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BACKGROUND: CO2 rebreathing is one of the risks associated with noninvasive ventilation (NIV), possibly contributing to failure. In a bench study, we showed that a novel mask design, with separate limbs for inflow and outflow gases, significantly reduced CO2 rebreathing in different ventilation settings. OBJECTIVES: The study aimed to test whether a new mask design could 1) reduce CO2 rebreathing in healthy volunteers during NIV (phase 1) and 2) reduce minute ventilation (phase 2). MATERIALS AND METHODS: Healthy volunteers were randomly assigned to NIV using two masks in a crossover design: a traditional single-limb mask for inflow and outflow gases and a mask with two separated limbs. In phase 1, six ventilation settings were tested for each mask: CPAP (PEEP 5 cmH2O) and pressure support ventilation (PSV, PS Level 5 cmH2O) using a mechanical ventilator with a bias flow of 8 or 20 L/min; free-flow CPAP (PEEP 5 cmH2O) with 60 or 90 L/min of gas flow. A nasal cannula was inserted in one nostril of the volunteers and connected to a CO2 gas analyzer to measure CO2 during the respiratory cycle. In phase 2, volunteers underwent a prolonged time of ventilation in CPAP 90 L/min and PSV with 20 L/min of bias flow. During free-flow CPAP, electrical impedance tomography was used to record the change in impedance during tidal breathing and then estimate tidal volume. RESULTS: Ten healthy adults were enrolled in phase 1, and 8 volunteers in phase 2. CO2 during inspiration was significantly lower in each setting with the two-limb versus the one-limb mask (p < 0.001). The maximum CO2 reduction was observed in the continuous-flow CPAP settings. EtCO2 was lower with the two-limb mask compared to the one-limb mask (p < 0.001). However, no difference in minute ventilation was observed between the two masks. CONCLUSION: The new mask design with two ports for inhaled and exhaled gases reduced the amount of CO2 rebreathing in all tested ventilation settings. The CO2 rebreathing reduction did not decrease minute ventilation in healthy volunteers.
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Máscaras , Ventilação não Invasiva , Adulto , Humanos , Dióxido de Carbono , Gases , Voluntários Saudáveis , Ventilação não Invasiva/instrumentação , Respiração Artificial , Estudos Cross-OverRESUMO
Background: The physiological and prognostical significance of accessory and expiratory muscles activation is unknown during a spontaneous breathing trial (SBT). We hypothesized that, in patients experiencing weaning failure, accessory and expiratory muscles are activated to cope with an increased respiratory workload. Purpose: To describe accessory and expiratory muscle activation non-invasively by surface electromyography (sEMG) during an SBT and to assess differences in electrical activity (EA) of the inspiratory and expiratory muscles in successful vs. failing weaning patients. Methods: Intubated patients on mechanical ventilation for more than 48 h undergoing an SBT were enrolled in a medical and surgical third-level ICU of the University Teaching Hospital. Baseline characteristics and physiological variables were recorded in a crossover physiologic prospective clinical study. Results: Of 37 critically ill mechanically ventilated patients, 29 (78%) patients successfully passed the SBT. Rapid shallow breathing index (RSBI) was higher in patients who failed SBT compared with the successfully weaned patients at baseline and over time (group-by-time interaction p < 0.001). EA of both the diaphragm (EAdisurf) and of accessory muscles (ACCsurf) was higher in failure patients compared with success (group-by-time interaction p = 0.0174 and p < 0.001, respectively). EA of expiratory muscles (ESPsurf) during SBT increased more in failure than in weaned patients (group-by-time interaction p < 0.0001). Conclusion: Non-invasive respiratory muscle monitoring by sEMG was feasible during SBT. Respiratory muscles EA increased during SBT, regardless of SBT outcome, and patients who failed the SBT had a higher increase of all the inspiratory muscles EA compared with the patients who passed the SBT. Recruitment of expiratory muscles-as quantified by sEMG-is associated with SBT failure.
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Objective.We will describe our clinical experience using electrical impedance tomography (EIT) in the management of mechanical ventilation in patients with acute respiratory failure and to determine to which extent EIT-guided positive end-expiratory pressure (PEEP) setting differed from clinically set values.Approach.We conducted a retrospective, observational cohort study performed in a hub centre for the treatment of acute respiratory failure and veno-venous extracorporeal membrane oxygenation (ECMO).Main results.Between January 2017 and December 2019, EIT was performed 54 times in 41 patients, not feasible only in one case because of signal instability. More than 50% was on veno-venous ECMO support. In 16 cases (30%), EIT was used for monitoring mechanical ventilation, i.e. to evaluate recruitability or sigh setting. In 37 cases (70%), EIT was used to set PEEP both with incremental (11 cases in nine patients) and decremental (26 cases, 18 patients) PEEP trial. Clinical PEEP before the decremental PEEP trial (PEEPPRE) was 14.1 ± 3.4 cmH2O and clinical PEEP set by clinicians after the PEEP trial (PEEPPOST) was 13.6 ± 3.1 (p = ns). EIT analyses demonstrated that more hypoxic patients were higher derecruited when compared to less hypoxic patients that were, on the contrary, more overdistended (p < 0.05). No acute effects of PEEP adjustment based on EIT on respiratory mechanics or regional EIT parameters modification were observed.Significance.The variability of EIT findings in our population confirmed the need to provide ventilation settings individually tailored and EIT was confirmed to be an optimal useful clinical bedside noninvasive tool to provide real-time monitoring of the PEEP effect and ventilation distribution.
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Respiração com Pressão Positiva , Insuficiência Respiratória , Impedância Elétrica , Humanos , Insuficiência Respiratória/terapia , Estudos Retrospectivos , TomografiaRESUMO
BACKGROUND: Pendelluft, the movement of gas within different lung regions, is present in animal models of assisted mechanical ventilation and associated with lung overstretching. Due to rebreathing of CO2 as compared to fresh gas, pendelluft might reduce ventilatory efficiency possibly exacerbating patient's respiratory workload during weaning. Our aim was to measure pendelluft by electrical impedance tomography (EIT) in patients who failed a spontaneous breathing trial (SBT). METHODS: This is an observational study conducted in a general intensive care unit of a tertiary-level teaching hospital. EIT signal was recorded in 20 patients while pressure support (PS) ventilation was progressively reduced from clinical level (baseline) to 2 cmH2O, as in an SBT; four ventral-to-dorsal lung regions of interest were identified for pendelluft measurement. A regional gas movement (> 6 mL) occurring in a direction opposite to the global EIT signal was considered diagnostic for high pendelluft. RESULTS: Eight patients out of 20 (40%) were classified as high-pendelluft; baseline clinical characteristics did not differ between high- and low-pendelluft patients. At PS reduction, pendelluft and EtCO2 increased more in the high-pendelluft group (p < .001 and .011, respectively). The volume of gas subject to pendelluft moved almost completely from the ventral towards the dorsal lung regions, while the opposite movement was minimal (16.3 [10:32.8] vs. 0 [0:1.8] mL, p = .001). In a subgroup of patients, increased pendelluft volumes positively correlated with markers of respiratory distress such as increased respiratory rate, p0.1, and EtCO2. CONCLUSIONS: Occult pendelluft can be measured by EIT, and is frequently present in patients failing an SBT. When present, pendelluft increases with the reduction of ventilator support and is associated with increased EtCO2, suggesting a reduction of the ability to eliminate CO2.