Ventilator output splitting interface 'ACRA': Description and evaluation in lung simulators and in an experimental ARDS animal model.

The current COVID-19 pandemic has led the world to an unprecedented global shortage of ventilators, and its sharing has been proposed as an alternative to meet the surge. This study outlines the performance of a preformed novel interface called 'ACRA', designed to split ventilator outflow into two breathing systems. The 'ACRA' interface was built using medical use approved components. It consists of four unidirectional valves, two adjustable flow-restrictor valves placed on the inspiratory limbs of each unit, and one adjustable PEEP valve placed on the expiratory limb of the unit that would require a greater PEEP. The interface was interposed between a ventilator and two lung units (phase I), two breathing simulators (phase II) and two live pigs with heterogeneous lung conditions (phase III). The interface and ventilator adjustments tested the ability to regulate individual pressures and the resulting tidal volumes. Data were analyzed using Friedman and Wilcoxon tests test (p < 0.05). Ventilator outflow splitting, independent pressure adjustments and individual tidal volume monitoring were feasible in all phases. In all experimental measurements, dual ventilation allowed for individual and tight adjustments of the pressure, and thus volume delivered to each paired lung unit without affecting the other unit's ventilation-all the modifications performed on the ventilator equally affected both paired lung units. Although only suggested during a dire crisis, this experiment supports dual ventilation as an alternative worth to be considered.

Exhalatory dynamic interactions between patients connected to a shared ventilation device.

In this work a shared pressure-controlled ventilation device for two patients is considered. By the use of different valves incorporated to the circuit, the device enables the restriction of possible cross contamination and the individualization of tidal volumes, driving pressures, and positive end expiratory pressure PEEP. Possible interactions in the expiratory dynamics of different pairs of patients are evaluated in terms of the characteristic exhalatory times. These characteristic times can not be easily established using simple linear lumped element models. For this purpose, a 1D model using the Hydraulic and Mechanical libraries in Matlab Simulink was developed. In this sense, experiments accompany this study to validate the model and characterize the different valves of the circuit. Our results show that connecting two patients in parallel to a ventilator always resulted in delays of time during the exhalation. The size of this effect depends on different parameters associated with the patients, the circuit and the ventilator. The dynamics of the exhalation of both patients is determined by the ratios between patients exhalatory resistances, compliances, driving pressures and PEEPs. Adverse effects on exhalations became less noticeable when respiratory parameters of both patients were similar, flow resistances of valves added to the circuit were negligible, and when the ventilator exhalatory valve resistance was also negligible. The asymmetries of driving pressures, compliances or resistances exacerbated the possibility of auto-PEEP and the increase in relaxation times became greater in one patient than in the other. In contrast, exhalatory dynamics were less sensitive to the ratio of PEEP imposed to the patients.

Effectiveness of Prone Positioning in Nonintubated Intensive Care Unit Patients With Moderate to Severe Acute Respiratory Distress Syndrome by Coronavirus Disease 2019.

BACKGROUND: In the treatment for severe acute respiratory distress syndrome (ARDS) from coronavirus disease 2019 (COVID-19), the World Health Organization (WHO) recommends prone positioning (PP) during mechanical ventilation for periods of 12-16 h/d to potentially improve oxygenation and survival. In this prospective observational study, we evaluated the ability of long PP sessions to improve oxygenation in awake intensive care unit (ICU) patients with moderate or severe ARDS due to COVID-19. METHODS: The study was approved by the ethics committee of Galicia (code No. 2020-188), and all patients provided informed consent. In this case series, awake patients with moderate or severe ARDS by COVID-19 admitted to the ICU at University Hospital of Santiago from March 21 to April 5, 2020 were prospectively analyzed. Patients were instructed to remain in PP as long as possible until the patient felt too tired to maintain that position. Light sedation was administered with dexmedetomidine. The following information was collected: number and duration of PP sessions; tissue O2 saturation (StO2) and blood gases before, during, and following a PP session; need of mechanical ventilation; duration of ICU admission; and ICU outcome. Linear mixed-effects models (LMM) were fit to estimate changes from baseline with a random effect for patient. RESULTS: Seven patients with moderate or severe ARDS by COVID-19 were included. All patients received at least 1 PP session. A total of 16 PP sessions were performed in the 7 patients during the period study. The median duration of PP sessions was 10 hours. Dexmedetomidine was used in all PP sessions. Oxygenation increased in all 16 sessions performed in the 7 patients. The ratio of arterial oxygen partial pressure to fractional inspired oxygen (PaO2/FIO2) significantly increased during PP (change from baseline 110 with 97.5% confidence interval [CI], 19-202) and, after PP, albeit not significantly (change from baseline 38 with 97.5% CI, -9.2 to 85) compared with previous supine position. Similarly, tissue oxygenation underwent a small improvement during PP (change from baseline 2.6% with 97.5% CI, 0.69-4.6) without significant changes after PP. Two patients required intubation. All patients were discharged from the ICU. CONCLUSIONS: We found that PP improved oxygenation in ICU patients with COVID-19 and moderate or severe ARDS. PP was relatively well tolerated in our patients and may be a simple strategy to improve oxygenation trying to reduce the number of patients in mechanical ventilation and the length of stay in the ICU, especially in COVID-19 pandemic.