Hourly Analysis of Mechanical Ventilation Parameters in Critically Ill Adult Covid-19 Patients: Association with Mortality

Objective: there exists controversy about the pathophysiology and lung mechanics of COVID-19 associated ARDS, because some report severe hypoxemia with preserved respiratory system mechanics, contrasting with “classic” ARDS. We performed a detailed hourly analysis of the characteristics and time course of lung mechanics and biochemical analysis of patients requiring invasive mechanical ventilation for COVID-19-associated ARDS, comparing survivors and non-survivors.Methods and measurements: retrospective analysis of the data stored in the ICU information system of patients admitted in our hospital ICU that required invasive mechanical ventilation due to confirmed SARS-CoV-2 pneumonia between March 5th and April 30th, 2020. We compare respiratory system mechanics and gas exchange during the first ten days of IMV, discriminating volume and pressure controlled modes, between ICU survivors and non-survivors.Results: 140 patients were analyzed, analyzing 11,138 respiratory mechanics recordings. Global mortality was 38.6%. Multivariate analysis showed that age (OR 1,092, 95% (CI 1,014-1,176)), previous use of ACEI/ARBs (OR 4,612, (95% CI 1,19-17,84)) and need of renal replacement therapies (OR 10,15, (95% CI 1,58-65,11)) were associated with higher mortality. Respiratory variables start to diverge significantly between survivors and non-survivors after the 96 to 120 hours from mechanical ventilation initiation, particularly respiratory system compliance. In non survivors, mechanical power at 24 and 96 hs was higher regardless ventilatory mode. Conclusions: in patients admitted for SARS-CoV-2 pneumonia and requiring mechanical ventilation, non survivors have different respiratory system mechanics than survivors in the first 10 days of ICU admission. We propose a checkpoint at 96-120 hs to assess patients` improvement or worsening in order to consider escalating to extracorporeal therapies.“TAKE HOME MESSAGE”: assessing respiratory mechanics in the first 96-120 hs from ICU admission could predict the outcome of Covid-19 patients under mechanical ventilation.

Early Extubation to Noninvasive Respiratory Support of Former Preterm Lambs Improves Long-Term Respiratory Outcomes

Invasive mechanical ventilation (IMV) and exposure to oxygen-rich gas during early postnatal life are contributing factors to long-term pulmonary morbidities faced by survivors of preterm birth and bronchopulmonary dysplasia. The duration of IMV that leads to long-term pulmonary morbidities is unknown. We compared two durations of IMV (3h versus 6d) during the first 6-7d of postnatal life in preterm lambs to test the hypothesis that minimizing the duration of IMV will improve long-term respiratory system mechanics and structural outcomes later in life. Moderately preterm (~85% gestation) lambs were supported by IMV for either 3h or 6d before weaning from all respiratory support to become former preterm lambs. Respiratory system mechanics and airway reactivity were assessed monthly from 1 to 6 months of chronological postnatal age by the forced oscillation technique. Quantitative morphological measurements were made for smooth muscle accumulation around terminal bronchioles and indices of alveolar formation. Minimizing IMV to 3h led to significantly better (p<0.05) baseline respiratory system mechanics and less reactivity to methacholine in the first 3 months of chronological age (2 months corrected age), significantly less (p<0.05) accumulation of smooth muscle around peripheral resistance airways (terminal bronchioles), and significantly better (p<0.05) alveolarization at the end of 5 months corrected age compared to continuous IMV for 6d. We conclude that limiting the duration of IMV following preterm birth of fetal lambs leads to better respiratory system mechanics and structural outcomes later in life.

In Vitro Estimation of Relative Compliance during High-Frequency Oscillatory Ventilation

High-frequency oscillatory ventilation (HFOV), which uses a small tidal volume and a high respiratory rate, is considered a type of protective lung ventilation that can be beneficial for certain patients. A disadvantage of HFOV is its limited monitoring of lung mechanics, which complicates its settings and optimal adjustment. Recent studies have shown that respiratory system reactance (Xrs) could be a promising parameter in the evaluation of respiratory system mechanics in HFOV. The aim of this study was to verify in vitro that a change in respiratory system mechanics during HFOV can be monitored by evaluating Xrs. We built an experimental system consisting of a 3100B high-frequency oscillatory ventilator, a physical model of the respiratory system with constant compliance, and a system for pressure and flow measurements. During the experiment, models of different constant compliance were connected to HFOV, and Xrs was derived from the impedance of the physical model that was calculated from the spectral density of airway opening pressure and spectral cross-power density of gas flow and airway opening pressure. The calculated Xrs changed with the change of compliance of the physical model of the respiratory system. This method enabled monitoring of the trend in the respiratory system compliance during HFOV, and has the potential to optimize the mean pressure setting in HFOV in clinical practice.

Lung Mechanics in Type L CoVID-19 Pneumonia: A Pseudo-Normal ARDS.

Since its outbreak, in January, 2020, it has been clear that CoVID-19 pneumonia is atypical. Despite a full concordance to Berlin criteria for Acute Respiratory Distress Syndrome (ARDS), respiratory system mechanics is preserved [1]. Mechanical ventilation and muscular paralysis are recommended in worsening respiratory insufficiency [2]; in a substantial number of cases, prone positioning significantly improves oxygenation.