lung may influence spontaneous breathing. The effects of carbon dioxide removal on spontaneous breathing during the earlier acute phases of ARDS remain to be elucidated.

Recruitment maneuvers in acute respiratory distress syndrome: The safe way is the best way

Acute respiratory distress syndrome (ARDS) represents a serious problem in critically ill patients and is associated with in-hospital mortality rates of 33%-52%. Recruitment maneuvers (RMs) are a simple, low-cost, feasible intervention that can be performed at the bedside in patients with ARDS. RMs are characterized by the application of airway pressure to increase transpulmonary pressure transiently. Once non-aerated lung units are reopened, improvements are observed in respiratory system mechanics, alveolar reaeration on computed tomography, and improvements in gas exchange (functional recruitment). However, the reopening process could lead to vascular compression, which can be associated with overinflation, and gas exchange may not improve as expected (anatomical recruitment). The purpose of this review was to discuss the effects of different RM strategies - sustained inflation, intermittent sighs, and stepwise increases of positive end-expiratory pressure (PEEP) and/or airway inspiratory pressure - on the following parameters: hemodynamics, oxygenation, barotrauma episodes, and lung recruitability through physiological variables and imaging techniques. RMs and PEEP titration are interdependent events for the success of ventilatory management. PEEP should be adjusted on the basis of respiratory system mechanics and oxygenation. Recent systematic reviews and meta-analyses suggest that RMs are associated with lower mortality in patients with ARDS. However, the optimal RM method (i.e., that providing the best balance of benefit and harm) and the effects of RMs on clinical outcome are still under discussion, and further evidence is needed.

Reduced pulmonary blood flow in regions of injury 2 hours after acid aspiration in rats

BACKGROUND

Aspiration-induced lung injury can decrease gas exchange and increase mortality. Acute lung injury following acid aspiration is characterized by elevated pulmonary blood flow (PBF) in damaged lung areas in the early inflammation stage. Knowledge of PBF patterns after acid aspiration is important for targeting intravenous treatments. We examined PBF in an experimental model at a later stage (2 hours after injury).

METHODS

Anesthetized Wistar-Unilever rats (n = 5) underwent unilateral endobronchial instillation of hydrochloric acid. The PBF distribution was compared between injured and uninjured sides and with that of untreated control animals (n = 6). Changes in lung density after injury were measured using computed tomography (CT). Regional PBF distribution was determined quantitatively in vivo 2 hours after acid instillation by measuring the concentration of [(68)Ga]-radiolabeled microspheres using positron emission tomography.

RESULTS

CT scans revealed increased lung density in areas of acid aspiration. Lung injury was accompanied by impaired gas exchange. Acid aspiration decreased the arterial pressure of oxygen from 157 mmHg [139;165] to 74 mmHg [67;86] at 20 minutes and tended toward restoration to 109 mmHg [69;114] at 110 minutes (P < 0.001). The PBF ratio of the middle region of the injured versus uninjured lungs of the aspiration group (0.86 [0.7;0.9], median [25%;75%]) was significantly lower than the PBF ratio in the left versus right lung of the control group (1.02 [1.0;1.05]; P = 0.016).

CONCLUSIONS

The PBF pattern 2 hours after aspiration-induced lung injury showed a redistribution of PBF away from injured regions that was likely responsible for the partial recovery from hypoxemia over time. Treatments given intravenously 2 hours after acid-induced lung injury may not preferentially reach the injured lung regions, contrary to what occurs during the first hour of inflammation. Please see related article: http://dx.doi.org/10.1186/s12871-015-0014-z.