Al-Ahmad, Abdullmohsen Mohammed
(2017)
Airway pressure release ventilation mode in lung injury.
PhD thesis, University of Nottingham.
Abstract
Airway pressure release ventilation (APRV) is a promising, unconventional mode of ventilation for the treatment of various respiratory diseases, including acute respiratory distress syndrome (ARDS). However, despite increasing global use and reported advantages of APRV over other modes, definitive conclusions cannot be drawn due to several concerns. First, the major confusion between APRV and other, similar modes, such as bi-phasic positive airway pressure (BIPAP). Second, clinical and methodological heterogeneity among published studies of APRV are understandably extensive, which contributes to outcome variability. Third, the absence of consensus on a standard protocol with clear rationale for the settings.
This thesis provides an overview of the spectrum of ventilator settings that may be designated as APRV, summarises the research and clinical use status of APRV, exemplifies the need to clarify the characteristics that comprise the mode, and to assure reports of APRV use, from case reports through RCTs, including adequate data for a proper assessment. It encourages continued publication of observational as well as experimental clinical trial data, and discusses the feasibility of analysis strategies that may expand the information available from small patient samples. It also presents an unpublished, comprehensive, multifaceted clinical practice protocol (Al-ahmad protocol) for the use of APRV.
Using the Al-ahmad protocol, four studies were conducted on non-spontaneously breathing patients who had ARDS (arising from a variety of pathologies). One study used a validated physiological simulator called integrated cardiopulmonary models (ICPMs) while the other three, were prospective cohort observational studies on real patients. The first study evaluated patients’ responses to changes in inspiratory pressure during conventional ventilation (CV) and APRV modes, using ICPMs vs. a real patient. The second study compared partial pressure of carbon dioxide (PaCO2) at any given ventilatory minute ventilation (MV) during CV and APRV. The third study aimed to identify proper configurations to optimise PaCO2 on patients with diverse pulmonary pathologies including restrictive (e.g. ARDS) and obstructive (e.g. chronic obstructive pulmonary disease) when using APRV. The fourth study compared oxygenation and haemodynamic status during CV and APRV.
Results from ICPMs appeared to be analogous for both modes except for the significant difference in MV and tidal volume observed in the simulated vs. real APRV patients. We found in our clinical studies that compared to conventional modes, APRV was associated with significantly lower PaCO2 at significantly lower levels of MV, better oxygenation, and haemodynamic status.
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