Past, present and future of conservative oxygen therapy in critical care

Conservative oxygen therapy (COT) is the administration lower levels of supplemental oxygen than usual in order to tolerate a lower level of arterial oxygenation (either the partial pressure (PaO2) or haemoglobin saturation (SaO2)) than normal. Its purpose is to reduce a patient’s overall exposure to additional oxygen in order to minimise the risk of oxyen toxicity.1 This approach to oxygen therapy has also been called permissive hypoxaemia (PH) and the terms are frequently used interchangeably; here, we refer to all efforts to reduce supplemental oxygen administration or arterial oxygenation as COT. Studies have been conducted across a wide range of medical conditions, to determine whether COT improves patient outcomes and there appears to be a signal of benefit among acutely unwell patients.2 The intention in this article, however, is to focus only on critically ill patients admitted to intensive care units (ICUs). These patients often present with acute hypoxaemic respiratory failure and require high concentration oxygen to restore normal arterial oxygenation. There is concern thatone of the central pillars of support for these patients, oxygen, may inadvertently be causing them harm, which we mistakenly ascribe to a worsening of their underlying pathology. There remains no consensus on how or when to use COT in critically ill patients and it is imperative we address these questions as soon as possible.