The use of noninvasive ventilation (NIV) in severe hypoxemic respiratory failure (partial pressure of oxygen in the alveoli [PaO2]/fraction of inspired oxygen [FIO2] ≤250 ) is controversial; but in centers with expertise on NIV, when used as a first-line therapy, NIV can avoid orotracheal intubation in 30% to 50% of cases. At beginning of the pandemic, NIV was not recommended for patients with influenza A H1N1 virus infection complicated by pneumonia, acute lung injury, or acute respiratory distress syndrome because although it could temporarily improve oxygenation, it did not necessarily change the natural disease course. In this regard, several authors have reported high rates of NIV failure in pandemic influenza A H1N1 pneumonia. However, other authors have more recently reported some cases demonstrating the effectiveness of NIV in severe respiratory failure related to H1N1 pneumonia.
Aim and Methods
In this prospective study, we aimed to assess the efficacy of NIV in avoiding endotracheal intubation and to identify predictors of success or failure. Seventy-five patients affected by influenza A H1N1 pneumonia were admitted to our hospitals: among them, 61 patients presented with acute respiratory failure, and 29 patients had severe respiratory failure; 5 patients with PaO2/FIO2 lower than 150 and SAPS II lower than 34 underwent NIV and were admitted to respiratory intermediate care unit.
Noninvasive ventilation failed in 3 of the 24 patients but had a good outcome in 21 patients. None of the patients treated with NIV died. The mean ± SD duration of NIV was 5.0 ± 1.9 days, and the mean ± SD hospital stay was 11.2 ± 4.0 days. The mean ± SD PaO2/FIO2 ratio at admission was 184.6 ± 29.2, and the mean ± SD SAPS II was 17.8 ± 2.6; the mean ± SD PaO2/FIO2 ratio after 1 hour of NIV was 239.1 ± 42.3. No patient had multiorgan failure. The PaO2/FIO2 ratio after 1 hour and SAPS II at admission were independent variables correlated with the success of NIV.
In our study, NIV had a success in 21 (87.5 %) of the 24 patients, and this is one of the higher rates of success described in the literature. In our opinion, the reasons explaining the results could be the selection of the patients to be treated with early severe respiratory failure (PaO2/FIO2 ≥150), and the strict adherence to the predictors of success for NIV such as SAPSII ≤34 and PaO2/FIO2 ≤175 after 1 hour of NIV.
Physicians should be aware of pulmonary complications of influenza A H1N1 and strictly select the patients to undergo NIV: it could have an effective and safe role in reducing the high demand for critical care beds, particularly during pandemics.