Why give oxygen postoperatively

Moreover, recommendations promoting high oxygen administration to prevent surgical site infections have been challenged, considering the lack of scientific investigations, and have not been widely accepted. Given the potential harmful effects of hyperoxemia, routine postoperative oxygen administration might not be recommended.

Recent clinical studies have indicated that a conservative approach to oxygen therapy, where oxygen administration is titrated to achieve slightly lower oxygen levels than usual, could be safely implemented and decrease acutely ill patients' susceptibility to hyperoxemia.

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Conservative oxygen therapy during mechanical ventilation in the ICU. N Engl J Med. Conservative versus conventional oxygen therapy for cardiac surgical patients: a before-and-after study. Anaesth Intensive Care. Oxygen therapy for acutely ill medical patients: a clinical practice guideline.

Conservative oxygen therapy did not significantly affect ventilator-free days, compared with usual liberal oxygen therapy. Overall, While these findings provide some reassurance to clinicians about the safety of the liberal use of oxygen that occurs in standard practice, they do not exclude clinically important effects of the oxygen regimens tested on mortality risk.

While it seems prudent to avoid both extreme hypoxaemia and extreme hyperoxemia, the most appropriate dose of oxygen to give to critically ill adults patients in the ICU remains uncertain. Furthermore, whether or not conservative oxygen therapy affects mortality overall, it is plausible that a particular oxygen regimen might benefits some patient groups and harms others. Patients with acute lung diseases including ARDS and pneumonia almost always require supplemental oxygen to prevent arterial hypoxemia.

For this group of patients, many factors might affect the optimal oxygen regimen. Even when a conservative approach to oxygen therapy is adopted, achieving a safe minimum arterial oxygen level may require a high FIO 2 and lead to pulmonary oxygen toxicity.

While giving oxygen liberally may worsen these effects, patients with lung pathologies can desaturate rapidly and unexpectedly due to problems like sputum plugging or ventilator dyssynchrony. The risk of unanticipated periods of hypoxaemia in a group of patients with limited respiratory reserve, might favour a relatively liberal approach. However, when oxygen is given liberally in patients with lung diseases, supranormal arterial oxygen levels can occur.

Such supranormal oxygen levels represent a physiological stressor and might potentially worsen patient outcomes. This trial was stopped early at an unplanned interim analysis after recruitment of patients because of concern about intestinal ischaemia events and deaths in the conservative oxygen therapy group. While patients with ARDS represent an important subset of patients with hypoxic respiratory failure, there is no evidence or particular reason to believe that patients with ARDS are more or less prone to pulmonary oxygen toxicity or to the systemic effects of hypoxaemia than patients with lung pathologies who do not have ARDS.

In relation to the ICU-ROX trial primary end point, alive ventilator-free days, there was no evidence of heterogeneity of treatment effect for patients with a PF ratio of less than mmHg compared to those with a PF ratio of mmHg or more [ 37 ].

There was also no statistically significant difference in ventilator free days by treatment group for patients with a low PF ratio who were assigned to conservative oxygen therapy or usual oxygen therapy in the ICU-ROX trial.

At 90 days, there was no statistically significant difference in mortality between the lower-oxygenation group and higher-oxygenation groups with Overall, the available data from RCTs do not support the need to aggressively down-titrate oxygen in patients with ARDS or with other causes of hypoxic respiratory failure [ 40 ].

Nevertheless, it is important to note that even the largest trial in patients with hypoxic respiratory failure, the HOT-ICU trial, was designed to test the hypothesis that conservative oxygen therapy would reduce 90 day mortality by an absolute margin of 5 percentage points [ 39 ]. Although an effect of this magnitude now appears very unlikely, a smaller, but still clinically important, effect on mortality cannot be excluded.

These recommendations were influenced, in large part, by the findings of a RCT of liberal versus titrated oxygen therapy in patients with severe exacerbations of emphysema and chronic bronchitis in the pre-hospital setting [ 43 ].

The liberal oxygen regimen was associated with more severe respiratory acidosis and hypercapnia, which likely contributed to the mortality risk as most deaths were due to respiratory failure. Since this initial report, similar increases in PaCO 2 with liberal oxygen therapy have been demonstrated in a range of other acute respiratory conditions including asthma [ 44 , 45 ], pneumonia [ 46 ] and chronic respiratory conditions such as obesity hyperventilation syndrome [ 46 ].

Among these patients, This was not a significant difference and there was no statistically significant heterogeneity of treatment response for COPD patients compared to non-COPD patients. These findings contrast with those of the previous pre-hospital trial [ 43 ]. The apparent difference may reflect the fact that intervention to treat worsening hypercapnic respiratory failure with non-invasive or invasive ventilation is straightforward in the ICU setting.

Given the reproducible physiological effect of liberal oxygen therapy on pCO 2 levels in spontaneously breathing patients, clinicians may prefer to implement conservative oxygen therapy where there is concern about the potential for liberal oxygen therapy to worsen hypercapnic respiratory failure. However, for patients who are invasively ventilated, there are no RCTs demonstrating that specific oxygen therapy regimens improve outcomes in patients with COPD or in other diseases associated with hypercapnic respiratory failure.

Sepsis is a common reason for ICU admission and many patients with sepsis receive supplemental oxygen. The presence of infection may be a relevant consideration when deciding how liberally to give oxygen. In a post-hoc analysis of the ICU-ROX trial, the day mortality rate for patients treated with usual liberal oxygen was seven percentage points lower than it was for patients who received conservative oxygen therapy [ 47 ]. While this was not a statistically significant difference, the analysis population was small, and the potential for clinically relevant benefit or indeed harm with liberal provision of oxygen to patients with sepsis cannot be excluded.

That said, data from the Hyper2S trial [ 48 ] suggest that therapeutic hyperoxemia using an FIO 2 of 1. Although the difference was not statistically significant, day mortality was eight percentage points higher for patients assigned to hyperoxemia than for those assigned to normoxia. Further research is required to determine the optimal approach to oxygen therapy for patients with sepsis and to establish whether a specific approach is needed for these patients. Moreover, although specific evidence from RCTs is lacking, because of direct pulmonary oxygen toxicity, it is possible that patients with lung pathologies and sepsis might have different oxygen requirements than patients with sepsis who do not have lung pathologies.

A primary injury occurs as a result of immediate cessation of cerebral oxygen delivery and is followed by a secondary injury occurring after resuscitation [ 49 ]. This secondary injury is, in part, the result of oxygen free radical production leading to intracellular oxidation and cellular injury [ 49 ].

While endogenous antioxidants can offset the effect of generation of free radicals and stabilise cellular function following restoration of blood flow to the brain, liberal provision of oxygen might tip the balance in favour of free radical production, cellular oxygenation and neuronal death. In a subsequent post-hoc analysis that included the patients with HIE from the ICU-ROX trial [ 51 ], important baseline covariates that predict outcome in cardiac arrest patients were collected.

Although baseline variables were not statistically significantly different by treatment group, many baseline covariates strongly predict adverse outcomes in this patient group [ 52 ] and, in an analysis adjusting for these baseline covariates, the confidence interval around the treatment estimate for the effect of conservative oxygen therapy on survival with favourable neurological outcome at day was sufficiently wide that it encompassed both clinically important benefit and harm [adjusted odds ratio 1.

An individual patient level data meta-analysis incorporating data from seven RCTs of conservative vs. However, despite statistically significant findings, based on the GRADE classification [ 54 ], these data represent low or very low certainty evidence due to a risk of bias, imprecision and indirectness.

Very few included studies [ 51 , 55 ] had data on post-hospital discharge neurological outcomes further emphasising the degree of uncertainty. While some prior observational studies have suggested that exposure to hyperoxemia is associated with increased mortality risk among post-cardiac arrest patients, the results RCTs indicate that the optimal oxygen regimen to reduce death and disability in post cardiac arrest patients remains uncertain.

One of the guiding principles of neuro-intensive care is that ischaemia is a major cause of secondary brain injury.

Despite this, apart from in patients with HIE, there are very few data from clinical trials evaluating the optimal oxygen regimen in neurocritical care patients.

It is notable that in patients with traumatic brain injury in particular, brain tissue oxygenation levels are often lower than normal and such low brain tissue oxygenation levels are associated with worse outcomes. Liberal provision of oxygen increases brain tissue oxygenation levels but its effects on patient outcomes is unknown.

As there are currently no data from RCTs evaluating oxygen regimens for neuro-intensive care patients, the optimal regimen for this patient group remains uncertain and it remains unclear whether or not patients with brain pathologies have different oxygen needs from other ICU patients.

Further research is needed to define the optimal oxygen regimen for intensive care patients. Given that many hundreds of thousands of patients receive mechanical ventilation in ICU every year, an absolute reduction in mortality of even 1.

For every , patients treated, this would equate to lives saved. The Mega-ROX trial, which is currently recruiting, will test the hypothesis that compared with liberal oxygen therapy targets, conservative oxygen therapy reduces mortality by 1. This 40,participant trial is being conducted in many countries. Because it is possible that conservative oxygen therapy will be best for patients with some diagnoses while liberal oxygen will be best for patients with other diagnoses i. Each of these nested trials will evaluate a pre-specified hypothesis in specific cohorts of critically ill patients i.

Supplemental oxygen therapy is one of the most common treatments in the perioperative and ICU setting. While it is highly plausible that the oxygen regimen used might affect patient outcomes, the optimal regimen is not yet certain and may well differ depending on the clinical circumstances.

Most research in the ICU has focussed on minimizing oxygen exposure while, in anaesthesia, interventions that increase oxygen exposure have been the principal subject of investigation. Currently, a reasonable approach in ICU patients is to aim for arterial oxygen levels that are within the normal range. In the peri-operative setting a broader range of arterial oxygen levels encompassing values that are higher than normal is reasonable.

However, in both situations, it is highly likely that further clinical trials will further our understanding and alter recommendations in the future. Evolution of air breathing: oxygen homeostasis and the transitions from water to land and sky.

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