Luigi Pisani

Weaning and the heart: From art to science

August 2014 • Volume 42 • Number 8 Despite decades of attempts to identify the exact mechanisms underlying weaning failure (1), a comprehensive diagnostic algorithm is not available. We still wonder, like Sinha and Donn (2) 14 years ago, whether weaning from mechanical ventilation is art or science. Prolonged weaning may be due to central or peripheral ventilatory drive abnormalities, unbalance between mechanical load and inspiratory muscle strength and, finally, poor cardiac tolerance of spontaneous ventilation (3). Often, different mechanisms coexist in a complex interplay. Weaning from mechanical ventilation may succeed at the first attempt (simple weaning), within 1 week (difficult weaning) or, finally, after more than 1 week (prolonged weaning) (4). The Ventila group, in a survey including more than 2,200 mechanically ventilated patients, found that the adjusted probability of death was higher (13% vs 7%) in patients requiring prolonged weaning compared with patients simple or difficult to wean (5). Prolonged ventilatory dependency is a medical challenge and represents a tremendous psychosocial burden for patients and their relatives. In this issue of Critical Care Medicine, Dres et al (6) report the performance of different methods to diagnose weaninginduced acute cardiogenic pulmonary edema (ACPE). Their data expand our knowledge and raise two relevant issues. First, the authors report a surprisingly high prevalence of weaning-induced ACPE (47.6%). These percentages are in keeping with other studies, for instance, Anguel et al (7): 52%, Jubran et al (8): 42%, and Lamia et al (9): 43%. All these studies relied on a pulmonary artery (PA) catheter to diagnose weaning-induced ACPE. Dres et al (6) report that it is the practice of their institution to perform right heart catheterization for all difficult-to-wean patients when obvious reasons for weaning failure have been discarded. However, inserting a PA catheter in critically ill patients is a debated issue, and this practice is actually uncommon, unless in reference centers like the one of the authors (10). Indeed, the rationale of the study by Dres et al (6) was essentially to validate less invasive alternatives to the “gold standard” PA catheter. Confirming previous studies (7, 11, 12), the authors report acceptable diagnostic power for either blood volume contraction indices (plasma protein and hemoglobin concentration) or brain natriuretic peptides. Furthermore, they show an even better diagnostic performance of weaning-induced increase in extravascular lung water (EVLW), disclosing a novel application field for transpulmonary thermodilution, a technique relatively less invasive than right heart catheterization (13). Second, the authors report that they started diuretics and nitrates after the diagnosis of weaning-induced ACPE. Any weaning trial, and in particular the T-tube spontaneous breathing trial, increases the metabolic oxygen requirements and creates an acute fluid challenge when the intrathoracic pressure shifts from positive (during mechanical ventilation) to negative (during spontaneous breathing). Administering diuretics is a logical approach: fluid overload may be a cofactor able to precipitate ACPE. Nevertheless, a word of caution is needed. The weaning trial may uncover left systolic or diastolic dysfunction, valvular disease, arrhythmias, and right ventricular failure (14). Patients with chronic obstructive pulmonary disease are particularly prone to right ventricular engorgement due to the relevant negative shift in intrathoracic pressure needed to overcome dynamic hyperinflation at the reinstitution of spontaneous breathing; in those patients, ACPE could arise due to leftward interventricular septal shift and diastolic stiffening of left ventricles (15). Accordingly, any suspect of weaninginduced ACPE should prompt a stepwise diagnostic flowchart. The therapeutical approach should then be tailored to the exact mechanism leading to cardiac failure in terms of drugs (e.g., β-blockers, diuretics, nitrates, vasodilators, and inotropes) and/ or other interventions (e.g., cardiac revascularization) (16). In conclusion, the study by Dres et al (6) is doubly important: it shows that measuring EVLW before and immediately after the weaning trial may disclose weaning-induced ACPE and emphasizes the impact of acute heart failure on ventilator dependency. Thanks to several small but focused studies like this one (7–9, 11, 12, 14, 16), we have a number of methods to suspect heart failure involvement in ventilator dependency. It is time to update our diagnostic algorithm for difficult-towean patients.

Potential Diagnostic Properties of Chest Ultrasound in Thoracic Tuberculosis—A Systematic Review

Background: Chest ultrasound (CUS) has been shown to be a sensitive and specific imaging modality for pneumothorax, pneumonia, and pleural effusions. However, the role of chest ultrasound in the diagnosis of thoracic tuberculosis (TB) is uncertain. We performed a systematic search in the medical literature to better define the potential role and value of chest ultrasound in diagnosing thoracic tuberculosis. Aim: To describe existing literature with regard to the diagnostic value of chest ultrasound in thoracic tuberculosis. Methods: MEDLINE, EMBASE, and Scopus databases were searched for relevant articles. We included studies that used chest ultrasound for the diagnosis or management of any form of thoracic tuberculosis, including pulmonary, pleural, mediastinal, and military forms. Results: We identified five main fields of chest ultrasound application: (1) Detection, characterization, and quantification of TB; (2) detection of residual pleural thickening after evacuation; (3) chest ultrasound-guided needle biopsy; (4) identification of pathologic mediastinal lymph nodes in children; and (5) identification of parenchymal ultrasound patterns. Effusion was also detected, in early stages, with signs of organization in 24–100% of patients. A low to moderate (10–23%), false negative rate was reported for chest ultrasound-guided needle biopsy. CUS was able to identify mediastinal lymph nodes in as many as 67% of patients with negative chest radiography. Conclusions: Very few studies with important methodological limitations analyze the role of chest ultrasound in the diagnosis of TB. The scarce available data suggests potential targets of future diagnostic or feasibility trials, such as the detection of tuberculosis–related pleural effusion, residual pleural thickening, lymphadenopathy, TB parenchymal patterns, or the use of CUS in biopsy guidance.

PRactice of VENTilation in Middle-Income Countries (PRoVENT-iMIC): rationale and protocol for a prospective international multicentre observational study in intensive care units in Asia

Introduction Current evidence on epidemiology and outcomes of invasively mechanically ventilated intensive care unit (ICU) patients is predominantly gathered in resource-rich settings. Patient casemix and patterns of critical illnesses, and probably also ventilation practices are likely to be different in resource-limited settings. We aim to investigate the epidemiological characteristics, ventilation practices and clinical outcomes of patients receiving mechanical ventilation in ICUs in Asia. Methods and analysis PRoVENT-iMIC (study of PRactice of VENTilation in Middle-Income Countries) is an international multicentre observational study to be undertaken in approximately 60 ICUs in 11 Asian countries. Consecutive patients aged 18 years or older who are receiving invasive ventilation in participating ICUs during a predefined 28-day period are to be enrolled, with a daily follow-up of 7 days. The primary outcome is ventilatory management (including tidal volume expressed as mL/kg predicted body weight and positive end-expiratory pressure expressed as cm H2O) during the first 3 days of mechanical ventilation—compared between patients at no risk for acute respiratory distress syndrome (ARDS), patients at risk for ARDS and in patients with ARDS (in case the diagnosis of ARDS can be made on admission). Secondary outcomes include occurrence of pulmonary complications and all-cause ICU mortality. Ethics and dissemination PRoVENT-iMIC will be the first international study that prospectively assesses ventilation practices, outcomes and epidemiology of invasively ventilated patients in ICUs in Asia. The results of this large study, to be disseminated through conference presentations and publications in international peer-reviewed journals, are of ultimate importance when designing trials of invasive ventilation in resource-limited ICUs. Access to source data will be made available through national or international anonymised datasets on request and after agreement of the PRoVENT-iMIC steering committee. Trial registration number NCT03188770; Pre-results.

Lung ultrasound and neonatal ARDS: is Montreux closer to Berlin than to Kigali?

We commend Daniele De Luca and colleagues on their Position Paper in The Lancet Respiratory Medicine, which advocates the Montreux definition as a concrete diagnostic approach for acute respiratory distress syndrome (ARDS) in neonates. The paper highlights the growing interest in neonatal ARDS, consistent with the longstanding interest in adult ARDS. The Montreux definition uses the following four diagnostic criteria: acute onset from a known clinical insult; exclusion of alternate diagnoses commonly present in neonates, and absence of congenital heart disease; an oxygen deficit with an oxygenation index of 4 or higher; and lung imaging showing diffuse, bilateral, and irregular opacities of the lungs, which are not fully explained by the exclusion criteria. Thus, the Montreux definition for ARDS in neonates largely resembles the Berlin definition for ARDS in adults. The chest film is the most ambiguous component of the Berlin definition, and not surprisingly the authors provided an extensive supplement about chest films, to aid the interpretation of the frequent equivocal cases. Lung ultrasound is a sensitive diagnostic technique that is easy to learn and easy to use, enabling rapid discrimination between normally aerated lung tissue and interstitial syndromes. In 2016, a modification of the Berlin definition for ARDS was proposed, also named after the location where it was developed: the Kigali modification of the Berlin definition. In the Kigali modification arterial blood gas results are replaced with pulse oximeter readings, lung ultrasound can be used instead of chest films for the diagnosis of ARDS, and minimal positive endexpiratory pressure readings are no longer a requirement. Following the application of these modifications, the investigators in Kigali could identify patients that probably would have been diagnosed with ARDS according to the Berlin definition, if blood gas analyses results, chest films, and mechanical ventilation had been available. Rigorous external validation of this approach is in progress, which is particularly appealing in resource– limited settings. In view of the non–invasive safety profile of lung ultrasound, replacing chest films with lung ultrasound is also attractive in newborn babies. Intuitive and validated approaches for lung ultrasound in neonates are becoming increasingly available, with considerable advances in research on meconium aspiration syndrome, respiratory distress syndrome, and transient tachypnoea in newborn babies. With regard to chest imaging, the Montreaux definition should move south, away from Berlin and toward Kigali. Investigation of lung ultrasound for the diagnosis of ARDS in neonates should be added to the research agenda.