Oxygen Therapy in Anaesthesia
The importance of avoiding hyperoxaemia is recognized within the British Thoracic Society (BTS) guidelines on oxygen therapy. These recommendations focus on the harm of inhibition of ventilation by oxygen in susceptible patients with chronic obstructive pulmonary disease (COPD), while arguably underplaying the direct harms of hyperoxaemia mediated through oxidative stress and cardiovascular effects. However, they provide a sensible middle ground based on currently available data. It may be that in time, we come to treat most patients in the same way as we now treat patients with COPD who are at risk of ventilatory failure. Consistent with the recommendations, a recent RCT in COPD demonstrated a survival benefit for patients treated with controlled oxygen therapy in comparison with those given unrestricted oxygen. Intriguingly, the mortality benefit in this study seems disproportionately large, given the effect on rates of mechanical ventilation, suggesting that alternative mechanisms of harm from hyperoxia may be important in this patient group as well.
In conclusion, oxygen is essential for the survival of all higher animals, including humans. Oxygen therapy is widespread and essential in the care of acutely ill patients and as part of perioperative care. However, the assumption that unlimited oxygen therapy is without harm merits challenge; it may be possible to have too much of a good thing. Data from a variety of clinical situations where anaesthetists deliver care suggest that unrestricted, and/or high concentration, oxygen therapy may be harmful and suggest the need for a fundamental re-evaluation of therapeutic goals. We should aim to get the right amount of oxygen to the right patient at the right time: the mantra of individualized (or stratified) medicine.
PH and PCAO are rational candidate strategies that we believe are likely to improve clinical outcomes. The clinical and cost-effectiveness of these strategies is uncertain and requires careful evaluation. While implementation of PCAO is consistent with current clinical guidelines and unlikely to be associated with harm, implementation of PH is more speculative (and potentially harmful) and evaluation of the safety and feasibility of this approach in perioperative and critical care settings is needed before clinical trials are contemplated. Development of biomarkers of susceptibility and tolerance of hypoxia and hyperoxia, including monitors of cellular oxygenation and oxidative stress, will be needed to underpin these studies. Addressing these challenges should be a research priority for our community.
In the meantime, current recommendations for oxygen therapy are a useful guide for clinicians at the bedside. The laudable goal of improving patient outcomes through carefully targeted administration of oxygen offers opportunities for innovation in devices, diagnostics, and therapies.
Current Clinical Guidelines
The importance of avoiding hyperoxaemia is recognized within the British Thoracic Society (BTS) guidelines on oxygen therapy. These recommendations focus on the harm of inhibition of ventilation by oxygen in susceptible patients with chronic obstructive pulmonary disease (COPD), while arguably underplaying the direct harms of hyperoxaemia mediated through oxidative stress and cardiovascular effects. However, they provide a sensible middle ground based on currently available data. It may be that in time, we come to treat most patients in the same way as we now treat patients with COPD who are at risk of ventilatory failure. Consistent with the recommendations, a recent RCT in COPD demonstrated a survival benefit for patients treated with controlled oxygen therapy in comparison with those given unrestricted oxygen. Intriguingly, the mortality benefit in this study seems disproportionately large, given the effect on rates of mechanical ventilation, suggesting that alternative mechanisms of harm from hyperoxia may be important in this patient group as well.
In conclusion, oxygen is essential for the survival of all higher animals, including humans. Oxygen therapy is widespread and essential in the care of acutely ill patients and as part of perioperative care. However, the assumption that unlimited oxygen therapy is without harm merits challenge; it may be possible to have too much of a good thing. Data from a variety of clinical situations where anaesthetists deliver care suggest that unrestricted, and/or high concentration, oxygen therapy may be harmful and suggest the need for a fundamental re-evaluation of therapeutic goals. We should aim to get the right amount of oxygen to the right patient at the right time: the mantra of individualized (or stratified) medicine.
PH and PCAO are rational candidate strategies that we believe are likely to improve clinical outcomes. The clinical and cost-effectiveness of these strategies is uncertain and requires careful evaluation. While implementation of PCAO is consistent with current clinical guidelines and unlikely to be associated with harm, implementation of PH is more speculative (and potentially harmful) and evaluation of the safety and feasibility of this approach in perioperative and critical care settings is needed before clinical trials are contemplated. Development of biomarkers of susceptibility and tolerance of hypoxia and hyperoxia, including monitors of cellular oxygenation and oxidative stress, will be needed to underpin these studies. Addressing these challenges should be a research priority for our community.
In the meantime, current recommendations for oxygen therapy are a useful guide for clinicians at the bedside. The laudable goal of improving patient outcomes through carefully targeted administration of oxygen offers opportunities for innovation in devices, diagnostics, and therapies.