Moderate ARDS not improving on high FiO2
A 56-year-old man is admitted to intensive care with severe community-acquired pneumonia and moderate ARDS. He weighs 80 kg and is 175 cm tall. He has been intubated for 72 hours. Ventilation: volume control, tidal volume 420 mL (predicted body weight 70 kg), respiratory rate 28/min, PEEP 14 cmH₂O, FiO₂ 1.0. Arterial blood gas: pH 7.28, PaCO₂ 52 mmHg, PaO₂ 90 mmHg, bicarbonate 24 mmol/L, lactate 1.8 mmol/L. Plateau pressure is 32 cmH₂O, driving pressure 14 cmH₂O. Compliance is 25 mL/cmH₂O. Sedation is with propofol and fentanyl; he is not triggering. Echocardiography shows normal left ventricular function, no patent foramen ovale, and a small pericardial effusion. He is receiving enteral nutrition and has a central line. The ICU has proning capability but no ECMO on site; the nearest ECMO centre is 90 minutes away by road.
1. What is the next ventilator and positioning intervention, and why?
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The PaO₂/FiO₂ ratio is 90 despite FiO₂ 1.0 and PEEP 14 cmH₂O, so this is moderate-to-severe ARDS. The plateau pressure is 32 cmH₂O and driving pressure 14 cmH₂O, so lung-protective ventilation is already reasonable. The next intervention is prone positioning for at least 16 hours per day, after checking for contraindications.
Rationale: proning recruits dorsal lung regions, improves ventilation-perfusion matching, and reduces mortality in moderate-to-severe ARDS when applied early and for prolonged periods. Before turning, confirm there is no open abdomen, unstable spine, raised intracranial pressure, or recent tracheostomy. Secure the endotracheal tube and lines, use a trained team, and protect pressure areas.
I would not immediately escalate to ECMO because proning has not yet been tried and the patient is not in refractory hypoxaemia for the required duration. I would also avoid a further increase in PEEP unless a recruitment manoeuvre is planned and monitored, because the plateau pressure is already 32 cmH₂O.
2. How would you assess whether proning is effective, and what complications would you monitor for?
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Effectiveness is assessed by improvement in PaO₂/FiO₂, a fall in driving pressure, and improved compliance, but a lack of immediate improvement does not justify stopping early. Reassess blood gases 1–2 hours after proning and continue for the planned 16-hour session unless there is haemodynamic instability or a complication. Some patients respond later, and mortality benefit is linked to the duration of prone sessions rather than a single gas exchange reading.
Complications to monitor:
- Airway: tube dislodgement, obstruction, or biting; secure the tube before turning and check capnography continuously.
- Lines and drains: disconnection or removal; pause enteral feed and check position.
- Pressure injuries: face, chest, pelvis, and knees; use gel pads and reposition the head every 2 hours.
- Haemodynamics: hypotension during turning; pre-oxygenate and turn slowly.
- Other: facial oedema, brachial plexus injury, vomiting, and corneal abrasion.
If oxygenation falls critically during proning, return to supine and reassess.
3. When would you refer this patient for ECMO, and what information would you send?
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Referral should be considered if, despite optimised ventilation, proning, and treatment of the cause, the patient has PaO₂/FiO₂ below 80 for more than 6 hours, PaO₂/FiO₂ below 50 for more than 3 hours, or pH below 7.25 with PaCO₂ above 60 mmHg despite lung-protective ventilation. Other triggers include refractory hypercapnia, pneumothorax with air leak, or failure to improve after a trial of proning.
This patient currently has a P/F of 90 and is not yet in the refractory category, so I would not refer immediately unless he deteriorates. Because the ECMO centre is 90 minutes away, early discussion is sensible once proning is started, so that transfer can be planned before irreversible organ failure.
Information to send: age, weight, diagnosis, ventilation settings and blood gases over time, proning history, echocardiography, vasopressor dose, renal and liver function, neurological status, contraindications to anticoagulation, and the local team's contact details. The decision to transfer should be made jointly with the ECMO centre, not by the referring unit alone.