El síndrome de dificultad respiratoria aguda (SDRA) es una lesión pulmonar inflamatoria caracterizada por hipoxemia de inicio agudo con infiltrados pulmonares bilaterales, que sigue asociándose a una alta morbilidad y mortalidad a pesar de los avances en la ventilación mecánica protectora. Evidencia reciente ha identificado la microbiota pulmonar como un posible factor que contribuye a la fisiopatología del SDRA. En condiciones fisiológicas, la microbiota pulmonar presenta una alta diversidad bacteriana y desempeña un papel importante en el mantenimiento de la homeostasis inmunitaria. Sin embargo, aún no se ha alcanzado un consenso sobre la muestra de referencia óptima para los estudios del microbioma. En pacientes críticos, particularmente aquellos con SDRA que requieren ventilación mecánica, un hallazgo constante es la disbiosis pulmonar, definida por una menor diversidad microbiana y una mayor abundancia de bacterias de origen intestinal. Varios factores contribuyen a este desequilibrio, incluyendo la hipoxemia, la exposición a antibióticos de amplio espectro y la naturaleza invasiva de la ventilación mecánica. La disbiosis se ha asociado con respuestas inflamatorias, tanto locales como sistémicas, y se ha propuesto como mediadora de la lesión pulmonar inducida por el ventilador. Clínicamente, se han asociado alteraciones en la microbiota pulmonar con desenlaces adversos en el SDRA, como la ventilación mecánica prolongada y el aumento de la mortalidad. Se requiere más investigación para esclarecer los mecanismos causales y evaluar si la modulación del microbioma pulmonar podría representar una diana terapéutica en el SDRA.

Double cycling with breath-stacking (DC/BS) during controlled mechanical ventilation is considered potentially injurious, reflecting a high respiratory drive. During partial ventilatory support, its occurrence might be attributable to physiological variability of breathing patterns, reflecting the response of the mode without carrying specific risks. This secondary analysis of a crossover study evaluated DC/BS events in hypoxemic patients resuming spontaneous breathing in cross-over under neurally adjusted ventilatory assist (NAVA), proportional assist ventilation (PAV +), and pressure support ventilation (PSV). DC/BS was defined as two inspiratory cycles with incomplete exhalation. Measurements included electrical impedance signal, airway pressure, esophageal and gastric pressures, and flow. Breathing variability, dynamic compliance (CLdyn), and end-expiratory lung impedance (EELI) were analyzed. Twenty patients under assisted breathing, with a median of 9 [5–14] days on mechanical ventilation, were included. DC/BS was attributed to either a single (42

Allowing spontaneous breathing with optimal inspiratory effort should be a priority in patients with acute respiratory failure under mechanical ventilation.Low and absent effort promote diaphragmatic dysfunction, creating difficulties in weaning, but also atelectasis and hypoxemia, while intense inspiratory efforts generate negative alveolar pressures and can induce lung (i.e., patient selfinflicted lung injury-P-SILI) and diaphragmatic injury (myotrauma) [1].Low effort even occurs despite apparently spontaneous "triggered" breaths, because assisted ventilation deliver minimal minute ventilation once triggered.The transition from controlled to assisted ventilation can be associated with vigorous efforts in patients with hypoxemic failure, difficult to control [2].In addition, lung injury and systemic inflammation are primers for P-SILI and myotrauma with excessive concentric or eccentric loading [1,3].Mechanisms of P-SILI include excessive global and regional lung stress (due to pendelluft) and increased transvascular pressure, and are directly associated with the magnitude and timing of inspiratory effort [3,4].There is also evidence of interaction between lung and other organs such as brain and kidneys.Therefore, monitoring respiratory drive and effort to adjust ventilatory settings and sedation seems necessary to achieve lung-and diaphragm-protective targets that should result in better clinical outcomes.This review describes the tools and the different parameters for monitoring respiratory effort, and suggests targets for respiratory drive and effort (Fig. 1).

"Electrical Impedance Tomography-based Ventilation Patterns for Evaluating Proper Ventilator Settings and to Classifying Lung Morphofunction." American Journal of Respiratory and Critical Care Medicine, 0(ja), pp.

In patients with chronic obstructive pulmonary disease (COPD), single lung transplantation (SLT) is sometimes performed as an alternative to bilateral lung transplantation due to limited organ availability. However, the postoperative management of SLT presents challenges, including complications related to the distinct compliance of each lung. This case report presents the case of a 65-year-old male patient who underwent SLT and was in the weaning period from mechanical ventilation. High-flow oxygen therapy (HFOT) was administered, and the physiological effects were measured using electrical impedance tomography (EIT). The results demonstrated that the application of HFOT increased air trapping and overdistention in the native lung without benefiting the transplanted lung. HFOT through a tracheostomy tube or nasal cannula resulted in a more heterogeneous distribution of ventilation, with increased end expiratory lung impedance, prolonged expiratory time constants, and an increase in silent spaces. The drop in tidal impedance after applying HFOT did not indicate hypoventilation but rather overdistention and air trapping in the native lung, while the transplanted lung showed evidence of hypoventilation. These findings suggest that HFOT may not be beneficial for SLT patients and could potentially worsen outcomes. However, due to the limited scope of this case report, further prospective studies with larger patient cohorts are needed to confirm these results.

In the acute distress respiratory syndrome (ARDS), specific lung regions can be exposed to excessive strain due to heterogeneous disease, gravity-dependent lung collapse and injurious mechanical ventilation. Computed tomography (CT) is the gold standard for regional strain assessment. An alternative tool could be the electrical impedance tomography (EIT). We aimed to determine whether EIT-based methods can predict the dynamic relative regional strain (DRRS) between two levels of end-expiratory pressure (PEEP) in gravity-non-dependent and dependent lung regions. Fourteen ARDS patients underwent CT and EIT acquisitions (at end-inspiratory and end-expiratory) at two levels of PEEP: a low-PEEP based on ARDS-net strategy and a high-PEEP titrated according to EIT. Three EIT-based methods for DRRS were compared to relative CT-based strain: (1) the change of the ratio between EIT ventilation and end-expiratory lung impedance in arbitrary units ([ΔZAU low-PEEP/EELIAU low-PEEP]/[ΔZAU high-PEEP/EELIAU high-PEEP]), (2) the change of ΔZ/EELI ratio calibrated to mL ([ΔZml low-PEEP/EELIml low-PEEP]/[ΔZml high-PEEP/EELIml high-PEEP]) using CT data, and (3) the relative change of ∆ZAU (∆ZAU low-PEEP/∆ZAU high-PEEP). We performed linear regressions analysis and calculated bias and limits of agreement to assess the performance of DRRS by EIT in comparison with CT. The DRRS assessed by (ΔZml low-PEEP/EELIml low-PEEP)/(ΔZml high-PEEP/EELIml high-PEEP) and ∆ZAU low-PEEP/∆ZAU high-PEEP showed good relationship and agreement with the CT method (R2 of 0.9050 and 0.8679, respectively, in non-dependent region; R2 of 0.8373 and 0.6588, respectively, in dependent region; biases ranging from − 0.11 to 0.51 and limits of agreement ranging from − 0.73 to 1.16 for both methods and lung regions). Conversely, DRRS based on EELIAU ([ΔZAU low-PEEP/EELIAU low-PEEP]/[ΔZAU high-PEEP/EELIAU high-PEEP]) exhibited a weak negative relationship and poor agreement with the CT method for both non-dependent and dependent regions (R2 0.3; bias of 3.11 and 2.08, and limits of agreement of − 2.13 to 8.34 and from − 1.49 to 5.64, respectively). Changes in DRRS during a PEEP trial in ARDS patients could be monitored using EIT, based on changes in ΔZmL/EELIml and ∆ZAU. The relative change ∆ZAU offers the advantage of not requiring CT data for calibration.

Background Internal redistribution of gas, referred to as pendelluft, is a new potential mechanism of effort-dependent lung injury. Neurally-adjusted ventilatory assist (NAVA) and proportional assist ventilation (PAV +) follow the patient’s respiratory effort and improve synchrony compared with pressure support ventilation (PSV). Whether these modes could prevent the development of pendelluft compared with PSV is unknown. We aimed to compare pendelluft magnitude during PAV + and NAVA versus PSV in patients with resolving acute respiratory distress syndrome (ARDS). Methods Patients received either NAVA, PAV + , or PSV in a crossover trial for 20-min using comparable assistance levels after controlled ventilation (> 72 h). We assessed pendelluft (the percentage of lost volume from the non-dependent lung region displaced to the dependent region during inspiration), drive (as the delta esophageal swing of the first 100 ms [ΔP es 100 ms ]) and inspiratory effort (as the esophageal pressure–time product per minute [PTP min ]). We performed repeated measures analysis with post-hoc tests and mixed-effects models. Results Twenty patients mechanically ventilated for 9 [5–14] days were monitored. Despite matching for a similar tidal volume, respiratory drive and inspiratory effort were slightly higher with NAVA and PAV + compared with PSV (ΔP es 100 ms of –2.8 [−3.8–−1.9] cm H 2 O, −3.6 [−3.9–−2.4] cm H 2 O and −2.1 [−2.5–−1.1] cm H 2 O, respectively, p < 0.001 for both comparisons; PTP min of 155 [118–209] cm H 2 O s/min, 197 [145–269] cm H 2 O s/min, and 134 [93–169] cm H 2 O s/min, respectively, p < 0.001 for both comparisons). Pendelluft magnitude was higher in NAVA (12 ± 7%) and PAV + (13 ± 7%) compared with PSV (8 ± 6%), p < 0.001. Pendelluft magnitude was strongly associated with respiratory drive (β = -2.771, p-value < 0.001) and inspiratory effort ( β = 0.026, p < 0.001), independent of the ventilatory mode. A higher magnitude of pendelluft in proportional modes compared with PSV existed after adjusting for PTP min ( β = 2.606, p = 0.010 for NAVA, and β = 3.360, p = 0.004 for PAV +), and only for PAV + when adjusted for respiratory drive (β = 2.643, p = 0.009 for PAV +). Conclusions Pendelluft magnitude is associated with respiratory drive and inspiratory effort. Proportional modes do not prevent its occurrence in resolving ARDS compared with PSV.

Prone positioning is an evidence-based treatment for patients with moderate-to-severe acute respiratory distress syndrome. Lung recruitment has been proposed as one of the mechanisms by which prone positioning reduces mortality in this group of patients. Recruitment-to-inflation ratio (R/I) is a method to measure potential for lung recruitment induced by a change in positive end-expiratory pressure (PEEP) on the ventilator. The association between R/I and potential for lung recruitment in supine and prone position has not been studied with computed tomography (CT) scan imaging. In this secondary analysis, we sought to investigate the correlation between R/I measured in supine and prone position with CT and the potential for lung recruitment as measured by CT scan. Among 23 patients, the median R/I did not significantly change from supine (1.9 IQR 1.6-2.6) to prone position (1.7 IQR 1.3-2.8) (paired t test p = 0.051) but the individual changes correlated with the different response to PEEP. In supine and in prone position, R/I significantly correlated with the proportion of lung tissue recruitment induced by the change of PEEP. Lung tissue recruitment induced by a change of PEEP from 5 to 15 cmH(2)O was 16% (IQR 11-24%) in supine and 14.3% (IQR 8.4-22.6%) in prone position, as measured by CT scan analysis (paired t test p = 0.56). In this analysis, PEEP-induced recruitability as measured by R/I correlated with PEEP-induced lung recruitment as measured by CT scan, and could help to readjust PEEP in prone position.

BACKGROUND:The usefulness of tracheostomy has been questioned in patients with COVID-19 and prolonged invasive mechanical ventilation (IMV).AIM:To compare the 90-day mortality rate of patients who underwent a tracheostomy due prolonged IMV with those that did not receive this procedure.MATERIAL AND METHODS:We studied a historical cohort of 92 patients with COVID-19 and prolonged IMV (> 10 days). The primary outcome was the 90-day mortality rate. Secondary outcomes included days on IMV, hospital/intensive care unit (ICU) length of stay, frequency of nosocomial infections, and thrombotic complications demonstrated by images. A logistic regression was performed to adjust the effect of tracheostomy by SOFA score and days on IMV.RESULTS:Forty six patients aged 54 to 66 years (72% males) underwent tracheostomy. They had a median of two comorbidities, and received the procedure after a median of 20.5 days on IMV (interquartile range: 17-26). 90-day mortality was lower in patients who were tracheostomized than in the control group (6.5% vs. 32.6%, p-value < 0.01). However, after controlling for confounding factors, no differences were found in mortality between both groups (relative risk = 0.303, p-value = 0.233). Healthcare-associated infections and hospital/ICU length of stay were higher in patients with tracheostomy than in controls. Thrombotic complications occurred in 42.4% of the patients, without differences between both groups. No cases of COVID-19 were registered in the healthcare personnel who performed tracheostomies.CONCLUSIONS:In patients with COVID-19 undergoing prolonged IMV, performing a tracheostomy is not associated with excess mortality, and it is a safe procedure for healthcare personnel.

Since the first description of ARDS, bilateral alveolar infiltrates on chest radiography have been recognized as characteristic of this syndrome, combined with hypoxemia and low respiratory system compliance (![Formula][1]).[1][2] Due to its simplicity, chest radiography is still a pillar of

Abstract Background Prone positioning is currently applied in time-limited daily sessions up to 24 h which determines that most patients require several sessions. Although longer prone sessions have been reported, there is scarce evidence about the feasibility and safety of such approach. We analyzed feasibility and safety of a continuous prolonged prone positioning strategy implemented nationwide, in a large cohort of COVID-19 patients in Chile. Methods Retrospective cohort study of mechanically ventilated COVID-19 patients with moderate-to-severe acute respiratory distress syndrome (ARDS), conducted in 15 Intensive Care Units, which adhered to a national protocol of continuous prone sessions ≥ 48 h and until PaO2:FiO2 increased above 200 mm Hg. The number and extension of prone sessions were registered, along with relevant physiologic data and adverse events related to prone positioning. The cohort was stratified according to the first prone session duration: Group A, 2–3 days; Group B, 4–5 days; and Group C, > 5 days. Multivariable regression analyses were performed to assess whether the duration of prone sessions could impact safety. Results We included 417 patients who required a first prone session of 4 (3–5) days, of whom 318 (76.3%) received only one session. During the first prone session the main adverse event was grade 1–2 pressure sores in 97 (23.9%) patients; severe adverse events were infrequent with 17 non-scheduled extubations (4.2%). 90-day mortality was 36.2%. Ninety-eight patients (24%) were classified as group C; they exhibited a more severe ARDS at baseline, as reflected by lower PaO2:FiO2 ratio and higher ventilatory ratio, and had a higher rate of pressure sores (44%) and higher 90-day mortality (48%). However, after adjustment for severity and several relevant confounders, prone session duration was not associated with mortality or pressure sores. Conclusions Nationwide implementation of a continuous prolonged prone positioning strategy for COVID-19 ARDS patients was feasible. Minor pressure sores were frequent but within the ranges previously described, while severe adverse events were infrequent. The duration of prone session did not have an adverse effect on safety.

Editor—In dual-patient ventilation, the tidal volume (VT) delivered to patients depends on their respiratory mechanics, which can vary significantly between them.1–4 Thus, dual-patient ventilation might provide non-protective high VT to one patient, while supplying inadequate ventilation to the other because of low VT.5,6 To address this issue, splitters capable of regulating VT individually through implementation of valves and flow limiters have been devised. Dual-patient ventilation has been used in patients with similar respiratory mechanics, both without and with a splitter.

COVID-19 is a recent respiratory illness with high morbidity and mortality; therefore, the study and characterization of blood markers associated with the improvement or deterioration of COVID-19 patients are crucial. This study compared levels of interleukin 6 (IL-6), procalcitonin (PCT), D-dimer, cortisol, dehydroepiandrosterone sulfate (DHEA-S), c-reactive protein (CRP), 25-OH vitamin D, anti-SARS-CoV-2 IgG antibodies, and viremia in mild–moderate and severe–critical COVID-19 patients. In addition, the time course of blood markers was studied in severe–critical cases. The results show that levels of IL-6, PCT, D-dimer, and CRP, the cortisol/DHEA-S ratio, as well as positive viremia and anti-Spike IgGs were higher in severe–critical patients requiring hospitalization. During follow-up, most severe–critical cases displayed similar time patterns of IL-6 and viral load, whereas anti-SARS-CoV-2 antibody curves showed an inverse pattern. A decrease in IL-6 levels was associated with the improvement of COVID-19 patients, mostly through a reduced oxygen requirement. This preliminary study suggests that an increase in serum IL-6, PCT, D-dimer and CRP levels and the cortisol/DHEA-S ratio could support the selection of patients with poorer prognosis and the need for an intensive or alternative treatment. Additionally, changes in IL-6 during hospitalization were associated with changes in patient’s status mainly with a decrease in oxygen requirements, which indicates that serial measurements of IL-6 could predict the outcome of severe–critical patients with COVID-19 pneumonia.