Strategies mitigating hypoxaemia in high-risk populations during anaesthesia and respiratory critical care: computational modelling studies

Alahmadi, Husam I. (2021) Strategies mitigating hypoxaemia in high-risk populations during anaesthesia and respiratory critical care: computational modelling studies. PhD thesis, University of Nottingham.

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Abstract

Assessing interventions applied during clinically-encounterable extreme scenarios is vital to enhance the quality of care. However, the studies that examine these situations are rare, ethically and clinically challenging. Computational modelling offers a reliable, efficient and almost ethical-free approach to investigate high-risk scenarios. This thesis evaluated interventions applied during (i) prolonged apnoea in obesity, (ii) airway obstruction in emergency crises, and (iii) hyperbaric oxygen therapy in severe hypoxaemic respiratory failure patients through a series of high-fidelity computational modelling studies.

Worldwide, there are more than 650 million obese individuals and anticipated to increase. In the context of anaesthesia and critical care, obese subjects are at increased risks during general anaesthesia, such as airway difficulties and apnoea intolerance (rapid occurrence of hypoxaemia). Developing and quantifying methods to extend the safe (non-hypoxaemic) apnoea time would increase their safety remarkably during this procedure. The thesis showed that the use of high-flow nasal oxygen significantly delayed the safe apnoea time in a bank of obese virtual subjects.

Persistent airway obstruction is not common in anaesthesia practice, but it could lead to catastrophic outcomes. Complete blockage of the upper airway was simulated until life-threatening hypoxaemia occurred, followed by relieving the obstruction and delivery of multiple patterns of tidal ventilation. Larger tidal volume did not achieve faster re-oxygenation compared to lower tidal volume.

Globally, up to 20 million acute respiratory failure patients receive mechanical ventilation annually. The mortality of acute respiratory distress syndrome (ARDS) remains considerably high despite the implementation of the lung-protective ventilation strategy. A bank of severe ARDS virtual patients was configured and underwent maximum lung-protective ventilation strategy at atmospheric pressure (with high positive end-expiratory pressure [PEEP]) and hyperbaric pressure (with low PEEP). The hyperbaric oxygen significantly increased the oxygen delivery to tissues even with a low fraction of inspired oxygen.

The thesis’s original contributions to knowledge are: first, it quantified the impact of airway obstruction and patency, high oxygen concentration and high-flow nasal oxygen, applied during apnoea, on the safe apnoea time in obesity. Second, it demonstrated that larger tidal ventilation during airway rescue is not necessary. Finally, it highlighted that hyperbaric oxygen therapy could provide adequate tissue oxygen delivery and may be considered as a rescue option for severe ARDS patients who remain hypoxaemic despite maximum lung-protective ventilation strategy.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Hardman, Jonathan G.
Laviola, Marianna
Keywords: Apnoeic oxygenation, Obesity, Acute Respiratory Distress Syndrome, refractory hypoxaemia, rescue intervention, Hyperbaric oxygen therapy
Subjects: W Medicine and related subjects (NLM Classification) > WF Respiratory system
Faculties/Schools: UK Campuses > Faculty of Medicine and Health Sciences > School of Medicine
Item ID: 64793
Depositing User: Alahmadi, Husam
Date Deposited: 04 Aug 2021 04:40
Last Modified: 04 Aug 2021 04:40
URI: http://eprints.nottingham.ac.uk/id/eprint/64793

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