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OBJECTIVE: Patients with acute respiratory failure often require mechanical ventilation to reduce the work of breathing and improve gas exchange; however, this may exacerbate lung injury. Protective ventilation strategies, characterized by low tidal volumes (≤ 8mL/kg of predicted body weight) and limited plateau pressure below 30cmH2O, have shown improved outcomes in patients with acute respiratory distress syndrome. However, in the transition to spontaneous ventilation, it can be challenging to maintain tidal volume within protective levels, and it is unclear whether low tidal volumes during spontaneous ventilation impact patient outcomes. We developed a study protocol to estimate the prevalence of low tidal volume ventilation in the first 24 hours of spontaneous ventilation in patients with hypoxemic acute respiratory failure and its association with ventilator-free days and survival. METHODS: We designed a multicenter, multinational, cohort study with a 28-day follow-up that will include patients with acute respiratory failure, defined as a partial oxygen pressure/fraction of inspired oxygen ratio < 300mmHg, in transition to spontaneous ventilation in intensive care units in Latin America. RESULTS: We plan to include 422 patients in ten countries. The primary outcomes are the prevalence of low tidal volume in the first 24 hours of spontaneous ventilation and ventilator-free days on day 28. The secondary outcomes are intensive care unit and hospital mortality, incidence of asynchrony and return to controlled ventilation and sedation. CONCLUSION: In this study, we will assess the prevalence of low tidal volume during spontaneous ventilation and its association with clinical outcomes, which can inform clinical practice and future clinical trials.
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Unidades de Cuidados Intensivos , Síndrome de Dificultad Respiratoria , Volumen de Ventilación Pulmonar , Humanos , América Latina/epidemiología , Síndrome de Dificultad Respiratoria/terapia , Síndrome de Dificultad Respiratoria/epidemiología , Síndrome de Dificultad Respiratoria/fisiopatología , Síndrome de Dificultad Respiratoria/mortalidad , Respiración Artificial , Insuficiencia Respiratoria/terapia , Insuficiencia Respiratoria/epidemiologíaRESUMEN
BACKGROUND: Adjusting trunk inclination from a semi-recumbent position to a supine-flat position or vice versa in patients with respiratory failure significantly affects numerous aspects of respiratory physiology including respiratory mechanics, oxygenation, end-expiratory lung volume, and ventilatory efficiency. Despite these observed effects, the current clinical evidence regarding this positioning manoeuvre is limited. This study undertakes a scoping review of patients with respiratory failure undergoing mechanical ventilation to assess the effect of trunk inclination on physiological lung parameters. METHODS: The PubMed, Cochrane, and Scopus databases were systematically searched from 2003 to 2023. INTERVENTIONS: Changes in trunk inclination. MEASUREMENTS: Four domains were evaluated in this study: 1) respiratory mechanics, 2) ventilation distribution, 3) oxygenation, and 4) ventilatory efficiency. RESULTS: After searching the three databases and removing duplicates, 220 studies were screened. Of these, 37 were assessed in detail, and 13 were included in the final analysis, comprising 274 patients. All selected studies were experimental, and assessed respiratory mechanics, ventilation distribution, oxygenation, and ventilatory efficiency, primarily within 60 min post postural change. CONCLUSION: In patients with acute respiratory failure, transitioning from a supine to a semi-recumbent position leads to decreased respiratory system compliance and increased airway driving pressure. Additionally, C-ARDS patients experienced an improvement in ventilatory efficiency, which resulted in lower PaCO2 levels. Improvements in oxygenation were observed in a few patients and only in those who exhibited an increase in EELV upon moving to a semi-recumbent position. Therefore, the trunk inclination angle must be accurately reported in patients with respiratory failure under mechanical ventilation.
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Insuficiencia Respiratoria , Humanos , Insuficiencia Respiratoria/fisiopatología , Insuficiencia Respiratoria/terapia , Respiración Artificial/métodos , Mecánica Respiratoria/fisiología , Postura/fisiología , Posicionamiento del Paciente/métodos , Torso/fisiopatología , Torso/fisiologíaRESUMEN
BACKGROUND: Andes virus (ANDV) is a zoonotic Orthohantavirus leading to hantavirus cardiopulmonary syndrome. Although most transmissions occur through environmental exposure to rodent faeces and urine, rare person-to-person transmission has been documented, mainly for close contacts. This study investigates the presence and infectivity of ANDV in body fluids from confirmed cases and the duration of viraemia. METHODS: In this prospective study, 131 participants with confirmed ANDV infection were enrolled in Chile in a prospective study between 2008 and 2022. Clinical samples (buffy coat, plasma, gingival crevicular fluid [GCF], saliva, nasopharyngeal swabs [NPS], and urine) were collected weekly for 3 weeks together with clinical and epidemiological data. Samples were categorised as acute or convalescent (up to and after 16 days following onset of symptoms). Infectivity of positive fluids was assessed after the culture of samples on Vero E6 cells and use of flow cytometry assays to determine the production of ANDV nucleoprotein. FINDINGS: ANDV RNA was detected in 100% of buffy coats during acute phase, declining to 95% by day 17, and to 93% between days 23-29. ANDV RNA in GCF and saliva decreased from 30% and 12%, respectively, during the acute phase, to 12% and 11% during the convalescent phase. Successful infectivity assays of RT-qPCR-positive fluids, including GCF, saliva, NPS, and urine, were observed in 18 (42%) of 43 samples obtained during the acute phase of infection. After re-culture, the capacity to infect Vero E6 cells was maintained in 16 (89%) of 18 samples. Severity was associated with the presence of ANDV RNA in one or more fluids besides blood (odds ratio 2·58 [95% CI 1·42-5·18]). INTERPRETATION: ANDV infection is a systemic and viraemic infection, that affects various organs. The presence of infectious particles in body fluids contributes to our understanding of potential mechanisms for person-to-person transmission, supporting the development of preventive strategies. Detection of ANDV RNA in additional fluids at hospital admission is a predictor of disease severity. FUNDING: National Institutes of Health and Agencia de Investigación y Desarrollo. TRANSLATION: For the Spanish translation of the abstract see Supplementary Materials section.
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Infecciones por Hantavirus , Orthohantavirus , Viremia , Esparcimiento de Virus , Humanos , Estudios Prospectivos , Masculino , Adulto , Infecciones por Hantavirus/transmisión , Infecciones por Hantavirus/epidemiología , Infecciones por Hantavirus/virología , Femenino , Orthohantavirus/aislamiento & purificación , Chile/epidemiología , Persona de Mediana Edad , Adulto Joven , Adolescente , ARN Viral , Animales , Niño , Chlorocebus aethiops , Anciano , Células VeroRESUMEN
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 [ΔPes 100 ms]) and inspiratory effort (as the esophageal pressure-time product per minute [PTPmin]). 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 (ΔPes 100 ms of -2.8 [-3.8--1.9] cm H2O, -3.6 [-3.9--2.4] cm H2O and -2.1 [-2.5--1.1] cm H2O, respectively, p < 0.001 for both comparisons; PTPmin of 155 [118-209] cm H2O s/min, 197 [145-269] cm H2O s/min, and 134 [93-169] cm H2O 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 (ß = -2.771, p-value < 0.001) and inspiratory effort (ß = 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 PTPmin (ß = 2.606, p = 0.010 for NAVA, and ß = 3.360, p = 0.004 for PAV +), and only for PAV + when adjusted for respiratory drive (ß = 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.
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OBJECTIVE: To investigate the mechanisms underlying the improved arterial oxygenation described with flow-limited expiration (FLEX) ventilation in anesthetized horses. ANIMALS: 5 healthy adult research horses. METHODS: Horses underwent volume-controlled ventilation for 60 minutes (VCV1), followed by 60 minutes of FLEX, and 30 minutes of VCV (VCV2). Main outcomes included the arterial partial pressure of oxygen-to-Fio2 (PF) ratio and electrical impedance tomography (EIT)-derived functional indices at the end of each phase. The EIT data were used to create regional maps of relative lung ventilation and perfusion as well as regional maps of ventilation/perfusion (V/Q) ratios. Ventilation indices derived from EIT included the fraction of expired volume in 1 second (FEV1; %) and the time it took for the EIT signal to drop to 50% of the peak signal at end-inspiration (TClose50; seconds). Data were analyzed with 2-way ANOVA for repeated measures. P < .05 was considered significant. RESULTS: The PF ratio increased significantly with FLEX compared to both VCV1 and VCV2 (P < .01). There were no differences in the relative distribution of ventilation nor perfusion between ventilation strategies. However, when ventilation and perfusion were superimposed and V/Q ratio maps were constructed, FLEX had a homogenizing effect toward values of 1.0. The FEV1 was shorter (P < .01) and the TClose50 was longer (P < .001) in all regions during FLEX compared to both VCV1 and VCV2. CLINICAL RELEVANCE: Our findings suggest that FLEX ventilation in anesthetized horses enhances regional V/Q matching, likely by prolonging expiratory aeration and reducing airway closure.
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Mechanical ventilation is a lifesaving intervention that may also induce further lung injury by exerting excessive mechanical forces on susceptible lung tissue, a phenomenon termed ventilator-induced lung injury (VILI). The concept of mechanical power (MP) aims to unify in one single variable the contribution of the different ventilatory parameters that could induce VILI by measuring the energy transfer to the lung over time. Despite an increasing amount of evidence demonstrating that high MP values can be associated with VILI development in experimental studies, the evidence regarding the association of MP and clinical outcomes remains controversial. In the present review, we describe the different determinants of VILI, the concept and computation of MP, and discuss the experimental and clinical studies related to MP. Currently, due to different limitations, the clinical application of MP is debatable. Further clinical studies are required to enhance our understanding of the relationship between MP and the development of VILI, as well as its potential impact on clinical outcomes.
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Pulmón , Lesión Pulmonar Inducida por Ventilación Mecánica , Humanos , Respiración , Respiración Artificial/efectos adversos , Lesión Pulmonar Inducida por Ventilación Mecánica/etiología , Lesión Pulmonar Inducida por Ventilación Mecánica/prevención & control , ComputadoresRESUMEN
BACKGROUND: Prophylactic high-flow nasal cannula (HFNC) oxygen therapy can decrease the risk of extubation failure. It is frequently used in the postextubation phase alone or in combination with noninvasive ventilation. However, its physiological effects in this setting have not been thoroughly investigated. The aim of this study was to determine comprehensively the effects of HFNC applied after extubation on respiratory effort, diaphragm activity, gas exchange, ventilation distribution, and cardiovascular biomarkers. METHODS: This was a prospective randomized crossover physiological study in critically ill patients comparing 1 h of HFNC versus 1 h of standard oxygen after extubation. The main inclusion criteria were mechanical ventilation for at least 48 h due to acute respiratory failure, and extubation after a successful spontaneous breathing trial (SBT). We measured respiratory effort through esophageal/transdiaphragmatic pressures, and diaphragm electrical activity (ΔEAdi). Lung volumes and ventilation distribution were estimated by electrical impedance tomography. Arterial and central venous blood gases were analyzed, as well as cardiac stress biomarkers. RESULTS: We enrolled 22 patients (age 59 ± 17 years; 9 women) who had been intubated for 8 ± 6 days before extubation. Respiratory effort was significantly lower with HFNC than with standard oxygen therapy, as evidenced by esophageal pressure swings (5.3 [4.2-7.1] vs. 7.2 [5.6-10.3] cmH2O; p < 0.001), pressure-time product (85 [67-140] vs. 156 [114-238] cmH2O*s/min; p < 0.001) and ΔEAdi (10 [7-13] vs. 14 [9-16] µV; p = 0.022). In addition, HFNC induced increases in end-expiratory lung volume and PaO2/FiO2 ratio, decreases in respiratory rate and ventilatory ratio, while no changes were observed in systemic hemodynamics, Troponin T, or in amino-terminal pro-B-type natriuretic peptide. CONCLUSIONS: Prophylactic application of HFNC after extubation provides substantial respiratory support and unloads respiratory muscles. Trial registration January 15, 2021. NCT04711759.
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This study aimed to develop a three-dimensional (3-D) method for assessing ventilation/perfusion (V/QÌ) ratios in a pig model of hemodynamic perturbations using electrical impedance tomography (EIT). To evaluate the physiological coherence of changes in EIT-derived V/QÌ ratios, global EIT-derived V/QÌ mismatches were compared with global gold standards. The study found regional heterogeneity in the distribution of V/QÌ ratios in both the ventrodorsal and craniocaudal directions. Although global EIT-derived indices of V/QÌ mismatch consistently underestimated both low and high V/QÌ mismatch compared with global gold standards, the direction of the change was similar. We made the software available at no cost for other researchers to use. Future studies should compare regional V/QÌ ratios determined by our method against other regional, high-resolution methods.NEW & NOTEWORTHY In this study, we introduce a novel 3-D method for assessing ventilation-perfusion (V/QÌ) ratios using electrical impedance tomography (EIT). Heterogeneity in V/QÌ distribution showcases the significant potential for enhanced understanding of pulmonary conditions. This work signifies a substantial step forward in the application of EIT for monitoring and managing lung diseases.
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Different techniques have been proposed to measure antibiotic levels within the lung parenchyma; however, their use is limited because they are invasive and associated with adverse effects. We explore whether beta-lactam antibiotics could be measured in exhaled breath condensate collected from heat and moisture exchange filters (HMEFs) and correlated with the concentration of antibiotics measured from bronchoalveolar lavage (BAL). We designed an observational study in patients undergoing mechanical ventilation, which required a BAL to confirm or discard the diagnosis of pneumonia. We measured and correlated the concentration of beta-lactam antibiotics in plasma, epithelial lining fluid (ELF), and exhaled breath condensate collected from HMEFs. We studied 12 patients, and we detected the presence of antibiotics in plasma, ELF, and HMEFs from every patient studied. The concentrations of antibiotics were very heterogeneous over the population studied. The mean antibiotic concentration was 293.5 (715) ng/mL in plasma, 12.3 (31) ng/mL in ELF, and 0.5 (0.9) ng/mL in HMEF. We found no significant correlation between the concentration of antibiotics in plasma and ELF (R2 = 0.02, p = 0.64), between plasma and HMEF (R2 = 0.02, p = 0.63), or between ELF and HMEF (R2 = 0.02, p = 0.66). We conclude that beta-lactam antibiotics can be detected and measured from the exhaled breath condensate accumulated in the HMEF from mechanically ventilated patients. However, no correlations were observed between the antibiotic concentrations in HMEF with either plasma or ELF.
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The 2021 wave of SARS-CoV-2 infection in Chile was characterized by an explosive increase in ICU admissions, which disproportionately affected individuals younger than 60 years. This second wave was also accompanied by an explosive increase in Gamma (P.1) variant detections and the massive vaccine rollout. We unveil the role the Gamma variant played in stressing the use of critical care, by developing and calibrating a queueing model that uses data on new onset cases and actual ICU occupancy, symptom's onset to ICU admission interval, ICU length-of-stay, genomic surveillance, and vaccine effectiveness. Our model shows that infection with the Gamma (P.1) variant led to a 3.5-4.7-fold increase in ICU admission for people younger than 60 years. This situation occurred on top of the already reported higher infection rate of the Gamma variant. Importantly, our results also strongly suggest that the vaccines used in Chile (inactivated mostly, but also an mRNA), were able to curb Gamma variant ICU admission over infections.
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COVID-19 , Sustancias Explosivas , Humanos , SARS-CoV-2/genética , COVID-19/epidemiología , Chile/epidemiología , Unidades de Cuidados IntensivosRESUMEN
Background: Treatment for critical care conditions, such as acute respiratory distress syndrome (ARDS), requires ready-to-administer injectable mesenchymal stromal cells (MSCs). A validated cryopreserved therapy based on MSCs derived from menstrual blood (MenSCs) is an attractive option that offers advantages over freshly cultured cells and allows its use as an off-the-shelf therapy in acute clinical conditions. The main goal of this study is to provide evidence on the impact of cryopreservation on different biological functions of MenSCs and to determine the optimal therapeutic dose, safety, and efficacy profile of clinical-grade, cryopreserved (cryo)-MenSCs in experimental ARDS. Methods: Biological functions of fresh versus cryo-MenSCs were compared in vitro. The effects of cryo-MenSCs therapy were evaluated in vivo in ARDS-induced (Escherichia coli lipopolysaccharide) C57BL/6 mice. After 24 h, the animals were treated with five doses ranging from 0.25×105 to 1.25×106 cells/animal. At 2 and 7 days after induction of ARDS, safety and efficacy were evaluated. Results: Clinical-grade cryo-MenSCs injections improved lung mechanics and reduced alveolar collapse, tissue cellularity, and remodelling, decreasing elastic and collagen fiber content in alveolar septa. In addition, administration of these cells modulated inflammatory mediators and promoted pro-angiogenic and anti-apoptotic effects in lung-injured animals. More beneficial effects were observed with an optimal dose of 4×106 cells/Kg than with higher or lower doses. Conclusion: From a translational perspective, the results showed that clinical-grade cryopreserved MenSCs retain their biological properties and exert a therapeutic effect in mild to moderate experimental ARDS. The optimal therapeutic dose was well-tolerated, safe, and effective, favouring improved lung function. These findings support the potential value of an off-the-shelf MenSCs-based product as a promising therapeutic strategy for treating ARDS.
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The transition from controlled to partial support ventilation is a challenge in acute respiratory distress syndrome (ARDS) patients due to the risks of patient-self-inflicted lung injury. The magnitude of tidal volume (VT) and intrapulmonary dyssynchrony (pendelluft) are suggested mechanisms of lung injury. We conducted a prospective, observational, physiological study in a tertiary academic intensive care unit. ARDS patients transitioning from controlled to partial support ventilation were included. On these, we evaluated the association between changes in inflammatory biomarkers and esophageal pressure swing (ΔPes), transpulmonary driving pressure (ΔPL), VT, and pendelluft. Pendelluft was defined as the percentage of the tidal volume that moves from the non-dependent to the dependent lung region during inspiration, and its frequency at different thresholds (- 15, - 20 and - 25%) was also registered. Blood concentrations of inflammatory biomarkers (IL-6, IL-8, TNF-α, ANGPT2, RAGE, IL-18, Caspase-1) were measured before (T0) and after 4-h (T4) of partial support ventilation. Pendelluft, ΔPes, ΔPL and VT were recorded. Nine out of twenty-four patients (37.5%) showed a pendelluft mean ≥ 10%. The mean values of ΔPes, ΔPL, and VT were - 8.4 [- 6.7; - 10.2] cmH2O, 15.2 [12.3-16.5] cmH2O and 8.1 [7.3-8.9] m/kg PBW, respectively. Significant associations were observed between the frequency of high-magnitude pendelluft and IL-8, IL-18, and Caspase-1 changes (T0/T4 ratio). These results suggest that the frequency of high magnitude pendelluft may be a potential determinant of inflammatory response related to inspiratory efforts in ARDS patients transitioning to partial support ventilation. Future studies are needed to confirm these results.
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Lesión Pulmonar , Síndrome de Dificultad Respiratoria , Humanos , Interleucina-18 , Estudios Prospectivos , Interleucina-8 , Respiración , Síndrome de Dificultad Respiratoria/terapia , Biomarcadores , Caspasa 1 , PulmónRESUMEN
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.
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PURPOSE: To evaluate cardiac function in mechanically ventilated patients with COVID-19. MATERIALS AND METHODS: Prospective, cross-sectional multicenter study in four university-affiliated hospitals in Chile. All consecutive patients with COVID-19 ARDS requiring mechanical ventilation admitted between April and July 2020 were included. We performed systematic transthoracic echocardiography assessing right and left ventricular function within 24 h of intubation. RESULTS: 140 patients aged 57 ± 11, 29% female were included. Cardiac output was 5.1 L/min [IQR 4.5-6.2] and 86% of the patients required norepinephrine. ICU mortality was 29% (40 patients). Fifty-four patients (39%) exhibited right ventricle dilation out of whom 20 patients (14%) exhibited acute cor pulmonale (ACP). Eight out of the twenty patients with ACP exhibited pulmonary embolism (40%). Thirteen patients (9%) exhibited left ventricular systolic dysfunction (ejection fraction <45%). In the multivariate analysis acute cor pulmonale and PaO2/FiO2 ratio were independent predictors of ICU mortality. CONCLUSIONS: Right ventricular dilation is highly prevalent in mechanically ventilated patients with COVID-19 ARDS. Acute cor pulmonale was associated with reduced pulmonary function and, in only 40% of patients, with co-existing pulmonary embolism. Acute cor pulmonale is an independent risk factor for ICU mortality.
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COVID-19 , Insuficiencia Cardíaca , Embolia Pulmonar , Enfermedad Cardiopulmonar , Síndrome de Dificultad Respiratoria , Humanos , Femenino , Masculino , Enfermedad Cardiopulmonar/etiología , Respiración Artificial/efectos adversos , Enfermedad Crítica , Estudios Transversales , Estudios Prospectivos , Embolia Pulmonar/complicaciones , Insuficiencia Cardíaca/complicaciones , Síndrome de Dificultad Respiratoria/terapiaRESUMEN
Vigorous spontaneous breathing has emerged as a promotor of lung damage in acute lung injury, an entity known as "patient self-inflicted lung injury". Mechanical ventilation may prevent this second injury by decreasing intrathoracic pressure swings and improving regional air distribution. Therefore, we aimed to determine the effects of spontaneous breathing during the early stage of acute respiratory failure on lung injury and determine whether early and late controlled mechanical ventilation may avoid or revert these harmful effects. A model of partial surfactant depletion and lung collapse was induced in eighteen intubated pigs of 32 ±4 kg. Then, animals were randomized to (1) SB-group: spontaneous breathing with very low levels of pressure support for the whole experiment (eight hours), (2) Early MV-group: controlled mechanical ventilation for eight hours, or (3) Late MV-group: first half of the experiment on spontaneous breathing (four hours) and the second half on controlled mechanical ventilation (four hours). Respiratory, hemodynamic, and electric impedance tomography data were collected. After the protocol, animals were euthanized, and lungs were extracted for histologic tissue analysis and cytokines quantification. SB-group presented larger esophageal pressure swings, progressive hypoxemia, lung injury, and more dorsal and inhomogeneous ventilation compared to the early MV-group. In the late MV-group switch to controlled mechanical ventilation improved the lung inhomogeneity and esophageal pressure swings but failed to prevent hypoxemia and lung injury. In a lung collapse model, spontaneous breathing is associated to large esophageal pressure swings and lung inhomogeneity, resulting in progressive hypoxemia and lung injury. Mechanical ventilation prevents these mechanisms of patient self-inflicted lung injury if applied early, before spontaneous breathing occurs, but not when applied late.
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Lesión Pulmonar Aguda , Lesión Pulmonar , Atelectasia Pulmonar , Lesión Pulmonar Aguda/etiología , Lesión Pulmonar Aguda/patología , Animales , Hipoxia/patología , Pulmón/patología , Lesión Pulmonar/etiología , Lesión Pulmonar/patología , Modelos Teóricos , Atelectasia Pulmonar/patología , Respiración , Respiración Artificial/efectos adversos , Respiración Artificial/métodos , Mecánica Respiratoria , PorcinosRESUMEN
At the beginning of the COVID-19 pandemic in Chile, in March 2020, a projection indicated that a significant group of patients with pneumonia would require admission to an Intensive Care Unit and connection to a mechanical ventilator. Therefore, a paucity of these devices and other supplies was predicted. The initiative "Un respiro para Chile" brought together many people and institutions, public and private. In the course of three months, it allowed the design and building of several ventilatory assistance devices, which could be used in critically ill patients.
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Humanos , Pandemias , COVID-19 , Respiración Artificial , Ventiladores Mecánicos , Chile/epidemiología , Unidades de Cuidados IntensivosRESUMEN
Defective management of secretions is one of the most frequent complications in invasive mechanically ventilated patients. Clearance of secretions through chest physiotherapy is a critical aspect of the treatment of these patients. Manual rib cage compression is one of the most practiced chest physiotherapy techniques in ventilated patients; however, its impact on clinical outcomes remains controversial due to methodological issues and poor understanding of its action. In this review, we present a detailed analysis of the physical principles involved in rib cage compression technique performance, as well as the physiological effects observed in experimental and clinical studies, which show that the use of brief and vigorous rib cage compression, based on increased expiratory flows (expiratory-inspiratory airflow difference of > 33L/minute), can improve mucus movement toward the glottis. On the other hand, the use of soft and gradual rib cage compression throughout the whole expiratory phase does not impact the expiratory flows, resulting in ineffective or undesired effects in some cases. More physiological studies are needed to understand the principles of the rib cage compression technique in ventilated humans. However, according to the evidence, rib cage compression has more potential benefits than risks, so its implementation should be promoted.
O manejo deficiente das secreções é uma das complicações mais frequentes em pacientes em ventilação mecânica invasiva. A depuração das secreções por meio da fisioterapia respiratória é um aspecto crítico do tratamento desses pacientes. A compressão torácica manual é uma das técnicas de fisioterapia respiratória mais praticadas em pacientes ventilados, mas seu impacto nos desfechos clínicos permanece controverso devido a questões metodológicas e ao pouco conhecimento sobre sua ação. Nesta revisão, apresenta-se uma análise detalhada dos princípios físicos envolvidos na execução da técnica de compressão torácica. Também investigam-se os efeitos fisiológicos observados em estudos experimentais e clínicos, que mostram que o uso de compressão torácica curta e vigorosa, baseada no aumento de fluxos expiratórios (diferença de fluxo aéreo inspiratório-expiratório > 33L/minuto), pode melhorar o movimento do muco em direção à glote. Por outro lado, o uso de compressão torácica suave e gradual ao longo de toda a fase expiratória não afeta os fluxos expiratórios, resultando em efeitos ineficazes ou indesejados em alguns casos. Mais estudos fisiológicos são necessários para entender os princípios da técnica de compressão torácica em pacientes ventilados. No entanto, de acordo com as evidências, a compressão torácica tem mais benefícios potenciais do que riscos, o que incentiva sua implementação.