Extracorporeal support to achieve lung-protective and diaphragm-protective ventilation

Ventilation during extracorporeal gas exchange in acute respiratory distress syndrome

PURPOSE OF REVIEW

Accumulating evidence ascribes the benefit of extracorporeal gas exchange, at least in most severe cases, to the provision of a lung healing environment through the mitigation of ventilator-induced lung injury (VILI) risk. In spite of pretty homogeneous criteria for extracorporeal gas exchange application (according to the degree of hypoxemia/hypercapnia), ventilatory management during extracorporeal membrane oxygenation (ECMO)/carbon dioxide removal (ECCO 2 R) varies across centers. Here we summarize the recent evidence regarding the management of mechanical ventilation during extracorporeal gas exchange for respiratory support.

RECENT FINDINGS

At present, the most common approach to protect the native lung against VILI following ECMO initiation involves lowering tidal volume and driving pressure, making modest reductions in respiratory rate, while typically maintaining positive end-expiratory pressure levels unchanged.Regarding ECCO 2 R treatment, higher efficiency devices are required in order to reduce significantly respiratory rate and/or tidal volume.

SUMMARY

The best compromise between reduction of native lung ventilatory load, extracorporeal gas exchange efficiency, and strategies to preserve lung aeration deserves further investigation.

Awake Extracorporeal Membrane Oxygenation for Acute Respiratory Distress Syndrome: Which Clinical Issues Should Be Taken Into Consideration

With the goal of protecting injured lungs and extrapulmonary organs, venovenous extracorporeal membrane oxygenation (VV-ECMO) has been increasingly adopted as a rescue therapy for patients with severe acute respiratory distress syndrome (ARDS) when conventional mechanical ventilation failed to provide effective oxygenation and decarbonation. In recent years, it has become a promising approach to respiratory support for awake, non-intubated, spontaneously breathing patients with respiratory failure, referred to as awake ECMO, to avoid possible detrimental effects associated with intubation, mechanical ventilation, and the adjunctive therapies. However, several complex clinical issues should be taken into consideration when initiating and implementing awake ECMO, such as selecting potential patients who appeared to benefit most; techniques to facilitating cannulation and maintain stable ECMO blood flow; approaches to manage pain, agitation, and delirium; and approaches to monitor and modulate respiratory drive. It is worth mentioning that there had also been some inherent disadvantages and limitations of awake ECMO compared to the conventional combination of ECMO and invasive mechanical ventilation. Here, we review the use of ECMO in awake, spontaneously breathing patients with severe ARDS, highlighting the issues involving bedside clinical practice, detailing some of the technical aspects, and summarizing the initial clinical experience gained over the past years.

Progress of mechanical power in the intensive care unit

Mechanical power of ventilation, currently defined as the energy delivered from the ventilator to the respiratory system over a period of time, has been recognized as a promising indicator to evaluate ventilator-induced lung injury and predict the prognosis of ventilated critically ill patients. Mechanical power can be accurately measured by the geometric method, while simplified equations allow an easy estimation of mechanical power at the bedside. There may exist a safety threshold of mechanical power above which lung injury is inevitable, and the assessment of mechanical power might be helpful to determine whether the extracorporeal respiratory support is needed in patients with acute respiratory distress syndrome. It should be noted that relatively low mechanical power does not exclude the possibility of lung injury. Lung size and inhomogeneity should also be taken into consideration. Problems regarding the safety limits of mechanical power and contribution of each component to lung injury have not been determined yet. Whether mechanical power-directed lung-protective ventilation strategy could improve clinical outcomes also needs further investigation. Therefore, this review discusses the algorithms, clinical relevance, optimization, and future directions of mechanical power in critically ill patients.

Urinary Titin N-Fragment as a Biomarker of Muscle Atrophy, Intensive Care Unit-Acquired Weakness, and Possible Application for Post-Intensive Care Syndrome

Titin is a giant protein that functions as a molecular spring in sarcomeres. Titin interconnects the contraction of actin-containing thin filaments and myosin-containing thick filaments. Titin breaks down to form urinary titin N-fragments, which are measurable in urine. Urinary titin N-fragment was originally reported to be a useful biomarker in the diagnosis of muscle dystrophy. Recently, the urinary titin N-fragment has been increasingly gaining attention as a novel biomarker of muscle atrophy and intensive care unit-acquired weakness in critically ill patients, in whom titin loss is a possible pathophysiology. Furthermore, several studies have reported that the urinary titin N-fragment also reflected muscle atrophy and weakness in patients with chronic illnesses. It may be used to predict the risk of post-intensive care syndrome or to monitor patients' condition after hospital discharge for better nutritional and rehabilitation management. We provide several tips on the use of this promising biomarker in post-intensive care syndrome.

Early Initiation of Awake Veno-Venous Extracorporeal Membrane Oxygenation Can Attenuate Muscle Atrophy and Weakness in Acute Respiratory Distress Syndrome

Patients with acute respiratory distress syndrome (ARDS) exhibit prominent muscle atrophy and weakness. Although these patients often require deep sedation to perform lung-protective ventilation, extracorporeal membrane oxygenation (ECMO) can keep patients awake and make mobilization possible. A 60-year-old man was treated with ECMO due to ARDS. A multidisciplinary team conducted mobilization with standing on day 3. During intensive care unit (ICU) stay, catabolism was ongoing (urinary titin: 24.1-38.4 pmol/mg Cr), but the rectus femoris muscle, measured by ultrasound, moderately decreased by 5.3%, 10.8%, and 13.0% on days 3, 5, and 7, respectively, with maintained Medical Research Council score of 58-60. Diaphragm thickness remained unchanged. On day 5, he was separated from ECMO. After ambulation training, he was discharged from ICU on day 7. He returned home without prominent physical dysfunction. Our experience indicates early initiation of awake ECMO can accompany mobilization and attenuate muscle atrophy and weakness in ARDS.

Real-Time Detection of Hemothorax and Monitoring its Progression in a Piglet Model by Electrical Impedance Tomography: A Feasibility Study

Hemothorax is a serious medical condition that can be life-threatening if left untreated. Early diagnosis and timely treatment are of great importance to produce favorable outcome. Although currently available diagnostic techniques, e.g., chest radiography, ultrasonography, and CT, can accurately detect hemothorax, delayed hemothorax cannot be identified early because these examinations are often performed on patients until noticeable symptoms manifest. Therefore, for early detection of delayed hemothorax, real-time monitoring by means of a portable and noninvasive imaging technique is needed. In this study, we employed electrical impedance tomography (EIT) to detect the onset of hemothorax in real time on eight piglet hemothorax models. The models were established by injection of 60 ml fresh autologous blood into the pleural cavity, and the subsequent development of hemothorax was monitored continuously. The results showed that EIT was able to sensitively detect hemothorax as small as 10 ml in volume, as well as its location. Also, the development of hemothorax over a range of 10 ml up to 60 ml was well monitored in real time, with a favorable linear relationship between the impedance change in EIT images and the volume of blood injected. These findings demonstrated that EIT has a unique potential for early diagnosis and continuous monitoring of hemothorax in clinical practice, providing medical staff valuable information for prompt identification and treatment of delayed hemothorax.