Respiratory management

1. Maintain adequate gas exchange with increased FIO2 and, depending on severity, either non-invasive respiratory support (e.g. CPAP, BiPAP) or positive pressure ventilation. Specific modes may be utilised, such as pressure controlled inverse ratio ventilation. While general agreement exists for minimising VT (6-7ml/kg) and plateau inspiratory pressures (<30cmH20) if possible, there is no consensus regarding the upper desired level of FIO2 and PEEP. Greater emphasis is currently placed on higher levels of PEEP (up to 20cm H2O) While the current European view favours the use of higher FIO2 (up to 1.0), a common US approach is to keep the FIO2 <0.60 but to maintain SaO2 with higher levels of PEEP. A recent study assessing higher levels of PEEP showed no outcome benefit.

2. Non-ventilatory respiratory support techniques such as ECCO2R can be used in severe ARDS but have yet to show convincing benefit over conventional ventilatory techniques.

3. Blood gas values should be aimed at maintaining survival without striving to achieve normality. Permissive hypercapnia, where PaCO2 values are allowed to rise, sometimes above 10kPa, has been associated with outcome benefit. Acceptable levels of SaO2 are controversial; in general, values >90-95% are targeted but in severe ARDS this may be relaxed to 80-85% or even lower provided organ function remains adequate.

4. Patient positioning may provide improvements in gas exchange. This includes kinetic therapy using special rotational beds, and prone positioning with the patient being turned frequently through 180°. Care has to be taken during prone positioning to prevent tube displacement and shoulder injuries.

5. Inhaled nitric oxide or epoprostenol improves gas exchange in some 50% of patients, though no outcome benefit has been shown.

6. High dose steroids commenced at 7-10 days are beneficial in 50-60% of patients, at least in terms of improving gas exchange.

7. Surfactant therapy is currently not indicated for ARDS.

8. Ventilator trauma is ubiquitous. Multiple pneumothoraces are common and may require multiple chest drains. They may be difficult to diagnose by X-ray and, despite the attendant risks, CT scanning may reveal undiagnosed pneumothoraces and aid correct siting of chest drains.

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