Very Low Tidal Volume Ventilation with Associated Hypercapnia - Effects on Lung Injury in a Model for Acute Respiratory Distress Syndrome

BACKGROUND: Ventilation using low tidal volumes with permission of hypercapnia is recommended to protect the lung in acute respiratory distress syndrome. However, the most lung protective tidal volume in association with hypercapnia is unknown. The aim of this study was to assess the effects of different tidal volumes with associated hypercapnia on lung injury and gas exchange in a model for acute respiratory distress syndrome. METHODOLOGY/PRINCIPAL FINDINGS: In this randomized controlled experiment sixty-four surfactant-depleted rabbits were exposed to 6 hours of mechanical ventilation with the following targets: Group 1: tidal volume = 8-10 ml/kg/PaCO(2) = 40 mm Hg; Group 2: tidal volume = 4-5 ml/kg/PaCO(2) = 80 mm Hg; Group 3: tidal volume = 3-4 ml/kg/PaCO(2) = 120 mm Hg; Group 4: tidal volume = 2-3 ml/kg/PaCO(2) = 160 mm Hg. Decreased wet-dry weight ratios of the lungs, lower histological lung injury scores and higher PaO(2) were found in all low tidal volume/hypercapnia groups (group 2, 3, 4) as compared to the group with conventional tidal volume/normocapnia (group 1). The reduction of the tidal volume below 4-5 ml/kg did not enhance lung protection. However, oxygenation and lung protection were maintained at extremely low tidal volumes in association with very severe hypercapnia and no adverse hemodynamic effects were observed with this strategy. CONCLUSION: Ventilation with low tidal volumes and associated hypercapnia was lung protective. A tidal volume below 4-5 ml/kg/PaCO(2) 80 mm Hg with concomitant more severe hypercapnic acidosis did not increase lung protection in this surfactant deficiency model. However, even at extremely low tidal volumes in association with severe hypercapnia lung protection and oxygenation were maintained

Auswirkungen des Blähmanövers zur Rekrutierung von Lungenvolumen auf die Hämodynamik, den Gasaustausch, die zerebrale Perfusion und Oxygenierung

Einleitung: Das Blähmanöver zur Rekrutierung von Lungenvolumen findet bei der Erstversorgung respiratorisch beeinträchtigter Neugeborener Anwendung, um unmittelbar nach der Geburt eine funktionelle Residualkapazität herzustellen. Die Blähmanöver erfolgen mit jeweils 15 Sekunden dauernder Applikation von Beatmungsdrücken (20, 25 und 30 cm H2O). Material und Methoden: Bei 6 Kaninchen wurden arterieller Blutdruck, zerebrale Perfusion, zentraler Venendruck, Herzfrequenz, Herzzeitvolumen, Sauerstoffsättigung, zerebraler Sauerstoffpartialdruck, Ösophagusdruck und Blutgasparameter unter der Applikation des Blähmanövers gemessen. Durch Lungenlavage und Füllung der Lunge mit Kochsalzlösung wurde eine surfactantdepletierte und partiell fruchtwassergefüllte Lunge eines kranken Frühgeborenen simuliert. Ergebnisse: In Abhängigkeit der Lungencompliance kam es zu erheblichen Beeinträchtigungen des Kreislaufs. Abhängig von der initialen Sauerstoffsättigung konnte der Gasaustausch für die Dauer des Blähmanövers verbessert werden. Die Auswirkungen waren am stärksten ausgeprägt, je höher der Beatmungsdruck gewählt wurde, je länger der Beatmungsdruck gehalten wurde und je höher die Lungencompliance war. Diskussion: Um die modellbedingten Einschränkungen wissend, muss dennoch von einer erheblichen hämodynamischen Schwankung während eines Blähmanövers ausgegangen werden. Die Untersuchungen liefern Hinweise für ein erhebliches Potential für eine Beeinträchtigung der Hämodynamik und der zerebralen Perfusion bei Früh- und Neugeborenen, die mit einem Blähmanöver behandelt werden. Andererseits konnte eine rasche Verbesserung der Oxygenierung im zentralen Nervensystem bei flüssigkeitsgefüllter Lunge nachgewiesen werden. Schlussfolgerung: Die Ergebnisse dieser Arbeit sollten Anlass zur Diskussion über Beatmungsdruckanstieg, -abfall und -dauer sein. Exaktere Aussagen zu tatsächlichen Abläufen beim Neugeborenen sollten anhand eines Modells mit intaktem neonatalen Kreislauf erarbeitet werden

Imaging Challenges in Patients with Severe Aortic Stenosis and Heart Failure: Did We Find a Way Out of the Labyrinth?

Aortic stenosis (AS) is the most frequent degenerative valvular disease in developed countries. Its incidence has been constantly rising due to population aging. The diagnosis of AS was considered straightforward for a very long time. High gradients and reduced aortic valve area were considered as “sine qua non” in diagnosis of AS until a growing body of evidence showed that patients with low gradients could also have severe AS with the same or even worse outcome. This completely changed the paradigm of AS diagnosis and involved large numbers of parameters that had never been used in the evaluation of AS severity. Low gradient AS patients may present with heart failure (HF) with preserved or reduced left ventricular ejection fraction (LVEF), associated with changes in cardiac output and flow across the aortic valve. These patients with low-flow low-gradient or paradoxical low-flow low-gradient AS are particularly challenging to diagnose, and cardiac output and flow across the aortic valve have become the most relevant parameters in evaluation of AS, besides gradients and aortic valve area. The introduction of other imaging modalities in the diagnosis of AS significantly improved our knowledge about cardiac mechanics, tissue characterization of myocardium, calcium and inflammation burden of the aortic valve, and their impact on severity, progression and prognosis of AS, not only in symptomatic but also in asymptomatic patients. However, a variety of novel parameters also brought uncertainty regarding the clinical relevance of these indices, as well as the necessity for their validation in everyday practice. The aim of this review is to summarize the prevalence of HF in patients with severe AS and elaborate on the diagnostic challenges and advantages of comprehensive multimodality cardiac imaging to identify the patients that may benefit from surgical or transcatheter aortic valve replacement, as well as parameters that may help during follow-up

The Prognostic Importance of Right Ventricular Longitudinal Strain in Patients with Cardiomyopathies, Connective Tissue Diseases, Coronary Artery Disease, and Congenital Heart Diseases

Right ventricular (RV) systolic function represents an important independent predictor of adverse outcomes in many cardiovascular (CV) diseases. However, conventional parameters of RV systolic function (tricuspid annular plane excursion (TAPSE), RV myocardial performance index (MPI), and fractional area change (FAC)) are not always able to detect subtle changes in RV function. New evidence indicates a significantly higher predictive value of RV longitudinal strain (LS) over conventional parameters. RVLS showed higher sensitivity and specificity in the detection of RV dysfunction in the absence of RV dilatation, apparent wall motion abnormalities, and reduced global RV systolic function. Additionally, RVLS represents a significant and independent predictor of adverse outcomes in patients with dilated cardiomyopathy (CMP), hypertrophic CMP, arrhythmogenic RV CMP, and amyloidosis, but also in patients with connective tissue diseases and patients with coronary artery disease. Due to its availability, echocardiography remains the main imaging tool for RVLS assessment, but cardiac magnetic resonance (CMR) also represents an important additional imaging tool in RVLG assessment. The findings from the large studies support the routine evaluation of RVLS in the majority of CV patients, but this has still not been adopted in daily clinical practice. This clinical review aims to summarize the significance and predictive value of RVLS in patients with different types of cardiomyopathies, tissue connective diseases, and coronary artery disease

Lung histology scores.

<p>Median (interquartile ranges); <i>*</i> = 40 vs 80, 40 vs 120, 40 vs 160; n.s.  =  not significant.</p

Bronchoalveolar lavage (BAL).

<p>Cell count (A) and differential cell count (B) were measured in the bronchoalveolar lavage fluid prior to intervention (initial BAL) and at the end of the experiment (final BAL). Data are averaged for the initial BAL and specified for the final BAL for group 40, group 80, group 120 and group 160. Median and interquartile ranges are shown. * = p<0.05 (ANOVA on ranks).</p

Markers of lung injury.

<p>The wet-dry weight ratio of the right lung (A). PaO₂ across time (B). Median and interquartile ranges are shown. *p<0.001 (ANOVA); **p<0.01 (repeated measures ANOVA on ranks).</p