A 47 year old man has severe ARDS following a perioperative aspiration. He is endotracheally intubated and ventilated in SIMV mode with PEEP 5 cm H2O and an FiO2 0.4 resulting in a PaO2 of 45 mm Hg (6 kPa). On the chest X-Ray, the endotracheal tube is properly positioned in the trachea. The only abnormality on the chest X-ray was bilateral diffuse alveolar infiltrates.
List the steps you could take to improve his oxygenation. Include a brief comment on the rationale for each step.
° Increase FiO2): Improve PAO2
° Increase PEEP
° surface area for gas exchange
° Improvement of atelectasis
° Redistribution of lung water
° Physio / suctioning
° Sedation / Consider Paralysis: Decrease O2 requirements and CO2 production
° Treat factors that increase metabolic demand, sepsis etc: Decrease O2 requirements and CO2 production
° Optimise fluid balance: balance of interstitial overload and maximising cardiac output and DO2
° Optimise Haemoglobin, optimal oxygen carriage / viscosity combination and minimise immune and volume effects of transfusion
Optimise Recruitment and FRC
° Lung recruitment manoeuvre: Opening collapsed alveoli, increasing FRC and area available for gas exchange
° Increase I:E Ratio towards 1:1: Increased FRC as above, recruitment, increase PAO2
° Inverse ratio ventilation: Longer in inspiration with potential to gas trap and provide autoPEEP above set PEEP with subsequent increase FRC and area for gas exchange.
° Prone position: better VQ matching, improved mechanical advantage, less lung compression from abdominal and mediastinal contents
Optimise Flow to Ventilated Alveoli
° Inhaled Nitric oxide: inhaled dilator delivered only to ventilated alveoli
° Prostacyclin: improved perfusion to ventilated alveoli
° Tracheal Gas insufflation and other measures to decrease circuit dead space: reduced dead space means lower CO2 with relative increase in partial pressure of O2
° ECMO, external membrane oxygenation and CO2 removal: lung rest and minimisation of VALI.
This question is about the ventilation strategies in ARDS, which is a topic discussed elsewhere:
Initial ventilator strategy:
Additional ventilator manoeuvres to improve oxygenation:
Non-ventilator adjunctive therapies for ARDS:
Ventilator strategies to manage refractory hypoxia
Non-ventilator adjuncts to manage refractory hypoxia