Oxygen Therapy in Anaesthesia
We have recently reviewed the literature related to oxygen therapy in critically ill patients. Hypoxaemia is a common clinical problem in critically ill patients and few critically ill patients avoid cellular hypoxia. However, in contrast to patients undergoing major surgery, critically ill patients may have a more sustained exposure to hypoxaemia, which raises the possibility that they may adapt to it in a manner analogous to the acclimatization that occurs in healthy individuals ascending to high altitude. Pulmonary oxygen toxicity, ventilator-associated lung injury, and cerebral haemorrhage after extra-corporeal membrane oxygenation are recognized adverse consequences of strategies to reverse hypoxaemia and normalize blood oxygen values. In such cases, striving to normalize arterial oxygenation may incur more harm than benefit as the interventions used have significant associated risks, and the evidence of benefit from restoring normoxaemia is limited.
As a facet of the uncertainty about the relationship between arterial oxygenation and clinical outcome in critically ill patients, there is a lack of evidence supporting improved outcomes with better oxygenation. This may be the result of complex biological interactions in critically ill patients that prevent the separation of 'signal' from 'noise' in such a heterogeneous cohort. Even in studies of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), there is no clear survival benefit from improved oxygenation. This should perhaps not be surprising when one considers that supplemental oxygen is a supportive therapy and has minimal direct effect on the underlying pathophysiology. Furthermore, hypoxaemia and cellular hypoxia are not prominent features of ARDS-related deaths. However, recent findings suggest that hypoxaemia may be a risk factor for the development of long-term cognitive and psychiatric impairment after ALI/ARDS, and this merits further investigation.
Critical Care
We have recently reviewed the literature related to oxygen therapy in critically ill patients. Hypoxaemia is a common clinical problem in critically ill patients and few critically ill patients avoid cellular hypoxia. However, in contrast to patients undergoing major surgery, critically ill patients may have a more sustained exposure to hypoxaemia, which raises the possibility that they may adapt to it in a manner analogous to the acclimatization that occurs in healthy individuals ascending to high altitude. Pulmonary oxygen toxicity, ventilator-associated lung injury, and cerebral haemorrhage after extra-corporeal membrane oxygenation are recognized adverse consequences of strategies to reverse hypoxaemia and normalize blood oxygen values. In such cases, striving to normalize arterial oxygenation may incur more harm than benefit as the interventions used have significant associated risks, and the evidence of benefit from restoring normoxaemia is limited.
As a facet of the uncertainty about the relationship between arterial oxygenation and clinical outcome in critically ill patients, there is a lack of evidence supporting improved outcomes with better oxygenation. This may be the result of complex biological interactions in critically ill patients that prevent the separation of 'signal' from 'noise' in such a heterogeneous cohort. Even in studies of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS), there is no clear survival benefit from improved oxygenation. This should perhaps not be surprising when one considers that supplemental oxygen is a supportive therapy and has minimal direct effect on the underlying pathophysiology. Furthermore, hypoxaemia and cellular hypoxia are not prominent features of ARDS-related deaths. However, recent findings suggest that hypoxaemia may be a risk factor for the development of long-term cognitive and psychiatric impairment after ALI/ARDS, and this merits further investigation.
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