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Upper abdominal surgery is the most frequently performed surgery type in Australia with approximately 175,000 operations annually and the incidence of surgery is continuing to rise per annum. Despite advances in perioperative practices, postoperative pulmonary complications (PPC) remain a common serious complication following upper abdominal surgery, with high-risk patients even more susceptible. Consequences of a PPC are considerable and a leading cause of postoperative morbidity and mortality. Atelectasis occurs in almost all patients immediately following surgery, and if unresolved, is thought to lead to the development of more severe PPCs including hypoxaemia, airway infection, and respiratory failure. Preoperative physiotherapy reduces PPC rates by half following upper abdominal surgery. However, despite the overall benefit in PPC reduction demonstrated with preoperative physiotherapy, high-risk patients continue to have an increased PPC incidence. Expert opinion and previous meta-analyses recommend the use of prophylactic non-invasive ventilation (NIV) to minimise PPC risk following upper abdominal surgery. Non-invasive ventilation provides positive airway pressure throughout the breath cycle and is suggested to re-open atelectatic alveoli, increase lung volume, and improve gas exchange. However, implementation of prophylactic postoperative NIV has not been adopted into routine physiotherapy clinical practice. The reasons for this low utilisation are hypothesised to be multifactorial and include perceived risks, associated staffing resources, and unknown optimal intervention dosages. No clear consensus exists to guide postoperative NIV management and safety of prophylactic NIV therapy in abdominal surgery has yet to be adequately reported. This thesis addresses some of the gaps in our current understanding of the role of prophylactic NIV therapy within the upper abdominal surgery population. This thesis was undertaken with the overall aim of evaluating the fea