A systematic review and meta-analysis looking at mortality and morbidity in 16,073 acutely ill adults treated with liberal versus conservative oxygen therapy suggested that SpO2 greater than 94-96% might be deleterious at 30 days. It is also well established thatpatients with chronic obstructive pulmonary disease (COPD) should receive oxygen therapy to achieve a SpO2 target of 88-92%.2
Although supplemental oxygen is valuable in many clinical situations, excessive or inappropriate supplemental oxygen can be deleterious. According to human and animal studies, high concentrations of inspired oxygen can cause a spectrum of lung injury, ranging from mild tracheobronchitis to diffuse alveolar damage. The latter is histologically indistinguishable from that observed in the acute respiratory distress syndrome.3
Saturation monitoring is a continuous variable and in a 24-hour period, with a heart rate of 70 beats/minute, there will be 100,800 readings. This measurement is subject to artefact and currently, in most clinical practice, there are 24 recorded data points in the ICU, with hourly observations. It is practically easier to set a target SpO2 as opposed to partial pressure of arterial oxygen (PaO2), as the former is much easier to measure continuously and a patient’s PaO2 can easily alter within minutes.
