Respiratory support during the influenza A (H1N1) pandemic flu in Sweden

Background Acute respiratory insufficiency characterised critically ill patients during the influenza A (H1N1) pandemic 20092010. Detailed understanding of disease progression and outcome in relation to different respiratory support strategies is important. Methods Data collected between August 2009 and February 2010 for a national intensive care unit influenza registry were combined with cases identified by the Swedish Institute for Infectious Disease Control. Results Clinical data was available for 95% (126/136) of the critically ill cases of influenza. Median age was 44 years, and major co-morbidities were present in 41%. Respiratory support strategies were studied among the 110 adult patients. Supplementary oxygen was sufficient in 15% (16), non-invasive ventilation (NIV) only was used in 20% (22), while transition from NIV to invasive ventilation (IV) was seen in 41% (45). IV was initiated directly in 24% (26). Patients initially treated with NIV had a higher arterial partial pressure of oxygen/fraction of oxygen in inspired gas ratio compared with those primarily treated with IV. Major baseline characteristics and 28-day mortality were similar, but 90-day mortality was higher in patients initially treated with NIV 17/67 (25%) as compared with patients primarily treated with IV 3/26 (12%), relative risk 1.2 (95% confidence interval 0.34.0). Conclusions Critical illness because of 2009 influenza A (H1N1) in Sweden was dominated by hypoxic respiratory failure. The majority of patients in need of respiratory support were initially treated with NIV. In spite of less severe initial hypoxemia, initiation of ventilatory support with NIV was not associated with improved outcome.