The effective exchange of the main respiratory gases - O2 and CO2 - at alveolar level constitutes the main requirement for a correct functioning of the respiratory system. In a subject for whom the functions of the latter result to be impaired, the resort to ventilatory support often demonstrates to be necessary. Recently, the interest in this support shifts towards non-invasive ventilation approaches (NIV), because of the advantage of the latter in not requiring patient intubation (with consequent deep sedation) and in facilitating patient weaning from the mechanical ventilator. Despite of the absence of invasiveness in this method, NIV has to deal with upper airways issue, not present in invasive ventilation where air insufflation occurs directly into trachea, bypassing the upper tract. Besides the determination of possible patient-ventilator asynchronies due to a reduced sedation of spontaneous breathing, upper airways introduce an anatomical dead space, which has to be minimized by optimizing the used ventilatory technique and related parameters. Traditional techniques are based on the delivery, at every breath, of intermittent positive pressures, determining high volume displacements; this was proved to cause often lung injuries, barotrauma and volutrauma. Since a fundamental parameter in assessing the effectiveness of gas exchanges in respiratory system is the diffusive coefficient of CO2 (DCO2) - given by the product between stimulus frequency and tidal volume - it has been decided to analyse if alveolar exchange improvement was significant when using ventilation techinques based on sinusoidal pressure signals at different frequencies. Moreover, a particular focus has been centered on High-Frequency Oscillatory Ventilation (HFOV), a recent ventilatory technique that delivers high peak-to-peak pressures (until 30 cmH2O) at high frequency (5 - 25 Hz) displacing lower volumes with respect to conventional techniques, thus reducing alveolar lesions but contributing, however, in improving gas exchange. The aim of this thesis work is hence to develop and size, at Politecnico di Milano, an innovative in-vitro model, representative of an adult respiratory system, on which testing the effectiveness of the introduced ventilation approaches on CO2 washout. Finally, preliminary studies on animal model have been performed at Genève University Hospital (Genève, CH), with the aim of assessing mechanical and physiological findings previously obtained in-vitro.
Lo scambio efficiente dei principali gas respiratori – O2 e CO2 - a livello alveolare costituisce il principale requisito per un corretto funzionamento del sistema respiratorio. In un soggetto in cui le funzioni di quest'ultimo risultino alterate, si dimostra spesso necessario il ricorso al supporto ventilatorio. Recentemente, l'interesse per tale supporto vira sempre più verso approcci di ventilazione non invasiva (NIV), per il vantaggio che questa offre nel non richiedere intubazione del paziente (con relativa profonda sedazione) e nella facilitazione per quest'ultimo nel processo di svezzamento dal ventilatore meccanico. Nonostante la quasi nulla invasività del metodo, la NIV deve affrontare il problema delle vie aeree superiori, non presente nella ventilazione invasiva dove l'insufflazione di aria avviene direttamente in trachea, bypassando il tratto superiore. Oltre a determinare probabili asincronie paziente-ventilatore dovute ad una ridotta sedazione del respiro spontaneo, le vie aeree superiori introducono uno spazio morto anatomico, che deve essere minimizzato ottimizzando la tecnica ed i parametri ventilatori in uso. Le tecniche tradizionali si basano sull'erogazione, ad ogni respiro, di pressioni positive intermittenti, determinanti alti volumi di aria scambiata; ciò si è dimostrato essere spesso causa di lesioni polmonari, barotrauma e volutrauma. Dato che un parametro fondamentale nel valutare l'efficienza dello scambio di gas nel sistema respiratorio è il coefficiente diffusivo di CO2 (DCO2) - dato dal prodotto di frequenza di stimolo e volume corrente - si è deciso di analizzare se, utilizzando tecniche ventilatorie basate sull'erogazione di segnali pressori sinusoidali a determinate frequenze, il miglioramento nello scambio alveolare fosse significativo. Inoltre, un focus particolare è stato incentrato sulla High-Frequency Oscillatory Ventilation (HFOV), una recente tecnica ventilatoria che eroga pressioni picco-picco elevate (fino a 30 cmH2O) ad alta frequenza (5 - 25 Hz), spostando volumi tidali nettamente inferiori alle tecniche convenzionali, riducendo così il rischio di danni alveolari ma contribuendo comunque a migliorare gli scambi gassosi. Lo scopo di questo lavoro di tesi è quindi quello di sviluppare e dimensionare, presso il Politecnico di Milano, un innovativo modello in-vitro indicativo del sistema respiratorio adulto, sul quale testare l'efficacia degli approcci ventilatori introdotti sulla rimozione della CO2. Infine, studi pilota su modello animale sono stati effettuati presso il Genève University Hospital a Ginevra (CH), con lo scopo di validare i risultati meccanici e fisiologici precedentemente ottenuti in vitro.
Effects of high frequency pressure oscillations during mechanical ventilation on gas exchange : a model study
BANI, DANIELE
2019/2020
Abstract
The effective exchange of the main respiratory gases - O2 and CO2 - at alveolar level constitutes the main requirement for a correct functioning of the respiratory system. In a subject for whom the functions of the latter result to be impaired, the resort to ventilatory support often demonstrates to be necessary. Recently, the interest in this support shifts towards non-invasive ventilation approaches (NIV), because of the advantage of the latter in not requiring patient intubation (with consequent deep sedation) and in facilitating patient weaning from the mechanical ventilator. Despite of the absence of invasiveness in this method, NIV has to deal with upper airways issue, not present in invasive ventilation where air insufflation occurs directly into trachea, bypassing the upper tract. Besides the determination of possible patient-ventilator asynchronies due to a reduced sedation of spontaneous breathing, upper airways introduce an anatomical dead space, which has to be minimized by optimizing the used ventilatory technique and related parameters. Traditional techniques are based on the delivery, at every breath, of intermittent positive pressures, determining high volume displacements; this was proved to cause often lung injuries, barotrauma and volutrauma. Since a fundamental parameter in assessing the effectiveness of gas exchanges in respiratory system is the diffusive coefficient of CO2 (DCO2) - given by the product between stimulus frequency and tidal volume - it has been decided to analyse if alveolar exchange improvement was significant when using ventilation techinques based on sinusoidal pressure signals at different frequencies. Moreover, a particular focus has been centered on High-Frequency Oscillatory Ventilation (HFOV), a recent ventilatory technique that delivers high peak-to-peak pressures (until 30 cmH2O) at high frequency (5 - 25 Hz) displacing lower volumes with respect to conventional techniques, thus reducing alveolar lesions but contributing, however, in improving gas exchange. The aim of this thesis work is hence to develop and size, at Politecnico di Milano, an innovative in-vitro model, representative of an adult respiratory system, on which testing the effectiveness of the introduced ventilation approaches on CO2 washout. Finally, preliminary studies on animal model have been performed at Genève University Hospital (Genève, CH), with the aim of assessing mechanical and physiological findings previously obtained in-vitro.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/164897