Understanding the mechanics of the respiratory system is crucial for optimizing ventilator settings and ensuring patient safety. While simple models of the respiratory system typically consider only flow resistance and lung compliance, lung tissue resistance is usually neglected. This study investigated the effect of lung tissue viscoelasticity on delivered mechanical power in a physical model of the respiratory system and the possibility of distinguishing tissue resistance from airway resistance using proximal pressure measured at the airway opening. Three different configurations of a passive physical model of the respiratory system representing different mechanical properties (Tissue resistance model, Airway resistance model, and No-resistance model) were tested. The same volume-controlled ventilation and parameters were set for each configuration, with only the inspiratory flow rates being adjusted. Pressure and flow were measured with a Datex-Ohmeda S/5 vital signs monitor (Datex-Ohmeda, Madison, WI, USA). Tissue resistance was intentionally tuned so that peak pressures and delivered mechanical energy measured at airway opening were similar in Tissue and Airway Resistance models. However, measurements inside the artificial lung revealed significant differences, with Tissue resistance model yielding up to 20% higher values for delivered mechanical energy. The results indicate the need to revise current methods of calculating mechanical power delivery, which do not distinguish between tissue resistance and airway flow resistance, making it difficult to evaluate and interpret the significance of mechanical power delivery in terms of lung ventilation protectivity.
BACKGROUND: Prolonged mechanical ventilation caused by ventilator-induced diaphragm dysfunction (VIDD) is a serious problem in critically ill patients. Identification of patients who will have difficulty weaning from ventilation along with attempts to reduce total time on mechanical ventilation is some of the aims of intensive care medicine. OBSERVATIONS: This article briefly summarizes current options for temporary phrenic nerve stimulation therapy in an effort to keep the diaphragm active as direct prevention and treatment of ventilator-associated diaphragmatic dysfunction in patients on mechanical ventilation. The results of feasibility studies using different approaches are promising but so far, the clinical relevance is low. One important question is which tool would reliably identify early signs of diaphragmatic dysfunction and also be useful in guiding therapy. The authors present a brief overview of the current options considering the advantages and disadvantages of the available examination modalities. Despite the fact that current data point out some limitations of ultrasound examination, we believe that it still has a unique position in the bedside examination of critically ill patients on mechanical ventilation. CONCLUSION: Temporary phrenic nerve stimulation, regardless of the specific approach used, has the potential to directly treat or reverse VIDD, and ultrasound examination plays an important role in the comprehensive care of critically ill patients.
- MeSH
- dýchání MeSH
- kritický stav * terapie MeSH
- lidé MeSH
- mechanické ventilátory MeSH
- nervus phrenicus * MeSH
- umělé dýchání MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- přehledy MeSH
Laparoscopic surgery with capnoperitoneum brings many advantages to patients, but also emphasizes the negative impact of anesthesia and mechanical ventilation on the lungs. Even though many studies use electrical impedance tomography (EIT) for lung monitoring during these surgeries, it is not clear what the best position of the electrode belt on the patient's thorax is, considering the cranial shift of the diaphragm. We monitored 16 patients undergoing a laparoscopic surgery with capnoperitoneum using EIT with two independent electrode belts at different tomographic levels: in the standard position of the 4th-6th intercostal space, as recommended by the manufacturer, and in a more cranial position at the level of the axilla. Functional residual capacity (FRC) was measured, and a recruitment maneuver was performed at the end of the procedure by raising the positive end-expiratory pressure (PEEP) by 5 cmH2O. The results based on the spectral analysis of the EIT signal show that the ventilation-related impedance changes are not detectable by the belt in the standard position. In general, the cranial belt position might be more suitable for the lung monitoring during the capnoperitoneum since the ventilation signal remains dominant in the obtained impedance waveform. FRC was significantly decreased by the capnoperitoneum and remained lower also after desufflation.
- MeSH
- elektrická impedance MeSH
- elektrody MeSH
- laparoskopie * MeSH
- lidé MeSH
- počítačová rentgenová tomografie * MeSH
- tomografie metody MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
Scarcity of medical resources inspired many teams worldwide to design ventilators utilizing different approaches during the recent COVID-19 pandemic. Although it can be relatively easy to design a simple ventilator in a laboratory, a large scale production of reliable emergency ventilators which meet international standards for critical care ventilators is challenging and time consuming. The aim of this study is to propose a novel and easily manufacturable principle of gas mixing and inspiratory flow generation for mechanical lung ventilators. Two fast ON/OFF valves, one for air and one for oxygen, are used to control the inspiratory flow generation using pulse width modulation. Short gas flow pulses are smoothed by low-pass acoustic filters and do not propagate further into the patient circuit. At the same time, the appropriate pulse width modulation of both ON/OFF valves controls the oxygen fraction in the generated gas mixture. Tests focused on the accuracy of the delivered oxygen fractions and tidal volumes have proved compliance with the international standards for critical care ventilators. The concept of a simple construction using two fast ON/OFF valves may be used for designing mechanical lung ventilators and thus suitable for their rapid production during pandemics.
- MeSH
- COVID-19 * terapie MeSH
- hromadné neštěstí * MeSH
- kyslík MeSH
- lidé MeSH
- mechanické ventilátory MeSH
- pandemie MeSH
- péče o pacienty v kritickém stavu MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Dynamic hyperinflation is reported as a potential risk during high-frequency oscillatory ventilation (HFOV), and its existence has been documented both by physical models and by CT. The aim of this study is to determine the suitability of electrical impendence tomography (EIT) for the measurement of dynamic lung hyperinflation and hypoinflation during HFOV. Eleven healthy pigs were anaesthetized and ventilated using HFOV. The difference between the airway pressure at the airway opening and alveolar space was measured by EIT and esophageal balloons at three mean airway pressures (12, 18 and 24 cm H2O) and two inspiratory to expiratory time ratios (1:1, 1:2). The I:E ratio was the primary parameter associated with differences between airway and alveolar pressures. All animals showed hyperinflation at a 1:1 ratio (median 1.9 cm H2O) and hypoinflation at a 1:2 (median -4.0 cm H2O) as measured by EIT. EIT measurements had a linear correlation to esophageal balloon measurements (r2 = -0.915, p = 0.0085). EIT measurements were slightly higher than that of the esophageal balloon transducer with the mean difference of 0.57 cm H2O. Presence of a hyperinflation or hypoinflation was also confirmed independently by chest X-ray. We found that dynamic hyperinflation developed during HFOV may be detected and characterized noninvasively by EIT.
- Publikační typ
- časopisecké články MeSH
At the time of COVID-19 pandemic onset in spring 2020 a project CoroVent was initiated with the aim to design and produce emergency lung ventilators and distribute them to hospitals. No flow and tidal volume sensors were available for the project. The lack of tidal volume sensors was a consequence of the rapidly increased demand for mechanical lung ventilators and their consumables. The aim of the study was to develop a special flow sensor CoroQuant for the CoroVent ventilators. The sensor based on pneumotachographic principle, manufactured by the plastic injection moulding of polypropylene, meets the requirements for precision of tidal volume measurement defined by international standard ISO 80601-2-12 for mechanical lung ventilators. CoroVent ventilators with CoroQuant sensors were distributed to 27 hospitals in the Czech Republic for free upon the requests from the medical facilities and started to be clinically used, thus preventing lack of lung ventilators in hospitals in the Czech Republic.
- Publikační typ
- časopisecké články MeSH
OBJECTIVE: Neonatal exposure to episodic hypoxemia and hyperoxemia is highly relevant to outcomes. Our goal was to investigate the differences in the frequency and duration of extreme low and high SpO2 episodes between automated and manual inspired oxygen control. DESIGN: Post-hoc analysis of a cohort from prospective randomized cross-over studies. SETTING: Seven tertiary care neonatal intensive care units. PATIENTS: Fifty-eight very preterm neonates (32 or less weeks PMA) receiving respiratory support and supplemental oxygen participating in an automated versus manual oxygen control cross-over trial. MAIN MEASURES: Extreme hypoxemia was defined as a SpO2 < 80%, extreme hyperoxemia as a SpO2 > 98%. Episode duration was categorized as < 5 seconds, between 5 to < 30 seconds, 30 to < 60 seconds, 60 to < 120 seconds, and 120 seconds or longer. RESULTS: The infants were of a median postmenstrual age of 29 (28-31) weeks, receiving a median FiO2 of 0.28 (0.25-0.32) with mostly receiving non-invasive respiratory support (83%). While most of the episodes were less than 30 seconds, longer episodes had a marked effect on total time exposure to extremes. The time differences in each of the three longest durations episodes (30, 60, and 120 seconds) were significantly less during automated than during manual control (p < 0.001). Nearly two-third of the reduction of total time spent at the extremes between automated and manual control (3.8 to 2.1% for < 80% SpO2 and 3.0 to 1.6% for > 98% SpO2) was seen in the episodes of at least 60 seconds. CONCLUSIONS: This study shows that the majority of episodes preterm infants spent in SpO2 extremes are of short duration regardless of manual or automated control. However, the infrequent longer episodes not only contribute the most to the total exposure, but also their reduction in frequency to the improvement associated with automated control.
- MeSH
- hypoxie etiologie terapie MeSH
- kojenec MeSH
- kyslík * MeSH
- lidé MeSH
- novorozenec nedonošený * MeSH
- novorozenec MeSH
- oxymetrie MeSH
- prospektivní studie MeSH
- retrospektivní studie MeSH
- Check Tag
- kojenec MeSH
- lidé MeSH
- novorozenec MeSH
- Publikační typ
- časopisecké články MeSH
The reliability of pulse oximetry is crucial, especially in cases of rapid changes in body oxygenation. In order to evaluate the performance of pulse oximeters during rapidly developing short periods of concurrent hypoxemia and hypercapnia, 13 healthy volunteers underwent 3 breathing phases during outdoor experiments (39 phases in total), monitored simultaneously by five different pulse oximeters. A significant incongruity in values displayed by the tested pulse oximeters was observed, even when the accuracy declared by the manufacturers were considered. In 28.2% of breathing phases, the five used devices did not show any congruent values. The longest uninterrupted congruent period formed 74.4% of total recorded time. Moreover, the congruent periods were rarely observed during the critical desaturation phase of the experiment. The time difference between the moments when the first and the last pulse oximeter showed the typical study endpoint values of SpO2 85% and 75% was 32.1 ± 23.6 s and 24.7 ± 19.3 s, respectively. These results suggest that SpO2 might not be a reliable parameter as a study endpoint, or more importantly as a safety limit in outdoor experiments. In the design of future studies, more parameters and continuous clinical assessment should be included.
- MeSH
- hypoxie diagnóza MeSH
- kyslík * MeSH
- lidé MeSH
- monitorování fyziologických funkcí MeSH
- oxymetrie * MeSH
- reprodukovatelnost výsledků MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
Oxygen is the most common drug used in the critical care of infants. There is significant morbidity and mortality associated with excess or inadequate levels. For this reason, an important element of many therapeutic interventions in the ICU requires assessment of their acute impact on oxygenation. It is common to normalize the arterial level of oxygen with the fraction of inspired oxygen (PF-ratio). Further, a change may often be more important than the absolute level. Though the PF-ratio is often reported, it was surmised that the rarely reported, relative magnitude of change in PF-ratio might be a useful metric for assessing the stability and effectiveness of therapy. Therefore, individual patient data from two different studies were evaluated. The cases included periods of therapeutic intervention and periods without intervention, thus permitting the evaluation of the PF-ratio's potential sensitivity to change and thresholds for relevant change. During surfactant administration in extremely preterm infants, the PF-ratio improved at least 25% in 91% of the infants, while 9% showed less than a 10% change. During high-frequency oscillatory rescue in children, the PF-ratio improved at least 25% in 76% of the infants, while 8% showed less than a 10% change. Consideration of thresholds of 50% and 5% reflected low prevalence. In periods of routine care, the prevalence of marked changes was less prevalent but still common (6% and 55%) and periods of little change more prevalent (21% and 21%). We believe this initial work supports the feasibility of using the magnitude of change in PF-ratio and provides a useful stimulus for additional evaluations.
- MeSH
- hyperoxie komplikace terapie MeSH
- hypoxie komplikace terapie MeSH
- jednotky intenzivní péče o novorozence MeSH
- lidé MeSH
- novorozenci extrémně nezralí MeSH
- oxygenoterapie * metody ošetřování škodlivé účinky MeSH
- saturace kyslíkem MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- metaanalýza MeSH
- práce podpořená grantem MeSH
BACKGROUND: The role of high-frequency oscillatory ventilation (HFOV) has long been debated. Numerous studies documented its benefits, whereas several more recent studies did not prove superiority of HFOV over protective conventional mechanical ventilation (CV). One of the accepted explanations is that CV and HFOV act differently, including gas exchange. METHODS: To investigate a different level of coupling or decoupling between oxygenation and carbon dioxide elimination during CV and HFOV, we conducted a prospective crossover animal study in 11 healthy pigs. In each animal, we found a normocapnic tidal volume (VT) after the lung recruitment maneuver. Then, VT was repeatedly changed over a wide range while keeping constant the levels of PEEP during CV and mean airway pressure during HFOV. Arterial partial pressures of oxygen (PaO2) and carbon dioxide (PaCO2) were recorded. The same procedure was repeated for CV and HFOV in random order. RESULTS: Changes in PaCO2 intentionally induced by adjustment of VT affected oxygenation more significantly during HFOV than during CV. Increasing VT above its normocapnic value during HFOV caused a significant improvement in oxygenation, whereas improvement in oxygenation during CV hyperventilation was limited. Any decrease in VT during HFOV caused a rapid worsening of oxygenation compared to CV. CONCLUSION: A change in PaCO2 induced by the manipulation of tidal volume inevitably brings with it a change in oxygenation, while this effect on oxygenation is significantly greater in HFOV compared to CV.
- MeSH
- dechový objem MeSH
- plíce MeSH
- prasata MeSH
- prospektivní studie MeSH
- výměna plynů v plicích * MeSH
- vysokofrekvenční ventilace * MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
