[ARDS and influenza A (H1N1): patients' characteristics and management in intensive care unit. A literature review]

Novel influenza A (H1N1) at the origin of the 2009 pandemic flu developed mainly in subjects of less than 65 years contrary to the seasonal influenza, which usually developed in elderly patients of more than 65 years. Elderly subjects are partly protected by old meetings with close stocks. Influenza A(H1N1) can arise in serious forms within 60 to 80% of cases a fulminant acute respiratory distress syndrome (ARDS) "malignant and fulminant influenza" in subjects without any comorbidity, which makes the gravity and the fear of this influenza. The fact that this influenza A (H1N1) can develop in healthy young patients and evolve in few hours to a severe ARDS with a refractory hypoxemia gave to the foreground the possible interest of the recourse to extracorporeal oxygenation (ECMO) in some selected severe ARDS (5-10%). The first publications of patients admitted in intensive care unit (ICU) for severe influenza A (H1N1) often associated to an ARDS reported a mortality rate from 15 to 40%. This mortality variability may be explained in part by different studied populations, ARDS characteristics and human and material resources in the ICUs between the countries. Indeed, the highest mortality rates (30-40%) have been reported by in Mexico which were affected the first by pandemic flu and which were not prepared. A bacterial pneumonia was associated to H1N1 influenza in approximately 30% of the cases as at admission in ICU or following the days of the admission justifying an early antibiotherapy associated to the antiviral treatment by oseltamivir (Tamiflu). Obesity, pregnancy and respiratory diseases (asthma, COPD) seem to be associated to the development of a severe viral pneumonia due to influenza A (H1N1) often with ARDS. Older age, high APACHE II and SOFA scores and a delay of initiation of the antiviral treatment by oseltamivir are associated to higher morbidity and mortality. Other analyses of the results obtained from the first published papers included more patients and future studies would permitted to better define the role of therapeutics such as steroids and ECMO.