Influenza-associated ARDS with refractory hypoxaemia
A 54-year-old man with type 2 diabetes presents with five days of fever, myalgia and cough and tests positive for influenza A H1N1. Within 24 hours of admission he becomes increasingly tachypnoeic and is intubated. Ventilation is volume-controlled with tidal volume 6 mL/kg predicted body weight, PEEP 14 cmH2O, FiO2 0.8, plateau pressure 30 cmH2O and driving pressure 16 cmH2O. Arterial blood gas on these settings shows PaO2/FiO2 110 mmHg. He requires noradrenaline 0.15 µg/kg/min, lactate is 2.8 mmol/L, and urine output is 0.5 mL/kg/h. Chest radiography shows bilateral infiltrates without cardiomegaly. He has no known bleeding disorder and no severe neurological injury. The intensive care team asks whether he needs more than lung-protective ventilation.
1. How would you classify the ARDS and what ventilation and supportive measures would you add?
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This is moderate ARDS by the Berlin definition: acute onset within one week, bilateral infiltrates not fully explained by cardiac failure, and PaO2/FiO2 110 mmHg on PEEP of at least 5 cmH2O. Continue lung-protective ventilation targeting tidal volume 6 mL/kg predicted body weight, plateau pressure below 30 cmH2O and driving pressure below 15 cmH2O. Consider prone positioning for at least 16 hours daily, since the PaO2/FiO2 ratio is below 150 mmHg; this reduces mortality in moderate-to-severe ARDS. Optimise PEEP with a titration strategy and consider neuromuscular blockade for the first 48 hours if there is severe dyssynchrony or very high driving pressure. Use conservative fluid management after initial resuscitation, treat the precipitating infection and review sedation and weaning daily.
2. When would you refer for extracorporeal membrane oxygenation, and what must be checked first?
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Refer for extracorporeal membrane oxygenation assessment if refractory hypoxaemia persists despite optimised ventilation and prone positioning-for example PaO2/FiO2 below 80 mmHg for more than six hours or below 50 mmHg for more than three hours-or if there is refractory hypercapnia with pH below 7.25 and PaCO2 above 60 mmHg despite protective ventilation. Before referral, confirm the diagnosis and reversibility, exclude significant intracerebral pathology, assess bleeding risk and vascular access, check ventricular function and ensure that the patient is in a centre with appropriate expertise. Advanced multiorgan failure, uncontrolled bleeding and a clearly futile prognosis are relative contraindications. Early discussion with the regional ECMO service is preferable to waiting until cardiovascular collapse.
3. What antimicrobial and corticosteroid decisions would you make?
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Start oseltamivir promptly, even beyond 48 hours of symptom onset, because severe influenza warrants treatment. Cover bacterial coinfection with a broad-spectrum regimen guided by local policy and cultures, then de-escalate when microbiology allows. Corticosteroids are not routine in influenza-associated ARDS and may increase secondary infection and prolong viral shedding; reserve them for another indication such as refractory septic shock or underlying obstructive lung disease with an exacerbation. Avoid high-dose steroids purely for ARDS. Review fluids, glycaemic control and thromboprophylaxis, and involve infectious diseases and critical care early. If he deteriorates further, reassess for nosocomial infection, pneumothorax and ventilator-associated complications.