ABSTRACT
Major changes in respiratory function occur in all patients after anaesthesia and surgical incisions, especially on the
thorax and upper abdomen, because of a decrease in the functional residual capacity with minimal change in the closing volume leading to airway closure during tidal breathing. Indeed, post-operative ARF is generally observed after abdominal and/or thoracic surgery. Anaesthesia, surgery and post-operative pain6 lead to respiratory function modifications, mainly hypoxaemia, which results from changes in ventilation/perfusion ratio. The latter is a consequence of both functional residual capacity and vital capacity reductions related to respiratory muscle dysfunction and atelectasis. Moreover, peri-operative related modifications of the ventilatory system and hypoxaemia frequently observed in the early post-operative period may be aggravated by other factors such as excessive perioperative vascular loading,7 transfusion-related acute lung injury, inflammation, sepsis and aspiration. The expected benefit of NIV would be to partially compensate for the affected respiratory function by reducing the work of breathing, by improving alveolar ventilation associated with increased gas exchange, by reducing left ventricular afterload with an increase in cardiac output and by reducing atelectasis.8
